Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Our original guided-wave optical microphone consists of a diaphragm and a single-mode optical waveguide. Sensitivity is an important specification for microphones, and is theoretically known to be dependent on diaphragm thickness. In this study, we fabricated three microphones with different diaphragm thicknesses, and experimentally examined the diaphragm thickness-dependent sensitivity.

DOI： 10.23919/MOC.2017.8244579

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DOI： 10.1117/12.2324692

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DOI： 10.1117/12.2288035

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DOI： 10.1117/12.2288086

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DOI： 10.1117/12.2288160

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DOI： 10.1117/12.2324829

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© Published under licence by IOP Publishing Ltd. DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) is the planned Japanese space gravitational wave antenna, aiming to detect gravitational waves from astrophysically and cosmologically significant sources mainly between 0.1 Hz and 10 Hz and thus to open a new window for gravitational wave astronomy and for the universe. DECIGO will consists of three drag-free spacecraft arranged in an equilateral triangle with 1000 km arm lengths whose relative displacements are measured by a differential Fabry-Perot interferometer, and four units of triangular Fabry-Perot interferometers are arranged on heliocentric orbit around the sun. DECIGO is vary ambitious mission, we plan to launch DECIGO in era of 2030s after precursor satellite mission, B-DECIGO. B-DECIGO is essentially smaller version of DECIGO: B-DECIGO consists of three spacecraft arranged in an triangle with 100 km arm lengths orbiting 2000 km above the surface of the earth. It is hoped that the launch date will be late 2020s for the present..

DOI： 10.1088/1742-6596/840/1/012010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS  

An optical range finder system that relies on laser diodes' frequency noise, instead of intensity or frequency modulations, and its improvement in resolution are reported. The distance to the target is measured by calculating the cross-correlation of two signals reflected from the target and reference mirrors. These two signals are converted from the laser diodes' frequency noise signals by frequency/intensity converters, such as a Fabry-Perot etalon. We obtained the distance to the target by checking time lags between the target and reference beams at the highest correlation coefficient. We also measured the change in the correlation coefficient around the peak sampling point by adjusting the reference-path length, achieving a resolving power of +/- 3 mm. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

DOI： 10.1117/1.OE.56.6.064101

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS  

Design guidelines for a guided-wave optical pressure sensor based on dependences of sensitivity and resonance frequency on diaphragm dimensions were considered. The guided-wave optical pressure sensor consists of a diaphragm and a single-mode waveguide on the diaphragm. According to our theoretical study, the edge of the diaphragm was found to be the best position to obtain the highest sensitivity. Also, sensitivity is proportional to the cube of the side length of the diaphragm but inversely proportional to the square of the diaphragm thickness. On the other hand, resonance frequency of the diaphragm is proportional to the diaphragm thickness and inversely proportional to the square of the side length. Dependences were experimentally examined for fabricated sensors with different diaphragm dimensions to confirm theoretical predictions. The experimental results agreed well with the theoretical predictions. Moreover, a design assistant chart for the sensor was proposed based on the dependences. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

DOI： 10.1117/1.OE.56.5.057108

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A stable microwave source using frequency stabilized diode lasers was developed. The Doppler-free spectra of Rb atoms produced by saturated absorption spectroscopy were used to obtain highly-sensitive control signals and lock the frequency of diode lasers to it. The beat frequencies between two independently stabilized diode lasers were 1.2 GHz and 2.9 GHz. The fluctuations in beat frequencies were 40 kHz and 400 kHz respectively in the best stability.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS  

Our proposed silicon-based guided-wave optical flow sensor consists of a diaphragm with a small opening used as an orifice and a waveguide across the diaphragm. The sensor operates based on Bernoulli's theorem and the elasto-optic effect. A sensor, which had a 10 x 10-mm(2), 50-mu m-thick diaphragm with a 0.34 x 0.34-mm(2) opening, was fabricated to demonstrate and confirm the sensor operation. Measured output power as a function of flow rate using oxygen gas agreed quite well with the theoretical prediction although slight deviation was seen in the high flow rate region. Moreover, according to Bernoulli's theorem, sensitivity is strongly dependent on sectional area of opening. So, three sensors with different opening areas, such as 0.28 x 0.28, 0.34 x 0.34, and 0.55 x 0.55 mm(2), were fabricated to examine such a dependence, which would be helpful to design the sensor. The measured sensitivity was found to be almost proportional to area of the opening, similar to the theoretical prediction. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

DOI： 10.1117/1.OE.55.1.017102

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_526

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_568

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Optical Society of America (OSA)  

Designing a silicon-based guided-wave optical pressure sensor, consisting of a diaphragm and a waveguide across the diaphragm, was considered based on dependences of sensitivity and resonance frequency on diagram dimensions.

DOI： 10.1364/acpc.2014.ath3a.209

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS  

We describe a method of generating physical random numbers by means of a diode laser that has an extremely wide-band frequency-noise profile. Fluctuations in the laser frequency affect the intensity of the light transmitted through the optical frequency discriminator, detected thereafter as random fluctuations. This allows us to simultaneously generate 8 random bit streams, due to the parallel processing of 8-digit binary numbers sampled by an 8-bit analog-to-digital converter. Finally, we generated physical random numbers at a rate of 3 Gbit/s, by combining one data stream with another stream that is delayed by 2 ms, by exclusive-OR. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.OE.52.1.014302]

DOI： 10.1117/1.OE.52.1.014302

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Our group has proposed a resonant-type guided-wave optical acoustic emission (AE) sensor, which consists of a diaphragm and a single-mode optical waveguide on the diaphragm. In this study, we examined output response characteristics of the AE sensor using an acoustic sound pulse, instead of an AE pulse. Output responses of a fabricated AE sensor were investigated for each parameter, namely pulse duration, sound pressure (amplitude) and frequency. A larger output signal was obtained due to resonance effect, but it lacked similarity to the original target pulse due to a narrow bandwidth and required approximately 10 ms to reach the steady state. However, based on the experimental results, a formula was derived to determine pulse duration and amplitude. In the case of out-of-resonance, output signal is more complex, but the frequency deviation from the resonance frequency could be determined from the beat-like phenomenon for long-duration pulse.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS  

In this study, an original scale-reduction rule without a drop in the sensitivity of a guided-wave optical pressure sensor was obtained using a micromachined diaphragm. The sensor has a rectangular diaphragm as a pressure-sensitive structure and a sensing waveguide across the diaphragm. Its sensitivity is theoretically known to be strongly dependent on the dimensions of the diaphragm. According to the theoretical results, the sensitivity can be kept constant even if the diaphragm dimensions are reduced as long as both the aspect ratio and the characteristic length of the diaphragm remain constant. Here, the characteristic length is introduced as the cube of either width or length of the rectangular diaphragm divided by the square of its thickness. Such a scale-reduction rule would be very useful for miniaturizing a sensor without reducing sensitivity, although it has not been experimentally confirmed. In this study, the scale-reduction rule was experimentally examined using three fabricated sensors with the same aspect ratio and the same characteristic length. The measured sensitivities of the three sensors were quite similar to each other, as theoretically predicted. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.OE.51.1.014401]

DOI： 10.1117/1.OE.51.1.014401

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

In a guided-wave optical microphone with a diaphragm used as a vibration plate, damping of diaphragm vibration is very significant in order to realize broad flat frequency response. In this study, a glass-based guided-wave optical microphone without a damping structure was experimentally examined to evaluate the damping ratio as the first phase in the optimization of damping. Damping ratio and resonance frequency were successfully evaluated to be 0.009 and 3.5 kHz, respectively, for a fabricated microphone with a diaphragm of 20 mm x 20 mm x 0.15 mm.

DOI： 10.1117/12.910286

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Our guided-wave optical microphone consists of a diaphragm and a single-mode optical waveguide on the diaphragm. Since sensitivity and frequency response are strongly dependent on waveguide position and diaphragm dimensions, designing the microphone is relatively complicated without a design guideline. In this report, a convenient and helpful chart diagram when designing the microphone is proposed based on theoretical and experimental results on dependences of sensitivity and resonance frequency on diaphragm dimensions. In addition, since damping of diaphragm vibration is also vital in obtaining a broader flat frequency response, squeeze-film air damping is discussed.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Our group has proposed and demonstrated a silicon-based guided-wave optical accelerometer with a proof mass centered on a diaphragm. It is strongly suggested that sensitivity is related to many factors, such as waveguide position, diaphragm dimensions, and size and weight of proof mass. These relationships need to be clearly identified in order to establish a design guideline. In this study, sensitivity dependences on waveguide position and diaphragm dimensions were experimentally examined. Regarding waveguide position, phase sensitivity was highest for the waveguide at the diaphragm edge, and was also relatively high for the waveguide at the edge of proof mass. Regarding diaphragm dimensions, phase sensitivity was found to be inversely proportional to the square of the diaphragm thickness, and proportional to the side length of the diaphragm.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Even as long ago as the 1960's, scientists understood that diode lasers' oscillation wavelengths demonstrated significant shifts to the shorter wavelength side, when subjected to strong magnetic fields, at extremely low temperatures. When we exposed Fabry-Perot type diode lasers oscillating at 780 nm to weak magnetic fields, at room temperature, the oscillation wavelength was observed to have shifted to the longer wavelength side. In discussions of shift mechanisms aimed at explaining how/why our results differ from those obtained in studies conducted in the 1960's, we noted a rise in temperature and an increase in the carrier density, and how it affected the characteristic shifts observed, when a magnetic field was applied to the Fabry-Perot type laser diodes parallel to the injection current. In the present work, we tested the oscillation wavelength shift of a vertical-cavity surface-emitting laser (VCSEL) in a magnetic field, because we expected that, by doing so, the VCSEL would show a shorter wavelength side shift.

DOI： 10.1117/12.908016

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Random numbers can be classified as either pseudo- or physical-random, in character. Pseudo-random numbers are generated by definite periodicity, so, their usefulness in cryptographic applications is somewhat limited. On the other hand, naturally-generated physical-random numbers have no calculable periodicity, thereby making them ideal for the task. Diode lasers' considerable wideband noise gives them tremendous capacity for generating physical-random numbers, at a high rate of speed. We measured a diode laser's output with a fast photo detector, and evaluated the binary-numbers from the diode laser's frequency noise characteristics. We then identified and evaluated the binary-number-line's statistical properties. We also investigate the possibility that much faster physical-random number parallel-generation is possible, using separate outputs of different optical-path length and character, which we refer to as "coherence collapse".

DOI： 10.1117/12.908011

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

External cavity diode laser (ECDL) systems are presently experiencing a surge in popularity as laser light-sources, in advanced optical communications- and measurement-applications. Because such systems require that their external reflectors be precisely controlled, to eliminate low frequency fluctuations in optical output, we conducted experiments with a two-cavity version of the ECDL system for a vertical cavity surface emitting laser (VCSEL). This technique brings the added advantages of a narrower linewidth than would be achievable via a single optical feedback. VCSELs are characterized by wider oscillation linewidths than edge emitting types, so the larger effect of double optical feedback system is expected.

DOI： 10.1117/12.909622

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A laser diode (LD) has been used in many areas, such as optical communication systems. However, its oscillation frequency changes, with variations in ambient temperature and injection current, so its frequency stabilization is of vital importance. In these situations, Rb saturated absorption spectroscopy is the method of choice. We use the beat signal, both for the purpose of evaluating frequency stability between two independently stabilized LDs, and for generating THz waves. This work shows a basic experiment using our beat signal observation, by high-speed photodetector. In addition, we have also used a frequency-stabilized etalon, to improve frequency selectivity.

DOI： 10.1117/12.908275

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The objectives of the DECi-hertz Interferometer Gravitational Wave Observatory (DECIGO) are to open a new window of observation for gravitational wave astronomy and to obtain insight into significant areas of science, such as verifying and characterizing inflation, determining the thermal history of the universe, characterizing dark energy, describing the formation mechanism of supermassive black holes in the center of galaxies, testing alternative theories of gravity, seeking black hole dark matter, understanding the physics of neutron stars and searching for planets around double neutron stars. DECIGO consists of four clusters of spacecraft in heliocentric orbits; each cluster employs three drag-free spacecraft, 1000 km apart from each other, whose relative displacements are measured by three pairs of differential Fabry-Perot Michelson interferometers. Two milestone missions, DECIGO pathfinder and Pre-DECIGO, will be launched to demonstrate required technologies and possibly to detect gravitational waves.

DOI： 10.1088/0264-9381/28/9/094011

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

As long ago as the 1960's, scientists understood that Diode lasers' oscillation wavelengths showed a significant shift to the shorter wavelength (high frequency) side, when exposed to strong (<4[T]) magnetic fields, at extremely low temperatures (<80[K]). Not surprisingly, then, in preliminary tests, when we exposed Fabry/Perot-type diode lasers oscillating at 780[nm] to weak magnetic fields (<1.4[T]), at room temperature (300[K]), we observed that the oscillation wavelength shifted to the longer (low frequency) wavelength side. In the present work, we used vertical-cavity surface-emitting lasers (VCSEL) to check whether its change into the shorter wavelength side takes place.
In discussions of shift mechanisms, we consider how wavelength (frequency) and optical output-power shifts are correlated. Our expanded knowledge base has forced us to use a completely different mechanism to explain how/why our results differ from those obtained in studies conducted in the 1960's. We are now introducing a mechanism that affects a rise in temperature and an increase in the carrier density, affect the characteristic shifts observed in our experiments, when a magnetic field is applied to the laser diodes parallel to the injection current.

DOI： 10.1117/12.875851

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Tungsten transport in halogen lamp operation was examined by fluid dynamics and thermo-chemical simulation. Partial pressures of almost all species dramatically increased around the coil leads. The cause appears to be a stagnant flow of filling gases. Results of a life test showed that tungsten was slightly deposited at the coil leads. Such a tungsten deposit can be attributed to a high concentration of tungsten compounds during the gas phase.

DOI： 10.2150/jlve.35.23

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One of the key elements in improving lamp efficiency is understanding and controlling the halogen transport process. Therefore, it is worthwhile to build a model that depicts this process and can be applied to the study of various types of lamps. We examined the halogen transport process in a lamp by using a hybrid simulation model based on fluid dynamics and chemical equilibrium.

DOI： 10.2150/jlve.35.7

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Random numbers can be classified as either pseudo- or physical-random in character. Pseudo-random numbers' periodicity renders them inappropriate for use in cryptographic applications, but naturally-generated physical-random numbers have no calculable periodicity, thereby making them ideally-suited to the task. The laser diode naturally produces a wideband "noise" signal that is believed to have tremendous capacity and great promise, for the rapid generation of physical-random numbers for use in cryptographic applications. We measured a laser diode's output, at a fast photo detector and generated physical-random numbers from frequency noises. We then identified and evaluated the binary-number-line's statistical properties. The result shows that physical-random number generation, at speeds as high as 40Gbps, is obtainable, using the laser diode's frequency noise characteristic.

DOI： 10.1117/12.875830

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Our group has developed a silicon-based guided-wave optical accelerometer with a proof mass centered on a diaphragm. For this type of accelerometer, it is strongly suggested that sensitivity is related to waveguide position, diaphragm dimensions, and size and weight of proof mass. In this study, sensitivity dependences on waveguide position and diaphragm thickness were considered experimentally. Experimental results demonstrated that the highest sensitivity could be obtained for the waveguide at the diaphragm edge and is inversely proportional to the square of the diaphragm thickness.

DOI： 10.1117/12.873660

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A space gravitational-wave antenna, DECIGO (DECI-hertz interferometer Gravitational wave Observatory), will provide fruitful insights into the universe, particularly on the formation mechanism of supermassive black holes, dark energy and the inflation of the universe. In the current pre-conceptual design, DECIGO will be comprising four interferometer units; each interferometer unit will be formed by three drag-free spacecraft with 1000 km separation. Since DECIGO will be an extremely challenging mission with high-precision formation flight with long baseline, it is important to increase the technical feasibility before its planned launch in 2027. Thus, we are planning to launch two milestone missions. DECIGO pathfinder (DPF) is the first milestone mission, and key components for DPF are being tested on ground and in orbit. In this paper, we review the conceptual design and current status of DECIGO and DPF.

DOI： 10.1088/0264-9381/27/8/084010

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Other Link： http://orcid.org/0000-0003-1318-2635

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTOPTICAL INSTRUMENTATION ENGINEERS  

Ongoing tests involving the application of double optical feedback to a vertical-cavity surface-emitting laser (VCSEL) are resulting in demonstrable and significant improvements in oscillation linewidth and frequency stability. We look into the workings of a double optical feedback system for a Fabry-Perot-type diode laser. We describe a single-mode VCSEL that is characterized by a narrow oscillation linewidth and a stable output intensity that shows no trace of the low-frequency fluctuation (LFF) that so often occurs in single optical feedback diode lasers. Initial tests use a beat note to do this. From there, we calculate the square root of the Allan variance to determine the level of frequency stability. We also evaluate the degree of LFF suppression achieved using its spectrum density and compare those results with what we obtained through single and double optical feedback and with no feedback whatsoever. (C) 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3284784]

DOI： 10.1117/1.3284784

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We introduced the vertical cavity surface emitting laser (VCSEL) as the laser diode in tour external cavity system. Because VCSELs are now commercially available, and the External cavity diode laser (ECDL) systems using them are expected to improve their frequency stability, we have replaced a Fabry-Perot type laser diode with a VCSEL, and examined its oscillation-frequency stability. Therefore we were able to expect that the VCSELs with our double optical feedback system have good oscillation frequency stability. The obtained VCSEL's oscillation-frequency stability, i.e., the square root of Allan variance sigma was 4x10(-10), at an averaging time of tau = 1 sec.

DOI： 10.1117/12.840609

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The semiconductor lasers in use today are on one hand, prized, and highly praised, for their small size, light weight, longevity and energy-efficiency, -and on the other, criticized for their susceptibility to frequency-fluctuations brought about by changes in temperature and driving current. Once this "wrinkle" is ironed out, semiconductor lasers will become the default light-sources, for satellites' onboard interferometers. Our studies have been directed at stabilizing oscillation frequency to the atomic absorption line, and using negative electrical feedback to the injection current. Frequency stabilization is accomplished, by either; a) applying direct modulation to the semiconductor laser's driving current, or b) modulating the reference frequency, to obtain the error signal needed for stabilization. In this instance, Faraday effect-based stabilization was used. This indirect oscillation frequency stabilization has no discernable effect on spectra width, but, stability was no better than that observed in the system using the direct modulation.
When we compared Faraday effect-and direct modulation-based methods of stabilization, in order to uncover the root-cause of the discrepancy, sensors picked up system noise, the source of which was heat generated by the heavy current applied to a magnetic coil used to apply the Faraday effect. We also substituted a permanent magnet for the electromagnet.

DOI： 10.1117/12.841526

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Random numbers can be classified as either pseudo- or physical-random in character. This work demonstrates how laser diodes' inherent noise can be exploited for use in generating physical-random numbers in cryptographic applications. In the initial stages of the experiment, we measured a laser diode's output, at a fast photo detector and generated physical-random numbers from intensity noises. We then identified and evaluated the binary-number-line's statistical properties. Our preliminary results show that fast physical-random numbers are obtainable, using the laser diode's frequency noise characteristics.

DOI： 10.1117/12.840626

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We have succeeded, thus far, in stabilizing laser diode (LD) frequencies to Rb absorption lines, by means of negative electrical feedback. While the absorption lines were stable over the long term, the Doppler Effect's influence was evident, in broadened spectrum linewidth. To avoid the problem in subsequent tests, we used Rb-saturated absorption signals.
In this work, we demonstrated potentials of two applications; one was as a reference signal source for estimation of other LD's frequency stabilization system, and the other was a light source for generation of THz radiation.

DOI： 10.1117/12.840610

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

DECIGO pathfinder (DPF) is a milestone satellite mission for DECIGO (DECi-hertz Interferometer Gravitational wave Observatory), which is a future space gravitational wave antenna. DECIGO is expected to provide fruitful insights into the universe, particularly about dark energy, the formation mechanism of supermassive black holes and the inflation of the universe. Since DECIGO will be an extremely challenging mission, which will be formed by three drag-free spacecraft with 1000 km separation, it is important to increase the technical feasibility of DECIGO before its planned launch in 2024. Thus, we are planning to launch two milestone missions: DPF and pre-DECIGO. In this paper, we review the conceptual design and current status of the first milestone mission, DPF.

DOI： 10.1088/0264-9381/26/9/094019

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Other Link： http://orcid.org/0000-0003-1318-2635

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTOPTICAL INSTRUMENTATION ENGINEERS  

The primary objective of the Decihertz Interferometer Gravitational Wave Observatory (DECIGO) mission is to detect and observe black holes' and galactic binaries' gravitational waves (GWs), at frequencies ranging from 10(-2) to 10(1) Hz (from 0.1 to 100 s in averaging time). This low-frequency range is inaccessible to ground-based interferometers, due to unshieldable background noise and to the fact that ground-based interferometers are limited to a few kilometers in length. Our research is focused on efforts to stabilize semiconductor, Nd:YAG, and fiber lasers, for use as GW detectors' optical sources. In present-day and future detectors, frequency and phase noise may place certain limitations on sensitivity and stability. Our goal is primarily to design robust experiments. In this report, we compare existing methods: Faraday, Faraday peak, and saturated absorption spectroscopy. In these, the laser frequency is stabilized to Rb as an atomic frequency reference by a feedback-loop control system. From the frequency stability of these models, we can predict the characteristics of the three systems through dynamic stability analysis, by analyzing the dynamic Allan variance. We find the optical frequency stability, expressed as the Allan deviation (the square root of the Allan variance), to be 3.3 x 10(-11), 2.9 x 10(-12), and 1.2 x 10(-12) in the respective methods. (C) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3089887]

DOI： 10.1117/1.3089887

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One of the key elements in improving lamp efficiency is understanding and controlling the halogen transport process. Therefore, it is worthwhile to build a model that depicts this process and can be applied to the study of various types of lamps. We examined the halogen transport process in a lamp by using a hybrid simulation model based on fluid dynamics and chemical equilibrium.

DOI： 10.2150/jieij.93.814

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Scientists throughout the world are seeking to enhance the capabilities of satellite-to-satellite tracking laser interferometer-based optical systems used to measure the alterations in earth's gravitational field that indicate critical changes in the environment. These systems must be able to measure infinitesimal fluctuations in the relative velocities of two satellites, using a light source that oscillates at a level of frequency stability rated better than 10-13 in the square root of the Allan variance. In our experiments, semiconductor laser frequency stabilization that typically requires a brief direct modulation of the laser injection current to obtain an error signal, was accomplished using the Faraday effect of Rb absorption lines. This effectively modulates the reference frequency of the stabilization system, i.e., the Rb absorption line, by modulating the magnetic field applied to the Rb absorption cell, instead of the oscillation frequency of the laser diode. Most recently, we used the Faraday method, in conjunction with a precision temperature controller. For present purposes, we also use the PEAK method, to obtain the most accurate signal possible, comparing it with saturated absorption spectroscopic readings, to determine the noise-source.

DOI： 10.1117/12.808803

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Tungsten transport in halogen lamp operation was examined by fluid dynamics and thermo-chemical simulation. Partial pressures of almost all species dramatically increased around the coil leads. The cause appears to be a stagnant flow of filling gases. Results of a life test showed that tungsten was slightly deposited at the coil leads. Such a tungsten deposit can be attributed to a high concentration of tungsten compounds during the gas phase.

DOI： 10.2150/jieij.93.827

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Language：Japanese   Publishing type：Research paper (scientific journal)  

The resonance frequencies of various diaphragms in glass-based guided-wave optical pressure sensors were examined experimentally. In this study, acoustic sound pressure was applied to six fabricated sensors with square diaphragms of different dimensions to evaluate frequency characteristics as well as resonance frequency. The measured resonance frequencies were proportional to the diaphragm thicknesses, and inversely proportional to the square of the side-length of diaphragms, as theoretically predicted. © 2009 The Institute of Electrical Engineers of Japan.

DOI： 10.1541/ieejsmas.129.357

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Optical Society of America (OSA)  

According to our previous theoretical study, sensor sensitivity is proportional to the cube of the side length of the diaphragm in a guided-wave optical pressure sensor consisting of a glass diaphragm and a single-mode waveguide on the diaphragm. Also, to obtain higher sensitivity, an aspect ratio of the diaphragm should be approximately 1 for two waveguide positions: the center and the edge of the diaphragm. In this study, sensitivity dependences on side length and aspect ratio of the diaphragm were experimentally examined. The obtained experimental results strongly supported the theoretical predictions. © 2008 Optical Society of America.

DOI： 10.1364/OE.16.015024

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTOPTICAL INSTRUMENTATION ENGINEERS  

We experimentally investigated the relationship between sensitivity and diaphragm thickness in a glass-based guided-wave optical pressure sensor using intermodal interference between the fundamental TM-like and TE-like modes. The sensor consists of a rectangular diaphragm and a straight single-mode waveguide on the diaphragm. The sensitivity is theoretically known to be inversely proportional to the square of the diaphragm thickness. In this study, to examine this relationship, four sensors with diaphragm thicknesses of 0.30 mm, 0.22 mm, 0.20 mm, and 0.15 mm were fabricated. The area of the diaphragm was 10 mm x 10 mm. For the waveguide position nearest to the center of the diaphragm, the measured sensitivities almost agreed with the theoretical ones. (C) 2008 Society of Photo-Optical Instrumentation Engineers.

DOI： 10.1117/1.2909669

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The precise interferometric systems employed in today's artificial satellites require semiconductor lasers of the highest callibur. But, one particularly large obstacle has stood in the way of their broad application; the stabilization of their oscillation frequencies. While a number of different approaches have been tested, none have provided overall, long-term stability. Most recently, we used a Doppler-free absorption line of Rb atoms with a precision temperature controller and an improved laser mount; in this instance, relative optical frequency stability rated 9.07x10(-13)<=sigma(2,tau)<= 7.54x10(-10), in averaging time for 0.01s <=tau <= 23s. Furthermore, we heated the Rb cell to up to 313K, in order to enhance the control signal and improve oscillation frequency stability.

DOI： 10.1117/12.761595

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The primary objective of the Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) mission is to detect and observe black holes' and galactic binaries' gravitational waves (GWs), at frequencies ranging from 10(-2) to 10(1) HZ. This low-frequency range is inaccessible to ground-based interferometers, due to unshieldable background noise, -and the fact that ground-based interferometers are limited to a few kilometers in length. Our research is focused on efforts to stabilize semiconductor-, Nd:YAG- and fiber- lasers, for use as GW detectors' optical sources. In present-day- and future detectors, frequency- and phase-noise may place certain limitations on sensitivity and stability. Our goals (shared with scientists around the world) are; first, to design robust experiments that will measure a variety of noises (- random-walk FM, flicker-FM, white FM, flicker PM and white PM), in order to verify existing models, and second, -to find ways to reduce sensitivity to spurious noise. Current models predict a variety of frequency- and phase-dependent noise slopes, but, a conclusive distinction between noise-models can only be made when the exact points at which the noises occurred are known. In order to increase the sensitivity of the experiment, the laser frequency is stabilized to an atomic-frequency-reference by a feedback-loop control system.

DOI： 10.1117/12.756222

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The precise interferometric systems employed in today's artificial satellites require semiconductor lasers of the highest callibur. But, one particularly large obstacle has stood in the way of their broad application; the stabilization of their oscillation frequencies. While a number of different approaches have been tested, none have provided overall, long-term stability. Most recently, we used a Doppler-free absorption line of Rb atoms with a precision temperature controller and an improved laser mount; in this instance, relative optical frequency stability rated 9.07 x 10(-13) <=sigma(2,tau)<= 7.54 x 10(-10), in averaging time for 0.01s <=tau <= 23s. By introducing optical feedback, which narrows the laser's linewidth, we obtained improved frequency stability.

DOI： 10.1117/12.756173

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The precise interferometric systems employed in today's artificial satellites require semiconductor lasers of the highest caliber. To this end, efforts to stabilize their oscillation frequencies and narrow spectrum line-widths continue relentlessly. While a number of different approaches have been tested, none have provided overall, long-term stability. Most recently, we employed a Doppler-free absorption line of Rb atoms, with a precision temperature controller and an improved laser mount. In this instance, relative optical frequency stability rated 9.07 x 10(-13)<=sigma(2,tau)<= 7.54x10(-10), in averaging time for 0.01s <=tau <= 23s. By introducing an optical feedback, which narrows the laser's linewidth, we obtained improved frequency stability.

DOI： 10.1117/12.788681

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

External cavity diode lasers (ECDL) are presently experiencing a surge in popularity, as laser light-sources for advanced optical measurement systems. While these devices normally require external optical-output controls, we simplified the setup, a bit, by adding a second external cavity. This technique boasts the added advantage of having a narrower oscillation-linewidth than would be achievable, using a single optical feedback. Because drive-current and atmospheric temperature directly impact the ECDL systems' oscillation frequency, during frequency stability checks, it was necessary, in this instance, to construct a slightly smaller ECDL system, which we mounted on a Super-Invar board, to minimize the influence of thermal expansion. Taking these and other aggressive and timely measures to prevent atmospheric temperature-related changes allowed us to achieve an improvement in oscillation-frequency stability, i.e., to obtain the square root of Allan variance sigma =2 x 10(-10), at averaging time tau = 10(-1).
We introduced a vertical-cavity surface-emitting laser (VCSEL) to the setup, for the simple reason that its frequency is far less susceptible to changes in temperature, than other lasers of its type. And, because VCSELs are widely available, and the ECDL systems that use them improve frequency stability, we replaced the Fabry-Perot semiconductor laser with a VCSEL.

DOI： 10.1117/12.761598

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Language：English   Publishing type：Research paper (other academic)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

In this study, the signal-to-noise ratio of a glass-based guided-wave optical microphone was successfully improved by both increasing sensitivity and reducing noise. The optical microphone has a square diaphragm as a pressure-sensitive structure and a straight single-mode waveguide across the diaphragm. Sensitivity of the microphone and resonance frequency of the diaphragm are dependent on the area and thickness of the diaphragm. In this study, in order to increase sensitivity, the diaphragm dimensions were enlarged from 16 mm x 16 mm x 0.15 mm in the previous study to 20 mm x 20 mm x 0.15 mm. According to theoretical calculations, the phase sensitivity and resonance frequency were 2.5 mrad/Pa and 3.4 kHz for a 20 mm x 20 mm x 0.15 mm diaphragm, respectively. The sensitivity was theoretically expected to be twice as high as that in the previous study. To reduce noise, a bandpass filter with passband from 300 Hz to 3 kHz was employed. After fabrication of the optical microphone, sound pressure, ranging from 100 to 122 dB-SPL, was applied to the microphone with a frequency of I kHz. The measured output of the optical microphone was almost proportional to the sound pressure, and the minimum detectable sound pressure level of the microphone was experimentally evaluated to be 100 dB-SPL.

DOI： 10.1117/12.698904

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Laser interferometers detect gravitational waves with a degree of accuracy and efficiency unimaginable even a few years ago. The semiconductor lasers that are the primary light source for these devices are small, lightweight, durable and energy-efficient. On the downside, the devices currently available are still marked by broad oscillation spectra, and heightened sensitivity to fluctuations in injection current and /or ambient temperature. By applying a small sine wave to the injection current, we modulate the oscillation frequency. This frequency-modulated beam is introduced to the Avalanche photo diode through the Rb cell in the saturated absorption optical setup. The resulting signal and a reference signal are detected simultaneously and combined, to produce an error signal, which, when fed back to the injection current, stabilizes the diode's oscillation frequency at 2.12x10(-12) <= sigma(2,tau)<= 5.88x10(-11) in the averaging time between 0.4s to 65s. An optical feedback method, which introduces the laser beam reflected by a mirror or a grating to the semiconductor laser itself, is reported to narrow oscillation linewidth and improve frequency stability. We are now combining these two techniques to further improve frequency stability.

DOI： 10.1117/12.698300

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

A method of detecting gravitational-field variations using laser diodes is described. While the GRACE project is currently using the Doppler microwave system to measure the velocities of satellites flying in tandem, in the future, more advanced laser interferometry will be employed. It is hoped that we will be able to measure infinitesimal changes in their velocities, by using frequency-stabilized lasers rated at better than 10(-13) in the square root of the Allan variance (sigma) for Is < tau < 100s. As laser light sources, these devices will be notable for their compactness, energy efficiency, lightweight and high frequency-stability. This thesis describes the improved frequency stabilization obtained through the use of the magneto-optical effect of the Rb-D-2 absorption line, and the adaptation of the PEAK method, in order to obtain a precise control signal. The method allows us to modulate the reference frequency of the stabilization system (the absorption spectrum of the Rb-D-2 absorption line) by modulating the magnetic field applied to the Rb absorption cell, instead of the oscillation frequency of the laser diode. In so doing we are able to achieve a frequency stabilized laser diode (sigma = 9 x 10(-12)), while maintaining its linewidth, at an averaging time of 40s. In the next stage, we will test frequency-stabilized laser optical sources that are to be used in detecting and observing gravitational waves.

DOI： 10.1117/12.698306

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

External cavity diode laser (ECDL) systems are presently experiencing a surge in popularity as laser light-sources, in advanced optical communications- and measurement-systems. Because such systems require that their external reflectors be precisely controlled, to eliminate low frequency fluctuations (LFF) in optical output, we conducted experiments with a two-cavity version, which easily eliminated LFFs, as expected. The technique has the added advantage of a narrower oscillation-linewidth than would be achievable, using a single optical feedback. However, the ECDL's oscillation frequency is susceptible to the influences of the drive-current, as well as changes, both in the refractive index, and the overall length of the external reflector that results from fluctuations in atmospheric temperature. We made every effort to maintain the length of the ECDL cavity, while evaluating oscillation-frequency stability. We used a Super-Invar board as the platform for our compact ECDL system to minimize the influence of thermal expansion, because of its low expansion coefficient. We then compared the effect of atmospheric temperature variations between two experimental conditions, with the Super-invar board and without it, and finally took note of the improvement in performance, using the board.

DOI： 10.1117/12.698961

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the future Japanese space gravitational wave antenna. It aims at detecting various kinds of gravitational waves between 1 mHz and 100 Hz frequently enough to open a new window of observation for gravitational wave astronomy. The preconceptual design of DECIGO consists of three drag-free satellites, 1000 km apart from each other, whose relative displacements are measured by a Fabry-Perot Michelson interferometer. We plan to launch DECIGO in 2024 after a long and intense development phase, including two pathfinder missions for verification of required technologies.

DOI： 10.1088/0264-9381/23/8/S17

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

External cavity diode laser (ECDL) systems are presently experiencing a surge in popularity as laser light-sources, in Z 4:1 advanced optical communications- and measurement-applications. Because such systems require that their external reflectors be precisely controlled, to eliminate low frequency fluctuations (LFF) in optical output, we conducted experiments with a two-cavity version of the ECDL system. This technique brings the added advantages of a narrower linewidth than would be achievable via a single optical feedback. However, the ECDL's oscillation frequency is susceptible to the influences of the driving current, changes in the refractive index, and changes in external-reflector length that result from fluctuations in atmospheric temperature. We made every effort to maintain the length of the ECDL cavity, while evaluating oscillation-frequency stability. We used a Super-Invar board as the platform for our ECDL system, in order to minimize the influence of thermal expansion. Moreover, our ECDL system combines an Rb cell within an external cavity; an arrangement designed to improve stability by restricting the LD frequency within both the external cavity mode and the Rb-saturated absorption spectrum. We used the square root of the Allan variance, when evaluating oscillation frequency stability, observing, in the process, that it improved stability by about one order of magnitude.

DOI： 10.1117/12.645759

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

In this study, stability of holographic gratings recorded in four photopolymer films with different dyes was experimentally examined. Also, dye concentration was optimized to get high diffraction efficiency. Each film contains triethanolamine and acrylamide in polyvinyl alcohol matrix, and one type of dye: eosin Y, methyl violet, rhodamine B or rose bengal. Dye concentrations were adjusted so that transmittances of the four films 60 mu m thick were approximately 94%. The photopolymer films were exposed by two intersecting beams of a YVO laser at 532 nm to form holographic grating with spatial frequency of 653 line/mm until the diffraction efficiency reached its maximum. The power of each recording beam was 10 mW, and its diameter was 2.25 mm each.
Diffraction efficiency was measured using a YVO laser beam for the recorded films undergoing either 300 sec reconstruction or 5-day dark storage. The photopolymer film containing eosin Y showed the best stability both for a 300 sec reconstruction and for 5-day storage. Regarding optimization of dye concentration, the diffraction efficiencies of more than 60% were obtained when an amount of eosin Y is between 1 mg and 50 mg, which was solved in 9.1 % polyvinyl alcohol aqueous solution of 110 g.

DOI： 10.1117/12.645913

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The present work discusses methods of stabilizing the frequencies of commercially-available laser diodes. Laser diodes are generally compact and long-lived. The frequency stability, which makes them ideal for onboard laser interferometer light-sources, in applications such as the satellite-to-satellite tracking systems used to verify fluctuations in earth's gravity field, which, in turn, indicate other critical changes in the environment, is the key characteristic of this work. We used the devices typically operating at 780nm, and their frequencies can be stabilized using either of two systems; one, employing the Doppler-free absorption line of Rb atoms and another, using the Faraday effect of the Rb absorption line. In both cases, the use of the proper modulation frequency and amplitude improved frequency stability, overall, attaining 2.05 x 10(-12) and 2.73 x 10(-11), respectively, in the square root of the Allan variance, by measuring the beat-note between two independently-stabilized laser diodes.

DOI： 10.1117/12.645751

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Semiconductor lasers' oscillation wavelengths respond to temperature-, injection current-, and magnetic field-fluctuations. As reported in the 1960's, the oscillation wavelength shortened, under magnetic fields stronger than 4T, at temperatures lower than 80K. However, when we exposed bulk-type semiconductor lasers oscillating at 780nm to relatively weak magnetic fields (less than 1.4T), at room temperature (300K), we observed that the oscillation wavelength shifted to the longer (lower frequency) side. In this work, we focused on the longer oscillation wavelength shift, the lower power side optical output-power shift, and the higher voltage side terminal voltage shift of a number of multi-quantum-well (MQW) laser diodes oscillating at 780nm, under the same experimental conditions as those used in our previous works. In discussions of these shift mechanisms, we consider how wavelength (frequency), optical output-power, and terminal voltage shifts are correlated. Because our new knowledge arrows us to employ mechanisms completely different from those used in studies dating as far back as the 1960's, we have introduced one whereby the shifts observed in our experiments result from temperature rises and longitudinal magneto-resistance effects. Also discussed, are the results of experiments conducted near the threshold current.

DOI： 10.1117/12.645485

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We report on the stabilization of a semiconductor laser's frequency, using Rb absorption lines. In order to improve overall frequency stability within our system, we adjusted the setup used in Rb- saturated absorption spectroscopy, and optimized modulation parameters such as modulation - frequency and -width, to more accurately detect the error signal. When we stabilized laser frequency using a Doppler-free absorption line of Rb atoms, a time-constant of 0.01sec, and a modulation frequency of 7.77kHz, relative optical frequency stability of 2.12x10(-12)<=sigma(2,tau)<= 5.88x10(-11) was achieved, in averaging time for 0.04s <=tau <= 65s.

DOI： 10.1117/12.645726

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Language：English   Publishing type：Research paper (international conference proceedings)  

External cavity diode laser (ECDL) systems are presently experiencing a surge in popularity as laser light-sources, in advanced optical communications- and measurement-applications. Because such systems require that their external reflectors be precisely controlled, to eliminate low frequency fluctuations (LFF) in optical output, we conducted experiments with a two-cavity version of the ECDL system. This technique brings the added advantages of a narrower linewidth than would be achievable via a single optical feedback. However, the ECDL's oscillation frequency is susceptible to the influences of the driving current, changes in the refractive index, and changes in external-reflector length that result from fluctuations in atmospheric temperature. We made every effort to maintain the length of the ECDL cavity, while evaluating oscillation-frequency stability. We used a Super-Invar board as the platform for our ECDL system, in order to minimize the influence of thermal expansion. Moreover, our ECDL system combines an Rb cell within an external cavity
an arrangement designed to improve stability by restricting the LD frequency within both the external cavity mode and the Rb-saturated absorption spectrum. We used the square root of the Allan variance, when evaluating oscillation frequency stability, observing, in the process, that it improved stability by about one order of magnitude.

DOI： 10.1117/12.645759

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

An original guided-wave optical pressure sensor, which has a semi-closed space with a small hole under a diaphragm, can be used even under high quasi-static pressure without sacrificing sensitivity, unlike conventional pressure sensors. Moreover, the sensor possesses characteristics of a high-pass filter, so that it responds to only the high-frequency components of pressure change. The cutoff frequency of the high-pass filter of the sensor property is a key factor in designing the sensor, and is acquired from the step response of the sensor. In a step-like change in ambient pressure, a pressure difference is induced on the diaphragm for a short while because the small hole restricts fluid flow between the semi-closed space and the surroundings. The reciprocal of the duration of the induced pressure difference corresponds to the cutoff frequency. In this study, the step response in relation to the cross-sectional area of the small hole was examined experimentally, and the measured durations were compared with the theoretical ones. In the experiment, the duration was approximately inversely proportional to the area of the small hole as theoretically predicted although the measured durations are larger by a factor of thousands than the calculated ones.

DOI： 10.1117/12.685977

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

A satellite-to-satellite laser interferometer is essential for a future gravity-field mission to improve the accuracy and spatial resolution of the Earth's gravity model. We have designed a ground-based simulator of a satellite-to-satellite interferometer, which aims to evaluate instrument error reflecting on the accuracy of the gravity-field retrieval and achieve the essential technologies required to measure the intersatellite range rate. The developed simulator was successfully operated with a range-rate sensitivity of 40 nm/s/<radical><radicand>Hz</radicand></radical> in the measurement band of 10(-2)-1 Hz. From a primary demonstration, it was confirmed to be available for experimental simulation of the satellite-to-satellite interferometer in the laboratory. The simulator will be a powerful tool for establishing guidelines for the development of future gravity missions. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.2140280

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In this paper, an original guided-wave optical pressure sensor that responds only to rapid pressure change is described. The proposed sensor is based on a conventional guided-wave optical pressure sensor using intermodal interference, with an added semi-closed space with a small hole under the bottom side of the diaphragm. By the addition of this semi-closed space, the sensor, unlike conventional sensors, can withstand high static pressure. When there is a sudden change in ambient pressure, pressure within the semi-closed space cannot quickly adjust due to the small hole that restricts fluid flow. So, pressure difference is induced on the diaphragm for a short while. Thus, the sensor shows a response only to changes in pressure, not to static pressure. We examined the step response of the sensor, that is, the output characteristics for sudden pressure change. The diaphragm dimensions of the fabricated sensor were 14 mm×14 mm×0.22 mm. Also, the volume of the semi-closed space was 14 mm×14 mm×1.8 mm, and the sectional area of the small hole was 93 μm×25 μm. In this experiment, the pressure in a 30 cm×28 cm×30 cm closed box, in which the fabricated sensor was placed, was suddenly increased by 0.78 kPa. Due to the pressure change, the output intensity decreased by approximately 20% of the initial intensity level. Approximately 1.4 sec after the step-like change in pressure, output intensity returned to the initial level.

DOI： 10.1117/12.588457

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We report on the stabilization of a semiconductor laser's frequency, using spectra-controlled etalon. As the spectra of an etalon are controlled by, one of the Rb absorption lines.. they provide highly stable reference frequencies in a broad frequency range. When we adapted the PEAK method to the etalon's spectra and used a Doppler-free absorption line of Rb atoms as the control signal for the newest model of our system, relative optical frequency stability of 2.91 x 10(-11) <= sigma(2,tau) <= 3.72 x 10(-10) was achieved in averaging time for 0.04 <= tau <= 100s.

DOI： 10.1117/12.589743

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Language：English   Publishing type：Research paper (scientific journal)  

Tungsten microcavity light sources and tungsten cluster light sources have interested us as light sources for next-generation having high luminous efficacy and long lifetime. The complex refractive index of tungsten requires the operating temperatures from 2000 K to 6500 K to evaluate the luminous efficacy and lifetime. Little is, known however, about the complex index of tungsten at such high temperatures. Since ellipsometry has a non-contact measurement technique, the complex refractive index of any metal can be measured even under extremely high temperature with high accuracy. We consider that ellipsometry is an effective measuring method. We thus designed and fabricated the ellipsometer to measure the complex refractive index of tungsten at room temperature. As the result, we established the ellipsometer improved from measurement of the complex refractive index of tungsten from 2000 K to 6500 K. In this paper, we report on the problems to measure the complex refractive index of tungsten using the ellipsometry, and the achieved accuracy of measurement. KEYWORDS: microcavity light source, cluster light source, tungsten, complex refractive index, ellipsometry. © 2005, The Illuminating Engineering Institute of Japan. All rights reserved.

DOI： 10.2150/jlve.29.55

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A scattering ellipsometry is a newly developed method to measure a complex refractive index of metal clusters at a high temperature region. The complex refractive index is required to determine a luminous efficacy, which is one of the most important factors to develop lamps, of cluster lamps. In this study, we built a scattering ellipsometer, and considered its accuracy of measurement through evaluations of the complex refractive index of gold particles at room temperature. In measurement, a Nd: YAG laser of 532 nm was used as the light source. The measured complex refractive index of gold particles was 0.31 in real part and 1.75 in imaginary part. A repeatable accuracy was evaluated 0.01 in real part and 0.02 in imaginary part from a standard deviation in measuring the complex refractive index 10 times in the same condition. Also, the size parameter of gold particles was 1.71, and its repeatable accuracy was 0.02. Such accuracy is sufficient to estimate characteristics of the cluster lamps, such as the spectral radiant flux, the luminous efficacy and so on. © 2005, The Institute of Electrical Engineers of Japan. All rights reserved.

DOI： 10.1541/ieejfms.125.461

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

In this paper, an original guided-wave optical pressure sensor that responds only to rapid pressure change is described. The proposed sensor is based on a conventional guided-wave optical pressure sensor using intermodal interference, with an added semi-closed space with a small hole under the bottom side of the diaphragm. By the addition of this semi-closed space, the sensor, unlike conventional sensors, can withstand high static pressure. When there is a sudden change in ambient pressure, pressure within the semi-closed space cannot quickly adjust due to the small hole that restricts fluid flow. So, pressure difference is induced on the diaphragm for a short while. Thus, the sensor shows a response only to changes in pressure, not to static pressure. We examined the step response of the sensor, that is, the output characteristics for sudden pressure change. The diaphragm dimensions of the fabricated sensor were 14 mmx14 mmx0.22 mm. Also, the volume of the semi-closed space was 14 mmx14 mmx1.8 mm, and the sectional area of the small hole was 93 mu mx25 mu m. In this experiment, the pressure in a 30 cmx28 cmx30 cm closed box, in which the fabricated sensor was placed, was suddenly increased by 0.78 kPa. Due to the pressure change, the output intensity decreased by approximately 20 % of the initial intensity level. Approximately 1.4 sec after the step-like change in pressure, output intensity returned to the initial level.

DOI： 10.1117/12.588457

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Holographic characteristics of two different films using methyl violet dyes in polyvinyl alcohol matrices are reported. One of the films, Film A, contains only methyl violet in the matrix. The other film, Film B, contains methyl violet, triethanolamine and acrylamide in the matrix. Diffraction efficiencies of the two films were measured and compared. Mechanisms of holographic recording and the functions of the dyes are discussed. The films were 8 pm thick.. Holographic gratings were recorded in the films by two intersecting YVO laser beams at 532 nm. The recording intensity of each beam was 25 mW, 50 mW and 100 mW, and the beam diameter was 2.25 mm. The spatial frequency of the grating was 653 line/mm. During recording, intensity of the diffracted light was simultaneously measured using a He-Ne laser at 633 nm. Regarding Film A, diffraction efficiency reaches a peak at a specific exposure time. This means that holographic grating grows according to exposure time in low exposure, but vanishes when over-exposed. In bright regions of the interference fringe on the film, the dyes are bleached. Changes of absorption and refractive index due to bleaching would result in the holographic grating. Regarding Film B, the diffraction efficiency was saturated in high exposure, and the maximum diffraction efficiency was not strongly dependent on the concentration of methyl violet. In the bright regions of the interference fringe on the film, excited methyl violet and triethanolamine cause polymerization of acrylamide. Changes in the refractive index due to the polymerization build the holographic grating.

DOI： 10.1117/12.588487

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Holographic characteristics of two different films using methyl violet dyes in polyvinyl alcohol matrices are reported. One of the films, Film A, contains only methyl violet in the matrix. The other film, Film B, contains methyl violet, triethanolamine and acrylamide in the matrix. Diffraction efficiencies of the two films were measured and compared. Mechanisms of holographic recording and the functions of the dyes are discussed. The films were 8 pm thick.. Holographic gratings were recorded in the films by two intersecting YVO laser beams at 532 nm. The recording intensity of each beam was 25 mW, 50 mW and 100 mW, and the beam diameter was 2.25 mm. The spatial frequency of the grating was 653 line/mm. During recording, intensity of the diffracted light was simultaneously measured using a He-Ne laser at 633 nm. Regarding Film A, diffraction efficiency reaches a peak at a specific exposure time. This means that holographic grating grows according to exposure time in low exposure, but vanishes when over-exposed. In bright regions of the interference fringe on the film, the dyes are bleached. Changes of absorption and refractive index due to bleaching would result in the holographic grating. Regarding Film B, the diffraction efficiency was saturated in high exposure, and the maximum diffraction efficiency was not strongly dependent on the concentration of methyl violet. In the bright regions of the interference fringe on the film, excited methyl violet and triethanolamine cause polymerization of acrylamide. Changes in the refractive index due to the polymerization build the holographic grating.

DOI： 10.1117/12.588487

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Semiconductor lasers' oscillation wavelengths respond to temperature- and magnetic field-fluctuations. As reported in the 1960's, these wavelengths shortened, at lower than 80K, under a magnetic field larger than 4T. This phenomenon attracted our attention, during preliminary experiments, because, when we exposed bulk-type semiconductor lasers oscillating at 780nm to relatively weak magnetic fields (less than 1.4T), at room temperature (300K), we observed that the oscillation wavelength shifted to the longer (lower frequency) side. For this work, we focused on the longer oscillation wavelength shift, the lower power side optical output-power shift, and the higher voltage side terminal voltage shift of a number of multi-quantum-well (MQW) laser diodes oscillating at 780nm, under the same experimental conditions as those used in our previous works. In discussions of these shift mechanisms, we consider how wavelength (frequency), optical output-power, and terminal voltage shifts are correlated. Our expanded knowledge base has forced us to employ mechanisms completely different from those used in studies dating as far back as the 1960's. We are now introducing a mechanism in which temperature rise and the longitudinal magneto-resistance effect cause the shifts observed in our experiments.

DOI： 10.1117/12.589744

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Currently in the initial stages of development, the endeavor aims to use satellite-to-satellite tracking laser interferometer-based optical technique, to document fluctuations in earth's gravitational field indicating other critical changes in the environment. This system must be able to measure infinitesimal changes in the relative velocity of the two satellites, using a laser light source, which oscillates at frequency stability better than 10(-13) in the square root of the Allan variance. We have stabilized the laser's oscillation frequency using the Faraday effect of Rb absorption lines. This method modulates the reference frequency of the stabilization system by modulating the magnetic field applied to the Rb, absorption cell, instead of the oscillation frequency of the laser diode. Furthermore, we have adapted the "double optical feedback" to the laser diode for narrowing its oscillation spectrum and improving its frequency stability. In recent years, a "femtosecond optical comb generator" has been developed as a new reference frequency source for absolute frequency measurement. This optical comb generator is controlled by the microwave frequency standards systems and provides stability of 4 x 10(-13) at an averaging time of 1s and at the order of 10(-15) at 1000s averaging time. We have measured the frequency stability of our system using the optical comb. We obtained the best spectrum narrowing effect using two gratings as external reflectors in the double optical feedback setup. The obtained results were 6.269 x 10(-11) <= sigma <= 1.516 x 10(-10)(24.11kHz <= f <= 58.31kHz) from Is to 39s in the averaging time.

DOI： 10.1117/12.590396

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In this paper, the feasibility of a glass-based guided-wave optical microphone is described. The optical microphone consists of a rectangular diaphragm and a straight waveguide on the diaphragm. The sensitivity of the microphone and the resonance frequency of the diaphragm are dependent on the diaphragm dimensions. In this study, to confirm operation of the proposed optical microphone, the target values for phase sensitivity and resonance frequency were set at 1.3 mrad/Pa and 5 kHz, respectively. By design considerations, the diaphragm dimensions were determined to be 16 mm× 16 mm×0.15 mm. After fabrication, a sound wave of 1 kHz and 25 Pa, corresponding to 122 dB-SPL (sound pressure level), was applied to the microphone. In the experiment, the intensity-modulated output with the same frequency as the applied sound wave was obtained, but the observed output was unexpectedly caused by misalignment of the optical components due to mechanical vibration. The estimated output signal by the normal operation of the microphone for a sound pressure of 25 Pa was 1/10 - 1/100 of the noise level, according to the measured output characteristic to static pressure. In order to detect normal speech ranging from 55 to 65 dB-SPL, the S/N ratio should be improved by a factor of more than 104.

DOI： 10.1117/12.649176

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Language：English   Publishing type：Research paper (international conference proceedings)  

In this paper, an optical microphone using a silicon-based guided-wave optical pressure sensor as an opto-mechanical transducer is reported. The pressure sensor consists of a rectangular diaphragm and a straight waveguide on the diaphragm. The sensitivity of the sensor and the resonance frequency of the diaphragm are important factors to determine the characteristics of the microphone, and depend on the diaphragm dimensions. In this study, to examine a feasibility of the proposed optical microphone, the target values of phase sensitivity and resonance frequency were set at 1.6 mrad/Pa and 7 kHz, respectively. By design considerations, the diaphragm dimensions were determined to be 7 mm× 7 mm× 23 μm. After fabrication of the optical microphone, sound pressure from 5 to 25 Pa, with a frequency of 1 kHz, was applied to the fabricated microphone with a 7 mm× 7 mm× 27 μm diaphragm. During measurement, a lock-in detection was taken because the fabricated pressure sensor had an unexpected low sensitivity, which resulted in an extremely low S/N ratio. The measured output voltage from the lock-in amplifier was proportional to the sound pressure as expected although the lock-in detection is not practical for the microphone.

DOI： 10.1117/12.588456

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

In this paper, an optical microphone using a silicon-based guided-wave optical pressure sensor as an opto-mechanical transducer is reported. The pressure sensor consists of a rectangular diaphragm and a straight waveguide on the diaphragm. The sensitivity of the sensor and the resonance frequency of the diaphragm are important factors to determine the characteristics of the microphone, and depend on the diaphragm dimensions. In this study, to examine a feasibility of the proposed optical microphone, the target values of phase sensitivity and resonance frequency were set at 1.6 mrad/Pa and 7 kHz, respectively. By design considerations, the diaphragm dimensions were determined to be 7 mm x 7 mm x 23 mu m. After fabrication of the optical microphone, sound pressure from 5 to 25 Pa, with a frequency of 1 kHz, was applied to the fabricated microphone with a 7 mmx 7 mmx 27 gm diaphragm. During measurement, a lock-in detection was taken because the fabricated pressure sensor had an unexpected low sensitivity, which resulted in an extremely low S/N ratio. The measured output voltage from the lock-in amplifier was proportional to the sound pressure as expected although the lock-in detection is not practical for the microphone.

DOI： 10.1117/12.588456

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

We have stabilized the oscillation frequency of a diode laser using the Faraday effect of Rb absorption lines. The stabilized laser frequency was measured by means of a femtosecond mode-locked pulse laser optical comb generator.

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2150/jieij.88.281

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present a new displacement measuring technique with simplicity, robustness, high sensitivity and wide measurement range. A set of a frequency shifter and a voltage-frequency converter is used to lock a homodyne interferometer on the half-bright fringe by eliminating the Doppler fringe resulting from mirror motion. The mirror displacement is directly retrieved from the feedback signal of a fringe control loop. By developing a table-top interferometer, we successfully demonstrated signal recovery without significant degradation. The achieved displacement sensitivity and measurement range of the interferometer were 24 nm Hz(-1/2) and 1.3 mm at a Fourier frequency of 0.1 Hz, respectively. This technique was found to have a potential for application to precise displacement measurements. It is, in particular, suitable for a satellite-to-satellite laser interferometer to determine Earth's gravity field.

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Our research purpose is to build an artificial neural network with an excellent color discrimination capability like human being on a computer. In this study, we built the network, which was trained to learn 10 colors with different hues in the Munsell color system. Then, we examined the response of the trained network when the network was interrogated about 10 non-learned colors. The network showed a good color discrimination capability, close to that of human being. © 2004, The Illuminating Engineering Institute of Japan. All rights reserved.

DOI： 10.2150/jlve.28.101

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In development of tungsten microcavity illuminants and tungsten cluster illuminants, the Complex Reractive Index of tungsten at the operating temperature of 2000–6000 K is necessary to evaluate their luminous efficacy and lifetime. Little is, however, known about the complex index of tungsten in such a high temperature region. In this study, we have determined the complex index of tungsten using an ellipsometer at room temperature. In measurement, a He-Ne laser of 633 nm and a Nd:YAG laser of 532 nm were used as the light sources. The measured complex index of tungsten was 2.0 to 3.0 in real part and 2.5 to 3.0 in imaginary part at 633 nm. Also, the corresponding components at 532 nm were 1.8 to 2.8 and 2.4 to 2.8. Repeatable accuracy was estimated about 1% in measuring the complex index repeatedly at the same point on individual tungsten plates. It was, however, found that the measured complex index was linearly proportional to the reflectivity. This dependence is attributed to surface conditions such as oxidation and roughness on a microscopic scale. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.

DOI： 10.1541/ieejfms.124.114

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

We have applied a precise amount of electrical feedback into laser injection current to stabilize the oscillation frequency of a semiconductor laser. This feedback method usually requires a small direct modulation to the laser injection current to obtain an error signal. This broadens the oscillation width of the laser diode, but certain applications, such as those related to coherent optical communications and measurements, require a narrower oscillation linewidth. Thus, we have attempted to obtain the error signal and stabilize the laser oscillation frequency in a narrower oscillation linewidth using the Faraday effect of the Rb absorption line. Our next task for the Faraday-effect-based method involves frequency stabilization, which we accomplish using a large frequency discrimination gain Gd. By incorporating our "PEAK" circuit, which utilizes the envelope detection method to determine the switching points between two different absorption signals, we increase Gd in our improved PEAK methods.

DOI： 10.1143/JJAP.43.2504

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Currently in the initial stages of development, the endeavor aims to use satellite-to-satellite tracking laser interferometer-based optical technique, to document fluctuations in earth's gravitational field indicating other critical changes in the environment. This system must be able to measure infinitesimal changes in the relative velocity of the two satellites, using a laser light source, which. oscillates at frequency stability better than 10(-13) in the square root of the Allan variance. The constraints placed upon the system will ultimately require that the interferometer's light-source be small, lightweight, extremely efficient, durable, and possess high frequency-stability. Present-day technology of a laser diode possesses all of these characteristics, except the last and most critical one; frequency stability. So, our ongoing efforts are all focused on the search for a method of stabilizing the oscillation frequency of the satellite-to-satellite laser-diode light source. We used a Rubidium absorption line as a frequency reference of the frequency stabilization system and the "double optical feedback" method to narrow the laser diode's oscillation linewidth, in order to improve its frequency stability. We have measured the frequency, to determine its degree of stability, by comparing the "femtosecond optical comb generator"- and laser diode-frequencies.

DOI： 10.1117/12.576544

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We normally apply a precise amount of electrical. feedback into the laser injection current, to stabilize the oscillation frequency of a semiconductor laser. This feedback method usually needs a small direct modulation to the laser injection current, to obtain an error signal. This broadens the oscillation width of the laser diode, but certain applications, such as those related to coherent optical communications, benefit from, and in fact require narrower oscillation linewidth. We obtain the error signal, and stabilize the laser oscillation frequency in narrower oscillation linewidth, using the Faraday effect of the Rb absorption line. Our next task involves frequency-stabilization, which we accomplish, using a large frequency discrimination gain (G(d)). By incorporating our "PEAK" circuit, which utilizes the envelope detection method to determine the switching points between two different absorption signals corresponding to the different magnetic fields and different polarization conditions, we increases the G(d) in our stabilization system.

DOI： 10.1117/12.474809

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

In this paper, an original scale-reduction rule without sensitivity loss in integrated optic pressure sensors based on the elasto-optic effect is described. The sensor has a rectangular diaphragm as a pressure-sensitive mechanical structure and a sensing waveguide on the diaphragm. In this type of sensor, sensitivity is theoretically known to be strongly dependent on the dimensions of the diaphragm. According to the theoretical results, the sensitivity can be kept constant even if the diaphragm dimensions are reduced as long as both the side length ratio and the characteristic length remain constant. Here, the characteristic length is introduced as the cube of the shorter side length of the diaphragm divided by the square of the thickness. Such a scale-reduction rule would be very significant in the miniaturizing of a sensor without reducing sensitivity, but it has not been experimentally confirmed. In this study, the scale-reduction rule was experimentally examined using three fabricated sensors, which had the same side length ratio. and the same characteristic length. The exact dimensions of the sensors were 2.0 mm X 10 mm X 35 mum, 2.5 mm X 12.5 mm X 49 mum and 3.0 mm X 15 mm X 64 mum. The measured sensitivities of the three sensors were quite similar to each other as theoretically predicted.

DOI： 10.1117/12.474347

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

In this paper, the relationship between sensitivity and diaphragm dimensions in a glass-based integrated optic pressure sensor is described. The sensor has a rectangular diaphragm as a pressure-sensitive structure and a straight sensing waveguide across the diaphragm. The sensor operation is based on the phenomenon that a phase difference between two orthogonal guided modes is induced by the elasto-optic effect in the presence of applied pressure. The sensitivity of the sensor is theoretically known to be dependent on the thickness and side length of the diaphragm. Such dependencies are worth investigating to obtain helpful design rules for miniaturization of the sensor, but have not been examined experimentally in detail. In this study, to examine the relationship between sensitivity and thickness, two sensors were fabricated with 10 mm x 10 mm x 0.3 mm (sensor #1) and 10 mm x 10 mm x 0.22 mm (sensor #2) diaphragms.. The sensitivity of sensor #2 was larger than that of sensor #1 by a factor of 1.72, which closely agreed with the theoretical factor of 1.86. Moreover, to determine the relationship between sensitivity and side length, two more sensors, besides sensor #2, with 7mm-square (sensor #3) and 14mm-square (sensor #4) diaphragms, were fabricated with a diaphragm thickness of 0.22 mm. The measured sensitivities agreed approximately with the theoretical ones although there was a slight difference in sensor #4.

DOI： 10.1117/12.474348

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The sensitivities of integrated optic pressure sensors with diaphragms theoretically are known to be strongly dependent on the position of the sensing waveguide on the diaphragm. According to the theoretical results, the diaphragm edge is the best position for the waveguide of a sensor based on the elasto-optic effect. The relationship between sensitivity and the waveguide position, however, has not been investigated experimentally, although it is important in the designing of such a sensor and in determining the misalignment tolerance of the sensing waveguide. In this study, this relationship in a glass-based integrated optic sensor by use of an intermodal interference was examined experimentally. © 2002 Optical Society of America.

DOI： 10.1364/AO.41.005016

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

In this paper, a silicon-based integrated optic pressure sensor using an intermodal interference between the fundamental TM-like and TE-like modes is described. The sensor consists of a micromachined rectangular diaphragm and a straight polystyrene optical waveguide passing over the diaphragm. Its sensitivity is theoretically known to be strongly dependent on the position of the waveguide over the diaphragm. To experimentally investigate such dependence, we fabricated a sensor with a 1.2 mm x 10 mm x 20 mum diaphragm, over which waveguides were placed at 50 mum intervals. The measured phase sensitivity was 98 mrad/kPa for the waveguide nearest to the diaphragm edge. The measurement was also carried out for the other waveguides. As theoretically expected, the largest sensitivity was obtained for the waveguide nearest to the edge.

DOI： 10.1080/014680302317244807

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We have been developing a silicon-based integrated optic pressure sensor using an intermodal interference between the fundamental TM-like and TE-like modes. The sensor has a micromachined diaphragm with a sensing waveguide as a pressure-sensitive structure. The sensor is theoretically known to have a strong dependence of sensitivity on the sensing waveguide on the diaphragm. According to the theoretical prediction for the sensor based on the elasto-optic effect, the waveguide should be placed along the diaphragm edge to maximize sensitivity. To date, such dependence has not been experimentally examined in detail. In this study, two sensors with 20 or more waveguides placed at 0.1 mm intervals on the diaphragm were fabricated to determine the relationship between sensitivity and waveguide position. The diaphragm dimensions were (1) 2.0 mm x 10 mm x 35 mum and (2) 3.0 mm x 15 mm x 64 mum. The ratio between width and length of each diaphragm was 1:5. The maximum sensitivity of 100 mrad/kPa was obtained for the waveguide nearest to the diaphragm edge with a wavelength of 633 nm. In addition, the measured sensitivities were very similar for the corresponding waveguide positions in the two sensors since a scaling factor, which is defined as the cube of the either side length divided by the square of the thickness, was set as a constant.

DOI： 10.1117/12.449164

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We have experimentally investigated how sensitivity is dependent on the position of a waveguide passing over a diaphragm in a silicon-based integrated optic pressure sensor based on the elasto-optic effect.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

A silicon-based integrated optical pressure sensor using an intermodal interference between the fundamental TM-like and TE-like modes is described. The sensor consists of a micromachined rectangular diaphragm and a straight polystyrene optical waveguide passing across the diaphragm, The use of the intermodal interference has the potential advantage of shortening the sensor length since it needs neither a Y-branch nor a 3-dB coupler. In the presence of the pressure difference on the diaphragm, the phase difference is yielded between the two guided modes by an anisotropic index change induced by the elasto-optic effect. The phase difference is finally transformed into a change in light intensity by an analyzing polarizer. We fabricated a sensor with a 1.2 mm X 10 mm x 20 mum diaphragm over which the waveguides were formed at 50 mum intervals. In the experiment, a linearly-polarized He-Ne laser beam at 633 nm was coupled to the two guided modes at equal intensity. The output intensity through a polarizer was sinusoidally changed at a period of 64 kPa, corresponding to a phase sensitivity of 98 mrad/kPa, for the waveguide nearest to the diaphragm edge. The measurement was carried out for other waveguide positions. The largest sensitivity was obtained for the waveguide nearest to the diaphragm edge as theoretically expected.

DOI： 10.1117/12.426824

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC JAPAN  

we theoretically and experimentally investigated fundamental characteristics of an integrated optic pressure sensor using intermodal interference between the lowest-order TM-like and TE-like modes. The sensor consists of a rectangular diaphragm and a straight single-mode waveguide along an edge of the diaphragm. Its operation is based on a difference of phase retardations produced in the two guided modes through the photoelastic effect. The sensor was fabricated by bonding two glass substrates together: a Coming 0211 glass 300 mu m thick to form a waveguide and a thick substrate with a 10 mm x 10 mm square hole to define the diaphragm. The fabricated sensor was successfully tested using a He-Ne laser at 633 nm. The halfwave pressure was measured to be 77 kPa which is almost double the theoretical estimate.

DOI： 10.1007/s10043-000-0144-4

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We have measured the oscillation characteristic shifts of laser diodes originated from a magnetic field. We observed wavelength shifts toward the longer wavelength side, i.e., a red shift, by using the beat note between test and reference lasers at room temperature in more than five different laser types, whereas the experiments in early 60's showed a blue shift at extremely low temperature and in a very strong magnetic field. We also observed output power shifts toward the lower power side. Both characteristic shifts showed the same tendencies at increased temperature. So, we considered the magnetic field increases the temperature of the laser diodes and then two characteristics will change. Our experiment, however, showed that the amounts of changes in temperature, estimated from each characteristic shift, do not coincide with each other. At the first stage of our experiment, we removed the packaging parts of laser diodes because they are made of ferromagnetic materials. However, we recently observed the wavelength shifts using the laser diodes with the packaging parts. We are now expecting the changes of the current flow around the active region in the magnetic field can explain this discrepancy by using the correlation analysis between these two shifts.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We have theoretically and experimentally investigated the fundamental characteristics of glass-based integrated optic pressure sensors with a conventional Mach-Zehnder (MZ) interferometer and with an intermodal (IM) interferometer consisting of a straight waveguide. Each sensor has a rectangular diaphragm as a pressure-sensitive mechanical structure. The sensing path of the MZ interferometer and the waveguide of the IM interferometer should be placed along the diaphragm edge to maximize the sensitivity of the sensors based on the elasto-optic effect, if the deflection of the diaphragm is small, the phase difference either between the sensing and reference waves for the MZ interferometer or between the fundamental TM-like and TE-like modes for the IM interferometer is proportional to the applied pressure. The sensors were fabricated using two glass substrates: a 0.3mm-thick Coming 0211 glass and a thick soda-lime glass with a 10mm X 10mm hole. After forming the waveguide on the 0211 glass, both substrates were bonded together with optical cement. For each sensor, the dimensions of the diaphragm were 10mm X 10mm X 0.3mm and the interaction length was 10mm. The sensitivities measured at 633mm in wavelength were 0.053rad/kPa for the MZ interferometer using the TM-like mode and 0.041rad/kPa for the IM interferometer. Each result was, however, half its theoretical estimate.

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

An integrated optic pressure sensor based on intermodal interferometry is described. The sensor consists of a straight waveguide supporting the lowest-order TM-like and TE-like modes and a rectangular diaphragm as a pressure sensitive region. The waveguide is placed along an edge of the diaphragm to maximize the sensitivity of the sensor. The output intensity of the sensor system is dependent on a difference of phase retardations induced in the two guided modes by the applied pressure via the photoelastic effect. The sensor was fabricated using two glass substrates: a Coming 0211 glass with a thickness of 300 mu m and a thick substrate with a 10mm x 10mm square hole to define the diaphragm. The two substrates were finally bonded together by UV curing adhesion after the waveguide was formed on the thin substrate. The fabricated sensor was tested using a He-Ne laser at 633nm. We successfully obtained the sinusoidal change of the output power versus the applied pressure. The halfwave pressure was evaluated to be about 80kPa experimentally.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

A detailed numerical comparison of the bandwidth-efficiency trade-off for second-harmonic generation (SHG) achieved by the formation of two-dimensional quadratic spatial solitons versus the more conventional method of gentle focusing in the middle of a nonlinear crystal is presented. Numerical simulations for type II SHG in potassium titanyl phosphate with constant wave-vector mismatch show that the 3-dB drop-off in SHG conversion efficiency can be many multiples of pi in detuning from the phase-match condition over a large range of walk-off angles and focal positions. (C) 1998 Optical Society of America [S0740-3224(98)01911-0].

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SCRIPTA TECHNICA-JOHN WILEY & SONS  

The frequency stability of a semiconductor laser deteriorated under direct frequency shift keying (FSK) when stabilization depended entirely upon an external frequency reference. Therefore, the PEAK method was devised for the purpose of improving frequency stability.
This method requires two distinct frequency components and, therefore, will not work effectively in a communications system that produces a succession of identical frequencies, as does the FSK method on occasion. This paper, then, explains the results of our comparative analysis of the two modulation methods.
The evaluation of frequency stability requires us to use a beat note between two stabilized laser beams, referred to here, as "signal" and "reference" lasers. The reference laser is stabilized by a method that takes advantage of the magneto-optical effect. This laser restrains the tendency of the beat note frequency to broaden in other stabilization methods, and even makes it possible to predetermine the beat frequency to be employed. The improvement in frequency stability obtained is about one order of magnitude. (C) 1998 Scripta Technica.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SCRIPTA TECHNICA-JOHN WILEY & SONS  

In papers published previously, we discussed the oscillation wavelength shift of a semiconductor laser in a magnetic field at room temperature. Observations were carried out by means of a monochromator that was able to measure the oscillation wavelength shift in a steady state only and that was subject to a certain degree of measurement error. In this work, we used the beat note between two semiconductor lasers as a means of observing the wavelength shift. This method reduces the overall measurement error to about one tenth that obtained when using the monochromator-and enables us to observe the time dependence of the wavelength shift, after establishing a magnetic field. The observed wavelength shift was delayed in comparison with the square of the magnetic flux density, which is proportional to the wavelength shift in a steady state. The delay was about 0.07 s, which is much longer than we actually expected, when changing the temperature in an active layer. (C) 1998 Scripta Technica.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The oscillation frequency of a semiconductor laser must be stabilized in coherent optical communications systems that use such devices, because the frequency fluctuates according to variations in either temperature or injection current. Therefore, we set about the task of stabilizing it, using the Rb-D-2 absorption line as an external frequency reference and negative feedback control. This method of stabilization requires the application of small sine wave modulation to obtain error signal by synchronous detection method While the highly sensitive control ensures improved signal stability, frequency stability is deteriorated under direct FSK (Frequency Shift Keying), because the oscillation spectrum of a semiconductor laser is broadened. We, therefore, devised the. "PEAK method", which improves frequency stability under direct FSK. The accurate measurement of frequency stability requires that the beat note between two stabilized laser frequencies, the signal and reference lasers, be measured. But beat note was sometimes outside the limits of our measuring equipment The reference laser frequency was therefore adjusted by using the magneto-optical effect to control the beat note frequency within measurable limits of this work. We calculated the square root of the Allan variance to estimate the frequency stability, thereby confirming the effectiveness of PEAK method.

DOI： 10.1117/12.326633

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The shift, which occurs in the oscillation wavelength of a semiconductor laser in a magnetic field, has been the subject of great interest, since the early 60's. During the course of the investigation, the observed shift was toward the short wavelength side, i.e., a blue shift, which was well accounted for, in terms of the Landau level. At present, we are studying how wavelength shift is affected, by applying, at room temperature, a relatively weak magnetic field, using recently developed visible and infrared diode lasers. By doing so, we have observed a red shift and a decrease in laser output-power, under a certain magnetic field conditions in its strength and direction. Since these two changes in wavelength and output power correspond to those observed at higher temperatures, we assumed that the orientation of the magnetic field affects current density in laser diodes. And then it alters temperatures around the active layer, which in turn influence oscillation wavelength and laser output-power. Also of note, was the fact that the red shift and the decrease in laser output-power occurred simultaneously, revealing an almost linear dependency on one another. This might possibly explain the heat, which developed as the result of applying the magnetic field. However, we recently observed an instance, in which visible MQW laser diodes did not exhibit this linear dependence. Because this phenomenon cannot be traced simply to the effects of heat, we are now examining it in terms of current-density alteration.

DOI： 10.1117/12.326632

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The oscillation frequency of semiconductor lasers fluctuates by a temperature or an injection current change. Semiconductor lasers are now used in many application fields such as optical fiber communications systems, compact disk and laser disk systems, and others, because these application fields don't need the high frequency stability in their light source. Therefore, we must stabilize the oscillation frequency of semiconductor lasers if we use them in a coherent optical communications or other coherent systems.
Some frequency stabilization experiments of semiconductor lasers using external frequency references have been reported in recent years. We have also stabilized them using the Rb-D-2 absorption line as an external frequency reference. Applying a small modulation directly to the injection current usually performs these stabilization methods. But the oscillation spectrum of the semiconductor laser is broadened by the modulation in this method.
So we devised two stabilization methods without any direct modulation, which use the magneto-optical effects called the Zeeman and the Faraday effects, and stabilized the oscillation frequency of the semiconductor laser. As a result, we got high frequency stability without any spectrum broadening caused by the modulation. The stabilized frequency was tuned in a wide range at almost the same stability condition.
Moreover, we devised an optical setup, which produces a high sensitive error signal between the reference frequency and the laser oscillation frequency. This method, which we named "PEAK method", is also combined with the Zeeman effect to improve the frequency controllability.

DOI： 10.1117/12.326635

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Characteristics of radiation from microcavities are investigated to verify the luminous efficacy of microcavity radiator that was estimated by John F. Waymouth in 1989. Electromagnetic waves in a rectangular microcavity and a cylindrical microcavity were analyzed based on the waveguide theory. The modes of electromagnetic waves in the microcavities are analyzed using a normalized eigenfunction. The conductivity and permittivity of metals are obtained by analyzing the motion equation of the free electron in the metals. The skin depth of tungsten is estimated with the emissivity of tungsten based on electromagnetic theory. Accordingly it is estimated that the luminous efficacy of radiation from the microcavity is expected to reach 118 Im/W. © 1998, The Illuminating Engineering Institute of Japan. All rights reserved.

DOI： 10.2150/jlve.22.1_12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SCRIPTA TECHNICA-JOHN WILEY & SONS  

We have stabilized the oscillation frequency of a 780-nm-band semiconductor laser using the D-2 absorption line of Rb atoms. The absorption line has a spectral width due to the natural width and Doppler width, which limits the stability of laser performance. In order to minimize the spectral spread of the absorption line, a Doppler effect-free absorption line whose spectral spread is close to the natural width was obtained by saturated absorption spectroscopy and was used for stabilization of the laser oscillation frequency However, the spectral width of the absorption line could not be further narrowed by optical means alone. In this study, the spectral width of the reference signal was further narrowed using the Zeeman effect of the Rb atomic absorption line and the newly developed PEAK and BOTTOM methods. Using this reference signal, the width of the frequency discrimination curve was narrowed. As a result, the laser oscillation frequency more accurately tracks the reference frequency. In addition it was confirmed that the frequency discrimination curve could be swept. (C) 1998 Scripta Technica.

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In this paper, sensitivity improvement of integrated optic micropressure sensors is discussed. The sensor is composed of a diaphragm and a ring resonator that is a multiple interference optical circuit. A part of the waveguide of the ring resonator is on the diaphragm. When a pressure is applied to the sensor, the diaphragm is deformed and the refractive index changes slightly so that a phase shift is induced on the guided wave propagating on the diaphragm. From the change of the resonant frequency caused by this phase change, the magnitude of the applied pressure is detected. In this study, particular emphasis is on the relationship between the diaphragm dimensions and the sensor sensitivity. From the analysis of the sensor operation, it is concluded that the use of a square-shaped diaphragm with a waveguide of the ring resonator at the edge in addition to employing the TM-like mode is most suited for a highly sensitive sensor. Further, from the evaluation of the minimum detectable pressure, it is expected that an integrated optic microprocessor sensor can be realized which is sensitive to such low pressure as underwater acoustics.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley and Sons Inc.  

Optical information retrieval systems based on Fourier optics and using holographic memories of high-density recording capability, which raise the possibility of parallel information processing, have been proposed for a long time. However, the development of spatial light modulators which are the key devices in such systems has been delayed considerably and, so far, there is no report on optical information retrieval systems using spatial light modulators. With this as background, a spatial light modulator (SLM) based on a large-permittivity crystal is fabricated and its operation in a small-size system is verified. First, based on the function of the spatial modulator, the hologram and the detection sections are designed and specifications of the system are decided. Next, the two different schemes of synchronous and direct detection methods are applied to the information retrieval of 18 bits consisting of nine pieces of holograms. As a result, it is understood that retrieval is possible using even the currently available spatial light modulators. The relation between the functions of the SLM and the system also is clarified. However, there are several problems in realization of such systems, a discussion of which is presented in this paper.

DOI： 10.1002/ecjb.4420790802

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

The oscillating frequency of a semiconductor laser was stabilized at the Rb-D2 absorption line under direct frequency shift keying (FSK). The control system equipped with a peak-hold circuit provided the frequency stability of 10(-9) > sigma(2, tau) > 10(-12) at the averaging time 0.05 s < tau < 40 s when the Doppler-limited absorption line was used as a frequency reference. This stability was better than that obtained by the traditional control system without the peak-hold circuit under direct FSK. Using the saturated absorption signal, the frequency stability was improved more than one order of magnitude in comparison with that obtained using the Doppler-limited absorption signal.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE - INT SOC OPTICAL ENGINEERING  

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The wavelength shift of laser diodes in a magnetic field has been known for a long time. However, most of the studies have been performed at very low temperatures in a strong magnetic field. An experiment is carried out using laser diodes which oscillate at room temperature and found that the wavelength shift changed significantly, being sensitive to an inner structure. Further, the wavelength shift occurred depending on a magnetic field direction. Previously, the wavelength shift was explained on the basis of the Landau level at very low temperatures in a strong magnetic field. However, such Landau levels are not formed in a relatively weak magnetic field at room temperature
and, thus, the present result cannot be accounted for by the existing theories. This paper describes the experimental results of various types of GaAlAs laser diodes and discusses the mechanism of the wavelength shift and the wavelength control. Copyright © 1993 Wiley Periodicals, Inc., A Wiley Company

DOI： 10.1002/ecjb.4420760402

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Language：English   Publisher：INSTITUTE OF PURE AND APPLIED PHYSICS  

A novel integrated optic accelerometer employing a cantilever on a silicon substrate is proposed. An analysis is carried out to demonstrate the feasibility of the proposed sensor and obtain the basic design concept. The sensitivity and the detectable frequency range of the acceleration can be set by proper selection of the cantilever dimensions and the added weight.

DOI： 10.1143/JJAP.28.287

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The encryption technique is necessary for the internet community. The encryption using the pseudo-random numbers is considered safe because it takes a lot of time to decode it. However, since high speed processing computers are emerging in these days, it may not safe anymore. On the other hand, quantum cryptographic communications which are theoretically impossible to decode have been advanced and need a large number of physical random numbers. This paper describes a method, whereby semiconductor laser diodes' frequency noise-signatures generate a series of physical random numbers. As a result, we generated random number bit strings at 40Gb/s in a VCSEL and at 50Gb/s in a FPLD.

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Because of their low cost, light weight, low power consumption and durability, semiconductor lasers are ideal, for use as optical range finder light-sources. Their oscillation-frequency fluctuations generate the physical random numbers, which are used to measure distances. While normal range finders use modulation signals, such as sharp pulses, the method we devised employs semiconductor lasers' frequency noise, and a frequency to intensity converter, such as the rubidium absorption profile, to produce physical random numbers. This allowed us to construct an optical range finder that requires no additional modulation of the semiconductor laser, - has a range of up to 50 meters, and resolution of 0.06 meters. We also consider the resolving power of this method without changing its sampling rate.

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Laser diodes' oscillation characteristics vary according to types of materials used in their composition, injection current, laser temperature, and the strength of an applied magnetic field. Regarding the applied magnetic field, other researchers have thus far conducted their tests using up to 4T magnetic fields, at a temperature less than 80K; figures cited in Landau level theory. We have studied the effect of a magnetic field on the oscillation characteristics at "room temperature (300K) and a relatively weak magnetic field (〜0.5T)". This work describes the shifts in oscillation frequency-, injection current- and voltage, of a vertical cavity surface emitting laser diode (VCSEL), and the mechanism by which the device's oscillation characteristics shift, when exposed to a magnetic field.

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Language：Japanese   Publisher：一般社団法人電子情報通信学会  

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Language：Japanese   Publisher：一般社団法人日本物理学会  

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The light output from a semiconductor laser has high speed noise in both intensity and frequency region. We generate physical random numbers from frequency noise which will be converted into intensity frequency noise by using a frequency discriminator. In this report, we compared two random numbers, one is generated from the free-running laser and the other is generated from the narrower-oscillation-width laser.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Recently, cryptographic is important to protect information. Now, the pseudo-random number is used for cryptographic. But, it will be deciphered easily because of the computer development in the near future. Physical random number attracts attention because it is difficult to be deciphered when the physical random number is used in coding system. On the other hand, it is difficult to create it fast. Therefore, many fast physical-random number generation methods, which use the wide intensity noise characteristic of a diode laser, have been reported. We demonstrated a fast physical random number generation using the laser diode's frequency noise characteristic.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

A semiconductor laser's frequency fluctuates owing to the refractive index fluctuations caused by the spontaneous emission in a laser cavity. In this study, a new application of semiconductor laser's frequency noise characteristics is discussed. We propose a new laser rangefinder using the semiconductor laser's frequency noise. This method calculates the correlation between the divided laser beams and determines the optical distance without any modulation, and its accuracy are expected unchanged even in a long distance measurement. We measured the distance from 0 to 35m using the proposed method.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Because a semiconductor laser's oscillation frequency changes easily, its frequency stabilization is necessary for many application fields. We stabilized semiconductor laser's oscillation frequency using the direct modulation method and measured two stabilized laser's relative frequency stability using the beat signal between two laser beams. Recently THz wave generationis focused, so we think we can use the semiconductor laser as the THz wave source. We measure the beat signal of 1.2GHz as abasic experiment.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have been constructed a physical random number generator which utilizes laser diode's frequency noise characteristics. A linewidth of a laser diode indicates the range in which its oscillation frequency fluctuates. In this study, we generate random numbers using a laser diode which operates in a free-running condition and in an external cavity diode laser system which have a narrow linewidth. We used the "FIPS140-2" test as a statistical test suitable for the evaluation of random numbers and compared the random numbers which are generated in our two laser systems so that we consider the influence of linewidth of laser diodes.

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The output characteristic of a diode laser is changed by the conditions of its injection current, its temperature, and the applied magnetic fields. We made a research on a Fabry-Perot type diode lasers, especially its oscillation frequency characteristic in a room temperature and relatively weak magnetic fields in our previous work. This work reports the characteristic of a VCSEL in a magnetic field. The obtained result is different from that of a Fabry-Perot type diode laser's case and the VCSEL's oscillation frequency shifted to the higher oscillation frequency side.

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The frequency of a semiconductor laser fluctuates around its center optical frequency, owing to a refractive index variation resulting from carrier density fluctuations. By using the frequency discriminator, the frequency noise is converted into the intensity noise, then the amplitude is converted into binary numbers and produce the physical random number from it. But it may degrade its random number characteristic when its center oscillation frequency varies. Here we measure the examination pass rate of the generated binary numbers through this test.

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The pseudo-random number is normally used for large-scale simulation and encryption of communication. On the other hand, the physical-random number is recently expected to be used in these fields because it has no calculable periodicity and so makes the safer cipher. Therefore, many fast physical-random number generations, which use the wide intensity noise characteristic of a diode laser, have been reported. Because the diode laser has very fast frequency noise, we propose the method using it here.

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Because a semiconductor laser's oscillation frequency changes easily, its frequency stabilization is necessary for many application fields. We measured this frequency stability using the beat signal between frequencies of two semiconductor lasers. We studied the generation method of terahertz waves by means of semiconductor laser's beat signals because this method has the potential of low cost, small size, and high performance Terahertz wave sources for medical and communication fields.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The Output characteristic of a diode laser is changed by the its conditions of injection current, temperature, and magnetic fields. So far, we researched on a Fabry-Perot type diode lasers, especially its t oscillation frequency characteristic in room temperature and relatively weak the magnetic fields. We studied the characteristic of a VCSEL in magnetic field. That result differed from the Fabry-Perot type diode laser's case and the VCSEL's oscillation frequency shifted to the higher oscillation frequency side.

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Diode lasers are characterized by wideband frequency-noise output that is easily detected by frequency-selective elements, that convert frequency deviation into intensity fluctuation. Any such intensity noise can be digitized by means of A/D converters; so, some of these digital signals demonstrate physical-random number characteristics. We demonstrated physical random number generation and evaluated the physical random numbers using NIST standard tests.

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Pseudo-random numbers' periodicity renders them inappropriate for use in cryptographic applications, but, naturally-generated physical-random numbers have no calculable periodicity, thereby making them ideally-suited to the task. Some experiments about physical-random number generation have reached to Gbps range by using laser diode's (LD's) intensity noises in recent years. The laser diode naturally produces a wideband "noise" signal that is believed to have tremendous capacity and great promise, for the rapid generation of physical-random numbers for use in cryptographic applications. The result shows that the fast physical-random number generation, as fast as 5Gbps, is obtainable, using the laser diode's frequency noise characteristic.

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本文データは学協会の許諾に基づきCiNiiから複製したものである

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Recently, the compact and highly coherent laser light source is required to be developed for the use in the laser interferometers on the artificial satellite. The semiconductor laser is a promising candidate of these light sources, but there is the defect that the oscillation frequency varies with the change of driving current and atmospheric temperature. Therefore we are using the atomic absorption line as a frequency reference, and stabilize the oscillation frequency of the semiconductor laser. We describe the oscillation frequency stabilization in which we used the magneto-optic effect for obtaining the error signal for the stabilization without directly modulating the injection current of the laser diode, i.e., without broadening the oscillation width of the diode laser. We tried to improve the frequency stability by reducing the temperature fluctuation using a permanent magnet instead of the electromagnet for obtaining the Faraday effect.

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DECIGO (DECI-hertz interferometer Gravitational wave Observatory) is the future Japanese space gravitational wave antenna with observation band around 0.1 Hz. It aims at detecting gravitational waves from various kinds of sources, with sufficient sensitivity to establish the gravitational wave astronomy. In the pre-conceptual design, DECIGO is formed by three drag-free spacecraft, 1000 km apart from one another. The relative displacements between proof masses housed in these spacecraft are measured by Fabry-Perot interferometers. We plan to launch DECIGO in 2024 after research and development phase, including two milestone missions (DECIGO pathfinder and Pre-DECIGO) for verification of required technologies. © 2008 World Scientific Publishing Co. Pte. Ltd.

DOI： 10.1088/1742-6596/120/3/032004

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We expect that semiconductor lasers are useful for precise interferometric systems employed in artificial satellites, by virtue of their overall compactness, lightweight, durability and energy-efficiency. However, stability of their oscillation frequency and broad-spectrum linewidth are obstacles in this area. Once we find a way to sidestep that issue by stabilization, satellite-to-satellite tracking laser interferometers will measure fluctuations in earth's gravitational field with a level of precision we can now only dream of. Thus far, we have succeeded in stabilizing semiconductor lasers' frequencies to Rb-saturated absorption lines. In order to narrow oscillation linewidth, we introduced "Double Optical Feedback". This double optical feedback system reduces oscillation linewidth and also reduces fluctuations in intensity and frequency, without resorting to mechanical control elements.

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Research, using tandem satellites' on-board tracking laser interferometers, is aimed at gauging the infinitesimal variations in the relative velocities of these orbiting bodies, to accurately measure fluctuations in earth's gravitational field. A major part of this effort has involved the stabilization of semiconductor lasers' frequencies to Fabry-Perot etalons and atomic absorption lines, and obtaining from them, the requisite control signal, by directly modulating the oscillation frequency. Taking advantage of the etalon's short-term stability and tunability over a wide frequency range, and the Rb absorption line's stability over the long term, we succeeded in stabilizing the frequency of a semiconductor laser.

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The recent development of FTTH (Fiber To The Home) can provide not only an Internet service but also IP phone and Cable TV system services. But, the faster communication links will be required for these services in the near future. So, we are interested in the fast modulation characteristics of a VCSEL (Vertical Cavity Surface Emitting Laser) and investigate the optical feedback method for improving the VCSEL's oscillation characteristics, which is important to use the VCSEL in the wavelength division multiplex system. Our experimental results showed that this system could narrow its oscillation linewidth and stabilize its oscillation frequency.

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External cavity diode lasers are presently experiencing a surge in popularity, as laser light-sources for advanced optical measurement systems. While these systems normally require an active cavity-control device, we removed this active element from the setup, by adding a second external cavity. This technique boasts the added advantage of having a narrower oscillation-linewidth than would be achievable, using a single optical feedback.

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Semiconductor lasers used as light sources for satellite-to-satellite tracking interferometers measure fluctuations in earth's gravitational field, accurately gauging infinitesimal variations in the relative velocities of satellites flying in tandem, at better than 10nm/s ; a feat that requires frequency stability better than 10^<-13> in the square root of Allan variance σ. Having stabilized semiconductor lasers' frequencies to external Fabry-Perot etalon- and atomic absorption line- references, we are able to take maximum advantage of the Fabry-Perot etalon's short-term stability and the Rb absorption line's stability over the long term, to create a robust, frequency-stabilized semiconductor laser system. We obtained the stability 9×10^<-13> by improving the temperature stability of our laser mount.

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Sensitivity of a guided-wave optical microphone is theoretically found to be inversely proportional to the square of the diaphragm thickness. Also, according to the theoretical analysis, sensitivity increases with an increase in side length ratio for the side length ratio of less than unity, but the sensitivity shows a plateau for the ratio of more than unity. These dependencies, however, have not been demonstrated experimentally, although they are important in the designing of the optical microphone. In this study, these dependencies were examined experimentally. Based on the sensitivity dependence with respect to the diaphragm dimensions, the optical microphone with a 20 mm×20 mm×0.15 mm diaphragm was fabricated, and then successfully detected a sound wave of 100 dB-SPL.

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Sensitivity of a guided-wave optical microphone is theoretically found to be inversely proportional to the square of the diaphragm thickness. Also, according to the theoretical analysis, sensitivity increases with an increase in side length ratio for the side length ratio of less than unity, but the sensitivity shows a plateau for the ratio of more than unity. These dependencies, however, have not been demonstrated experimentally, although they are important in the designing of the optical microphone. In this study, these dependencies were examined experimentally. Based on the sensitivity dependence with respect to the diaphragm dimensions, the optical microphone with a 20 mm×20 mm×0.15 mm diaphragm was fabricated, and then successfully detected a sound wave of 100 dB-SPL.

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Random numbers can be classified as either pseudo-random or physical random in character. Pseudo-random numbers' periodicity renders them inadequate for coding purposes, in an age of ultra high-speed calculation, whereas Naturally-generated physical random numbers have no calculable periodicity. This work demonstrates how semiconductor lasers' inherent noise can be exploited for use in generating the physical random number and applying it in the field of cryptography.

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In 1916, Albert Einstein argued for the existence of gravitational waves. But, confirmation of his ideas would not come, until 1991, when the binary neutron star, PSR1913+16 was discovered. We now understand that gravitational waves carry information of ultimate states in space to us. And, while we know that these tide-like forces move at the speed of light, we have yet to detect them directly. To verify the existence of gravitational waves, we need laser interferometers that are far more powerful than those currently in uses, and have been conducting experiments with frequency-stabilized atomic absorption line-based semiconductor lasers. While these devices hold some promise, we are still contending with their absorption lines' broad linewidths. In the interim, we are using the PEAK method, to obtain a stabilization point.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Wavelength stability and spectrum purity are crucial, when a semiconductor laser is used as a light source, in precision optical measurement systems. This paper reports the improvements of a semiconductor laser's characteristics using the double optical feedback system, which consists of two mirrors or two diffraction gratings. The double optical feedback can lessen the laser linewidth and improve the frequency stability. However, a long-term stability level worsens because the length of an external resonator changes by the atmospheric temperature variation. Some experiments, which can suppress the influence of the temperature change, are reported in this paper.

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Other Link： http://id.nii.ac.jp/1141/00052364/

Language：Japanese   Publisher：一般社団法人電子情報通信学会  

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Wavelength stability and spectrum purity are crucial, when a semiconductor laser is used as a light source, in precision optical measurement systems. This paper reports the frequency stabilization of a semiconductor laser using the double optical feedback system, which is consist of two mirrors or two diffraction gratings. The double optical feedback can lessen the laser linewidth and improve the frequency stability. However, a long-term stability level worsens because the length of an external resonator changes by the atmospheric temperature variation. Some experiments, which can suppress the influence of the temperature change, are reported in this paper.

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We have improved the frequency stabilization system of a semiconductor laser, which uses a Fabry-Perot etalon as a frequency reference, by controlling the etalon spectrum using the Rb absorption line. Because the stabilization system using the etalon has a wide control range but a defect in its long-term stability, we combined the etalon system with the atomic absorption system, which can provide the control signal for the long-term stabilization. This paper reports an experiment using the saturated absorption spectroscopy of the Rb absorption line to obtain the control signal for the etalon and then to improve the frequency stability of the semiconductor laser

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Other Link： http://id.nii.ac.jp/1141/00052149/

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Wavelength stability and spectrum purity are crucial, when a semiconductor laser is used as a light source, in coherent optical communications systems and precision optical measurement systems. This paper reports the frequency stabilization of a semiconductor laser using the double optical feedback system, which is consist of two mirrors or two diffraction gratings. The double optical feedback can lessen the laser linewidth and improve the frequency stability. However, a long-term stability level worsens because the length of an external resonator changes by the atmospheric temperature variation. Some experiments, which can suppress the influence of the temperature change, are reported in this paper.

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A satellite gravity mission is proposed to monitor the Earth's environment in Japan. In the mission, a satellite-to-satellite laser interferometer (SSI) will be employed to amplify the gravitational signal by measuring the relative velocity of twin satellite in the low earth orbit. The maximum range-rate we must measure is predicted to be 0.1 m/s, whereas the required sensitivity is lOnm/s in the measurement band of 10^<-2> 〜 1 Hz to detect the changes in the geoid with millimeter-level accuracy. We are developing a ground simulator to study the feasibility of the SSI for the future mission.

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Semiconductor laser's oscillation wavelengths are altered significantly, when semiconductor laser are exposed to magnetic fields. When we set some bulk type semiconductor lasers oscillating at 780nm in weak magnetic fields (〜1.4T), at room temperature (300K). When the magnetic field is applied to the laser diodes parallel to the injection current, we observed that the oscillation wavelength shifted to the longer wavelength (low frequency) side in our preliminary works. In this work, we report the longer wavelength side shift, the lower optical output-power side shift, and the higher side terminal voltage shift of some multi-quantum-well (MOW) laser diodes oscillating at 780nm. We are now introducing the mechanism, in which the temperature rise and the longitudinal magneto-resistance effect cause the characteristics shifts observed in our experiments.

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In this work, in order to employ semiconductor lasers as light sources for optical frequency-, or phase-based systems, we constructed an external frequency reference system that boasted high stability in a wide frequency range. While, ino our previous experiments, we stabilized the oscillation frequency of a laser diode using one of the spectra of an etalon, and controlled its spectrum, using the Rb-D_2 absorotion line, this paper describes the outcome of a trial, where an adapted version of the PEAK method improved the laser diode's frequency stability, to one of the etalon spectra, by using a saturated Rb-D_2 absorption he as the control signal for the etalon.

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There is an idea to measure the time varying gravity field for the global observation of the environmental changes, using the laser interferometric technique for satellite-to-satellite tracking instead of using the radio technique as used in the current inter-satellite system, GRACE. It is required to measure the changes of the relative velocity between the twin satellites better than lOnm/s in averaging time for 1s ≦ τ ≦ 100s by using a frequency-stabilized laser light source which oscillates in frequency stability better than 10^<-12> in the square root of the Allan variance in this optical system. We are investigating availability of a diode laser as a light source of a laser interferometer in satellite by stabilizing its oscillation frequency using "double optical feedback" method to narrow its oscillation linewidth.

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Other Link： http://id.nii.ac.jp/1141/00051613/

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We have stabilized the oscillation frequency of a laser diode using the magneto-optical effect of the Rb absorption line with "PEAK" method. In recent years, a "femto second mode lock pulse laser optical comb generator" has been developed as a new reference frequency source. We used the "double optical feedback" method to narrower the oscillation line width of our stabilized laser diode and measured the stability by using the optical comb.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have studied the oscillation frequency stabilization of a semiconductor laser in a 1.5μm wavelength region using an inner second harmonic generation of 1.56μm laser light and the Rb D_2 absorption line as an external frequency reference. However, the output power of the inner SHG is too weak for the frequency stabilization, so we tried to increase it by introducing an optical feedback method. This method is also effective for decreasing the oscillation linewidth and improving the semiconductor laser frequency stability. In this experiment, we decreased the fundamental spectrum width of a semiconductor laser and examined the improvement of the semiconductor laser frequency stability by using the optical feedback method.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have measured the optical output power and the oscillation wavelength shifts of visible and infrared semiconductor lasers of some different inner structures in a magnetic field. From the experimental result of our early experiments, we thought that the characteristic changes of semiconductor lasers are due to temperature increase inside thesemiconductor laser. We, however, obtained the result that needs the explanation using not only the effect of a temperature butalso that of carrier density by the experiment of semiconductor lasers oscillating at different wavelengths and having different inner structures. We report our experiment to examine the shift mechanism in detail.

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Language：Japanese   Publisher：一般社団法人電子情報通信学会  

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Language：Japanese   Publisher：一般社団法人電子情報通信学会  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

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Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

The tungsten microcavity light source and the tungsten cluster light source have recently attracted interest as next-generation light sources that have a high luminous efficacy and a long lifetime. The complex index of refraction of tungsten requires a 2000 to 6500K operating temperature to evaluate the luminous efficacy and lifetime. Little is, known however, about the complex index of tungsten at such high temperatures. We consider that ellipsometry is an effective measuring method because it can measure complex index of refraction without metallic contact at these temperatures. We thus designed and fabricated an ellipsometer and used it to measure the complex index of refraction of tungsten at room temperature. As a result, we established that with an improved ellipsometer the complex index of refraction of tungsten could be measured at 2000-6500K. In this paper, we report on the problems of measuring metallic complex index of refraction precisely using ellipsometry and on the achieved measurement accuracy.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

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Other Link： http://id.nii.ac.jp/1141/00051400/

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Other Link： http://id.nii.ac.jp/1141/00051443/

Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

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An atom, such as a Rb, has absolutely stable absorption line at its peculiar frequency. One, therefore, can not select an arbitrary frequency using an atomic absorption line. On the other hand, the transmitted light spectrum of a Fabry-Perot etalon is affected by an environmental temperature, because the cavity length of etalon changes with the temperature variation. So, we constructed highly stable and broad frequency reference using the merits of Rb absorption line and etalon spectrum, and then stabilized the oscillation frequency of a semiconductor laser.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have stabilized the oscillation frequency of a semiconductor laser using the Faraday effect of the Rb absorption line. Our method modulates the reference frequency instead of the laser frequency, so the oscillation linewidth is not broadened by our stabilization procedure. We have obtained high stability by using the PEAK method, which we devised. We also improved the frequency stability by making the experimental setup smaller and simpler, and reducing the noise source.

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

A kind of small variations of a pendulum is reported as a result of a "gravito-radiative-force", which is one of the gravitational effects derived from the general theory of relativity. The same report also describes the experimental results in which two pendulums moved to the same direction at the same time due to the gravito-radiative-force. This study is planned to confirm this experimental result using the optical measurement system. Our experimental setup is located in a tunnel where we can expect very small level of external noises. We have observed the effects of earthquakes and tidal forces in our measurement.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have studied the oscillation frequency stabilization of semiconductor lasers in a 1.5μm wavelength region using an inner second harmonic generation of 1.56μm laser light by adapting the Rb D_2 absorption line as an external frequency reference. However, the output power of inner SHG is too weak for the frequency stabilization, so we tried to increase it by using an optical feedback method. This method is also effective for decreasing the oscillation width of semiconductor lasers. In this experiment, we survey two DFB lasers with various optical feedback intensity.

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Language：Japanese  

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Other Link： http://id.nii.ac.jp/1141/00051221/

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Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

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Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have stabilized an oscillation frequency of a semiconductor laser using the Rb absorption line as an external frequency reference by feeding back the frequency difference between the laser frequency and the external reference frequency. We built up the experimental setup in a very quiet condition of the astronomical observatory site and compared the stability of our experimental setup in a two conditions, i.e., the normal laboratory at the university and the room in a specially designed turnel for the precise measurement.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The oscillation frequency stabilization of a semiconductor laser is usually demonstrated by the direct modulation of its injection current, although this method increases its oscillation linewidth. This linewidth broadening, however, must be removed in some application fields. We, therefore, stabilized its oscillation frequency using the Faraday effect of the Rb absorption line. Our method modulates the reference frequency instead of the laser frequency, so the oscillation linewidth is not broadened by this method. We examined the relation between the strength of a small modulation signal for the stabilization and the frequency stability. We also examined the improvement of the frequency stability using the PEAK method, which we devised to obtain the large reproducible control signal for the frequency stabilization.

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Other Link： http://id.nii.ac.jp/1141/00051036/

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The oscillation frequency stabilization of a semiconductor laser is usually demonstrated by the direct modulation of its injection current, although this method increases its oscillation width. This broadening of the oscillation width, however, must be removed in some application fields. We, therefore, stabilized the oscillation frequency of a semiconductor laser using the Faraday effect of the Rb-D_2 absorption line and the PEAK method, which we devised to obtain the reproducible and large control signal for the frequency stabilization. Our method modulates the reference frequency of the Rb-D_2 absorption line instead of the laser frequency, so the oscillation spectrum is not broadened by this stabilization method.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Other Link： http://hdl.handle.net/10191/8849

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We observed the oscillation-wavelength and optical-output shifts of several semiconductor lasers in a magnetic field. We obtained that a certain thermal effect arising from an applied magnetic field altered the characteristics of infrared semiconductor lasers. It was recently observed, however, that fluctuations in carrier density arising from the aforementioned field also exert considerable influence on the wavelength of a visible semiconductor laser. Also of note, is the fact that multiquantum well lasers displayed characteristics at variance with anything previously encountered. This paper, then, details observations made regarding changes in overall characteristics and discusses the mechanism by which they occur.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

A laser interferometer is a measuring system which measures a spatial variation accurately. Therefore, it is used in a variety of precise measurements. The detection of a gravity wave, whose existence is predicted by the theory of relativity, is its remarkable example. On the other hand, anisotropy of space, which is also derived from the theory of relativity as a zero-frequency gravity wave, is reported to be detectable using a plumb line. We, therefore, started to investigate a method detecting the movement of the plumb line using a semiconductor laser. We proposed a laser interferometer, which detect three dimensional movement and discussed its resolving power with the theoretical estimation here.

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Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We stabilized the oscillation frequency of a semiconductor laser under direct frequency shift keying (FSK) and improved the measuring system of its frequency stability. Semiconductor laser frequency stability is deteriorated under direct FSK when a conventional external frequency reference is employed for the frequency stabilization. Therefore, we devised the control system named "PEAK method", which improves the frequency stability. The accurate measurement of frequency stability requires that the beat note between two stabilized laser beams, the signal and reference laser beams, be measured. The reference laser frequency was adjusted for controlling the beat frequency within the measurable range in this work.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have, during the last decade, examined the mechanisms of oscillation wavelength and light output shifts in six near infrared semiconductor lasers subjected to magnetic fields. In this work, we observed these same shifts of visible wavelength semiconductor lasers and examined the shift mechanisms of lasers oscillating at different wavelengths. The observations were performed, case by case, using a monochromator and a beat note.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Other Link： http://hdl.handle.net/10191/9027

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Other Link： http://hdl.handle.net/10191/9026

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have reported the oscillation frequency stabilization of a semiconductor laser without a direct modulation. This is because the direct modulation broadens the oscillation frequency. We used the Rb absorption line as a frequency reference and applied a modulated magnetic field to the Rb cell. This method modulates the reference frequency by magneto-optical effects and provides the frequency stabilization without frequency broadening. We also applied the optical feedback techniques for narrowing the oscillation width. The influence of the optical feedback upon the spectrum under the frequency stabilization is confirmed.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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We have reported the oscillation wavelength shift of semiconductor lasers in a magnetic field at room temperature. The observation method using the monochromator has reading errors and is applicable to measure the oscillation wavelength shift only in a steady state. In this work, we used the beat note between two semiconductor lasers for observing the wavelength shift. This method reduces the reading error to about one tenth of that obtained by the monochromator and enables to observe the time dependence of the wavelength shift. We explain our experimental results and discuss the mechanism of this wavelength shift, here.

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Language：Japanese   Publisher：The Illuminating Engineering Institute of Japan (IEIJ)  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Integrated optic pressure sensor with high sensitivity and small dimensions is proposed.The sensor is composed of a diaphragm and a ring resonator of which a part is placed on the diaphragm.The diaphragm is deformed by applying pressure.The deformation induced strain in the diaphragm.By the photo-elastic effect,the refractive index changes and then the guided wave propagating on the diaphragm undergoes phase shift.The phase shift is detected from a change in resonant frequency of a ring resonator which is a optical circuit with the highest phase sensitivity.Sensitivity of the sensor depends on shape and dimensions of the diaphragm and finess of the ring resonator.In this report,the relations between the sensitivity and the shape and dimensions are mainly described. According to the theore tical results,the sensor has a potential of sensing low pressure such as acoustic pressure field.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have reported the oscillation wavelength shift of semiconductor lasers in a magnetic field at room temperature.The observation method using the monochromator has reading errors and the method using the atomic absorption line has a restrictions in the oscillation wavelength of the semiconductor laser.Both methods can observe the wavelength shift only in a steady state.In this work,we used the beat note between two semiconductor lasers for observing the wavelength shift.This method provides the better resolution and can be applied to observe the time dependence.We explain our experimental results and discuss the mechanism of this wavelength shift,here.

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The traditional frequency stabilization method of a semiconductor laser using the Rb absorption line as a frequency reference is difficult under direct frequency shift keying(FSK). Moreover,if the signal is modulated by the pulse-duration modulation(PDM)scheme,the frequency stabilily is degraded by the moving frequency-locking point due to the modulation signal.The peak-hold method,which has been devised for improving frequency stability under direct FSK,is clearly demonstrated here for the PDM-FSK scheme and its stability is confirmed unchanged in several modulation conditions.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have stabilized the oscillation frequency of a semiconductor laser under direct frequency shift keying (FSK)using the saturated absorption signal of the Rb atoms.By using the saturated absorption signal,we can obtain the narrow frequency reference signal,which is the Doppler free signal.The frequency stability using the saturated absorption signal is better than that of the normal absorption signal by about one order of magnitude.In this paper,we discuss the better stabilization conditions,by considering the transmitted light intensity under direct FSK using thesaturated absorption signal.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have already reported the oscillation wavelength shift of GaAlAs laser diodes in a magnetic field at room temperature.In this work,we confirmed the reproducibility of the dependence of the wavelength shift on the angle between directions of the magnetic field and the semiconductor laser.In order to investigate the cause of the error observed in the experiment by now,we measured the time dependence of the oscillation wavelength shiftafter we applied the magnetic field.We also measured the output laser power change in a magnetic field.Here,we discuss the mechanism of this wavelength shift by using our experimental results.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

An information retrival system based on the Fourier optics is described.The system enables to pick out required data from a-huge amount of information in parallel using a spatial light modulator(S.L.M).In the system,hologram is used as a storage medium to densely store digital information..We built and tested a experimental system by which nine pieces of information with eighteen bits each could be accessed.The system was influenced by aberration of lenses and performance of S.L.M,for example S, N in detection,the processing time of the system,the number of data in a piece of imformation and so on.The system is expected to be practically used when a higher-performance S.L.M is developed.

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Other Link： http://hdl.handle.net/10191/9028

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

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Language：Japanese   Publisher：レ-ザ-学会  

DOI： 10.2184/lsj.20.3_160

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Language：Japanese   Publisher：レ-ザ-学会  

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