Seishi Sekine

Relationship between sensitivity and waveguide position on the diaphragm in integrated optic pressure sensors based on the elasto-optic effect

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.

Silicon-Based Integrated Optic Pressure Sensor Using Intermodal Interference between TM-Like and TE-Like Modes

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 2 10 mm 2 20 w m diaphragm, over which waveguides were placed at 50 w m 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.

Optical computing using optical flip-flops in Fourier processors: use in matrix multiplication and discrete linear transforms.

An architecture and the algorithms for matrix multiplication using optical flip-flops (OFFs) in optical processors are proposed based on residue arithmetic. The proposed system is capable of processing all elements of matrices in parallel utilizing the information retrieving ability of optical Fourier processors. The employment of OFFs enables bidirectional data flow leading to a simpler architecture and the burden of residue-to-decimal (or residue-to-binary) conversion to operation time can be largely reduced by processing all elements in parallel. The calculated characteristics of operation time suggest a promising use of the system in a real time 2-D linear transform.

Optical microphone using a silicon-based guided-wave optical pressure sensor

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 mmX7 mmX23 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 mmX7 mmX27 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.

Sensitivity dependence with respect to diaphragm dimensions in a glass-based integrated optic pressure sensor

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 phenonemon that a phase difference between two orthogonal guilded 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 agree approximately with the theoretical ones although there was a slight difference in sensor #4.

Stability of holographic gratings recorded on photopolymer using different dyes

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 μm 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.

Glass-based integrated optic pressure sensors with a Mach-Zehnder interferometer and with an intermodal interferometer

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 Corning 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 633nm in wavelength were 0.053rad/kPa for the MZ interferometer using the TM-like mode and 0.041rad/lPa for the IM interferometer. Each result was, however, half its theoretical estimate.

Fast and highly parallel content addressing of a large amount of information recorded in a holographic memory

It has recently become possible to fabricate spatial light modulators for holographic information retrieval. We analyze the signal-to-noise ratios in two typical holographic information retrieval systems, serial and inverted, and we discuss the possibilities of implementing holographic information retrieval with a newly proposed spatial light modulator that uses a Fabry-Perot étalon with a piezoelectrically driven mirror.

Feasibility of guided-wave optical microphone based on elasto-optic effect

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.

Scale-reduction rule for diaphragm dimensions to miniaturize a silicon-based integrated optic pressure sensor without reducing sensitivity

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 sube 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 10mmx35 μm, 2.5 mmx12.5 mmx49 μm and 3.0 mmx15 mmx64 μm. The measured sensitivities of the three sensors were quite similar to each other as theoretically predicted.