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To realize a high efficiency electrically addressable phase-only modulator, we have coupled a liquid crystal display (LCD) to an optically addressed parallel-aligned nematic liquid crystal spatial light modulator (PAL-SLM) with a set of lenses. Phase modulation exceeding 3ϖ at 532 nm wavelength was obtained. We obtained linear transfer characteristics for phase modulation at various desired phase levels after calibration and adjustment of the transfer characteristics of the PAL-SLM and the LCD. Diffraction efficiency of 40% for binary phase grating and of 90% for 8-level blazed phase grating, which were very close to the simulation values, were observed. The power loss of the readout light was caused when passed through a half mirror, therefore, we examined a setup using an oblique readout light at the modulator. Very high diffraction efficiency was obtained from the setup by optimizing the polarization direction and optical path for this light, and the orientation of liquid crystals. Since the modulator can perform at better than 90% diffraction efficiency and at nearly 100% reflectivity, various high efficiency systems utilizing such modulators are expected.

An optically addressed parallel-aligned nematic-liquid-crystal spatial light modulator (PAL-SLM) has been studied as a dynamic phase-only light modulation device. The phase modulation characteristics of the PAL-SLM using a liquid crystal display (LCD) as an addressing mask were investigated by analyzing diffraction efficiencies resulting from binary gratings projected from the LCD. A more than 2π phase-only modulation depth was achieved. The highest first-order diffraction efficiency of approximately 38% was also obtained; this is close to the theoretical limit. The experimental results of diffraction efficiencies depending on the phase modulation depth are in good agreement with the simulation for the system operation.

An architecture for a novel adaptive optical processing system using optical associative memory with learning capability is proposed. The optical system consists of an optical preprocessor for feature extraction and optical associative memory. The feature-extraction ability can give excellent processing capability to the optical associative memory. In order to demonstrate this system, an optical Fourier transform is used as the preprocessor, and the system can achieve shift invariance. An all-optical configuration of the system is proposed, and the experimental results applied to handwritten-character recognition by using an hybrid opto-electronic system are shown and discussed.

The architectural considerations and experimental results of a new optical parallel are presented. An array logic concept is introduced as the building blocks of the processor. The processor performs programmable logic operations. Polarization modulation and spatial separation of the modulated light, together with the operation kernel, are keys to programmability for any Boolean logic operation. The operation kernel determines the logic operation to be executed according to instructions simply by spatially filtering encoded light. Real-time programmable cascade logic operations for three patterns are demonstrated experimentally using a liquid crystal spatial light modulator as the operation kernel.

The learning capabilities of optical associative memory called the optical associatron are experimentally shown. The experimental system has a simple architecture for optical associative memory; in particular, the system has versatile adaptive learning capabilities implemented with microchannel spatial light modulators. In this paper, various experimental results of learning and recalling processes on the system are shown. Based on the results, the behavior of learning on the optical associative memory is discussed. In addition, a modified method of learning is proposed and verified on the system. A method for implementation of error backpropagation is also proposed.

A new neural network architecture for optical computing is proposed. This architecture can be used for implementing a simple system based on a modified theory of the associative memories. It is shown that the memorized patterns can be recalled perfectly by an experimental system using two microchannel spatial light modulators. The modified theory and principle of operation of the optical associatron system are discussed, and the system itself and basic experimental results are also described.

We report holographic generation of higher-order Laguerre-Gaussian (LG) beams using a liquid crystal on silicon spatial light modulator (LCOS-SLM) device. In our experimental set-up, a flat-top light beam was projected on the LCOS-SLM to generate LG beams of various mode indices without changes of the optical system. Additionally, the size of the holographic phase pattern was optimized for each beam to maximize the mode purity of the obtained beam. Holographic generation of LG beams is easily influenced by a distortion of the optical system and deviation of the phase setting from an ideal one. Nevertheless, we obtained high-quality LG beams with an additional phase pattern on the LCOS-SLM for canceling the distortion of the optical system and with calibration of the phase control voltage for precise expression of the phase patterns. Numerical analyses are also performed for two-dimensional beam profiles to verify the quality of the obtained beams. Through fitting the obtained profiles to theoretical ones, we calculate the correlation coefficients R between the observed and fitted profiles to find that R > 0.95 for all beams and that the correlation coefficients behave similarly to the theoretically estimated mode purities, facts indicating that the quality of the obtained LG beams is close to the theoretical limit in our experiments.

A novel optical information processing system by synthesis of the coherence function is built up to extract a two dimensional image from a three-dimensional object at a tenable depth with neither mechanical scanning nor digital calculation. In this system, a two-dimensional optical lock-in amplifier with the microchannel spatial light modulator is developed to detect selectively the coherence component, so that the limitation to the depth resolution introduced by the holographic detection which was used in our previous systems is overcome. Selective image extraction Is demonstrated successfully.

In order to overcome the limitation of the image processing speed of the conventional video camera system, we have designed and constructed a column parallel vision (CPV) system. The CPV system realizes an intelligent and general purpose image processing capability with higher frame rate within 1 millisecond (i.e. 1000 frames/s). The system mainly consists of three parts; a sensing unit, a parallel processing unit and a control unit. The sensing unit has a 128x128 photodiode (PD) array, 128-column parallel amplifier array and A/D converter array to achieve high-speed frame rate and has been integrated in a CMOS chip. The parallel processing unit is composed of fully 128x128 processing elements (PEs) to perform a real-time image processing. The control unit has functions of PD/PE control and interface to the host computer. We have confirmed that the CPV system can process general image processing functions within a few ten microseconds. We have also demonstrated that the system can be worked as a tracking system with high-speed feedback loop and have evaluated the accuracy of the position calculation for the desired target.

An electrically addressed spatial light modulator (SLM), which is non-pixellated and has a high diffraction efficiency, has been developed by combining an optically addressed liquid crystal SLM with a CRT. It has been confirmed that the designed SLM has excellent performance for CGH (computer generated hologram) reconstruction.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We made a parallel aligned liquid crystal spatial light modulator (PAL-SLM) respond within 6 ms to meet requirements for a single-SLM color projection system. This was done by adjusting thicknesses of its optical addressing layer and its light modulating layer.

An optical correlator has been used in fingerprint identification, and in order to test its properties in a practical application a compact joint transform correlation system was constructed. The system’s identification performance was qualitatively and statistically evaluated, based on fingerprint data gathered from 500 fellow workers. The power of parallelism and fast processing of optical processing enabled the system to verify an individual’s identity in less than 0.1 s on each try. The system performed a verification with a 4.1% false rejection rate and no false acceptance in “three-try.”

A novel optical information processing system by synthesis of the coherence function is proposed. By modulating the frequency of a laser diode in an interferometer with appropriate waveform, the system synthesizes the coherence function into a delta-function-like peak at a depth tunable by the frequency modulation parameter, and thus can extract 2D images from 3D object at arbitrary depth in the form of interference component. To detect selectively the interference component, a 2D optical lock-in amplifier with the microchannel spatial light modulator is developed, so that the limitation to the depth resolution introduced by the holographic detection which was used in our previous systems is overcome, Selective image extraction is demonstrated successfully with neither mechanical scanning nor digital calculation.

Parallel aligned liquid crystal-spatial light modulator (PAL-SLM) has been applied to an optical interconnection system by a CGH technique. In the system, the PAL-SLM is expected to have electrically addressed capability. We have developed a CRT coupled PAL-SLM that can be electrically addressed. For that purpose, the CRT have been designed and evaluated on a fluorescence spectrum and an afterglow time of a phosphor to suit PAL-SLM features. And we have also evaluated two coupling methods between the CRT and the PAL- SLM ; one is a relay lens coupling method and the other is a fiber optic plate (FOP) coupling method. Consequently, it can be concluded that a combination of a red phosphor with a long afterglow time and the FOP coupling method is suitable for the CGH application. We can get a fine and noiseless CGH reconstruction image by using this module.

Optically addressed liquid crystal phase only spatial light modulator has been developed. The transfer characteristics and the diffraction efficiency of the device are discussed theoretically and experimentally. 1. INTRODUCTION In the optical information processing such as remote sensing, optical communication and optical computing,numerous optical systems such as adaptive optics have been stadied to retrieve the phase information associated with the information transmission. The phase filters have also been studied to control the optical phase term in the Fourier transform domain, in which the optical phase is controlled in a two dimensional (2-1)) fashion. Attempts have been madeto use the spatial light modulators (SLMs) as a 2-D phase modulator in such a system1)'2).Various types of SLMS have been developed3'4). However most of them make use of the intensity modulation oflight such as scattering, beam deflection and change of polarization. Few are especially developed for use as a 2D phase

A speckle photographic technique was employed for the measurement of displacement of diffuse objects. In this method a double exposure is made on an FLC-SLM and the speckle correlation is detected with a position-sensitive detector. Use of this system means easy successive detection of displacement. In addition, the feedback control signals which regulate the FLC-SLM double-writing signals from PSD are expected to expand the measurable range and increase measurement accuracy. This approach has the advantage of measuring displacements of less than 1.0 ms in successive periods of several milliseconds. Experimental results are presented.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An optically addressed parallel-aligned nematic-liquid-crystal spatial light modulator is developed for applications in optical information processing and interferometry. Its performance, including diffraction efficiency, is measured, and a theoretical analysis of diffraction efficiency is performed. A comparison between the experimental results and the theoretical analysis shows good agreement. The diffraction efficiency of near-sinusoidal gratings written on the device is of the order of 30%, which is close to theoretical maximum.

Optical parallel processing is an attractive technique for treating today's vast quantities of information in parallel. In this field, a spatial light modulator which modulates the light in two dimensions is required. We have developed a microchannel spatial light modulator (MSLM) using LiNbO3 for a modulating material. However, it has physical limitations in readout light intensity, the spatial resolution and operating speed. In order to improve the characteristics of MSLM, liquid crystal (LC) is adopted for the modulating material. In this paper, the structure of the device and the operating principle are explained. The basic experimental results of the device are also shown.

An optical parallel processor based upon polarization encoding that performs neighborhood operations is implemented by newly introducing an optical shifter. The experimental results of edge extraction are demonstrated.

A new experimental system of optical neurocomputing, called optical associatron, is shown. The experimental system has a simple architecture for optical associative memory. Especially, the system has versatile adaptive learning capabilities implemented by using Microchannel Spatial Light Modulators (MSLMs). In this paper, various experimental results of learning and recalling on the experimental system are shown. Based on the results, behavior of learning on the optical associative memory is discussed and a modified method of learning is proposed and verified on the experimental system. In addition, a method of implementation of error back propagation is proposed.

Optical parallel processing based upon various polarization encodings(1) is a promissing concept for the practical implementation. The optical processor performing programmable and cascade operations on real-time basis, has been constructed.(2)

operation withMicrochannel Spatial Light ModulatorTsutomu Hara, Naohisa Mukohzaka, Yoshiji SuzukiHamamatsu Photonics K.K.1126 -1 Ichino -cho, Hamamatsu, JapanAbstractA two dimensional optical logic operation with three microchannel spatial lightmodulators (MSLMs) is demonstrated. In this proposed system

Space-variant logic operations are carried out using an optical parallel processor that is based on polarization encoding and subsequent spatial separation of the encoded light. In this processor a liquid-crystal spatial light modulator is used as an operational kernel that allows a programmable space-variant operation to be performed on a real-time basis by spatially filtering the encoded light pixel by pixel.