Development of a spatial light modulator: a randomly addressed liquid-crystal-over-nMOS array

Demonstration of a non-orthogonal Lloyd's mirror interferometer with a spatial light modulator for arbitrary two-dimensional pattern fabrication

A new, to the best of our knowledge, method of generating interference patterns based on a non-orthogonal Lloyd's mirror interferometer with a spatial phase modulation is proposed. In the proposed method, a spatial light modulator (SLM) is introduced to a conventional non-orthogonal Lloyd's mirror interferometer so that arbitrary interference patterns, such as line interference patterns with varied line-spacing or two-dimensional patterns, can be generated by controlling the wavefronts of the laser beams at each position on the substrate. In this paper, as the first step of the research, the feasibility of the proposed method is theoretically confirmed by calculating interference patterns to be obtained when a spatial modulation of the phase delay is applied to the laser beams. A prototype of a non-orthogonal one-axis Lloyd's mirror interferometer with an SLM in its optical path is also designed and constructed. Some basic experiments are carried out to demonstrate the feasibility of the generation of interference patterns having varied line-spacing and two-dimensional patterns by the proposed method.

Large arrays of spatial light modulators hybridized to silicon integrated circuits

Large, high-frame-rate spatial light modulators are key components required for the realization of real-time optical processors. We report a 128 × 128 array of GaAs-based optical modulators that we hybridized to a Si integrated circuit by using In bump bonds to form a spatial light modulator. These optical modulators are composed of a series of quantum wells within an asymmetric Fabry-Perot cavity to control the optical properties. The resulting 128 × 128 element array operates in an intensity-only reflection mode at greater than 100,000 frames per second. This array interfaces to a 486-based personal computer through a standard industry standard architecture bus.

Improving the performance of liquid-crystal-over-silicon spatial light modulators: issues and achievements

The performance of liquid-crystal-over-silicon spatial light modulators has advanced rapidly in recent years. Most progress has centered around new device designs with increased bandwidth. In this paper we report on a number of techniques to improve the optical quality; these have applications in both current and future devices.

256 × 256 liquid-crystal-on-silicon spatial light modulator

A 256 × 256 pixel spatial light modulator (SLM) is designed and constructed by the use of liquid-crystalon-silicon technology. The device is a binary electrically addressed SLM with a measured zero-order contrast ratio of 70:1 and an imaged contrast ratio of 10:1. The pixel pitch is 21.6 µm, which gives an array size of 5.53 mm. The electronic load time is 43 µs, and the 10%-90% switching time of the liquid crystal is ~75-80 µs at room temperature, which implies a maximum frame rate of ~8.3 kHz. We discuss the design trade-offs that are intrinsic to this type of device and describe how the primary application for the device in an optical correlator influenced the final design.

Optical correlator using very-large-scale integrated circuit/ferroelectric-liquid-crystal electrically addressed spatial light modulators

The use of 2-kHz 64 × 64 very-large-scale integrated circuit/ferroelectric-liquid-crystal electrically addressed spatial light modulators as the input and filter planes of a VanderLugt-type optical correlator is discussed. Liquid-crystal layer thickness variations that are present in the devices are analyzed, and the effects on correlator performance are investigated through computer simulations. Experimental results from the very-large-scale-integrated/ferroelectric-liquid-crystal optical-correlator system are presented and are consistent with the level of performance predicted by the simulations.

Optical competitive learning with, VLSI/liquid-crystal winner-take-all modulators

A new approach to self-aligning unsupervised optical learning based on the competitive learning algorithm and adaptive holographic interconnectións is introduced. A volume hologram is used to diffract the light from an input spatial light modulator so that it focuses upon a custom winner-take-all very-large-scale-integrated circuit liquid-crystal spatial light modulator. The units that receive the most light switch to a reflective state, and the light reflected from the winning pixels interferes in the volume of the dynamic hologram with the phase conjugate of the input pattern in order to add an outer-product perturbation to the current holographic interconnection. As a set of input patterns is cycled through many times, the system learns to diffract the light from a particular input class upon a self-organized set of detectors that recognize similar input patterns without the aid of a teacher or any required alignment. Beam-propagation simulations are used to show that the holographic optical learning network faithfully reproduces the behavior of the ideal competitive learning algorithm. A winner-takeall detector/modulator device containing a total of 576 optical neurons grouped into 31 separate competitive patches in the required sparse-grid topology has been successfully fabricated, and experimental results are presented.

Optoelectronic array that computes error and weight modification for a bipolar optical neural network

The design, fabrication, and results of an optoelectronic device that computes the weight changes required by the delta-rule learning algorithm and encodes the result on a pair of optical beams are presented. This very-large-scale-integrated ferroelectric liquid-crystal array was designed specifically to permit bipolar optoelectronic neural networks to learn without the limitations of an external controlling computer. The device contains 64 smart pixels, which represent the processing elements in an artificial neural network. Each processing element consists of two photodetectors, a current-to-voltage converter, two comparators, two switches, and two output liquid-crystal modulating pads. The device has a measured contrast ratio of 10:1, a 10%-to-90% rise time of 350 micros, and a 90%-to-10% fall time of 150 micros.

Charge-transfer-plate spatial light modulators

Charge-transfer-plate spatial light modulators (CTPSLM's) are a class of devices that employ chargetransfer plates as the interface between the charge-generation element and the light-modulation element. Both optically addressed and electrically addressed devices have been built. Chargegenerating elements for the optically addressed devices include photoconductors, photodiode and phototransistor arrays, optoelectronic integrated circuit chips, and photocathode-microchannel-plate assemblies. For electrically addressed devices, electron guns, very large-scale integrated circuits, thin-film transistors, and matrix electrodes are among the possible charge-generation elements. Lightmodulation elements used in CTPSLM's include liquid crystals, electro-optic organic and inorganic crystals, polymers, deformable membrane mirrors, oil films, multilayer dielectric films, and electroluminescent films. In principle, all combinations of charge-generation elements and light-modulating elements are possible. This paper explores the fundamental performance limitations of CTP technology, and describes the design, operation, and applications of five different CTPSLM's (three based on membrane-mirror technology and two on liquid-crystal technology).

Surface-plasmon spatial light modulators based on liquid crystal

The development of a new class of spatial light modulator (SLM), which uses modulation of lossy guided waves generated by surface-plasmon resonance, is described. The potential advantages of this technique are explained, including increased response uniformity and enhanced sensitivity and speed. An optically addressed SLM that is based on a nematic liquid crystal with a spatial resolution better than 10 line pairs/mm (at 50% modulation transfer function) is demonstrated. For the design of devices that are based on newer smectic liquid crystals the use of anisotropy-induced polarization mixing and the so-called pseudoplasmon modes are described. Such modes offer controllable sensitivity-spatial resolution characteristics in simple liquid-crystal SLM structures. Within a typical SLM resolution requirement of 10 line pairs/mm, for example, the sensitivity can be optimized to obtain a theoretical reflectivity modulation from 0 to 0.7 for a liquid-crystal director modulation of 5 degrees .

Electrically addressed spatial light modulator that uses a dynamic memory

The operating characteristics of a 64 x 64 array electrically addressed spatial light modulator that uses a dynamic memory on a very-large-scale-integration chip and a ferroelectric liquid-crystal modulator are discussed.

Optically addressed thresholding very-large-scale-integration/liquid-crystal spatial light modulators

Two 32 x 32 array optically addressed thresholding spatial light modulators consisting of a very-large-scale-integration chip and a ferroelectric liquid-crystal modulator are presented. The intensity contrast ratios range from 3:1 and 11:1, and the response times range from 500 micros to 6 ms.

Ferroelectric-liquid-crystal/silicon-integrated-circuit spatial light modulator

We present the design and characterization of a spatial light modulator (SLM) comprising a ferroelectric-liquid-crystal light-modulating layer on top of a silicon integrated circuit. Our SLM consists of two electrically addressed arrays on the same integrated-circuit die. The first, a 1 x 128 linear array with a 20-microm center-to-center element spacing, used shift register addressing, while the second, a 64 x 64 square array with 60-microm pitch, used static random access memory addressing. The resulting SLM could be addressed at frame rates of up to 4.5 kHz and gave singleelement intensity contrast ratios of 12:1.

Evolutionary development of advanced liquid crystal spatial light modulators

Taking into account recent developments and present trends in devices and component technologies, the future development of electrically addressed liquid crystal spatial light modulators is considered. In particular, the combination of single-crystal-silicon active backplane and chiral smectic C liquid crystal technologies is shown to be promising. The ultimate limitations of such technologies for producing faster devices of higher complexity and functionality are assessed, and an advanced device, presently under development, is described.