Showing papers on "Spatial light modulator published in 1987"

Spatial light modulator

Abstract: Spatial light modulators which use a substrate having a buried channel charge-coupled device (CCD) formed therein, wherein the amount of charge in the charge storage wells associated with the electrodes of the CCD is controlled by an electrically or optically addressed data signal. The level of charge in such charge storage wells controls the electric field beneath the electrodes so that the intensity of electromagnetic energy (e.g., light) directed through The CCD is spatially modulated by the charge levels in the charge storage wells in accordance with the Franz-Keldysh electroabsorption effect.

Optical Information Processing With The Double Phase Conjugate Mirror

Abstract: The operation of the double phase conjugate mirror (DPCM) is described. It can be regarded as a bidirectional spatial light modulator and controllable filter. Two independent image-bearing beams that may be derived from different lasers exchange their spatial information as they are coupled into each other in a photorefractive crystal. The,DPCM is also shown to be an optical thresholder and spatial filtering device, displaying edge enhancement. We propose the use of a resonator with two facing DPCMs to implement iterative image processing algorithms.

Ferroelectric Liquid Crystal Spatial Light Modulator

Abstract: Ferroelectric liquid crystal devices are capable of fast switching and intrinsic bistability. These advantages over nematic liquid crystals are important in a photoaddressed two-dimensional spatial...

High-speed 2 × 2 electrically driven spatial light modulator made with GaAs/AlGaAs multiple quantum wells(MQWs)

Abstract: A 2 × 2 array of individually driven MQW modulators has been fabricated. Because of the large electroabsorption effect in MQWs, good on/off ratios can be achieved in a single pass through a set of 50 MQWs. Each device has an on/off ratio of approximately 1.45 : 1, and the modulator displays rise and fall times of roughly 400 ps.

Optical preprocessing using liquid crystal televisions.

Abstract: The suitability of a low-cost liquid crystal TV to function as a spatial light modulator in an optical preprocessor for an electronic pattern recognition system is investigated. The application presented is optical edge enhancement. The liquid crystal TV performs reasonably well where high-quality images are not required. Three optical edge enhancement methods are presented: spatial filtering; image cancellation; and phase cancellation. The phase cancellation method was discovered during the course of this research.

Spatial-Light-Modulator Interconnected Computers

Abstract: Optical technologies perform the basic computer operations of communications, switching, and storage, have already proven superior to electronics for many communications situations, and advances in devices and materials suggest that optics are important for switching and storage. The spatial light modulator (SLM) is one of the devices expected to play an important role in optical computing. An SLM acts as a piece of film whose transmittance or reflectance may be varied spatially and temporally by electronic or optical means. Types of SLMs, the use of optics for computation and three proposed, as well as diverse optical computing systems that use SLMs for interconnections are described in this article.

Associative memory system with spatial light modulator and feedback for adjustable thresholding and enhancement

Abstract: An associative memory system incorporating a hologram, a spatial light modulator (SLM) and thresholding components in a feedback loop to derive an enhanced reference beam for use in reconstructing a stored image. In a preferred embodiment, the SLM includes a liquid crystal light valve (LCLV). A polarizing thresholding analyzer device provides adjustable thresholding. An enhanced thresholded reference beam thereby derived is sent back to the hologram for readout and the stored image is reconstructed at the output plane of the system. In an alternative embodiment, two spatial light modulators and two feedback loops are provided in a resonator configuration.

Theoretical analysis of an electrically addressed viscoelastic spatial light modulator

Abstract: The time behavior and the spatial-frequency response of a deformable viscoelastic control layer are analyzed in view of its intended use as a spatial light modulator in a solid-state light valve. Direct electrical addressing of the viscoelastic spatial light modulator (VSLM) is incorporated in the analytical model by means of electrostatic potentials that vary sinusoidally in one lateral dimension. First, the electrostatic boundary-value problem of the VSLM is solved, and the resulting compressional forces are determined; then the elastohydrodynamic boundary-value problem is solved on the basis of the so-called Voigt model, and the mechanical stresses acting on the VSLM are calculated. Finally, analytical solutions for the deformation amplitude are found by use of equilibrium conditions for the electrostatic and the viscoelastic stresses. The resulting deformation amplitudes of the VSLM are given as functions of time and of spatial frequency with viscosity, shear modulus, surface tension, layer thickness, electric bias, and spatial modulation depth as parameters. An extensive discussion of these results concludes the present study.

High efficiency spatial masks

Abstract: A blazed output for a grating or filter is obtained by writing the real part of a complex function on a first portion of a recording medium and the imaginary part on a second portion of the recording medium, and introducing a phase shift between the first portion and second portion. A spatial light modulator, such as a magneto optic spatial light modulator (MOSLM) is preferably divided along the diagonal bisector of the MOSLM. The Fourier transform of the input function is taken and the cosine transform is written on the MOSLM to one side of the bisector and the sine transform is written on the other side of the bisector. A 90° phase shift is introduced between the two halves of the MOSLM, for example, through use of a quarterwave plate arrangement. An analyzer polarizer converter provides a binarized output. Blazing may be achieved such that substantially all of incident light may be directed into a desired order. Light may be uniquely and dynamically directed as for example in optical interconnects. Optical pattern recognition may be accomplished by eliminating undesirable recognitions of inverted objects.

Spatial light modulator.

Abstract: An electrostatically deflectable plate spatial light modulator with light reflecting plates (106) composed of aluminum alloy and with symmetrically located supporting hinges (108) connecting the plates (106) to support posts (104); this provides a thick stiff plate and a thin compliant hinges with deflection perpendicular to the plane of the plates.

Spatial light modulators and their applications

Abstract: The function of an optically addressed spatial light modulator (SLM) is to convert the intensity distribution of an incident scene into a coherent image, or into a high brigthness incoherent image. The applications of these transducers are therefore very large since they extend, from the field of coherent optical processing and computing (Incoherent to coherent conversion) to the high resolution video image projection. A great interest is now devoted to the technological developments of these devices in several laboratories using different approaches. The basic principle of operation of an optically addressed light valve is the following. A photosensitive layer detects the incident intensity distribution and induces a charge distribution onto a material which modifies its optical properties as a function of the photoinduced voltage. Finally, the incoherent or coherent illumination beam transmitted (or reflected) by the SLM sees its amplitude or phase spatially modulated. In the last few years, the list of spatial light modulators under research and development expanded considerably.

Optical expert systems.

Abstract: A general approach to using spatial light modulators in expert systems and in related AI methods is discussed. The information capacity of such system can far exceed the capacity of the spatial light modulator itself.

Optical multiple-output and multiple-valued logic operation based on fringe shifting techniques using a spatial light modulator

Abstract: Optical parallel logic operation is performed on the interference fringe shifted corresponding to the optical input. In the spatial light modulator, the optical input induces the refractive-index change which results in the shift of the fringe formed with the readout beam. The multiple-output scheme of logic gates is achieved by spatially dividing the output fringe. The multiple-valued logic is also implemented by adjusting the phase change for the multiple level of the optical input. Moreover, complementary logic pairs are always simultaneously provided when this method is used.

Multichannel optical correlator/convolver utilizing the magnetooptic spatial light modulator

Abstract: The paper describes a multichannel correlator/convolver architecture utilizing an acoustooptic light modulator for the one dimensional channel and a magnetooptic spatial light modulator (MOSLM) for the second two-dimensional parallel channel. The MOSLM allows greater parallelism to be implemented in this correlator/convolver design than was previously reported. The implementation of 24 parallel channels with a 48 x 48 device is demonstrated. Experimental data are presented and the ways of increasing the number of parallel channels using commercially available MOSLMs and other previously discussed techniques, such as frequency multiplexing, are discussed. It is shown that over 2000 parallel channels are possible at 32-bit accuracy. A technique for obtaining a limited gray scale is also discussed.

Deformable Surface Spatial Light Modulator

Abstract: A spatial light modulator (SLM) based on a deformable gel surface is presented. It has remarkable optical properties and its construction and operation are comparatively simple. It can be optically addressed through a photoconductor layer. The surface relief pattern is read out by total reflection and a schlieren optical system. The device provides good wavefront quality (X/10 over the whole aperture of 30 x 50 mm2) and has a spatial resolution of 10 line pairs/mm. Contrast ratios for modulation up to 40:1 were measured. The input sensitivity is typically 0.3 mW/cm2. The rise and decay times are both approximately 20 ms. Besides its primary application as a light valve in large screen TV projection, it can be used in optical information processing systems, e.g., as an incoherent-to-coherent transducer. Combined with a CRT, the SLM can be addressed electronically.

Implementation of Boolean logic gates using a microchannel spatial light modulator with liquid-crystal televisions.

Abstract: A programmable optical system that can perform binary Boolean logic operations with a microchannel spatial light modulator (MSLM) is presented. The MSLM is used as an adder, an inverter, a subtractor, or a buffer. We used three liquid-crystal televisions with a computer as input interfacing devices. Through the use of its feedback loop, the system can consecutively execute a series of logic operations. Experimental results are provided.

Near bandgap radiation modulation spatial light modulators

Abstract: A near bandgap radiation modulation spatial light modulator (NBRM-SLM) using multiple quantum wells (MQWs) (34). Generally, the MQW NBRM SLM of the present invention comprises a MQW optical modulator (34) and driver means for driving the MQW optical modulator. The MQW NBRM SLMs of the present invention can be configured in a plurality of configurations. The driver and MQW optical modulator may be configured in hybrid or monolithic configurations. The MQW optical modulator can be operated in either transverse or longitudinal electric field modes. The MQW NBRM SLM structures can be operated using either electroabsorption or electrorefraction effects, and in transmissive or reflective modes. The structures are operable with different addressing and write-in mechanisms, including photo-activation and electronic addressing. Alternate embodiments have special features such as cascaded heterojunction MQWs and pixelized submicron metal mirror. The disclosed invention provides an improved, high speed, high resolution, semiconductor drive-compatible, spatial light modulator using multiple quantum wells.

Optical target recognition system

Abstract: Prior art optical image correlators are extremely cumbersome and do not use spatial light modulators. To determine whether an of-interest target is within a scene, the present invention optical correlator uses a laser diode, a spatial light modulator, a holographic lens array, a matched filter array and an inverse transform lens. In particular, the laser diode generates a coherent laser beam, which is expanded and collimated. Information of the of-interest target is encoded thereon by the spatial light modulator. The encoded laser beam is then directed to the holographic lens array, which replicates from the single laser beam a plurality of similar beams. These beams are focused onto a matched filter array having multiple matched filters, the number of which corresponds to the number of incoming beams. If there is a close match between an incoming beam and a corresponding matched filter, a high intensity light is emitted from that particular matched filter toward the inverse transform lens, from when the high intensity beam is focused onto a correlation plane, where the existence of of-interest targets is ascertained.

Interferometric/feedback spatial light modulation system and method

Abstract: A spatial light modulator and associated method are disclosed which achieve an intensity-to-intensity spatial transformation between a noncoherent input beam and a coherent output beam. An intermediate intensity-to-phase modulator provides a coherent, spatially phased modulated readout beam that is combined with a coherent reference beam in an interferometer to yield the desired coherent, spatially intensity modulated output beam. The interferometer also produces a feedback beam with a spatial intensity modulation complementary to that of the input and output beams. The feedback beam is combined with the input beam in a feedback loop that significantly improves the system's response time, and can also enhance the linearity of its transfer characteristic.

Real-time joint transform correlator with phase conjugation for distortion correction

Abstract: A joint transform correlator has been demonstrated that incorporates phase conjugation in a BaTiO3 crystal to correct for distortions in a liquid-crystal television (LCTV) spatial light modulator. The optical arrangement permits real-time operation in spite of the relative slowness of the photorefractive effect. Correlation outputs displayed on a video monitor are illustrated for inputs to the LCTV from a video camera viewing a stationary scene. The sensitivity of the correlator to target rotation is also presented.

Spatial Light Modulators For Optical Information Processing

Abstract: A review of spatial light modulator technologies is presented, including the decription and performance parameters of the main devices, general issues, and their main applications for optical information processing and displays; emerging new technologies as well as future prospects for spatial light modulators are discussed.

Spatial light modulator

Abstract: An electro-optical device for providing spatial modulation of an incoming electromagnetic wave signal, and preferably a two-dimensional incoming signal applied orthogonally to an input plane of the device, which device includes an array of modulation regions for providing such modulation of portions of the incoming signal. An array of first reflective mirrors are positioned so as to direct the incoming electromagnetic wave signal portions through the interaction layer regions of the modulation regions in a direction substantially parallel thereto and an array of second reflective mirrors directs the modulated electromagnetic wave signal portions outwardly from the device to provide a two-dimensional spatially modulated output electromagnetic wave signal.

Infrared crystalline spatial light modulator

Abstract: A spatial light modulator system having an electro-optic crystal responsive to infrared radiation. An electric field is established across opposed faces of the crystal, and the field is modulated on a point by point basis over one crystal face using a suitable charge distribution write source. Infrared radiation traversing the crystal is modified in polarization in accordance with the pattern imposed on the crystal to simulate an infrared target for testing infrared seekers.

Optical Image Correlation Using A Deformable Mirror Device: A Feasibility Study

Abstract: The use of a deformable mirror device (DMD) as an input spatial light modulator and/or as a phase-only spatial filter in a coherent optical correlator is investigated. Both Vander Lugt and joint transform correlator geometries are analyzed, and the results of computer simulations using a simplified phase device model are presented. Detailed geometrical and diffraction models of Texas Instruments' cantilever beam DMD are developed and used to simulate an input phase device in a Vander Lugt correlator. The results are encouraging for those interested in using the DMD for image correlation applications.

Introduction to Optical Signal Processing with Photorefractive Materials

Abstract: Information processing by coherent optical systems, such as optical correlators, spectrum analyzers of two-dimensional signals and others, requires development of recyclable photosensitive media to be used in spatial light modulators and holographic filters. In many cases, the optical processing system as a whole, and its separate elements, are treated in the framework of the theory of linear space-invariant systems [1,2]. Here the notions of the impulse response and transfer function are introduced. It is just these parameters which give a rather complete idea about the information capabilities of the system as a whole and its separate elements.

Computer Generated Hologram and Magneto-Optic Spatial Light Modulator for Optical Pattern Recognition.

Abstract: : This thesis investigates the integration of an optical system for real-time position, scale, and rotation invariant pattern recognition. Specifically a Litton Magneto-Optic Spatial Light Modulator is interfaced to a Zenith 248 microcomputer and AT&T frame grabber. A user interfaces written in C allowed arbitrary patterns to be written to the SLM by a user. Patterns can be generated in computer code, transferred form a CCD camera (via the frame grabber), taken from an image file on computer disk, or taken from a VAX image file. The ability to locally generate a computer generated hologram using the computer generated interferogram method on the Sun workstations and Imagen laser printer was developed. The CGH developed was used in an optical coordinate transformation to create a position, scale, and rotation invariant feature space. CCD cameras were used throughout the optical processor for display/analysis. The entire system was developed and tested using various templates and real scenes.

Real-time joint transform correlation by partially coherent readout illumination.

Abstract: A real-time joint Fourier transform image correlator that uses partially coherent readout illumination to perform signal detection in complex amplitude is described. The interference between the Fourier transforms of input images is obtained by coherent light. However, the correlation signal is produced by partially coherent illumination, which is used to read out the Fourier transforms interference intensity from the output of the spatial light modulator (liquid crystal image transducer). The advantage of this technique is the reduction in the spatial phase variations in the output wavefront of the image transducer. Such nonuniformities may arise from nonflatness and mismatch of various output layers in some devices that can degrade the performance of the correlator. We present experimental results to show that the phase distortion effects present in the output surface of the device can be reduced by using partially coherent readout illumination. It is also shown that the correlation bandwidth obtained by the proposed system is smaller compared to VanderLugt filtering under quasi-monochromatic illumination. As a result, a brighter correlation peak intensity is produced, and a better correlation SNR is obtained. Pattern recognition experiments using naturally illuminated real objects are presented, and the effects of relaxed coherence on the real-time joint transform correlator is determined.