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Optical correlation of multiple tracks of conventional optical-disk data, digitally encoded by transitions in reflectance rather than absolute reflectance, can be improved with a pulse-counting version of the digital-multiplication-by-analog-convolution algorithm, which also avoids analog weighting.

We describe the design and development of an acousto-optical wideband correlator that we integrated into a digital signal-processing system testbed. We report its measured performance and compare it with various theoretical performance measures, one of which compares the optical system with an equivalent efficient digital correlator. The measured performance of the optical system was 20 to 70 times that of a VAX 6410 computer using a fast-Fourier-transform correlation algorithm and a vector processor, even though the electronic interface system limited the performance of the optical system to less than 0.5% of its potential. We also compare the system with commercially available digital signal-processing boards.

The special issue of Applied Optics on spatial light modulators presents a collection of papers that describe improvements in basic devices, smart pixels, and system applications.

Architectural prototypes and algorithms for performing many simultaneous complex correlations between external data and data stored on optical disks are presented. External data are modulated onto an addressing light beam acoustooptically. Analog correlation outputs are obtained at low bandwidth. Data may be encoded on the disk either digitally, and correlated by using a digital multiplication by analog convolution scheme, or by analog area modulation. Bipolar correlations are shown possible without data biasing when two auxilliary diode lasers are used in a sign determination scheme. Error issues include variations in reflectances of encoded bits and raw disk errors.

We have demonstrated and analyzed an analog electronic constant false alarm rate processor that discriminates against distributed clutter for an acoustooptic correlator of a potentially large time-bandwidth product.

Optical associative, parallel-processing architectures are being developed using a multimodule approach, where a number of smaller, adaptive, associative modules are nonlinearly interconnected and cascaded under the guidance of a variety of organizational principles to structure larger architectures for solving specific problems. A number of novel optical implementations with versatile adaptive learning capabilities are presented for the individual associative modules, including holographic configurations and five specific electrooptic configurations. The practical issues involved in real optical architectures are analyzed, and actual laboratory optical implementations of associative modules based on Hebbian and Widrow-Hoff learning rules are discussed, including successful experimental demonstrations of their operation.

Experimental parameters of the photoemitter membrane spatial light modulator (PEMLM) photocathode, microchannel plate (MCP), and membrane are measured to determine the constraints they impose on the fabrication and performance of the device. An analysis of the PEMLM has shown that the ratio of the MCP strip current to the membrane tension is proportional to the ultimate limit of the device time response. Experimental measurements indicate that the ultimate performance has not been obtained. A different selection of the membrane material can improve the time response by lowering the tension. But the material selection is greatly restricted by the need to incorporate a visible photocathode for applications utilizing feedback. The use of high temperature stable membranes with low tensions and high strip current MCPs should enhance the PEMLM's time response.

A triangular, common-path interferometric rf spectrum analyzer arrangement has been demonstrated which has the property of high immunity to ambient vibration. Calculations show the TCPI arrangement, with two counter-propagating laser beams, is highly angle compensated and alignment stable when components are disturbed in position or orientation. Proper light polarization and Bragg cell geometry allows one Bragg cell to diffract primarily the clockwise beam and the other Bragg cell the counterclockwise beam. A birefringent quartz wedge shifts the heterodyne signal to a nonzero IF carrier frequency. Measured ambient phase noise is less than two degrees and calculated values indicate that further improvement may be possible.

Several acoustooptic devices have been developed for use as electronic signal processors at the Harry Diamond Laboratories. These devices use the Bragg interaction between a coherent light beam and surface acoustic waves propagating in a transparent crystalline delay line. Both real-time convolution and correlation of signals have been performed, and a real-time continuous Fourier transform has also been achieved. A programmable memory correlator has been demonstrated. This device uses a newly discovered photorefractive effect to store an image of a surface acoustic wave in a lithium niobate delay line. An acoustooptic implementation of the triple-product convolver is under active development. This device has been proposed for use in conjunction with charge-coupled-device chirp-Z-transform modules to perform very long discrete Fourier transforms and to do omega-k beam forming.

An acoustooptic technique was used to design and construct a prototype of a processor capable of multiplying a 128 x 128 complex-element matrix by a 128 complex-element vector. The device was specified to execute 10(5) matrix-vector products per second with 8-bit resolution. The performance of each component of the prototype was evaluated, as was the impact of component performance on system performance.