Roger A. Lilly

Optical-data-processing properties of a liquid-crystal television spatial light modulator

The potential of the extremely inexpensive Radio Shack liquid-crystal television (LCTV) as a two-dimensional spatial light modulator has been investigated. The LCTV modulates the transmission of coherent or incoherent light and can either be electronically addressed through a microcomputer or optically addressed with a TV camera. We have measured the transmission characteristics of the device, examined its diffraction pattern, and tested its use as an input device for an optical correlator. We have discovered that, with proper modifications, it has potential for optical-data-processing applications.

Optical correlator performance of binary phase-only filters using Fourier and Hartley transforms

Theoretical studies of the performance capabilities of binary phase-only filters (BPOFs), constructed using both Fourier and Hartley transforms, are presented. A thorough analysis of the Fourier BPOF is given. We show that, although BPOFs constructed using Fourier transforms perform well in optical correlator systems, they are also subject to additional noise sources and have the possibility of generating large false correlation signals. We then present an analysis of BPOFs constructed using the Hartley transform. We show that BPOFs made using the Hartley transform provide superior false correlation rejection and more uniformly sized correlation signals for heavily multiplexed BPOFs, compared with those made using the Fourier transform. We also present a technique for constructing Hartley BPOFs. Therefore, although it is well known that the quality of the correlation signal depends on the object, this work demonstrates that the quality of the correlation signal can also depend on the technique used in the synthesis of the BPOF.

Multiplexed phase-encoded lenses written on spatial light modulators

We report the writing of Fresnel phase-encoded lenses onto programmable spatial light modulators (SLMs). When the product of the phase-encoded lens and the two-dimensional Fourier transform of a desired output spatial pattern is written onto the SLM, the desired spatial pattern is focused at programmable distances from the SLM. More importantly the inverted version of the desired pattern normally produced is encoded onto a diverging beam and is not imaged. Theoretical analysis and experimental results using the magneto-optic SLM are presented.

Multiplexing capabilities of the binary phase-only filter.

Theoretical studies of the multiplexing capabilities of binary phase-only filters (BPOF) for use in optical correlator systems are presented. We show that the BPOF has an inherent capability for simultaneously recognizing an object and an inverted version of the object. More complex multiplexing capabilities are examined including (1) use of a BPOF made from eight rotated versions of a letter to recognize any of the rotated input letters, (2) use of a BPOF made using the fifty-two letters of the alphabet (upper and lower case) to recognize any one letter, and (3) use of a BPOF made from a complex sentence to pick out a desired word. Finally, we present additional information on the generation of the BPOF using a MacIntosh computer system.

High efficiency optical reconstruction of binary phase-only filters using the Hughes liquid crystal light valve

The Hughes liquid crystal light valve (LCLV) has been evaluated for its applicability in writing and reading binary phase-only filters (BPOFs) in optical correlators. Experimental measurements of relevant performance characteristics of the LCLV as well as experimental results demonstrating its use for reconstructing BPOFs are reported. We also find that this device allows a significant optical system throughput. In addition, we discuss generation of the BPOF with a MacIntosh computer system.

Fresnel lens-encoded binary phase-only filters for optical pattern recognition

We describe a technique for reducing false signals from optical correlators using binary phase-only filters (BPOFs). Since the impulse-response function of the BPOF contains both the target object and the inverted version of it, the output consists of the correlation of the input object with both of these objects. In our research a Fresnel phase plate lens is encoded onto the BPOF. As a result the correlation with the desired target is on a converging beam, and the correlation with the undesired inverted image of the target is on a diverging beam. Experimental results show that these filters reject inverted input objects.

Programmable optical interconnections with large fan-out capability using the magneto-optic spatial light modulator.

We report the use of two-dimensional, binary phase-only diffraction gratings written on a programmable magnetooptic spatial light modulator to interconnect optically an input laser beam to multiple output locations. We show that we can achieve programmable weighted interconnects between the source and two output locations as well as a fan-out capability to as many as 128 separate output locations.

Multichannel optical correlator/convolver utilizing the magnetooptic spatial light modulator

We describe a multichannel correlator/convolver architecture utilizing an acoustooptic light modulator for the 1-D input channel and a magnetooptic spatial light modulator (MOSLM) for the second 2-D parallel channel. The MOSLM allows greater parallelism to be implemented into this correlator/convolver design than was previously reported. We demonstrate the implementation of 24 parallel channels with a 48 x 48 device. We present experimental data and discuss ways of increasing the number of parallel channels using commercially available MOSLMs and other previously discussed techniques such as frequency multiplexing. We show that over 2000 parallel channels are possible at 32-bit accuracy. A technique for obtaining a limited gray scale is also discussed.

Applicability Of The Liquid Crystal Television For Optical Data Processing

The pocket-size liquid crystal television (LCTV) has been investigated for its potential as a two dimensional spatial light modulator. The LCTV can be addressed using both a microcomputer and a TV camera. We have measured various characteristics of this device including transmission control, bipolar modulation capabilities, and have tested its usage as an input device for an optical correlator. Optical phase distortions of the device can be compensated by a liquid gate. These results suggest that this device has great potential for optical pattern recognition and optical data processing applications.

Smoothing of the edge-enhanced impulse response from binary phase-only filters using random binary patterns

We report a technique for reducing the edge-enhanced impulse response from binary phase-only filters (BPOFs). In this technique, the object used to make the filter is multiplied by a random binary pattern. Then the BPOF is constructed. Experimental details are presented.