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No description available.

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Advantages of optics over electronics in signal processing derive from the fact that many operations, such as addition, multiplication, correlation, and filtering, can be performed in parallel on two-dimensional data samples. However, this advantage is attainable only if information can be input/output or processed at sufficient speed and space bandwidth. Although acousto-optic devices have been used to provide impressive throughput, they are inherently one-dimensional and do not possess any information-storage capability beyond the acoustic transit time (≤50 μs). Hence, a high-resolution high-speed two-dimensional transducer (or spatial light modulator, SLM) with real-time update capability is required. Unfortunately, none of the existing SLMs perform well enough to fully utilize the inherent speed and parallelism of the optics. This dissertation addresses the development of an SLM that has the potential to meet most of the performance requirements of advanced optical information-processing applications--the photoemitter membrane light modulator (PEMLM). At the heart of the PEMLM is a microchannel plate (MCP) with a flexible membrane covering each pore. In operation, the write image incident on a photocathode, which is placed on the input side of the MCP, creates an electron image. This electron image is then amplified by the MCP and deposited onto the membrane array. The membrane elements, which are electrically and mechanically isolated from each other, are deflected by the induced electrostatic forces. These deflections represent the stored information. Readout of stored information is accomplished by sensing the phase changes induced in an optical-readout beam reflected from the deformed membrane array. A sandwich-type electrostatic grid structure positioned between the MCP and membrane greatly enhances the versatility of the PEMLM by facilitating the use of secondary emission for active electron removal and various intrinsic operations. The theoretical analysis and experimental characterizations performed on prototype devices indicates that PEMLM is capable of higher throughput than most other SLMs, with expected resolutions approaching 50 lp/mm over 10⁷ resolution elements and framing rates greater than 1 KHz. MCP gains provides quantum-limited sensitivity. The PEMLM also promises information-storage times of minutes to hours, greater than 2π phase modulation, good image quality, and an option for serial addressing. In addition, the PEMLM can intrinsically perform operations such as intensity thresholding, contrast modification, edge enhancement, binary logic, synchronous detection, and image addition/subtraction.

This dissertation considers a method for processing two-dimensional (2-D) signals (e.g. imagery) by transformation to a coordinate space where the 2-D operation separates into orthogonal 1-D operations. After processing, the 2-D output is reconstructed by a second coordinate transformation. This approach is based on the Radon transform, which maps a two-dimensional Cartesian representation of a signal into a series of one-dimensional signals by line-integral projection. The mathematical principles of this transformation are well-known as the basis for medical computed tomography. This approach can process signals more rapidly than conventional digital processing and more flexibly and precisely than optical techniques. A new formulation of the Radon transform is introduced that employs a new transformation--the central-slice transform--to symmetrize the operations between the Cartesian and Radon representations of the signal and to aid in analyzing operations that may be susceptible to solution in this manner. It is well-known that 2-D Fourier transforms and convolutions can be performed by 1-D operations after Radon transformation, as proven by the central-slice and filter theorems. Demonstrations of these operations via Radon transforms are described. An optical system has been constructed to derive the line-integral projections of 2-D transmissive or reflective input data. Fourier transforms of the projections are derived by a surface-acoustic-wave chirp Fourier transformer, and filtering is performed in a surface-acoustic-wave convolver. Reconstruction of the processed 2-D signal is performed optically. The system can process 2-D imagery at approximately 5 frames/second, though rates to 30 frames/second are achievable if a faster image rotator is added. Other signal processing operations in Radon space are demonstrated, including Labeyrie stellar speckle interferometry, the Hartley transform, and the joint coordinate-frequency representations such as the Wigner distribution function. Other operations worthy of further study include derivation of the 2-D cepstrum, and several spectrum estimation algorithms.

This dissertation discusses a certain aspect of opitcal data processing--namely the concept of performing a convolution operation of an incoherent optical light field with a specified processing kernel. The theory that shows that an incoherent imaging system performs a convolution by the very process of imaging is reviewed. The constraints on the form of processing kernel are discussed. The most severe constraint is the restriction of positive real kernels. Methods for extending the versatility of incoherent systems to include bipolar and even complex kernels are described. The most promising methods are those that encode the bipolar or complex information on either a spatial or temporal carrier frequency. The dissertation includes a presentation of two systems that are applicable to the demodulation of the signals generated by a temporal carrier approach. One of the systems introduces the concept of bipolar detection, which may have a strong influence on the performance of incoherent optical processing systems in the future. The other system is a synergism of optical and digital components that produces a hybrid system capable of high performance. The main motivation of this investigation was an outgrowth of our interest in developing a computed tomography system based on film recording of the projection data. The theory of computed tomography is reviewed in this text and an optical processing system based in part on the hybrid approach to the filtering operation is presented. This system represents a very concrete example of the capabilities of an incoherent optical processor.

This dissertation covers theoretical and experimental work on applying optical processing techniques ot the operation of a Boltzmann machine. A Boltzmann machine is a processor that solves a problem by iteratively optimizing an estimate of the solution. The optimization is done by finding a minimum of an energy surface over the solution space. The energy function is designed to consider not only data but also a priori information about the problem to assist the optimization. The dissertation first establishes a generic line-of-approach for designing an algorithmic optical computer that might successfully operate using currently realizable analog optical systems for highly-parallel operations. Simulated annealing, the algorithm of the Boltzmann machine, is then shown to be adaptable to this line-of-approach and is chosen as the algorithm to demonstrate these concepts throughout the dissertation. The algorithm is analyzed and optical systems are outlined that will perform the appropriate tasks within the algorithm. From this analysis and design, realizations of the optically-assisted Boltzmann machine are described and it is shown that the optical systems can be used in these algorithmic computations to produce solutions as precise as the single-pass operations of the analog optical systems. Further considerations are discussed for increasing the usefulness of the Boltzmann machine with respect to operating on larger data sets while maintaining the full degrees of parallelism and to increasing the speed by reducing the number of electronical-optical transducers and by utilizing more of the available parallelism. It is demonstgrated how, with a little digital support, the analog optical systems can be used to produce solutions with digital precision but without compromising the speed of the optical computations. Finally there is a short discussion as to how the Boltzmann machine may be modelled as a neuromorphic system for added insight into the computational functioning of the machine.