Acoustically steered and rotated true-time-delay generator based on wavelength-division multiplexing.

The acoustically steered and rotated (ASTRO) true-time-delay (TTD) generator, capable of two-dimensional (2D) multiple beam generation without causing extraneous beams, is described. It is based on wavelength-division multiplexing to encode and decode various linear chirp time delays with wavelengths. An array of equally spaced light stripes with linear chirp time delays among them is formed and is subsequently rotated to a desired angle by use of our nonmechanical acousto-optic dove prism, believed to be novel. Our architecture reduces hardware complexity significantly by avoiding redundancy in conventional TTD generators. Experimental results to prove the concept of 2D multiple beam generation are shown. Also, an extension of the system for bidirectional communications is proposed. Various technical issues for practical applications are discussed.

High-speed temporal characterization and visualization of spatial light modulators and flat-panel displays.

An apparatus that can characterize and visualize temporal dynamics of spatial light modulators (SLM's) and flat-panel displays is constructed and evaluated by use of a commercially available SLM. The apparatus is based on the stroboscopic video sampling method and has a temporal resolution of the order of microseconds, permitting measurement of a long event (>100ms) with a high signal-to-noise ratio. Experimental results demonstrate the visualization of the temporal image sequencing and addressing in an SLM.

Transverse grating-assisted narrow-bandwidth acousto-optic tunable filter.

An experimental acousto-optic tunable filter that has a narrow spectral bandwidth (0.2 nm at 1550 nm) and a fast (10-micros) tuning capability with a continuous tuning range of approximately 50 nm is described. The tunable filter consists of an acousto-optic beam deflector with a diffraction grating whose grating vector is transverse to the direction of light propagation.

Nonmechanical image rotation with an acousto-optic dove prism.

We report what we believe to be the first method for nonmechanical and programmable image rotation. The method uses a pair of crossed acousto-optic beam deflectors and a polygon mirror to emulate the mechanical dove prism. It is capable of fast (of the order of microseconds) image rotation to an arbitrary angle in a programmable manner. An experimental result that proves the concept is provided.

Fast reconfigurable optical image switching/routing system.

A novel system that is capable of switching/routing two-dimensional images in arbitrary configurations is described. The switching network can be reconfigured in a few microseconds with high light efficiency.

All-optical image transmission through a single-mode fiber.

All-optical transmission of two-dimensional images through a single single-mode fiber with a two-dimensional multicolor surface-emitting laser array and a volume hologram is described. A preliminary experimental result to prove the concept of the idea is demonstrated by transmitting a simple 2 x 2 image over a distance of 1 mile (1.61 km).

Compact and robust incoherent holographic correlator using a surface-emitting laser-diode array.

A compact and robust holographic correlator using a vertical-cavity surface-emitting microlaser diode array is described. The system is based on the unique coherence property of the surface-emitting microlaser array: temporally highly coherent and spatially incoherent. The performance of the system is experimentally demonstrated, and the application of the system for neural network implementations is proposed.

Simplified holographic associative memory using enhanced nonlinear processing with a thermoplastic plate.

A simplified holographic associative memory by enhanced nonlinear recording using a thermoplastic plate is described. The system is based on two new concepts: The system utilizes the second-order diffraction instead of the first-order diffraction, and to enhance the second-order diffraction efficiency, a novel angle-tuning recording using a thermoplastic plate is employed. As a result, the size of the system is reduced by one half with a remarkable increase (as much as approximately 100 times) in light efficiency compared with that of the conventional systems, and the need for critical alignment is eliminated. Experimental results demonstrating the performance of the system are provided.

Optoelectronic chip implementation of a quadratic associative memory.

High-order associative memories are of interest because of their potentially large storage capacity. We describe an optoelectronic implementation of a second-order, or quadratic, associative memory. The two-layer network is based on an inner-product representation, which allows for a compact implementation using an optical chip design. Experimental results obtained from our system are discussed.

Holographic associative memory for word-break recognition.

We describe a holographic associative memory that is able to identify individual words and insert word breaks in a concatenated word string. The system is shift invariant and has error-correction capability. Experimental results obtained from the system are presented.

Influence of interconnection weight discretization and noise in an optoelectronic neural network.

The effect of discretizing interconnection weight strengths in an optoelectronic learning neural network based on the backpropagation algorithm is investigated. We discuss how discretization arises in such an implementation. Using computer simulations we find that learning performance, as tested on the two-input XOR problem, is poor but that the addition of noise to the system results in substantial improvement.

Holographic implementation of a learning machine based on a multicategory perceptron algorithm.

An optical learning machine that has multicategory classification capability is demonstrated. The system exactly implements the single-layer perceptron algorithm and is fully parallel and analog. Experimental results on the learning by examples obtained from the system are described.