Optical neural networks: an introduction to a special issue by the feature editors

This feature of Applied Optics is devoted to papers on the optical implementation of neural-network models of computation. Papers are included on optoelectronic neuron array devices, optical interconnection techniques using holograms and spatial light modulators, optical associative memories, demonstrations of optoelectronic systems for learning, classification, and target recognition, and on the demonstration, analysis, and simulation of adaptive interconnections for optical neural networks using photorefractive volume holograms

Multilayer optical learning networks

A new approach to learning in a multilayer optical neural network based on holographically interconnected nonlinear devices is presented. The proposed network can learn the interconnections that form a distributed representation of a desired pattern transformation operation. The interconnections are formed in an adaptive and self-aligning fashioias volume holographic gratings in photorefractive crystals. Parallel arrays of globally space-integrated inner products diffracted by the interconnecting hologram illuminate arrays of nonlinear Fabry-Perot etalons for fast thresholding of the transformed patterns. A phase conjugated reference wave interferes with a backward propagating error signal to form holographic interference patterns which are time integrated in the volume of a photorefractive crystal to modify slowly and learn the appropriate self-aligning interconnections. This multilayer system performs an approximate implementation of the backpropagation learning procedure in a massively parallel high-speed nonlinear optical network

Adaptive optical networks using photorefractive crystals

The capabilities of photorefractive crystals as media for holographic interconnections in neural networks are examined. Limitations on the density of interconnections and the number of holographic associations which can be stored in photorefractive crystals are derived. Optical architectures for implementing various neural schemes are described. Experimental results are presented for one of these architectures

Optical computing: introduction by the guest editors to the feature in the 1 May 1988 issue

The feature in the 1 May 1988 issue of Applied Optics includes a collection of papers originally presented at the 1987 Lake Tahoe Topical Meeting on Optical Computing. These papers emphasize digital optical computing systems, optical interconnects, and devices for optical computing, but analog optical processing is considered as well

Secondary Grating Formation by Readout at Bragg-null Incidence

We show that when a dynamic hologram is read out by illumination at the Bragg nulls of a previously recorded grating the diffracted beam inside the medium can result in the recording of two secondary gratings that alter the final selectivity curve. This is confirmed experimentally. This effect can cause cross talk in hologram multiplexing that is stronger than interpage cross talk when a small number of holograms with high diffraction efficiencies are multiplexed

Generation Of Synthetic Aperture Radar Images Using Acousto-Optics

The applicability of Synthetic Aperture Radar (SAR) imaging to many practical problems is severely limited by the excessive computational load associated with the technique. In this paper we describe a simple real-time, SAR processor which is implemented with acousto-optic and charge-coupled devices. This device will be useful in applications where real-time image formation is essential and in applications where present processors are not cost effective. It could also be used to preview large sets of imagery. The device is very compact and hence it has the potential to operate aboard the vehicle that collects the SAR data

Pulsed ultrasound-modulated optical tomography using spectral hole-burning

We present a novel optical quantum sensor using spectral hole-burning for detecting signals in ultrasound-modulated optical tomography. In this technique, we utilize the capability of sub-MHz spectral filtering afforded by a spectral hole burning crystal to select the desired spectral component from the ultrasound-modulated diffuse light. This technique is capable of providing a large etendue, processing a large number of speckles in parallel, tolerating speckle decorrelation, and imaging in real-time. Experimental results are presented

Tracking antenna arrays for near-millimeter waves

A two-dimensional monolithic array has been developed that gives the elevation and azimuth of point source targets. The array is an arrangement of rows and columns of antennas and bismuth bolometer detectors on a fused quartz substrate. Energy is focused onto the array through a lens placed on the back side of the substrate. At 1.38 mm with a 50 mm diameter objective lens, the array has demonstrated a positioning accuracy of 26 arcmin. In a differential mode this precision improves to 9 arcsec, limited by the mechanics of the rotating stage. This tracking could be automated to a fast two-step procedure where a source is first located to the nearest row and column, and then precisely located by scanning. With signal processing the array should be able to track multiple sources