Optical neurodevices using a smart detector array

Abstract

A smart detector of GaAs-based MSM structure that has the functions of variable sensitivity and analog memory has been developed. The variable sensitivity is based on the phenomenon that the photocurrent is proportional to the electric field applied to the electrodes. The analog memory is based on the optical properties of impurities in the GaAs film. This detector is quite useful as an optical synapse because of the analog operation, memory function, and simple structure for a 2-D integration. Two kinds of novel neurodevices are introduced. The first device is an optical learning chip with analog memory. Its functions are to acquire the knowledge, to store it as the synaptic weights at learning phase, and to perform the vector-matrix multiplication at retrieval phase. The optical learning chip consisting of a 32 × 32 smart detector array and a line-shaped LED array with 32 elements, which are monolithically integrated on a GaAs substrate, was fabricated. The pattern classification experiment was successfully performed. The second device is an artificial retina for direct image processing. The input image is projected on the 2-D smart detector array as the synaptic matrix. The function of the retina can be chosen by an electric control signal as an input vector. Edge detection was successfully made by using the artificial retina with 64 × 64 elements.