Image Correlation Using Photorefractive GaAs

Abstract

Image correlation can be implemented optically, which takes full advantages of light, namely parallel operation and global interconnection with the Fourier transform provided by lens. Photorefractive compound semiconductors can provide this type of implementation1. This paper presents results from a detailed investigation on potentials of the photorefractive GaAs correlator for practical applications. The results illustrate that the matched filter formation rate in photorefractive GaAs crystal can be higher than 1000 frames per second. The filter contains complex values, leading to high quality correlation as demonstrated. Other advantages verified by experiments include real object image input with no need for preprocessing Fourier transform; edge enhancement automatically processed in the correlation process; dynamic spatial invariance, substantial enhancement of the signal by using a DC electric field providing high dynamic range; and easy alignment. In addition, this paper also presents the result of an experiment on imaging by phase conjugation in GaAs with 1.3 micron semiconductor injection lasers. This result provides realistic potentials to develop compact correlation modules using photorefractive semiconductors with semiconductor lasers. These modules could be building blocks for future "intelligent" automatic pattern recognition systems.