Abstract

In many applications it is desirable to implement a correlation system capable of performing color pattern recognition. With mixed gas lasers such as the argon–krypton laser, it is possible to have a single source produce a collinear beam composed of red, green, and blue wavelengths. In this paper we investigate recording reflection and transmission matched spatial filters in photorefractive LiNbO₃. We limit our discussion to simultaneous recording of the filter as opposed to sequential recording. We show that the reflection filter suffers from low diffraction efficiency as a result of grating competition, while the transmission filter suffers from wavelength crosstalk caused by grating beating. Finally, we demonstrate a transmission filter that uses a grating in the input plane to separate the wavelengths in the filter plane, and eliminate the color crosstalk.

© 1991 Optical Society of America