Experimental implementation of a photorefractive joint transform correlator with circular harmonic filters

We present an experimental realization of optical correlation for real-time rotational-invariance pattern recognition by means of a photorefractive joint transform correlator. Single and multiple circular harmonic components have been used to form correlation filters. The correlator operates with a liquid crystal television as the input images and a photorefractive crystal Bi₁₂SiO₂₀ (BSO) as the recording medium. Suitable pre-processing of the references at the object plane makes up for the lack of light transmission. The properties of circular harmonic phase-only filter and circular harmonic matched filter have been compared. Also the noise robustness of these filters has been tested by tracking an object against a non-overlapping noise background. Analysis and experimental results are presented.