Parallel classification of multiple objects using a phase-only multichannel optical correlator

We present a technique that allows us to increment the number of objects to be detected and classified simultaneously in an optical patterns recognition process. It basically consists of the multiplexing of several phase-only filters. The elimination of the convolution signal at the final correlation plane, by means of the direct implementation of phase-only filters, allows an increase in the number of channels to be used in a Vander Lugt correlator. The difference among these composed filters and others proposed before lies in the way they are synthesized. Usually filters are physically implemented by using amplitude media, and it is necessary to perform an encoding of the phase information. In the proposed method, no encoding technique is used to convert the phase values into amplitude ones. The implementation of this kind of filter is carried out by using liquid crystal displays working in phase-only mode. We present in this work numerical simulations and experimental results obtained from the implementation of two different kinds of phase-only filters. Impulse responses and correlation signals are analyzed.