Third Order Nonlinear Optical Correlators in a 4f Configuration

This paper reviews two optical correlator systems using third order nonlinear effects in a 4f imaging system. The first one describes the joint transformation correlator based on the 4-wave mixing phenomenon generating a conjugate wave described by the convolution and correlation of three incident waves in the nonlinear medium. This system has been studied by different authors who have performed successful image correlation experiments. The second one describes the forward nonlinear correlator due to the Kerr effect allowing the autocorrelation and convolution of several optical fields (composed of several objects). The advantage of these two systems is that they perform operations in real time, the response of the nonlinear medium being almost instantaneous. The ability of these systems to parallelize the computation makes them potential candidates for the realization of real time image processing or for cryptography.