Real-time screen-aided multiple-image optical holographic matched-filter correlator

The basic principle and experimental results of applying a specific contact screen for performing multiplex holographic filtering in a real-time coherent optical correlator are presented. The specific design and fabrication of a 1- and 2-D gray density contact screen as well as a 2-D dichromated gelatin phase screen are described. The 2-D density-type screen can yield nearly an equal intensity 5 x 5 array of spectrum islands at the Fourier plane of a Fourier transform lens in a coherent optical image processor. The main drawback of the density-type screen is the lack of required light efficiency at the Fourier plane because of the blocking of light by the silver particles in the screen. Dichromated gelatin phase screens can be made to alleviate this problem, but it is very difficult to fabricate a phase screen exactly according to our design due to inherent experimental limitations. Nevertheless a functional phase screen has been made for the desired correlation functions. Experimental results have demonstrated that the phase screen is reasonably efficient for the multiplex holographic filtering in the real-time correlator.