Optical speckle correlator using the phase modulation property of liquid crystal television

Recently, LCTV has been used in the field of optical information processing because of the low cost of the device and the ease of commercial availability. Although we can expect high diffraction efficiency of light by using a phase-only spatial light modulator, it is difficult to obtain perfect phase-only modulation in a conventional twisted nematic LCTV device. Both the intensity and phase modulation ratios through the LCTV panel are affected by the polarization of input light and the applied video signal voltage. In this paper, we study the intensity and phase modulation properties of a twisted nematic-type LCTV. A nonlinear optical correlator is proposed based on the phase modulation property of the LCTV. To obtain high diffraction efficiency, the video signal having 0 and π phase values is written onto the LCTV panel by the binarization of the input pattern. The dc component in the correlation pattern is suppressed by the phase-only modulation of the LCTV and a clear correlation signal is obtained.