Optical image encryption based on polarization encoding by liquid crystal spatial light modulators

This work describes a polarization-encoding scheme with cascaded liquid crystal spatial light modulators for two-dimensional exclusive OR logic encryption. The transfer characteristic of the encryption system is analysed to determine suitable polarization modulation for optical realization. Performance is compared across systems that use various displays, including twisted nematic, supertwisted nematic and homogeneously parallel aligned nematic liquid crystal devices. Experiments show that binary image encryption/decryption is accomplished with fair image quality by choosing the orientation of the polarization and modulation conditions. Both simulated and experimental results are presented and discussed.