Design and implementation of an optical joint transform encryption system using complex-encoded key mask

We investigate the practical design of a complex-encoded key mask for optical encryption and decryption based on joint transform correlation architecture. The mask is created by using two coupled liquid-crystal spatial light modulators, one operating in amplitude mode and the other in phase mode. We develop a modified iterative Fourier transformation algorithm to design an optimal complex key mask, which is applied and mapped to the complex modulation of the liquid-crystal devices for optical implementation. The limitations of the devices on the system design are investigated and analyzed. The width constraints of the key mask are also derived, based on the joint transform correlation architecture for optical realization. Experimental results show the decryption performance and the shift-invariance of the complex key mask.