Position multiplexing for multiple-image encryption

In a double random-phase encoding system operating in the Fresnel domain, the recovered image would become meaningless noise when the random phase masks shifted sufficiently far from their original positions. Hence multiple images can be encrypted and decrypted with different sets of spatial position parameters. This technique is referred to as position multiplexing. We first describe the basic principle of multiple-image encryption by use of position multiplexing, and then numerically analyse the factors that affect the minimum position separation and the multiplexing capacity. We also present methods to enlarge the multiplexing capacity.