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Multiple phases retrieval for optical security systems using random-phase encoding

The technique of the multiple phases retrieval algorithm (MPRA) for designing optical security and verification systems is proposed in this paper. This technique is based on a 4-f optical correlator, which is a common architecture for optical image encryption and verification systems. In the proposed systems, however, two or more phase masks are iteratively retrieved by using the MPRA to obtain the target image. The convergent speed of the iteration process in the MPRA is significantly increased and the recovered image is much more similar to the target one than those in previous approaches. Moreover, the system security is increased since only the pair-wise retrieved phase masks can correctly recover the target images. To avoid carrying two phase keys, one of the phase mask serves as the key and the other phase mask can be stored in the database of the security system as an active lock. Finally, according to our simulation results, the misalignment effects for the phase mask in the Fourier plane are more series than that in the input plane.