Phase-only optical encryption based on the zeroth-order phase-contrast technique

Abstract

A phase-only encryption/decryption scheme with the readout based on the zeroth-order phase-contrast technique ZOPCT, without the use of a phase-changing plate on the Fourier plane of an optical system based on the 4f optical correlator, is proposed. The encryption of a gray-level image is achieved by multiplying the phase distribution ob- tained directly from the gray-level image by a random phase distribution. The robustness of the encoding is assured by the nonlinearity intrinsic to the proposed phase-contrast method and the random phase distribution used in the encryption process. The experimental system has been implemented with liquid-crystal spatial modulators to generate phase- encrypted masks and a decrypting key. The advantage of this method is the easy scheme to recover the gray-level information from the de- crypted phase-only mask applying the ZOPCT. An analysis of this de- cryption method was performed against brute force attacks. © 2009 Society