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Security validation based on orthogonal polarization multiplexing in three-dimensional space.

To enhance the security and practicality of the optical validation technique, a multiple-level security validation method is proposed based on orthogonal polarization multiplexing in a three-dimensional (3D) space. First, the original image is partitioned into two complementary images. Each image is divided into several subblocks. Then, two phase-only masks are generated by adopting the multiple diffractive planes and multiple signal windows phase-retrieval algorithm to reproduce a 3D diffraction field with all of the subblocks randomly distributed in specific locations. One of the phase masks is taken as the fixed system lock. The other one is preserved to act as the validation key. At last, the two diffraction beams of two phase-only masks are converted into orthogonal polarization states when illuminated by a collimated wave. As a result, the simultaneous control of both intensity and polarization distributions in desired longitudinal planes and transversal positions is achieved. A 3D polarization mapping protocol is established to generate the 3D polarization key. During validation, both the validation key and the 3d polarization key must be correct for a person to receive access permission. Experimental results show that the method is easy to implement and offers multiple-level validation functionality.