A novel security technique based on polarization encryption is proposed and is applied to a secure holographic memory system. Original binary data are described as two orthogonal linear polarization states. These input polarization states can be modulated by two polarization modulation masks located at the input and the Fourier planes. Each modulation mask can convert an input polarization state into an arbitrary elliptical polarization state. After the encryption of the polarization state, this encrypted polarization state is recorded as a hologram that can generate a vector phase conjugate beam. In the decryption process, the vector phase conjugate readout can cancel the polarization modulation at each mask and then the original polarization state can be recovered. The encryption and the decryption are demonstrated experimentally in a bacteriorhodopsin film.
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