We propose an all-optical encryption memory using the photorefractive four wave mixing and random phase masks. In our encryption method, the image data are encrypted to white noise by the phase shift patterns added on the signal beam with the image data and the reference beam through the random phase masks. Only reading beam with the phase-conjugated distribution of the reference beam can restore the encrypted data. If the encrypted data are read out by incorrect phase pattern, the output data can't be obtained because of the wavefront mismatch between the recorded hologram and the reading beam. We evaluate the encryption and decryption process by analyzing the diffraction efficiency with consideration of the angular spectrum. We show that high performance encryption that high contrast and high gradation image data can be decrypted accurately and the output data are perfectly dark by using the incorrect decryption key can be realized theoretically.
We have proposed an all-optical memory with authentication and unlawful access detection using photorefractive four-wave mixing. If the data is read out by the reading beam with the improper key, the output intensity is scarcely zero and any output isn't obtained. Therefore we can judge at a glance whether or not the used decoding key is the proper key. We analyze the diffraction efficiency with consideration of the phase mismatching to evaluate the fidelity of the hologram. In this analysis, we examine the property of the crystal that depends on three-dimensional coupling coefficient. We simulate the encoding and decoding process with some image data in this all-optical memory with authentication and unlawful access detection. We show that the encoded image is restored to its original image in case of retrieving with the proper key, on the other hand the retrieved image of which intensity is scarcely zero is obtained in case of retrieving with the improper key.