Optical binary image encryption using aperture-key and dual wavelengths

We described a method where the secret binary image that has been encoded into a single amplitude pattern in Fresnel domain can be recovered based on phase retrieval with an aperture-key and wavelength keys, and no holographic recording is needed in the encryption. The predesigned aperture-key not only realizes the intensity modulation of the encrypted image, but also helps to retrieve the secret image with high quality. All the necessary decryption keys can be kept in digital form that facilitates data transmission and loading in image retrieval process. Numerical simulation results are given for testing the validity and security of the proposed approach.