Key rotation multiplexing for multiple-image optical encryption in the Fresnel domain

We introduce a key rotation multiplexing method into the double random phase encoding system for multiple-image optical encryption in the Fresnel domain. Each plaintext is encoded into a stationary-white-noise ciphertext by the same only phase mask located at the input plane, and another only phase mask with a certain rotation angle located at the transform plane. All ciphertexts encoded from different plaintexts are added together to produce a final ciphertext, which serves as a single data source for different plaintexts decryption. Thus, the mask located at transform plane can be utilized to decrypt different plaintexts with a certain rotation angle. Also, we perform computer simulations to investigate how the quantization level of decrypted key and CCD, respectively, affect the decrypted quality and the number of images that can be multiplexed.