Modified optical asymmetric image cryptosystem based on coherent superposition and equal modulus decomposition

We propose a modified optical asymmetric cryptosystem based on coherent superposition and equal modulus decomposition (EMD). In the encryption process, the asymmetric cells of the previous cryptosystem is cascaded, while some small changes are made. In the first cell, only one mask, whose phase is not equal with the public key, is generated to be used as the input of the second cell. As a consequence, the modified cryptosystem decreases available constrain conditions for attackers, resulting in a high robustness of the cryptosystem against the attack based on iterative Fourier transform. Furthermore, the modified scheme maintains the good performance of our previous cryptosystem, especially the benefit of key management. Some numerical simulations are presented to verify the validity and the performance of the modified cryptosystem.