Phase-only optical image encryption and hiding based on normalization and orthogonalization phase-shifting algorithm

Optical encryption technology using phase-shifting interferometry (PSI) is widely used in many security fields, showing the advantages of parallel processing and the high security due to the information can be encrypted in multiple dimensions. The traditional PSI- based encryption methods are realized by the traditional multi-step phase-shifting algorithms (PSAs), although they are fast and accurate, the phase shifts deviation (PSD) caused by phase shifter detuning often affect the performance of the above methods. In order to solve this problem, a phase-only encryption method combining a normalization and orthogonalization phase-shifting algorithm (NOPSA) is proposed to eliminate the influence of PSD on the effective on decryption. First, the original image is phase encoded and encrypted by a phase key loaded on a liquid crystal spatial light modulator (SLM). Subsequently, the modulated reference light will be overlapped with the object wave to form interference pattern. Finally, the encrypted image hiding can be implemented based on NOPSA. Compared with the current PSI- based encryption methods, its obvious advantage is that when the phase shifts are not accurate or unknown, the proposed method can still achieve high quality encryption and hiding, which broadens the working conditions of PSI- based encryption methods.