Orbital angular momentum holographic encryption based on position multiplexing and frequency shift

Abstract

A large-capacity, large-size image information encryption technique based on orbital angular momentum (OAM) holography and optical multiplexing is proposed. Large-size images undergo non-equal segmentation using frequency-shifted phase, followed by sampling and the sampling interval is determined by the spatial frequency of the spiral phase plates with different topological charges. These sampled sub-images are modulated by random and frequency-shifted phases, coherently superimposed to form an OAM-preserving hologram after Fourier transform and Fresnel diffraction. These OAM-preserving holograms, encoded with helical phases of different topological charges, are coherently superimposed to obtain the OAM multiplexed holograms. For decryption, the OAM multiplexed selective hologram is irradiated with a specific vortex beam, and multiple large-size decrypted images are obtained at the correct Fresnel transmission position after modulation with other synchronous optical keys. The frequency shift technique solves the constraints of the photoelectric modulator and improves the encryption capability and security of the system. Additionally, position multiplexing technology enhances OAM holography's encryption capacity, addresses the capacity limitations caused by the Nyquist-Shannon theorem, and mitigates crosstalk issues. Therefore, this system has excellent information encryption performance realizing parallel encryption and high-quality decryption of large-capacity and large-size image information.