Enhancing a holography capacity and security by vortex-beam multiplexing and double random phase encoding for propagating information

Abstract Traditional Gaussian-light-based holography mainly uses the amplitude and phase of light as degrees of freedom for propagating information, and the channel capacity is physically limited due to lack of more multiplexed dimensions. For enhancing the capacity and security of a hologram, a novel hologram is proposed by employing multiplexed orbital angular momentum (OAM) modes and a double random phase encoding (DRPE) method. The DRPE method, which employs two statistically independent random phase masks in the input plane and Fourier transform plane respectively, combines the random phase masks with the original information, making it virtually impossible to retrieve the original data without knowledge of both random phase keys. Besides, the employed OAM modes also can be used to encrypt the holograms due to the fact that only the correctly-selected OAM beams can recover the primordially-propagated information. For further increasing the security of a hologram, a DRPE method is also adopted in both spatial and frequency domains. By implementing DRPE in dual domains, the encryption process creates a multi-layered security architecture, which significantly increasing the computational complexity required for unauthorized decryption. For verifying the valid of the proposed scheme, a verification scheme is also established, where three OAM modes are employed. The achieved results demonstrate that the propagated three gray images can be successfully reconstructed with a higher peak signal to noise ratio (PSNR). In addition, the recovered images show that the proposed holograms have a stronger anti-noise performance under three different noises, and have a stronger sensitivity to key. The decrypt sequence between spatial domain and frequency domain also makes an important impact on the reconstructed images, which can further improve the security of the hologram during information propagation. Consequently, the proposed method can significantly enhance the capacity and security performance of holographic information.