Abstract
We propose an angle multiplexing method for optics-based image encryption using a phase-only computer-generated hologram (POCGH) in the tilted Fresnel transform (TFrT) domain. Modified Gerchberg-Saxton algorithms, based on the three types of rotation manipulation in both the hologram and reconstruction planes, are used with their corresponding TFrT parameters to extract the phase-only functions (POFs) of the target images. All the extracted POFs are then phase-modulated and summed to obtain the final POCGH, which is capable of multiplexing and avoiding overlap in the reconstructed images. The computer simulation results show that the images corresponding to the various rotation manipulations at the hologram and image reconstruction planes can be successfully restored with high correlation coefficients. Due to the encrypted nature of the multiplexed images, a higher system security level can be achieved, as the images can only be correctly displayed when all the required parameters in the TFrT are available. The angle sensitivity on the image quality for each manipulation is also investigated.
Highlights
Optical security has received great attention and seen dramatic development since the last century due to the inherent diversity of optical signals and the high precision requirements of optical devices/architectures, which can significantly enhance system security levels [1]
This paper proposes a generalized angle-multiplexing method for multiple image encryption based on the tilted Fresnel transform (TFrT) with a phase-only computer-generated hologram (POCGH) composed of multiple phase-only functions (POFs)
Let the POCGH be of size 1920 by 1080 with a 6.8 μm pitch, the wavelength of the incident light be 632 nm, and the distance z0 be 1.3 m, so that the approximations used in deriving the ĝn
Summary
Optical security has received great attention and seen dramatic development since the last century due to the inherent diversity of optical signals and the high precision requirements of optical devices/architectures, which can significantly enhance system security levels [1]. Among the various types of applications, image encryption is very advantageous because of the parallel-processing capabilities of optics. Javidi first proposed a double-random-phase encoding (DRPE) method to encrypt an image into a noise-like complex signal [2]. Thereafter, optics-based encryption methods utilizing on Fourier, fractional Fourier, or Fresnel transforms (FrT) with various optical architectures have been aggressively developed for image encryption and verification uses [2,3,4,5,6,7,8,9,10,11]. An image can be encrypted as a phase-only function (POF) and reconstructed by determining the diffraction field at the reconstruction plane with the FrT. The POF can be determined by using the Gerchberg-Saxton algorithm (GSA) [12], and can serve as a type of phase-only computer-generated hologram (POCGH)
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