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In this article, we report an optical scanning holography (OSH) system that is equipped with biometric and the asymmetrical Rivest–Shamir–Adleman (RSA) encryption. Past research works have demonstrated that either encryption alone is vulnerable to certain types of attacks if both the encrypted and source data are available. Essentially, given sufficient time and computation power, it is possible to deduce the encryption key from these two datasets. Our proposed method can be divided into two stages. In the first stage, biometric encryption is incorporated in the OSH system to convert the image of a physical object into a biometric encrypted hologram. In the second stage, the biometric encrypted hologram is encoded with differential pulse code modulation (DPCM), and the polarity of the DPCM data is encrypted with the RSA algorithm. Due to the cascade of these two stages, it is not possible to identify both the source and encrypted data in each stage, and use them to hack the decryption key. We have demonstrated fast capturing and encryption of physical objects with our proposed method, and shown that that when either the biometric or the RSA encryption key is missing, the hologram cannot be recovered and the reconstructed image is incomprehensible. While we have demonstrated our idea with OSH, the proposed technique is applicable to any digital holographic systems.

A sampled phase-only hologram (SPOH) is the phase component of the hologram of an object image with pixels being sampled with a periodic grid-cross pattern. The reconstructed image of a SPOH is a sparse image with abundant empty voids and degradation in sharpness and contrast. In this paper we proposed a method based on a new sampling scheme, together with stochastic binary search (SBS), to obtain an optimal sampling lattice that can be applied to generate phase-only holograms with enhanced reconstructed image. Experimental results show that with our proposed method, the fidelity and quality of the reconstructed image are increased.

In this research, the accuracy of image classification with Fourier Ptychography Microscopy (FPM) has been systematically investigated. Multiple linear regression shows a strong linear relationship between the results of image classification accuracy and image visual appearance quality based on PSNR and SSIM with multiple training datasets including MINST, Fashion MNIST, Cifar, Caltech 101, and customized training datasets. It is, therefore, feasible to predict the image classification accuracy only based on PSNR and SSIM. It is also found that the image classification accuracy of FPM reconstructed with higher resolution images is significantly different from using the lower resolution images under the lower numerical aperture (NA) condition. The difference is yet less pronounced under the higher NA condition. Published version

This feature issue of Applied Optics is dedicated to the international meeting of Information Photonics 2020 (IP’20), which was held September 11–12, 2020, in Taipei, Taiwan. IP’20 covered a broad range of topics, including advanced display techniques, optical computing, and optical storage. This feature issue, however, limits topics to unconventional imaging techniques, such as digital holography, artificial-intelligence associated imaging, compressive imaging, and single-pixel imaging.

'Phase-only Fresnel holograms,' which can be displayed on a single SLM without the need for lenses or complicated optical accessories, substantially simplifies 3-D holographic display systems. Exploring essential concepts, theories, and formulations of these phase-only Fresnel holograms, this book provides comprehensive coverage of modern methods for generating such holograms, which pave the way for commercial products such as compact holographic projectors, heads-up displays, and data security enhancement. Relevant MATLAB codes are provided for readers to implement and evaluate the theories and formulations of different methods, and can be used as a quick start framework for further research and development. This is a crucial and up-to-date treatment of phase-only Fresnel holograms for students and researchers in electrical and electronic engineering, computer science/engineering, applied physics, information technology, and multimedia technology, as well as engineers and scientists in industry developing new products on 3-D displays and holographic projection.

In this paper, we proposed a new technique to realize a high-quality three-dimensional (3D) display by using binary holograms. First, we applied a localized random down-sampling (LRDS) mask to down-sample the object function and generated a binary CGH by direct sign-thresholding. Subsequently, we devised the display by adaptive intensity accumulation (AIA). In AIA, multiple CGHs of the same object are generated. However, selective sampling points of the same scene are removed according to the reconstructed image of previous binary CGHs as the second and more binary CGHs are generated. Finally, these holograms are sequentially displayed on a fast spatial light modulator, a digital micromirror device (DMD). Thus, a high-quality 3D image is reconstructed without artifacts and speckle noise.

The papers in this special section focus on the technology of digital holography and presents industrial applications for its use. Optical holography is a technique developed in the 1960s for recording a three-dimensional (3-D) scene on photographic film which is commonly referred to as hologram. Being different from classic photography that captures the intensity information from a single view point, a hologram is capable of recording the entire optical waves that are scattered from a 3-D object. Theoretically, when a hologram is illuminated by a coherent beam, the 3-D image it records will be reconstructed to the observer with complete depth and disparity information. It has been anticipated by many researchers of the 3-D technology that holography is likely to be the ultimate solution for the realization of 3-D display systems. Before the emergence of high-speed computers, optical holography has also been successfully applied in various kinds of tedious signal processing tasks. Notably, it has been demonstrated that computation intensive problems like Fourier transform and correlation can be obtained instantly through an optical system of lenses with coherent illumination. Despite these encouraging factors, it turns out that the practical applications of optical holography are rather restricted. The barricade could be attributed to the high complexity of the optical system and the strict demands on the environmental conditions that are required in setting up a holographic system.