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Holographic techniques are indispensable tools for modern optical engineering. Over the past two decades, research about incoherent digital holography has continued to attract attention. Optical scanning holography (OSH) can obtain incoherent holograms using single-pixel detection and structured illumination with Fresnel zone patterns (FZPs). Particularly by changing the size of a detector, OSH can also obtain holograms under coherently illuminated conditions. Since 1979, OSH has continuously evolved. According to the evolution of semiconductor technology, spatial light modulators (SLMs) come to be useful for various imaging fields. By using SLM techniques for OSH, the practicality of OSH is improved. These SLM-based OSH methods are termed computational OSH (COSH). In this review, the configurations, recording and reconstruction methods, and proposed applications of COSH are reviewed.

Fresnel incoherent correlation holography (FINCH) was a milestone in incoherent holography. In this roadmap, two pathways, namely the development of FINCH and applications of FINCH explored by many prominent research groups, are discussed. The current state-of-the-art FINCH technology, challenges, and future perspectives of FINCH technology as recognized by a diverse group of researchers contributing to different facets of research in FINCH have been presented.

Holographic recording media can store the amplitude and the phase, or the complex amplitude, of a beam on the basis of holography. Owing to this characteristic, digital data can be encoded onto the complex amplitude of a signal beam in holographic data storage. However, most of conventional holographic storage systems encode digital data onto the amplitude alone because there are difficulties for modulating and detecting the phase. To solve the difficulties, a holographic storage system using digital holographic techniques has been proposed. With the help of digital holographic techniques, it is possible to modulate and detect the complex amplitude of a signal beam. Moreover, the proposed system can modulate the complex amplitude of a reference beam. In this paper, by making use of the capability, a correlation-based multiplexing with uncorrelated reference beams is demonstrated in the proposed system. Multiple holograms can be recorded in the same volume of a recording medium with no need for mechanical movements. Experimental results show that the proposed system with a correlation-based multiplexing can improve the storage capacity and can utilize the full potential of a recording medium without crosstalk noise stem from the optical setup. [ABSTRACT FROM AUTHOR]

Single-exposure generalized phase-shifting digital holography enables one to remove the zeroth-order and conjugate terms from the single hologram. For the phase-shifting, a random-complex-amplitude encoded wave is used as the reference wave. This encoded wave can be made by a commercially available element. Selective calculation is proposed for the improvement of reconstructed images in single-exposure generalized phase-shifting digital holography. Three calculations are used as a function of the complex amplitude quantities of the reference wave on the each pixel of the image sensor. The selective calculation improves the quality of the reconstructed image compared with applying only one of the three calculations to the hologram. The derivation of the three calculations and the reason why the number of calculations is three are presented. A parameter is defined and used to select the appropriate calculation from the three calculations. Relationships between the proposed method and the previous method for the improvement of the reconstructed images in single-exposure generalized phase-shifting digital holography are discussed. Two kinds of experimental results are given to confirm the effectiveness of the proposed method. One shows the dependence on the speckle size of the reference wave. The other shows the feasibility to dynamic phenomena. [ABSTRACT FROM AUTHOR]

We present a method to solve a distance issue. In digital holography, the reconstruction distance is different from the original one because of the difference of the pixel size between an imaging device and a display device. In general, the distance is larger because the pixel size of the display is larger than that of the imaging device. This makes it hard to recognize perception of the stereoscopic effect when holographic reconstructed images are used for the stereopsis system. Typically, a numerical propagation method and a spherical phase addition are used to shorten the distance. However, each method is not shortened enough. To clear the criterion, the limitation of each method is verified. By combining two methods, the reconstruction distance is shortened from 4440 to 547 mm. In addition, it is successfully shown that the proposed combining method is useful for the stereopsis by visual perception evaluation. [ABSTRACT FROM AUTHOR]

This paper studies a new real-time phase-shifting method for the analysis of isochromatic and isoclinic parameters in photoelasticity. By rotating an analyzer at a constant rate and an output quarter-wave plate at a double rate of the analyzer and recording images by a CCD camera continuously, sequential images which brightness is integrated by sensors in a CCD camera during phase-shifting are obtained. Then, the distributions of the isochromatic and isoclinic parameters are obtained immediately and quantitatively using the proposed phase-shifting algorithm. The proposed method can be applied to high-speed inspection of optical elements or glass products. Also, it is expected that slowly varying time-dependent problems can be analyzed by the proposed method. [ABSTRACT FROM AUTHOR]

Phase-unwrapping-free and iterative reconstruction methods for propagated refractive index (RI) tomography, which introduces lightwave back-propagation to a filtered back-projection method, are proposed. The phase-unwrapping-free method utilizes phase retrieval using a transport-of-intensity equation that does not require phase unwrapping. This method overcomes phase unwrapping problems of high calculation cost and phase unwrapping error when measuring millimeter-thick and/or large-RI-changes specimens. In the iterative method, a simultaneous iterative reconstruction technique in X-ray computed tomography is applied to the propagated RI tomography. This method leads to the reduction of the radial artifacts and the elimination of the need for a high-pass filter regardless of the shape and size of specimens. Hence, the accuracy of a reconstructed RI map is improved. Numerical simulations and optical experiments are carried out to prove the feasibility of the proposed methods. [ABSTRACT FROM AUTHOR]

Refractive index (RI) tomography based on not quantitative phase imaging (QPI) but optical coherence tomography (OCT) is proposed. In conventional RI tomography, the phase unwrapping process deteriorates measurement accuracy owing to the unwrapping error. To eliminate the unwrapping process, the introduction of OCT is proposed, because OCT directly provides optical thickness. The proposed method can improve measurement accuracy owing to the removal of the phase unwrapping error. The feasibility of the method is confirmed by numerical simulations and optical experiments. These results show that the proposed method can reduce measurement errors even when an object shows phase changes much larger than a wavelength. [ABSTRACT FROM AUTHOR]

Information security and authentication are important challenges facing society. Recent attacks by hackers on the databases of large commercial and financial companies have demonstrated that more research and development of advanced approaches are necessary to deny unauthorized access to critical data. Free space optical technology has been investigated by many researchers in information security, encryption, and authentication. The main motivation for using optics and photonics for information security is that optical waveforms possess many complex degrees of freedom such as amplitude, phase, polarization, large bandwidth, nonlinear transformations, quantum properties of photons, and multiplexing that can be combined in many ways to make information encryption more secure and more difficult to attack. This roadmap article presents an overview of the potential, recent advances, and challenges of optical security and encryption using free space optics. The roadmap on optical security is comprised of six categories that together include 16 short sections written by authors who have made relevant contributions in this field. The first category of this roadmap describes novel encryption approaches, including secure optical sensing which summarizes double random phase encryption applications and flaws [Yamaguchi], the digital holographic encryption in free space optical technique which describes encryption using multidimensional digital holography [Nomura], simultaneous encryption of multiple signals [Pérez-Cabré], asymmetric methods based on information truncation [Nishchal], and dynamic encryption of video sequences [Torroba]. Asymmetric and one-way cryptosystems are analyzed by Peng. The second category is on compression for encryption. In their respective contributions, Alfalou and Stern propose similar goals involving compressed data and compressive sensing encryption. The very important area of cryptanalysis is the topic of the third category with two sections: Sheridan reviews phase retrieval algorithms to perform different attacks, whereas Situ discusses nonlinear optical encryption techniques and the development of a rigorous optical information security theory. The fourth category with two contributions reports how encryption could be implemented at the nano- or micro-scale. Naruse discusses the use of nanostructures in security applications and Carnicer proposes encoding information in a tightly focused beam. In the fifth category, encryption based on ghost imaging using single-pixel detectors is also considered. In particular, the authors [Chen, Tajahuerce] emphasize the need for more specialized hardware and image processing algorithms. Finally, in the sixth category, Mosk and Javidi analyze in their corresponding papers how quantum imaging can benefit optical encryption systems. Sources that use few photons make encryption systems much more difficult to attack, providing a secure method for authentication. [ABSTRACT FROM AUTHOR]

In a digital holographic reconstruction, only images located at the reconstruction distance are in focus. A speckle reduction technique is proposed to improve digital holographic in-focus imaging. The extended focused image is obtained from a depth map created by evaluating the edge sharpness of object images. In order to show the performance and effectiveness of the proposed technique for extended focused imaging, we conducted the demonstration experiments using two objects, which are a resolution chart and two screws. [ABSTRACT FROM AUTHOR]