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.

Computational ghost imaging (CGI) allows us to reconstruct images under a low signal-to-noise-ratio condition. However, CGI cannot retrieve phase information; it is unsuitable for observation of transparent objects such as living cells. A phase imaging method with CGI architecture is proposed. The proposed method realizes phase imaging with a simple optical setup by introducing pupil modulation differential phase contrast (PMDPC) to CGI. In PMDPC, phase information can be obtained from intensity distributions, which have phase gradient information, and its optical setup is similar to that of CGI. Therefore, the two methods are highly compatible, and the introduction of PMDPC to CGI can be easily achieved. Numerical simulation and an optical experiment demonstrated the feasibility of the proposed method.

The imaging quality of quantitative phase imaging (QPI) based on the transport of intensity equation (TIE) can be improved using a higher-order approximation for defocused intensity distributions. However, this requires mechanically scanning an image sensor or object along the optical axis, which in turn requires a precisely aligned optical setup. To overcome this problem, a computer-generated hologram (CGH) technique is introduced to TIE-based QPI. A CGH generating defocused point spread function is inserted in the Fourier plane of an object. The CGH acts as a lens and grating with various focal lengths and orientations, allowing multiple defocused intensity distributions to be simultaneously detected on an image sensor plane. The results of a numerical simulation and optical experiment demonstrated the feasibility of the proposed method.

Motionless optical scanning holography (MOSH) has been proposed for threedimensional incoherent imaging in single-pixel holography with a simple optical setup. To reduce the measurement time in MOSH, a spatially divided phase-shifting technique is introduced. The proposed method realizes measurements four times faster than the original MOSH, owing to the simultaneous lateral and phase shifts of a time-varying Fresnel zone plate. A hologram reproduced by the proposed method forms a spatially multiplexed phase-shifting hologram similar to parallel phase-shifting digital holography. The effectiveness of the proposed method is numerically and experimentally verified.

Fresnel incoherent correlation holography (FINCH) is a technology that can acquire three-dimensional information of incoherent objects such as fluorescence with an in-line optical system. However, it is difficult to apply FINCH to dynamic phenomena, since FINCH has to detect phase-shifted holograms sequentially to eliminate twin and zero-order images. In this paper, a method in which the phase-shifted holograms can be obtained simultaneously with an in-line setup by using an optimized simulated diffraction optical element (sDOE), realized by a phase-only spatial light modulator, is proposed. The optimized sDOE is an optical device with a dual-focus lens, 2D grating, and spatial phase shifter. Therefore, the sDOE is called a dual-focus checkerboard lens. The optical experiment confirms the feasibility of the proposed method. (C) 2020 Optical Society of America

Holographic data storage (HDS) based on a computer-generated hologram (CGH) technique has been proposed as a promising approach to realize an in-line and simple HDS system. This work focuses on multiplexed recording for CGH-based HDS, and the approach based on the reference wave correlation is introduced to the HDS. For the proposed method, the processes for a CGH design are modified to generate reference waves with different phase distributions for each recording. Since holograms are recorded to the same region in a medium with independent reference waves, recorded data-pages are selectively reconstructed by the corresponding reference wave illuminations. The experimental demonstration confirms the feasibility of the proposed method, and the theoretical characteristic for the number of recordable multiplexed holograms is estimated by the numerical simulation.

Optical scanning holography (OSH) is an attractive technique since 3D information can be obtained with a single pixel detector. However, OSH requires an interferometer, scanning architecture, and a frequency shifter to scan a time-varying Fresnel zone plate (FZP), which makes the optical setup complicated. To reduce the complexity, the polarization sensitivity of a spatial light modulator (SLM) is applied. The proposed method implements a time-varying FZP with an in-line optical setup by using only an SLM. Observing results for a USAF pattern and a fluorescent bead reveals the feasibility of the new motionless holographic 3D imaging technique. (C) 2020 Optical Society of America

A reconstruction method for multilevel complex encoded data-pages is proposed to increase the recording density of computer-generated-hologram-based holographic data storage by using off-axis digital holography. Although the detection process is based on off-axis digital holography, the proposed method keeps the optical setup a simple and common-path configuration owing to the computer-generated holography. Five-level complex encoded data-pages can be experimentally reconstructed. (C) 2020 Optical Society of America

Deep-learning-based single-pixel phase imaging is proposed. The method, termed deep ghost phase imaging (DGPI), succeeds the advantages of computational ghost imaging, i.e., has the phase imaging quality with high signal-to-noise ratio derived from the Fellgett's multiplex advantage and the point-like detection of diffracted light from objects. A deep convolutional neural network is learned to output a desired phase distribution from an input of a defocused intensity distribution reconstructed by the single-pixel imaging theory. Compared to the conventional interferometric and transport-of-intensity approaches to single-pixel phase imaging, the DGPI requires neither additional intensity measurements nor explicit approximations. The effects of defocus distance and light level are investigated by numerical simulation and an optical experiment confirms the feasibility of the DGPI.

A phase imaging technique based on the transport of intensity equation with polarization directed flat lenses is demonstrated. Transport-of-intensity phase imaging enables one to obtain a phase distribution from throughfocus intensity distributions by solving the transport of intensity equation. In general, the through-focus intensity distributions are obtained by mechanical scanning of an image sensor or target object. Therefore, a precise alignment of an optical system is required. To solve this issue, the introduction of polarization directed flat lenses is presented. In the proposed method, two intensity distributions at different depth positions on the optical axis are obtained without mechanical scanning by changing polarization states of incident light. The feasibility of the proposed method is confirmed by an optical experiment.

Since a complex amplitude distribution can be obtained in only a single two-dimensional plane using conventional imaging techniques, it is hard to obtain in-focus complex amplitude of three-dimensional structure (not a thin object) or multiple objects in different depth positions. The disadvantage often turns an obstacle to practical applications such as cell observation, particle measurement, and industrial inspection. To overcome the problem, adaptive autofocusing algorithm (AAA) is proposed. AAA consists of a complex amplitude measurement, numerical propagation, and local sharpness evaluation. In the proposed method, object positions can be determined for each pixel in the complex amplitude distribution using adaptively chosen area size of local sharpness evaluation. The proposed method gives a complex amplitude distribution which focuses on all objects or structure over an entire field of view. An optical experiment is carried out using the transport of intensity equation as a complex amplitude measurement. Performance of the proposed method is confirmed using living leaves of the moss Physcomitrella patens. Experimental results show that the object positions can be determined pixelwise and a focused complex amplitude distribution can be obtained by the proposed method.

Conventional computer-generated-hologram-based holographic data storage (CGH-HDS) needs to use a multilevel modulatable spatial light modulator (SLM). A binary SLM usually has a higher refresh rate than a multilevel one, and it enables HDS to increase the data transfer rate. To increase the data transfer rate by using a binary SLM, the introduction of a binary CGH is proposed. In general, a binary CGH degrades the image quality of reconstructed intensity distribution and emphasizes high spatial frequency components of datapages. In the proposed method, reconstructed intensity distributions that satisfy image quality as datapages can be obtained with low-pass filtering with an aperture at a plane of a recording medium. The optimum size of an aperture is numerically evaluated. The proposed method is experimentally verified. Moreover, the proposed method can achieve single and multiplexed recording of three datapages by a spherical reference beam with a binary CGH. (C) 2019 Optical Society of America

Minimally invasive imaging using weak illumination is required in the biomedical field. Computational ghost imaging (CGI) achieves imaging under illumination. However, CGI requires a large number of measurements to obtain an image. The number of measurements increases as illumination weakens. In this paper, decreasing the number of measurements of CGI with designed low spatial frequency masks is proposed. The proposed method allows us to image an object with a smaller number of measurements than with the conventional method. Numerical simulations and experiments confirm the feasibility of the proposed method. (C) 2018 Optical Society of America.

To increase the recording density of computer-generated-hologram (CGH)-based holographic data storage, a phase data page reconstruction method by the transport of intensity equation (TIE) is proposed. The TIE generally requires a scanning image sensor because the phase retrieval process needs at least two defocused intensity distributions. Although the TIE is applied, the proposed method enables detection of the distributions simultaneously by utilizing an extra conjugate component reconstructed from the CGH. Experimental results show that the proposed method allows reconstructing of a phase data page without any additional elements, which keeps the optical setup simple and low cost. (C) 2018 Optical Society of America

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. (c) 2018 The Japan Society of Applied Physics

Phase imaging by digital holography is widely used. An in-line optical setup is preferable for a practical use. A twin image, however, is a serious obstacle to achievement of high-quality phase imaging in in-line digital holography. For in-line digital holography, a time-division phase-shifting method or a wave-splitting phase-shifting method is used to eliminate the twin image. The former requires multiple exposures, and the latter requires specially designed optical elements. To solve these problems, a twin-image reduction method using a diffuser is proposed. In the proposed method, recording a digital hologram using a diffuser and signal processing enable reduction of the twin image on a reconstructed plane. A preliminary experimental result confirms the feasibility of the proposed method. (C) 2018 Optical Society of America

Computational ghost imaging (CGI) allows us to obtain a sample image under a low signal-to-noise-ratio (SNR) condition. However, phase information cannot be obtained by CGI; therefore, observation of transparent objects such as living cells is difficult. Although interferometry has been applied to CGI for phase retrieval, its optical setup is cumbersome. In this paper, an alternative approach, which is based on a transport-of-intensity equation, is proposed. Compared with conventional interferometric methods, the optical setup of the proposed method is robust because it does not require additional optical elements. The proposed method achieves phase retrieval by slight modification of the standard CGI setup. Numerical and optical experiments with low SNR confirm the effectiveness of the proposed method. (C) 2018 Optical Society of America

Computational ghost imaging (CGI) is expected to be applied to noninvasive biomedical imaging because of its characteristic which allows us to obtain the object's image under a low signal to noise ratio (SNR) condition. However only an amplitude distribution can be obtained by the CGI. Therefore the imaging of the pure phase objects is difficult. Although the phase shifting digital holography has been used for reconstruction of the complex amplitude in the CGI, its experimental setup is cumbersome and sensitive to vibrations. Furthermore four holograms are required for the reconstruction of the complex amplitude because of the phase shifting algorithm, rendering the acquisition time of the phase image slow. Therefore the method is difficult to be applied to the biomedical imaging. An alternative non-interferometric method is proposed in this study. The proposed method uses the transport of intensity equation for the phase retrieval of the pure phase objects, termed transport-of-intensity CGI (TI-CGI). In the TI-CGI, the phase distribution is retrieved from a single defocused image obtained by a modulated optical setup of the CGI, achieving the fast and robust imaging compared with the conventional phase shifting method. Therefore the TI-CGI may be more suitable for the biomedical imaging than the phase shifting method. The TI-CGI is demonstrated by an optical experiment under the low SNR condition generated by the neutral density filters with 1% and 0.1% transmittance. The experimental results conform the effectiveness of the TI-CGI.

Wavefront sensing techniques are mainly needed in an adaptive optics system for high resolution imaging. One of them is a Shack-Hartmann method which is composed of very simple structure. Although the method is widely utilized, it also has the limitation for the measurable magnitude of wavefront aberrations. To overcome the problem, the improved Shack-Hartmann method for larger aberrated wavefronts has been proposed. In this paper, the principle of the proposed method and the numerical evaluation of the performance of the proposed method are presented.

Holographic data storage (HDS) is one of attractive solutions for archiving huge number of data produced all over the world. A coaxial system in HDS has some advantages of simple setup, tolerance to vibrations, and so on. In a coaxial system, the two-dimensional (2D) shift multiplexing is achieved by lateral medium shifts corresponding to disk rotation. Also, the multi-layer recording with a kinoform varifocal lens has also been proposed, which is based on adding a defocus phase distribution to signal and reference patterns displayed on a spatial light modulator (SLM) [1]. In this paper, we propose the three-dimensional (3D) shift multiplexing combining these multiplexed schemes and the criteria to determine the appropriate recording condition. The proposed method confirms the feasibility of improving the recoring density in coaxial HDS.

By using transport of intensity equation (TIE), phase distribution of an object is retrieved from through-focus intensity images. This technique allows simple and robust phase imaging compared with an interferometric approach. However, it is hard to measure phase distribution when a dynamic object moves in the direction of an optical axis. To clear this problem, autofocusing TIE which is based on local statistics is proposed. The proposed technique achieves the detection of the object plane and the retrieval of a focused object phase distribution simultaneously. In this approach, an object plane is determined by the focusing techniques based on local statistics such as variance, gradient, and Laplacian of amplitude distribution, after phase distribution in an image sensor plane is retrieved by the TIE. The performance of these three statistics is evaluated in numerical and optical experiments, and a suitable focus value is determined for precise phase imaging.

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. (C) 2017 The Japan Society of Applied Physics

Interpixel cross talk decreases the quality of a reconstructed signal in holographic data storage and imposes a limitation on its storage capacity. To reduce the interpixel cross talk, an orthogonal polarization encoding method is proposed. In the proposed method, the polarization state of each pixel is set to be orthogonal with that of surrounding pixels. This prevents the interference between nearest- neighboring pixels and significantly reduces the gross of the interpixel cross talk. The quality of the data page obtained with the proposed method is numerically and experimentally evaluated. Those results suggest that the proposed method can improve the quality of a reconstructed signal. (C) 2017 Optical Society of America

A generalized sequential four-step phase-shifting color digital holography is proposed. As an arbitrary phase-shift quantity is independent from wavelengths, it can be used for four-step phase-shifting color digital holography. Furthermore, no constraint on the phase-shifting quantities or statistical property on the hologram is required in the proposed method. Experimental results using a reflective object are shown to confirm the proposed phase-shifting digital holography. (C) 2017 Optical Society of America

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.

Spatially incoherent Fourier digital holography using a rotational shearing interferometer for four-step phase-shifting method is proposed. The previous incoherent Fourier holography using a rotational shearing interferometer [Watanabe and Nomura (Appl. Opt. 54: A18, 2015)] employs the two-step phase-shifting method in the vertical and horizontal polarizations. The reconstructed image contains a large bias term. This paper proposes introduction of two kinds of wave plates in one path of a rotational shearing interferometer for a four-step phase-shifting method. A Fourier hologram is obtained from the four recorded holograms for eliminating the bias term and the twin image. The numerical simulation and the optical experiment demonstrate improvement of the image quality of reconstructed image by the twin image and bias level reduction. Furthermore, the effect of the size of an image sensor on the image quality in rotational shearing interferometer is also investigated by the numerical simulations.

© 2017 IEEE. Digital holography provides a method of the 3-D recording and numerical reconstruction by a simple optical system and a computer. Quantitative measurement and numerical refocusing are major characteristics. So far, many physical parameters such as amplitude, phase, polarization, fluorescence, and spectra can be obtained independently. Recently, multimodal imaging that can obtain simultaneously two or more physical parameters by combining digital holographic microscope and other optical microscopes such as a fluorescence optical microscope and a Raman scattering microscope has emerged. In this review, physical parametric imaging techniques based on digital holography are presented and then these techniques are enhanced to develop multimodal imaging based on digital holography.

A holographic data storage system based on a computer-generated hologram (CGH) is simple and compact because a hologram of a data page is recorded through an imaging system without an additional optical path for a reference beam. In this paper, to improve the recording density of the holographic data storage based on a CGH, a shift multiplexing method using a spherical wave is proposed. A data page to be stored and a spherical wave are simultaneously reconstructed from a single CGH. This allows shift multiplexing by displacing a recording medium. Experimental results show that the proposed method can improve shift selectivity and enables us to implement shift multiplexing. (C) 2017 Optical Society of America

Digital super-resolution holographic data storage based on Hermitian symmetry is proposed to store digital data in a tiny area of a medium. In general, reducing a recording area with an aperture leads to the improvement in the storage capacity of holographic data storage. Conventional holographic data storage systems however have a limitation in reducing a recording area. This limitation is called a Nyquist size. Unlike the conventional systems, our proposed system can overcome the limitation with the help of a digital holographic technique and digital signal processing. Experimental result shows that the proposed system can record and retrieve a hologram in a smaller area than the Nyquist size on the basis of Hermitian symmetry. (C) 2016 Optical Society of America

The possibility of incoherent digital holography has been widely studied because it is free from coherent light sources. Here spatially incoherent Fourier digital holography is described. The incoherent hologram is obtained by a rotational shearing interferometer. The hologram obtained by the interferometer is a cosine transform of a spatially incoherent object. After describing the principle of a rotational shearing interferometer, methods to obtain Fourier transform of an object presented.

A phase object mapping technique is proposed to measure a phase distribution of objects which exist in different depth positions. The proposed method is confirmed by a numerical simulation.

A coaxial polarization holographic data recording is proposed, and a proof-of-principle experiment is demonstrated for the first time, to the best of our knowledge. A proposed recording system allows us to record and retrieve a volume polarization hologram using a simple optical setup, as compared with conventional polarization holographic data storage systems. By using the proposed system, the data pages encoded on horizontal and vertical linearly polarized beams were simultaneously recorded, and each data page was successfully retrieved without any error. Moreover, the effectiveness of a random phase mask was experimentally and quantitatively confirmed in polarization holographic data storage. (C) 2016 Optical Society of America

A holographic data storage system using digital holography is proposed to record and retrieve multilevel complex amplitude data pages. Digital holographic techniques are capable of modulating and detecting complex amplitude distribution using current electronic devices. These techniques allow the development of a simple, compact, and stable holographic storage system that mainly consists of a single phase-only spatial light modulator and an image sensor. As a proof-of-principle experiment, complex amplitude data pages with binary amplitude and four-level phase are recorded and retrieved. Experimental results show the feasibility of the proposed holographic data storage system. (C) 2016 Optical Society of America

We propose an adaptive point-spread spherical wave synthesis method based on the point-source hologram technique for fast hologram pattern generation. The calculation time of the hologram generation is reduced by decreasing the number of reconstructed point sources composing an object. A larger point source is reconstructed in the area where an object can be partially expressed by low resolution. The point-spread is adjusted corresponding to the spatial frequency of an object. The effectiveness of the proposed method is confirmed by a computer simulation using two-dimensional images.

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 [Perez-Cabre], 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.

A Shack-Hartmann wavefront sensor (SHWFS) that consists of a microlens array and an image sensor has been used to measure the wavefront aberrations of human eyes. However, a conventional SHWFS has finite dynamic range depending on the diameter of the each microlens. The dynamic range cannot be easily expanded without a decrease of the spatial resolution. In this study, an adaptive spot search method to expand the dynamic range of an SHWFS is proposed. In the proposed method, spots are searched with the help of their approximate displacements measured with low spatial resolution and large dynamic range. By the proposed method, a wavefront can be correctly measured even if the spot is beyond the detection area. The adaptive spot search method is realized by using the special microlens array that generates both spots and discriminable patterns. The proposed method enables expanding the dynamic range of an SHWFS with a single shot and short processing time. The performance of the proposed method is compared with that of a conventional SHWFS by optical experiments. Furthermore, the dynamic range of the proposed method is quantitatively evaluated by numerical simulations. (C) 2016 Optical Society of America

A phase imaging based on the transport of intensity equation using multiple bandpass filters is proposed. The proposed method enables us to measure a phase distribution quantitatively from through-focus intensity images obtained by using a white light source and multiple bandpass filters. The technique improves the accuracy of a phase measurement by increasing the number of intensity images obtained at different defocused positions. The feasibility of the phase measurement and the improvement in the accuracy with increasing the through-focus images are confirmed by numerical simulations and optical experiments. (C) 2016 Optical Society of America

A linear phase encoding is presented for realizing a compact and simple holographic data storage system with a single spatial light modulator (SLM). This encoding method makes it possible to modulate a complex amplitude distribution with a single phase-only SLM in a holographic storage system. In addition, an undesired light due to the imperfection of an SLM can be removed by spatial frequency filtering with a Nyquist aperture. The linear phase encoding is introduced to coaxial holographic data storage. The generation of a signal beam using linear phase encoding is experimentally verified in an interferometer. In a coaxial holographic data storage system, single data recording, shift selectivity, and shift multiplexed recording are experimentally demonstrated. (C) 2016 Optical Society of America

The image quality improvement method using a spatial-domain mask is proposed. In the proposed method, a single hologram is required for speckle reduction. The speckle noise of the reconstructed image is suppressed by averaging different speckle patterns. The different speckle patterns are generated by shifting the rectangular aperture in the hologram plane. The experiment results including a modulation transfer function are presented to confirm the performance of the proposed method.

A multilayer recording method using a varifocal lens generated with a kinoform is presented. In this recording method, a focus position is axially displaced by adding a defocus phase to a phase modulation pattern, which consists of a random phase mask and a computer-generated reference pattern. Shift selectivity and multiplexed recording are experimentally investigated in coaxial holographic data storage. Experimental results show that the proposed method allows the recording of holograms along an optical axis without any mechanical movement. (C) 2015 Optical Society of America

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.

A speckle reduction method based on a spherical waves synthesis with low-coherence digital holography for hologram generation is proposed. An object information is experimentally obtained from a number of recorded low-coherence digital holograms. A hologram is generated by synthesizing the fields of spherical waves with the obtained information. The performance of the proposed method as hologram generation from a distribution contained spike noises like speckles is confirmed. The image quality is evaluated by the speckle contrast of the reconstructed image.

A digital holographic Mueller matrix imaging method is proposed. A Mueller matrix is obtained from Stokes vectors that are calculated from the complex amplitude of the two orthogonal polarized lights. The complex amplitude is obtained by digital holography. In the proposed method, three-dimensional Mueller matrix imaging is achieved by 12 recordings. Optical experimental results confirm the feasibility of the proposed method by measuring the Mueller matrices of four linear polarizers, a quarter-wave plate, and two linear polarizers placed at different positions. (C) 2015 Optical Society of America

A computer-generated reference pattern (CGRP) allows improvement in light efficiency and the quality of reconstructed data in coaxial holographic data storage. In this Letter, a multiplexed recording method with uncorrelated CGRPs is proposed. With this method, crosstalk from adjacent holograms is suppressed without shifting a medium. To confirm the feasibility of the proposed method experimentally, shift selectivity is investigated, and then multiplexed recording is performed. Experimental results show that the proposed method enables high-density recording compared with conventional shift multiplexing. In addition, a theoretical analysis implies that at least 100 uncorrelated CGRPs can be designed and used for multiplexed recording. (C) 2015 Optical Society of America

A method to expand the dynamic range for a Shack - Hartmann wavefront sensor (SHWFS) is proposed. An SHWFS consists of a microlens array and an image sensor, and it has been widely used to measure the wavefront aberration of a lightwave in various fields. However, a very large aberrated wave cannot be correctly measured due to the finite dynamic range that depends on the diameter of each microlens. The proposed method enables an SHWFS to measure wavefronts with larger aberrations by applying holography and pattern matching technologies. For measurement of a spherical wave, the proposed method is compared with a conventional one by numerical simulations and optical experiments. Their results confirm the performance of the proposed method. (C) 2015 Optical Society of America

The method to record an incoherent Fourier hologram is proposed. The interference patterns in the dual channel rotational shearing interferometer are obtained as the figure of the cosine and the sine transformation in the vertical and the horizontal polarization, respectively. The proposed optical system is simple without spatial light modulators or mechanical phase shifting devices. The experiment, in which the letter "A" displayed on a liquid crystal display with a blue LED backlight was used as an object, confirms the proposed method to obtain an incoherent Fourier hologram. (C) 2014 Optical Society of America

The systems to record incoherent holograms using a rotational shearing interferometer is demonstrated. The systems can record incoherent holograms by self-interference of the two coherent object points created by the beam splitter from one object point. In general, the rotational shearing interferometer cannot reproduce any depth information. The proposed rotational shearing interferometer has the advantage of obtaining depth information by the reconstruction owing to lenses for the shear which is parallel to the optical axis. A preliminary experiments were performed. The object images at some reconstruction distances were reconstructed numerically. The experimental results confirm the proposed system.

A Shack-Hartmann wavefront sensor (SHWFS) which consists of a microlens array and an image sensor has been used to measure the wavefront aberrations in various fields owing to its advantages such as simple configuration. However, a conventional SHWFS has the finite dynamic range. The dynamic range cannot be expanded without sacrificing the spatial resolution and the sensitivity in a conventional SHWFS. In this study, the SHWFS using a dual microlens array to solve the problem is proposed. In the proposed method, an astigmatic microlens is arranged at the center of a group of 2 x 2 spherical microlenses. A pattern image including spots and linear patterns is obtained at the focal plane by the dual microlens array. The pattern image can be separated into two images as if two microlens array with different diameter were used by discriminating spots from linear patterns with the pattern matching technique. The proposed method enables to expand the dynamic range of an SHWFS by using the separated two images. The performance of the proposed method is confirmed by the numerical simulation for measuring a spherical wave.

Digital holography is a useful technique for recording the fully complex field of a wavefront. However, the quality of a reconstructed image of a digital hologram is not good, because it is suffering from speckles. To improve the image quality, a speckle reduction method in digital holography using various rectangular apertures is proposed. Different-sized rectangular apertures are applied for the hologram. Furthermore, the position of the aperture is arbitrary. Owing to the various size and position, the generated speckles have the various sizes and patterns. By averaging the speckle, the speckle noise can be reduced. Some reconstructed images based on the experimental results are shown to confirm the proposed method. For quantitative evaluation, the speckle contrast is also shown.

As one of the wave-splitting phase-shifting digital holography, single-exposure generalized phase-shifting digital holography has been proposed. In the digital holography, the phase-shift quantity, which corresponds to the difference between the phase quantities of the reference wave on the adjacent pixels, is not restricted but generalized. Owing to the generalized phase-shifting, a random-phase wave as the reference wave can be used. The proposed phase-shifting digital holography enables us to record a fully-complex field of a dynamic phenomena without dc and conjugate terms using a commercially available optical devices. Constraints on the reference wave and the object wave suitable for the phase-shifting digital holography are introduced. Experimental results are presented to confirm the constraints.

A multilayer recording using a varifocal lens generated with a phase-only spatial light modulator (SLM) is proposed. A phase-only SLM is used for not only improving interference efficiency between signal and reference beams but also shifting a focus plane along an optical axis. A focus plane can be shifted by adding a spherical phase to a phase modulation pattern displayed on a phase-only SLM. A focal shift with adding a spherical phase was numerically confirmed. In addition, shift selectivity and recording performance of the proposed multilayer recording method were numerically evaluated in coaxial holographic data storage.

Super-resolution holographic data storage allows us to record and retrieve a data page with a smaller aperture than a Nyquist aperture. This system has a potential to realize a high-density recording compared with a conventional holographic storage system. Recording a phase data page in super-resolution holographic data storage to improve light efficiency is proposed. The phase data page is designed for the super-resolution holographic data storage to suppress the zero-order beam of a signal beam in a Fourier plane. The numerical experiments show the feasibility of the proposed method.

The system to record incoherent holograms using a rotational shearing interferometer is proposed. It enables us to record a hologram without coherent illumination such as a laser. The systems can record an incoherent hologram by self-interference. A rotational shearing interferometer to record incoherent cosine hologram is described. Furthermore, a rotational shearing interferometer with lenses to record incoherent hologram is described. It has the advantage of obtaining depth information by the reconstruction owing to lenses for the shear which is parallel to the optical axis. The preliminary experiments were performed. An LED and a liquid crystal display with an LED backlight were used as incoherent objects. The incoherent holograms were recorded. The object images were reconstructed numerically. The experimental results confirm the proposed incoherent holography using a rotational shearing interferometer.

Incoherent holography enables us to use a spatially incoherent illumination for recording holograms. In this paper, we describe incoherent holograms which can be recorded by the optical setups based on the rotational shearing interferometer. The experiment in which a LED was used an incoherent object confirms obtaining the holograms as the figures of a cosine transformation and a Fresnel zone-like pattern.

The proposed holographic Shack-Hartmann wavefront sensor can measure a wavefront aberration with large dynamic range. It is realized by introducing a holographic optical element and pattern matching technique. To confirm the flexibility of the sensor, measurements of the wavefronts with various aberrations are numerically demonstrated.

A speckle-reduction method with random locations of sparse object points is proposed for image quality improvement based on a time-multiplexing approach in holographic reconstruction. The object points of a reconstructed image are divided into groups of sparse object points. Pixel separation of the periodic location, in general, is used for the sparse object points. However, an unwanted periodic fringe pattern is caused, and it dominantly degrades the reconstructed image quality. The proposed random pixel separation enables the reconstructed image quality to improve more effectively. The numerical simulation and the optical experiment are presented to confirm the performance of the proposed method. (C) 2014 Optical Society of America

A single-shot three-dimensional (3D) shape measurement by low-coherent optical path difference digital holography with small energy consumption is proposed. The use of a superluminescent diode makes it possible. Weighting of the single hologram and numerical reconstruction give the 3D shape of an object. Experimental results using a simple object (the surface of a button cell battery) are given. By comparison with experimental results using a vertical scanning method, the proposed method is confirmed. The effects of a shift interval of the hologram and a zero-order component on a measurement result are also discussed. (C) 2014 Optical Society of America

Arbitrary pattern in an arbitrary domain can be realized by computer generated hologram (CGH). If CGH is applied to the optical data storage, the complexity of the optical system can be eased. For example, a single spatial light modulator (SLM) can be used to express a fully-complex filed of a lightwave. Holographic data storage with a single amplitude SLM by use of CGH is presented. A signal beam and a reference beam are generated by a computer generated hologram (CGH). Owing to the characteristics of the CGH, the incident angle of a reference beam can be changed. This means that angular multiplexing is available.

A design method of an input phase mask for holographic memory is proposed. In the method, a modification of a design procedure and another restraint condition are applied to our conventional design method. The light use efficiency and the quality of a reconstructed image are improved. The performance of an input phase mask designed by the method is confirmed by numerical simulations. Finally, a suitable design condition of an input phase mask is determined from simulation results. (C) 2014 Optical Society of America

A high-resolution and multilevel designed reference pattern (DRP) is presented for improvement of both light utilization efficiency and the signal-to-noise ratio (SNR) of reconstructed images in coaxial holographic data storage. With a DRP, the desired Fourier power spectrum of a reference beam is obtained. Numerical and experimental results show that the DRP increases the SNR compared with that of a random phase mask (RPM). Moreover, the light utilization efficiency of the DRP is higher than that of a high-resolution RPM. In addition, the effect of the phase level and the pixel pitch of DRPs on the SNR and the light utilization efficiency are investigated. (C) 2014 Optical Society of America

Single-exposure generalized phase-shifting digital holography enables one to remove the zerothorder 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. (C) 2014 Society of Photo-Optical nstrumentation Engineers (SPIE)

The simultaneous measurement method of a refractive index distribution and a thickness distribution using low-coherence digital holography with a vertical scanning is proposed. The proposed method consists of a combination of digital holography and low-coherence interferometry. The introduction of a datum plane enables the measurement of both a refractive index distribution and a thickness distribution. By the optical experiment, the potential of the proposed method is confirmed.

The retrieving method of a complex amplitude-modulated data page by the gen- eralized phase-shifting method is proposed in coaxial holographic data storage. The numerical simulation shows the feasibility of the proposed coaxial system. © 2014 Optical Society of America.

The retrieving method of a complex amplitude-modulated data page by the gen- eralized phase-shifting method is proposed in coaxial holographic data storage. The numerical simulation shows the feasibility of the proposed coaxial system. © 2014 Optical Society of America.

The retrieving method of a complex amplitude-modulated data page by the gen- eralized phase-shifting method is proposed in coaxial holographic data storage. The numerical simulation shows the feasibility of the proposed coaxial system. © 2014 Optical Society of America.

The retrieving method of a complex amplitude-modulated data page by the gen- eralized phase-shifting method is proposed in coaxial holographic data storage. The numerical simulation shows the feasibility of the proposed coaxial system. © 2014 Optical Society of America.

The retrieving method of a complex amplitude-modulated data page by the gen- eralized phase-shifting method is proposed in coaxial holographic data storage. The numerical simulation shows the feasibility of the proposed coaxial system. © 2014 Optical Society of America.

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. (C) 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)

We propose the designed reference pattern on the basis of the Nyquist aperture for a coaxial holographic memory and investigate its recording performance by numerical simulations. By using the designed reference pattern, the Fourier power spectrum of a reference beam spreads uniformly within the Nyquist aperture, thereby an interference efficiency, a signal-to-noise ratio (SNR) and a symbol error rate (SER) are improved relative to conventional method with a random binary phase mask. Moreover, in the case of applying the 1.25 times aperture than the Nyquist size, the proposed method can record data pages with higher SNR and lower SER than that of conventional method with 2 times aperture than the Nyquist size. Numerical results imply that our proposed method can record data pages at a smaller area of recording media than that of conventional method. (c) 2013 The Japan Society of Applied Physics

In holographic displays, it is undesirable to observe the speckle noises with the reconstructed images. A method for improvement of reconstructed image quality by synthesizing low-coherence digital holograms is proposed. It is possible to obtain speckleless reconstruction of holograms due to low-coherence digital holography. An image sensor records low-coherence digital holograms, and the holograms are synthesized by computational calculation. Two approaches, the threshold-processing and the picking-a-peak methods, are proposed in order to reduce random noise of low-coherence digital holograms. The reconstructed image quality by the proposed methods is compared with the case of high-coherence digital holography. Quantitative evaluation is given to confirm the proposed methods. In addition, the visual evaluation by 15 people is also shown. (C) 2013 Optical Society of America

The appropriate reference wave in single-exposure phase-shifting digital holography using a random-complex-amplitude encoded reference wave is experimentally investigated. Although the reference wave is generalized, the quality of reconstructed images depends on it. Furthermore, when the reference wave satisfies a certain condition, reconstructed images cannot be obtained in this method. After the certain condition is presented, the appropriate condition is studied using a speckle property. Experimental results are given to investigate the relations between the quality of reconstructed images and the sizes of speckles of the reference waves. The results prove that the appropriate reference wave exists in this method. (C) 2013 Optical Society of America

The improved single-exposure phase-shifting digital holography using a random-phase reference wave is proposed. The algorithm for obtaining a complex amplitude of an object wave is improved. In the proposed algorithm, the reference wave is treated as not a random-phase but a random-complex amplitude. Therefore, the algorithm uses proper amplitude information of the reference wave. Both numerical simulations and experimental results are given to confirm the effectiveness of the proposed algorithm. (C) 2012 Optical Society of America

A lensless digital holographic tomography using not a filtered back projection method but a light back propagation method is proposed. In the proposed method, the phase distribution on the detector is used for a light propagation. On the contrary, in the conventional method, the phase information is used for a back projection. Owing to the propagation, the deflection from a true optical path is reduced in the proposed method. For the measurement of a specimen with a huge refraction angle, it is shown that our proposed method improves on measurement accuracy compared with a conventional filtered back projection method. Numerical simulations are given to confirm the feasibility of the proposed method.

The measurement method of a refractive index distribution and a physical thickness distribution using digital holography with a low-coherent light source is proposed. The introduction of a datum plane enables the simultaneous measurement of a refractive index and a physical thickness distributions. By the optical experiments, the potential of the proposed method is confirmed. For the reduction of measurement time, the relation between stepping intervals of a reference mirror and measurement results are also discussed.

Design methods of a reference pattern and an input phase mask for a coaxial holographic memory are described. By the proposed method, it is expected that the useless consumption of the dynamic range of a recording medium will decrease, and the light efficiency and the interference efficiency between the signal beam and the reference beam will be improved. A reference pattern and an input phase mask are designed by a simulated annealing. The performance of the proposed design method is confirmed by numerical simulations and optical experiments. Furthermore, the holographic memory system using both the designed reference pattern and the designed input phase mask is also confirmed by numerical simulations and optical experiments. (C) 2011 The Japan Society of Applied Physics

A single-shot digital holography using a generalized wave-splitting phase-shifting method is introduced. The complex-amplitude encoded reference wave is used for hologram recording. The method enables us to use an ordinary camera to record a phase-shifted digital hologram. Some computational/ experimental results are given to confirm the method. © 2011 IEEE.

We propose a single-exposure phase-shifting digital holography based on a wave-splitting method using a random-phase reference wave. A random-phase reference wave gives random-phase distribution on the digital hologram. Using the amplitude and the phase distributions of the reference wave, the fully complex amplitude of the object wave is obtained. The proposed method requires not devised optical systems but ordinary imaging devices, such as CCD cameras. A preliminary experimental result is given to confirm the proposed method. (C) 2010 Optical Society of America

The wave-splitting phase-shifting digital holography using a pixelated microretarder array is proposed. By using four intensity images recorded by the pixelated microretarder array, Stokes parameters of the incident wave can be calculated. The fully complex amplitude distribution of the object wave can be obtained by using Stokes parameters, if the polarization states of the object and reference waves are linear and orthogonal. Two sets of experimental results are provided to verify the feasibility of the proposed method. One is the result for a movie recording using a CW laser and the other is the result for instant recording using a single pulsed laser.

The both profilemotry and reflectmetry of a 3D object by use of digital holography with low coherent light source is proposed. For noise reduction, integration of digital holograms is introduced. © 2010 Optical society of America.

The method to improve of a viewing-zone angle and an image quality of a digital hologram is presented. A number of digital holograms of a central object are recorded from the position on the circumference. The holograms are used for a hologram synthesis to improve the image quality from whole viewing-zone angle. The synthesis is achieved by a correlation between a hologram and numerically propagated holograms. The large-sized synthesized digital hologram has a wide viewing-zone angle and less speckles. Some experimental results are shown to confirm the proposed method.

A single-exposure generalized phase-shifting digital holography based on a wave-splitting method. A phase-encoded reference wave is used for phase-shifting. Using the known amplitude and phase distributions of the reference wave, the fully complex amplitude of the object wave is obtained. The proposed method requires not devised optical systems but ordinary imaging devices, such as CCD cameras. A preliminary experimental results with a spherical wave and a random phase wave as reference waves are given to confirm the proposed method.

A polarimetric imaging method of a 3D object by use of on-axis phase-shifting digital holography is presented. The polarimetric image results from a combination of two kinds of holographic imaging using orthogonal polarized reference waves. Experimental demonstration of a 3D polarimetric imaging is presented. Pattern recognition by use of polarimetric phase-shifting digital holography is also presented. Using holography, the amplitude and phase difference distributions between two orthogonal polarizations of 3D phase objects are obtained. This information contains both complex amplitude and polarimetric characteristics of the object, and it can be used for improving the discrimination capability of object recognition. Preliminary experimental results are presented to demonstrate the idea.

This paper presents an overview of the potential of free space optical technology in information security, encryption, and authentication. Optical waveform posses many degrees of freedom such as amplitude, phase, polarization, spectral content, and multiplexing which can be combined in different ways to make the information encoding more secure. This paper reviews optical techniques for encryption and security of two-dimensional and three-dimensional data. Interferometric methods are used to record and retrieve data by either optical or digital holography for security applications. Digital holograms are widely used in recording and processing three dimensional data, and are attractive for securing three dimensional data. Also, we review optical authentication techniques applied to ID tags with visible and near infrared imaging. A variety of images and signatures, including biometrics, random codes, and primary images can be combined in an optical ID tag for security and authentication.

The method to generate a quasi-cylindrical digital hologram is presented. A number of digital holograms of an central object recorded on concyclic positions are used for superposition. The superposition is achieved by numerical propagation of the hologram. Some experimental results are shown to confirm our proposed method. © 2009 Optical society of America.

A polarimetric imaging method of a 3-D object by use of wavefront-splitting phase-shifting digital holography is presented. Phase-shifting digital holography with a phase difference between orthogonal polarizations is used. The use of orthogonal polarizations can make it possible to record two phase-shifted holograms simultaneously if we use pixelated polarimetric optical elements. By combining the holograms with the distributions of a reference wave and an object wave, the complex field of the object wavefront can be obtained. The polarimetric image results from a combination of two kinds of holographic imaging using orthogonal polarized reference waves. An experimental demonstration of a 3-D polarimetric imaging is presented. © 2009 Springer-Verlag New York.

A method to improve the image quality of a digital holographic reconstructed image by means of speckle reduction is proposed. The size and position of the speckles are changed according to the wavelengths to record a digital hologram. By superposing reconstructed images with different wavelengths, the effect of speckle is reduced so that the image quality is improved. Optical experiments are given to confirm the proposed method. (c) 2008 Optical Society of America

The phase-shifting digital holography by use of a micro-retarder array is proposed. The micro-retarder array consists of four kinds of different directions of fast axes. The combination of the micro-retarder array and a polarizer gives us the four intensity distributions corresponding to the direction of the fast axes. From four intensity images,we can calculate Stokes parameters of the incident wave. Furthermore, we can obtain fully-complex amplitude distribution of the object wave by using Stokes parameters, if the both polarization states of the object wave and the reference wave are linear and they are orthogonal. Some experimental results are given to confirm our proposed recording method.

A polarimetric imaging method of a 3D object by use of digital holography is presented. The phase-shifitng digital holography using orthogonal polarization is adopted. The polarimetric image results from a combination of two kinds of holographic imaging using orthogonal polarized reference waves. Experimental demonstration of a 3D polarimetric imaging is presented. © 2007 American Institute of Physics.

Phase-shifting digital holography with a phase difference between orthogonal polarizations is proposed. The use of orthogonal polarizations can make it possible to record two phase-shifted holograms simultaneously. By combining the holograms with the distributions of a reference wave and an object wave, the complex field of the object's wavefront can be obtained. Preliminary experimental results are shown to confirm the proposed method. (C) 2006 Optical Society of America.

The one-shot phase-shifting digital holography using phase difference of orthogonal polarizations is proposed. Using a CCD camera with pixelated polarizers, three images for phase analysis can be obtained simultaneously. The proposed method can be applied to a moving object, because a complex field of the wavefront of a 3D object can be obtained in a single exposure.

The secure optical memory system based on a double-random phase-encoding optical encryption system is proposed. The quality of decrypted data can be improved by designing an input phase mask to utilize the bandwidth the bandwidth of the optical system effectively. We propose the certification method of the data recorded into the optical memory by using a designed input phase mask as a phase code. Computer simulations confirm the possibility of the proposed certification system.

The method to reduce speckles in a reconstructed image of a digital hologram is proposed. The size and position of the speckles are changed according to both the wavelengths to be recorded and the distances from the object the hologram. The superposition of the reconstructed images recorded with different wavelength/distance holograms gives the image with reduced speckles.

The out-of-plane displacement of a cantilever is measured by phase-shifting digital holography. From four phase-shifted holograms of a cantilever recorded by a CCD image sensor, a complex amplitude at each pixel of the CCD plane is obtained using the conventional phase-shifting method. The complex amplitude of a cantilever is reconstructed from the complex amplitude of the CCD plane using the Fresnel diffraction integral. The phase difference distribution on the cantilever before and after deformation, i.e., the out-of-plane displacement distribution, is calculated. In order to decrease the effect of speckle noise, a new method using divided holograms is proposed. The theory and experimental results are shown.

A polarization-encoding system for optical security verification is proposed. The polarization information is bonded to an identification card for security verification. As the polarization state cannot be imaged by an ordinary intensity-sensitive device such as a CCD camera, it can provide an additional degree of freedom in using optics to secure information. The expressions for polarization encoded input images are developed using Jones polarization calculus. A nonlinear joint transform correlator is used to provide an optical validation system. Computer simulations and optical experimental results are shown in support of the proposed method.

We have proposed a secure optical data-storage system with a random phase key code based on a configuration of a joint transform correlator. The method to design the key code has been proposed. Computer simulations and optical experiments confirm our proposed system.

Secure optical storage based on a configuration of a joint transform correlator (JTC) using a photorefractive material is presented. A key code designed by an optimized algorithm so that its Fourier transform has a uniform amplitude distribution and a uniformly random phase distribution is introduced. Original two-dimensional data and the key code are placed side-by-side at the input plane. Both of them are stored in a photorefractive material as a joint power spectrum. The retrieval of the original data can be achieved with the same key code. We can record multiple two-dimensional data in the same crystal by angular multiplexing and/or key-code multiplexing.

Measurement of the out-of-plane displacement of a cantilever is performed by phase-shifting digital holographic interferomety. Phase-shifting method is used for the phase analysis of the hologram recorded on a CCD sensor. The complex amplitude of the reconstructed object is obtained from the complex amplitude of the CCD plane using the Fresnel diffraction algorithm. The difference of the phase distributions before and after deformation, i.e. out-of-plane displacement is calculated. In order to decrease the effect of speckle pattern, the hologram is divided into 16 parts. The phase is obtained from the phase with the maximum amplitude among the complex amplitudes obtained from all the separated holograms. As the result, by eliminating the effect of speckle, a smooth phase difference distribution is obtained.

The method to design an input phase mask for the double-random phase-encoding optical encryption is proposed. The input phase;mask is designed so that the extend of the Fourier spectrum of the product of an input image and the input phase mask corresponds to the space bandwidth of the optical system. By using the designed input phase mask, we show that the bit-error rate is improved.

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.

A secure optical storage based on a configuration of a joint transform correlator by use of a photorefractive material is presented. A key code designed through the use of an optimized algorithm so that its Fourier transform has a uniform amplitude distribution and a uniformly random phase distribution is introduced. Original two-dimensional data and the key code are placed side-by-side at the input plane. Both of them are stored in a photorefractive material as a joint power spectrum. The retrieval of the original data can be achieved with the same key code. We can record multiple two-dimensional data in the same crystal by angular multiplexing and/or key code multiplexing. (C) 2003 Optical Society of America.

In this study, the deflection distribution of a cantilever is measured combining the holographic interferometry and phase-shifting digital holography. Holographic interferometry can measure with high accuracy, high sensitivity, and full-field by noncontacting. But the development processing of a film is troublesome by holographic interferometry. Digital holography record on CCD and it reconstructs it with a computer. Therefore, development processing is not needed and it is early reproducible by digital holography. Digital holography has the amplitudes information and phase information in digital information. By the holographic interferometer, the sum of complex amplitude before and after deformation is reconstructed. In this study, the sum of complex amplitude before and after deformation is calculated and reconstructed. Therefore, phase difference computed for digital information and the displacement of a nano-meter order will be able to measure with this method.

To analyze fringe patterns, frequency and phase analysis of fringes becomes popular. It provides accurate results and automated processing. In this paper, the theories of the frequency and phase domain methods such as the Fourier transform method, the wavelet transform method and the phase-shifting method are proposed for photoelastic fringe pattern analysis. The applications of these methods are described.

A digital holographic data reconstruction method with data compression is proposed. We show the number of quantization level of a digital hologram can be reduced. By computer simulations it is confirmed that the method is especially useful for binary images. For gray scale images, we propose a bit plane decomposition method. By this method, we show both high reconstructed image quality and a high compression ratio can be achieved. This method is applicable to both a normal digital hologram and an encrypted digital hologram.

A three-dimensional (3-D) linear prediction method for lossless coding of RGB images is proposed. In this method, an RGB signal is divided into three components and piled up as a 3-D signal. In order to remove redundancy among these components, a signal value is predicted from its neighboring points and transformed into an error signal. The prediction value is given by a linear combinaion of the neighboring points. Coefficients for those points are calculated with the least square method. Since the proposed method employs hybrid prediction including 2-D prediction and inter-component prediction, it can remove both the redundancy among adjecent pixels and that among three components at the same time. In this paper, several static or dynamic prediction methods are performed and entropies of the error signals are discussed. On an average for nine test images, the entropy of error signal generated by the proposed method is 7% smaller than that by inter-component prediction.

A hybrid pattern matching system using the binary versions of the Hartley and related transformations is presented. These transformations can be obtained by an incoherent optical system described in this paper. *Using them, the spurious correlation signals inherent in an incoherent pattern matching system based on the optical cosine transformation are removed. Experimental demonstrations in an incoherent-optical/digital- electronic hybrid system are also presented. © 1990 Optical Society of America.

A hybrid image processing system for high speed pattern matching is presented. The system consists of an incoherent optical system and an electronic digital image processor. The optical system makes use of the matched filtering technique based on incoherent holography. The incoherent holograms of an input object and a reference object are binarized. This binarization of holograms has two major advantages: (1) it sharpens the autocorrelation peak, and (2) it makes real time processing possible. We demonstrate the high potential of this method by presenting computer simulations and experiments. © 1989, Optical Society of America.

A deep-learning-based phase retrieval method is proposed for computational ghost imaging (CGI). In the method, a defocused intensity distribution of an object is obtained by the CGI. An object's phase distribution is retrieved from the intensity distribution by a trained deep neural network. The advantage of the method is that the phase retrieval can be achieved with a low signal to noise ratio. The effects of noise level and defocus distance are investigated.

Pattern recognition by use of polarimetric phase-shifting digital holography is presented. Using holography, the amplitude distribution and phase difference distribution between two orthogonal polarizations of three-dimensional (3D) or two-dimensional phase objects are obtained. This information contains both complex amplitude and polarimetric characteristics of the object, and it can be used for improving the discrimination capability of object recognition. Experimental results are presented to demonstrate the idea. To the best of our knowledge, this is the first report on 3D polarimetric recognition of objects using digital holography. (C) 2007 Optical Society of America.

A polarimetric imaging method of a 3D object by use of on-axis phase-shifting digital holography is presented. The polarimetric image results from a combination of two kinds of holographic imaging using orthogonal polarized reference waves. Experimental demonstration of a 3D polarimetric imaging is presented. (c) 2007 Optical Society of America.

We present multi-spectral holographic three-dimensional image fusion using the discrete wavelet transform (DWT). The fusion results are compared with those of the Gaussian and Laplacian pyramid fusion methods. The advantage of the DWT over other methods is that it has more flexibility in controlling high frequency components as well as low frequency components, which improves the fused image quality. A wavelength tunable solid-state pumped laser is used to record up to 11 holograms with wavelengths from 567 to 613 nm. We present the fused reconstructed holographic images including multi-spectral fused images from the recorded multiple holograms. Fused multi-wavelength reconstructed holographic images provide multi-spectral information about the objects.

A method to design an input phase mask for double-random phase-encoding optical encryption is proposed. The input phase mask is iteratively designed so that the extent of the Fourier spectrum of the product of an input image and the input phase mask correspond to the space bandwidth of the optical system. By using the designed input phase mask, we show that the bit-error rate is improved. We also discuss the number of phase levels of the designed input phase mask. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

A method to design an input phase mask for double-random phase-encoding optical encryption is proposed. The input phase mask is iteratively designed so that the extent of the Fourier spectrum of the product of an input image and the input phase mask correspond to the space bandwidth of the optical system. By using the designed input phase mask, we show that the bit-error rate is improved. We also discuss the number of phase levels of the designed input phase mask. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

An encrypted digital holographic data reconstruction method with data compression is proposed. We show that the number of quantization levels of the digital hologram can be reduced. By computer simulations, we confirm that the method is especially useful for binary images. For gray-scale images, we propose a bit plane decomposition method. By this method, we show that both high reconstructed image quality and a high compression ratio can be achieved. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

An encrypted digital holographic data reconstruction method with data compression is proposed. We show that the number of quantization levels of the digital hologram can be reduced. By computer simulations, we confirm that the method is especially useful for binary images. For gray-scale images, we propose a bit plane decomposition method. By this method, we show that both high reconstructed image quality and a high compression ratio can be achieved. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

The quasi one-shot phase-shifting digital holography using phase difference of orthogonal polarizations is proposed. The use of orthogonal polarizations can make it possible to record two phase-shifted holograms simultaneously. By combining the holograms with distributions of a reference wave and an object wave, the complex field of the wavefront of a 3D object can be obtained. As two phase-shifted holograms can be obtained simultaneously in the proposed method, even a moving object can be recorded.

The quasi one-shot phase-shifting digital holography using phase difference of orthogonal polarizations is proposed. The use of orthogonal polarizations can make it possible to record two phase-shifted holograms simultaneously. By combining the holograms with distributions of a reference wave and an object wave, the complex field of the wavefront of a 3D object can be obtained. As two phase-shifted holograms can be obtained simultaneously in the proposed method, even a moving object can be recorded.

To improve the image quality of the decrypted image through the double-random phase-encoding optical encryption, the design method of the input phase mask is proposed. The input phase mask is iteratively designed so that the extent of the Fourier spectrum of the product of an input image and the input phase mask matches to the space bandwidth of the optical system. By using the designed input phase mask, we show that the bit-error rate is improved. We also discuss the number of the phase levels of the designed input phase mask.

To improve the image quality of the decrypted image through the double-random phase-encoding optical encryption, the design method of the input phase mask is proposed. The input phase mask is iteratively designed so that the extent of the Fourier spectrum of the product of an input image and the input phase mask matches to the space bandwidth of the optical system. By using the designed input phase mask, we show that the bit-error rate is improved. We also discuss the number of the phase levels of the designed input phase mask.

An encryption method of a 3-D object based on the phase modulation of an object wave is proposed. The phase of the object wave is modulated by a virtual optical random phase mask using a digital holographic technique. The keys of an encryption step are both a phase distribution and a position of the virtual optical phase mask. If either of them is not correct, we cannot decrypt the 3-D object. Owing to a characteristic of a hologram, we can see some parallax of a reconstructed 3-D object. Experimental results are presented to confirm the proposed method. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

An encryption method of a 3-D object based on the phase modulation of an object wave is proposed. The phase of the object wave is modulated by a virtual optical random phase mask using a digital holographic technique. The keys of an encryption step are both a phase distribution and a position of the virtual optical phase mask. If either of them is not correct, we cannot decrypt the 3-D object. Owing to a characteristic of a hologram, we can see some parallax of a reconstructed 3-D object. Experimental results are presented to confirm the proposed method. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

The out-of-plane displacement of a cantilever is measured by phase-shifting digital holography. Fourier transform phase-shifting method is used for phase analysis. The 36 holograms with phase-shift are recorded by a CCD. The complex amplitude of the CCD plane is obtained using the Fourier transform phase-shifting method. The complex amplitude of reconstructed plane is obtained from the complex amplitude of the CCD plane using Fresnel diffraction algorithm. A difference of the phase distribution of before and after deformation, i.e. out-of-plane displacement is calculated. The smooth phase difference is obtained by the Fourier transform phase-shifting method.

Deformation measurement of a cantilever based on digital holographic interferometry is presented. The digital holo,,, rams of the cantilever before and after deformation are obtained by use of phase-shifting technique. By using the phase-shifting digital holography. the object wave information without zeroth order diffraction wave can be extracted. The phase difference of the reconstructed cantilever before and after deformation is obtained numerically using discrete Fresnel diffraction integral. Owing to the numerical analysis, the deformation of the cantilever can be obtained with high resolution of nanometer dimensions. The optical experimental results are shown to confirm our proposed method. Furthermore, we propose a mechanical movement free double-exposure method in phase-shifting digital holography using a laser diode.

Deformation measurement of a cantilever based on digital holographic interferometry is presented. The digital holo,,, rams of the cantilever before and after deformation are obtained by use of phase-shifting technique. By using the phase-shifting digital holography. the object wave information without zeroth order diffraction wave can be extracted. The phase difference of the reconstructed cantilever before and after deformation is obtained numerically using discrete Fresnel diffraction integral. Owing to the numerical analysis, the deformation of the cantilever can be obtained with high resolution of nanometer dimensions. The optical experimental results are shown to confirm our proposed method. Furthermore, we propose a mechanical movement free double-exposure method in phase-shifting digital holography using a laser diode.

An encrypted optical storage based on a joint transform correlator architecture by using a photorefractive material is presented. A key code designed by optimized algorithm so that its Fourier transform has a uniform amplitude distribution and a random phase distribution is introduced. Original two-dimensional data and the key code are placed side by side at the input plane. Both of them are stored in a photorefractive material as a joint power spectrum. The retrieval of the original data can be achieved with the same key code. We can record multiple two-dimensional data in a same crystal by angular multiplexing. Furthermore we can record by key code multiplexing because another designed key code can produce another independent phase distribution. We demonstrate the concept of the optical data storage system by computer simulations.

An encrypted optical storage based on a joint transform correlator architecture by using a photorefractive material is presented. A key code designed by optimized algorithm so that its Fourier transform has a uniform amplitude distribution and a random phase distribution is introduced. Original two-dimensional data and the key code are placed side by side at the input plane. Both of them are stored in a photorefractive material as a joint power spectrum. The retrieval of the original data can be achieved with the same key code. We can record multiple two-dimensional data in a same crystal by angular multiplexing. Furthermore we can record by key code multiplexing because another designed key code can produce another independent phase distribution. We demonstrate the concept of the optical data storage system by computer simulations.

A double-random-phase optical encryption system that uses an optimally designed binary key is proposed. Computer simulation results are presented to demonstrate the effectiveness of the proposed system.

A digital holographic data reconstruction method with data compression is proposed. We show the number of quantization level of a digital hologram can be reduced. By computer simulations it is confirmed that the method is especially useful for binary images. For gray scale images, we propose a bit plane decomposition method. By this method, we show both high reconstructed image quality and a high compression ratio can be achieved. This method is applicable to both a normal digital hologram and an encrypted digital hologram.

A digital holographic data reconstruction method with data compression is proposed. We show the number of quantization level of a digital hologram can be reduced. By computer simulations it is confirmed that the method is especially useful for binary images. For gray scale images, we propose a bit plane decomposition method. By this method, we show both high reconstructed image quality and a high compression ratio can be achieved. This method is applicable to both a normal digital hologram and an encrypted digital hologram.

A double-random-phase optical encryption system that uses an optimally designed binary key is proposed. Computer simulation results are presented to demonstrate the effectiveness of the proposed system.

A polarization-encoding system for optical security verification is proposed. The polarization-encoded information can be used for secure verification. The polarization state of the input image can provide an additional degree of freedom in using optics to secure information. The expressions for polarization-encoded input images are developed using Jones polarization calculus. A nonlinear joint transform correlator is used to provide optical validation. Computer simulations and optical experimental results are shown in support of the proposed method.

A double-random-phase optical encryption system that uses a binary key code is proposed. The key code is generated as a binary computer-generated hologram. The binary key code can be displayed on a binary spatial light modulator (SLM) such as a ferroelectric liquid-crystal display. The use of a binary SLM enables us to renew the key at high speed. A joint transform correlator based on a photorefractive crystal in the Fourier domain is used to perform shift-invariant encryption and decryption. Computer simulations of the effects of using a binary encoded key code instead of a complex amplitude key code are shown. Preliminary optical experimental results are presented to demonstrate the effectiveness of the proposed system. (C) 2000 Optical Society of America OCIS codes: 070.2580, 070.4550, 070.4560, 090.1760, 200.3050, 200.4740.

A double-random-phase optical encryption system that uses a binary key code is proposed. The key code is generated as a binary computer-generated hologram. The binary key code can be displayed on a binary spatial light modulator (SLM) such as a ferroelectric liquid-crystal display. The use of a binary SLM enables us to renew the key at high speed. A joint transform correlator based on a photorefractive crystal in the Fourier domain is used to perform shift-invariant encryption and decryption. Computer simulations of the effects of using a binary encoded key code instead of a complex amplitude key code are shown. Preliminary optical experimental results are presented to demonstrate the effectiveness of the proposed system. (C) 2000 Optical Society of America OCIS codes: 070.2580, 070.4550, 070.4560, 090.1760, 200.3050, 200.4740.

A polarization-encoding system for optical security verification is proposed. The polarization-encoded information can be used for secure verification. The polarization state of the input image can provide an additional degree of freedom in using optics to secure information. The expressions for polarization-encoded input images are developed using Jones polarization calculus. A nonlinear joint transform correlator is used to provide optical validation. Computer simulations and optical experimental results are shown in support of the proposed method. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)02209-1].

An optical double random-phase encryption method using a joint transform correlator architecture is proposed. In this method, the joint power spectrum of the image to be encrypted and the key codes is recorded as the encrypted data. Unlike the case with classical double random-phase encryption, the same key code is used to both encrypt and decrypt the data, and the conjugate key is not required. Computer simulations and optical experimental results using a photorefractive-crystal-based processor are presented. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)03508-X].

An optical double random-phase encryption method using a joint transform correlator architecture is proposed. In this method, the joint power spectrum of the image to be encrypted and the key codes is recorded as the encrypted data. Unlike the case with classical double random-phase encryption, the same key code is used to both encrypt and decrypt the data, and the conjugate key is not required. Computer simulations and optical experimental results using a photorefractive-crystal-based processor are presented. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)03508-X].

An information security method that uses a digital holographic technique is presented. An encrypted image is stored as a digital hologram. The decryption key is also stored as a digital hologram. The encrypted image can be electrically decrypted by use of the digital hologram of the key. This security technique provides secure storage and data transmission. Experimental results are presented to demonstrate the proposed method. (C) 2000 Optical Society of America.

An information security method that uses a digital holographic technique is presented. An encrypted image is stored as a digital hologram. The decryption key is also stored as a digital hologram. The encrypted image can be electrically decrypted by use of the digital hologram of the key. This security technique provides secure storage and data transmission. Experimental results are presented to demonstrate the proposed method. (C) 2000 Optical Society of America.

An information security method that uses a digital holographic technique is presented. An encrypted image is stored as a digital hologram. The decryption key is also stored as a digital hologram. The encrypted image can be electrically decrypted by using the digital hologram of the key. This security technique is useful for secure storage and data transmission. Experimental results are presented to demonstrate the proposed method.

A double random phase optical encryption system that uses a binary key code is proposed. The key code is generated as a binary computer generated hologram. The binary key code call be displayed on a binary spatial light modulator such as a ferroelectric liquid crystal display. The use of a binary spatial light modulator enables us to renew the key at high speed. A joint transform correlator based on a photorefractive crystal in the Fourier domain is used to perform shift invariant encryption and decryption. Computer simulations of the effects of using a binary encoded key code instead of a complex amplitude key code are shown. Preliminary optical experimental results are presented to demonstrate the effectiveness of the proposed system.

A double random phase optical encryption system that uses a binary key code is proposed. The key code is generated as a binary computer generated hologram. The binary key code call be displayed on a binary spatial light modulator such as a ferroelectric liquid crystal display. The use of a binary spatial light modulator enables us to renew the key at high speed. A joint transform correlator based on a photorefractive crystal in the Fourier domain is used to perform shift invariant encryption and decryption. Computer simulations of the effects of using a binary encoded key code instead of a complex amplitude key code are shown. Preliminary optical experimental results are presented to demonstrate the effectiveness of the proposed system.

An information security method that uses a digital holographic technique is presented. An encrypted image is stored as a digital hologram. The decryption key is also stored as a digital hologram. The encrypted image can be electrically decrypted by using the digital hologram of the key. This security technique is useful for secure storage and data transmission. Experimental results are presented to demonstrate the proposed method.

An idea for security verification of identification such as passports, credit cards, and others in terms of difficulty of reproduction is proposed The polarization information is used for security verification. As the state of the polarization encoded cannot be seen by an ordinary intensity sensitive device such as a CCD camera, it cannot be copied For optical validation system, a joint transform correlator is used. Computer simulations and optical experimental results are shown to confirm our proposed method.

A novel architecture for the double random phase encoding optical encryption system using a joint transform correlator is proposed. In the proposed method, the joint power spectrum of the image to be encrypted and the key code is recorded as the encrypted power spectrum. Owing to the joint transform architecture, the alignment of the image and the key code is robust. Computer simulations using a computer generated hologram is presented to confirm our proposed system.

A novel architecture for the double random phase encoding optical encryption system using a joint transform correlator is proposed. In the proposed method, the joint power spectrum of the image to be encrypted and the key code is recorded as the encrypted power spectrum. Owing to the joint transform architecture, the alignment of the image and the key code is robust. Computer simulations using a computer generated hologram is presented to confirm our proposed system.

A technique to reduce the influence of the dc and the complex-conjugate correlation signals that are inherent in a joint transform correlator is proposed. The key part of this technique is the use of a phase mask. The mask contributes only extraneous signals, so the influence of the signals is reduced. The desirable correlation signal is not affected, and its shape is retained. Computer simulations confirm the performance of the proposed phase-encoded joint transform correlator. (C) 1998 Optical Society of America.

The application of a phase-encoded joint transform correlator to decryption of an optical image encryption system by a double-random phase encoding is described.

The phase-encoded joint transform correlator as a decoder of an optical double random phase encoding system is described. By using the phase-encoded joint transform correlator, it is possible to decode the encrypted image with the same random phase mask which was used in the encryption procedure. The decoding algorithm and optical systems are described. Computer simulations confirm the proposed decoding algorithm.

The phase-encoded joint transform correlator as a decoder of an optical double random phase encoding system is described. By using the phase-encoded joint transform correlator, it is possible to decode the encrypted image with the same random phase mask which was used in the encryption procedure. The decoding algorithm and optical systems are described. Computer simulations confirm the proposed decoding algorithm.

A blind deconvolution method using the concept of subband filter banks has been proposed. This method makes possible the speedy convergence of solution, due to estimation of supports of the reconstructed images by a deconvolution in the lower layer. We apply the method to blind deconvolution by a simulated annealing algorithm and confirm its usefulness.

A blind deconvolution method using the concept of subband filter banks has been proposed. This method makes possible the speedy convergence of solution, due to estimation of supports of the reconstructed images by a deconvolution in the lower layer. We apply the method to blind deconvolution by a simulated annealing algorithm and confirm its usefulness.

Although the discrete cosine transform (DCT) and wavelet transform have been used as effective techniques for reducing the redundancy of image waveforms, they have the problems of high complexity and causing block distortion. Tn this paper, a Haar wavelet transform with interband prediction is proposed that permits high-speed processing and which is suitable for coding as a subband decomposition technique since it generates little block distortion in the decoded images. The interband prediction method of this proposed transform method uses the derivative of the low-band waveform to predict the high-band waveform each time a band is split into two subbands. This results in a transform process that gives a prediction residual signal with lower entropy. During the inverse transform, the prediction coefficients obtained from the forward transform are used to predict the high-frequency waveforms and then, by adding the prediction residual, the original high frequency waveforms are reconstructed. Because the high-frequency waveforms are generated that smoothly interpolate the up-sampled, low-frequency waveforms, any block effects from this prediction technique are difficult to see in the decoded image. A detailed analysis of the proposed interband prediction process is performed by interpreting the proposed transform as a subband decomposition process that is based on the use of a symmetric short-kernel filter (SSKF) filter bank; then experiments are conducted that demonstrate its performance as a subband decomposition for coding of real image data and the possibility of progressive build-up of the decoded images. Results show that this transform method is effective for coding image data.

Although the discrete cosine transform (DCT) and wavelet transform have been used as effective techniques for reducing the redundancy of image waveforms, they have the problems of high complexity and causing block distortion. Tn this paper, a Haar wavelet transform with interband prediction is proposed that permits high-speed processing and which is suitable for coding as a subband decomposition technique since it generates little block distortion in the decoded images. The interband prediction method of this proposed transform method uses the derivative of the low-band waveform to predict the high-band waveform each time a band is split into two subbands. This results in a transform process that gives a prediction residual signal with lower entropy. During the inverse transform, the prediction coefficients obtained from the forward transform are used to predict the high-frequency waveforms and then, by adding the prediction residual, the original high frequency waveforms are reconstructed. Because the high-frequency waveforms are generated that smoothly interpolate the up-sampled, low-frequency waveforms, any block effects from this prediction technique are difficult to see in the decoded image. A detailed analysis of the proposed interband prediction process is performed by interpreting the proposed transform as a subband decomposition process that is based on the use of a symmetric short-kernel filter (SSKF) filter bank; then experiments are conducted that demonstrate its performance as a subband decomposition for coding of real image data and the possibility of progressive build-up of the decoded images. Results show that this transform method is effective for coding image data.

An incoherent-only optical and electronic digital joint-transform correlator is proposed. A technique for the removal of extraneous signals inherent in the incoherent-only joint-transform correlator is also presented. A computer simulation and experimental results confirm the performance of the proposed incoherent-only joint-transform correlator.

An incoherent-only optical and electronic digital joint-transform correlator is proposed. A technique for the removal of extraneous signals inherent in the incoherent-only joint-transform correlator is also presented. A computer simulation and experimental results confirm the performance of the proposed incoherent-only joint-transform correlator.

We present the principle and implementations of high-speed pattern matching with the incoherent holographic technique along with its experimental results. © 1990, SPIE.

We present the principle and implementations of high-speed pattern matching with the incoherent holographic technique along with its experimental results. © 1990, SPIE.

To measure different parameters of a spherical lens simultaneously, a method by low-coherence interferometry with a low temporal coherent light source is proposed. This proposed method can obtain both the radius of curvature and the central thickness of a spherical lens in a single optical system. Owing to the property of low temporal coherence, the contrast of interference fringe pattern, hologram, varies with the optical path difference of an object beam and a reference beam. This enables the central thickness of the test lens to acquire with a Michelson interferometer. Simultaneously, the spherical shape of the test lens, namely the radius of curvature, can be obtained from a hologram which contains information of the wavefront curvature from the reected beam of the spherical surface of the test lens.

A scanless phase retrieval method based on the transport of intensity equation is proposed for refractive index tomography. A phase distribution is measured from defocused intensity distributions obtained with oblique illumination of different tilt angles.

In-line digital holography using a random phase modulation is proposed. Owing to the random phase modulation, twin-image problem inherent to the in-line optical setup is relieved. Furthermore, because no multiplexed recording is required, dynamic phenomena can be recorded. This idea is inspired by double-random phase- encryption. The difference between the proposed method and the double-random phase-encryption is brie y described. Preliminary experimental results confirm the feasibility of the proposed method. The difference of coherence of a light source is also discussed.

Utilization of phase information can increase the recording density of holographic data storage. In this paper, a transport of intensity equation is introduced to computer-generated-hologram-based holographic data storage, which can obtain the phase datapage while keeping an optical setup simple and compact. Moreover, two defocused intensity distributions for the transport of intensity equation can be simultaneously obtained by using a conjugate beam from the computer-generated hologram.

A deep-learning-based phase retrieval method is proposed for computational ghost imaging (CGI). In the method, a defocused intensity distribution of an object is obtained by the CGI. An object's phase distribution is retrieved from the intensity distribution by a trained deep neural network. The advantage of the method is that the phase retrieval can be achieved with a low signal to noise ratio. The effects of noise level and defocus distance are investigated.

Three-dimensional imaging is very attractive for biomedical fields, industrial inspecting, and so on. Computational optical sensing and imaging is widely studied due to the recent development of imaging device, computational power, and so on. It is also used for three-dimensional sensing and imaging. In this area, random amplitude or phase modulation is introduced to improve its performance. In this paper, computational ghost imaging using a designed random amplitude modulation is presented. Owing to the designed random amplitude modulation, the number of measurements can be reduced. A phase modulation for twin image reduction of in-line digital holography is also presented. Owing to the random phase modulation, the overlapping an object image and its conjugate image can be reduced.

In-line digital holography is conventional but still attractive because of its simple optical setup. In general, sequential phase-shifting technique is mandatory to remove twin-image which makes the reconstructed image quality low. However, sequential phase-shifting technique requires multiple recording. Multiple recording means that it is not suitable for a dynamic phenomenon. In this paper, two kinds of a single-shot in-line digital holography without twin-image using a diffused illumination are presented. One is a generalized phase-shifting digital holography and the other is a computational removal of twin-image. The ideas and their experimental results are given to confirm the feasibility.

Computational ghost imaging (CGI) is expected to be applied to noninvasive biomedical imaging because of its characteristic which allows us to obtain the object's image under a low signal to noise ratio (SNR) condition. However only an amplitude distribution can be obtained by the CGI. Therefore the imaging of the pure phase objects is difficult. Although the phase shifting digital holography has been used for reconstruction of the complex amplitude in the CGI, its experimental setup is cumbersome and sensitive to vibrations. Furthermore four holograms are required for the reconstruction of the complex amplitude because of the phase shifting algorithm, rendering the acquisition time of the phase image slow. Therefore the method is difficult to be applied to the biomedical imaging. An alternative non-interferometric method is proposed in this study. The proposed method uses the transport of intensity equation for the phase retrieval of the pure phase objects, termed transport-of-intensity CGI (TI-CGI). In the TI-CGI, the phase distribution is retrieved from a single defocused image obtained by a modulated optical setup of the CGI, achieving the fast and robust imaging compared with the conventional phase shifting method. Therefore the TI-CGI may be more suitable for the biomedical imaging than the phase shifting method. The TI-CGI is demonstrated by an optical experiment under the low SNR condition generated by the neutral density filters with 1% and 0.1% transmittance. The experimental results conform the effectiveness of the TI-CGI.

Wavefront sensing techniques are mainly needed in an adaptive optics system for high resolution imaging. One of them is a Shack-Hartmann method which is composed of very simple structure. Although the method is widely utilized, it also has the limitation for the measurable magnitude of wavefront aberrations. To overcome the problem, the improved Shack-Hartmann method for larger aberrated wavefronts has been proposed. In this paper, the principle of the proposed method and the numerical evaluation of the performance of the proposed method are presented.

Digital holography provides a method of the 3-D recording and numerical reconstruction by a simple optical system and a computer. Quantitative measurement and numerical refocusing are major characteristics. So far, many physical parameters such as amplitude, phase, polarization, fluorescence, and spectra can be obtained independently. Recently, multimodal imaging that can obtain simultaneously two or more physical parameters by combining digital holographic microscope and other optical microscopes such as a fluorescence optical microscope and a Raman scattering microscope has emerged. In this review, physical parametric imaging techniques based on digital holography are presented and then these techniques are enhanced to develop multimodal imaging based on digital holography.

The possibility of incoherent digital holography has been widely studied because it is free from coherent light sources. Here spatially incoherent Fourier digital holography is described. The incoherent hologram is obtained by a rotational shearing interferometer. The hologram obtained by the interferometer is a cosine transform of a spatially incoherent object. After describing the principle of a rotational shearing interferometer, methods to obtain Fourier transform of an object presented.

A phase object mapping technique is proposed to measure a phase distribution of objects which exist in different depth positions. The proposed method is confirmed by a numerical simulation.

The modified Michelson type interferometer with lenses for a radial shear to record incoherent holograms is proposed. It enables us to record a hologram by self-interference without coherent illumination such as a laser. The interferometer has two wave plates which can realize phase-shifting incoherent holography. The feature can avoid a very large bias term and the twin image, which are the inherent problem of incoherent holography by self-interference. The advantages of the proposed method using lenses and wave plates are easy adjustment of the zone plate and simplification of the optical system. A preliminary experiment using an LED as an incoherent object was performed to confirm the four step phase-shifting by wave plates.

Shift multiplexing method using a spherical wave is proposed for a holographic memory system based on a computer-generated hologram (CGH). In the proposed method, a propagated signal beam along an optical axis is generated by a CGH. The zero order beam of the CGH is obtained as a point source in the Fourier plane. This point source becomes a spherical reference beam on a recording medium by displacing a Fourier transform lens. The use of the spherical reference beam allows us to implement shift multiplexing in the holographic memory based on a CGH. Shift selectivity of the proposed method is numerically evaluated. In addition, shift multiplexing with the proposed method is numerically demonstrated.

Two methods to apply the generalized phase-shifting digital holography to color digital holography are proposed. One is wave-splitting generalized phase-shifting color digital holography. This is realized by using a color Bayer camera. Another is multiple exposure generalized phase-shifting color digital holography. This is realized by the wavelength-dependent phase-shifting devices. Experimental results for both generalized phase-shifting color digital holography are presented to confirm the proposed methods.

A holographic storage system based on digital holography is proposed for recording and retrieving a phase data page in a compact and simple optical setup. In the proposed recording system, complex amplitude distribution can be modulated using a single phase-only spatial light modulator. The complex amplitude distribution of a retrieved phase data page is detected with the Fourier fringe analysis. The use of digital holographic techniques enables realizing a compact and simple holographic recording system, which is independent of misalignment problem in conventional holographic storage systems. The capability of the proposed recording system is numerically and experimentally evaluated.

Arbitrary pattern in an arbitrary domain can be realized by computer generated hologram (CGH). If CGH is applied to the optical data storage, the complexity of the optical system can be eased. For example, a single spatial light modulator (SLM) can be used to express a fully-complex filed of a lightwave. Holographic data storage with a single amplitude SLM by use of CGH is presented. A signal beam and a reference beam are generated by a computer generated hologram (CGH). Owing to the characteristics of the CGH, the incident angle of a reference beam can be changed. This means that angular multiplexing is available.

Single exposure phase-shifting digital holography is mandatory for recording/analyzing dynamic phenomena. As one of the candidate for the single exposure phase-shifting digital holography is the wave-splitting phase-shifting digital holography. We have proposed generalized phase-shifting digital holography as one of the wave-splitting phase-shifting digital holography. In the digital holography, the phase-shift quantity, which corresponds to the difference between the phase quantities of the reference wave on the adjacent pixels is generalized different from ordinal wave-splitting methods. Owing to the generalized phase-shifting, we can use a random-phase wave as the reference wave. The proposed phase-shifting digital holography enables us to record a fully-complex field of a dynamic phenomena without dc and conjugate terms using a commercially available optical devices. The relation between the property of the reference wave and the quality of the reconstructed images are discussed. Experimental results are given to confirm the proposed phase-shifting digital holography.

A Shack-Hartmann wavefront sensor (SHWFS) which consists of a microlens array and an image sensor has been used to measure the wavefront aberrations in various fields owing to its advantages such as simple configuration. However, a conventional SHWFS has the finite dynamic range. The dynamic range cannot be expanded without sacrificing the spatial resolution and the sensitivity in a conventional SHWFS. In this study, the SHWFS using a dual microlens array to solve the problem is proposed. In the proposed method, an astigmatic microlens is arranged at the center of a group of 2 x 2 spherical microlenses. A pattern image including spots and linear patterns is obtained at the focal plane by the dual microlens array. The pattern image can be separated into two images as if two microlens array with different diameter were used by discriminating spots from linear patterns with the pattern matching technique. The proposed method enables to expand the dynamic range of an SHWFS by using the separated two images. The performance of the proposed method is confirmed by the numerical simulation for measuring a spherical wave.

A Mueller matrix imaging method by use of the characteristics of digital holography is proposed. In the proposed method, only two exposures are required to obtain the Mueller matrix. The Mueller matrix can be calculated from Stokes vectors. Stokes vectors can be obtained from two fully-complex amplitude distributions. Fully complex amplitude distributions can be obtained by digital holography. The optical experiments by using two kinds of specimens which are four linear polarizers and a quarter wave plate are shown to demonstrate the proposed method.

The quasi one-shot phase-shifting digital holography using phase difference of orthogonal polarizations is proposed. The use of orthogonal polarizations can make it possible to record two phase-shifted holograms simultaneously. By combining the holograms with distributions of a reference wave and an object wave, the complex field of the wavefront of a 3D object can be obtained. As two phase-shifted holograms can be obtained simultaneously in the proposed method, even a moving object can be recorded.

To improve the image quality of the decrypted image through the double-random phase-encoding optical encryption, the design method of the input phase mask is proposed. The input phase mask is iteratively designed so that the extent of the Fourier spectrum of the product of an input image and the input phase mask matches to the space bandwidth of the optical system. By using the designed input phase mask, we show that the bit-error rate is improved. We also discuss the number of the phase levels of the designed input phase mask.

助言・指導

法人の科学技術の振興に関する諸事業を総合的かつ効果的に推進するために、参与会を構成し、この法人の運営に関し、助言指導いただく。

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関西工業教育協会令和３年度第１回評議員会において書面審議いただく。

応用光学，情報フォトニクス，計測技術

位相計測技術に関するオンライン講演

国際交流事業

12/2から12/10まで和歌山大学に滞在された南教授の対応（授業見学のスケジューリング，交渉など）．,相手国:メキシコ合衆国

外国人研究者等の受入

外国人研究者等の受入,氏名:Nishchal Naveen

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Visiting Lecturerとしての講演（Indian Institute of Space Science and Technology）および大学院生との学術交流,相手国:India

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Visiting Lecturerとしての講演（Government Engineering College, Trivandrum）,相手国:India

学術雑誌等の編集委員・査読・審査員等

編集査読委員等

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学術雑誌等の編集委員・査読・審査員等

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学術雑誌等の編集委員・査読・審査員等

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小・中・高校生を対象とした学部体験入学・出張講座等

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日本光学会機関誌Optical Review 責任編集,任期:2年

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OSJ – OSA Joint Symposia on Digital Photonics

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Optoelectronics Imaging/Spectroscopy and Signal Processing Technology

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実行委員長として国際ワークショップの円滑な運営に尽くす．

学協会、政府、自治体等の公的委員

学術講演会の円滑な運営をおこなう,任期:1年

国や地方自治体、他大学・研究機関等での委員

国や地方自治体、他大学・研究機関等での委員,任期:2012/08/01～2014/03/31

国や地方自治体、他大学・研究機関等での委員

国や地方自治体、他大学・研究機関等での委員,任期:2012/05/08～2013/03/31

国や地方自治体、他大学・研究機関等での委員

国や地方自治体、他大学・研究機関等での委員,任期:2012/05/24～2012/12/28

学協会、政府、自治体等の公的委員

韓国光学会の学術雑誌「the Journal of the Optical Society of Korea」の企画・編集等を国際委員としての立場からおこなう.

学協会、政府、自治体等の公的委員

光学技術とコンピュータ技術を巧みに組み合わせたディジタルオプティクス分野の普及,開拓,人的ネットワークの構築を目指した研究会の幹事である.,任期:2009.4～

学協会、政府、自治体等の公的委員

光の物理的特性を有効に用いた光情報技術により、画像情報や映像情報を利用したさまざまな課題の効果的な解法を検討し,個別の問題解決に役立つ研究者ネットワークを構築をおこない,その延長としての公的プロジェクトなどの将来計画の策定を進める,,任期:2008.4～

学協会、政府、自治体等の公的委員

Program Committee,任期:継続中

学協会、政府、自治体等の公的委員

大容量記憶を目指したホログラフィックメモリの開発をめざして研究会等の企画・運営をおこなっている.,任期:2006.4～

学協会、政府、自治体等の公的委員

2010年代のユビキタス・センサーネットワークの構築に資する新たなフォトニクス情報システムの開発に必要な,技術課題の抽出,新技術の提案,アーキテクチャの提案および具体的スペックの提示を目的とした活動である.,任期:2006.4～

学協会、政府、自治体等の公的委員

光学技術を利用した情報処理分野の発展や若手研究者の育成を中心におこなっている.,任期:2001.4～

社会との連携を推進する活動

システム工学部創立20周年記念式典に出席し，卒業生との交流を図った．

社会との連携を推進する活動

システム工学部同窓会近況報告会に出席し，卒業生との交流を図った．

ボランティア活動等

ボランティア活動等