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In this paper, we propose a real-time incoherent digital holographic (IDH) recording system free from bias and twin-image noises. A motionless three-step polarization-encoded phase-shifter operating at 99 Hz is realized with two electrically controllable birefringence-mode liquid crystal cells operating in tandem with a geometric phase lens and polarizers. Based on the proposed optical configuration, a coaxial straight-line self-interference IDH recording system is devised. Notably, the elimination of bias and twin-image noise from three phase-shifted images is demonstrated as a proof of concept. Moreover, complex-valued holographic video acquisitions with a resolution greater than 20 megapixels are demonstrated, with an effective acquisition frequency of 33 Hz.

The reconstructed image acquired from the incoherent holographic system contains a high degree of the grainy noise component. We propose a learning-based noise reduction scheme to mitigate such noise in the complex-valued domain.

Raw data compression is mandatory for monitoring of processes by dynamic speckle analysis when two-dimensional activity maps are built by pointwise statistical processing of correlated speckle patterns formed on the surface of diffusely reflecting objects under laser illumination. Coarse quantization of speckle patterns enables storage and transfer of a huge amount of images, but it may be inefficient at spatially varying speckle statistics, such as for patterns recorded at non-uniform illumination or reflectivity. We prove efficacy of coarse quantization of the raw speckle data with varying statistics for a normalized algorithm by simulation and a polymer drop drying experiment. Both uniform and non-uniform quantization are proposed for treating such data. Decreasing the bit depth from 8 to 3 is possible without worsening the quality of the activity map.

In a digital hologram, the maximum viewing angle of a computer-generated hologram (CGH) is limited by pixel pitch due to the diffraction grating equation. Since reducing pixel size of display panel is challenging and costly, we propose a method to expand the viewing angle of a digital hologram by attaching an aligned pixelated random phase mask (PRPM) onto the CGH pattern based on analysis of simulation results. By introducing a phase-averaging process to the widely used iterative Fourier transform algorithm, an optimized CGH pattern can be obtained in conjunction with a PRPM. Based on scalar diffraction theory, viewing angle enhancement characteristics were verified by comparing the perspective views of a two-plane hologram using a virtual eye model. In addition, we performed full electromagnetic simulations that included effects due to potential fabrication errors such as misalignment, thickness variation, and internal reflections and diffractions between the CGH and random mask patterns. From the simulation results, by attaching a 1.85 µm-sized pixel pitch PRPM to a 3.7 µm CGH, the viewing angle can be easily expanded almost identical to that of a CGH with 1.85 µm-pixel pitch.

The visibility of the reconstructed image degraded by the residual bias noise, obtained from the geometric-phase self-interference incoherent digital holography, can be enhanced applying the bias level shifting method to the complex hologram.

We propose a speckle reduction technique in electronic holographic display systems, where digital micro‐mirror array devices are used as spatial light modulators. By adopting a programmable filtration in a general 4‐f optic configuration, it is shown that the signal spectrum components in the frequency domain of a viewing‐window‐based holographic display system can be selectively filtered. Compared to the widely utilized single‐sideband filtration techniques in electronic holographic display systems, our proposed programmable filtration can be utilized to effectively reduce the speckles in the reconstruction of point‐cloud‐based computer‐generated holograms. Experimental results are presented to verify our proposed concept.

We propose a holographic stereogram synthesis method which uses holograms that are optically captured by self-interference incoherent digital holography (SIDH) based on a geometric phase lens. SIDH is a promising solution for hologram acquisition under low-coherence lighting condition. A mechanical scanning system is constructed to acquire multiple perspective holograms. Numerical simulations and experimental analyses conducted using high-resolution diffractive optical element demonstrate that the proposed method can produce a wide-viewing hologram which can realize realistic 3D scenarios with depth cues such as accommodation and motion parallax. The future objectives include the implementation of a multiple-camera system for holographic videos.

The single-shot full-color incoherent holography based on the geometric phase is introduced. Especially, this system resolves the color dispersion effect of the geometric phase lens by the nature of the holographic recording.

We have successfully implemented and reported 360-degree viewable tabletop-style holographic display prototype systems. In order to support 360 degree horizontal viewing angle, which is very much wider than previous systems, we used binary amplitude modulating DMD device as SLM of the display system. DMD has higher total data rate due to its high refresh rate, which is denoted as extended SBP or eSBP, than other SLM devices like LCD or LCoS. This is much beneficial for the system design aiming at wider viewing angle or larger image size. However, Binary amplitude modulating hologram has inherent limitation in terms of resulting hologram image quality, and thus there has been lots of studies on quality-improving coding algorithms like BERD or DBS. In this paper, pros and cons of using DMD in holographic display system are discussed, and in-depth analysis and experimental results are presented on the behavior and limitations of the reconstructed image quality based on our prototype system. Image quality is measured with various metrics like 3D-MTF, depth resolution and color reproducing fidelity for different pixel resolutions from QVGA up to 4K UHD. 3D-MTF represents lateral image resolution and depth resolution has to do with degree of supporting accommodation of human vision in holographic displays. Based on these observations, we draw some projection on the required pixel resolutions of binary modulating SLM device for achieving acceptable hologram image quality.

PURPOSE To quantify stereopsis at distance resulting from binocular fusion in patients with impaired binocular vision using a three-dimensional (3-D) display stereotest. METHODS A total of 68 patients (age range, 6 to 85 years) with strabismus (40 esotropes and 28 exotropes) whose stereoacuity could not be measured with the near and distance Randot stereotests were included. Contour-based circles with a wide range of crossed horizontal disparities (2500 to 20 arcsec) displayed on a 3-D monitor were presented to subjects at 3 m. Between the patients who had stereoacuity of at least 2500 arcsec and those with no measurable stereoacuity, parameters including age, sex, best-corrected visual acuity, spherical equivalent refractive error, Worth 4 dot test results, and type and angle of deviation were compared. RESULTS Stereoacuity at distance of 2500 arcsec or better was detected in 25 (63%) of 40 esotropes, and 16 (57%) of 28 exotropes, although stereoacuity of 800 arcsec or better was found only in two (5%) esotropes and one (4%) exotrope. Patients with stereopsis were significantly younger (19.3 ± 16.9 years) than those with no measurable stereopsis (31.5 ± 26.4 years) (p = 0.040). There were no significant differences in best-corrected visual acuity, presence of amblyopia >20/100, spherical equivalent refractive error, type of deviation, deviation angle, sex, and Worth 4 dot test results between these groups. CONCLUSIONS Stereopsis at distance resulting from binocular fusion that cannot be measured with conventional stereoacuity tests may be preserved in patients with impaired binocular vision. The 3-D display stereotest can be useful for quantifying stereopsis at distance resulting from binocular fusion.

We present study of the parameters of polarization holographic gratings recorded in thin films of the azopolymer PAZO (Poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) and in a composite PAZO-based organic/inorganic material with incorporated TiO2 nanoparticles with size 21 nm and different concentrations. The gratings are inscribed by two plane waves with left and right circular polarization from a He-Cd gas laser (442 nm) at recording angle 20°. Along with the anisotropic grating in the volume of the media, surface relief is also formed. Gratings with different spatial frequencies are obtained by varying the recording angle. The diffraction efficiency kinetics is probed at 635 nm and the height of the relief gratings is determined by AFM. Our results indicate that the diffraction efficiency for the hybrid samples is enhanced with respect to the pure azopolymer films. Comparison is also made between polarization response of samples deposited from water and from methanol solution.

Most of the previously-tried prototype systems of digital holographic display are of front viewing flat panel-type systems having narrow viewing angle, which do not meet expectations towards holographic displays having more volumetric and realistic 3-dimensional image rendering capability. We have developed a tabletop holographic display system which is capable of 360&deg, rendering of volumetric color hologram moving image, looking much like a real object. Multiple viewers around the display can see the image and perceive very natural binocular as well as motion parallax. We have previously published implementation details of a mono color version of the system, which was the first prototype. In this work, we present requirements, design methods, and the implementation result of a full parallax color tabletop holographic display system, with some recapitulation of motivation and a high-level design concept. We also address the important issue of performance measure and evaluation of a holographic display system and image, with initial results of experiments on our system.

We propose a method of expanding the viewing angle of the computer generated hologram(CGH) by attaching a pixelated high-resolution random phase mask. The viewing angle is increased according to the resolution of the random phase mask.

We propose a method to measure spatial resolution and depth of focus of reconstructed hologram images, which can be applied to general digital holographic displays. Experimental results for a projection-type holographic display are presented.

Polarization holography offers the possibility to register not only the intensity and phase of light, but also its polarization. When the interfering beams are with orthogonal linear polarizations, in addition to the photoinduced linear birefringence in the media, chiral structures are formed. They strongly influence the properties of the recorded polarization diffraction gratings. In the present work, we study photoinduced chirality in thin films, based on the azopolymer poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt], shortly PAZO. Nanocomposite samples are also studied, prepared from the same azopolymer, doped with TiO2 nanoparticles with size 21 nm. Exciting light from a He-Cd laser ( λ = 442 nm) has been used, with input ellipticity varying from –1 (left circularly polarized light) to +1 (right circularly polarized light). The dependences of the output ellipticity and the angle of self-rotation of the polarization azimuth on the input ellipticity are presented. This allows us to estimate the effective value of the photoinduced circular birefringence and to evaluate the diffraction efficiency of a polarization holographic grating recorded with two plane waves with orthogonal linear polarizations.

Generally in electronic holographic display systems, coherent light sources are used to reconstruct holograms. The random distribution of phase profile of an object image causes unwanted dark and bright spots to degrade reconstructed hologram images. In addition, a periodic structure of available spatial light modulators such as liquid crystal on silicon devices and digital micro-mirror devices generates various diffractive signals when they are illuminated by coherent light sources. Consequently, it is necessary to select a proper signal band in spatial frequency domain by effectively filtering out unwanted signals. In this paper, the speckle pattern in a table-top holographic display system is measured and the method for reducing the speckle patterns is to be shown.

We have designed and successfully implemented 360-degree viewable holographic display prototype systems. Core idea of the system design lies in the exploitation of fast operating speed of DMD for binary amplitude modulation of light field, being distributed to more than 1,000 viewpoints along the 360 degree viewing circumference. Slanted downward viewing angle and 360 degree viewable 3-dimensional(3D) image over the center of tabletop display is achieved by specially designed optics. As a result, solid-looking 3D moving color images of larger than 3 inches are rendered and observed by several viewers at the same time from different viewing positions. We have implemented and experimented several variations of the system. They are tiling of SLM modules(2x2 tiling with 4 DMDs for mono-color display and 1x2 tiling with 6 DMDs for color display), using different SLMs(DMD of pixel pitch 13.68μm and resolution 1,024x768, DMD of pixel pitch 10.8μm and resolution 1,920x1,200), and applying different structure of image floating optics((1)double parabolic mirrors, (2)one parabolic mirror and one beam splitter, (3)two spherical and one flat mirror). We report the result of various display system implementations based on several combinations of above-mentioned design options.

Space bandwidth product (SBP) is one of the most significant limitation for displaying the digital holographic display. Due to the SBP problem, the size and viewing angle of displayed holograms cannot be enlarged simultaneously. To overcome the SBP problem, holographic projection system has been researched. It uses a field lens to converge diffracted light from a spatial light modulator (SLM) into a viewing window, where the observer can see whole hologram image displayed on the SLM. However, it has a problem that the viewing distance between the display and observer cannot be controlled and fixed on the viewing window plane. We propose a method to control the position of viewing window formation in the holographic projection system by using an electrically focus tunable lens. We added the focus tunable lens in the holographic projection system, and the position of the viewing window can be controlled by its lens power variation. The principle of controlling viewing window in the proposed system is described, and the relationship among the optical power of focus tunable lens, location and size of the viewing window is analyzed. A computer generated hologram encoding based on Fresnel diffraction theory is developed to generate hologram contents for the proposed system with consideration of varying optical power of the focus tunable lens. Test-bed is built to verify the feasibility of the proposed method, and the experimental results confirm that the proposed method can effectively control the viewing window position of the holographic projection system.

We propose a numerical compensation method for reconstructed depth distortions caused by inaccurate optical alignment on a holographic projection system. The feasibility of the proposed compensation method is verified by experiments.

In digital holographic display systems, lasers are widely adopted as light sources in retrieving holograms. In addition, random phase profile is applied in calculating computer generated holograms, which causes granular patterns, i.e. speckles, composed of dark and bright spots so that it affects the image quality of reconstructed holograms. In this paper, we propose a method to measure and estimate speckle patterns in our recently-developed 360-degree tabletop holographic display systems.

In this paper, we use an optical method for the implementation of spatially-tiled digital micro-mirror devices (DMDs) to expand space bandwidth product in general digital holographic display systems. In concatenating more than two spatial light modulators (SLMs) optically, there may exist both phase discontinuity and amplitude mismatching of hologram images emanating from two adjacent SLMs. To observe and estimate those properties in digital holographic display systems, we adopt quantitative phase imaging technique based on transport of intensity equation.

The phase-shifting method is a simple and efficient approach to extract complex hologram information free of bias and twin-image noise. In this study, the geometric phase-shifting method is utilized for a self-interference incoherent digital holographic recording system based on the Michelson-type interferometer. The phase-shifting module consists of a horizontal polarizer, and two achromatic quarter-wave plates are employed inside the interferometer, replacing conventional phase-shifting devices, such as the piezo-actuated mirror. Since the phase-shifting amount of the introduced method herein is theoretical, regardless of the input wavelength, the simultaneous recording of step-wise phase-shifted interferograms for different color channels is available. Therefore, the multi-color hologram recording is achieved with fewer numbers of exposures. The demonstration of multi-color hologram recording and reconstruction are presented to validate the proposed idea.

To generate finite-power Airy beams, a novel holographic method is proposed. We record the interference pattern between an Airy beam (signal beam) and plane wave (reference beam) on a photopolymer, then decode the hologram by illuminating with the reference beam. The reconstructed beams still present the non-diffraction, acceleration, and self-healing features of optical Airy beams. In addition, angular multiplexing of two Airy beams with opposite acceleration directions is presented.

A major advantage of wavefront reconstruction based on a series of diffracted intensity images using only single-beam illumination is the simplicity of setup. Here we propose a fast-converging algorithm for wavefront calculation using single-beam illumination. The captured intensity images are resampled to a series of intensity images, ranging from highest to lowest resampling; each resampled image has half the number of pixels as the previous one. Phase calculation at a lower resolution is used as the initial solution phase at a higher resolution. This corresponds to separately calculating the phase for the lower- and higher-frequency components. Iterations on the low-frequency components do not need to be performed on the higher-frequency components, thus making the convergence of the phase retrieval faster than with the conventional method. The principle is verified by both simulation and optical experiments.

Graphics processing unit (GPU) based fast calculation method for computer generated spherical hologram (CGSH) of a real-existing object is proposed. Three-dimensional (3D) point cloud is constructed by capturing a real-existing object from multiple directions using a depth camera. The GPU based calculation is used in both hologram generation part and numerical reconstruction part of the CGSH. The improved calculation efficiency is verified by comparing the computation speed between central processing unit (CPU) based and GPU based implementation.

A method to uniformize the brightness of elemental image for the frontal projection-type three-dimensional (3D) display is proposed. A frontal projection three-dimensional display which is possible to realize glasses-free 3D display by combining a polarizing screen with a front projector has been proposed recently. This method uses a quarter-wave retarding film (QWRF) and a polarizer with slits, and makes the audience see different directional views. This structure can change the polarization state orthogonally, so the image from projector is partially blocked when the image is reflected and meets the films. However, in this method, the quality of the reconstructed 3D image could be degraded since the light intensity at the barrier-free regions of parallax barrier polarizer is brighter than that at the parallax barrier polarizer. We proposed two methods to relieve this difference, a parallax barrier rearrangement method and gray level compensation of illumination. By adopting two methods, we anticipate that the quality of reconstructed 3D image can be enhanced because of brightness uniformity in directional-view images in the frontal projection-type 3D display method.