Wide-viewing holographic stereogram based on self-interference incoherent digital holography.

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.

Quantization of dynamic speckle patterns with spatially varying statistics.

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.

Numerical analysis on a viewing angle enhancement of a digital hologram by attaching a pixelated random phase mask.

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.

Michelson-interferometric-configuration-based incoherent digital holography with a geometric phase shifter.

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.

360-degree tabletop electronic holographic display.

We demonstrate a tabletop holographic display system for simultaneously serving continuous parallax 3.2-inch 360-degree three-dimensional holographic image content to multiple observers at a 45-degree oblique viewing circumference. To achieve this, localized viewing windows are to be seamlessly generated on the 360-degree viewing circumference. In the proposed system, four synchronized high-speed digital micro-mirror displays are optically configured to comprise a single 2 by 2 multi-vision panel that enables size enlargement and time-division-multiplexing of holographic image content. Also, a specially designed optical image delivery sub-system that is composed of parabolic mirrors and an aspheric lens is designed as an essential part for achieving an enlarged 3.2-inch holographic image and a large 45-degree oblique viewing angle without visual distortion.

Recent progress in see-through three-dimensional displays using holographic optical elements [Invited].

The principles and characteristics of see-through 3D displays are presented. We especially focus on the integral-imaging display system using a holographic optical element (IDHOE), which is able to display 3D images and satisfy the see-through property at the same time. The technique has the advantage of the high transparency and capability of displaying autostereoscopic 3D images. We have analyzed optical properties of IDHOE for both recording and displaying stages. Furthermore, various studies of new applications and system improvements for IDHOE are introduced. Thanks to the characteristics of holographic volume grating, it is possible to implement a full-color lens-array holographic optical element and conjugated reconstruction as well as 2D/3D convertible IDHOE. Studies on the improvements of viewing characteristics including a viewing angle, fill factor, and resolution are also presented. Lastly, essential issues and their possible solutions are discussed as future work.

Quantification of Stereopsis in Patients with Impaired Binocularity.

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.

Three-dimensional/two-dimensional convertible projection screen using see-through integral imaging based on holographic optical element.

We propose a 3D/2D convertible screen using a holographic optical element and angular multiplexing method of volume hologram. The proposed screen, named a multiplexed holographic optical element screen (MHOES), is composed of passive optical components, and displaying modes between 3D and 2D modes are converted according to projection directions. In a recording process, the angular multiplexing method by using two reference waves with different incidence angles enables the functions of 3D and 2D screens to be recorded in a single holographic material. Also, in order to avoid the bulky experimental setup due to adopting different projectors for the 3D and 2D modes, the projection part is realized based on a prism. The designed projection part enables the single projector to present 3D on 2D mode, where the 3D and 2D contents are simultaneously displayed in one scene, without active components. The optical characteristics of MHOES are experimentally analyzed, and displaying experiments with a full-color MHOES are presented in order to verify the 3D/2D convertibility and see-through properties.

See-through integral imaging display using a resolution and fill factor-enhanced lens-array holographic optical element.

We report on the development of a high-resolution see-through integral imaging system with a resolution and fill factor-enhanced lens-array holographic optical element (HOE). We propose a procedure for fabricating of a lens pitch controllable lens-array HOE. By controlling the recording plane and performing repetitive recordings process, the lens pitch of the lens-array HOE could be substantially reduced, with a high fill factor and the same numerical aperture compared to the reference lens-array. We demonstrated the feasibility by fabricating a lens-array HOE with a 500 micrometer pitch. Since the pixel pitch of the projected image can be easily controlled in projection type integral imaging, the small lens pitch enhances the quality of the displayed 3D image very effectively. The enhancement of visibility of the 3D images is verified in experimental results.

Two-dimensional and three-dimensional transparent screens based on lens-array holographic optical elements.

Two-dimensional (2D) and three-dimensional (3D) transparent screens can be created using lens-array holographic optical elements (HOEs). Lens-array HOEs can be used to perform 2D and 3D imaging for Bragg matched images while maintaining the transparent properties of the images in the background scenes. 2D or 3D imaging on the proposed screen is determined by the relative size of an elemental-lens on the lens-array to a pixel on the projected image. The 2D and 3D displays on the lens-array HOEs are implemented by the diffusion of light on each elemental-lens and by taking advantage of reflection-type integral imaging, respectively. We constructed an HOE recording setup and recorded two lens-array HOEs having different optical specifications, permitting them to function as 2D and 3D transparent screens. Experiments regarding 2D and 3D imaging on the proposed transparent screens are carried out and the viewing characteristics in both cases are discussed. The experimental results show that the proposed screens are capable of providing 2D and 3D images properly while satisfying the see-through properties.

Solution for pseudoscopic problem in integral imaging using phase-conjugated reconstruction of lens-array holographic optical elements.

We propose an optical pseudoscopic to orthoscopic conversion method for integral imaging using a lens-array holographic optical element (LAHOE), which solves the pseudoscopic problem. The LAHOE reconstructs an array of diverging spherical waves when a probe wave with the phase-conjugated condition is imposed on it, while an array of converging spherical waves is reconstructed in ordinary reconstruction. For given pseudoscopic elemental images, the array of the diverging spherical waves integrates the orthoscopic three-dimensional images without a distortion. The principle of the proposed method is verified by the experiments of displaying the integral imaging on the LAHOE using computer generated and optically acquired elemental images.

Real-time integral imaging system for light field microscopy.

We propose a real-time integral imaging system for light field microscopy systems. To implement a 3D live in-vivo experimental environment for multiple experimentalists, we generate elemental images for an integral imaging system from the captured light field with a light field microscope in real-time. We apply the f-number matching method to generate an elemental image to reconstruct an undistorted 3D image. Our implemented system produces real and orthoscopic 3D images of micro objects in 16 frames per second. We verify the proposed system via experiments using Caenorhabditis elegans.

Reflection-type integral imaging system using a diffuser holographic optical element.

A reflection-type integral imaging (InIm) system using a diffuser holographic optical element (DHOE) is proposed for improving the fill factor of displayed three-dimensional images. The DHOE performs an optical function similar to that for a conventional diffuser only for Bragg matched light, while Bragg mismatched light passes through the DHOE. Elemental images projected under Bragg matching condition are scattered by the DHOE. Meanwhile, light reflected by a concave mirror-array becomes Bragg mismatched light, and is integrated into three-dimensional images without the fill factor problem. The optical characteristics of the DHOE are examined by measuring diffraction efficiencies, and the feasibility of the fill-factor-improved InIm is verified by a concave mirror-array and DHOE.

Full-color lens-array holographic optical element for three-dimensional optical see-through augmented reality.

A novel system of optical see-through augmented reality (AR) is proposed by making use of a holographic optical element (HOE) with full-color and lens-array functions. The full-color lens-array HOE provides see-through property with three-dimensional (3D) virtual images, for it functions as a conventional lens array only for Bragg-matched lights. An HOE recording setup was built, and it recorded a 30 mm × 60 mm sized full-color lens-array HOE by using the techniques of spatial multiplexing for large-area recording and wavelength multiplexing for full-color imaging. The experimental results confirm that the suggested full-color lens-array HOE can provide the full-color 3D virtual images in the optical see-through AR system.

Projection-type dual-view three-dimensional display system based on integral imaging.

A dual-view display system provides two different images in different directions. Most of them only present two-dimensional images for observers. In this paper, we propose a projection-type dual-view three-dimensional (3D) display system based on integral imaging. To assign directivities to the images, a projection-type display and dual-view screen with lenticular lenses are implemented. The lenticular lenses split the collimated image from the projection device into two different directions. The separated images are integrated by a single lens array in front of the screen, and full-parallax 3D images are observed in two different viewing regions. The visibility of the reconstructed 3D images can be improved by using high-density lenticular lenses and a high numerical aperture lens array. We explain the principle of the proposed method and verify the feasibility of the proposed system with simulations and experimental results.

Generation of finite power Airy beams via initial field modulation.

We investigate the finite power Airy beams generated by finite extent input beams such as a Gaussian beam, a uniform beam of finite extent, and an inverse Gaussian beam. Each has different propagation behavior: A finite Airy beam generated by a uniform input beam keeps its Airy profile much longer than the conventional finite Airy beam. Also, an inverse Gaussian beam generates a finite Airy beam with a good bent focusing in free space. In this paper, the analysis and experimental results of finite Airy beams are presented.

Bi-sided integral imaging with 2D/3D convertibility using scattering polarizer.

We propose a two-dimensional (2D) and three-dimensional (3D) convertible bi-sided integral imaging. The proposed system uses the polarization state of projected light for switching its operation mode between 2D and 3D modes. By using an optical module composed of two scattering polarizers and one linear polarizer, the proposed integral imaging system simultaneously provides 3D images with 2D background images for observers who are located in the front and the rear sides of the system. The occlusion effect between 2D images and 3D images is realized by using a compensation mask for 2D images and the elemental images. The principle of proposed system is experimentally verified.

Resolution enhancement of holographic printer using a hogel overlapping method.

We propose a hogel overlapping method for the holographic printer to enhance the lateral resolution of holographic stereograms. The hogel size is directly related to the lateral resolution of the holographic stereogram. Our analysis by computer simulation shows that there is a limit to decreasing the hogel size while printing holographic stereograms. Instead of reducing the size of hogel, the lateral resolution of holographic stereograms can be enhanced by printing overlapped hogels, which makes it possible to take advantage of multiplexing property of the volume hologram. We built a holographic printer, and recorded two holographic stereograms using the conventional and proposed overlapping methods. The images and movies of the holographic stereograms experimentally captured were compared between the conventional and proposed methods. The experimental results confirm that the proposed hogel overlapping method improves the lateral resolution of holographic stereograms compared to the conventional holographic printing method.

A frontal projection-type three-dimensional display.

In a typical auto-stereoscopic three-dimensional display, the parallax barrier or lenticular lens is located in front of the display device. However, in a projection-type auto-stereoscopic display, such optical components make it difficult to display elemental images on the screen or to reconstruct a three-dimensional image, even though a projection-type display has many advantages. Therefore, it is necessary to use a rear projection technique in a projection-type auto-stereoscopic display, despite the fact that this is an inefficient use of space. We propose here a frontal projection-type auto-stereoscopic display by using a polarizer and a quarter-wave retarding film. Since the proposed method uses a frontal projection scheme and passive polarizing components, it has the advantage of being both space saving and cost effective. This is the first report that describes a frontal projection-type auto-stereoscopic display based on a parallax barrier and integral imaging by using a projector. Experimental results that support the proposed method are provided.

Effect of fundamental depth resolution and cardboard effect to perceived depth resolution on multi-view display.

In three-dimensional television (3D TV) broadcasting, we find the effect of fundamental depth resolution and the cardboard effect to the perceived depth resolution on multi-view display is important. The observer distance and the specification of multi-view display quantize the expressible depth range, which affect the perception of depth resolution of the observer. In addition, the multi-view 3D TV needs the view synthesis process using depth image-based rendering which induces the cardboard effect from the relation among the stereo pickup, the multi-view synthesis and the multi-view display. In this paper, we analyze the fundamental depth resolution and the cardboard effect from the synthesis process in the multi-view 3D TV broadcasting. After the analysis, the numerical comparison and subjective tests with 20 participants are performed to find the effect of fundamental depth resolution and the cardboard effect to the perceived depth resolution.