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We propose a phase-shifting interferometry technique using only two in-line phase-shifted self-interference holograms. There is no requirement for additional recording or estimation in the measurement. The proposed technique adopts a mathematical model for self-interference digital holography. The effectiveness of the proposed technique is demonstrated by experiments on incoherent digital holographic microscopy and color-multiplexed fluorescence digital holography with computational coherent superposition. Two-color-multiplexed four-step phase-shifting incoherent digital holography is realized for the first time, to the best of our knowledge, using the proposed technique.

Several types of augmented reality three-dimensional display systems are introduced. All systems consist of a holographic optical element fabricated by wavefront printing technique to be used as an optical functional screen.

Light field 3D displays require a precise alignment between the display source and the micromirror-array screen for error free 3D visualization. Hence, calibrating the system using an external camera becomes necessary, before displaying any 3D contents. The inter-dependency of the intrinsic and extrinsic parameters of display-source, calibration-camera, and micromirror-array screen, makes the calibration process very complex and error-prone. Thus, several assumptions are made with regard to the display setup, in order to simplify the calibration. A fully automatic calibration method based on several such assumptions was reported by us earlier. Here, in this paper, we report a method that uses no such assumptions, but yields a better calibration. The proposed method adapts an optical solution where the micromirror-array screen is fabricated as a computer generated hologram with a tiny diffuser engraved at one corner of each elemental micromirror in the array. The calibration algorithm uses these diffusing areas as markers to determine the relation between the pixels of display source and the mirrors in the micromirror-array screen. Calibration results show that virtually reconstructed 3D scenes align well with the real world contents, and are free from any distortion. This method also eliminates the position dependency of display source, calibration-camera, and mirror-array screen during calibration, which enables easy setup of the display system. This research was funded by Japan Society For Promotion Of Science (JSPS) Grant No. 18H03281. Jackin, BJ (corresponding author), Kyoto Inst Technol, Ctr Design Centr Engn, Kyoto 6068585, Japan. lode.jorissen@uhasselt.be; oi.ryutaro@nict.go.jp; k.wakunami@nict.go.jp; y-ichihashi@nict.go.jp; gauthier.lafruit@ulb.ac.be; k.yamamoto@nict.go.jp; philippe.bekaert@uhasselt.be; jackin@kit.ac.jp

Phase-shifting interferometry selectively extracting wavelength information has been proposed since 2013, which is called computational coherent superposition (CCS) of multiple wavelengths. In this proceeding, we apply CCS to self-interference incoherent holography and construct single-path, mechanical-motion-free, wavelength-multiplexed, incoherent multicolor digital holographic microscopy systems. Also, we numerically investigate quantum fluctuation in phase-shifting interferometry for the sensing of weak light such as natural light and nonlinear light. After that, we briefly discuss the difference between the digital holography systems with CCS and phase-shifting interferometry with a Bayer color image sensor.

We can record digitally-designed information of three-dimensional (3D) objects or optical elements on a holographic photosensitive material by using wavefront printing technology. But the hologram data generated from the digitally-designed information are very huge and there are often the occurrences of the unnecessary bidirectional communications. To solve this problem, we studied on a special-purpose computer for wavefront printing technology. This technique consists of generating the light-ray information from digitally-designed information of 3D objects, converting the light-ray information to the wavefront information and generating the hologram data locally from the wavefront information in interaction. In this paper, we designed the emulator of the special-purpose computer for wavefront printing technology and obtained the amount of information (the number of bits) required for the circuit by comparing the 3D images reconstructed from the holograms generated by the emulator. As a result, the amount of information of the wavefront information converted from the light-ray information most affected the quality of the 3D images reconstructed from the holograms generated by the emulator and we can design the emulator that can reduce the noise component from those 3D images. In the future, we will design the special-purpose computer for wavefront printing technology by using hardware description language and implement that special-purpose computer on a programmable logic device such as a field programmable gate array.

We present approaches for simultaneous, holographic, and microscopic multicolor motion-picture sensing of multiple natural light sources. We utilize single-shot incoherent digital holography with a polarization-imaging sensor, phase-shifting interferometry, and computational coherent superposition (CCS) as approaches.

The use of a holographic optical element as the substitution of the fine pointing mechanism in free-space optical communications is proposed. The coupling characteristics of the transmission-type hologram to a single mode fiber is experimentally investigated to show its advantage to the use of the reflection-type.

Light-in-flight recording by holography can record light propagation with a single-shot exposure in principle and can reconstruct it as spatially and temporally continuous motion pictures. We calculated computer-generated holograms based on light-in-flight recording by holography, and printed them by a wavefront printer in order to prove the validity of the numerical simulation model based on light-in-flight recording by holography. Because we reconstructed motion pictures of light propagation from the printed holograms, we successfully showed the validity of the numerical simulation model.

Recent advances in the creation of microlens arrays as holographic optical elements allow the creation of projector-based see-through light field displays suitable for augmented reality. These systems require an accurate calibration of the projector with relation to the microlens array, as any small misalignment causes the 3D reconstruction to fail. The methods reported so far require precise placement of the calibration camera w.r.t. the lens array screen, which affects the display configuration. We propose a calibration approach which is more robust, and which allows free camera placement. Hence, it does not limit the capabilities of the system. Both a homography-based technique and structured light play a central role in realizing such a method. The method was tested on a projection-based integral imaging display system consisting of a consumer-grade projector and a digitally designed holographic optical element based micromirror array screen. The calibration method compensates for the lens distortion, intrinsics, and positioning of the projector with relation to the screen. The method uses a single camera and does not require the use of obtrusive markers as reference. We give an in-depth explanation of the different steps of the algorithm, and verify the calibration using both a simulated and a real-world setup., SCOPUS: ar.j, info:eu-repo/semantics/published

Concave micro-mirror arrays fabricated as holographic optical elements are used in projector-based light field displays due to their see-through characteristics. The optical axes of each micro-mirror in the array are usually made parallel to each other, which simplifies the fabrication, integral image rendering, and calibration process. However, this demands that the beam from the projector be collimated and made parallel to the optical axis of each elemental micro-mirror. This requires additional collimation optics, which puts serious limitations on the size of the display. In this Letter, we propose a solution to the above issue by introducing a new method to fabricate holographic concave micro-mirror array sheets and explain how they work in detail. 3D light field reconstructions of the size 20 cm×10 cm and 6 cm in depth are achieved using a conventional projector without any collimation optics. Japan Society for the Promotion of Science (JSPS) (16H01742, 18H03281, 26790064).

In this paper, we introduce hologram printing technology. This technology includes the following technologies, computer-generated hologram, hologram printer, duplication, and application-depended technologies. When this technology is applied to static hologram, the media can present static 3D objects more clearly than traditional 3D technologies such as lenticular lens and integral photography(IP) because it is based on holography. When this technology is applied to holographic optical elements(HOE), the HOE will be useful for many purposes especially for large optical elements. For example, when it is used as screen, the visual system which consists of the screen and projector can present dynamic 2D or 3D objects. Since this technology digitally designs hologram/HOE and manufactures them by wavefront printer, it is good at generating small lot of production. As a result, it is effective for the research stage of both 2D and 3D display. In addition, it is also effective for commercial stage due to simple duplication method.

A hologram of a scene can be digitally created by using a large set of images of that scene. Since capturing such a large amount is infeasible to accomplish, one may use view synthesis approaches to reduce the number of cameras and generate the missing views. We propose a view interpolation algorithm that creates views inside the scene, based on a sparse set of camera images. This allows the objects to pop out of the holographic display. We show that our approach outperforms existing view synthesis approaches and show the applicability on holographic stereograms.

See-through head-up 3D display is being reported, which uses a commercial projector as the light source and a lens array in the form of holographic optical element (HOE). By introducing novel technique in the fabrication process of the HOE based lens array, we have significantly simplified the display system by not using any collimation optics. Light field reconstructions of a 3D scene of size 20cm (Width) × 10cm (Height) × 5 cm (Depth) is successfully demonstrated with a view angle of 10-degrees.

This paper shows the process used to calculate a computer-generated hologram (CGH) for real scenes under natural light using a commercial portable plenoptic camera. In the CGH calculation, a light field captured with the commercial plenoptic camera is converted into a complex amplitude distribution. Then the converted complex amplitude is propagated to a CGH plane. We tested both numerical and optical reconstructions of the CGH and showed that the CGH calculation from captured data with the commercial plenoptic camera was successful.

Wavefront printer can record arbitrary designed wavefront not only for static 3D visualization but also for holographic screen to be used on projection-type holographic display. Some applications related to the wavefront printer are introduced.

A calibration technique for integral photography(IP) based 3D display that uses a commercial projector and digitally designed holographic optical element (DDHOE) as lens array is reported. This is an automated method that compensates for both lens distortion and DDHOE-projector alignment errors which shows huge improvement in reconstruction quality. This method requires less number of input images for calibration compared to existing ones.

We present optical experimental results for a high-resolution three-dimensional (3D) holographic display system based on dense ray sampling and integral imaging capture. Holograms are generated based on re-sampling the rays from 2D images captured by an integral imaging system. In addition, we demonstrate a depth of field extension technique during the integral imaging capture by combining an amplitude modulated lens technique and a blind convolution approach. The optically reconstructed images of the holographic display system are shown and compared with conventional integral imaging-based holographic displays for different scenes.

The use of a holographic optical element (HOE) is proposed as a substitute for the fine-pointing mechanism (FPM) in free-space optical communications. A HOE possessing a function to transform the propagation angle of the received beam to a designed direction is fabricated. The coupling characteristics of the received beam to a single-mode fiber are experimentally evaluated. The results confirm the potential of the proposed method and show the advantages over the FPM.

Owing to the limited spatio-temporal resolution of display devices, dynamic holographic three-dimensional displays suffer from a critical trade-off between the display size and the visual angle. Here we show a projection-type holographic three-dimensional display, in which a digitally designed holographic optical element and a digital holographic projection technique are combined to increase both factors at the same time. In the experiment, the enlarged holographic image, which is twice as large as the original display device, projected on the screen of the digitally designed holographic optical element was concentrated at the target observation area so as to increase the visual angle, which is six times as large as that for a general holographic display. Because the display size and the visual angle can be designed independently, the proposed system will accelerate the adoption of holographic three-dimensional displays in industrial applications, such as digital signage, in-car head-up displays, smart-glasses and head-mounted displays., The design of holographic displays usually involves a trade-off between size and viewing angle. Here, the authors combine holographic projection with a digitally designed holographic optical element so that display size and the visual angle can be designed independently.

A hologram recording technique, generally called as “wavefront printer”, has been proposed by several research groups for static three-dimensional (3D) image printing. Because the pixel number of current spatial light modulators (SLMs) is not enough to reconstruct the entire wavefront in recording process, typically, hologram data is divided into a set of subhologram data and each wavefront is recorded sequentially as a small sub-hologram cell in tiling manner by using X-Y motorized stage. However since previous works of wavefront printer do not optimize the cell size, the reconstructed images were degraded by obtrusive split line due to visible cell size caused by too large cell size for human eyesight, or by diffraction effect due to discontinuity of phase distribution caused by too small cell size. In this paper, we introduce overlapping recording approach of sub-holograms to achieve both conditions: enough smallness of apparent cell size to make cells invisible and enough largeness of recording cell size to suppress diffraction effect by keeping the phase continuity of reconstructed wavefront. By considering observing condition and optimization of the amount of overlapping and cell size, in the experiment, the proposed approach showed higher quality 3D image reconstruction while the conventional approach suffered visible split lines and cells.

We introduce a new algorithm for calculating computer generated hologram (CGH) using ray-sampling (RS) plane. RS plane is set at near the object and the light-rays emitted by the object are sampled at the plane. Then the light-rays are transformed into the wavefront with using the Fourier transforms. The wavefront on the CGH plane is calculated by wavefront propagation simulation from RS plane to CGH plane. The proposed method enables to reproduce high resolution image for deep 3D scene with angular reflection properties such as gloss appearance.

To replicate holograms, contact copying has conventionally been used. In this approach, a photosensitive material is fixed together with a master hologram and illuminated with a coherent beam. This method is simple and enables high-quality copies; however, it requires a large optical setup for large-area holograms. In this paper, we present a new method of replicating holograms that uses a relatively compact optical system even for the replication of large holograms. A small laser spot that irradiates only part of the hologram is used to reproduce the hologram by scanning the spot over the whole area of the hologram. We report on the results of experiments carried out to confirm the copy quality, along with a guide to design scanning conditions. The results show the potential effectiveness of the large-area hologram replication technology using a relatively compact apparatus.

Several wavefront printers have been recently proposed. Since the printers can record an arbitrary computer-generated wavefront, they are expected to be useful for fabricating complex mirror arrays used in front projection 3-D screens without using real existing optics. We prototyped two transparent reflective screens using our hologram printer in experiments. These screens could compensate for a spherically distorted reference wave caused by a short projection distance to obtain an ideal reference wave. Owing to the use of the wavefront-printed screen, the 3-D display was simply composed of a normal 2-D projector and a screen without using extra optics. In our binocular system, reflected light rays converged to the left and right eyes of the observer and the crosstalk was less than 8%. In the light field system, the reflected light rays formed a spatially sampled light field and focused a virtual object in a depth range of ±30 mm with a ±13.5-deg viewing angle. By developing wavefront printing technology, a complex optics array may easily be printed by nonprofessionals for optics manufacturing.

金沢大学理工研究域機械工学系, Although electro-holography can reconstruct three-dimensional (3D) motion pictures, its computational cost is too heavy to allow for real-time reconstruction of 3D motion pictures. This study explores accelerating colour hologram generation using light-ray information on a ray-sampling (RS) plane with a graphics processing unit (GPU) to realise a real-time holographic display system. We refer to an image corresponding to light-ray information as an RS image. Colour holograms were generated from three RS images with resolutions of 2,048 × 2,048; 3,072 × 3,072 and 4,096 × 4,096 pixels. The computational results indicate that the generation of the colour holograms using multiple GPUs (NVIDIA Geforce GTX 1080) was approximately 300-500 times faster than those generated using a central processing unit. In addition, the results demonstrate that 3D motion pictures were successfully reconstructed from RS images of 3,072 × 3,072 pixels at approximately 15 frames per second using an electro-holographic reconstruction system in which colour holograms were generated from RS images in real time. © 2018 The Author(s).

This paper proposes a high-quality fast depth estimation method based on a non-iterative edge-adaptive local cost optimization for super multi-view images (SMV). Depth candidates are increasingly updated by evaluating a cost function involving three-view matching error and depth continuity terms. A simple differentiator detects a texture edge and controls the depth continuity weight. Experimental results show an increase in speed of approximately 9.7 to 67 times with the same quality for computer graphic images and approximately 111 times with less than 1dB quality degradation for camera images compared to a graph-cuts based algorithm. Its predictable estimation time is an advantage for real-time free-navigation systems using SMV.

We propose a method of compensating for luminance differences between spatial light modulators (SLMs) in an electronic holography display system that uses multiple reflection amplitude modulation type SLMs, which are tiled by optical means without gaps. Luminance differences between SLMs are caused by characteristic differences of the optical components in each SLM. We developed a compensation method that is applied after the calculation of hologram data is completed. This method can conserve linearity between the compensation control value of the hologram and the power of the optical output. Moreover, it is robust enough to deal with a nonlinear response of the SLMdevices and its calculation cost is low. We apply this method to a 16 (4×4) 4K×2K-pixel SLM-system to improve the image quality of a large full-parallax holographic three-dimensional image.

To develop a 3D display which can show true 3D images is very important and necessary. Holography has great potential to achieve the objective because holography can actually reconstruct the recorded object in space by reconstruction of wavefront. Further, computer generated hologram (CGH) is used to solve the major issue of conventional holography, which means the recoding process is quite complicated and needs the real objects. The reconstructed image, however, will be blurred and with the unexpected light if using only one phase-only spatial light modulator (PSLM). Although to use two PSLMs by dual-phase modulation method (DPMM) can modulate the phase and the amplitude information simultaneously to enhance the quality of the reconstructed image, it is hard to use in practical application because of the extremely high accurate calibration of the two PSLMs. Therefore, double phase hologram (DPH) was proposed to use only one PSLM to modulate the phase and the amplitude information simultaneously to make the reconstructed image be more focused and eliminate the unexpected light.

In this paper, we propose a new method of using multiple spatial light modulators (SLMs) to increase the size of three-dimensional (3D) images that are displayed using electronic holography. The scalability of images produced by the previous method had an upper limit that was derived from the path length of the image-readout part. We were able to produce larger colour electronic holographic images with a newly devised space-saving image-readout optical system for multiple reflection-type SLMs. This optical system is designed so that the path length of the image-readout part is half that of the previous method. It consists of polarization beam splitters (PBSs), half-wave plates (HWPs), and polarizers. We used 16 (4 × 4) 4K×2K-pixel SLMs for displaying holograms. The experimental device we constructed was able to perform 20 fps video reproduction in colour of full-parallax holographic 3D images with a diagonal image size of 85 mm and a horizontal viewing-zone angle of 5.6 degrees.

Computational holography based on the mutual conversion between ray information and wavefront is introduced. By dealing with ray and wavefront domains properly in the hologram calculation process, the proposed method can be compatible both domain's advantages. In the optical experiment, some main features of proposed method; the photorealistic image reconstruction by using computer graphics technique, the correct occlusion effect by just ray overwriting process, and also the reproducibility even for the deep 3D scene at high resolution, are demonstrated by the electronic-holography system developed by NICT.

In this paper, we overview a high resolution three-dimensional (3D) holographic display using 2D images captured in an integral imaging system and dense ray resampling technique. Holograms are generated the resampled rays from the 2D images. This method can improve the display resolution because each object is captured in focus and light-ray information is interpolated and resampled with high density on ray-sampling plane located near the object. Numerical experimental results for different scenes show that the presented holographic display technique can reconstruct multiple objects at different depths with higher resolution compared to conventional integral imaging-based holographic displays.

The electronic holographic three-dimensional images produced by reflection-type multiple spatial light modulators have limited scalability. We propose latitude enhancement method with a newly devised space-saving image-readout optical system to produce large color full-parallax images.