Real-time interactive holographic 3D display with a 360° horizontal viewing zone

Real-time computing for a holographic 3D display based on the sparse distribution of a 3D object and requisite Fourier spectrum

In holographic three-dimensional (3D) displays, the surface structures of 3D objects are reconstructed without their internal parts. In diffraction calculations using 3D fast Fourier transform (FFT), this sparse distribution of 3D objects can reduce the calculation time as the Fourier transform can be analytically solved in the depth direction and the 3D FFT can be resolved into multiple two-dimensional (2D) FFTs. Moreover, the Fourier spectrum required for hologram generation is not the entire 3D spectrum but a partial 2D spectrum located on the hemispherical surface. This sparsity of the required Fourier spectrum also reduces the number of 2D FFTs and improves the acceleration. In this study, a fast calculation algorithm based on two sparsities is derived theoretically and explained in detail. Our proposed algorithm demonstrated a 24-times acceleration improvement compared with a conventional algorithm and realized real-time hologram computing at a rate of 170 Hz.

Multiplexed digital volume reflection holograms generated from digital transmission holograms

Interference from co-propagation of the object and reference beams can be digitally recorded for a digital transmission hologram (DTH). Volume holograms, as in display holography, which have been traditionally recorded in bulk photopolymer or photorefractive materials using a counter-propagating object and writing beams, are read out using multispectral light and offer the advantage of excellent wavelength selectivity. In this work, the reconstruction from a single digital volume reflection hologram (DVRH) and wavelength multiplexed DVRHs derived from respective single and multi-wavelength DTHs is investigated, using coupled wave theory and an angular spectral approach. The dependence of the diffraction efficiency on volume grating thickness, wavelength, and incident angle of the reading beam is studied.

Enlargements of Viewing Zone and Screen Size of Holographic Displays Using MEMS SLM Combined with Scanning Systems

The problems of conventional holographic display techniques, which are the requirements of a sub-micron pixel pitch and ultra-high resolution for spatial light modulators (SLMs) to enlarge the viewing zone and screen size, can be addressed using microelectromechanical systems (MEMS) SLMs combined with spatial scanning systems. Various scanning systems have been efficiently combined with high-speed image generation of MEMS SLMs based on the time-multiplexing technique. The horizontal scanning system enlarged the viewing zone and screen size, the circular scanning system provided 360° three-dimensional (3D) images, and the RGB scanning system generated color 3D images. The screen size can be increased scalably using a multichannel system based on the space-multiplexing technique. The use of a short laser pulse illumination system eliminates the mechanical scanning system and greatly simplifies the display system. The measurements of the accommodation responses of human eyes showed that 3D images generated by the screen scanning holographic display have a possibility to solve the visual fatigue issue caused by the vergence–accommodation conflict, which prevents the long-time usage of conventional 3D displays.

3D single-shot ptychography with highly tilted illuminations

A method based on highly tilted illumination and non-paraxial iterative computation is proposed to improve the image quality of single-shot 3D ptychography. A thick sample is illuminated with a cluster of laser beams that are separated by large enough angles to record each diffraction pattern distinctly in a single exposure. 3D structure of the thick sample is accurately reconstructed from recorded diffraction patterns using a modified multi-slice algorithm to process non-paraxial illumination. Sufficient number of recorded diffraction patterns with noticeably low crosstalk enhances the fidelity of reconstruction significantly over single-shot 3D ptychography methods that are based on paraxial illumination. Experimental observations guided by the results of numerical simulations show the feasibility of the proposed method.

Aerial holographic 3D display with an enlarged field of view by the time-division method

We propose a method to enlarge the field of view (FOV) of holographic 3D displays in both the horizontal and vertical directions. The FOV was enlarged by using two galvano mirrors and a high-speed spatial light modulator. These optical elements were placed so that the imaging relation was satisfied among them and they were synchronously driven at a high speed to implement the time-division method. Using this method, a floating 3D object could be successfully reconstructed in mid-air near the focal point of the final lens at the rate of 10 Hz. The FOV was enlarged five times and two times in the horizontal and vertical directions, respectively.

An interactive holographic projection system that uses a hand-drawn interface with a consumer CPU

Holography is a promising technology for photo-realistic three-dimensional (3D) displays because of its ability to replay the light reflected from an object using a spatial light modulator (SLM). However, the enormous computational requirements for calculating computer-generated holograms (CGHs)—which are displayed on an SLM as a diffraction pattern—are a significant problem for practical uses (e.g., for interactive 3D displays for remote navigation systems). Here, we demonstrate an interactive 3D display system using electro-holography that can operate with a consumer’s CPU. The proposed system integrates an efficient and fast CGH computation algorithm for line-drawn 3D objects with inter-frame differencing, so that the trajectory of a line-drawn object that is handwritten on a drawing tablet can be played back interactively using only the CPU. In this system, we used an SLM with 1,920 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\times $$\end{document}× 1,080 pixels and a pixel pitch of 8 μm × 8 μm, a drawing tablet as an interface, and an Intel Core i9–9900K 3.60 GHz CPU. Numerical and optical experiments using a dataset of handwritten inputs show that the proposed system is capable of reproducing handwritten 3D images in real time with sufficient interactivity and image quality.

Holographic augmented reality based on three-dimensional volumetric imaging for a photorealistic scene

In this paper, we propose a new system for a real-time holographic augmented reality (AR) video service based on a photorealistic three-dimensional (3D) object point for multiple users to use simultaneously at various locations and viewpoints. To observe the object from all viewpoints, a camera system capable of acquiring the 3D volume of a real object is developed and is used to generate a real object in real-time. Using the normal of the object point, the observable points are mapped to the viewpoint at which the user is located, and a hologram based on the object point is generated. The angle at which the reflected light from each point is incident on the hologram plane is calculated, and the intensity of the interference light is adjusted according to the angle to generate a hologram with a higher 3D effect. The generated hologram is transmitted to each user to provide a holographic AR service. The entire system consists of a camera system comprising eight RGB-D (depth) cameras and two workstations for photorealistic 3D volume and hologram generation. Using this technique, a realistic hologram was generated. Through experiments displaying holograms simultaneously from several different viewpoints, it is confirmed that multiple users can concurrently receive hologram AR.

Reconstruction of a three-dimensional color-video of a point-cloud object using the projection-type holographic display with a holographic optical element

Here, we managed to reconstruct a three-dimensional color video of a point-cloud object using a projection-type holographic display with a holographic optical element as an optical screen. The holographic optical element has the function of an off-axis concave mirror and has been created by the wavefront printer digitally. We defined and implemented an algorithm to reconstruct a three-dimensional image at a chosen position considering the specification of the holographic optical element designed digitally. We successfully demonstrated a reconstruction of the color video in question, composed of three-dimensional images through the holographic optical element.