Inline dual-phase modulation method for acompact lensless holographic display.

Holographic display system with enhanced viewing angle using boundary folding mirrors

A liquid crystal panel for a video projector is often used for holographic television. However, its pixel size and pixel number are not enough for practical holographic 3-D display. Therefore, a multipanel configuration is generally used to increase the viewing window and displayed image size, and many spatial light modulators should be used in them. We propose a novel method to increase the viewing window of a holographic display system. The proposed method, which is implemented by using a mirror module and 4-f lens set, is to reconfigure the beam shape reflected by a spatial light modulator. The equipment is applied to a holographic display system, which has only a single spatial light modulator; a hologram could be displayed in a wider viewing window by the equipment than that of the conventional method. By the proposed method, the resolution of the reconfigured spatial light modulator has double resolution in the horizontal direction. Inversely, the vertical resolution is decreased. Even if the vertical resolution is decreased, a viewer could get 3-D effect because humans get more 3-D information in the horizontal direction. We have experimented using a liquid crystal on silicon (LcOS), whose resolution is 4096×2160 pixels. The reconfigured resolution by the mirror module is 8192×1080 pixels. From the experiments, the horizontal viewing window is almost two times wider than that without the mirror module. As a result, the hologram can be observed binocularly.

Holographic displays hold the promise of providing authentic depth cues, resulting in enhanced immersive visual experiences for near-eye applications. However, current holographic displays are hindered by speckle noise, which limits accurate reproduction of color and texture in displayed images. We present HoloChrome, a polychromatic holographic display framework designed to mitigate these limitations. HoloChrome utilizes an ultrafast, wavelength-adjustable laser and a dual-Spatial Light Modulator (SLM) architecture, enabling the multiplexing of a large set of discrete wavelengths across the visible spectrum. By leveraging spatial separation in our dual-SLM setup, we independently manipulate speckle patterns across multiple wavelengths. This novel approach effectively reduces speckle noise through incoherent averaging achieved by wavelength multiplexing, specifically by using a single SLM pattern to modulate multiple wavelengths simultaneously on one or more SLM devices. Our method is complementary to existing speckle reduction techniques, offering a new pathway to address this challenge. Furthermore, the use of polychromatic illumination broadens the achievable color gamut compared to traditional three-color primary holographic displays. Our simulations and tabletop experiments validate that HoloChrome significantly reduces speckle noise and expands the color gamut. These advancements enhance the performance of holographic near-eye displays, moving us closer to practical, immersive next-generation visual experiences.

Recent developments in ultra-high-definition (UHD) displays have a major impact on holographic displays as well as conventional display systems. A spatial light modulator (SLM) can reproduce hologram data through wavefront modulation of the incident light, and a holographic printer can record a high-quality hologram by sequentially recording a number of holograms reproduced by the SLM on a holographic material. As UHD (4K) resolution SLMs have been popularized, higher quality holograms can be reproduced compared to previous 2K resolution SLMs. When applied to the holographic printer, it is possible to manufacture holographic optical elements (HOEs) having a multifunctioning property and a wide field of view. In this paper, we introduce the holographic printer system using an amplitude UHD SLM and its applications. The holographic printer consists of optical systems to generate high-quality hologram from UHD SLM and mechanical systems to record the hologram on holographic material. The details of the total system are introduced. Furthermore, we introduce a holographic near-eye display system using UHD SLM and an image combiner HOE which is manufactured by the holographic printer.

In this paper we present a single SLM color holographic 3D display with spatial only multiplexing method. SLM is illuminated simultaneously with three beams. A color (RGB) filter mask placed in front of the SLM surface distributes illuminating beams accordingly to component holograms. After propagation modulated wavefronts overlap in space and create a real color 3D image. The display works with native SLM frame rate, but with the cost of spatial bandwidth product reduction. In the paper we present the method capabilities and discuss its limitations. Finally, we present the display implementation and resulting color holographic reconstruction of computer generated 3D object. Full Text: PDF References T. Kozacki, G. Finke, P. Garbat, W. Zaperty, M. Kujawinska, Wide angle holographic display system with spatiotemporal multiplexing, Opt. Express 20, 27473-27481 (2012) CrossRef F. Yaras, H. Kang, L. Onural, Real-time phase-only color holographic video display system using LED illumination, Appl. Opt. 48, p.48-53 (2009) CrossRef T. Shimobaba, A. Shiraki, N. Masuda, T. Ito, An electroholographic color reconstruction by time division switching of reference lights, J. Opt. A, v. 9, p. 757-760 (2007) CrossRef H. Sasaki, K. Yamamoto, Y. Ichihashi, T. Senoh, Image Size Scalable Full-parallax Coloured Three-dimensional Video by Electronic Holography, Scientific Reports, 4, pp.1-6 (2014) CrossRef M. Makowski et al., Simple holographic projection in color, Opt. Express 20, 25130-25136 (2012) CrossRef M. Makowski et al., Extremely simple holographic projection of color images, Proc. of SPIE - The International Society for Optical Engineering, 8280, art. no. 82800V (2012) CrossRef W. Zaperty, T. Kozacki, M. Kujawinska, Color holographic 3D display unit with aperture field division, International Conference of 3D Displays and Systems, Korea (2014) DirectLink T. Kozacki, On resolution and viewing of holographic image generated by 3D holographic display, Opt. Express 18, 27118-27129 (2010) CrossRef A. Lizana, et al., Wavelength dependence of polarimetric and phase-shift characterization of liquid crystal on silicon display, J. Europ. Opt. Soc.Rap. Public, (3), 08012 (2008) CrossRef M. Kujawinska et al., Multiwavefront digital holographic television, Opt. Express 22, 2324-2336 (2014) CrossRef M. Kujawinska, et al., Generation of holographic content based on coherent and noncoherent capture (International Conference of 3D Displays and Systems, Korea, 2014) DirectLink

Holographic display and imaging are usually implemented with coherent lasers, which usually suffer from speckles. Incoherent light sources have long been highly desired for holographic applications, but the corresponding spatial modulation scheme is still lacking. Here we demonstrate a hyperspectral complex field modulation based on a single spatial light modulator (SLM) for an incoherent white light-emitting diode (LED) with a 200 nm bandwidth. The technique encodes the complex fields of multiple wavelengths into a phase hologram. The hologram has an analytical expression and is the superposition of multiple fringe patterns with different frequencies. By tuning the local fringe frequency on the hologram, one can modulate the local output spectrum. The method is applied for sweeping wavelength and projecting color images, where tens of spectral channels are modulated independently. Moreover, the method can achieve complex modulation and is applied in multi-plane holographic projections.

Among the important features of holographic displays are the wide viewing angles and the full color of the reconstructed images. The present work focuses on achievement of both features. We propose an increased-viewing-angle full-color holographic display using two tiled phase-only spatial light modulators (SLMs), a 4f concave mirrors system, and a temporal-spatial multiplexing method. The 4f optical system consists of two concave mirrors and serves to increase the viewing angle. A temporal-spatial multiplexing synchronization control (TSMSC) method is developed to achieve a full-color image and to remove the color crosstalk of the image. We calculate RGB phase-only holograms of a computer-generated color pyramid by using a slice-based Fresnel diffraction algorithm. The experimental results indicate that the proposed display system is feasible to reconstruct a full-color holographic 3D image with a viewing angle of 12.8°, which is about 3.8 times wider than the viewing angle formed by a single SLM.

Metasurface holography has emerged as a transformative technology with significant potential in information encryption, virtual displays, and high-capacity data storage. However, developing a holographic display system with ultrahigh information capacity and multidimensional multiplexing remains a major challenge. To address this issue, we propose a Janus metasurface holographic display scheme featuring asymmetric transmission and multi-depth imaging at microwave frequencies, enabled by complex-amplitude modulation. The modified three-dimensional holography method we proposed enables the complex-amplitude modulation devices to acquire the ability of manipulating multi-depth holographic displays. By simultaneously multiplexing the propagation direction and propagation distance of incident waves, a large number of distinct holographic images can be reconstructed throughout the entire propagation space. As a proof of concept, we experimentally demonstrate the reconstruction of five distinct letter images, each located on different planes along opposite propagation directions. The measured results show excellent agreement with simulations, validating the proposed strategy. This approach paves the way for metasurface-based holographic display systems featuring ultrahigh information capacity, robust holographic encryption, and high-efficiency data storage.

A fast iterative solving method of fuzzy relational equation is proposed. It is derived by eliminating a redundant comparison process in the conventional iterative solving method (Pedrycz, 1983). The proposed method is applied to image reconstruction, and confirmed that the computation time is decreased to 1 / 40 with the compression rate of 0.0625. Furthermore, in order to make any initial solution converge on a reconstructed image with a good quality, a new cost function is proposed. Under the condition that the compression rate is 0.0625, it is confirmed that the root mean square error of the proposed method decreases to 27.34% and 86.27% compared with those of the conventional iterative method and a non iterative image reconstruction method, respectively.

For practical holographic video display, it is important to generate holographic fringes as fast as possible. It is also important to display the full-color image with a simple display system. In our previous study, a full-color hologram was realized as a rainbow hologram, which discards the vertical parallax to reduce computation complexity. Its color reproduction, however, is not enough. Since this hologram uses the horizontal slit, proper color reproduction can be obtained only from a narrow viewing area in the vertical direction. In contrast, the image hologram provided a good contrast image, although it had only a single color. Also, the image hologram has full-parallax information. In this work, we investigate the image hologram for fast calculation and the display optics for full-color holograms with full parallax. Since image points are located close to the hologram, the required computation area of the image hologram becomes much smaller than that of the entire hologram. Therefore, vastly improved computational speed is obtained. The full-color hologram is displayed on a holographic video display system, which uses part of the original optics and liquid crystal on silicon (LCoS) panels of the conventional video projector to separate and combine color components. From the experimental results, we obtain a full-parallax reconstructed image and better color reproduction compared with the rainbow hologram.

In this paper, a color holographic display system based on the utilization of effective viewing area (EVA) is proposed. Color reconstruction is achieved by using a single spatial light modulator (SLM). The EVA of three color reconstructed images is analyzed based on the holographic diffraction theory and the principle of geometrical optics. Then, the effective holograms of three colors are calculated based on the EVA of the system. When three color lasers are used to collimate the SLM, three color reconstructed images can be coincided in the same position with a fast speed of calculation. Moreover, the chromatic aberration can be eliminated and the experimental results verify the feasibility of the proposed system.

A new holography display technology based on a phase-only spatial light modulator (SLM) is proposed. The normal use of laser diode (LD) light source led to the inevitable speckle noise introduced by the coherence of the laser beam. Algorithms and special diffractive optical elements have been proposed to reduce the speckle noise. In this paper, a selected light-emitted diode (LED) light source was used in the holographic display system to replace the LD light source. The temporal coherence and spatial coherence of the LED were studied. Though the temporal coherence of LED is short, the spatial coherence of the light field can be improved by optimizing the optical paths such as decreasing the emitting area of the light source and so on. A high-power LED with a narrow band-width was selected. An algorithm to generate computer-generated hologram for the SLM was proposed. The phase-only holograms for the display were computed using the coherent light algorithm. Then the phase holograms were uploaded to the SLM. LED was used as the light source to illuminate the SLM uniformly, and the reconstructions can be observed by naked eye. It is demonstrated that LED is an acceptable light source for holographic display. The reconstruction results showed that the speckle noise and multiple reflections were eliminated when LED was used as the light source.

The near-eye display feature in emerging spatial computing systems produces a distinctive visual effect of mixing virtual and real worlds. However, its application for all-day wear is greatly limited by the bulky structure, energy expenditure, and continuous battery heating. Here, we propose a lightweight holographic near-eye display system that takes advantage of solar energy for self-charging. To guarantee the collection of solar energy and near-eye display without crosstalk, we implement holographic optical elements (HOEs) to diffract sunlight and signal light into a common waveguide. Then, small-area solar cells convert the collected solar energy and power the system. Compact power supply components replace heavy batteries, thus contributing to the lightweight design. The simple acquisition and management of solar energy provide the system with sustainable self-charging capability. We believe that the lightweight design and continuous energy input solution will significantly promote the popularity of near-eye display in our daily lives.

Gratings are widely used as coupling parts in a waveguide display system for achieving a much lighter and more compact system, but their diffraction efficiency needs to be improved. Two combined gratings for integrating a subwavelength binary grating and volume holographic grating (VHG) are applied as incoupler and outcoupler of a holographic waveguide display system. Two basic design rules are put forward to guarantee the maximum diffraction energy guided into the waveguide and finally coupled out to enter into the user's eyes: one is the grating vector matching rule, the other is the refractive index matching rule on the interface of the binary grating and the VHG. The finite element method is used to simulate the couple-in parts and the whole waveguide display system. The combined grating with the metal binary grating is different from that with a dielectric binary grating for achieving higher diffraction efficiency and an additional second peak in the diffraction efficiency curve varied with the relative position between the binary grating and the VHG. The simulation results indicate that a VHG+Ag combined grating can obtain much higher diffraction efficiency compared to gold, aluminum, and other dielectric materials. In addition, several factors such as the Bragg wavelength, the index modulation of VHG, binary grating thickness, and the filling factor of the binary grating are discussed for the VHG+Ag combined grating. Moreover, a higher diffraction efficiency in the holographic waveguide system can be obtained by using VHG+Ag-VHG+Ag combined gratings as the incoupler and outcoupler.

Light emitting diode (LED) has been a prominent component for illumination source of holographic displays. It can replace laser in that it alleviates speckle noise in reconstructed hologram and is regarded as a safer source. However, LED-based holographic displays can reconstruct an image in a limited depth range due to partially coherent characteristic of LED itself. In this paper, we propose a prototype of LED-based holographic near-eye display with focus tunable lens to expand the depth range. The feasibility of the system is supported by several experimental results.