Holographic display system with enhanced viewing angle using boundary folding mirrors

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.

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.

This study presents an innovative inline dual-phase modulation technique for compact lensless holographic displays. By utilizing a single spatial light modulator (SLM) and employing two-phase components derived from double-phase holography symmetrically positioned in the upper and lower halves of the SLM, we achieve a holographic display through the superposition of a digital phase grating. This approach eliminated the need for bulky 4-F systems, resulting in a compact optical setup. Numerical simulations demonstrate that the proposed method provides high-precision image reconstruction using a single SLM, and the experimental results confirm its efficacy in achieving image reconstruction with minimal speckle noise compared to the conventional iterative random phase method. Additionally, incorporating an initial random phase reduces artifacts in practical experimental settings, producing less speckle noise than the conventional iterative random phase method. Moreover, based on the proposed method, a beam splitter was used for further coupling in the reconstruction plane, resulting in an expanded display area while maintaining a compact system. The proposed method can simplify various holographic display systems, including projection, near-eye, and 3D displays.

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.

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.

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

Phase-only liquid crystal spatial light modulator (SLM) has been widely used for accurate phase-manipulation in holographic display, optical tweezers, lithography, etc. Due to the nonlinear optical response of liquid crystal and manufacturing defects, the grayscale-phase response could be different for every single SLM device. The calibration for phase modulation is needed for improving the performance of the SLM involved system. The principles of phase-only SLM are reviewed. The main phase calibration methods for SLM are discussed and compared.

We propose a three-dimensional (3-D) holographic display system which consists of a phase-only spatial light modulator (SLM) and a modified 4-f system. The 3-D scene is generated from OpenGL, and the point source algorithm with anti-aliasing technique is used to generate the Fresnel hologram. A modified 4-f system is proposed to produce distortion-free magnification of the 3-D image and eliminate the zero-order interruption of the 3-D holographic imaging system. This method can make efficient utilization of the space-bandwidth product of the SLM, which promises the image quality and keeps the 3-D imaging zone unchanged. Numerical simulations and optical experiments are performed, and the results show that our proposed method can reconstruct enlarged 3-D optical image with correct magnification factor and low image noise.

Holographic display system that uses six phase-only spatial light modulators (SLMs) performs holographic reconstructions from the phase-hologram of a point cloud that is extracted from 3D object. The SLMs are tiled as a three by two matrix on a virtual planar surface. The alignment is successful and the display system generates large holographic reconstructions. The proposed system can be used either to obtain reconstructions of large objects with a narrow field of view or reconstructions of smaller objects with a broader field of view. Therefore, since field of view is broader for smaller objects, observer has the flexibility to move around the reconstruction within a larger angle. This flexibility increases the motion parallax and as a consequence it increases the quality of 3D perception. Results show that even with three SLMs in horizontal direction the 3D perception is significantly increased. Experimental results are satisfactory.

In a digital holographic display, it is not desirable to observe the conjugate image and zeroth-order diffracted light in the reconstructed image. To remove noise, various methods have been proposed to limit the noise bandwidth in the Fraunhofer region using optics. In general, a 4-F relay optic-based noise-filtering system is used in these noise-filtering methods. However, in the case of a holographic display configuration, where a conventional 4-F relay optics-based noise-filtering optical system is applied, the optical performance at a critical level is required because the diffraction angle and display area become larger. Here, we propose parallel noise filtering as a new method to remove the optical noise in a holographic display. The proposed parallel noise-filtering method can be achieved by applying a new noise-filtering optical system based on 2-F relay optics. The proposed technique significantly reduces the burden on the holographic display optics configuration and dramatically reduces the optical path to enable a holographic display with a commercially available form factor.

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.

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.

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.

Coarse Wavelength Division Multiplexing (CWDM) technologies are being widely deployed internationally in metropolitan and access networks due to the increased demand for delivering more bandwidth to the subscriber, created by the need of enhanced services, (Koonen, 2006). For metro, and mainly for access networks applications, an increment in capacity may be achieved with a cost-effective multiplexing technology without the need for the high channel counts and closely spaced wavelengths typically used in long haul networks. A channel space of 20 nm, as proposed in the G. 694.2 ITU Rec., can be used relaxing the processing tolerances and potentially lowering the cost of components. CWDM technology reaches those requirements and it has been proposed for these applications. It is in this context that holographic optical devices have a potential use. This chapter describes the theory, design, and experimental results of a generic multipurpose device that can operate as a tunable wavelength filter, wavelength multiplexer and wavelength router. This device could be especially useful in optical network applications based on both Coarse and Dense Wavelength Division Multiplexing technology (CWDM/DWDM). The enabling component is a Ferro-electric Liquid Crystal (FLC) Spatial Light Modulator (SLM) in which dynamic holograms are implemented in real time. As a consequence, the device will be able to carry out different functions according to the hologram recorded on the SLM. The great advantage of this device is polarization insensitivity in the region of operation, allowing low cross-talk and simple handling. As hologram management is the basis for this device, some topics in the Computer Generated Hologram (CGH) design process are commented on and general guidelines are also considered. Laboratory experiments have demonstrated the capability of a phase FLC-SLM, with the great advantage of polarization insensitivity operation, to diffract the incident light according its wavelength and hologram patterns, for the use in the former applications. Two typical applications of this technology are described: the first one is a design of an equalized holographic Reconfigurable Optical Add-Drop Multiplexer ( ROADM), where this device can address several wavelengths at the input to different output fibers, according to the holograms stored in a SLM (Spatial Light Modulator), all the outputs being equalized in power; the second one is dealing with the design of an holographic router with loss compensation and wavelength conversion whose main application is in Metro networks in the interconnection nodes. This device uses a SOA (Semiconductor Optical Amplifier), in the non linear region, to do the wavelength conversion and, in addition, to supply the gain in order to compensate for the intrinsic losses of the holographic device.