Integral imaging-based 2D/3D convertible display system by using holographic optical element and polymer dispersed liquid crystal

Holographic multiplane augmented reality head-up display with switchable display modes based on polymer dispersed liquid crystal

The multiplane augmented reality (AR) head-up display (HUD) is important in improving driving safety and comfort. In this paper, we propose an AR-HUD with switchable display modes based on polymer dispersed liquid crystal (PDLC) and lens holographic optical elements (HOEs), which can provide two display modes: the dual-virtual-image mode and the virtual-real-image mode. The dual-virtual-image mode can produce two virtual images at different depths, which can provide a better sense of reality integration for the driver to improve driving safety and comfort. The virtual-real-image mode can produce one far virtual image and one near real image at different depths, and it provides a larger eye box (EB) for both driver and passengers in the car and a higher image contrast. The two display modes can be switched by an electronically controlled scattering module consisting of a pair of PDLC films. The proposed AR-HUD system is compact and equipped with multiplane display and mode-switching functions, and is expected to be applied in the future.

Cascaded transflective liquid crystal planar lenses enable multi-plane augmented reality

In this Letter, we report and experimentally demonstrate the multi-plane augmented reality (AR) by combining the reflective polarization volume lens (PVL) and electrically controlled transmissive Pancharatnam-Berry (PB) liquid crystal (LC) lens. This strategy is based on the electrically controlled power-based approach, which significantly alleviates the challenge of vergence-accommodation conflict (VAC) of the current near-eye display (NED). As a proof of concept, a birdbath architecture dual-plane optical see-through (OST) display was implemented experimentally by changing the power of the lens. The proposed method is expected to be a novel, to the best of our knowledge, NED that is compact, light, and fatigue-free.

Depth-Enhanced Holographic Super Multi-View Maxwellian Display Based on Variable Filter Aperture

The super multi-view (SMV) near-eye display (NED) effectively provides depth cues for three-dimensional (3D) displays by projecting multiple viewpoint images or parallax images onto the retina simultaneously. Previous SMV NED suffers from a limited depth of field (DOF) due to the fixed image plane. Aperture filtering is widely used to enhance the DOF; however, an invariably sized aperture may have opposite effects on objects with different reconstruction depths. In this paper, a holographic SMV display based on the variable filter aperture is proposed to enhance the DOF. In parallax image acquisition, multiple groups of parallax images, each group recording a part of the 3D scene on a fixed depth range, are captured first. In the hologram calculation, each group of wavefronts at the image recording plane (IRP) is calculated by multiplying the parallax images with the corresponding spherical wave phase. Then, they are propagated to the pupil plane and multiplied by the corresponding aperture filter function. The size of the filter aperture is variable which is determined by the depth of the object. Finally, the complex amplitudes at the pupil plane are back-propagated to the holographic plane and added together to form the DOF-enhanced hologram. Simulation and experimental results verify the proposed method could improve the DOF of holographic SMV display, which will contribute to the application of 3D NED.

Depth-assisted calibration on learning-based factorization for a compressive light field display

Due to the widespread applications of high-dimensional representations in many fields, the three-dimension (3D) display technique is increasingly being used for commercial purpose in a holographic-like and immersive demonstration. However, the visual discomfort and fatigue of 3D head mounts demonstrate the limits of usage in the sphere of marketing. The compressive light field (CLF) display is capable of providing binocular and motion parallaxes by stacking multiple liquid crystal screens without any extra accessories. It leverages optical viewpoint fusion to bring an immersive and visual-pleasing experience for viewers. Unfortunately, its practical application has been limited by processing complexity and reconstruction performance. In this paper, we propose a dual-guided learning-based factorization on polarization-based CLF display with depth-assisted calibration (DAC). This substantially improves the visual performance of factorization in real-time processing. In detail, we first take advantage of a dual-guided network structure under the constraints of reconstructed and viewing images. Additionally, by utilizing the proposed DAC, we distribute each pixel on displayed screens following the real depth. Furthermore, the subjective performance is increased by using a Gauss-distribution-based weighting (GDBW) toward the concentration of the observer's angular position. Experimental results illustrate the improved performance in qualitative and quantitative aspects over other competitive methods. A CLF prototype is assembled to verify the practicality of our factorization.

A comprehensive review of optical diffusers: progress and prospects

Optical diffusers made of polymer composite materials are vital for many photonic and optoelectronic applictions such as backlight unit (BLU) in liquid crystal displays (LCDs), light extraction unit of organic light emitting diodes (OLEDs), and solar cells. We have described the types of optical diffusers, the theory and measurement of light scattering, some common approaches for fabricating optical diffusers, the potential applications and recent developments of optical diffusers containing optical physical unclonable functions (PUFs), optical random number generators, passive stretchable radiative coolers, diffuser -based deep neural networks, lensless cameras or imaging systems, and three dimensinonal (3D) displays including two dimensional (2D)/3D switchable displays, which provide effective ways for designing high-performance optical films in the applications of optical devices. To satisfy the requirements for applications in stretchable optoelectronics and optomechanics, tunable optical diffusers stimulated by electric field, heat, light, mechanical field, or ultrasound attract much attention. Polymer/liquid crystal (LC) composite films with tunable light transmittance, haze, and diffusing intensity have been firstly provided and set a great foundation for the next generation of flexible and switchable optical diffusers.

Polymer-Dispersed Liquid Crystal Films on Flexible Substrates with Excellent Bending Resistance and Spacing Stability

Polymer-dispersed liquid crystals (PDLCs) are very attractive due to their electrically switchable properties. However, current PDLC films still have problems such as high driving voltages, low contrast ratio (CR), and poor bending resistance and spacing stability. To solve these problems, a PDLC film with a system of coexisting polymer spacer columns and polymer network was proposed. First, based on the adhesive systems of IBMA and UV6301, the effects of IBMA concentration and LC content on the morphology of the polymer network and the electro-optical properties of PDLC were investigated, respectively. Then, the effects of the process conditions of mask polymerization such as temperature, time, and UV light intensity on the morphology and electro-optical properties of the polymer spacer columns were systematically investigated. It was found that PDLC films with the coexistence system exhibit both excellent electro-optical properties and outstanding bending resistance and spacing stability. Thus, it provides new practical possibilities for the preparation of high-performance PDLC films used in flexible devices.

High Resolution Multiview Holographic Display Based on the Holographic Optical Element

Limited by the low space-bandwidth product of the spatial light modulator (SLM), it is difficult to realize multiview holographic three-dimensional (3D) display. To conquer the problem, a method based on the holographic optical element (HOE), which is regarded as a controlled light element, is proposed in the study. The SLM is employed to upload the synthetic phase-only hologram generated by the angular spectrum diffraction theory. Digital grating is introduced in the generation process of the hologram to achieve the splicing of the reconstructions and adjust the position of the reconstructions. The HOE fabricated by the computer-generated hologram printing can redirect the reconstructed images of multiview into multiple viewing zones. Thus, the modulation function of the HOE should be well-designed to avoid crosstalk between perspectives. The experimental results show that the proposed system can achieve multiview holographic augmented reality (AR) 3D display without crosstalk. The resolution of each perspective is 4K, which is higher than that of the existing multiview 3D display system.

Multiplane holographic augmented reality head-up display with a real-virtual dual mode and large eyebox

We propose a multiplane augmented reality (AR) head-up display (HUD) with a real-virtual dual mode based on holographic optical elements (HOEs). The picture generation unit (PGU) is only a single free-focus projector, and the optical combiner includes a HOE lens (HOEL) for long-distance virtual image display and a HOE diffuser (HOED) for in-plane real image display. A HOED with directional scattering characteristics in the real image mode can significantly increase the size of the eyebox (EB) without increasing the size of the HOE, and a HOEL with a flexible design for the optical focal length in the virtual image mode can be used to achieve a different depth of the AR display. The proposed AR HUD system, which has a compact structure and offers high light transmittance, high energy usage, a multiplane display, and a large EB, is expected to be widely used in the future.

Vari-focal liquid microlens array using an electrically responsive fluid actuated by a ring array patterned electrode

A transparent fluid dibutyl adipate (DBA) is suitable for fabricating the adaptive lens due to its unique deformation under a direct current (DC) electric field. In this report, a DBA liquid microlens array (LMA) with a tunable focal length is demonstrated. A hydrophobic layer deposited in the ring array patterns on the electrode induced the formation of the DBA liquid microdroplets array self-assembly. The electronegative DBA liquid tends to move to the anode at a DC voltage. The proposed DBA LMA with a diameter of 100 µm can change its focal length from 0.92 to 1.42 mm when the voltage changes from 0 to 200 V. The response time is relatively fast (∼790m s). Due to the high optical transmittance (∼91%) and good thermal stability in the temperature range of -24.8-161.5^∘C, our DBA LMA shows good focusing properties and has potential applications in the field of image processing, portable electronic devices, beam steering, ophthalmology, and 3D displays.

Aerosol jet printing polymer dispersed liquid crystals on highly curved optical surfaces and edges

We demonstrate a new technique for producing Polymer Dispersed Liquid Crystal (PDLC) devices utilising aerosol jet printing (AJP). PDLCs require two substrates to act as scaffold for the Indium Tin Oxide electrodes, which restricts the device geometries. Our approach precludes the requirement for the second substrate by printing the electrode directly onto the surface of the PDLC, which is also printed. The process has the potential to be precursory to the implementation of non-contact printing techniques for a variety of liquid crystal-based devices on non-planar substrates. We report the demonstration of direct deposition of PDLC films onto non-planar optical surfaces, including a functional device printed over the 90° edge of a prism. Scanning Electron Microscopy is used to inspect surface features of the polymer electrodes and the liquid crystal domains in the host polymer. The minimum relaxation time of the PDLC was measured at 1.3 ms with an 800 Hz, 90 V, peak-to-peak (Vpp) applied AC field. Cross-polarised transmission is reduced by up to a factor of 3.9. A transparent/scattering contrast ratio of 1.4 is reported between 0 and 140 V at 100 Hz.

Distortion-Corrected Integral Imaging 3D Display System Based on Lens Array Holographic Optical Element

We propose a distortion-corrected integral imaging (II) 3D display system based on lens array holographic optical element (LAHOE). The LAHOE is used as a projection screen. The projection beam of the LAHOE is parallel light. Hence, the projection system consists of a spatial light modulator, a reverse projection lens, a relay optical element, and a telecentric lens. The acquired 3D data and the reconstructed 3D image of II are symmetrically related to each other. Therefore, there is lens distortion in the projection system. To avoid affecting the viewing experience of the viewers, the elemental image array (EIA) is projected obliquely on the LAHOE, causing the lateral distortion of the EIA. There is a position deviation in the projection system, so the projected EIA has geometric deformation. Due to the distortion of the EIA, it is difficult to precisely align the projected EIA and LAHOE, which results in serious flip of the reconstructed 3D images. The distortion of the EIA affects the asymmetry of the 3D image reconstruction. Lens distortion can be solved by the distortion compensation method. Lateral and the geometric deformation can be solved by the perspective transformations in computer graphics. After correction, the undistorted EIA is projected, and the projected EIA on the LAHOE has little distortion. In the process of 3D image reconstruction, the causes of asymmetry affecting 3D image reconstruction are analyzed, and the issues that generate these asymmetric factors are addressed. Experimental results indicate that a better 3D display effect is achieved.

Pixelated volume holographic optical element for augmented reality 3D display

Augmented reality (AR) three-dimensional (3D) display is the hardware entrance of metaverse and attracts great interest. The fusion of physical world with 3D virtual images is non-trivial. In this paper, we proposed an AR 3D display based on a pixelated volume holographic optical element (P-VHOE). The see-through combiner is prepared by spatial multiplexing. A prototype of AR 3D display with high diffraction efficiency (78.59%), high transmission (>80%) and non-repeating views is realized. Virtual 3D objects with high fidelity in depth is reconstructed by P-VHOE, with a complex wavelet structural similarity (CW-SSIM) value of 0.9882. The proposed prototype provides an efficient solution for a compact glasses-free AR 3D display. Potential applications include window display, exhibition, education, teleconference.

Resolution-preserving passive 2D/3D convertible display based on holographic optical elements

We propose and demonstrate a resolution-preserving passive 2D/3D convertible display by two individual wavelengths. It uses a holographic optical element to generate two images and passively separate the exit pupils for these two wavelengths, which forms two viewpoints for each of the observer's eyes. Due to Bragg-mismatched reconstruction of two similar but distinct wavelengths, the images are separated in space. They can be fused into one through the convergence function of human eyes. By switching the input image source, the conversion between 2D and 3D mode can be realized. This method is resolution-preserving and 2D/3D convertible with no extra active components. For experimental verification, a proof-of-concept projection-type prototype is assessed.

A Light Field Display Realization with a Nematic Liquid Crystal Microlens Array and a Polymer Dispersed Liquid Crystal Film

This study demonstrates a light field display system using a nematic liquid crystal (LC) microlens array (MLA) and a polymer dispersed liquid crystal (PDLC) film. LC-MLA without polarization effects presented high-resolution intermediate 3D images by adopting a depolarization algorithm. The adopted PDLC film modulated the reconstructed 3D images to deliver full-parallax images efficiently with a wide FOV. The experimental result shows that the peak signal to noise ratio (PSNR) value of photograph accurate display results improves compared to the pure LC-MLA method. The proposed method is an essential step toward high-quality light field display.

Recent Advances in Planar Optics-Based Glasses-Free 3D Displays

Glasses-free three-dimensional (3D) displays are one of the technologies that will redefine human-computer interfaces. However, many geometric optics-based 3D displays suffer from a limited field of view (FOV), severe resolution degradation, and visual fatigue. Recently, planar optical elements (e.g., diffraction gratings, diffractive lenses and metasurfaces) have shown superior light manipulating capability in terms of light intensity, phase, and polarization. As a result, planar optics hold great promise to tackle the critical challenges for glasses-free 3D displays, especially for portable electronics and transparent display applications. In this review, the limitations of geometric optics-based glasses-free 3D displays are analyzed. The promising solutions offered by planar optics for glasses-free 3D displays are introduced in detail. As a specific application and an appealing feature, augmented reality (AR) 3D displays enabled by planar optics are comprehensively discussed. Fabrication technologies are important challenges that hinder the development of 3D displays. Therefore, multiple micro/nanofabrication methods used in 3D displays are highlighted. Finally, the current status, future direction and potential applications for glasses-free 3D displays and glasses-free AR 3D displays are summarized.

All-In-Focus Polarimetric Imaging Based on an Integrated Plenoptic Camera with a Key Electrically Tunable LC Device

In this paper, a prototyped plenoptic camera based on a key electrically tunable liquid-crystal (LC) device for all-in-focus polarimetric imaging is proposed. By using computer numerical control machining and 3D printing, the proposed imaging architecture can be integrated into a hand-held prototyped plenoptic camera so as to greatly improve the applicability for outdoor imaging measurements. Compared with previous square-period liquid-crystal microlens arrays (LCMLA), the utilized hexagonal-period LCMLA has remarkably increased the light utilization rate by ~15%. Experiments demonstrate that the proposed imaging approach can simultaneously realize both the plenoptic and polarimetric imaging without any macroscopic moving parts. With the depth-based rendering method, both the all-in-focus images and the all-in-focus degree of linear polarization (DoLP) images can be obtained efficiently. Due to the large depth-of-field advantage of plenoptic cameras, the proposed camera enables polarimetric imaging in a larger depth range than conventional 2D polarimetric cameras. Currently, the raw light field images with three polarization states including I0 and I60 and I120 can be captured by the proposed imaging architecture, with a switching time of several tens of milliseconds. Some local patterns which are selected as interested target features can be effectively suppressed or obviously enhanced by switching the polarization state mentioned. According to experiments, the visibility in scattering medium can also be apparently improved. It can be expected that the proposed polarimetric imaging approach will exhibit an excellent development potential.

Optofluidic lenticular lens array for a 2D/3D switchable display

In this paper, we propose an optofluidic lenticular lens array (OLLA) for a two-dimensional/three-dimensional (2D/3D) switchable display. The OLLA includes a bottom substrate layer with lenticular lens structure, a microfluidic layer with microchannels, and a top substrate layer with inlets as well as outlets. A micro gap is formed between the lenticular lens of the bottom substrate layer and the top substrate layer. When air is in the micro gap, the OLLA behaves as a lenticular lens array, which can realize 3D display. When fluid is filled in the micro gap, because the refractive index of the fluid is the same with the lenticular lens structure, the OLLA equivalents to a transparent flat panel, which can realize a 2D display. Experiments verify that a switchable 2D/3D display prototype based on this OLLA and a smartphone achieves both high-resolution 2D display and high-quality 3D display.

Augmented Reality Vector Light Field Display with Large Viewing Distance Based on Pixelated Multilevel Blazed Gratings

Glasses-free augmented reality (AR) 3D display has attracted great interest in its ability to merge virtual 3D objects with real scenes naturally, without the aid of any wearable devices. Here we propose an AR vector light field display based on a view combiner and an off-the-shelf purchased projector. The view combiner is sparsely covered with pixelated multilevel blazed gratings (MBG) for the projection of perspective virtual images. Multi-order diffraction of the MBG is designed to increase the viewing distance and vertical viewing angle. In a 20-inch prototype, multiple sets of 16 horizontal views form a smooth parallax. The viewing distance of the 3D scene is larger than 5 m. The vertical viewing angle is 15.6°. The light efficiencies of all views are larger than 53%. We demonstrate that the displayed virtual 3D scene retains natural motion parallax and high brightness while having a consistent occlusion effect with natural objects. This research can be extended to applications in areas such as human–computer interaction, entertainment, education, and medical care.

Optical See-through 2D/3D Compatible Display Using Variable-Focus Lens and Multiplexed Holographic Optical Elements

An optical see-through two-dimensional (2D)/three-dimensional (3D) compatible display using variable-focus lens and multiplexed holographic optical elements (MHOE) is presented. It mainly consists of a MHOE, a variable-focus lens and a projection display device. The customized MHOE, by using the angular multiplexing technology of volumetric holographic grating, records the scattering wavefront and spherical wavefront array required for 2D/3D compatible display. In particular, we proposed a feasible method to switch the 2D and 3D display modes by using a variable-focus lens in the reconstruction process. The proposed system solves the problem of bulky volume, and makes the MHOE more efficient to use. Based on the requirements of 2D and 3D displays, we calculated the liquid pumping volume of the variable-focus lens under two kinds of diopters.

Performance improvement for compressive light field display based on the depth distribution feature

Compressive light field (CLF) display using multi-layer spatial light modulators (SLMs) is a promising technique for three-dimensional (3D) display. However, conventional CLF display usually uses the reference plane with fixed depth, which does not consider the relationship between the depth distribution of the object and the image quality. To improve the quality of the reconstructed image, we further analyze the relationship between them in the paper. The theoretical analysis reveals that the object with a closer distance to the physical layer has a better reconstruction quality when the SLM layers have the same pixel density. To minimize the deviation between the reconstructed light field and the original light field, we propose a method based on the depth distribution feature to automatically guide the light field optimization without increasing the layered number or the refresh rate. When applied to a different scene, it could detect the dense region of depth information and map them as close to the physical layers as possible by offsetting the depth of the reference plane. Simulation and optical experiments with the CLF display are demonstrated to verify the proposed method. We implement a CLF display that consists of four-layer stacked display panels and the distance between two adjacent layers is 5cm. When the proposed method is applied, the peak signal-to-noise ratio (PSNR) is improved by 2.4dB in simulations and 1.8dB in experiments.

Analysis and removal of crosstalk in a time-multiplexed light-field display

Time-multiplexed light-field displays (TMLFDs) can provide natural and realistic three-dimensional (3D) performance with a wide 120° viewing angle, which provides broad potential applications in 3D electronic sand table (EST) technology. However, current TMLFDs suffer from severe crosstalk, which can lead to image aliasing and the distortion of the depth information. In this paper, the mechanisms underlying the emergence of crosstalk in TMLFD systems are identified and analyzed. The results indicate that the specific structure of the slanted lenticular lens array (LLA) and the non-uniformity of the emergent light distribution in the lens elements are the two main factors responsible for the crosstalk. In order to produce clear depth perception and improve the image quality, a novel ladder-type LCD sub-pixel arrangement and a compound lens with three aspheric surfaces are proposed and introduced into a TMLFD to respectively reduce the two types of crosstalk. Crosstalk simulation experiments demonstrate the validity of the proposed methods. Structural similarity (SSIM) simulation experiments and light-field reconstruction experiments also indicate that aliasing is effectively reduced and the depth quality is significantly improved over the entire viewing range. In addition, a tabletop 3D EST based on the proposed TMLFD is presented. The proposed approaches to crosstalk reduction are also compatible with other lenticular lens-based 3D displays.

Electrically Controlled Liquid Crystal Microlens Array Based on Single-Crystal Graphene Coupling Alignment for Plenoptic Imaging

As a unique electric-optics material, liquid crystals (LCs) have been used in various light-control applications. In LC-based light-control devices, the structural alignment of LC molecules is of great significance. Generally, additional alignment layers are required for LC lens and microlens, such as rubbed polyimide (PI) layers or photoalignment layers. In this paper, an electrically controlled liquid crystal microlens array (EC-LCMLA) based on single-crystal graphene (SCG) coupling alignment is proposed. A monolayer SCG with high conductivity and initial anchoring of LC molecules was used as a functional electrode, thus no additional alignment layer is needed, which effectively simplifies the basic structure and process flow of conventional LCMLA. Experiments indicated that a uniform LC alignment can be acquired in the EC-LCMLA cell by the SCG coupling alignment effect. The common optical properties including focal lengths and point spread function (PSF) were measured experimentally. Experiments demonstrated that the proposed EC-LCMLA has good focusing performance in the visible to near-infrared range. Moreover, the plenoptic imaging in Galilean mode was achieved by integrating the proposed EC-LCMLA with photodetectors. Digital refocusing was performed to obtain a rendering image of the target.

Resolution Improvement of Light Field Imaging via a Nematic Liquid Crystal Microlens with Added Multi-Walled Carbon Nanotubes

A relatively simple method to improve the image resolution of light field based on a liquid crystal (LC) microlens doped with multi-walled carbon nanotubes (MWCNTs) was developed and evaluated. As the nanoparticles were doped in LC, its electro-optical features could enhance, leading to a short response time compared to the pure LC microlens. With the maximum use of the proposed LC microlens, a method combining aperiodicity extraction and weighted average algorithm was adopted to realize the high-resolution light field imaging. The aperiodicity extraction method was proposed, which could effectively improve resolution of view angle image. For synthesizing the full resolution image at 0 Vrms and the extracted view angle image of light field imaging at 2.0 Vrms, the final high-resolution light field imaging could be obtained in a short time by weighted average algorithm. In this way, the common problem of low resolution in light field imaging could be solved. This proposed method was in good agreement with our experimental results. And it was also in line with the development of the trend of the smart imaging sensor combining algorithm with hardware.

2D/3D mixed frontal projection system based on integral imaging

Two-dimensional (2D)/three-dimensional (3D) convertible or mixed display is one of the most important factors for the fast penetration of 3D display into the display market. In this paper, we propose a 2D/3D mixed frontal projection system that mainly contains a liquid crystal micro-lens array (LCMLA) and a quarter-wave retarding film with pinholes (QWRF-P). The LCMLA exhibits the focusing effect or no optical effect depending on the polarization direction of the incident lights. The forward incident lights pass through the LCMLA without any bending. After passing through the QWRF-P twice, half of the backward lights change the polarization direction with 90°, and the other half remains. Using our designed system, different display modes, including 2D display, 3D display, and 2D/3D mixed display, can be realized. The unique feature of the proposed 2D/3D mixed frontal projection system is that it can switch the display modes by simply changing the image sources without the need of any active optical devices. Moreover, the proposed system is compact, simple and space-efficient, which is suitable for the application in glassless 3D cinema and home 3D theatre.

Depth-of-Field-Extended Plenoptic Camera Based on Tunable Multi-Focus Liquid-Crystal Microlens Array

Plenoptic cameras have received a wide range of research interest because it can record the 4D plenoptic function or radiance including the radiation power and ray direction. One of its important applications is digital refocusing, which can obtain 2D images focused at different depths. To achieve digital refocusing in a wide range, a large depth of field (DOF) is needed, but there are fundamental optical limitations to this. In this paper, we proposed a plenoptic camera with an extended DOF by integrating a main lens, a tunable multi-focus liquid-crystal microlens array (TMF-LCMLA), and a complementary metal oxide semiconductor (CMOS) sensor together. The TMF-LCMLA was fabricated by traditional photolithography and standard microelectronic techniques, and its optical characteristics including interference patterns, focal lengths, and point spread functions (PSFs) were experimentally analyzed. Experiments demonstrated that the proposed plenoptic camera has a wider range of digital refocusing compared to the plenoptic camera based on a conventional liquid-crystal microlens array (LCMLA) with only one corresponding focal length at a certain voltage, which is equivalent to the extension of DOF. In addition, it also has a 2D/3D switchable function, which is not available with conventional plenoptic cameras.

Dual-view integral imaging display using a polarizer

We propose a dual-view integral imaging display using a polarizer. It consists of a display panel, a polarizer, a microlens array, and two pairs of polarizer glasses. The polarizer comprises the left and right subpolarizers whose polarization directions are orthogonal. Two kinds of elemental images are captured from different three-dimensional scenes and located on the left and right half of the display panel. The lights emitting from two kinds of elemental images are polarized by the left and right subpolarizers. The polarization directions of the two pairs of polarizer glasses used in the left and right viewing zones are the same as those of the right and left subpolarizers, respectively. Two different three-dimensional images are simultaneously viewed in the left and right viewing directions by wearing two pairs of polarizer glasses. A prototype of the proposed dual-view integral imaging display is developed, and the experimental results verify the hypothesis.

High-Resolution Hologram Calculation Method Based on Light Field Image Rendering

A fast calculation method for a full parallax high-resolution hologram is proposed based on elemental light field image (EI) rendering. A 3D object located near the holographic plane is firstly rendered as multiple EIs with a pinhole array. Each EI is interpolated and multiplied by a divergent sphere wave and interfered with a reference wave to form a hogel. Parallel acceleration is used to calculate the high-resolution hologram because the calculation of each hogel is independent. A high-resolution hologram with the resolution of 200,000 × 200,000 pixels is calculated within only eight minutes. Full parallax high-resolution 3D displays are realized by optical reconstructions.

Full-color computer-generated holographic near-eye display based on white light illumination

We propose a full color computer generated holographic near-eye display (NED) based on white light illumination. The method inspired from color rainbow holography is used for calculation of 2D and 3D color holograms. The parameters of the color hologram calculation are designed based on the parameters of the spatial light modulator (SLM) with 4K resolution. A slit type spatial filter is designed in frequency domain to extract red, green and blue frequency components for full color display. A NED system including a white light source, an achromatic collimating lens, a 4K SLM, a 4f optical filtering system, and an achromatic lens as eyepiece is designed and developed. The main contribution of this paper is the first time to apply the rainbow holography concept to the dynamic full color NED with a compact display system. The optical experiments prove the feasibility of the proposed method.

2D/3D mixed display based on integral imaging and a switchable diffuser element

In this paper, we present a 2D/3D mixed system with high image quality based on integral imaging and a switchable diffuser element. The proposed system comprises a liquid crystal display screen, lens array, switchable diffuser element and projector. The switchable diffuser element can be controlled to present 2D/3D mixed images or 2D and 3D images independently, and can reduce the Moire fringe and black grid. In addition to the improved display quality, the proposed system has advantages of a simple structure and is low cost, which contribute to the portability and practicability.

A Fast Computer-Generated Holographic Method for VR and AR Near-Eye 3D Display

A fast computer-generated holographic method with multiple projection images for a near-eye VR (Virtual Reality) and AR (Augmented Reality) 3D display is proposed. A 3D object located near the holographic plane is projected onto a projection plane to obtain a plurality of projected images with different angles. The hologram is calculated by superposition of projected images convolution with corresponding point spread functions (PSF). Holographic 3D display systems with LED as illumination, 4f optical filtering system and lens as eyepiece for near-eye VR display and holographic optical element (HOE) as combiner for near-eye AR display are designed and developed. The results show that the proposed calculation method is about 38 times faster than the conventional point cloud method and the display system is compact and flexible enough to produce speckle noise-free high-quality VR and AR 3D images with efficient focus and defocus capabilities.

Electrically controlled liquid-crystal microlens matrix with a nested electrode array for efficiently tuning and swinging focus

A new type of electrically controlled liquid-crystal microlens matrix (EC-LCMM) with a nested electrode array for efficiently tuning and swinging focus, which means that the focus position can be adjusted in three dimensions, is proposed. The EC-LCMM is constructed by a 10 × 10 arrayed annular-sector-shaped aluminum electrode with a central microhole of 140μm diameter and three annular-sectors of 210μm external diameter and the period length of 280μm. To the arrangement of the patterned electrode, both the 10 × 10 LC microlens array based on the annular-sector-shaped aluminum electrode and the 9 × 9 LC microlens array based on an arrayed quasi-quadrilateral-ring-shaped electrode can be obtained. The 9 × 9 LC microlens array is formed by matching adjacent four annular-sector-shaped sub-electrodes in the 10 × 10 LC microlenses. The developed EC-LCMM can be used to electrically tune focus along the optical axis and also swing focus over a focal plane selected. The typical performances include: electrically tunable focusing in a driving voltage range of 3~7V_rms, the focal length in a range of 2~0.6mm, and the maximum focus swing distance being 16μm. For effectively describing the focus swing efficiency, the parameters of SF and SA are defined, which are the ratios between the focus swinging distance and the current focal length along the optical axis, and between the focus swinging extent and the external diameter of a single annular-sector-shaped aluminum electrode, respectively. The SF and SA of the EC-LCMM are ~16‰ and ~7.6%, respectively. It can be expected that the complex wavefront can be more efficiently measured and adjusted according to the EC-LCMM-based Shack-Hartmann wavefront measuring and adjusting architecture.