Waveguide Display Research Articles

Large-size PVG-based waveguide simulation and uniformity optimization for AR-HUD.

Polarization volume grating (PVG), a kind of diffractive optical element, is applied widely for augmented reality (AR) near-eye display (NED) lately. However, PVG-based AR head-up display (AR-HUD) requires a large-size exit pupil and uniform efficiency, and there is presently no systematic simulation method for this type of application. Here, we introduce a unique simulation analysis method via the large-size PVG-based waveguide technology for AR-HUD. Through the self-built particle swarm optimization (PSO) algorithm, on the waveguide structure of 290 mm × 160 mm × 3 mm, with an eyerelief distance of 600 mm, the binocular field of view uniformity reaches 35.37% at an eye box of 100 mm × 50 mm, and the monocular uniformity can reach 31.65% and 32.48% respectively. The design scheme in this paper provides guidance for the large-size diffractive waveguide display for AR-HUD.

Wide-field-of-view and high-resolution waveguide display based on the coupling-collimation system

Waveguide display is a common augmented reality (AR) solution. In traditional waveguide display systems, the design of the couplers and the design of the collimators are separated. In order to achieve high imaging resolution under a large field of view, complex collimating lens groups are often required. In this work, a waveguide display scheme based on the coupling-collimation system is proposed. This system consists of a freeform liquid crystal diffractive optical element on the waveguide and a freeform element outside the waveguide, replacing the conventional in-coupler and collimator. Through the overall optimization of the coupling-collimation system, a wide-field-of-view and high-resolution waveguide display can be realized with a simple and compact structure. We demonstrate the effectiveness and superiority of this scheme by exemplifying several design results. The proposed scheme is expected to facilitate the design of waveguide displays with higher performance.

Compensated DOE in a VHG-based waveguide display to improve uniformity

Augmented reality head-mounted displays (AR-HMDs) utilizing diffractive waveguides have emerged as a popular research focus. However, the illuminance uniformity over the fields of view (FOV) is often unsatisfactory in volume holographic grating (VHG) based waveguide displays. This paper proposes a high uniformity AR waveguide display system. Firstly, the angular uniformity of the VHG-based waveguide displays is analyzed. Subsequently, diffractive optical elements (DOEs) are seamlessly integrated onto the outer coupling surface of the waveguide substrate to improve the angular uniformity through phase compensation. To design the DOE phase, the multi-objective stochastic gradient descent (MO-SGD) algorithm is proposed. A single DOE is used to compensating various images form the image source. A hybrid loss, which includes the learned perceptual image patch similarity (LPIPS) metric, is applied to enhance the algorithm performance. Simulation results show that the proposed method effectively suppresses illumination degradation at the edge FOV in exit pupil images of the waveguide display system. In the results, the peak signal-to-noise ratio (PSNR) is improved by 5.54 dB. Optical experiments validate the effectiveness of the proposed method. The measured nonuniformity (NU) against FOVs is improved by 53.05% from 0.3749 to 0.1760.

P‐4.25: AR Waveguide Display with Enlarged Eyebox Based on Polarization Volume Gratings

P‐4.25: AR Waveguide Display with Enlarged Eyebox Based on Polarization Volume Gratings

14‐2: Research Progresses and Challenges for Polarization Volume Gratings Based Waveguide Display

14‐2: Research Progresses and Challenges for Polarization Volume Gratings Based Waveguide Display

Angular uniformity improvement of diffractive waveguide display based on region geometry optimization.

Augmented reality (AR) near-eye displays have significantly progressed due to advances in nanostructure fabrication. However, for diffractive waveguide AR displays requiring exit pupil expansion, the angular uniformity of each exit pupil position still needs to improve. In this paper, an angular uniformity improvement method based on region geometry optimization is proposed. This optimization method essentially introduces the interaction number of the light with the grating as one of the variables to manipulate the energy distribution. This distribution is obtained by the rigorous coupled wave analysis (RCWA) method and ray tracing process and is further optimized by a multi-objective genetic algorithm. A model is built, and the feasibility of the proposed method is verified. The diffractive waveguide system has a 10m m×10m m exit pupil size at the eye relief of 25mm and a field of view (FOV) of 21∘×12∘. After the optimization, the overall optical efficiency of the central field and the angular uniformity at the center exit pupil position increased from 0.9% and 66% to 3.1% and 80%, respectively.

Genetic-algorithm-based waveguide display system with a multiplexed volume holographic grating.

Most of the current holographic waveguide display systems are designed based on the center beam. When the incident beam consists of rays with different angles, the field of view and optical efficiency would greatly reduce. The heavy angular dependence of the volume holographic grating (VHG) and the back-coupling loss are two main reasons. This paper proposes a design method of the waveguide display system with multiplexed VHG, which is based on a genetic algorithm to optimize and calculate the parameters both of the VHG and the waveguide. The simulation results show that the diagonal field of view of the holographic waveguide system is increased to 28°, and its optical efficiency is improved by 30%. The design method of the waveguide system with the multiplexed grating proposed in this paper can effectively expand the field of view and improve the optical efficiency.

Accommodation-capable holographic waveguide head-up display with extended field of view

Augmented reality (AR) displays are enhancing user experiences by offering immersive three- dimensional (3D) content, with head-up display (HUD) being a prime application for driving safety. To enable AR-HUDs to provide sufficient information to driver, it is essential to ensure a wide field of view (FOV). Traditional methods like the magnifier principle have limitations stemming from optical aberrations and bulky form factor. Recently, optical waveguide has been used as pupil expander, which has attracted increasing attention as an optical element for compact form factor and exit-pupil expansion. However, waveguide display as exit-pupil expander only offer 2D images with infinite depth, causing mismatch issue between virtual content and real scenes. In this paper, we propose a lensless holographic waveguide display consisting of a laser light source, a spatial light modulator (SLM), a waveguide to generate accommodation-capable images, effectively extending FOV. The key distinction of this research lies in the optical design of the waveguide, which defines multiple shifted copies of the modulated wavefield as replicated virtual SLMs. A formalized algorithm is devised based on a bold assumption that numerous virtual SLMs replicated by a waveguide are considered as a single ultra-high resolution SLM. The effectiveness of the algorithm has been demonstrated through extensive validation through numerical observation simulations and optical experiments. Notably, optical experiments convincingly demonstrate the system’s ability to produce accommodation-capable true 3D content, with a four-fold extension of FOV compared to a single SLM at an observation distance of 150 mm. Additional optical experiments highlight the successful integration of AR technology, an important component for automotive HUD.

Design optimization of polarization volume gratings for full‐color waveguide‐based augmented reality displays

AbstractReflective polarization volume gratings (PVGs) can be used as input and output couplers in a diffractive waveguide‐based augmented reality (AR). To improve the stability and wearing comfort, a thin and lightweight full‐color waveguide display is needed. In this paper, we propose a single full‐color waveguide AR display based on PVGs. By analyzing the optical system, we derived the field of view limit by optimizing a three‐layer PVG as an in‐coupler. Pairing with a single‐layer, thin PVG as an out‐coupler, we can achieve a relatively uniform exit pupil of 8 mm at horizontal pupil expansion direction.

Single-image-source binocular waveguide display based on polarization volume gratings and lenses.

Waveguide displays, a highly competitive solution for augmented reality (AR), have attracted a lot of interest. A polarization-dependent binocular waveguide display using polarization volume lenses (PVLs) and polarization volume gratings (PVGs) as input and output couplers, respectively, is proposed. Light from a single image source is delivered to the left and right eyes independently according to its polarization state. Compared with traditional waveguide display systems, no additional collimation system is needed due to the deflection and collimation capabilities of PVLs. Leveraging the high efficiency, wide angular bandwidth, and polarization selectivity of liquid crystal elements, different images can be independently and accurately produced in the two eyes when the polarization of the image source is modulated. The proposed design paves the way for a compact and lightweight binocular AR near-eye display.

40.3: Polarization‐dependent Binocular Waveguide Display with Patterned Cholesteric Liquid Crystal Optics

We demonstrate a polarization-dependent binocular waveguide display for augmented reality. Two polarization volume lenses (PVLs) are used to collimate and couple the light emitted from a single display panel into the waveguide, and two polarization volume gratings (PVGs) are used to couple the light out to the human eyes. With the proposed design, different high-quality images can be independently produced in the two eyes.

The Projection Lens Design for Holographic Waveguide Display with One-dimensional Exit Pupil Expansion

The Projection Lens Design for Holographic Waveguide Display with One-dimensional Exit Pupil Expansion

Quantitative analysis on self-focusing properties of H-PDLC flexible curved radius gratings.

In general, the shape of traditional holographic grating is fixed and immutable, the period will not change after fabrication, this means that the modulation effect on the light field is unalterable. However, traditional grating cannot satisfy all requirements of current optical systems. In order to increase the versatility of holographic grating, a flexible curved radius grating (FCRG) which consists of holographic polymer-dispersed liquid crystal (H-PDLC) was proposed. The FCRG has an important self-focusing property that it can be adjusted the focal length by changing its own radius of curvature correspondingly. In this paper, we use the scalar diffraction theory to analysis the interference and diffraction processes for FCRG under different conditions, then a relationship equation has been deduced to express quantitatively about FCRG between its radius and focal length. According to the relationship, a tunable holographic element is achieved for the function of mechanically-controlled self-focusing effect. Experiments show that the FCRG has two conjugated focusing effects on the positive first-order and negative first-order, both two effects can achieve focus-adjusted ability by changing their radius of curvature. The FCRG provides a way for the coupler of curved waveguide display system for augmented reality in the future.

P‐2.7: Optimization of Field of View in a Full‐color Waveguide Display Based on Polarization Volume Grating

We propose a PVG-based bandwidth composite structure, explore the multi-period formation method and bandwidth expansion characteristics of the composite grating, and study different color waveguide display schemes. We analyzed the advantages and disadvantages of full-color waveguide displays with one-, two- and three-layer waveguides. Finally, based on the grating bandwidth composite structure, a two-layer waveguide is designed and fabricated to achieve full-color near-eye display. The display effect is shown on the AR display prototype. The demonstrated waveguide system is a full-color display with a diagonal field of view of about 50�. The brightness is as high as 242 cd/m2 per lumen with a transparency of 75% for ambient light. This work shows the good application prospect of PVG coupler in augmented reality color display.

15.4: Holographic Waveguide Display with Large Field of View Based on Volume Holographic Grating

The field of view of waveguide display systems based on volume holographic gratings is often limited by the grating diffraction response bandwidth, which still cannot meet people's needs for large field of view displays. In order to expand the viewing angle of the waveguide display, the influencing factors of the viewing angle of the waveguide display are analyzed based on the strictly coupled wave theory model, and a double‐layer volume grating waveguide structure that can effectively expand the diffraction response bandwidth is proposed. The grating is prepared by the variable‐angle fractional exposure method, and the holographic waveguide display system is built. The results show that the horizontal and vertical viewing angles of the display system can be expanded to 33° and 22°, respectively, and the diagonal viewing angle is 40°.

15.2: Design and Realization of Full‐Color VHG Holographic Waveguide Display

To realize the chromatic display function of VHG holographic waveguide display system, we firstly study the preparation process and holographic peformance of color‐sensitive acrylate based photopolymer. Based on the prepared photopolymer, we fabricated the RGB holographic waveguide device with the multiwavelength laser exposure method. Thus, for verifying the display function of the prepared device , the chromatic holographic waveguide near‐eye display module using the LCoS projector engine was developed. The application potential of the color‐sensitive photopolymer in holographic waveguide was also demonstrated.

Subwavelength dielectric grating structures with tunable higher order resonance for achromatic augmented reality display.

Color non-uniformities caused by a dispersion effect can seriously affect the image quality for a diffractive waveguide display system. In this work, we propose a subwavelength multilayered dielectric grating structure by a rigorous coupled wave analysis as a novel coupling grating, to the best of our knowledge, for waveguide-based near-eye displays to overcome the "rainbow" effect. Such a grating structure exhibits a tunable high-efficiency resonance in first-order diffraction due to resonant coupling of incident light with the grating structure. A further analysis of the resonant behaviors helps us get a clear understanding of the underlying physics for the mode excitation and resonant coupling process. The first-order resonance with a diffraction efficiency of more than 60% can be achieved with the resonant angle continuously shifted to get a large field of view. The resonant angle, diffraction efficiency, and spectral linewidth can be easily tuned by the geometrical parameters of the grating structure.

Uniformity improvement of two-dimensional surface relief grating waveguide display using particle swarm optimization.

Augmented reality head-mounted displays (AR-HMDs) based on diffractive waveguides have been a challenging and rewarding research topic focusing on near-eye displays. The size of the exit pupil and uniformity of the image illuminance are two important factors that affect the display performance of the diffractive waveguide. In this paper, a novel method for optimizing high uniformity of two-dimensional (2D) diffractive waveguide is proposed. A straight-line 2D surface relief grating (SRG) waveguide with divided grating regions is designed. An illuminance uniformity evaluation model of the energy propagation process is established, and non-sequential ray tracing is utilized to optimize the diffraction efficiency of multi-regions grating to achieve illuminance uniformity distribution. Then, the uniformity distribution of the diffraction efficiency in different fields of view (FOVs) is realized by combining the particle swarm optimization (PSO) algorithm and rigorous couple wave analysis (RCWA) to optimize the grating structural parameters, which further ensures the uniformity of the exit pupil illuminance and angular illuminance. The waveguide with exit pupil expansion (EPE) has exit pupil size of 16 mm × 14 mm at an eye relief (ERF) of 20 mm, exit pupil illuminance uniformity of 91%, and angular uniformity illuminance of 64%.

Realizing the imaging simulation of reflective polarization volume gratings.

Near-eye holographic waveguide display system using novel reflective polarized volume gratings (RPVG) have lately gotten a lot of interest. However, from polarization characteristics to imaging simulation, there is no systematic approach based on RPVG. Here, a full methodology for solving this problem using the rigorous coupled wave analysis (RCWA) model is presented. This self-built RCWA model is used to examine the optical behavior of RPVG. This excellent portability of the RCWA model makes it possible for RPVG as a diffractive optical element, which is integrated into the commercial optical software Zemax via a self-compiled dynamic link library (DLL), and a full-color imaging simulation of the based-RPVG waveguide display system is obtained. Our work provides an instructive imaging analysis method using the RPVG for holographic waveguide display.

Image quality enhancement of transparent waveguide display using a twisted nematic mode polymer-stabilized liquid crystal.

In this study, a twisted nematic mode polymer-stabilized liquid crystal (TN mode PSLC) integrated with a crossed polarizer was used to create a transparent waveguide display. When a voltage was applied, the PSLC scattered the waveguide light with a high polarization selectivity such that no substantial loss of the outgoing light intensity was observed after integrating the polarizer. However, with a crossed polarizer, in the ON state, the background light was not only scattered but also absorbed by the analyzer. Using this device configuration, with a 12 µm cell gap and 7% monomer concentration, we successfully realized a normally transparent waveguide display. The contrast ratio of the waveguide outgoing light was 26 and that of the undesired background reached 90. This device can display images due to waveguide edge-lit light scattering and simultaneously block the background information to improve the image quality.