In this paper, we develop a precise simulation platform to investigate the effects of lightguide geometry when integrated with volume holographic optical elements (VHOEs). The simulation is based on practical optical parameters and physical configurations. Distortion in the viewed image along the horizontal field of view (HFOV) is attributed to inappropriate lightguide thickness; a thicker lightguide can result in a broken or discontinuous HFOV. Similarly, distortion in the vertical field of view (VFOV) arises from excessive lightguide length, leading to noticeable VFOV shrinkage. Furthermore, VFOV distortion may vary between the left and right sides of a single image due to differences in the effective propagation distance within the lightguide. The simulated distortions in both HFOV and VFOV show strong agreement with experimental results. In addition, all the lightguide effects are theoretically clarified. This detailed analysis offers valuable insights for optimizing lightguide design and contributes to the advancement of HUD and near-eye display technologies with see-through functionality.

This paper proposes an optimized spectrum distribution of the input image to significantly enhance the optical efficiency of volume holographic optical element (VHOE)-based lightguides with exit pupil expansion (EPE). VHOEs-based lightguides can suppress the eye-glow effect and use multiplexing to expand field of view (FOV) with good color performance. Along with the demonstration of good image quality, it makes VHOEs one of the best choices for couplers of EPE lightguide. This method utilizes the Model named "Volume Hologram being an Integrator of the Lights Emitted from Elementary Light Sources (VOHIL)" to derive an analytical solution for the wavelength-angular degeneracy properties of VHOEs, enabling the authors to calculate the peak wavelength distribution that passes through the lightguide. To prove the concept, by meticulously controlling the wavelength distribution and the full width at half maximum of the input light spectrum with a dispersion holographic optical element, a remarkable increase in efficiency is achieved. This approach yields an optical efficiency of 9% for the lightguide with a 30 degrees FOV, representing a 5.63-fold improvement over conventional VHOE-based EPE lightguides. It is three times better than the best record of published efficiency in SRG-based EPE lightguides. This breakthrough has significant potential for advancing the development of high-performance, user-friendly near-eye glasses.

Angle multiplexing is a crucial technique for volume holographic gratings in grating-based lightguide display systems, enabling an extended image field of view (FOV). However, Bragg mismatch diffraction caused by different angle-multiplexed gratings introduces crosstalk, leading to ghost images. In this paper, we analyze the underlying causes of ghost image formation due to angle-multiplexed gratings and propose an optimized recording method to minimize crosstalk noise. Our approach ensures that each recorded volume grating generates a uniform grating vector across the surface of the holographic film, resulting in consistent grating periods among all angle-multiplexed gratings. This uniformity corrects the diffraction angles of crosstalk, aligning them with the original signal diffraction angle and effectively suppressing ghost images.

A diffractive-based lightguide AR/MR glasses system incorporating volume holographic optical elements (VHOEs) is presented. Compared to surface-relief gratings (SRGs), VHOEs offer greater fabrication flexibility, simplified processing, and the ability to suppress backward diffraction (eyeglow). However, the inherent Bragg selectivity of VHOEs limits the achievable field of view (FOV) and color uniformity. In this paper, the design enables a see-through, full-color image with a 50 degrees field of view (FOV). To achieve this, the VHOEs are divided into two groups: one for smaller diffraction angles and the other for larger diffraction angles. Two glass substrates are used to guide the images from these groups. Holographic multiplexing is employed to achieve a 50 degrees FOV for red, green, and blue images. By incorporating the dispersive Bragg condition of the VHOE, wavelength multiplexing is applied to both the in-coupling and out-coupling VHOEs to enable a full-color display. However, this also introduces color dispersion, leading to non-uniform color appearance. To mitigate this issue, an advanced optimization of the illumination spectrum is proposed, enhancing color uniformity. This technology relies purely on optical management and holds significant potential for achieving uniform color appearance in lightguide displays utilizing VHOEs.

In this paper, we present an enhanced approach‐a drive signal management scheme employed on a micro‐display device of optical engine to retune the color uniformity of an Augmented Reality (AR) eyewear display with a the Volume Holographic Optical Elements (VHOEs)‐based waveguide. Our method streamlines multiplexing complexity, necessitating just one optical waveguide and three RGB gratings to attain a full‐color eyewear display with nearly a 16° horizontal field of view (FOV) and less than 3% ΔELab color non‐uniformity.

As augmented reality (AR) glasses technology evolves, volume holographic diffractive waveguide designs are increasingly adopted to enhance portability and performance. Traditionally, these systems require separate geometric and wave optics approaches to handle ray propagation and holographic element diffraction, adding significant complexity to the design process. This study presents an innovative pure ray tracing simulation method that integrates geometric and wave optics seamlessly. By incorporating Kogelnik's coupled wave theory, our model accurately predicts the diffraction behavior of volume holographic optical elements (VHOEs) and converts this information into ray data for tracing, enabling exact AR imaging simulations. Applied to the design of volume holographic waveguide AR glasses, human vision simulations, and experiments validated this method's reliability, demonstrating its versatility and effectiveness. This model improves design efficiency and promotes innovative advancements in cross-theoretical optical system design, positioning it as a crucial tool for future AR glasses development. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

SUMMARYIn this paper, we delve into the distinctive color characteristics resulting from color dispersion in SRG and wavelength degeneracy in VHOE, exploring their application in a diffractive light guide for near-eye glasses. The assessment of color performance involves three gratings that cover red, green, and blue light, respectively. With a laser-like spectrum emanating from the display panel, the color gamut achieves an impressive 194% sRGB. However, this narrow-band spectrum proves unsuitable for a VHOE light guide. In contrast, a broad-band spectrum, such as that generated by an LED, results in a common color gamut of 133% sRGB for an SRG light guide and 130% sRGB for a VHOE light guide in the presence of two multiplexed holograms. This innovative approach elucidates the color performance of diffractive light guides like SRG and VHOE, affirming their suitability for crafting high-quality near-eye glasses.

In this paper, we will discuss about the color performance and image quality of the Volume-Holographic-Optical-Element (VHOE)-based AR devices using two different type of volume holograms: transmission or reflection-type VHOEs. The simulation results show that color distortion occurring in these two types of VHOE-based AR devices are quite different and resulting from different characteristics of Bragg diffraction from those VHOEs. The reflective VHOE-based AR devices show better overall performance in terms of color, field of view and image quality.

This paper explores the diffraction region between thin and thick holograms, commonly referred to as the transition region. The VOHIL model is used to assess the internal interference conditions along a specified diffraction direction. We examine the maximum phase difference between the two endpoints of the hologram for both the +1st-order and -1st-order diffractions through internal interference. This analysis leads to a criterion that aligns with the Klein parameter. Additionally, a new parameter, the de-phase factor, is introduced to assess the feasibility of diffraction along a chosen direction from a whole-field perspective. The variation of the de-phase factor in the -1st-order diffraction is slower compared to other directions, except for the +1st-order diffraction, owing to the natural existence of the -1st-order diffraction at every tiny hologram unit. The primary way to stop the -1st-order diffraction is by adjusting the thickness if the incident angle is fixed. Thus, examining the -1st-order diffraction is an effective way to check if a hologram is under the Bragg condition. Although rigorous simulation methods, such as rigorous coupled-wave analysis, can provide more precise results, the proposed analysis scheme, based on the VOHIL model, offers valuable physical insights into these characteristics.

In this paper, we introduce an approach to precisely adjust the color uniformity of an Volume-Holographic-Device (VHOE) based Augmented Reality (AR) eyewear display by multiplexing volume gratings in the coupling device plus drive signal management scheme implemented on a micro-display panel of an optical engine. Our approach can simplify the complexity of optical configuration, requiring only a single optical waveguide plus two VHOEs which contains three RGB gratings in each for coupling-in and -out device to achieve a full-color eyewear display with an expansive horizontal field of view (FOV) of nearly 30 degrees and less than 3% Delta E-Lab color non-uniformity.

We delve into the distinctive color gamut characteristics resulting from color dispersion of surface relief grating (SRG) and wavelength degeneracy of volume holographic optical element (VHOE) in a diffractive light guide. While a laser-like spectrum achieves an impressive 194% sRGB color gamut for both cases, it proves unsuitable for VHOE light guides due to limitations in breaking the field of view (FOV) of the display. Conversely, a broad-band light source, such as LEDs, offers continuous FOV but reduces the common color gamut to 50% sRGB. We then present a newly designed VHOE light guide capable of achieving the common color gamut of 130% sRGB using two multiplexed holograms of each color, closely matching the 133% sRGB achieved by an SRG light guide. This article presents the first theoretical methodology to elucidate color performance of diffractive light guides utilizing VHOEs with holographic multiplexing, affirming their suitability for crafting high-quality near-eye display.

A projection lens with a 30-degree field of view is developed for use in augmented reality (AR) glasses, including a waveguide combiner designed for a 0.35-inch LCoS panel. The entrance pupil diameter of the lens is 14 mm and the lens has an effective focal length of 16.443 mm; an F-number of 1.175. This paper has four key issues: optical projection lens design, lens manufacturing and assembly tolerance analysis, projection lens resolution testing, and AR glasses system resolution testing of panel images projected by the projection lens. After lens manufacture, the lens was tested, achieving a central field image quality of 57 cycles/mm, an angular resolution of 33 pixels per degree (PPD), a 0.7 field image quality of 40.3 cycles/mm, and an angular resolution of 23 pixels per degree (PPD). Imaging performance testing based on a diffraction-type waveguide shows a resolution of 57 cycles/mm in the center area and an angular resolution of 33 PPD.

In this study, we propose a novel high-concentration photovoltaic (HCPV) cell by considering both the light leakage characteristics of the Fresnel-lens-based solar cell modules and the performance issues arising from cloud shading in practical use. We use our self-constructed systems to conduct field measurements for up to half a year under various environmental conditions. According to the acquired results, it was surprising to know that in the area other than the focusing area, the so-called light leakage region, there always bears illuminance of about 20,000–40,000 lx whether it is a sunny day or a cloudy day with different cloud conditions. Such an interesting result is caused by the light scattering of the clouds and the inherent leakage characteristic of a Fresnel lens. To prove this important finding, we simulated the illuminance of the Fresnel lens structure used in the measurement with apertures of different sizes to determine the detected area. In the laboratory, the diffuse plates were used to mimic the situation of varying cloud layer thicknesses. The trend of calculated and measured results fitted well with the field measurements. Also, the experimental and simulation results show that the round angle and draft facet of the Fresnel lens were responsible for light leakage. This finding prompted us to propose a hybrid high-concentration solar module in which more cost-effective polycrystalline silicon solar cells are placed around the high-efficiency wafer of HCPV to capture the dissipated light leakage and convert it into usable electricity.