This paper introduces an innovative approach to integral volumetric imaging employing time and polarization multiplexing techniques to present volumetric three-dimensional images. Traditional integral volumetric imaging systems with a coarse lens array often face moiré pattern issues stemming from layered panel structures. In response, our proposed system utilizes a combination of time and polarization multiplexing to achieve two focal planes using a single display panel.
A new folded optical system with an enhanced efficiency using two polarization‐selective cholesteric liquid crystal reflectors is proposed. In conventional pancake optics, the optical path length is tripled but its efficiency drops to 25%. Our new configuration provides 50% efficiency, while the optical path length is doubled.
Liquid crystal Pacharatnam-Berry phase optical elements (PBOEs) have found promising applications in augmented reality and virtual reality because of their slim formfactor, lightweight, and high optical efficiency. However, chromatic aberration remains a serious longstanding problem for diffractive optics, hindering their broader adoption. To overcome the chromatic aberrations for red, green and blue (RGB) light sources, in this paper, we propose a counterintuitive multi-twist structure to achieve narrowband PBOEs without crosstalk, which plays a vital role to eliminate the chromatic aberration. The performance of our designed and fabricated narrowband Pacharatnam-Berry lenses (PBLs) aligns well with our simulation results. Furthermore, in a feasibility demonstration experiment using a laser projector, our proposed PBL system indeed exhibits a diminished chromatic aberration as compared to a broadband PBL. Additionally, polarization raytracing is implemented to demonstrate the versatility of the multi-twist structure for designing any RGB wavelengths with high contrast ratios. This analysis explores the feasibility of using RGB laser lines and quantum dot light-emitting diodes. Overall, our approach enables high optical efficiency, low fabrication complexity, and high degree of design freedom to accommodate any liquid crystal material and RGB light sources, holding immense potential for widespread applications of achromatic PBOEs.
In lightweight augmented reality (AR) glasses, the light engines must be very compact while keeping a high optical efficiency to enable longtime comfortable wearing and high ambient contrast ratio. "Liquid-crystal-on-silicon (LCoS) or micro-LED, who wins?" is recently a heated debate question. Conventional LCoS system is facing tremendous challenges due to its bulky illumination systems; it often incorporates a bulky polarizing beam splitter (PBS) cube. To minimize the formfactor of an LCoS system, here we demonstrate an ultracompact illumination system consisting of an in-coupling prism, and a light guide plate with multiple parallelepiped extraction prisms. The overall module volume including the illumination optics and an LCoS panel (4.4-μm pixel pitch and 1024x1024 resolution elements), but excluding the projection optics, is merely 0.25 cc (cm3). Yet, our system exhibits an excellent illuminance uniformity and an impressive optical efficiency (36%–41% for a polarized input light). Such an ultracompact and high-efficiency LCoS illumination system is expected to revolutionize the next-generation AR glasses.
We demonstrate a foveated AR display based on a single microdisplay light engine by using a temporal polarization multiplexing method, enabled by two polarization selective flat cholesteric liquid crystal lenses. The angular resolution of the foveal view is enhanced by 3.12x while maintaining a compact formfactor.
Abstract Pancake lens has been widely used in virtual reality (VR) and mixed reality (MR) due to its compact form factor. However, using a half mirror (HM) to fold the optical path results in a tremendous optical loss. To enhance the optical efficiency while keeping a compact form factor, we present a new folded optical system incorporating a nonreciprocal polarization rotator. In our proof‐of‐concept experiment using a commercial Faraday rotator (FR), the theoretically predicted 100% efficiency is validated. Besides, the angular response of terbium gallium garnet (TGG) material is simulated for the first time and the results indicate that such an FR is relatively insensitive to the incident angle, which can dramatically enhance the contrast ratio of our pancake design. Finally, the potential application of such pancake optics for ultracompact near‐infrared (NIR) night vision goggles is also discussed.
Abstract Augmented reality (AR) displays, as the next generation platform for spatial computing and digital twins, enable users to view digital images superimposed on real-world environment, fostering a deeper level of human-digital interactions. However, as a critical element in an AR system, optical combiners face unprecedented challenges to match the exceptional performance requirements of human vision system while keeping the headset ultracompact and lightweight. After decades of extensive device and material research efforts, and heavy investment in manufacturing technologies, several promising waveguide combiners have been developed. In this review paper, we focus on the perspectives and challenges of optical waveguide combiners for AR displays. We will begin by introducing the basic device structures and operation principles of different AR architectures, and then delve into different waveguide combiners, including geometric and diffractive waveguide combiners. Some commonly used in-couplers and out-couplers, such as prisms, mirrors, surface relief gratings, volume holographic gratings, polarization volume gratings, and metasurface-based couplers, will be discussed, and their properties analyzed in detail. Additionally, we will explore recent advances in waveguide combiner design and modeling, such as exit pupil expansion, wide field of view, geometric architectures of waveguide couplers, full-color propagation, and brightness and color uniformity optimization. Finally, we will discuss the bottlenecks and future development trends in waveguide combiner technologies. The objective of this review is to provide a comprehensive overview of the current state of waveguide combiner technologies, analyze their pros and cons, and then present the future challenges of AR displays.
We present a novel design for a full-color, wide Field-of-View (FoV) Augmented Reality (AR) display, which ingeniously employs a single waveguide along with advanced polarization multiplexing reflective polarization holograms. This innovative approach surmounts the narrow FoV limitation of the present single-waveguide, full-color AR displays. The employed reflective polarization holograms are devised to operate with high efficiency across the entire visible spectrum, accommodating the incident angles required by the expanded FoV. This novel design represents a significant leap forward in AR technology, laying a foundation for immersive and vivid AR experiences.
We present a novel design for a full-color, wide Field-of-View (FoV) Augmented Reality (AR) display, which ingeniously employs a single waveguide along with advanced polarization multiplexing reflective polarization holograms. This innovative approach surmounts the narrow FoV limitation of the present single-waveguide, full-color AR displays. The employed reflective polarization holograms are devised to operate with high efficiency across the entire visible spectrum, accommodating the incident angles required by the expanded FoV. This novel design represents a significant leap forward in AR technology, laying a foundation for immersive and vivid AR experiences.
A catadioptric lens structure, also known as pancake lens, has been widely used in virtual reality (VR) displays to reduce the formfactor. However, the utilization of a half mirror (HM) to fold the optical path thrice leads to a significant optical loss. The theoretical maximum optical efficiency is merely 25%. To transcend this optical efficiency constraint while retaining the foldable characteristic inherent to traditional pancake optics, in this paper, we propose a theoretically lossless folded optical system to replace the HM with a nonreciprocal polarization rotator. In our feasibility demonstration experiment, we used a commercial Faraday rotator (FR) and reflective polarizers to replace the lossy HM. The theoretically predicted 100% efficiency can be achieved approximately by using two high-extinction-ratio reflective polarizers. In addition, we evaluated the ghost images using a micro-OLED panel in our imaging system. Indeed, the ghost images can be suppressed to undetectable level if the optics are with antireflection coating. Our novel pancake optical system holds great potential for revolutionizing next-generation VR displays with lightweight, compact formfactor, and low power consumption.
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