Recent Technological Advancements in Color Sequential Front-Lit LCOS for AR Displays

Liquid crystal on silicon (LCOS) is a promising imager for augmented reality (AR) displays due to its high resolution and high brightness. In addition, because the LCOS projection system is an étendue-matching system, transmission losses in AR displays can be minimized. However, such systems typically require a polarization beam splitter (PBS), which makes the projector too bulky for AR applications. Several approaches have been proposed to reduce projector size(1) using a single PBS to sharethe optical path forlight source coupling,polarization conversionand LCOS imaging; or (2) adopting an off-axis projection design to eliminate the PBS. To date, the smallest reported projector has a volume of approximately 0.7 cc, based on a 0.14”color-sequential LCOS.In this work, we propose an alternative approach in which the PBS is replaced by a polarization-sensitive lightguide (LG). Such device is so calledcolor sequential front-lit LCOS. Recently, the micro-mirrorarrayin the LG has been optimized to enable bidirectional light input, resulting in a 1.6ximprovement in efficiency. Experimental measurements show that the proposed color sequential front-lit LCOS can deliver up to 1 lm, corresponding to 350 kcd/m² at 100% average picture level (APL), under 200 mW LED input power. Leveraging this new component, the volume of a 0.17-inch color sequential front-lit LCOS with a resolution of 720x720 is reduced to 0.09 cc. The total volume and weight of the corresponding 30° field-of-view (FOV) projector, including the collimator, are less than 0.34 cc and 0.79 g, respectively.AnANSI contrast ratio of 40:1 and a 140% sRGB color gamut are achieved, and it is expected that the contrast ratio can be improved by a factor of 2–3 through content-adaptive brightness control or zonal lighting techniques. Furthermore, to minimize transmission losses in AR display systems, the emission cone of the color sequential front-lit LCOS is limited to ±14.5°.

These results demonstrate that the newly proposedcolor sequentialfront-lit LCOS architecture offers a compelling combination of compactness, efficiency, and optical performance, making it a strong imager candidate forAR displays.

用于AR显示的时序型彩色自发光LCOS技术最新进展

硅基液晶(LCOS)因其高解析度和高亮度而成为增强现实(AR)显示中的一种极具潜力的成像器件。此外，由于LCOS投影系统属于光展度(étendue)匹配系统，AR显示中的传输损耗可以被有效降低。然而，此类系统通常需要使用偏振分光棱镜(PBS)，这使得投影模组体积过大，不利于AR应用。为缩小投影模组尺寸，业界已提出多种解决方案，例如(1)采用单个PBS实现共用光源耦合、偏振转换以及LCOS成像的光路；或(2)通过离轴投影设计以消除PBS。截至目前，已报道的设计基于0.14”彩色时序LCOS技术的最小投影模组体积约为0.7c.c。

本研究提出一种“时序型彩色自发光LCOS”的创新型结构：核心是以偏振敏感光波导(LG)替代传统PBS。其中该光波导中的微镜阵列结构经过优化，实现了双向光输入，使光效率提升1.6倍。实验测量表明，在200mW LED输入功率下，时序型彩色自发光LCOS对应100%平均图像等级(APL)可实现高达35万尼特(nits)的亮度与1流明(lm)输出。基于这一新型元件，0.17”、解析度为720X720的时序型彩色自发光LCOS体积可缩减至0.09c.c.。在包含30°视野角(FOV)投影镜头在内的投影模组体积仅0.34c.c.、重量只有0.79公克。该系统亦实现了140% sRGB色域，及40:1的ANSI对比度。预计通过引入内容自适应亮度控制或分区照明方案，其对比度还可提升2-3倍。同时为降低AR显示系统的传输损耗，时序型彩色自发光LCOS将发光锥角限制在±14.5°范围内。

此研究结果表明，新提出的时序型彩色自发光LCOS架构在紧凑性、光效与光学性能方面实现了卓越平衡，为AR显示系统提供了极具竞争力的成像解决方案。