偏振光复用的液晶体光栅波导AR近眼显示系统

Polarized light multiplexing liquid crystal grating waveguide for AR near-eye display systems

光波导组合器在增强现实显示的出瞳扩展和外观薄化方面颇具优势。出瞳扩展技术是通过在耦出区域诱导多次衍射,将光线引导至人眼。然而,这种多次衍射可能导致出瞳亮度在沿光路径的空间分布上逐渐减弱,从而造成亮度不均。特别是当使用液晶制备而成的偏振体全息光栅作为耦合元件时,由于光栅仅对一种圆偏振光敏感,与之正交的圆偏振光会被直接透射,导致波导系统的能量利用率并不高。针对这一挑战,本文提出了一种实现左旋和右旋圆偏振光复用的偏振体全息光栅光波导AR显示光学系统,同时实现了大出瞳尺寸和良好入眼均匀性。在理论设计和仿真方面,首先通过k空间理论设计了大视场角下的光栅结构,再以微型发光二极管(Micro-LED,μLED)作为微显示屏,设计了一套与之匹配的投影镜头,并对整个波导系统进行了成像仿真。在实验部分,制备了中心波长为532 nm、出瞳尺寸为45 mm×25 mm的偏振体全息光栅波导。实验结果显示,该波导系统在基板折射率为1.51下的对角线视场角达到了预期的32.86°。相比于仅响应单一圆偏振光的方案,采用九点法测得的均匀性提升了48.8%,整体均匀性提升了34.1%,波导组合器的光学效率也实现了1.2倍的提升。本文工作为偏振体全息光栅波导的设计提供了宝贵的指导和参考。

The thin optical waveguide combiner is responsible for pupil expansion of augmented reality(AR)displays.The exit pupil guides the display information into human eyes by inducing multiple diffractions from the coupling region with extension.However,this multiple diffraction may lead to the gradual weakening of exit pupil brightness along the spatial distribution of the light path,resulting in uneven brightness.In particular,when the coupling elements are fabricated by liquid crystal polarization volume grating(LCPVG),which is only sensitive to a kind of circularly polarized light according to the Bragg grating property,the orthogonal circularly polarized light will be directly transmitted,wasting the rest of display information.To address this issue,this paper proposes an optical waveguide AR display system based on LCPVG,which provides the left-handed and right-handed circular polarization light multiplexing,achieving large pupil area with good uniformity.The LCPVG is designed in the k-space to achieve the maximum field of view with the diffraction wavelength of 532 nm,combining the microdisplay unit which consists of a micro-LED(μLED)display with a set of matching projection lenses,providing the exit pupil size of 45 mm×25 mm.The experimental results show that the diagonal field of view of the waveguide system reaches the expected 32.86°with the substrate refractive index of 1.51.Compared with the scheme that only responds to a single circular polarized light,the uniformity measured by the nine-point method is increased by 48.8%,the overall uniformity is increased by 34.1%,and the optical efficiency of the waveguide combiner is also improved by 1.2 times.This work provides valuable guidance and reference for the design of polarization volume grating waveguides for AR display systems.