Breaking the optical efficiency limit of virtual reality with a nonreciprocal polarization rotator

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.