Optimizing microdisplay requirements for pancake VR applications

• Published in: Journal of the Society for Information Display Vol. 31; no. 5; pp. 264 - 273
• Main Authors: Hsiang, En‐Lin, Yang, Zhiyong, Wu, Shin‐Tson
• Format: Journal Article
• Language: English
• Published: Campbell Wiley Subscription Services, Inc 01.05.2023
• Subjects: Density; Dimming; Dynamic range; high‐resolution density; Image degradation; Light emitting diodes; microdisplays; pancake lens; Virtual reality; virtual reality displays; Vision systems; Visual acuity
• ISSN: 1071-0922; 1938-3657
• DOI: 10.1002/jsid.1199

Virtual reality (VR) devices use imaging optics to magnify the microdisplay images for providing an immersive viewing experience. A microdisplay is preferred to have high‐resolution density and high dynamic range to meet the demanding requirements of human vision system (HVS), for example, visual acuity >60 pixels per degree and grayscale depth >10 bits. However, increasing resolution density and dynamic range often lead to a reduced optical efficiency and sophisticated fabrication process of the microdisplay panels. In this paper, we systematically analyze the image degradation mechanisms of VR devices caused by both imaging optics and microdisplay and find that the image degradation caused by imaging optics significantly unleash the requirements of microdisplay, such as contrast ratio, number of local dimming zones, and resolution density. For example, aberrations of the imaging optics reduce the resolution density requirement of the microdisplay, and stray light of the imaging optics relieves the contrast ratio requirement of the microdisplay. These results help prevent excessive design of microdisplay, for example, mini‐light‐emitting diode (LED) backlit liquid‐crystal displays (LCDs), organic LEDs, or micro‐LEDs, in a pancake lens‐based VR headset. We develop an optical model for evaluating the image quality of a VR headset and facilitating the correlation between display light engine and imaging system. The root causes of image quality degradation at different frequency contents are revealed. The optical system determines the image quality of high‐frequency contents, while the light engine governs the quality of low‐frequency contents.