Stray light and tolerance analysis of an ultrathin waveguide display

Waveguides are becoming increasingly popular in the field of near-eye display because of their low thickness and light weight. However, ghost stray light generated in the waveguide and the double-image problem caused by low parallelism precision seriously degrade the display quality. In this study, the causes of stray light are investigated, an effective solution is proposed, and a coupling-in structure is designed to suppress stray light. The Monte Carlo tolerances on the parallelism errors based on the visual acuity for the two substrates and the partially reflective mirror array (PRMA) of the waveguide are implemented. Results show that the fabrication accuracy of the substrates and the PRMA should be controlled within 6″ and 9″, respectively. A 2.4 mm thick waveguide with stray light of less than 1% is designed. The field of view is 36° in the pupil-expanding direction, and the diameter of the exit pupil is 11.6 mm at an eye relief of 20 mm. Finally, a proof-of-concept prototype is fabricated and demonstrated.