Stray light analysis of geometric waveguide

Abstract

In the field of augmented reality (AR), geometric waveguide has become one of the effective solutions of near-eye display due to their thinness and high transmittance. To obtain clearer viewing experiences, the causes of the stray light are analyzed and solved. The improper tilt angle and the difference in parallelism of the partially reflective mirrors array (PRMA)units may cause stray light or overlapping ghost images, and the refractive indices of the glue and the glass also plays an important role as the appearance of several opposite ghost images. The results show that by adjusting the tilt angle of the PRMA, the stray light within the major area of the eye box can be eliminated. Then a 1.8 mm thick waveguide with stray light of less than 1% is designed. The refractive index of the glass is 1.502 and that of the matched glue is 1.500. The FOV of the designed system is 40°, the size of eye box is 10 mm × 10 mm, and the eye relief is 20 mm. The distribution of the stray light on the observed virtual image is simulated. Finally, a proof-of-concept prototype with eliminated stray light is fabricated and demonstrated.