Research on slanted trapezoidal surface relief grating

Abstract

With the rapid development of augmented reality technology, people can clearly see the superposition of virtual and real world images at the same time. The diffractive optical waveguide has obvious advantages over the geometric optical waveguide because of its high diffraction efficiency, light weight and difficulty in generating ghost images. Therefore, the use of holographic gratings as coupling elements for planar waveguides has been widely used in head-mounted display systems. Because high efficiency grating is required as coupling element in coupling, we use slanted trapezoidal surface relief grating as coupling element of the planar waveguide. In this paper, a slanted trapezoidal surface relief grating has been designed as a high-efficiency coupling element with a grating period of 520 nm and a material of BaK3 glass with a refractive index of 1.54. By optimizing the structure of the slanted grating, the relationship between the groove parameters and the diffraction efficiency of the slanted rectangular grating and the slanted trapezoidal grating is analyzed in detail. The results show that under the normal incidence of light at 630 nm, the groove depth is 450 nm, and the slant angle θ1 is 40°, when the -1 order diffraction efficiency of the TE polarized light is higher than 80%, the ranges of the slant angle θ2 and of the maximum diffraction efficiency value would be obtained. This can greatly improve the coupling efficiency of the holographic planar waveguide.