High efficiency and large angle polarization independent beam deflection metagrating by Bayesian optimization.

Directional emission sources are required in wide application scenarios such as 3D displays and optical communication. The integration of beam deflection metasurfaces on emission devices can construct a compact directional emission source. However, most reported metasurfaces and metagratings focus on the deflection of linear polarized light with relatively small angles(< 30 degrees), which limits their further application for unpolarized light sources. In this work, a nanorod-based two-dimensional metagrating is proposed for a polarization independent incident beam with a large deflection angle ranging from 30 degrees to 75 degrees, and a maximum beam deflection efficiency of 90.1%. An efficient global optimization method based on Bayesian optimization is developed for the design of metagrating and demonstrates a faster converge speed and a better beam deflection performance compared with traditional particle swarm optimization. The proposed metagrating and optimization method also provides useful guidance for the design of polarization independent functional meta-devices.