Quasi-continuous metasurface for high-efficiency beam deflection based on multi-objective level-set optimization

Abstract

In recent years, metasurface has received significant attention because of its outstanding ability to manipulate electromagnetic waves at a subwavelength scale. In this paper, combined with an adjoint method, the multi-objective level-set optimization of geometric phase metasurface for high-efficiency beam deflection is exploited. It is shown that the geometric shape of the discrete metasurface is optimized towards a continuous shape. The final quasi-continuous metasurface achieves the absolute efficiency improvement from 22.63% to 76.08%; meanwhile, the polarization conversion efficiency maintains above 95.00% during the whole optimization process. An important consideration during the structural design is the tolerance of the structural parameters’ fluctuation in the manufacturing process. We investigate the robust metasurface optimization by geometrically considering contractive and expansile devices directly into the algorithm. The results suggest that when absolute efficiency exceeds 60.00%, compared with non-robust design, the acceptable edge deviation range of robust optimized metasurface is enhanced from 13 nm to 17 nm. Furthermore, this method can also be extended to the optimization design of other mico-/nano- optical devices.