Design and optimization method of chiral metasurfaces with structural discretization and genetic algorithms

Metasurfaces including chiral metasurfaces have attracted extensive attention due to their ability to flexibly manipulate various parameters of light fields, such as amplitude, phase and polarization, based on the subwavelength-scale structures. However, conventional design and optimization of a 2D metasurface usually rely on experience-driven and time-consuming trial-and-error procedure for searching effective structures and the followed case-by-case optimization, in which the structures are usually limited to simple and regular geometries. Here, we propose a design and optimization method of chiral metasurfaces with the combination of structural discretization and genetic algorithms. Based on the proposed method, design and optimization of a broadband chiral metasurface working in the visible wavelength region was conducted with an arbitrarily given C-2 symmetric structure without complicated structural searching and time-consuming optimization process. Simulation results show that an average circular dichroism of 0.73 (peaking at 0.88) and an average circular polarization extinction ratio (CPER) of 11.5 dB (up to 27.4 dB) can be obtained in the wavelength range spans from 605 nm to 720 nm. This proposed method provides a new approach for the design and optimization of chiral metasurfaces or other metasurfaces.