Design of Chiral Metasurfaces for Emission Efficiency Using Particle Swarm Optimization

We demonstrate the numerical optimization and design of thermal emission metasurfaces that selectively radiate mid-infrared (mid-IR) circularly-polarized light. The proposed three-dimensional chiral structure, formed by the multilayer stacking of antenna elements, inherently exhibits circular polarization selectivity and asymmetry. However, the radiation performance is limited by the vast high-dimensional parameter space required for the structure optimization. Here, we report that the Particle Swarm Optimization (PSO) algorithm, enhanced with a revised objective function and a novel constraint handling technique, which significantly increases both the absorption efficiency and the circular dichroism (CD). By redefining the shape parameters to include inter-layer gap and dielectric thickness as dynamic variables, the optimized structure achieved a CD 0.71, a clear improvement over conventional designs. These results pave the way for realizing compact, high-performance emitters/absorbers for applications such as chiral sensing, optical manipulation, and mid-IR spectroscopy, potentially replacing existing bulkier solutions.