The metalens, a significant branch of metasurfaces, holds substantial application potential. However, it often faces issues such as chromatic aberration and narrow bandwidth. This paper compares various optimization methods for the inertia weight (ω) and learning factors (C) of the particle swarm optimization (PSO) algorithm and integrates it with the genetic algorithm (GA). After the comparison, we selected the optimized algorithm that best fits our needs to design a broadband achromatic metalens operating in the wavelength range of 1–1.25 µm. The average efficiency reached 76%, providing a valuable reference for the development and application of achromatic metalenses.

Circularly polarized light (CPL) detection sensors have significant potential for applications in quantum communication and biosensing. In this work, we propose a three-layer complementary chiral metasurface (TCCM) for on-chip integration in the mid-infrared range (2–6 μm). The TCCM consists of an Al nanorod layer, a SiO₂ dielectric layer, and an Al nanoslit layer, with strong circular dichroism (CD) achieved through the symmetry breaking of the inclined rectangular rods. Finite-difference time-domain (FDTD) simulation results demonstrate that the electric fields excited by left circularly polarized (LCP) light and right circularly polarized (RCP) light exhibit different bonding and antibonding modes, which explains the CD mechanism. The CD response and spectral tunability are influenced by the angle and length of the inclined rectangular rods. Through simulation optimization of structural parameters, a maximum CD value of 0.72 is achieved. Compared to traditional multilayer chiral metasurfaces, the TCCM simplifies the fabrication process. These findings provide valuable insights and practical strategies for the development of compact infrared devices, particularly in optical communication, chiral sensing, and full-Stokes polarization detection.