Reflective metalens with broadband achromatic polarization-insensitive properties in the near-infrared

We demonstrate theoretically that Au-SiO2-TiO2 reflective elliptical arrays are capable of achieving polarization -insensitive broadband achromatic focusing. The reflective metalens is insensitive to polarization at all incident polarized angles, and the structural unit aspect ratio is cut in half, according to numerical investigations. Adopting particle swarm optimization (PSO) based on the transmission phase principle to accomplish achromatic property. In addition, we analyzed the chromatic property of metalens without and with the PSO algorithm and compared the results. The maximum confocal bandwidth without the PSO algorithm is 80 nm, and the focusing efficacy is approximately 30%. By employing the PSO algorithm, the achromatic bandwidth is increased to 200 nm within the wavelength range of 840-1040 nm, while the focusing efficiency is decreased by 10-20%. The proposed near-infrared shortwave achromatic metalens could be utilized in technologies such as laser night vision and light detection and ranging.