Design of polarization-insensitive metalens with linear dispersion via improved particle swarm algorithm

Metalens have become one of the most promising metasurfaces for applications in recent years because of their thinness and compactness. Similar to other diffractive elements, the dispersion of metalens is difficult to modulate in the same way as conventional refractive elements. Here, we present a method for designing the polarization-insensitive metalens with linear dispersion via improved particle swarm algorithm (PSO). The metalens operates in the wavelength range of 1.1 ~ 1.3 μm with NA values of 0.36 ~ 0.41. With centrosymmetric nanopillars, the metalens was constructed to be polarization insensitive. By optimizing the reference phase at the center of the metalens using the improved PSO, we are able to obtain a relatively low wave aberration. The optimization convergence rate can be further enhanced with this method compared to the traditional PSO algorithm. FDTD simulation was conducted to abtain the farfield focusing performance of the designed metalens. The dispersion linearity of the metalens is about 11.5% according to the analysis. The dispersion engineering approach proposed in this paper is expected to be applied to micro-spectrometers and other similar devices in the future through further optimization.