Design of a wide bandwidth achromatic metalens based on phase change material GST with aperture sharing

基于相变材料GST与孔径共享宽带宽消色差透镜的设计

Received: 9 January 2023

Abstract

This paper proposes the use of aperture sharing synergistic operation in the structure of the metalens, together with the rational selection of the scattering unit size according to the linear relationship between the output phase and frequency of the scattering unit, and the selection of the slope of the phase variation with frequency, combined with the modulation of the phase change material Ge₂Sb₂Te₅ crystallization rate m value, in the set wavelength band, for different wavelengths of incident light through the metasurface can produce a uniform phase distribution. The method is used to achieve a polarization-insensitive achromatic metalens in the 9.5-13 μm continuous wavelength band by adjusting the m value of the phase transition material Ge₂Sb₂Te₅ crystallization rate and producing a phase distribution with a uniform focal length for different wavelengths of incident light passing through the metasurface. The simulation results show that the focal length of the achromatic metasurface varies by 3.57 μm in the working band, with an error of about 4.3% from the set focal length, and the full width of the half-peak of the focal point at all wavelengths of incidence reaches the diffraction limit, and the focusing efficiency exceeds 60%. The achromatic metalens proposed in this paper provides a new idea for the design of achromatic metasurfaces and promotes the research of phase change materials in broadband achromatic metasurfaces.

摘要

提出了在超构透镜结构上采用孔径共享协同操作的方法，根据散单元输出相位与频率呈线性关系，再结合调控相变材料Ge2Sb2Te5晶化率m值，在设定的波段内合理选择散射单元的尺寸，不同波长入射光经过超表面后能产生符合统一焦距要求的相位分布，从而使消色差超透镜的带宽得到相应拓宽，设计了9.5~13 μm连续波段内的偏振不敏感消色差超表面透镜。仿真结果表明, 消色差超表面在工作波段内的焦距变化为3.57 μm, 与设定焦距的误差约为4.3%, 并且各波长入射下的焦点半峰全宽均达到了衍射极限, 聚焦效率超过60%。提出的消色差超表面透镜, 为消色差超表面的设计提供了新的思路, 促进了相变材料在宽带消色差超表面方面的研究。