Cascaded metasurfaces for high-purity vortex generation
Feng Mei, Geyang Qu, Xinbo Sha, Jing Han, Moxin Yu, Hao Li, Qinmiao Chen, Ziheng Ji, Jincheng Ni, Cheng‐Wei Qiu, Qinghai Song, Yuri S. Kivshar, Shumin Xiao
Abstract
Abstract We introduce a new paradigm for generating high-purity vortex beams with metasurfaces. By applying optical neural networks to a system of cascaded phase-only metasurfaces, we demonstrate the efficient generation of high-quality Laguerre-Gaussian (LG) vortex modes. Our approach is based on two metasurfaces where one metasurface redistributes the intensity profile of light in accord with Rayleigh-Sommerfeld diffraction rules, and then the second metasurface matches the required phases for the vortex beams. Consequently, we generate high-purity LG p,l optical modes with record-high Laguerre polynomial orders p = 10 and l = 200, and with the purity in p , l and relative conversion efficiency as 96.71%, 85.47%, and 70.48%, respectively. Our engineered cascaded metasurfaces suppress greatly the backward reflection with a ratio exceeding −17 dB. Such higher-order optical vortices with multiple orthogonal states can revolutionize next-generation optical information processing.