Switchable optical vortex beam generator based on an all-dielectric metasurface governed by merging bound states in the continuum
Hang Liu, Kun Wang, Huifang Ma, Jingxiang Gao, Meng Liu, Huiyun Zhang, yuping zhang
Abstract
The polarization topology around the bound states in continuum (BIC) affects the optical vortex (OV) beam generation. We propose a cross-cross-shaped resonator based on a THz metasurface to realize an OV beam generator in real space by exploiting the inherent winding topology around the BIC. The BIC merging at the point Γ is achieved by tuning the width of the cross resonator, which significantly improves the Q factor and enhances the field localization. Furthermore, the switching between the high-order OV beam generator governed by the merged BIC and the low-order OV beam generator is realized. This extends the application of BIC in modulating orbital angular momentum.