High-efficiency nonlocal reflection-type vortex beam generation based on bound states in the continuum  

作　　者：Tongyu Li Jiajun Wang Wenjie Zhang Xinhao Wang Wenzhe Liu Lei Shi Jian Zi 

机构地区：[1]State Key Laboratory of Surface Physics,Key Laboratory of Micro-and Nano-Photonic Structures(Ministry of Education)and Department of Physics,Fudan University,Shanghai 200433,China [2]Department of Physics,The Hong Kong University of Science and Technology,Hong Kong,China

出　　处：《National Science Review》2023年第5期195-201,共7页国家科学评论（英文版）

基　　金：supported by the China National Key Basic Research Program(2022YFA1404800);the National Natural Science Foundation of China(12234007 and 12221004);supported by the Science and Technology Commission of Shanghai Municipality(19XD1434600,2019SHZDZX01,19DZ2253000,20501110500 and 21DZ1101500)。

摘　　要：Momentum-space polarization vortices centered at symmetry-protected bound states in the continuum of a periodic structure,e.g.photonic crystal slab,provide a novel nonlocal approach to generate vortex beams.This approach enjoys a great convenience of no precise alignment requirements,although the generation efficiency of the nonlocal generators requires further optimization before the practical application.In this work,we propose a temporal-coupled-mode-theory-based guideline for high-efficiency nonlocal reflection-type vortex generator design.The conversion efficiency of the vortex beam is found to be limited by the ratio of the radiative loss to the intrinsic absorption in practical systems.To increase this ratio through mode selection and structure design,the photonic crystal slabs are theoretically designed and experimentally characterized,showing a maximum on-resonance conversion efficiency of up to 86%.Combining high efficiency with simple fabrication and no re quirement for precise alignment,reflection-type photonic crystal slabs could offer a new and competitive way to generate vortex beams flexibly.

关 键 词：photonic crystal slab vortex beam bound states in the continuum 

分 类 号：O43[机械工程—光学工程]