Merging bound states in the continuum by harnessing higher-order topological charges  

作　　者：Meng Kang Li Mao Shunping Zhang Meng Xiao Hongxing Xu Che Ting Chan 

机构地区：[1]School of Physics and Technology,and Key Laboratory of Artificial Micro-and Nano-structures of Ministry of Education,Wuhan University,Wuhan 430072,China [2]Department of Physics,The Hong Kong University of Science and Technology,Hong Kong,China [3]Wuhan Institute of Quantum Technology,Wuhan 430206,China [4]School of Microelectronics,Wuhan University,Wuhan 430072,China

出　　处：《Light(Science & Applications)》2022年第9期2098-2106,共9页光（科学与应用)（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant No.91850207,11904264 and 12134011)and the National Key R&D Program of China(Grant No.2021YFA1401104,2017YFA0303504).M.X.is also supported by the startup funding of Wuhan University.S.Z.is also supported by the Young Top-notch Talent for Ten Thousand Talent Program(2020-2023).Workdone in HongKong is supported by RGC Hong Kong(AoE/P-502/20,N_HKUST608/17)and the Croucher Foundation(CAS20SCO1).

摘　　要：Bound states in the continuum(BICs)can confine light with a theoretically infinite Q factor.However,in practical on-chip resonators,scattering loss caused by inevitable fabrication imperfection leads to finite Q factors due to the coupling of BICs with nearby radiative states.Merging multiple BICs can improve the robustness of BICs against fabrication imperfection by improving the Q factors of nearby states over a broad wavevector range.To date,the studies of merging BICs have been limited to fundamental BICs with topological charges±1.Here we show the unique advantages of higher-order BICs(those with higher-order topological charges)in constructing merging BICs.Merging multiple BICs with a higher-order BIC can further improve the Q factors compared with those involving only fundamental BICs.In addition,higher-order BICs offer great flexibility in realizing steerable off-T merging BICs.A higher-order BIC at F can split into a few off-T fundamental BICs by reducing the system symmetry.The split BICs can then be tuned to merge with another BIC,e.g.,an accidental BIC,at an off-Γpoint.When the in-plane mirror symmetry is further broken,merging BICs become steerable in the reciprocal space.Merging BICs provide a paradigm to achieve robust ultrahigh-Q resonances,which are important in enhancing nonlinear and quantum effects and improving the performance of optoelectronic devices.

关 键 词：TOPOLOGICAL CHARGES STATES 

分 类 号：O17[理学—数学]