Dual quasibound states in the continuum in compound grating waveguide structures for large positive and negative Goos-Hänchen shifts with perfect reflection
Feng Wu, Ma Luo, Jiaju Wu, Caifu Fan, Xin Qi, Yiran Jian, Dejun Liu, Shuyuan Xiao, Gengyan Chen, Haitao Jiang, Yong Sun, Hong Chen
Abstract
Based on the selective excitations of the forward and backward propagating resonant guided modes, we achieve $dual$ bound states in the continuum ($dual$ BICs) in a compound grating waveguide structure composed of a four-part periodic grating layer and a waveguide layer. Assisted by the quasi-BIC corresponding to forward propagating resonant guided mode (quasi-BIC 1) and the one corresponding to backward propagating resonant guided mode (quasi-BIC 2), large $positive$ and $negative$ GH shifts can be simultaneously realized. Also, in contrast to the GH shift enhanced by conventional transmission-type resonance, large positive and negative GH shifts assisted by dual quasi-BICs possess 100% reflectance, which can be more easily detected and utilized. Our work provides a route to design GH-shift-based high-performance sensors, wavelength division (de)multiplexers and light storage devices.