Enhancing the Goos-Hänchen shift based on quasi-bound states in the continuum through material asymmetric dielectric compound gratings

Quasi-bound state in the continuum(QBIC)resonance is gradually attracting attention and being applied in Goos-Hänchen(GH)shift enhancement due to its high quality(Q)factor and superior optical confinement.Currently,symmetry-protected QBIC resonance is often achieved by breaking the geometric symmetry,but few cases are achieved by breaking the material symmetry.This paper proposes a dielectric compound grating to achieve a high Q factor and high-reflection symmetry-protectede QBIC resonance based on material asymmetry.Theoretical calculations show that the symmetry-protected QBIC resonance achieved by material asymmetry can significantly increase the GH shift up to-980 times the resonance wavelength,and the maximum GH shift is located at the reflection peak with unity reflectance.This paper provides a theoretical basis for designing and fabricating high-performance GH shift tunable metasurfaces/dielectric gratings in the future.

High performance optical sensor based on double compound symmetric gratings

A high performance optical sensor based on a double compound symmetric gratings(DCSGs) structure is designed. The reflection spectrum of the DCSG is investigated by utilizing a method that combines a theoretical model with the eigenmode information of the grating structure. The theoretical results, which are observed to agree well with those acquired by rigorous coupled-wave analysis, show that the linewidth of the reflection spectrum decreases upon the increasing distance between the grating strips. This research work will lay a foundation for studying high performance integrated optical sensors in miniature nanostructures.