Giant Enhancement of the Goos-Hanchen Shift Assisted by Quasibound States in the Continuum

We achieve reflection-type bound states in the continuum (BICs) in the compound grating waveguide structure by tuning the excitation of the guided modes. Assisted by the quasi-BICs with ultrahigh Q factors, the Goos-Hanchen (GH) shift can be greatly enhanced to larger than or equal to four orders of wavelength. In addition, different from the large GH shift based on the Brewster dip or transmission-type resonance, the maximum GH shift assisted by the reflection-type quasi-BIC is located at the reflectance peak with unity reflectance, which can be more easily detected in the experiment. Based on the quasi-BIC-assisted giant GH shift, we propose an ultrasensitive temperature sensor with a minimum resolution in the order of 10(-4) degrees C. Our work provides a route, under the current experimental conditions, to design ultrasensitive sensors, light information storage devices, wavelength division de/multiplexers, optical switches, and polarization beam splitters based on this giant GH shift together with high reflectance.