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In optics, the two main mechanisms for enhancing the Goos-H\"anchen (GH) shift of a reflected light beam have a common shortcoming: The maximum shift is located exactly at the reflectance dip, which makes the reflected beam hard to detect. Here the authors tune the excitation of guided modes in a compound grating-waveguide structure, to realize quasibound states in the continuum (quasi-BICs) with ultrahigh Q-factors. Assisted by these quasi-BICs, the GH shift at the reflectance peak can be greatly enhanced. This giant GH shift with high reflectance can be used for e. g. ultrasensitive sensors, wavelength-division (de) multiplexers, optical switches, and polarization beam splitters.
Wu et al. (Tue,) studied this question.