Fig. 1. Optical BIC phenomenon and its research progress

Fig. 2. BIC in THz metasurface.(a) Structure of symmetric protection BIC; (b) transmission spectrum of symmetric protection BIC;(c) angular dependence of Q factor of symmetric protection BIC^[18];(d) structure of F-W BIC;(e) dependence of F-W BIC resonance on the detuning frequency; (f) transmission spectra near F-W BIC^[20]

Fig. 3. Influence of in-plane asymmetric alignment BIC radiation Q factor ^[27]. (a) Dependence of Q factor on asymmetric parameter α; (b) definition of the asymmetric parameter α for different metasurfaces

Fig. 4. Topological properties of BIC^[46]. (a) Schematic diagram of metasurface resonance radiation field decomposition;(b) node line diagram of c_x and c_y in k-space region near BIC; (c) two possible configurations of polarization field near BIC

Fig. 5. Point C and the process of merging BIC. (a) Schematic diagram of point c generated from BIC^[52]; (b) merging process of BIC; (c) change of radiation loss γ of BIC during the merging process^[51]

Fig. 6. Quasi-BIC resonant sensing. (a) ‒(c) Quasi-BIC highly sensitive sensor based on metal structure^[53]; (d) ‒(g) quasi-BIC highly sensitive sensor based on all-dielectric structure^[56]

Fig. 7. Chiral quasi-BIC. Chiral quasi-BIC supported by plasmonic resonators^[63], (a) geometry of chiral quasi-BIC, (b) ‒(d) reflection spectra of chiral quasi-BIC supported by different geometries; chiral quasi-BIC supported by dielectric metasurface ^[64], (e) ‒(g) far-field polarization patterns of chiral quasi-BIC metasurface under different symmetry-breaking conditions, (h) magnetic field component along the z-direction, (i) CD spectrum

Fig. 8. Fingerprint detection of quasi-BIC metasurface^[74]. (a) Complex refractive index and three surface coating cases for equal volumes of trace samples; (b) ‒(e) angle-multiplexed reflectance spectra and their envelopes are provided for a bare metasurface; (f) absorbance envelopes of three cases

Fig. 9. Near-field imaging with quasi BIC ^[76-77]. (a) Extraction of target image pixels and reconstruction process based on metasurfaces; (b) side view and top view photographs and scanning electron microscope images of the sample; (c)-(e) experimental results of terahertz near-field display at different frequencies

Table 1. Q-factor of various BIC terahertz metasurfaces