Quasi-Bound States in the Continuum and Sensing Performance With Polarization-Selective in All-Dielectric THz Metasurface

Metasurface based on bound states in the continuum (BIC) has emerged as a significant tool to enhance sensing performance, primarily due to their high Q-factor resonance. Conventional metal-based metasurface has been limited in further improving the Q-factor due to unavoidable ohmic losses. In this article, a low-loss all-dielectric metasurface based on quasi-BICs is proposed to address the limitation in terahertz (THz) refractive index sensing. Multiple resonant peaks with high Q-factor is generated under the incident of different polarization. Due to the special distribution of the field enhancement generated by the sensor structure, the resonant peaks exhibit a notable redshift phenomenon in response to the increase in the refractive index of the analyte. Taking advantage of this behavior, we achieve refractive index sensing with remarkable sensitivity, amounting to 442 GHz/RIU and the figure of merit reached 10 787 in different modes, within the frequency range of 1.3-1.5 THz. The all-dielectric metasurface proposed has the potential to achieve the high-sensitivity sensing of biological molecules and chemical substances.