Polarization Modulation and Optical Sensing Enabled by Nonradiative Modes in Dielectric Metasurfaces

All-dielectric metasurfaces exhibit lower ohmic losses than plasmonic metasurfaces. However, the dominant radiation losses still greatly hinder their applications and further development. Nonradiative modes such as bound states in continuum (BICs) and anapole modes have recently emerged as key research focuses. In this work, we theoretically propose an all-dielectric metasurface consisting of an array of regular octagons with nanopores to simultaneously realize anapole modes and BICs. By introducing symmetry breaking, two symmetry-protected BICs are transformed into quasi-BICs with ultra-high quality ( $Q$ )-factors of 26892 and 51874. The metasurface displays distinct polarization insensitivity of anapole mode and polarization dependence of quasi-BICs. Moreover, superior multi-mode and low-loss refractive index sensing performance is also realized with large sensitivities of 210, 191 and 241.7-nm/RIU and high figures of merit (FOMs) of 3500, 1910 and 69 RIU−1 in the wavelength range between 1200 and 1400-nm. These demonstrate that this all-dielectric metasurface has excellent potential in strong coupling regime, quasi-BICs polarization modulation, and high-sensitive refractive index sensing, etc.