Ultrasensitive Refractive Index Sensing Based on the Quasi-Bound States in the Continuum of All-Dielectric Metasurfaces

摘要

Symmetry-protected quasi-bound states in the continuum (BIC) controlledby metasurfaces with broken in-plane symmetry are widely exploited toachieve highly surface-sensitive and spectrally sharp resonances for nanophotonicbiosensors. Through the engineering of silicon-based asymmetricnanobar pairs, a quasi-BIC mode is excited showing a dominant toroidaldipole (TD) and electric quadrupole (EQ) resonant feature in the near-infraredand performs ultrahigh sensitivity in the refractometric monitoring of localenvironment changes. Contrary to the typical electric and magnetic Mie-typeresonances of dielectric resonators with the enhanced field mostly inside theresonator volume, the TD-EQ quasi-BIC mode is found to exhibit strong andtightly confined optical fields at the surface of tilted nanobar pairs, and itsrefractive-index (RI) sensitivity can be dramatically increased for nanopillarswith larger aspect-ratio. The measured (simulated) sensitivity and figure ofmerit for nanobar pairs with a height of 450 nm reach 608 nm/RIU and 46(612 nm/RIU and 85), respectively. Such ultrahigh sensitive all-dielectric platformcan be fabricated through complementary metal-oxide-semiconductorcompatible process and is promising for on-chip integration and sensorminiaturization to a wide range of diagnostic applications.