Ultra-slow-light and perfect light modulator based on quasi-BIC metasurface

Traditional electromagnetically induced transparency (EIT) typically exhibits a low and unadjustable quality (Q) factor, while leading to a low group delay of slow-light effect, but the emergence of bound states in the continuum (BIC) offers a straightforward and effective solution to this issue. In this work, we present an ultra-slow-light metasurface driven by multiple symmetrically protected BIC (SP-BIC) that generates three EIT windows based on three wavelength-stabilized quasi-BIC (QBIC) in two distinct methods. The first EIT is indirectly excited by coupling a QBIC with a leakage mode, resulting in a maximum group delay of 105 ps. The latter two EITs are directly excited by the QBIC, producing group delays as high as 2771 ps, which is 2-3 orders of magnitude larger than previously reported. Both group delay and Q-factor adhere to the inverse square law concerning asymmetry parameters, and the relationship between Q-factor and group delay is further summarized. As a sensor, the metasurface achieves a maximum sensing sensitivity of 415.5 nm/RIU. Furthermore, the first EIT is situated at 1550 nm, where the transverse magnetic (TM) light is fully transmitted, while the transverse electric (TE) light is fully reflected. Metasurface can function as a perfect polarization splitter and filter, and this result can be extended to encompass the entire optical communication spectrum from the O band to U band. The potential applications of these findings include optical communication, slow light, sensing, and filtering technologies.