Enhancing Linear and Nonlinear Transparent Responses in Stripe-Coupled Metasurface via BIC

We investigate the linear and nonlinear optical responses of a dielectric metasurface exhibiting electromagnetically induced transparency based on bound states in the continuum (BIC) in the near-infrared region. The metasurface is composed of periodically arranged silicon square ring resonators on the top of the SiO2substrate, with an embedded silicon coupling stripe within each unit cell to break in-plane structural symmetry and facilitate quasi-BIC excitation. Under normal incidence, the proposed design achieves a maximum figure of merit of 2.39 × 104, demonstrating an ultrahigh-Qresonance. Additionally, the metasurface supports efficient third harmonic generation effectively with the maximum conversion efficiency of 6.95%. These results provide a promising platform for the applications in high-Qphotonics and advanced nonlinear optical devices.