Continuous Domain Quasi-Bound State Enhances the Nonlinear Effects of Silicon Carbide

We propose a silicon carbide (3C-SiC) periodic grating structure based on quasi-bound states in the continuum (q-BICs), which is used to significantly enhance the second-order optical nonlinear effect, including second-harmonic generation (SHG) and sum-frequency generation (SFG). By introducing a four-segment sub-wavelength grating on the SiC thin film and tailor the dimension, the structure successfully excites two q-BIC modes with ultra-high Q factor (resonant wavelengths at 1713.2 nm and 1804.6 nm respectively), realizing enhanced localization and nonlinear interaction of the strong light field. The simulation results show that under oblique incidence, the structure significantly enhances SFG efficiency and exhibits strong robustness to variations in key structural parameters. In addition, the study also reveals the coexistence of forward and backward SHG, and resonant wavelength tuning can be achieved by adjusting the structure dimension. This work not only provides a new path to enhance the nonlinear conversion efficiency of SiC thin films and solve the problem of difficult phase matching, but also lays the theoretical and technical foundation for the development of compact, efficient and integrated SiC-based nonlinear photonic devices.