Polarization-controlled dynamically switchable high-harmonic generation from all-dielectric metasurfaces governed by dual bound states in the continuum

Tailoring optical nonlinear effects (e.g., harmonic generation, sum-frequency mixing, etc.) in the recently emerging all-dielectric platform is important for both fundamental science and industrial development of high-efficiency, ultrafast, and miniaturized photonic devices. In this paper, we propose a method for the dynamically switchable high-harmonic generation in silicon nanodimer metasurfaces by exploiting the polarization-controlled dual bound states in the continuum (BIC). Owing to the high-quality factor of BIC resonances, efficient harmonic signals including the third-harmonic generation and fifth-harmonic generation from a direct process as well as a cascaded process by degenerate four-wave mixing are obtained. Moreover, the BIC and their resonantly enhanced harmonics can be switched on or off with high selectivity with respect to the fundamental pump polarization. Compared with previous reports, our paper provides a simple but effective tuning strategy by fully exploring the structural symmetry and polarization degree of freedom rather than resorting to additional external stimuli, which would possess great advantages in designing tunable and switchable nonlinear light sources for chip-scale applications.