Nonlinear Imaging Through Magnetic Dipole Quasi-Bic Ultra-Thin Resonators

We propose an ultra-thin silicon metasurface supporting a high-quality leaky mode which is formed by partially breaking a bound-state-in-the-continuum (BIC) generated by the collective magnetic dipole (MD) resonance excited in the subdiffractive periodic systems. Such a quasi-BIC MD state leads to a robust near-field enhancement and a significant boost of the nonlinear process, resulting in measured 500-fold enhancement of third-harmonic emission in comparison to the conventional silicon disk metasurface. We further experimentally demonstrate the highly-efficient nonlinear image tuning via polarisation and wavelength control, opening the way for various applications in high-performance nonlinear metadevices including tunable laser, tunable displays, nonlinear imaging.