Electrically Tunable Second-Harmonic Generation in High-Q Organic DAST All-Dielectric Nonlinear Metasurfaces

Simultaneously enhancing and dynamically tuning second-harmonic generation (SHG) remains a major challenge in nanophotonics. Here, we propose a DAST-based organic all-dielectric nonlinear metasurface that combines symmetry-protected quasi-bound states in the continuum (quasi-BICs) with the strong second-order nonlinearity and electro-optic response of DAST. The quasi-BIC resonance enhances SHG efficiency by approximately 1000-fold. Applying a low voltage of 5 V significantly boosts the resonance Q-factor from 2876 to 4831. This enables an unprecedented maximum SHG conversion efficiency of 89.5% and a remarkable modulation depth of 275%. This work provides a versatile paradigm for active optical nonlinearities in organic metasurfaces, paving the way for advanced tunable nanophotonic devices.