Local-to-Nonlocal Second-Harmonic Generation from Electrically Tunable Intersubband Polaritonic Metasurfaces

Nonlinear optical metasurfaces enable subwavelength control of light-matter interactions, yet simultaneous tunability of harmonic signal intensity and spectral response remains a fundamental challenge. Here, a local-to-nonlocal second harmonic (SH) generation process is presented, enabled by an electrically tunable polaritonic metasurface, allowing independent control of the SH spectral peak wavelength and intensity. The metasurface combines a localized surface plasmon resonance at the fundamental frequency with a transverse magnetic guided-mode resonance at the SH frequency. By engineering modal overlap within a multiple quantum well layer, voltage-controlled modulation of SH intensity and angle-controlled spectral tuning is achieved, demonstrating two decoupled degrees of freedom associated with local and nonlocal modes. Angle-resolved nonlinear reflection measurements confirm the independent tunability of the metasurface, validating the separation of excitation and emission pathways. This hybrid approach provides a general framework for nonlinear metasurfaces with enhanced flexibility and functional control, paving the way for applications in nonlinear signal processing, angle-multiplexed photonics, and entangled photon-pair generation for quantum optics.