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.