Dynamic Control of Phase Matching in Nonlinear Metasurfaces Using Pancharatnam-Berry Phase

Reconfiguring the spectral output of nonlinear metasurfaces after fabrication remains challenging. We address this by exploiting the nonlinear Pancharatnam-Berry phase of $C_{3v}$ -symmetric plasmonic metasurfaces. By integrating two metasurfaces inside a multipass cell, we experimentally demonstrate continuous spectral tuning of second-harmonic generation (SHG) phase-matching peaks across a 900-970 nm pump range by rotating one metasurface relative to the other. The extracted geometric phase follows the $3\sigma \theta$ dependence, and a full $2\pi$ tuning cycle is completed with $120°$ of physical rotation. This establishes geometric-phase metasurfaces as a reconfigurable nonlinear platform, where mechanical rotation enables post-fabrication and broadband tuning of nonlinear optical responses.