Structured-light manipulation via the nonlinear Berry phase

Structured-light manipulation has advanced rapidly, but most existing approaches rely on linear modulation. The nonlinear geometric phase offers a route to combine frequency conversion with wavefront control during harmonic generation. However, a platform that simultaneously provides solid-state stability and multifunctional structured-light generation remains needed. Here, we demonstrate a nonlinear structured-light platform based on the nonlinear Berry phase in lithium tantalate (LiTaO₃). An eight-segment device with stepwise-rotated optical axes imprints a discrete 2π phase winding on the second-harmonic (SH) field. Under circularly polarized excitation, it directly generates spin-dependent SH vortex beams with a central phase singularity. Under linear excitation, the coherent superposition of opposite-spin components produces vector vortex beams with spatially varying polarization. Coherent interference with a Gaussian SH reference further yields skyrmion-like polarization textures with a phase-tunable orientation. These results establish the nonlinear Berry phase as a versatile approach for frequency conversion, phase and polarization control, and topological-field generation.