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Second-harmonic generation and manipulation in lithium niobate slab waveguides by grating metasurfaces

Nonlinear optical processes in waveguides play important roles in compact integrated photonics, while efficient coupling and manipulations inside the waveguides still remain challenging. In this work, we propose a new scheme for second-harmonic generation as well as beam shaping in lithium niobate slab waveguides with the assistance of well-designed grating metasurfaces at λ=1064  nm. By encoding the amplitude and phase into the holographic gratings, we further demonstrate strong functionalities of nonlinear beam shaping by the metasurface design, including dual focusing and Airy beam generation. Our approach would inspire new designs in the miniaturization and integration of compact multifunctional nonlinear light sources on chip.