Nonlinearity Manipulation for Highly Efficient Modal Phase-matched Second Harmonic Generation on Thin-Film Lithium Niobate

Abstract

While modal phase matching (MPM) shows great potential for adaptable engineering in quadratic nonlinear optical processes, poor mode overlap in traditional MPM persists as a key challenge. In this paper, a flexible domain engineering method are proposed and demonstrated for second-harmonic generation (SHG) on thin-film lithium niobate (TFLN). By meticulously tuning the electric field intensity applied to the poling electrodes with an Al₂O₃ layer, the depth of domain inversion layer in TFLN can be controlled flexibly and locally, leading to the manipulation of nonlinearity, which effectively increases the mode overlap. SHG in the dual-layer TFLN ridge waveguides has been experimentally realized with a normalized conversion efficiency of 8300% W⁻¹ cm⁻². The flexible and fabrication-friendly approach provides a versatile method for diverse MPM scenarios, and presents considerable potential for efficient quadratic nonlinear processes.