Efficient Second Harmonic Generation in a Reverse-Polarization Dual-Layer Crystalline Thin Film Nanophotonic Waveguide

Second harmonic generation (SHG), one of the most significant chi((2)) nonlinear optical processes, plays a crucial role in a wide variety of optical and photonic applications. Designing various delicate schemes to achieve highly efficient SHG has become a long-standing and challenging topic in nonlinear optics. Despite numerous success on SHG based on birefringent phase-matching and quasi-phase-matching, so far, modal phase-matching (MPM) for SHG in tightly light-confined structures has still in its infancy. Here, a new scheme is proposed to realize efficient SHG via MPM by using a nanophotonic LiNbO3 thin-film waveguide consists of two bonded layers with internally reversed polarizations. In such a dual-layer ridge waveguide based on lithium niobate on insulator (LNOI), upon optical excitation at 1574.6 nm, SHG is observed at 787.3 nm with a high conversion efficiency of 5540% W-1 cm(-2) experimentally. This work advances the understanding on modal phase-matched SHG and other quadratic optical nonlinear processes, offering additional strategies for developing high-performance nonlinear photonic devices in on-chip platforms.

Automated summary

A new scheme is proposed in this study to achieve efficient second harmonic generation (SHG) via a nanophotonic LiNbO3 thin-film waveguide with a conversion efficiency of 5540% W-1 cm(-2). The design of a dual-layer ridge waveguide has advanced the understanding of modal phase-matched SHG and other quadratic optical nonlinear processes.