Efficient Parametric Frequency Conversions in Chalcogenide‐Loaded Etchless Thin‐Film Lithium Niobate Waveguides

Abstract Parametric frequency conversion based on second‐order nonlinearity ( χ (2) ) is critical in many applications. The implementation of second‐order nonlinearity on integrated photonic platforms, in particular on the lithium niobate‐on‐insulator platform, has attracted considerable interest due to its low power consumption and small footprint. However, high‐efficiency on‐chip parametric frequency conversion remains challenging due to fabrication complexity. Here, efficient parametric frequency conversions via modal phase matching (MPM) in etchless thin‐film lithium niobate (TFLN)‐chalcogenide glass (ChG) hybrid waveguides fabricated by a simplified process free from domain engineering and etching of TFLN are proposed and demonstrated. An overall conversion efficiency of 25.55% W −1 for second‐harmonic generation is experimentally achieved in a 1‐cm‐long waveguide, significantly over the reach of the etchless counterparts and in the same order of magnitude as those of the etched cases based on MPM. Broadband frequency conversion with a 3‐dB bandwidth of 57 nm is achieved based on cascaded second‐harmonic generation and difference‐frequency generation via MPM in a nanophotonic waveguide using a continuous‐wave pump. This device shows great promise for efficient on‐chip parametric frequency conversion, enabling a wide range of photonic applications, and paving the way for further integration with various advanced ChG photonic devices toward on‐chip multifunctional microsystems.