Second Harmonic Generation in Modal Phase-Matched Thin-Film Lithium Tantalate Ridge Waveguide

We demonstrate efficient and thermally stable second-harmonic generation (SHG) in x-cut thin-film lithium tantalate (TFLT) ridge waveguides via modal phase matching (MPM). The experimental characterizations reveal a normalized conversion efficiency (NCE) of 17.2% W^-1 cm^-2 in a 4 mm long waveguide. Notably, the device exhibits a temperature-dependent phase-matching wavelength slope of 0.007 nm/°C, which shows a two-orders-of-magnitude improvement in thermal stability over conventional periodically poled lithium niobate/lithium tantalate optical devices. Our work indicates that MPM in TFLT is an attractive strategy for integrated nonlinear optical applications, particularly for the on-chip frequency conversion of both classical and quantum light signals without on-chip domain-poling processes.