Efficient and tunable frequency conversion using periodically poled thin-film lithium tantalate nanowaveguides.

Thin-film lithium tantalate (TFLT) has recently emerged as a promising photonic platform for chip-scale nonlinear optics due to its weaker photorefraction, higher optical damage threshold, broader transparency window, and lower birefringence compared to that of thin-film lithium niobate. Here we report the first functional second harmonic generator achieved through high-fidelity poling of z-cut TFLT waveguides, based on a low-loss lithium tantalate integrated photonic platform. As a result, quasi-phase matching is performed between telecom (1,550 nm) and near-visible (775 nm) wavelengths in a straight waveguide and prompts strong second-harmonic generation with a normalized efficiency of 229 %/(W·cm). An absolute conversion efficiency of 5.5 % is achieved with a pump power of 700 mW in the waveguide. Such a second-harmonic generator exhibits stable temperature tunability (-0.44 nm/°C), which is important for applications that require precise frequency alignment such as atomic clocks and quantum frequency conversion.