Efficient Cryogenic Nonlinear Conversion Processes in Periodically-Poled Thin-Film Lithium Niobate Waveguides

Periodically poled thin-film lithium niobate (TFLN) waveguides, which enable efficient quadratic nonlinear processes, serve as crucial foundation for classical and quantum signal processing. To expand their application scope, the first investigation of nonlinear conversion processes in periodically poled TFLN waveguides at cryogenic conditions (7 K) is provided. Through systematic experimental characterization, it is found that the periodically poled TFLN waveguide retains its high conversion efficiency at both cryogenic and room temperatures for both classical second-harmonic generation and quantum photon-pair generation processes. Particularly, the photon-pair source at cryogenic conditions shows high brightness (≈8 MHz µW⁻¹) and broad bandwidth (>100 THz). These results demonstrate the significant potential of TFLN wavelength conversion devices for cryogenic applications and foster future scalable quantum photonic systems.