Integrated broadband and high-efficiency difference frequency generation

High-efficiency integrated difference frequency generation (DFG) has long been pursued for optical communications and signal processing. Recent developments of the thin-film lithium niobate platform enable strong optical confinement in nanoscale waveguides, greatly enhancing the nonlinear efficiencies. However, the absolute DFG conversion efficiencies (CEs) in recent studies are limited because of fail to satisfy the phase-matching condition strictly. Here, we demonstrate an integrated DFG device based on an adapted thin-film periodically poled lithium niobate waveguide. The generated idler wave achieves a maximum output power of 13.2 dBm and a CE of 48.6%. Furthermore, our device exhibits flat optical responses and high-quality eye diagrams when converting a signal at 1638 nm to an idler at 1556 nm, enabling bringing unique-band light into the amplifier's gain band. By overcoming the efficiency limitations of previous DFG implementations, our work opens wider possibilities for practical applications in optical communications, wavelength conversion, and signal amplification.