Low-power integrated optical amplification through second-harmonic resonance

Optical amplifiers are fundamental to modern photonics, enabling long-distance communications¹, precision sensing^2,3 and quantum information processing^4,5. Erbium-doped amplifiers dominate telecommunications but are restricted to specific wavelength bands^1,6, whereas semiconductor amplifiers offer broader coverage but suffer from high noise and nonlinear distortions⁷. Optical parametric amplifiers (OPAs) promise broadband, quantum-limited amplification across arbitrary wavelengths⁸. However, their miniaturization and deployment have been hampered by watt-level power requirements. Here we demonstrate an integrated OPA on thin-film lithium niobate that achieves >17 dB gain with <200 mW input power-an order of magnitude improvement over previous demonstrations. Our second-harmonic-resonant design enhances both pump generation efficiency (95% conversion) and pump power utilization through recirculation, without sacrificing bandwidth. The resonant architecture increases the effective pump power by nearly an order of magnitude compared with conventional single-pass designs, while also multiplexing the signal and pump. We demonstrate flat near-quantum-limited noise performance over 110 nm. Our low-power architecture enables practical on-chip OPAs for next-generation quantum and classical photonics.