A photonic integrated continuous-travelling-wave parametric amplifier

The ability to amplify optical signals is of pivotal importance across science and technology typically using rare-earth-doped fibres or gain media based on III–V semiconductors. A different physical process to amplify optical signals is to use the Kerr nonlinearity of optical fibres through parametric interactions 1 , 2 . Pioneering work demonstrated continuous-wave net-gain travelling-wave parametric amplification in fibres 3 , enabling, for example, phase-sensitive (that is, noiseless) amplification 4 , link span increase 5 , signal regeneration and nonlinear phase noise mitigation 6 . Despite great progress 7 – 15 , all photonic integrated circuit-based demonstrations of net parametric gain have necessitated pulsed lasers, limiting their practical use. Until now, only bulk micromachined periodically poled lithium niobate (PPLN) waveguide chips have achieved continuous-wave gain 16 , 17 , yet their integration with silicon-wafer-based photonic circuits has not been shown. Here we demonstrate a photonic-integrated-circuit-based travelling-wave optical parametric amplifier with net signal gain in the continuous-wave regime. Using ultralow-loss, dispersion-engineered, metre-long, Si 3 N 4 photonic integrated circuits 18 on a silicon chip of dimensions 5 × 5 mm 2 , we achieve a continuous parametric gain of 12 dB that exceeds both the on-chip optical propagation loss and fibre–chip–fibre coupling losses in the telecommunication C band. Our work demonstrates the potential of photonic-integrated-circuit-based parametric amplifiers that have lithographically controlled gain spectrum, compact footprint, resilience to optical feedback and quantum-limited performance, and can operate in the wavelength ranges from visible to mid-infrared and outside conventional rare-earth amplification bands. By using Si 3 N 4 photonic integrated circuits on a silicon chip, a continuous-travelling-wave parametric amplifier is shown to yield a parametric gain exceeding both on-chip propagation loss as well as fibre–chip–fibre coupling losses.