An ultra-broadband photonic-chip-based parametric amplifier

Optical amplification, crucial for modern communication, primarily relies on erbium-doped fibre amplifiers (EDFAs)^1,2. Yet, EDFAs only cover a portion of the low-loss spectrum of optical fibres. This has motivated the development of amplifiers operating beyond the erbium gain window. Pioneering work on optical parametric amplifiers (OPAs)^3,4 using intrinsic third-order optical nonlinearity has led to demonstrations of increased channel capacity. OPAs offer high gain, can reach the 3-dB quantum limit for phase-preserving amplifiers and exhibit unidirectional operation. However, power requirements for highly nonlinear fibres^3,5-8 or bulk waveguides^9,10 have impeded their adoption. By contrast, OPAs based on integrated photonic circuits offer the advantages of substantially increased mode confinement and optical nonlinearity but have been limited in bandwidth^11,12. We overcome this challenge by using low-loss gallium phosphide-on-silicon dioxide^13-15 photonic integrated circuits (PICs) and attain up to 35 dB of parametric gain with waveguides only a few centimetres long in a compact footprint of 0.25 square millimetres. Fibre-to-fibre net gain exceeding 10 dB across an ultra-broad bandwidth of approximately 140 nm (that is, 17 THz) is achieved, with a threefold increase in the gain window compared with C-band EDFAs. We further demonstrate a high dynamic range for input signals, spanning six orders of magnitude, while maintaining a low noise figure. We exploit these performance characteristics to amplify coherent communication signals. This marks, to our knowledge, the first ultra-broadband, high-gain, continuous-wave amplification in a photonic chip, opening up new capabilities for next-generation integrated photonics.