Fig. 2: Experimental set-up, signal spectrum and high-power amplification.

a, Experimental set-up. BP is a band-pass filter, PC is a polarization controller, WDM is a wavelength division multiplexer, D is a pump dump, A is a variable attenuator and DUT is the device under test. b, Spectra of the input signal and amplified output signal (with sharp absorption lines owing to atmospheric water vapour seen in the spectrum between 1,810 nm and 1,940 nm). c, On-chip output signal power as a function of pump power for on-chip signal power ranging from 18 mW to 36 mW. d, Net on-chip gain as a function of pump power. The error bars in c and d represent the uncertainty owing to input and output coupling loss around the mean value estimated from at least four different measurements.