Fig. 3: Experimentally measured optical parametric wavelength conversion in the topological boundary states.

a Four-wave mixing spectrum for 5 ps pump pulses and as a function of pump peak power. The different spectra represent increasing pump peak powers from 0.9 to 7.5 W. Signal sidebands characteristic of parametric gain are shown to develop when the pump is on. b Measured (blue diamonds) and calculated (green dashed line) signal gain as a function of peak power calculated using the coupled equations. Measured (fuchsia squares) and calculated (cyan dashed line) idler conversion efficiency as a function of pump peak power. c Four-wave mixing spectra as a function of signal wavelength. The signal spectrum with the pump off is shown as the black dashed line. The locations of the generated idlers are shown in fuchsia. d Measured (blue diamonds) and calculated (green dashed line) signal gain as a function of signal wavelength. Measured (fuchsia squares) and calculated (cyan dashed line) idler conversion efficiency as a function of signal wavelength. Calculations were performed using the coupled equations. e Four-wave mixing spectra when 1 ps pulses are used as the pump. The pump spectrum with the signal off is the red solid line, whereas the spectrum where both pump and signal are on is shown as the blue dotted line. In this case, no idler is observed.