a) USPDC photon generation rate with respect to wavelength and pump power. The PPLN temperature is 56.8 °C. 1561 nm laser is OFF. b) (black squares) SFG signal power as a function of the pump power, with an input signal power at 1561 nm of 3.56 W defined at the PPLN input (red triangles) Number of photons detected per GHz per second at the SFG wavelength of 632.7 nm, as a function of the pump power, when the 1561 nm laser is OFF, as in Figure. 3a (red dashed line) Corresponding second-order polynomial fit.