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[38]

The conversion efficiency is calculated as the ratio between the on-chip idler peak power and the on-chip signal power, both evaluated at the end of the waveguide. The input on-chip signal power was about 47 µW (= −13.3 dB) at 1640 nm on the second-order mode. At the end of the waveguide, considering 4.6  dB·cm−1 of propagation losses and 1.5 cm waveguide length, the signal power on the second-order mode is −20.2  dBm. The off-chip generated average idler power is about −74.2  dBm, as shown in Fig. 8(a). Considering the coupling losses for the first-order mode, 5.3 dB, the on-chip average idler power is −68.9  dBm. Considering that the pump laser has 10 MHz repetition rate and 40 ps pulse width, the on-chip idler peak power, at the end of the waveguide, is −34.9  dBm. Therefore, the conversion between the signal power, −20.2  dBm, and the idler peak power, −34.9  dBm, is −14.7  dB.