Fig. 3: High-performance OPO.

a Representative spectrum from an OPO device producing (13.8 ± 1.1) mW of on-chip idler power for an on-chip pump power of (87.3 ± 3.0) mW, corresponding to a conversion efficiency of (0.21 ± 0.03) (in terms of photon flux). A power of 0 dB is referenced to 1 mW (i.e., dBm); the offset between the plotted dB values and the on-chip power values P_p and P_i are due to fiber coupling and other insertion losses (see Supplementary Material for details). The inset displays η_i and P_i for different pump power (increasing from green to red) and pump frequency detuning. b, c Peak conversion efficiency \({\eta }_{i}^{{{{{{\mathrm{max}}}}}}}\) (b) and on-chip idler power P_i (c) as a function of resonator-waveguide gap for a series of OPO devices. \({\eta }_{i}^{{{{{{\mathrm{max}}}}}}}\) and P_i monotonically increase with decreasing gap (increased coupling) until a gap of 200 nm, at which point \({\eta }_{i}^{{{{{{\mathrm{max}}}}}}}\) is reduced, as discussed in the text. The dashed gray line in b shows the theoretical value for \({\eta }_{i}^{{{{{{\mathrm{max}}}}}}}\) based on the coupling parameters extracted in Fig. 2c, and the dashed orange line is the absolute theoretical maximum, where 50% of the pump photons are converted to the idler and the other 50% are converted to the signal. Two different data points are shown at a gap of 300 nm, corresponding to different OPOs. The OPO spectrum from the green data point in c is shown in Fig. 4(b) and represents the highest η_i = 0.29 ± 0.04 with corresponding P_i = (18.3 ± 2) mW that we have observed. The uncertainty values and error bars in b–d are one standard deviation values and are due to the combined uncertainty of coupling losses on and off of the chip and the transmission losses of different optical components between the output coupling fiber and the detector (see Methods for details). For visual clarity, when the error bars are smaller than the data point size, they are omitted.