**3.1 Conversion efficiency and OPO threshold**

We calculate conversion efficiencies with a code developed in the team, based on the work presented in [15]. **Table 3** shows the nonlinear conversion efficiency at several ridge widths for a waveguide of thickness 0.95 μm surrounded by Al0.8Ga0.2As and air. The corresponding pump powers necessary for an OPO threshold are presented in **Figure 3**. Propagation losses are assumed to be 0.1 cm<sup>−</sup><sup>1</sup> . The threshold pump power lies in the 10–100 mW range.
