**4. Discussion**

We demonstrated phase-matched optical SHG from the telecom range in suspended submicron AlGaAs waveguides with two different designs: a nanowire and a nanorib. The two approaches exhibit similar performances in terms of injection and propagation loss at ω, which are low enough to fabricate 1 mm long devices and in terms of nonlinear efficiency. Propagation loss at 2ω is intrinsically higher due to scattering and residual absorption, and it limits the SHG efficiency with respect to the expected values. Yet, the experimental conversion efficiency is higher than in oxidized form birefringent AlGaAs nonlinear waveguides (<sup>≈</sup> 10% W−1mm−2), [37,38] and comparable to state-of-the-art SiO2 cladded submicron GaAs waveguides (<sup>≈</sup> 130% W−1mm−2) [23]. While the optical performances are almost identical for the two designs, the nanorib exhibits far better mechanical properties. Its mechanical robustness makes its processing easier, not requiring CO2 supercritical drying, with a higher fabrication yield and less delicate handling. In addition, its ability to withstand several wetting and flash drying cycles without any damage makes the nanorib perfectly adapted to chemical and biological sensing in liquids, which could be easily injected through the etch windows.

**Author Contributions:** Conceptualization, G.L.; Investigation, M.R., S.S., P.F.; Technology contributions, A.L., I.F.; Supervision, G.L.; Writing and editing, I.R., M.R., G.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** I.R.'s post-doc grant was co-funded by the Université de Paris and the SEAM Labex.

**Conflicts of Interest:** The authors declare no conflict of interest.
