Quantifying and mitigating optical surface loss in suspended GaAs photonic integrated circuits.

Understanding and mitigating optical loss is critical to the development of high-performance photonic integrated circuits (PICs). In particular, in high refractive index contrast compound semiconductor (III-V) PICs, surface absorption and scattering can be a significant loss mechanism, and needs to be suppressed. Here, we quantify the optical propagation loss due to surface state absorption in a suspended GaAs PIC platform, probe its origins using x-ray photoemission spectroscopy and spectroscopic ellipsometry, and show that it can be mitigated by surface passivation using alumina (AlO).