Laser-assisted selective tuning of silicon nanophotonic structures

Silicon photonic integrated circuits have advanced to the point where thousands of components can now be combined into functioning optical circuits. A variety of quantum technologies are based upon the integrated silicon photonics platform, including pure photonics approaches as well as those based upon emerging silicon spin-photon interfaces. Integrated photonic components, such as grating couplers, photonic crystal cavities, and waveguides, are subject to slight manufacturing variations. For quantum technology applications, such variations often need to be minimized and ideally eliminated through careful post-processing. The laser-assisted "spot oxidation" post-processing technique is able to locally and permanently shift the resonance wavelength of nanophotonic devices using a 532nm continuous wave laser. While global tuning techniques affect entire chips, spot-oxidation is of interest because it can locally correct for specific manufacturing variations among many components within a single chip in an automated way. Yet prior to this work it was unclear if spot oxidation could be made compatible with photonic structures with SiO2 top-cladding, which are more robust and attractive for commercial deployment. Here, we apply laser-assisted tuning to silicon-on-insulator (SOI) devices with SiO2 top-cladding in the telecommunication O-band. In this work, we successfully tune both photonic crystal nanobeam cavities and sub-wavelength grating couplers up to 1.04(5)nm and 9(1)nm, respectively. This will enable higher-yield photonic circuits, as well as allow us to permanently locally tune optical structures into resonance with optically active colour centres in silicon.