Trimming of microring resonators by photo-oxidation of a plasma-polymerized organosilane cladding material

As the complexity of microphotonic devices grows, the ability to precisely trim microring resonators becomes increasingly important. Photo-oxidation trimming uses UV irradiation to oxidize a cladding layer composed of polymerized hexamethyldisilane (6M2S) deposited with plasma-enhanced chemical vapor deposition (PECVD). PECVD 6M2S has optical properties that are compatible with microring devices, and its high cross linking renders it insoluble. Photo-oxidation decreases the refractive index of PECVD 6M2S by nearly 4%, permitting large resonance shifts that are not feasible with thermal trimming techniques. Resonance shifts from single-mode, $100\mu \mathrm{m}$ diameter ${\mathrm{Si}}_3{\mathrm{N}}_4$ $(\mathit{n}=2.2)$ rings were as large as $12.8\mathrm{nm}$ for the TE mode and $23.5\mathrm{nm}$ for the TM mode.