Trimming of microring resonators by photooxidation 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 microm diameter Si3N4 (n =2.2) rings were as large as 12.8 nm for the TE mode and 23.5 nm for the TM mode.