Post-fabrication resonance trimming of Si 3 N 4 photonic circuits via localized thermal annealing of a sputter-deposited SiO 2 cladding

We report a resonance trimming technique, applicable to waveguides employing an SiO2 cladding. The SiO2 is deposited by a room temperature sputtering process. Resonance shifts of micro-ring resonators of 4.4 nm were achieved with furnace annealing, whereas a resonance shift of 1.4 nm was achieved using integrated micro-heaters. For our device layout, with 30 μm ring separation, the thermal cross-talk is negligible, and isolated trimming of each micro-ring is achieved. Three, single-channel ring filters on the same substrate were aligned to the same wavelength within a 20 pm precision. The stability of trimmed micro-rings was assessed following extended storage in atmospheric ambient. For a ring shifted by 4.4 nm using furnace annealing, relaxation of 540 pm is observed, while for a ring shifted by 1.4 nm using integrated heaters, the relaxation is 270 pm.