Resonant-wavelength tuning of microring filters by oxygen plasma treatment

The resonant-wavelength tuning of integrated-optic microring filters in silicon nitride using oxygen plasma treatment is demonstrated. During the treatment, high-energy oxygen ions in the plasma enter into the device surface such that the material composition is converted to SiO_xN_y. The corresponding index variation results in a modification of the effective index of the guide mode and, therefore, the tuning of the resonant wavelength of microring filters. The effects of treatment parameters, such as radio-frequency power, oxygen flow rate, and treatment time, on the characteristics of microring filters are discussed. Experimental results show that the resonant wavelengths of microring filters can be effectively tuned over a range larger than their free spectral ranges.