Polarisation independent optical ring resonators on silicon on insulator

Because of their compact size, ring resonators can be a cost effective solution for many Dense Wavelength Division Multiplexing (DWDM) components, as well as many low cost applications such as part of optical sensor circuits, or low cost optical signal processing. Modulators, filters, add-drop multiplexers, and switches are all components that can be realised with a ring resonator. Their potentially large Free Spectral Range (FSR), finesse, and quality factor, together with the potential for low cost fabrication, make them a viable alternative to many current DWDM devices. However, for such devices to be commercially viable, they need to be insensitive to the polarisation state of the input signal. The results obtained herein show that a single input/output optical racetrack resonator has been fabricated so that the minima in the resonance spectra align to better than 1pm. The rings also exhibit relatively low loss with measured Q-factors of approximately 90,000 and finesse values of 12.