Precise fabrication of coupled ring-resonator structures

We report improvements in fabrication precision obtained in coupled ring-resonator slow-wave structures on an SOI platform. Optical delay lines were formed by using a cascade of coupled resonant cavities to slow the propagation of light through the combined effects of resonance and increased optical path length. Mismatch between the resonance frequencies of individual rings has the additional effect of broadening the spectrum - and such mismatch can compromise the correct operation of the fabricated device structures. Single-ring resonator, bus-coupled ring resonator all-pass filters and directly coupled ring resonators in apodised structures have been fabricated, in order to assess the variability of the process.