Crosstalk bandwidth of grating-assisted ring resonator add/drop filter

Ring resonators are used in all-optical networks to provide add/drop functionality. As a result, crosstalk suppression is one of the most important aspects to be considered in their design to ensure optical signal integrity. It is known that sidewall roughness causes a splitting of the mode at resonance due to the interaction between the forward and backward travelling waves. In this paper, this effect is used to increase the crosstalk suppression bandwidth over the value that could be expected from a smooth-walled resonator. This paper presents a general form for the spectral response of a ring resonator add/drop filter in the presence of sidewall roughness. The derived analytical model is verified against numerical, and published experimental, results of a randomized rough-walled ring resonator. The paper then derives the performance of a ring resonator with a periodic variation of the sidewall, a design which is more controllable during manufacture than a purely randomized variation. It concludes with the design of a grating-assisted single ring resonator that provides a 32 GHz crosstalk suppression bandwidth. The proposed design can be used to drop 10 Gbps signals with low level of crosstalk using a small size filter (compared to a conventional double ring based filter of similar bandwidth) which improves the integration density of optical devices.