Opt Quant Electron DOI 10.1007/s11082-014-9969-0 Crosstalk bandwidth of grating-assisted ring resonator add/drop filter R. Mansoor · H. Sasse · S. Ison · A. Duffy Received: 2 May 2014 / Accepted: 17 June 2014 © Springer Science+Business Media New York 2014 Abstract 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. Keywords Back-reflection · Crosstalk · Grating reflectivity · Ring resonator add/drop filter · Sidewall roughness 1 Introduction The optical waveguide micro-ring resonator is a promising technology for integrated photonic devices in wavelength division multiplexing (WDM) networks (Bianco et al. 2011; Koziel and Ogurtsov 2014; Cox et al. 2014). Silicon-on-insulator (SOI) photonic micro-ring devices have R. Mansoor (B ) · H. Sasse · S. Ison · A. Duffy De Montfort University, Leicester, UK e-mail: P10005332@myemail.dmu.ac.uk R. Mansoor Ministry of Industry and Minerals, Baghdad, Iraq 123