Regular papers

Coupled-resonator optical waveguides: Q-factor influence on slow-light propagation and the maximal group delay

Department of Photonics Engineering, DTU Fotonik, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark

^* asger@mailaps.org

Received: 24 November 2009

Abstract

Coupled-resonator optical waveguides hold potential for slow-light propagation of optical pulses. The dispersion properties may adequately be analyzed within the framework of coupled-mode theory. We extend the standard coupled-mode theory for such structures to also include complex-valued parameters which allows us to analyze the dispersion properties also in presence of finite Q factors for the coupled resonator states. Near the band-edge the group velocity saturates at a finite value υg/c∝1/Q while in the band center, the group velocity is unaffected by a finite Q factor as compared to ideal resonators without any damping. However, the maximal group delay that can be envisioned is a balance between having a low group velocity while not jeopardizing the propagation length. We find that the maximal group delay remains roughly constant over the entire bandwidth, being given by the photon life time τ_p = Q/Ω of the individual resonators.