Coupled-resonator optical waveguides: Q-factor and disorder influence

TL;DR

This paper analyzes how finite Q factors and disorder, including Anderson localization, limit the slow-light capabilities and maximum delay times in coupled-resonator optical waveguides (CROWs).

Contribution

It provides analytical insights into how Q factor and disorder constrain the group delay and device length in CROWs, highlighting the impact of Anderson localization.

Findings

Maximum delay time limited by photon lifetime of a single resonator

Finite Q restricts group index and device length

Disorder induces destructive interference and localization

Abstract

Coupled resonator optical waveguides (CROW) can significantly reduce light propagation pulse velocity due to pronounced dispersion properties. A number of interesting applications have been proposed to benefit from such slow-light propagation. Unfortunately, the inevitable presence of disorder, imperfections, and a finite Q value may heavily affect the otherwise attractive properties of CROWs. We show how finite a Q factor limits the maximum attainable group delay time; the group index is limited by Q, but equally important the feasible device length is itself also limited by damping resulting from a finite Q. Adding the additional effects of disorder to this picture, limitations become even more severe due to destructive interference phenomena, eventually in the form of Anderson localization. Simple analytical considerations demonstrate that the maximum attainable delay time in CROWs is limited by the intrinsic photon lifetime of a single resonator.