Fano lines in the reflection spectrum of directly coupled systems of waveguides and cavities: measurements, modeling and manipulation of the Fano asymmetry

TL;DR

This paper investigates Fano resonance lines in the reflection spectra of directly coupled waveguide-cavity systems, revealing how coupling conditions influence the Fano line shape and providing insights into the underlying reflection and coupling processes.

Contribution

It presents experimental measurements and an analytical model demonstrating the sensitivity of Fano asymmetry to coupling conditions in directly coupled waveguide-cavity systems.

Findings

Fano line shape is influenced by the coupling process, not waveguide termini.

Small fiber movements can drastically alter the Fano asymmetry.

The Fano parameter is highly sensitive to coupling conditions.

Abstract

We measure and analyze reflection spectra of directly coupled systems of waveguides and cavities. The observed Fano lines offer insight in the reflection and coupling processes. Very different from side-coupled systems, the observed Fano line shape is not caused by the termini of the waveguide, but the coupling process between the measurement device fiber and the waveguide. Our experimental results and analytical model show that the Fano parameter that describes the Fano line shape is very sensitive to the coupling condition. A movement of the fiber well below the Rayleigh range can lead to a drastic change of the Fano line shape.