Non reflection and perfect reflection via Fano resonance in waveguides

TL;DR

This paper analyzes Fano resonance in waveguides, demonstrating how it causes abrupt changes in scattering behavior, enabling perfect transmission or reflection of waves, with theoretical justification and numerical illustrations.

Contribution

It provides a rigorous asymptotic analysis of Fano resonance in waveguides, showing how it leads to non reflection or perfect reflection at specific frequencies.

Findings

Scattering matrix is discontinuous at trapped mode frequencies.

Rapid change in scattering behavior near resonance frequencies.

Constructed waveguides with perfect transmission or reflection.

Abstract

We investigate a time-harmonic wave problem in a waveguide. By means of asymptotic analysis techniques, we justify the so-called Fano resonance phenomenon. More precisely, we show that the scattering matrix considered as a function of a geometrical parameter $\varepsilon$ and of the frequency $\lambda$ is in general not continuous at a point $(\varepsilon,\lambda)=(0,\lambda^0)$ where trapped modes exist. In particular, we prove that for a given $\varepsilon\ne0$ small, the scattering matrix exhibits a rapid change for frequencies varying in a neighbourhood of $\lambda^0$. We use this property to construct examples of waveguides such that the energy of an incident wave propagating through the structure is perfectly transmitted (non reflection) or perfectly reflected in monomode regime. We provide numerical results to illustrate our theorems.