Compact surface Fano states embedded in the continuum of waveguide arrays

TL;DR

This paper reports the theoretical design and experimental observation of a compact surface Fano state in a waveguide array, which is embedded in the continuum and remains localized despite spectral broadening.

Contribution

It introduces a novel waveguide configuration that supports a Fano state embedded in the continuum, combining theoretical analysis with experimental validation.

Findings

Surface Fano state is experimentally observed in waveguide arrays.

The Fano state remains localized despite spectral broadening.

The state is compact with energy confined to a few waveguides.

Abstract

We describe theoretically and observe experimentally the formation of a surface state in a semi-infnite waveguide array with side-coupled waveguide, designed to simultaneously achieve Fano and Fabry-Perot resonances. We demonstrate that the surface mode is compact, with all energy concentrated in few waveguides at the edge and no field penetration beyond the side-coupled waveguide position. Furthermore, we show that by broadening the spectral band in the rest of the waveguide array it is possible to suppress exponentially localized modes, whereas the Fano state having the eigenvalue embedded in the continuum is preserved.