Gap opening and split band edges in waveguides coupled by a periodic system of small windows

TL;DR

This paper investigates how periodic small holes in coupled waveguides influence spectral gaps and band edges, demonstrating control over gap positions and number through geometric parameters.

Contribution

It introduces a model of coupled waveguides with periodic holes, analyzing how geometric variations affect spectral gaps and band extrema, with asymptotic calculations.

Findings

Spectral gaps can be opened and controlled by adjusting waveguide widths and hole spacing.

Extrema of band functions can be positioned inside the Brillouin zone.

Asymptotic formulas for gap lengths and extremum locations are derived.

Abstract

At the example of two coupled waveguides we construct a periodic second order differential operator acting in a Euclidean domain and having spectral gaps whose edges are attained strictly inside the Brillouin zone. The waveguides are modeled by the Laplacian in two infinite strips of different width that have a common interior boundary. On this common boundary we impose the Neumann boundary condition but cut out a periodic system of small holes, while on the remaining exterior boundary we impose the Dirichlet boundary condition. It is shown that, by varying the widths of the strips and the distance between the holes, one can control the location of the extrema of the band functions as well as the number of the open gaps. We calculate the leading terms in the asymptotics for the gap lengths and the location of the extrema.