Giant stop bands and defect modes in one-dimensional waveguide with dangling side branches

Abstract

We investigate both the photonic and electronic band structure of a comb-like waveguide geometry in which dangling side branches are grafted along an infinite one-dimensional waveguide. In a periodic (superlattice like) waveguide, we report the opening-up of stop bands which originate both from the periodicity of the system and the resonant states of the grafted branches (which play the role of resonators). Wide gaps (narrow bands) can be obtained by grafting several dangling side branches at every node. The stop bands still remain even for identical constituent materials. We also propose a tandem structure composed of two or several successive combs which differ by their physical characteristics that allows an ultrawideband filter. This behavior results from the superposition of the bandgaps in the successive structures. The presence of a defect branch in the comb can give rise to localized modes inside gaps. These states appear as very narrow peaks in the transmission spectrum and therefore may have useful applications in the frame of photonic bandgap materials or electronic band engineering of nanostructures.