Complex modes in an open lossless periodic waveguide

Abstract

Guided modes of an open periodic waveguide, with a periodicity in the main propagation direction, are Bloch modes confined around the waveguide core with no radiation loss in the transverse directions. Some guided modes can have a complex propagation constant, i.e. a complex Bloch wavenumber, even when the periodic waveguide is lossless (no absorption loss). These so-called complex modes are physical solutions that can be excited by incident waves whenever the waveguide has discontinuities and defects. We show that the complex modes in an open dielectric periodic waveguide form bands, and the endpoints of the bands can be classified to a small number of cases, including extrema on dispersion curves of the regular guided modes, bound states in the continuum, degenerate complex modes, and special diffraction solutions with blazing properties. Our study provides an improved theoretical understanding on periodic waveguides and a useful guidance to their practical applications.

References in corpus (6)

• The physics of exceptional points
• Bloch bound states in the radiation continuum in a periodic array of dielectric rods
• Quasinormal-mode analysis of grating spectra at fixed incidence angles
• Exceptional points for resonant states on parallel circular dielectric cylinders
• Exceptional Points of Resonant States on a Periodic Slab
• Indirect link between resonant and guided modes on uniform and periodic slabs

Cited by in corpus (2)

• Complex modes in optical fibers and silicon waveguides
• Frequency perturbation theory of bound states in the continuum in a periodic waveguide