Elimination of polarization degeneracy in circularly symmetric bianisotropic waveguides: a decoupled case

TL;DR

This paper demonstrates that polarization degeneracy in circularly symmetric bianisotropic waveguides can be eliminated by intrinsic coupling, leading to potential applications in compact polarization control devices.

Contribution

It introduces a method to break polarization degeneracy in symmetric waveguides through intrinsic bianisotropic coupling, supported by numerical and theoretical analysis.

Findings

Polarization degeneracy can be eliminated in symmetric waveguides.

x and y-polarized modes can be decoupled with specific bianisotropic parameters.

x-polarized modes become lossy, y-polarized modes remain unchanged.

Abstract

Mode properties of circularly symmetric waveguides with one special type of bianisotropy are studied using finite element approach. We find that the polarization degeneracy in circularly symmetric waveguides can be eliminated, by introducing intrinsic crossing coupling between electric and magnetic moments in the constituent units of the waveguide media. Breaking the polarization degeneracy in high order mode groups is also confirmed numerically. With the bianisotropic parameters chosen in this work, the x and y-polarized modes remain decoupled. Typically, the y-polarized modes remain completely unchanged, while the x-polarized modes are turned into leaky modes that are lossy along propagation direction. A perturbation model from coupled mode theory is developed to explain the results and shows excellent agreement. Such asymmetric behavior between different polarizations might be feasible and useful for developing compact polarizers in terahertz or mid-infrared regime.