Infrared Wave Propagation in a Helical Waveguide with Inhomogeneous Cross Section and Applications

This paper presents an improved approach for the propagation of electromagnetic (EM) fields along a helical dielectric waveguide with a circular cross section. The main objective is to develop a mode model for infrared (IR) wave propagation along a helical waveguide, in order to provide a numerical tool for the calculation of the output fields, output power density and output power transmission for an arbitrary step's angle of the helix. Another objective is to apply the inhomogeneous cross section for a hollow waveguide. The derivation is based on Maxwell's equations. The longitudinal components of the fields are developed into the Fourier- Bessel series. The transverse components of the fields are expressed as functions of the longitudinal components in the Laplace plane and are obtained by using the inverse Laplace transform by the residue method. The separation of variables is obtained by using the orthogonal- relations. This model enables us to understand more precisely the influence of the step's angle and the radius of the cylinder of the helix on the output results. The output power transmission and output power density are improved by increasing the step's angle or the radius of the cylinder of the helix, especially in the cases of space curved waveguides. This mode model can be a useful tool to improve the output results in all the cases of the hollow helical waveguides (e.g., in medical and industrial regimes).