An analytical study of the modal characteristics of annular step-index waveguide of elliptical cross section with two conducting helical windings on the two boundary surfaces between the guiding and the non guiding regions
We study an optical fiber with a guiding region bounded by two ellipses. There are two conducting helical windings on the two interfaces between the annular guiding region and the inner and outer cladding regions. The field components are determined for the different regions and they are matched at the boundaries using appropriate boundary conditions. This leads to an eighth order determinantal equation. The characteristic equation and the cutoff condition of the proposed waveguide are then obtained.