Unattenuated global modes in a planar dielectric waveguide with a flare in the direction of propagation

Abstract

In this paper, continuing our earlier work on the modal properties of a planar waveguide with a flare, we examine whether unattenuated guided modes can exist in such waveguides. We use the scalar wave approximation and the cylindrical polar coordinates (ρ, φ, z) in a new way. Ordinarily, the guiding region lies between two distinct values of ρ, and the propagation is along the z-axis. In our case, however, we take the propagation in the ρ-direction, and the guiding region is bounded by two planes corresponding to two slightly different values of φ. This represents a planar waveguide with a flare, and we obtain the modal characteristic equation for unattenuated modes. Numerical computation shows the surprising result that global unattenuated modes can be sustained in such a structure for ν = 0, where ν is the modal index corresponding to the φ-coordinate.