Although this is not found in step-index fibers
because eigenvalues are different each other, this could happen under the weakly-guiding approximation , where degeneracy can be overcome grouping degenerated modes into a new set of propagating modes, known as linearly polarized (LP) modes, which can also be analyzed by using the same formulation.
Normalized propagation coefficient plotted as a function of the number of basis functions for: (a) truncated parabolic refractive index profile fiber; (b) step-index fiber
; (c) step-index fibers
with different values of V.
The graded-index rays follow a sinusodial path compared to the zig-zag path of the step-index fiber
, shown in Figure 5.
Singh, II, "Modal characteristic equation and dispersion curves for an elliptical step-index fiber
with a conducting helical winding on the core cladding boundary: An analytical study," J.
Fiber optics is discussed next in chapters on transmission characteristics of step-index optical fibers, input and output characteristics of weakly guiding step-index fibers
, birefringence in single-mode fibers, and manufactured fibers.