Modal propagation constants, group delays, and eigenfields for practical multimode graded-index fibers

Abstract

Using a Rayleigh–Ritz formulation, modal propagation constants, group delays, and eigenfields are evaluated for practical multimode graded-index profiles by a solution of the scalar-wave equation. The fiber-index core may consist of a Taylor port, a central Gaussian dip, and damped ripples and is surrounded by a uniform cladding. Laguerre Gaussian expansion functions are applied, permitting analytical simplification of the general formulation. For a graded-index fiber with dip and V value of 20.8, modal group delays are determined with an accuracy of the order of 0.5 psec/km. For a larger fiber with V = 69, the method permits accurate and fast interpretation of differential-mode delay measurements.