Nondegenerate solution of TE and TM modes in step-index fibers using power-series expansion method

The power-series expansion method has been used to compute the exact cutoff frequencies of TM modes in step-index fibers for various values of relative refractive index difference (Δ), ranging from 0.005 to 0.1. The difference between the propagation constants of TM and TE modes, intermodal delay between TM and TE modes, and their variation with respect to the relative refractive-index difference has also been calculated. Numerical results show that for a fiber with
\Delta = 0.005
the intermodal delay between TM
01
and TE
01
modes is of the order of 1.5 ps/km at frequencies far away from cutoff, whereas it is of the order of 0.62 ns/km for
\Delta = 0.1
.