Mode properties and dispersion for two optical fiber-index profiles by the propagating beam method
- 15 September 1980
- journal article
- Published by Optica Publishing Group in Applied Optics
- Vol. 19 (18), 3140-3150
- https://doi.org/10.1364/ao.19.003140
Abstract
The propagating beam method generates solutions for the electric field in a graded-index optical fiber that emphasize beam characteristics rather than modal properties. Through Fourier analysis with respect to axial distance z, these solutions can be made to yield such mode properties as the propagation constants βn, the mode group delays ∂βn/∂ω, and the mode eigenfunctions. The propagating beam method has been applied to a detailed study of two index profiles with finite thickness cladding: an axisymmetric power-law (α = 1.85) profile both without and with an on-axis dip. In nine successive computer runs, eighty-five and eighty-four bound or guided modes were excited and characterized for the two respective profiles. The mode group delays near cutoff for both profiles show large deviation from those derived with the WKB method. In addition, sets of almost degenerate modes near cutoff show large differences in group delay. Modes with low azimuthal quantum number are strongly perturbed by the central dip. It is found that rms pulse dispersion is quite sensitive to the inclusion or exclusion of modes near cutoff, but that frequency response bandwidth is not. This leads to the conclusion that fiber bandwidth cannot be accurately inferred from rms pulse dispersion and may explain why broadband multimode fibers exist dispite strong perturbation of the modes near cutoff.This publication has 15 references indexed in Scilit:
- Computation of mode eigenfunctions in graded-index optical fibers by the propagating beam methodApplied Optics, 1980
- Computation of mode properties in optical fiber waveguides by a propagating beam methodApplied Optics, 1980
- Calculation of dispersion in graded-index multimode fibers by a propagating-beam methodApplied Optics, 1979
- Light propagation in graded-index optical fibersApplied Optics, 1978
- Pulse broadening in near-optimum graded-index fibresOptical and Quantum Electronics, 1978
- Guided modes in graded index optical fibersJournal of the Optical Society of America, 1977
- Influence of a central depression on the dispersion characteristics of a graded-index profileElectronics Letters, 1977
- Pulse broadening in graded-index optical fibersApplied Optics, 1976
- Multimode Theory of Graded-Core FibersBell System Technical Journal, 1973
- Scalar Analysis of Radially Inhomogeneous Guiding MediaJournal of the Optical Society of America, 1967