On electromagnetic wave propagation in an optical fiber having a core radius with a periodic axial variation

Abstract

A study is made of the modal properties of electromagnetic waves propagating along a dielectric fiber having a periodically varying core cross-sectional size along the direction of propagation. The maximum variation of the core radius is assumed to be small, and a full cycle of variation occurs over a large change in the axial variable z compared with the core radius. The general characteristic equation and cutoff conditions are derived, assuming that the component of the propagation vector β along the axis varies with the axial coordinate z. In general, β is complex, showing an attenuation or a reinforcement because of alternate flair and constriction. As an illustration, a numerical estimate of ∂β / ∂z as a function of z is made for some modes with simple and special properties where attenuation is negligible, and the axial electric and magnetic fields are in phase. The method can easily be extended to include more general cases by means of straightforward but tedious numerical work. © 1996 John Wiley & Sons, Inc.