ON ELECTROMAGNETIC-WAVE PROPAGATION IN AN OPTICAL-FIBER HAVING A CORERADIUS WITH A PERIODIC AXIAL VARIATION

A study is made of the modal properties of electromagnetic waves propa gating along a dielectric fiber having a periodically varying core cro ss-sectional size along the direction of propagation. The maximum vari ation of the core radius is assumed to be small, and a full cycle of v ariation occurs over a large change in the axial variable z compared w ith the core radius. The general characteristic equation and cutoff co nditions are derived, assuming that the component of the propagation v ector beta along the axis varies with the axial coordinate z. In gener al, beta is complex, showing an attenuation or a reinforcement because of alternate flair and constriction. As an illustration, a numerical estimate of partial derivative beta/partial derivative 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 genera l cases by means of straightforward but tedious numerical work. (C) 19 96 John Wiley & Sons, Inc.