Excitation of Bound Modes in an Optical Fibre

Abstract

Simple approximate formula for the excitation of an optical fibre by a plane wave focused through a lens are presented. The formula are valid for any mode of a weakly guiding fibre, and depend only on the angle of incidence of the plane wave striking the lens and a single parameter which contains all the waveguide information. The same results apply to the case of a uniform beam exciting a fibre. The fraction of power excited in the first two modes is compared with numerical results.