MODE COUPLING IN LARGE-DIAMETER POLYMER-CLAD SILICA FIBERS

摘要

Intermodal diffusion in a large-diameter plastic-clad silica step-index fiber is measured with a near-field projection of the modal pattern onto a CCD camera. The diffusion process is found to obey a 1/theta(2) dependence (where theta is the axis-crossing angle of the mode). The diffusion constant is estimated to be 1.3 x 10(-5) rad(2) m(-1). The contribution of mode mixing to evanescent-wave spectroscopy in such fibers is discussed. When all bound meridional modes are launched, the effect of diffusion is a small reduction-some 10% maximum-in the fraction of evanescent-wave power outside the core for the 0.4 numerical aperture fiber used. [References: 11]