Attenuation at 10.6 µm in loaded and unloaded polycrystalline KRS-5 fibers

Extruded polycrystalline KRS-5 fiber exhibits a large amount of residual strain. This strain, which results from the large forces applied in the extrusion process, is a major contribution to the total attenuation. To study the effect of strain on fiber loss, the total attenuation coefficient alpha(T) and the attenuation coefficient due to scattering, alpha(S), are measured as a function of stress applied along the fiber axis. The applied stress sigma induces a change in the refractive index, which in turn leads to bulk scattering and excess fiber loss. It is found that alpha(T)=about sigma squared, which is in accord with an extension of a recent theory by Harrington and Sparks (1983).