Optical fiber protection by powder filled coatings

Abstract

The optically transmissive fiber of a fiber optic cable is protected from degradation by corrosion from environmental fluids in high pressure and/or temperature environments. The light transmitting fiber is surrounded with one or more protective layers which contain finely divided particles, typically of the same composition as the corrodible components of the fiber, with the particles functioning to absorb and neutralize the corrosivity of the environmental fluids. These fluids cannot be entirely prevented from slowly penetrating the protective layers or coatings over time, particularly under the influence of the elevated temperatures or pressures. The particles are typically of a metal or metal oxide matching the metal or metal oxide constituent of the outer portions of the optical fiber itself. These particles typically are suspended in the polymeric, buffering layer directly surrounding the optical fiber. The particles are in a powdered form of micron size or smaller. This small size avoids micro bending losses typically associated with the presence of inhomogeneous layers adjacent to the optically transmitting fiber. Preferably before being buffer coated, the optical fiber is given a protective metal or metal oxide surface layer and a coupling agent layer may also be added between the fiber and buffer layer. This coupling layer is also doped with powders of the corrosion protecting elements. Outer layers such as cable sheathing may also include doping compounds to absorb or neutralize the corrosive environmental fluids.