Richard Garner Huff

Critical particle size of contaminants in high and low modulus coatings for high-strength optical lightguides

The critical size of coating contamination for glass fiber lightguides requiring high prooftest levels was determined for high- and low-modulus coatings. The critical size for highly adhering coatings, regardless of the modulus, is between 3 and 10 μm. The critical size of coating contamination for coatings which exhibit poor coating to fiber adhesion was found to be on the order of the Griffith flaw size for the given prooftest level.

Hermetically Coated Optical Fibers: Hydrogen Permeation And Fatigue Properties

Hydrogen permeation rates have been measured for fibers coated with a CVD applied amorphous carbon hermetic barrier. The H2 permeation was characterized by measuring optical loss increases at elevated temperatures at both high and low hydrogen pressures. Very low predicted values for the rates of hydrogen permeation over a wide range of operating temperatures were found, with an experimentally determined activation energy of 23.7 kcal/mole. In-situ measurements of loss increases upon exposure to hydrogen have shown the existence of a lag time where no hydrogen reaches the core of the fiber. Fiber strengths for the carbon coated hermetic fibers are typically 500-600 ksi. Fatigue properties are markedly improved by the presence of this type of hermetic coating. Dynamic fatigue results show extremely high n values on the order of 350-1000. Static fatigue tests in 21 ° C air and 50% relative humidity give n values of about 200. This is a great improvement over the fatigue results for non-hermetic fibers which exhibit n values of approximately 20.

Deposition of Hermetic Carbon Coatings on Silica Fibers

Carbon coated optical fibers have recently been shown to have excellent resistance to both static fatigue and hydrogen induced losses. The deposition technique used to form the carbon coating strongly affects the coatings ability to resist these degradation mechanisms. The system developed by AT&T utilizes an atmospheric CVD chamber in which a hydrocarbon has is pyrolyzed on the fiber surface. The heat retained in the fiber from the fiber forming process is used to drive the reaction, and high draw speeds are typically used to attain the ˜900°C temperature required to deposit the hermetic form of the carbon coating. Deposition rates of ˜1μm/sec are required to produce the ˜500 A coating.

Multikilometer lengths of 3.5-GPa (500 ksi) prooftested fiber

Approximately 70 km of fibers were drawn from synthetic silica rods and prooftested at four stresses between 1.4 GPa (200 ksi) and 3.5 GPa (500 ksi). The longest lengths achieved were 17.3 km passing 1.4 GPa (200 ksi), 13.4 km passing both 2.1 GPa (300 ksi) and 2.8 GPa (400 ksi), and 9.3 km passing 3.5 GPa (500 ksi). Tensile tests comparing fibers previously prooftested at 1.4 GPa (200 ksi) with those tested through 3.5 GPa (500 ksi) show no detectable degradation due to the high-strength prooftesting.