Ting-Ying Shen

Residual stress measurement in carbon coatings of optical fibers from the fiber bending curvature and coating thickness difference

The residual stress measurement in carbon coatings of optical fibers is theoretically and experimentally investigated. A simple formula used to measure the residual stresses in the thin film deposited on a cylindrical substrate with the bending curvature is proposed. During a temperature drop, the carbon-coated optical fiber is bent due to the nonuniform deposition of coating materials. The axial residual stresses in carbon coatings of optical fibers can be measured from the fiber bending curvature and coating thickness difference. Furthermore, if Young’s modulus of carbon coatings is known, the thermal expansion coefficient of carbon coatings can be determined.

Design of double-coated optical fibers to minimize long-term tensile-force-induced delamination of polymeric coatings from glass fibers

The design of double-coated optical fibers to minimize long-term tensile-force-induced delamination of polymeric coatings from glass fibers is investigated using viscoelastic theory. To prevent the delamination of polymeric coatings from glass fibers, the tensile-force-induced interfacial shear stress between the glass fiber and primary coating should be always smaller than its interfacial shear strength in the long term. The tensile-force-induced interfacial shear stress can be minimized by properly selecting physical properties of polymeric coatings and their thicknesses. The method for the minimization of the long-term tensile-force-induced delamination of polymeric coatings from glass fibers in double-coated optical fibers is proposed.

Effect of temperature cycling on the static fatigue of double-coated optical fibers

This study theoretically investigates the effect of temperature cycling on the static fatigue of double-coated optical fibers. The tensile force and temperature cycling induced tensile stresses on the glass fiber of double-coated optical fibers are determined using the viscoelastic theory. Optical fibers lifetime is dominated by the tensile stress on the glass fibers, which is a function of the material properties and thickness of the polymeric coating. To minimize these stresses on the glass fiber, the radius, Young’s modulus, and thermal expansion coefficient of the secondary coating should be reduced, while the relaxation time of the secondary coating should be increased. Additionally, based on strength consideration, the radius and Young’s modulus of the polymeric coating should be sufficiently thick or hard to support the external mechanical stresses. Meanwhile, based on the microbending-insensitivity consideration, the relaxation time of the primary coating should be reduced.

Design of tightly jacketed double-coated optical fibers to minimize long-term hydrostatic-pressure-induced microbending losses

The design of tightly jacketed double-coated optical fibers to minimize long-term hydrostatic-pressure-induced microbending losses is investigated. Microbending loss in these fibers is dominated by compressive radial stress at the interface between the glass fiber and the primary coating, which is a function of the polymeric materials properties and their thicknesses. To minimize the long-term hydrostatic-pressure- induced microbending losses, one should decrease the Youngs modulus, Poisson ratio, and relaxation time of the primary coating as well as the radius and Poisson ratio of the secondary coating, and increase the Youngs modulus and relaxation time of the secondary coating as well as the radius, Youngs modulus, Poisson ratio, and relaxation time of the jacket. Alternatively, the radius of the primary coating has its optimum value.

Long-term thermally interfacial-shear-stress-induced delamination of polymeric coatings from glass fibers in double-coated optical fibers

This study investigates the delamination of polymeric coatings from glass fibers in double-coated optical fibers, induced by long-term thermal interfacial shear stress. The shear stress between the fiber and the primary coating should always be lower than the interfacial shear strength to prevent delamination. It can be minimized by properly selecting the physical properties of the coatings as follows: The thickness and Youngs modulus of the secondary coating can be decreased so long as the requirement for the strength of the secondary coating is satisfied. The thickness of the primary coating can be increased if the spring constant of the optical fiber is chosen to prevent microbending of the glass fiber at low temperature. Meanwhile, Poissons ratio of the primary coating is set very close to 0.5. The Youngs modulus and the relaxation time of the primary coating, and the thermal expansion coefficient and the relaxation time of the secondary coating, should all be minimized.

The Design of Hermetically Double-Coated Optical Fibers to Minimize Hydrostatic Pressure–Induced Stresses

The design of hermetically double-coated optical fibers to minimize hydrostatic pressure–induced stresses is investigated. Several stresses are important in the hermetically double-coated optical fibers, and they would produce the excess bending losses or the failure of hermetic coatings. These stresses can be minimized by appropriately selecting materials properties of hermetic coatings and their thicknesses. The hydrostatic pressure–induced stresses in optical fibers with some selected metallic coatings are also considered. The results show that chromium has the best performance in the minimization of hydrostatic pressure–induced stresses. However, lead and indium are poor materials.

Thermally and mechanically induced microbending losses in single-coated optical fibres in the long term

The thermally and mechanically induced microbending losses in single-coated optical fibres in the long term are investigated by the viscoelastic theory. The microbending loss is dominated by the compressive radial stress at the interface between the glass fibre and the polymeric coating, which is a function of the material properties of the polymeric coating and its thickness. To minimize the thermally and mechanically induced microbending losses in the long term, the radius, Youngs modulus, thermal expansion coefficient and relaxation time of the polymeric coating should be decreased, but the Poissons ratio of the polymeric coating should be increased. Additionally, based on strength consideration, the radius and Youngs modulus of the polymeric coating should be thick or hard enough to support the mechanical stresses.