Effect of the coating thickness and roughness on the mechanical strength and thermally induced stress voids in nickel-coated optical fibers prepared by electroless plating method

The effect of the coating thickness and roughness on the mechanical strength and thermally induced stress voids in nickel-coated optical fibers is theoretically and experimentally investigated. Seven samples of nickel-coated optical fibers with identical fiber length but different coating thickness are prepared using electroless plating method. The thickness of the nickel coating is controlled by the plating time, with the thicknesses being 35, 65, 119, 218, 308, 419 and 565 nm, respectively. The mechanical and thermal stresses in these nickel-coated optical fibers are analyzed. The atomic force microscope measurement reveals that the roughness of the nickel coating is unchanged when the coating thickness is not larger than 65 nm. However, as the coating thickness is not less than 65 nm, the coating roughness increases with increasing the coating thickness. To increase the tensile strength of the nickel-coated optical fiber, the coating thickness should be not less than 65 nm, and the surface roughness of the nickel coating should not exceed 2.93 nm. Alternatively, if the coating thickness is in the range of 35 to 218 nm, thermally induced stress voids are less found in the nickel coatings. However, if the coating thickness is in the range of 308 to 565 nm, the number of thermally induced stress voids increases with increasing the coating thickness. To minimize these voids, the surface roughness of the nickel coating should also be decreased