Geometrical Uniformity of Plastic Coatings on Optical Fibers

The use of plastic coatings in optical-fiber technology is multifaceted. The refractive index of many polymer materials is less than that of fused silica, enabling them to be used directly as the cladding for fused silica cores. 1-3 The resulting waveguides, suitable for many communication applications, 4 - 5 are relatively easy to fabricate, possess low loss and large numerical aperture, and are LED-compatible. Plastic coatings are also applied as an overcoat to glass-clad optical fibers. They reduce microbending loss,6'7 maintain the pristine strength of the fibers,8 and provide for abrasion and mechanical protection of the fibers during cable-manufacturing processes. In yet other applications, coatings have been proposed as a method of decreasing crosstalk between optical fibers9 and as a way of improving the long-term stability of fibers in uncontrolled environments. To be most effective in all of the above applications, the coating must be applied uniformly and concentrically around the fiber. This is a necessity for routine handling and splicing as well as for optimum strength and transmission characteristics. The coatings are applied by various methods, and techniques have been proposed and implemented with varying degrees of success to aid in their concentric application. In general, micropositioning and microscopic observations are necessary to align the fiber at the start of each application 5 and only by preparing and microscopically 1525