High-Speed Measurement and Control of Fiber-Coating Concentricity

The concentricity of an optical fiber in a plastic coating affects the fiber strength, transmission loss, and the connectorization process. Self-centering coating techniques, such as the flexible tip applicator,1 or hydrodynamically designed applicators,2 have not been completely effective in maintaining the fiber centered in the coating. An alternative to such passive fiber centering is to measure and control the location of the fiber in the coating. Eichenbaum has described a technique in which the coated fiber is illuminated by a laser beam (Fig. 1) and the symmetry of certain features of the forward scattering pattern are used to determine coating concentricity.3 His model analyzed coatings whose refractive index is greater than that of the fiber, and eccentricities are normal to the direction of the laser beam. The effects of refractive index and relative fiber and coating diameters for the concentric case are also described. The model is limited, however, to fiber offset normal to the direction of incidence and does not consider the effect of the fiber core upon the forward-scattered pattern. 2065