The Centering of Optical Fiber Coatings by Monitoring Forward Scattering Patterns-Theory and Practice

Abstract

The forward scattering pattern from a transversely illuminated polymer‐coated optical fiber is modeled with a ray‐tracing program. For polymers with a refractive index higher than that of silica, the scattering pattern contains caustic surfaces. If the coating is eccentric in a direction perpendicular to the incident rays, we show that the positions of the caustic surfaces (θA) vary monotonically with eccentricity at the rate of 0.85°/μm for small eccentricities for a coating with a 1.539 refractive index and 59.3‐μm thickness on a 110‐μm diameter silica fiber. Another identifiable feature of the pattern (θB) has a predicted small‐signal sensitivity of 1.1°/μm. The information obtained from the pattern can be used to insure well‐centered coatings on optical fibers. A simple interpretation of the scattering pattern provides an error signal to guide compensatory coating cup alignment. The results are reported of well‐centered runs obtained on two separate drawing lines by this means.

A technique for optical fibre primary coating using glass applicators

“…Applicators of coating material are usually either splittable metal dies (France and Dunne 1976) or non-splittable dies made from silicone resin (Hart and Albarino 1977) which are flexible and to some extent self-aligning. Feedback control has been used to improve coating concentricity during a draw (Eichenbaum 1980).…”