Rapid Automatic Index Profiling of Whole-Fiber Samples: Part 2

Rapid Automatic Index Profiling of Whole-Fiber Samples: Part II By H. M. PRESBY, D. MARCUSE, H. W. ASTLE, and L. M. BOGGS (Manuscript received May 1, 1978) Automatic, nondestructive methods have been developed for measuring and analyzing the refractive index distribution of a fiber that is immersed in index-matching oil and illuminated transversely to its axis in a single-pass interference microscope. The output field of the microscope is automatically processed with a video-digitized, computer-controlled system, and the profile is determined by the solution of an integral equation that can handle arbitrary variations in the index distribution. The resulting profiles are reproducible to approximately 1 percent and can be determined within a few minutes after fiber fabrication. Details of a rapid video scanning procedure and of error estimates involved in solving the integral equation are presented along with representative profiles. I. INTRODUCTION One of the most important parameters in determining the usefulness of graded-index multimode optical fibers in high-capacity communication systems is their refractive index profile. The closer the profile conforms to the required optimum distribution, the greater the resulting bandwidth of the fiber. As demand for high-capacity fibers increases and as fabrication facilities are optimized to produce them dependably, it becomes very important to have reliable, accurate, and fast methods to measure the fiber's refractive index distribution.