Automatic geometric measurements of single-mode and multimode optical fibers

An automatic method has been developed to measure the outer diameter, the core diameter, the degree of ellipticity, and the core concentricity of both single mode and multimode optical fibers. A short length of fiber (~I cm) is prepared by scoring and breaking, and one end face is observed with a microscope utilizing transmitted light illumination. The image is processed with a computer-controlled automatic video-analysis- system which tracks and locates the outer and core boundaries, performs various fitting routines, calculates the desired quantities, and produces a plot of fiber boundaries and core offset, all within 3 min. The reproducibility of the measurements depends upon the quality of the sample and is on the order of 0.1 microm for eccentricity values of good fiber samples with surfaces free from dirt and cracks and on the order of (1/2)% for the core radius.