Measurement of the core diameter of graded-index optical fibers: an interlaboratory comparison.

An interlaboratory measurement comparison of optical fiber-core diameter was conducted by the National Bureau of Standards (NBS) in cooperation with the Electronic Industries Association. Participants include NBS and three fiber manufacturers. Six graded-index fibers were measured by all participants using the transmitted near-field method. As a group, the transmitted near-field measurements were consistent and exhibited an average standard deviation of 0.5 microm for 50-microm core fibers. These results were also compared to diameters determined by refracted near-field and transverse interference measurements contributed by other laboratories. For smooth-index profiles, all three methods agree within ~1 microm; substantial differences between the transmitted near-field and the other two methods can exist for fibers having step structure near the core-cladding boundary.