A microscopic bright-field image technique for the measurement of averaged index profiles of quasi-axially symmetric large-mode-area microstructured fibers

We report on a nondestructive and noninterferometric technique for the experimental investigation of an approximation for the averaged index profile of quasi-axially symmetric large-mode-area microstructured optical fibers (MOFs). MOFs with a solid silica core surrounded by cladding, which consists of a system of air channels in silica, running along the fiber in a hexagonal structure around the core were analyzed. We used the transversal gradient of the phase, which was obtained from microscopic bright-field images of the studied quasi-axially symmetric MOFs. The inverse Abel transform was then applied to receive the approximation of the averaged index profile of the tested MOFs. The results of our investigations are presented.