Selective mode excitation of graded index optical fibers

A method is described permitting excitation of a small number of modes in graded index fibers, the order of the launched mode being easily varied and determined. Using this launching technique, it is possible to determine the index profile and index difference of graded core fibers; results are compared with those obtained by other techniques. Other important fiber parameters, such as the differential attenuation and the differential propagation delay time as a function of the mode parameter, are also obtained, giving an insight into the fundamental propagation characteristics of the fiber.