Intermodal dispersion and mode coupling in perfluorinated graded-index plastic optical fiber

Graded-index multimode perfluorinated plastic optical fibers typically exhibit bandwidths much greater than would be expected from their index profiles. To resolve this discrepancy, we have conducted the first measurements of differential mode delay in such fibers. These measurements show intermodal dispersion that increases as the square root of fiber length, implying strong mode coupling in these fibers. Significant power transfer between modes occurs at lengths less than 20 m, so that mode coupling results in improved bandwidth on length scales relevant for local area networks. The observed coupling arises from extrinsic nonuniformities of the waveguide.