Impulse response of clad optical multimode fibers

Loss, coupling, and delay differences among the modes of multimode fibers influence their response to intensity-modulated optical signals. This “baseband” response is derived here from a time-dependent continuous description of the power flow in the fiber. Particular attention is given to the output as a function of angle and to the impulse response, its width and symmetry. We find that coupling narrows the impulse response but, at the same time, causes additional loss. Under practical conditions, this loss may limit the usefulness of coupling for the purpose of reducing the mode dispersion. We calculate a possible data rate of 12 Mb/s for a 10-km repeater spacing and an effective numerical aperture of 0.1, but we show that further improvements can be gained from an optimization of the coupling characteristic and of other parameters.