Modal Dispersion : A broadening of a waveform over long distances. Modal Dispersion (or Inter-modal Dispersion) occurs in multi-mode fibers, because light is bounced down different reflective paths (e.g. modes) in the fiber. As the distance increases, the path (mode) begins to spread and the arrival time for the different light rays begins to vary. A large variance (dispersion) increases the chance that the optical receiver may interpret the incoming signals incorrectly. Modal dispersion is a major problem with multi-mode fibers.