Modal Bandwidth

   Modal Bandwidth, in the discipline of telecommunications, refers to the signaling rate per distance unit. The signaling rate can typically be measured in MHz, and the modal bandwidth is expressed as MHz•km (multiplied).
The Modal bandwidth of a multimode fiber is determined from the optical output power frequency spectrum. The frequency at    which the amplitude drops three decibels (dB) relative to the zero frequency component of the fiber is defined as the −3 dB bandwidth (or modal bandwidth) of the fiber optic cable.