Common modal bandwidth specifications for multimode fiber are 400 MHz/Km for 50μ fiber and 160 MHz/Km for 62.5μ. If a transmission system requires 200 MHz of bandwidth to transmit an optical signal, there will be a limit well under 1 Km for 62.5 μ fiber, but the 50μ fiber will be able to go 2 Km before fiber modal bandwidth will limit the signal integrity.

Chromatic bandwidth refers to the characteristic of different colors of light that travel at different speeds through the fiber core. Lasers have a very narrow spectral emission, generating very few “colors” and will produce less chromatic dispersion. LEDs have a much wider emission spectrum and will produce many colors of light limiting the bandwidth of a signal that passes through the fiber. 

Both types of dispersion are dependant upon the light source used in the transmitter. An LED will produce a wider spectral output than a laser would. They will also produce more launch modes. It’s the combination of these two characteristics that can cause a transmission system to have a shorter distance capability than the loss budget may indicate.

These characteristics also apply to singlemode fiber. However, they do not present bandwidth issues unless the distance is very great.