In fiber optic light can travel in two forms that characterize the fiber itself with two types: single-mode fibre and multimode fibre.

In multimode fibre the core diameter is big (50 um – 300 um) therefore can travel more light rays. Some of the signal goes straight down the fiber while the rest of the signal bounces off the cladding. This makes for signal dispersion, which limits the bandwidth. Because the signals are not shooting straight down the cable like they are in single mode, the signals take longer to reach the end of the fiber. Monomode fibre has high attenuation so that is used for small distances and bandwidth.