There are four different mode types, each mode is distinguished by its core size and capabilities. They are known as Multimode and Singlemode fibres.

Multimode fibres consist of OM1 (62.5/125), OM2 (50/125) and OM3 (50/125 enhanced). These multimode fibres have a larger core size than singlemode fibres. The 62.5/125 and the 50/125 modes are used with LED sources at wavelengths of 850 and 1300 nm for short distances. These modes are used for lower speed networks such as LAN.

Multimode OM3 fibre is a more advanced form of 50/125 and is used with Gigabit transmission equipment.

Singlemode fibre (OS1) has a smaller core size (9 microns) and is used in CATV and telecommunications applications with laser sources at 1300 and 1500 nm. Singlemode is used where information is required to be transmitted over very long distances at high speeds.