The differences between Multi-mode and Single-mode fibre

Fibre cables vary enormously, in the type of fibre, the construction and materials and the number of fibres present. Optical fibres are extremely thin strands of very high purity silica (glass), which transmit light from one end to the other with minimal loss.

Types of Fibre
There are two primary types of fibre – multimode and singlemode.

Multimode fibre can carry multiple light rays (modes) at the same time by having varying optical properties at the core; essentially light travelling the shortest path (down the middle) travels the slowest.The larger core simplifies connections and takes advantage of the lower cost LED & VCSEL technologies which operate in the 850nm window. Due to dispersion the range is limited so it tends to be used as premises cabling when less than a kilometre. It comes in two core sizes, 62.5 and 50 microns.

Singlemode fibre has a much smaller core size of 9 microns and has a single light path and can travel much longer distances of up to 100km. These require more expensive electronics which operate in the 1310 and 1550nm windows and are typically used in longer distance LAN’s, Cable TV and telephony applications.