Singlemode vs Multimode

Over the past several years’ demand for higher bandwidth and faster speed connections has increased the growth of fibre optic cable market, especially the single mode fibre (SMF) and multimode fibre (MMF). Although these two types of fibre optic cables are used in numerous applications, they are very different from one another in terms of construction, fibre distance, cost and fibre colour. Single mode fibre means the fibre permits one form of light mode to be propagated at a time, however multimode fibre means the fibre can propagate multiple modes at a time. The difference between the two mainly lies in the fibre core diameter, wavelength, light source and bandwidth.

Core Diameter
The core diameter of single mode fibre is way much smaller than the multimode fibre. The typical core diameter for single mode fibre is 9µm and the typical core diameter for multimode fibre is 50µm and 62.5µm. This difference of core diameter enables MMF to have higher “light gathering” ability and simplify connections.

Wavelength & Light Source
The single mode fibre uses a laser or laser diode source to produce the light injected into the cable, the most commonly used single mode fibre wavelength is 1310nm & 1550nm. While due to the large core size of the multimode fibre, light sources like LEDs (light emitting diodes) and VCSELs (vertical cavity surface-emitting lasers) that work at the 850nm and 1310nm wavelength are used in MMF.

The single mode fibre bandwidth is theoretically unlimited due to the fact that it allows one light of mode to pass through at a time. However, the multimode fibre bandwidth is limited due to its light mode and the maximum bandwidth.

Differences in Distance

According to the chart illustrated above, it can be observed that SMF distance is visibly longer than that of MMF cables at the data rate from 1G to 10G, however, OM3/OM4/OM5 fibre optic supports higher data rate due to the larger core size and also because it supports multiple light modes. The limitation of distance is due to model dispersion, which is a common phenomenon in multimode step-index fibre.
In the end, it can be concluded that both single-mode and multimode have their own characteristics. Single-mode fibre cabling system is suitable for long-reach data transmission applications and widely deployed in carrier networks, MANs and PONs. On the other side, the multimode fibre cabling system has a shorter reach and is widely deployed in the enterprise, data centres, and LANs. No matter which one you choose, choosing the one that best suits your network demands is an important task for every network designer.


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