Difference Between Single Mode & Multi Mode Fiber Optic Bandwidth

Written by tim brugger
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Difference Between Single Mode & Multi Mode Fiber Optic Bandwidth
The fibre optic bandwidth right for your application depends on your objective. (Comstock/Comstock/Getty Images)

Optical fibre has become the standard for the telecommunications and computer networking industries for several reasons. Fibre optics are easily bent and manipulated and can be bundled to streamline installations. Optical fibre can transmit much more data than copper cable, the industry norm before the advent of fibre optics. There are both multi and single-mode fibre optic alternatives, each of which has its strengths and weaknesses.

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Number of Fibers

The most obvious difference between single and multi-mode fibre optics are the number of fibres used; 1 vs. 2. This impacts the bandwidth as the diameter of the core (the area the light or laser travels with the data being transferred) of the single-mode optic is considerably smaller. However, while smaller in diameter, the single-mode optic cable does benefit from this smaller core in other areas such as speed and the distance the data can travel.

Bandwidths of Each

Single and multi-mode fibre optic cables come in a variety of widths. The typical diameter of a single-mode cable core is between 8 to 10 microns. Multi-mode fibre optic cable has a much greater width, usually between 50 and 62.5 microns. The additional width of the multi-mode cable does not necessarily make it better, there are some negative aspects to this additional capacity.

Speed and Distance

As a rule, the longer data must travel, the smaller the core should be. Therefore, single-mode fibre optics are preferred for instances the cable must be run over longer distances, generally over 6-10 miles. The compressed light travels faster as there is less "bouncing" from one side to the other in route. For shorter data links, such as Local Area Networks (LANs) and distances within a few miles, multi-mode cable is often the fibre optic of choice. There are cost as well that may be factor in determining which is preferable for your needs.

Mode Specific Equipment and Costs

Single-mode cable and equipment are both more expensive than multi-mode. This includes the cable itself, as well as the transmitters and receivers required to first send the data via light or laser, and then "re-code" it for deciphering on the receiving end. Also, you can't use multi-mode equipment on a single mode fibre optic; it must be single mode specific. The multi-mode equipment is not capable of shooting enough light through the single-mode cable, as it is designed for a much wider core. Though it is more expensive, single-mode cable is much easier to upgrade as needs change.

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