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Ministry of Defence BT Inmarsat Science & Technology Facilities Council

Single Mode Cabling v Multimode Cabling

With data throughput demands constantly increasing, and loss budgets continually dropping, it's important to understand the standards when designing data centre cabling infrastructures. As you are well aware, electricity and electrical components are fully ingrained in almost every aspect of modern day living, and too often we don’t realise just how important the cabling connecting your device really is.

Mode Fibre

Single Mode Cabling

Single mode cables have a core of 8 to 10 microns. In single mode cables, light travels toward the centre of the core in a single wavelength. This focusing of light allows the signal to travel quicker and over extended distances without a loss of signal quality that can occur with multimode cabling.

Single Mode fibre optic cable has a small diametral central that allows only one mode of light to broadcast. Due to this, the number of light reflections created as the light passes through the core decreases, lowering attenuation and creating the ability for the signal to travel further. This application is typically used in long distance, higher bandwidth runs by Telecommunications companies, Universities and large corporations.

Multimode Cabling

Multimode cables have a core of either 50 or 62.5 microns. In multimode cables, the larger diametral core allows numerous modes of light to propagate. Due to this, the number of light reflections created as the light transmits through the core rises, creating the ability for more data to pass through at one time. Because of the high dispersal and weakening rate with this type of fibre, the quality of the signal is reduced over long distances. This application is typically used for short distance, data and audio/video applications in local area networks. RF broadband signals, such as what cable companies commonly use, cannot be transmitted over multimode fibre.

Which are better?

That all depends on your usage! Single mode Cables are the best choice for transmitting data over long distances. They are usually used for connections over large areas, such as college campuses and remote offices. They have a higher bandwidth than Multimode cables to deliver up to twice the throughput.

Multimode Cables are a good choice for transmitting data and voice signals over shorter distances. They are typically used for data and audio/visual applications in local-area networks and connections within buildings or remote office in close proximity to one another.

Should I install single mode or multimode fibre?
Again it depends, multimode fibre can transmission distances of up to approximately 10 miles and will allow the use of relatively inexpensive fibre optic transmitters and receivers. There will be bandwidth limitations of a few hundred MHz per Km of length. Consequently, a 10-mile link will be limited to about 10 to 30 MHz. For data such as CCTV this will be fine but for high speed data transmission it may not be adequate.

Whereas, single mode fibre is better used for distances well in excess of 10 miles but will require the use of single mode transmitters. The higher cost of these optical emitters mean that single mode equipment can be anywhere from 2 to 4 times as expensive as multimode equipment. So deciding between single mode cabling and multimode cabling entirely depends on your use.