Single Mode vs Multimode Fiber

Posted September 14th, 2020 by Gary & filed under Blog, Fibre Optic Cabling, Tips and Advice.

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: Fibre Cabling Terminations

Fibre optic cabling is a very common aspect of most structured cabling installations. Therefore crossing the correct type of fibre cable is imperative to the successful operation of your technology. In addition within those types you need to choose the correct category within that cable type bracket. Therefore the below compares Single Mode vs Multimode Fiber and the differences between them

All fibre cables are constructed of individual cores with which within the light is transported from transmitter to receiver. This cores are mode of either glass or plastic. Furthermore that consist of the actual inner core and the cladding surrounding and protecting that tube. In addition fibre cables can contain numerous cores within a single cable. Thus bundles of 4,8,12,16,24,48 are commonly founds in a single fibre optic cable.

Further articles on Fibre Optics and FAQ’s can be found on our Fibre Optic Knowledge Centre HERE

Singlemode Fiber

The terminology of a singlemode fiber comes from the situation that is transmits a single mode of light down its cores. The transmission is via a laser from the transmitting device. A single mode of light its transported directly the core with minimal reflection within

The inner core is smaller than its counter part for this reason and is referred to as 9/125. This is a 9 micron diameter core coated in a 125 micron cladding. Due to the transmission properties there is less dispersion of light as it travels along the core and therefore there is less loss of the original signal. Thus singlemode fiber is more suited to higher bandwidth requirements. Furthermore it is more suited to longer transmission distance applications.

The cable is categorised into 2 sub sections.

OS1 and OS2 differ mainly in their cable construction. Thus OS1 is commonly a tight buffered construction and for internal applications. Likewise OS2 is usually a blown fibre or loose tube construction and for external purposes

They have similar transmission characteristics. However due to less attenuation (transmission loss) on OS2 cables it can transmit similar speeds over longer distances. For example some manafacturers will state OS1 transmitting 10GBE up to 2km and OS2 transmitting 10GBE upto 10km

This is due to the attenuation loss on OS1 being 1dB/km and Os2 being 0.4dB/km. Less attenuation equals greater transmission range

Due to the specialist equipment for transmission the overall cost of a single-mode system is higher than that of multi-mode. However the cable can cheaper to purchase and is the same cost to install.

Multimode Fiber

Multimode receives it names in an opposite way to its counterpart. Multiple / Many modes of light are transmitted down its core all of which travel are different wavelengths are in a different path. The light source is usually an LED source

Thus the light is similar to that of shining a torch into the core. Subsequently there is greater modal dispersion (Loss) of the light as it travels.

For this reason multimode doesn’t have the same transmission distance capability as singlemode.

The cores in a multi-mode fibre are considerably larger than single-mode. 4 of the main categories are 50/125 and the legacy OM1 is 62.5/125. Notice that the cladding for all fibre cables remains the same and only the internal core size changes

The 5 categories of multi-mode fibre are

Each category is an improvement on its predecessor. Therefore this results in a greater ability to transmit greater bandwidth. Further higher grades are able to transmit the same speeds as the previous grade but over longer distances.

The Chart below compares the different cables and their transmission capabilities