Knowledge
Singlemode or multimode: OS2 and OM4
Why nearly everything is singlemode, when multimode works out cheaper and what distance has to do with it.
OS2 singlemode has a 9 µm core and one light path; OM4 multimode has 50 µm and several, so the pulse spreads out over distance. OM4 reaches 150 m at 40GBASE-SR4 and 100 m at 100GBASE-SR4; OS2 runs to kilometres. Multimode only pays on short links within one hall, because the transceivers are cheaper. Four of our five fibre types are OS2; the tight-buffered indoor cable comes in both OS2 and OM4.
The difference between singlemode and multimode lies in the core of the fibre. OS2 singlemode has a 9 µm core and carries one light path. OM4 multimode has a 50 µm core and carries several at once. Those several paths each travel a slightly different route, so the pulse spreads out over distance. That is exactly what limits the reach of multimode.
In metres: OM4 reaches 150 m at 40GBASE-SR4 and 100 m at 100GBASE-SR4. 40GBASE-SR4 and 100GBASE-SR4 are Ethernet standards for 40 and 100 Gbit/s over multimode. SR stands for short reach, and the 4 for four fibres transmitting and four receiving at the same time. OS2 has no such limit: the transceivers and the optical budget decide how far you can go, and that runs to kilometres. As soon as a link leaves the building or grows longer than a hall, singlemode is the logical choice.
Why multimode exists at all is down to the optics at either end. Within one hall or one equipment room, with links under a hundred metres, multimode transceivers are cheaper than singlemode. Across a handful of links that saving is negligible compared with the cable and splicing costs; across hundreds of links in a data centre it adds up.
Our range shows how that works out. Four of the five fibre types are OS2 singlemode, 9/125 µm to G.652.D: loose tube for duct and tray, an armoured version for direct burial and against rodents, a universal indoor-outdoor cable and ADSS for overhead routes. The tight-buffered indoor cable comes in both OS2 and OM4. Outside the data centre singlemode has become the standard, and the list shows it.
Do not mix the two in one route. A singlemode transceiver on a multimode fibre does not give a reliable link, and a splice between a 9 µm core and a 50 µm one is not a splice. So settle the choice before anything is pulled or spliced, and stick with it all the way to the patch cabinet.
For the buyer: in your enquiry, state the fibre type, the fibre count, the construction (loose tube, tight-buffered, armoured or ADSS) and whether the cable enters the building. That last point decides whether a CPR class is needed: our loose-tube outdoor cables with a PE sheath have none, and for an indoor route with a CPR requirement you take the LSZH version.
Do you know the distance but not yet the optics? Send the link length, the speed and whether the cable enters the building. We will tell you whether it should be OS2 or OM4 and whether a CPR class is required.