Optical Fiber
There are two classifications for optical fiber: single-mode (SMF) and multi-mode (MMF). In SMF light follows a single path through the fiber while in MMF it takes multiple paths resulting in differential mode delay (DMD). SMF is used for long distance communication and MMF is used for distances of less than 300 m. SMF has a narrower core (8.3 µm) which requires a more precise termination and connection method. MMF has a wider core (50 or 62.5 µm). The advantage of MMF is that it can be driven by a low cost Vertical-cavity surface-emitting laser (VCSEL) for short distances, and multimode connectors are cheaper and easier to terminate reliably in the field. The advantage of SMF is that it can work over longer distances.
In the 802.3 standard reference is made to FDDI-grade MMF fiber. This has a 62.5 µm core and a minimum modal bandwidth of 160 MHz*km at 850 nm. It was originally installed in the early 1990s for FDDI and 100BaseFX networks. The 802.3 standard also references ISO/IEC 11801 which specifies optical MMF fiber types OM1, OM2, OM3 and OM4. OM1 has a 62.5 µm core while the others have a 50 µm core. At 850 nm the minimum modal bandwidth of OM1 is 200 MHz*km, of OM2 500 MHz*km, of OM3 2000 MHz*km and of OM4 4700 MHz*km. FDDI-grade cable is now obsolete and new structured cabling installations use either OM3 or OM4 cabling. OM3 cable can carry 10GbE 300 metres using low cost 10GBASE-SR optics (OM4 can manage 400 metres) .
To distinguish SMF from MMF cables, SMF cables are usually yellow, while MMF cables are orange (OM1 & OM2) or aqua (OM3 & OM4). However, in fibre optics there is no agreed colour for any specific optical speed or technology with the exception being angular physical connector (APC), it being an agreed colour of green.
There are also active optical cables (AOC). These have the optical electronics already connected eliminating the connectors between the cable and the optical module. They plug into standard optical module sockets. They are lower cost than other optical solutions because the manufacturer can match the electronics to the required length and type of cable.
Read more about this topic: 10-gigabit Ethernet
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