Fibre — SM vs MM
Definition
Optical fibre used in AV networks is either single-mode (SM) or multimode (MM). Single-mode fibre has a core of about 9 µm in a 125 µm cladding (9/125 µm), low attenuation and a reach of tens of kilometres with laser sources at 1310 or 1550 nm, for example 10 km for 10GBASE-LR and 40 km for 10GBASE-ER. Multimode fibre has a 50/125 µm core in grades OM2 to OM5 (62.5/125 µm for OM1) and uses cheaper 850 nm VCSEL optics over shorter distances: 300 m on OM3 and 400 m on OM4 at 10GBASE-SR. Under the TIA-598 colour code, single-mode jackets are yellow, OM1 and OM2 orange, OM3 and OM4 aqua and OM5 lime green, a colour added in TIA-598-D; some manufacturers use violet for OM4. Single-mode and multimode optics are not interchangeable, and a link that mixes fibre and transceiver types is outside the standards and usually fails.
In the field
The jacket colour identifies the fibre type at a glance, and the connectors follow a similar code: blue for single-mode UPC, green for single-mode APC, beige or aqua for multimode. APC and UPC connectors are not mated with each other, because their end faces are polished at different angles. Within a venue, OM3 or OM4 multimode usually covers the distances; between buildings or over long outdoor runs, single-mode is the usual choice.
Related lessons
Sources
- Cisco, 10GBASE SFP+ Modules Data Sheet, 10GBASE-SR 850 nm : 300 m OM3, 400 m OM4 ; LR 1310 nm 10 km ; ER 1550 nm 40 km · cisco.com
- TIA-598-C (Wikipedia, pointeur secondaire), gaines : monomode jaune, OM1/OM2 orange, OM3/OM4 aqua · en.wikipedia.org
- Fiber Optic Association, Fiber Optic Cable Color Codes : couleurs des gaines et des connecteurs (monomode bleu, APC vert, multimode beige/aqua) · thefoa.org
- Multi-mode optical fiber (Wikipedia, pointeur secondaire) : cœurs 62,5/125 µm (OM1) et 50/125 µm (OM2 à OM5), OM5 vert citron, OM4 parfois violet · en.wikipedia.org
- Cabling Installation & Maintenance, TIA approves lime green as identifying color for OM5 fiber-optic cable : vert citron retenu pour l'OM5, publié dans l'addendum TIA-598-D-2 · cablinginstall.com