Fibre carries data as light rather than current, which gives it three advantages copper cannot match: distance measured in kilometres rather than metres, complete immunity to electromagnetic interference, and full electrical isolation between the equipment at each end. That last point matters for runs between separate buildings, where differing ground potentials can otherwise destroy switch ports.
Multimode grades
OM3 carries 10 Gigabit to 300 metres and is the established laser optimised multimode fibre. OM4 extends the same wavelength to 400 metres and handles 40G and 100G over shorter distances. OM5 adds wideband short wavelength division multiplexing, allowing several wavelengths down one fibre and supporting 400G in the same duplex pair. Multimode is the standard choice inside a building or campus.
Single mode
OS2 uses a 9 micron core and carries far greater distances, tens of kilometres, at the cost of more expensive optics. It is the answer for long haul, carrier and metropolitan links, and increasingly for campus backbones where future capacity matters more than transceiver price.
Connectors and MPO
LC is the dominant small form factor connector, SC is the older square latch type still common in existing infrastructure, and ST is bayonet style, mostly found in legacy installations. MPO and MTP trunks carry twelve or more fibres in one ferrule for high density backbone and spine to leaf links. Type A, B and C polarity determine how the fibres map end to end, and mixing them is the most common cause of a dark link.
Fiber grades at a glance
| Grade |
Type |
Core |
Jacket color |
10 Gbps reach |
40/100 Gbps reach |
| OM1 |
Multimode |
62.5 µm |
Orange |
33 m |
— |
| OM2 |
Multimode |
50 µm |
Orange |
82 m |
— |
| OM3 |
Multimode |
50 µm |
Aqua |
300 m |
100 m |
| OM4 |
Multimode |
50 µm |
Aqua or violet |
400 m |
150 m |
| OS2 |
Single-mode |
9 µm |
Yellow |
10 km+ |
10 km+ |
Match the fiber grade and connector type (LC, SC, ST) to the transceivers at both ends; multimode and single-mode never mix on one link.
Common questions
Should I use multimode or single-mode fiber? Inside a building or across a campus run under about 400 m, multimode OM3 or OM4 with inexpensive VCSEL optics. Between buildings or for anything measured in kilometers, single-mode OS2. The cable must match the transceivers at both ends; the two never mix on one link. Our fiber grade guide maps each grade to real distances.
Can I use an OM3 patch cable with OM4 equipment? Yes. OM3 and OM4 share the same 50 µm core and connectors, so they interoperate; the link simply runs at OM3 distances. Do not mix either with OM1 (62.5 µm core).
LC, SC or ST: which connector do I need? LC is the small connector on modern SFP, SFP+ and QSFP transceivers; SC is the larger push-pull connector on older patch panels and ONTs; ST is the bayonet connector on legacy panels. Patch cables come in every pairing, so match each end to the port it plugs into.
What is the difference between UPC and APC? The polish on the ferrule end face. UPC (blue) is flat and is standard for data links; APC (green) is angled at 8° to cut back-reflection, and is used in FTTH, CATV and long single-mode runs. UPC and APC connectors must never be mated to each other.
Shop by use: Server rack cables & power cords
Further reading: Which Fiber Optic Cable Do You Need? · A Short History of Fiber Optics
