Fibre Patch Lead Connector Types: LC, SC, ST, FC and MPO Explained
Order a fibre patch lead and you immediately hit an alphabet soup: LC, SC, ST, FC, MPO, UPC, APC, OS2, OM4. It's a lot, and getting any one of them wrong means a lead that physically won't plug in or won't perform. The good news is that there's a clear logic to it. A fibre lead is defined by three things — the connector, the polish and the fibre type — and once you can read those, the soup makes sense.
The connectors
| Connector | How to spot it & where it's used |
|---|---|
| LC | The small one, with a push-pull latch like an RJ45 clip and a 1.25 mm ferrule. By far the most common today — it's what plugs into SFPs, mini-GBICs and modern switches. Usually supplied duplex (two clipped together). |
| SC | The larger square push-pull connector, 2.5 mm ferrule. Older and bulkier than LC but still widely seen on legacy equipment and some patch fields. |
| ST | A round bayonet connector you twist and lock, 2.5 mm ferrule. Common on older multimode installs and patch panels. |
| FC | A round metal connector that screws on, with an alignment key, 2.5 mm ferrule. Mostly singlemode and test/measurement gear, where the screw fit holds alignment. |
| MPO / MTP | The multi-fibre connector — one rectangular ferrule carrying 12 or 24 fibres at once. Used for high-density trunks and 40/100G data-centre links. |
The polish: UPC vs APC
Look at the ferrule colour and you'll often see blue or green. That's the polish. UPC (usually blue) is a flat, ultra-polished finish — the default for most multimode and general use. APC (usually green) is polished at an 8-degree angle, which sends back-reflection away from the core. APC is the choice for singlemode runs sensitive to return loss, like long-haul and some broadcast or PON systems. The key rule: don't mate UPC to APC. The end-faces won't sit flush, and you'll wreck both performance and, potentially, the connectors.
The fibre itself: singlemode vs multimode
Finally, the glass inside has to match at both ends. The two families aren't interchangeable:
| Type | Core & use |
|---|---|
| Multimode (OM3 / OM4 / OM5) | Larger core (typically 50 micron). Driven by cheaper LED/VCSEL sources over shorter distances — the usual choice inside a building or campus. Often aqua or lime-green jacketed. |
| Singlemode (OS2) | Tiny ~9 micron core, laser sources, very long distances — telephony, between sites, carrier links. Usually yellow jacketed. |
You can't run a multimode lead on a singlemode link or vice versa, even if the connectors fit. The transceivers and the fibre have to belong to the same family.
Putting it together
So a fully specified lead reads like “LC-LC, OS2 singlemode, APC” or “LC-SC, OM4 multimode, UPC”. Work through the three questions — what connector does each end need, what fibre type is the link, and which polish — and you've specified it correctly. If the two ends need different connectors (say, LC at the switch and SC at an older panel), that's fine: a hybrid lead with a different connector at each end is a standard thing to order.
DTT UK supplies fibre patch leads, plus fibre patch panels and media converters in LC, SC, ST, FC and MTRJ, in both multimode and singlemode — so a mixed-connector link can be built from one place.
Frequently asked questions
Speccing a fibre link? Browse our fibre patch leads, panels and media converters — LC, SC, ST and FC, multimode and singlemode. Need a hybrid or a non-standard length? We can put it together — send us the spec.