Fiber optic connector types
How to tell the common fiber connectors apart on the job, and what the color of the connector body tells you about the fiber and the polish.
Connector chart
| Connector | Ferrule | Latch | Where you see it |
|---|---|---|---|
| SC | 2.5 mm | Push-pull, square body | FTTH, ONTs, splitters, older patch panels. The standard PON connector. |
| LC | 1.25 mm | Latch tab, like a small phone plug | SFP optics, switches, data centers, high-density panels. Often in duplex pairs. |
| ST | 2.5 mm | Bayonet twist-lock | Older multimode networks, industrial and campus links. |
| FC | 2.5 mm | Threaded screw-on | Test equipment, OTDR ports, older telco gear. Holds up to vibration. |
| MPO / MTP | Multi-fiber, rectangular | Push-pull | Trunks of 8, 12, 16 or 24 fibers in data centers. MTP is a branded MPO. |
| MU | 1.25 mm | Push-pull, small SC | Some telco and Japanese equipment. |
| E2000 | 1.25 mm | Push-pull with spring shutter | European carrier networks, high-power links. |
| Hardened (OptiTap and similar) | 2.5 mm (SC inside) | Threaded, sealed | Outdoor FTTH terminals and drops, no closure needed. |
What the connector color means
| Color | Meaning |
|---|---|
| Blue | Single-mode, UPC polish |
| Green | Single-mode, APC (angled) polish |
| Beige / black | Multimode OM1 or OM2 |
| Aqua | Multimode OM3 or OM4 |
| Violet (erika violet) | Multimode OM4 (some makers) |
| Lime green | Multimode OM5 |
Color is a convention, not a guarantee. Mislabelled jumpers and mixed colors do turn up, so on anything that matters check the jumper's printed legend and look at the end face.
Ferrule size matters for adapters and cleaners
SC, ST and FC share a 2.5 mm ferrule; LC, MU and E2000 use 1.25 mm. Hybrid adapters (SC to LC, for example) exist, but cleaning sticks, inspection tips and test leads have to match the ferrule. A 2.5 mm cleaner will not reach the end face of an LC in a bulkhead.
Polish: PC, UPC and APC
The end of the ferrule is polished to make the fibers touch. UPC (ultra physical contact) is domed and flat across the core. APC (angled physical contact) is polished at 8° so reflected light is sent into the cladding instead of back down the fiber. APC and UPC connectors look alike apart from the color and must never be mated together. See APC vs UPC for the details.
Typical connector loss
A clean, modern factory-polished connector pair typically measures around 0.2 to 0.3 dB. TIA-568 allows up to 0.75 dB per mated pair for design. A connector reading over 0.5 dB is usually dirty: clean it, inspect it with a scope, and test again before you replace anything.