The common fibre connector types are LC (1.25 mm ferrule, push-pull), SC (2.5 mm, push-pull), FC (2.5 mm, threaded), ST (2.5 mm, bayonet), MPO/MTP (many fibres in one ferrule) and E2000 (2.5 mm with a built-in shutter). Field and military links use expanded beam and circular MIL-style connectors. Most types come in UPC or APC polish.
How a fibre connector works
A fibre connector holds the fibre in a precision ferrule, usually zirconia ceramic, and presses it end to end against a second ferrule inside an adaptor (also called a mating sleeve or coupler). Light crosses where the two polished end faces touch, which is why these are called physical contact (PC) connectors. Loss depends on how well the two cores line up and how clean the end faces are.
Connector families differ in ferrule diameter, in the coupling mechanism that holds the plug in the adaptor, and in how many fibres one plug carries. A good single-fibre PC connector typically loses a few tenths of a dB per mated pair. ANSI/TIA-568 allows up to 0.75 dB per mated pair when a channel loss budget is calculated, and many buyers specify a lower maximum on their drawings.
Fibre connector types compared
| Connector | Ferrule | Coupling | Interface standard | Typical use |
|---|---|---|---|---|
| LC | 1.25 mm | Push-pull latch | IEC 61754-20 | Data centres, enterprise panels, SFP and QSFP duplex transceivers |
| SC | 2.5 mm | Push-pull snap | IEC 61754-4 | Telecom, FTTH and PON, older enterprise panels |
| FC | 2.5 mm | Threaded coupling nut, keyed | IEC 61754-13 | Test instruments, laser and sensing systems, high-vibration sites |
| ST | 2.5 mm | Bayonet twist-lock | IEC 61754-2 | Legacy multimode networks, industrial control, security systems |
| MPO/MTP | Rectangular MT ferrule, commonly 8, 12, 16 or 24 fibres | Push-pull, guide pins | IEC 61754-7 | Data centre trunks, 40G to 800G parallel optics |
| E2000 | 2.5 mm | Push-pull with spring-loaded shutter | IEC 61754-15 | European carrier networks, APC and higher-power links |
| Expanded beam | Lens; faces do not touch | Threaded or bayonet, often hermaphroditic | Manufacturer and military specifications | Broadcast field work, defence, mining |
| MIL-style circular | Several fibre termini in one circular shell | Threaded or bayonet | MIL-DTL-38999 style shells | Aircraft, vehicles, ships, rugged equipment |
Single-fibre connectors
LC
The LC is a small form factor connector with a 1.25 mm ferrule and a latch like a telephone jack. Two LCs clipped together make the duplex connector used on almost every SFP, SFP+ and duplex QSFP transceiver. An LC duplex fits in roughly the panel space of one SC, which is why it dominates data centres and high-density patch panels.
SC
The SC has a square body and a 2.5 mm ferrule, and it latches with a straight push. It is easy to handle with gloves and remains the common connector in fibre-to-the-home and passive optical networks, usually in green APC form.
FC
The FC screws onto its adaptor with a threaded nut and is keyed, so it holds position under vibration and keeps the same rotational alignment every time it is mated. That makes it a frequent choice on test instruments, laser sources, sensing systems and polarisation-maintaining links. It is slower to mate in a dense panel.
ST
The ST uses a spring-loaded bayonet: push and twist a quarter turn. It was the standard multimode connector in early campus networks and is still found in industrial control, security and older building plant. New designs rarely choose it, but replacement cords are often needed to match installed panels.
E2000
The E2000 has a 2.5 mm ferrule and a spring-loaded cover that closes over the end face when the plug is withdrawn. The shutter keeps dust off the ferrule and blocks laser light from the eye. It is widely used by European carriers, often in APC polish.
Multi-fibre connectors: MPO and MTP
An MPO connector carries several fibres in one rectangular MT ferrule, commonly 8, 12, 16 or 24. Two steel guide pins on the male plug locate in holes on the female plug, so an MPO link always mates a pinned end to an unpinned end. A key on the housing fixes orientation, and the adaptor is either key-up to key-down or key-up to key-up depending on the polarity method.
Multimode MPO connectors are normally flat polished; single-mode MPO connectors are normally angle polished. MTP is a registered trademark for an MPO-compatible connector with tighter tolerances and some mechanical refinements, and it mates with standard MPO. Our guide to MTP vs MPO covers the differences, and the MTP/MPO cable range lists the trunk, patch and breakout assemblies Radix builds.
Rugged connectors: expanded beam, MIL-style and others
Physical contact connectors need clean, undamaged end faces. In mud, sand or salt spray, and where cables are mated hundreds of times, that is hard to maintain. Two families address it.
Expanded beam connectors place a lens in front of each fibre. The light is widened into a beam many times larger than the core and crosses a small air gap to a matching lens. Dust blocks a smaller share of the light and the faces never touch, so wear is low. The cost is higher insertion loss, often around 1 dB per mated pair. Radix makes expanded beam connectors for field and defence cable assemblies.
MIL-style circular connectors use a threaded or bayonet metal shell, often in the MIL-DTL-38999 pattern, holding several fibre termini and sometimes electrical contacts. The termini are physical contact, so cleaning still matters, but the shell gives sealing, strain relief and resistance to shock. Radix makes MIL connectors in multi-channel layouts.
Other rugged formats include compact ODC-style outdoor connectors with two or four channels, and opticalCON connectors, which put an LC duplex inside a metal housing with a protective cover for broadcast and live events.
UPC vs APC polish
Polish type matters as much as the connector body. A UPC (ultra physical contact) end face is domed and meets its partner square on. An APC (angled physical contact) end face is polished at 8 degrees, so light reflected at the joint leaves the core instead of travelling back to the source.
| Polish | End face | Usual body colour | Return loss (typical industry values) | Typical use |
|---|---|---|---|---|
| UPC | Domed, flat contact | Blue (single-mode), beige or aqua (multimode) | 50 dB or better on single-mode | Ethernet, data centres, most digital links |
| APC | Domed, 8 degree angle | Green | 60 dB or better | PON and FTTH, RF over fibre, CATV, reflection-sensitive systems |
Never mate APC to UPC. The angled and flat faces leave a gap that causes high loss and can damage both end faces. Multimode single-fibre connectors are almost always PC or UPC.
How to choose a connector
- Match the equipment port first. Transceivers, test sets and patch panels fix the connector at each end of a cord. A hybrid cord, such as LC to SC or LC to FC, joins two different families.
- Density: LC for duplex links in panels, MPO where many fibres need to move as one.
- Vibration: FC or a threaded circular connector stays put.
- Dirt and repeated mating in the field: expanded beam, or a sealed circular connector with caps.
- Reflection-sensitive signals: APC polish, on single-mode only.
Radix builds fibre optic patch cords and assemblies with any of these connectors at either end. List the connector, polish, fibre type and length for each end in your quote request.
Each common connector has its own guide with sizes, polish options and ordering details: the LC connector, the SC connector, the ST and FC connectors and the MPO connector. For end faces, see UPC vs APC.
Questions buyers ask
What is the most common fibre connector?
In data centres and enterprise networks it is the LC, mainly as a duplex pair on transceivers and patch panels. In fibre-to-the-home and passive optical networks, the SC/APC is the most common. MPO is the standard for multi-fibre trunks.
Can an LC connector be connected to an SC connector?
Not directly, because the ferrules are different sizes (1.25 mm and 2.5 mm). The usual answer is a hybrid patch cord with LC on one end and SC on the other. Hybrid adaptors exist but add loss and are less reliable.
Can I mate an APC connector with a UPC connector?
No. The 8 degree angled face and the flat face do not meet properly, which leaves an air gap, causes high loss and can scratch both end faces. Keep APC and UPC segregated, and use the green body colour to identify APC.
What do connector colours mean?
By common practice, blue is single-mode UPC, green is single-mode APC, beige is OM1 multimode, black is OM2 and aqua is OM3 or OM4. OM4 is sometimes violet and OM5 lime green. Colours help in the rack, but the cable legend and drawings are the real reference.
Is MTP the same as MPO?
MTP is a branded MPO-compatible connector made to tighter tolerances. It mates with standard MPO connectors of the same fibre count and gender. Buyers usually specify MTP where low loss across several mated pairs matters.
Which fibre connector suits harsh field conditions?
Expanded beam connectors are the most tolerant of dirt and repeated mating, at the cost of higher insertion loss. Sealed MIL-style circular connectors give better loss and good environmental protection, but their physical contact termini need careful cleaning.