An LC connector is a small form factor fibre optic connector with a 1.25 mm ceramic ferrule and a push-pull latch, defined in IEC 61754-20. It is made as a simplex plug or a duplex pair at 6.25 mm pitch, in single-mode UPC, single-mode APC and multimode versions. Duplex LC is the standard port on SFP, SFP+ and many QSFP transceivers.
What an LC connector is
The LC connector was developed by Lucent Technologies in the 1990s, and the name is usually read as Lucent Connector. Its interface is standardised in IEC 61754-20. It holds the fibre in a 1.25 mm zirconia ferrule, half the diameter of the 2.5 mm ferrule used by SC, FC and ST, so the whole plug takes roughly half the panel space. For a side-by-side view of the other families, see our guide to fibre connector types.
An LC plug is built from a few parts:
- Ferrule: zirconia ceramic, 1.25 mm in diameter, with the fibre bonded in a central bore and the end face polished.
- Spring: pushes the ferrule forward so the two end faces meet under a controlled force inside the adaptor.
- Housing and latch: a moulded body with a flexible latch arm on top, similar to the latch on an RJ45 plug. Press the arm to release.
- Crimp sleeve: anchors the aramid strength yarn of the cord to the connector body, so a pull on the cable does not load the fibre.
- Boot: bend relief for the cable, sized for 0.9 mm buffered fibre, 1.6 mm to 2.0 mm cordage, or 3.0 mm cordage.
The action is push-pull: push to latch, press the arm and pull to release.
Simplex, duplex and uniboot LC
A simplex LC carries one fibre. Most links need two fibres, one per direction, so LC plugs are usually supplied as a duplex pair. A duplex clip holds two simplex plugs side by side at a centre-to-centre pitch of 6.25 mm, which matches the duplex LC port on transceivers and the duplex LC adaptor. The clip also links the two latch arms so one press releases both.
Zipcord duplex
The traditional duplex LC cord uses two round cables joined by a thin web, each commonly 1.6 mm to 2.0 mm, with one plug per leg. It is simple and easy to split, but two cables take more room in cable managers.
Uniboot duplex
A uniboot LC carries both fibres inside one round cable, usually 2.0 mm to 3.0 mm, ending in a single boot that holds both plugs. The cord is thinner per link, which helps airflow and bend management in dense racks. Most uniboot designs let the user reverse polarity in the field.
Pull tab
In dense panels the latch arm can be hard to reach. Many LC cords are offered with a pull tab or extended boot that releases the latch from behind, so a cord can be removed without disturbing its neighbours.
A duplex LC adaptor fits the panel cut-out of a simplex SC adaptor, and a quad LC adaptor fits the cut-out of a duplex SC. That footprint relationship is why moving a panel from SC to LC doubles its fibre count.
LC/UPC, LC/APC and multimode LC
LC connectors are made in single-mode UPC, single-mode APC and multimode versions. Housing or boot colour follows industry convention. The cable legend and drawings remain the real reference.
| Version | Fibre | End face | Usual colour | Return loss (typical industry values) | Typical use |
|---|---|---|---|---|---|
| LC/UPC single-mode | OS2 | Domed, flat contact | Blue | 50 dB or better | Ethernet optics, data centre and telecom links |
| LC/APC single-mode | OS2 | Domed, 8 degree angle | Green | 60 dB or better | RF over fibre, PON equipment, reflection-sensitive links |
| LC multimode | OM1, OM2 | PC or UPC | Beige | Lower; rarely the limiting figure | Older campus and building links |
| LC multimode, laser optimised | OM3, OM4, OM5 | PC or UPC | Aqua; OM4 sometimes violet, OM5 lime green | Lower; rarely the limiting figure | Short-reach 10G to 100G in data centres |
LC/APC is less common than SC/APC because most duplex transceivers have UPC ports. Never mate an APC plug with a UPC plug: the angled and flat faces leave an air gap, loss is high and both end faces can be damaged. Our guide to UPC vs APC polish explains the difference in detail.
Insertion loss for a mated single-mode LC pair with clean end faces is commonly 0.3 dB or less (a typical industry value). ANSI/TIA-568 allows up to 0.75 dB per mated pair when a channel loss budget is calculated. Low-loss grades are sold with tighter limits, so state the maximum per mated pair you need and ask how it is tested.
Duplex LC polarity and how to flip a uniboot
Every duplex link has to cross over once, so the transmitter at one end reaches the receiver at the other. On a duplex LC the two positions are labelled A and B, usually on the clip or boot. A standard A-B patch cord connects position A at one end to position B at the other, which is the crossover TIA-568 describes for duplex patch cords. An A-A cord runs straight through and is used only where the crossover happens elsewhere in the channel, as in some MPO cassette designs.
When a link stays down and the optics test good, reversed polarity is a common cause. The fix depends on the cord:
- Uniboot cords: most let you swap the two plugs without tools. Typically you slide the clip or latch housing back, rotate the plugs (or the boot) through 180 degrees and push it home, so A and B change sides. Methods differ between makers, so follow the one shown on the cord.
- Zipcord cords with a removable clip: take the clip off, swap the two plugs and refit it. Update the A and B labels so the records stay correct.
- Fixed duplex cords: replace the cord with one of the correct polarity rather than forcing the clip.
On MPO trunk systems the polarity needed at the duplex LC cord depends on the trunk and cassette method, so specify cords against the whole channel design, not port by port.
Where LC connectors are used
- Transceivers: SFP, SFP+ and SFP28 optics for 1G, 10G and 25G have a duplex LC receptacle. Duplex QSFP+ and QSFP28 optics for 40G and 100G, such as LR4 and CWDM4 types, also use duplex LC. Short-reach parallel optics such as 40G SR4 and 100G SR4 use MPO instead.
- Breakouts: an MPO to LC breakout splits an 8-fibre or 12-fibre MPO into duplex LC legs, for example one 40G SR4 port into four 10G links. See our MTP/MPO breakout cables.
- Patch panels and cassettes: duplex or quad LC adaptors on fibre panels, and MPO to LC cassettes that turn a trunk into rows of duplex LC ports.
- Telecom and enterprise plant: ODFs, wall boxes, media converters and test equipment, often alongside SC.
Very small form factor connectors such as CS, SN and MDC are denser still and appear on some recent high-speed optics, but duplex LC remains the default LC fiber connector for two-fibre links.
LC vs SC connector
| Feature | LC | SC |
|---|---|---|
| Ferrule | 1.25 mm | 2.5 mm |
| Interface standard | IEC 61754-20 | IEC 61754-4 |
| Release | Press the latch arm | Pull the outer grip |
| Duplex pitch | 6.25 mm | 12.7 mm |
| Panel density | About twice SC in the same space | Lower |
| Common polish | Mostly UPC, APC available | UPC and APC both common |
| Typical home | Transceivers, data centre panels, cassettes | FTTH and PON, ODFs, older enterprise kit |
| Handling | Small; a pull tab helps in tight panels | Larger; easy with gloves |
Loss performance is similar when both are well made. The choice is driven by the equipment port and by density. LC and SC do not mate directly, so an LC transceiver feeding an SC panel needs an LC to SC hybrid patch cord. Hybrid adaptors exist, but they add a joint and are best kept for testing.
What to specify when ordering LC patch cords
- Connector at each end: LC to LC, or LC to another family such as SC, FC or ST.
- Simplex or duplex, and for duplex, zipcord or uniboot.
- Fibre type: OS2 single-mode, or OM1, OM2, OM3, OM4 or OM5 multimode, matched to the optics and the installed plant.
- Polish at each end: UPC or APC (APC on single-mode only).
- Polarity: A-B crossover (the usual choice) or A-A, and whether a field-reversible uniboot is wanted.
- Length and tolerance, measured connector tip to connector tip.
- Cable diameter and jacket: for example 2.0 mm or 3.0 mm, LSZH, or a riser or plenum rating where the local code calls for one.
- Boot style: standard, short, angled or pull tab.
- Loss limits and test records: maximum insertion loss per mated pair, minimum return loss, and whether a test sheet should ship with each cord.
- Labelling: jacket legend and ID labels at each end.
Radix builds LC to LC patch cords and LC assemblies to order in Pune. Send the details above, with quantities, through the quote request form.
Questions buyers ask
What is the difference between LC and SC connectors?
LC has a 1.25 mm ferrule and a latch arm; SC has a 2.5 mm ferrule and a square push-pull body. A duplex LC takes about the same panel space as one simplex SC, so LC is used where density matters. SC remains common in FTTH, PON and telecom frames.
What does LC stand for in fibre optics?
LC is usually read as Lucent Connector, after Lucent Technologies, which developed it. Some people call it the little connector or local connector. The interface itself is defined in IEC 61754-20.
Is an LC connector single-mode or multimode?
Both. The LC body is the same, but the ferrule bore and polish are made for the fibre type. Blue usually marks single-mode UPC, green single-mode APC, beige OM1 or OM2, and aqua OM3 or OM4. Check the cable legend rather than relying on colour alone.
What is an LC duplex connector?
It is two simplex LC plugs held together by a clip at 6.25 mm pitch, one fibre for transmit and one for receive. It plugs into the duplex LC port on SFP and SFP+ transceivers and into duplex LC adaptors on patch panels.
How do I reverse the polarity on an LC uniboot cord?
On most uniboot designs you slide the clip or latch housing back, rotate the plugs or boot through 180 degrees and push it home, which swaps positions A and B. The exact method varies by maker. Clean and inspect the end faces before reconnecting.
Can I connect LC/APC to LC/UPC?
No. The 8 degree angled face and the flat face leave an air gap, which causes high loss and can damage both connectors. Where an APC port has to meet a UPC port, use a cord with APC on one end and UPC on the other.