An FC to LC patch cord has a threaded, keyed FC connector at one end and a push-pull LC connector at the other. It links FC ports on test equipment, lasers, telecom frames and industrial devices to LC transceivers and panels. FC/PC and FC/APC polishes must never be mixed in one joint. Radix Fibrotech makes FC to LC and FC to FC cords to order in Pune.
FC to LC patch cord and FC to FC patch cord options
An FC to LC patch cord has an FC connector at one end and an LC connector at the other. An FC to FC patch cord has FC at both ends. FC connectors have a 2.5 mm ferrule in a metal body with a threaded coupling nut. LC connectors have a 1.25 mm ferrule in a small plastic housing with a latch. Radix Fibrotech makes both cord types to order in Pune, and each option below is set per order line. The fibre connector types guide compares FC with the other common connectors.
| Option | Choices | Notes |
|---|---|---|
| Cord pair | FC to LC, FC to FC, or FC to another connector such as SC | FC to LC is the usual hybrid for instruments feeding LC equipment |
| Fibre | OS2 single-mode (G.652.D or bend-insensitive G.657); 50/125 µm or 62.5/125 µm multimode | Most FC use is single-mode; multimode FC appears on older instruments and sensor links |
| End faces | FC/PC, FC/UPC or FC/APC at the FC end; UPC or APC at the LC end | Multimode FC is PC or UPC only |
| Fibre count | Simplex, or duplex with two FC legs to one duplex LC clip | Instrument ports are mostly simplex |
| Key | Narrow or wide key, if the port or adapter needs a particular one | State it when matching an older panel or instrument |
| Jacket | LSZH, PVC or armoured | Armoured where cords lie on lab floors or plant walkways |
| Diameter | 2.0 or 3.0 mm simplex; 2.0 mm duplex zip | 3.0 mm is easier to handle on a bench |
| Length | Any length to order | Bench leads are short; frame runs are longer |
How the FC connector holds a joint
The FC ferrule sleeve carries a key, and the connector carries a knurled nut. The key slides into a slot in the adapter and stops the ferrule turning. The nut then screws onto the adapter thread and draws the two ferrule faces together. Because the nut locks the joint and the key fixes its rotation, an FC connection keeps its alignment when a bench is bumped or a machine vibrates. That is why FC remains on instruments and industrial gear, even though push-pull connectors are faster to use. A threaded nut takes longer to fit than a click and is awkward in a crowded panel.
Line the key up with the slot first, then tighten the nut by finger. A tool or a hard twist adds nothing to performance and can damage the thread or the adapter. A loose nut is the more common fault, because the faces drift apart and loss rises.
FC/PC, FC/UPC and FC/APC
FC is made in three polishes. PC and UPC end faces are domed and meet square on. An APC end face is cut at 8 degrees, which sends reflected light out of the core. PC has a lower return loss than UPC, so read the maker's datasheet before treating the two as equal. The usual colour code is blue for UPC and green for APC, but many FC connectors have plain metal bodies, so the polish is printed on the boot, the label or the jacket legend. An FC/APC end must go only into an FC/APC port. The UPC vs APC guide explains the end-face geometry.
Where FC connectors are still used
Test and measurement
OTDRs, power meters, light sources, optical spectrum analysers and attenuators often have FC ports or interchangeable adapters that accept FC. A cord from the instrument to an LC panel or transceiver is an FC to LC cord. Every cord in a measurement adds its own loss and reflection, so test leads should be short, inspected and cleaned before each use.
Labs, photonics and sensing
Laser sources, modulators, fibre lasers, interferometers and spectrometers frequently have FC/PC or FC/APC outputs. The threaded joint stays put while a bench is handled, and the key repeats the same alignment each time the cord is removed and refitted.
Telecom and transport equipment
Older exchange frames, DWDM shelves and some analogue video transport equipment carry FC. FC/APC is common where reflections would disturb a laser or an RF signal, and FC/PC where the port was built to the older standard.
Industrial links
Machine-mounted sensors and equipment exposed to vibration sometimes keep FC for its locked joint. Match these ports by polish, key width and fibre type, and choose an armoured jacket if the cord is exposed.
Choosing the polish at each end of a hybrid cord
Each end of a hybrid cord mates with its own port, so the polish at the two ends can differ. What cannot be mixed is polish inside one joint. The table shows common pairings.
| FC-side port | LC-side port | Cord to order |
|---|---|---|
| FC/PC test port | LC/UPC transceiver or panel | FC/PC to LC/UPC |
| FC/APC laser or OTDR port | LC/UPC transceiver or panel | FC/APC to LC/UPC |
| FC/APC port | LC/APC port on telecom or RF gear | FC/APC to LC/APC |
| Multimode FC/PC port | Multimode LC panel or SFP | FC/PC to LC/UPC, 50/125 µm or 62.5/125 µm to match |
Ethernet LC optics are almost always UPC, so the LC end of a cord to an SFP is normally UPC even when the FC end is APC. An APC link under test needs APC test leads at both ends, otherwise the reading includes a mismatch. For LC to LC and LC to SC cords see LC to SC patch cords.
Common mistakes with FC cords
- Mating APC with PC or UPC. The angled and domed faces leave an air gap, loss rises, and the faces can chip.
- Forcing the nut without seating the key. If the key is not in its slot the joint cannot seat, and tightening only strains the thread.
- Ignoring key width. Narrow-key and wide-key FC parts exist, and a mismatch will not seat. Check older panels before ordering.
- Using a multimode cord on a single-mode instrument. The core size must match the instrument port and the link under test.
- Skipping inspection. Instrument ports are shared by every cord that is plugged in, so one dirty ferrule contaminates the next. Inspect and clean both the cord and the port.
- Assuming an APC end suits an Ethernet SFP. Most LC optics are UPC, so an LC/APC end on a cord for them is a mismatch.
Testing and reports for FC cords
Radix tests each FC cord before dispatch. Single-mode cords are measured for insertion loss at 1310 and 1550 nm and for return loss, multimode cords at 850 and often 1300 nm, and end faces are inspected under magnification against IEC 61300-3-35 criteria. APC cords are measured against APC reference leads.
If the cord will be used as a measurement reference lead, say so in the quote and give the maximum insertion loss you need per connector. Reference-grade limits are tighter than ordinary patching, and the quote should show whether they can be met. Ask for the report format you need, such as a printed sheet or a serialised spreadsheet matched to the cord label.
What to send us for a quote
List each configuration on its own line, with:
- the connector and polish at end A and end B, for example FC/APC to LC/UPC
- single-mode or multimode, with the fibre standard or core size
- simplex or duplex
- key width, if the FC port needs a particular one
- jacket and outer diameter
- length and tolerance
- maximum insertion loss and minimum return loss, if the project sets them
- label text and test report format
- quantity for that line
Send the list through the request a quote page. Single-mode options are covered on the single-mode patch cords page.
Questions buyers ask
What is an FC to LC patch cord used for?
It connects equipment with an FC port, such as an OTDR, light source, laser or older telecom unit, to equipment with an LC port, such as an SFP transceiver or a modern patch panel. The FC end threads onto the instrument and the LC end clicks into the LC port.
Can I connect an FC/APC cord to an FC/PC port?
No. The 8 degree angled face of FC/APC does not meet a domed PC or UPC face squarely, so loss rises and the faces can be damaged. Order the polish at the FC end to match the port it plugs into.
Is FC still used, or has LC replaced it?
LC has replaced FC in data centres and enterprise networks. FC remains on test equipment, laboratory and photonics instruments, some telecom and transport gear and some industrial links, so hybrid FC to LC cords are still ordered for them.
How tight should the FC nut be?
Finger-tight, with the key already seated in the adapter slot. Using a tool does not improve the joint and can damage the thread. If loss drifts upward on a bench link, check first that the nut has not worked loose.
Does a duplex FC to LC cord exist?
Yes. A duplex hybrid has two FC connectors on separate legs at one end and a duplex LC clip at the other. Most instrument ports are simplex, so a simplex cord is the usual order, but two-fibre FC equipment can use the duplex form.
What should I specify for an FC to FC reference lead?
Fibre type, polish (PC, UPC or APC) at both ends, length, and the maximum insertion loss per connector. Add the report format. The polish must match the link under test, so an APC link needs APC leads.