A fibre pigtail is a short length of optical fibre with a factory-fitted connector on one end and bare fibre on the other. The bare end is fusion spliced to a fibre of the installed cable in a splice tray or ODF, and the connector plugs into a panel adapter. Pigtails come as 900 µm buffered or 2 mm and 3 mm jacketed fibre, single-mode or multimode.
What a fibre pigtail is
A fibre pigtail is a short length of optical fibre with a connector fitted and polished in the factory on one end and bare fibre on the other. The bare end is fusion spliced to a fibre of the installed cable, and the connector plugs into the back of an adapter on a patch panel, optical distribution frame (ODF) or termination box. US catalogues list the same part as a fiber pigtail.
Pigtails are the usual way to terminate loose tube outdoor cable. Its 250 µm coated fibres are too fragile to take a connector directly, so each one is joined to a pigtail inside a splice tray and the pigtail connector does the patching. Every port then has a factory end face, and the only joint made in the field is the splice.
Lengths are commonly 1 to 2 m, enough to coil the slack in a tray and still reach the adapter. Some installers cut a patch cord in half to make two pigtails, which works when the cord fibre matches the cable fibre.
Pigtail vs patch cord
| Feature | Pigtail | Patch cord |
|---|---|---|
| Connectors | One end only; the other end is bare fibre | Both ends |
| How it is installed | Fusion spliced to the installed cable | Plugged in by hand, no splice |
| Where it sits | Inside a splice tray, ODF, termination box or joint closure | In the open, between panel ports and equipment |
| Usual fibre packaging | 900 µm tight buffer, or 2 mm or 3 mm jacketed cable | 2 mm or 3 mm simplex or duplex jacketed cable |
| Testing | Connector tested in the factory; the finished link tested after splicing | Tested end to end in the factory |
| If damaged | Cut out and a new pigtail spliced in | Unplugged and replaced |
A patch cord connects two ports. A pigtail terminates a cable so that it has ports to connect to.
Pigtail fibre and buffer types
900 micron tight-buffered pigtails
Most pigtails used in splice trays are 900 µm tight-buffered fibre: the 250 µm coated fibre with a hard plastic buffer over it and no outer jacket. They are small enough to route a dozen or more through one tray, they coil in tight spaces, and the buffer strips back cleanly for splicing. There is no aramid strength yarn, so a 900 µm pigtail should stay inside an enclosure.
2 mm and 3 mm jacketed pigtails
Jacketed pigtails use 2.0 mm or 3.0 mm simplex cable with aramid yarn under a PVC or LSZH jacket. They suit pigtails that leave the enclosure, cross a rack to reach equipment, or have connectors handled often. The jacket and yarn are cut back at the splice end, and the splice still needs a protected tray.
Single-mode and multimode
The pigtail fibre must match the cable fibre. Single-mode pigtails use 9/125 µm fibre, usually ITU-T G.652.D, or bend-insensitive G.657.A1, which loses less light in the tight coils of a splice tray. The two are compatible and are routinely spliced together. Multimode pigtails use 50/125 µm fibre for OM3, OM4 and OM5, or 62.5/125 µm for OM1 plant. Splicing 62.5 µm to 50 µm fibre adds loss in one direction, and single-mode should never be spliced to multimode. Jacketed pigtails follow the usual jacket colours: yellow for single-mode, aqua for OM3 and OM4, orange for OM1 and OM2.
SC pigtail, LC pigtail and polish options
The pigtail connector must match the adapters in the panel. SC and LC pigtails are the most common in new work: SC in many ODFs and FTTH termination boxes, LC in high-density panels and data centre equipment. FC remains in older telecom and test equipment, and ST in older multimode and industrial plant.
| Polish | End face | Usual connector body colour | Typical use |
|---|---|---|---|
| UPC single-mode | Domed, physical contact | Blue | Ethernet and most single-mode data links |
| APC single-mode | Domed and angled at 8 degrees | Green | FTTH and PON, RF video overlay, links sensitive to reflection |
| PC or UPC multimode | Domed, physical contact | Beige, or aqua for OM3 and OM4 | Multimode links |
APC and UPC connectors must not be mated with each other: the angled and flat faces leave an air gap, with high loss and strong reflection. Order the pigtail polish to match the patch cords that will plug into the front of the panel. The guide to UPC vs APC polish explains the end-face geometry.
Colour-coded 12-fibre pigtail sets
Pigtails for trays and ODFs are usually supplied in sets of 12, each buffer coloured to the TIA-598 sequence: blue, orange, green, brown, slate, white, red, black, yellow, violet, rose and aqua. Fibre 1 of the incoming tube is spliced to the blue pigtail, fibre 2 to orange, and so on, so the port order on the panel follows the colour order in the cable. A crossed pair at this stage is found only when the link is tested.
For 24 fibres or more, the second set repeats the colours and the tray or adapter row identifies which tube it belongs to. Record tube colour, fibre colour and port number on the panel label. Some operators use their own colour schemes, so check the cable datasheet before ordering pigtails. The fibre colour codes guide lists tube and fibre colours in full.
How pigtails are spliced and stored
- Strip the cable sheath at the enclosure entry, clamp the strength member and leave a service loop of cable outside or inside the enclosure.
- Route the loose tube to the splice tray and remove it to expose the 250 µm fibres.
- Strip the pigtail buffer back to the coated fibre and slide a heat-shrink splice protection sleeve over one of the two fibres.
- Strip both fibres to the 125 µm cladding, clean them and cleave them.
- Fusion splice, then shrink the sleeve over the joint and seat it in the tray holder.
- Coil both fibres in the tray without going below their bend radius, and route the connector end to the back of its adapter.
Leave the dust cap on the connector until the port is ready to patch. The fibre optic splicing guide covers fusion and mechanical splicing in more detail.
Loss and end-face considerations
A pigtail termination adds two loss points to each end of a link: the splice and the mated connector at the panel. ANSI/TIA-568 allows up to 0.3 dB per splice and 0.75 dB per mated connector pair in a loss budget. A fusion splice between matched fibres is normally well inside that figure, and the factory test report should give the measured insertion loss of each pigtail connector.
Most connector faults start at the end face. A pigtail can sit in a tray for months before it carries traffic, so inspect the end face with a fibre microscope and clean it before the first mating. Return loss depends on polish: UPC connectors are commonly specified at 50 dB or better and APC at 60 dB or better. After splicing, an OTDR trace from the far end shows the loss of each splice and confirms that the fibres are in the right order.
When a pre-terminated assembly replaces pigtail splicing
Pigtail splicing suits outside plant cable, long routes where cable must be pulled through duct before it is terminated, and repairs. Inside buildings and data centres, where the route can be measured and the cable pulled with connectors already fitted, a factory-terminated assembly removes the splicing step.
- Fan-out or breakout assemblies have a connector on every fibre at both ends and are tested as one unit.
- MPO trunks plug into cassettes at each end and suit high-count data centre links. See MTP/MPO trunk cables.
- Pre-terminated outdoor assemblies arrive with a pulling grip protecting the connectors, for short duct runs between buildings.
The trade-off is length. A pre-terminated cable has to be ordered to the measured route plus slack, while pigtail splicing lets the installer cut cable to length on site.
Radix Fibrotech builds custom fibre optic assemblies to the customer's drawing, with the fibre, connectors, polish and leg lengths specified. Describe what you need, including fibre type, count, connector, polish, buffer and length, in a request for a quote and ask for the loss values that apply to the build.
Questions buyers ask
What is a fibre pigtail used for?
A fibre pigtail gives an installed cable a factory-polished connector. Its bare end is fusion spliced to a cable fibre inside a splice tray, and its connector plugs into a patch panel or ODF adapter. Patch cords then connect that port to equipment.
What is the difference between a pigtail and a patch cord?
A pigtail has a connector on one end and bare fibre on the other, and is spliced to installed cable. A patch cord has connectors on both ends and plugs in without splicing. Pigtails live inside enclosures; patch cords run in the open between ports and equipment.
What does SC/APC pigtail mean?
It is a single-mode pigtail with an SC connector polished at an 8 degree angle, normally with a green connector body. SC/APC pigtails are common in FTTH and PON networks. They must mate only with other APC connectors, never with UPC.
Why do pigtails come in 12 colours?
The 12 colours follow the TIA-598 fibre sequence, from blue to aqua. Splicing each cable fibre to the pigtail of the same colour keeps the panel port order the same as the fibre order in the cable, which makes tracing and testing simpler.
Can a pigtail be joined with a mechanical splice?
Yes. A mechanical splice aligns the two fibres in a sleeve with index-matching gel and needs no fusion splicer. It usually has higher loss and reflection than a fusion splice, so it is used mainly for repairs and some FTTH drops rather than backbone terminations.