An MPO connector is a multi-fibre push-on optical connector that aligns 8 to 32 fibres at once in a rectangular MT ferrule, using two guide pins on the male plug and two holes on the female plug. Its interface is defined in IEC 61754-7 and TIA-604-5. MPO connectors terminate data centre trunks, patch cords and breakouts for parallel optics.
Parts of an MPO connector
An MPO connector is a multi-fibre push-on plug built around an MT (mechanical transfer) ferrule. The ferrule is a moulded rectangular block with the fibres laid in a row at 250 micron spacing and a guide hole on each side of the row. Behind it sit a spring and, on male plugs, a pin clamp holding two steel guide pins. The housing carries the key, and an outer sleeve slides back to release the latch, which gives the push-pull action. A boot provides strain relief where the cable leaves the plug. The interface, meaning the ferrule, pin and key dimensions that let plugs from different makers mate, is defined in IEC 61754-7 and in North America in TIA-604-5 (FOCIS 5).
The whole ferrule face is polished at once. The fibre tips stand slightly proud of the ferrule face, and the polish has to keep every fibre within a tight height range so that all of them touch their partners when the spring presses the faces together. A low or dirty fibre affects its own lane while the rest of the connector still passes, so test reports for MPO assemblies list loss fibre by fibre.
This guide covers the connector itself. For the trunks, patch cords and breakouts built with it, see what an MPO cable is.
MPO connector types
| Variant | Ferrule layout | Key | Common polish | Typical uses |
|---|---|---|---|---|
| MPO-8 | 12-position row with 8 fibres fitted, middle 4 empty | Standard | Flat for multimode, APC for single-mode | Four-lane optics such as 40GBASE-SR4, 100GBASE-SR4 and 400GBASE-DR4; Base-8 cabling |
| MPO-12 | One row of 12 | Standard | Flat or APC | Base-12 trunks and cassettes, general structured cabling |
| MPO-16 | One row of 16 | Offset | Flat or APC, set by the transceiver | Eight-lane optics such as 400GBASE-SR8 and 800G SR8 and DR8 modules |
| MPO-24 | Two rows of 12 | Standard | Usually flat, multimode | High-density trunks; the older 100GBASE-SR10 interface |
| MPO-32 | Two rows of 16 | Offset | Flat or APC | High-density trunks in 16-fibre systems |
MPO-12 vs MPO-16
MPO-12 has long been the base unit of data centre fibre, and four-lane optics use eight of its twelve positions. Eight-lane optics at 400G and 800G need 16 fibres, eight to transmit and eight to receive, which fit one MPO-16 row. The MPO-16 has an offset key so that it cannot be plugged into a 12-fibre adapter by mistake. The two families do not intermate. A mixed link needs a conversion cord or module, and the panel adapters must be the 16-fibre type. Ferrules with more rows exist for specialist uses, but the five variants above cover almost all structured cabling.
MPO male vs female
Gender on an MPO connector means pins. A male (pinned) plug has two guide pins standing out from the ferrule face. A female (unpinned) plug has two open holes. Every mated pair must be one of each. Two male plugs cannot seat, and forcing them can chip the ferrule faces. Two female plugs will latch in an adapter, but nothing aligns the fibres, so the loss is high and unstable.
Parallel optic transceivers have pinned ports, so a patch cord that plugs into a QSFP or similar module must be female at that end. In structured cabling, trunks are often female at both ends and plug into pinned connectors on the back of cassettes or fan-out modules. Show the gender at both ends of every assembly on the order, because the same assembly in the other gender will not fit.
On many generic MPO plugs the gender is fixed when the connector is built. MTP, a branded MPO from US Conec, has a removable housing that lets pins be added or removed with the right tool, as explained in MTP vs MPO.
Keys, adapters and polarity
The key is a raised rib on one long side of the housing. Viewed with the key up and looking into the end face, fibre position 1 is on the left, and many housings carry a white mark on the position 1 side.
MPO adapters come in two orientations. A key-up to key-down adapter, called Type A, joins two plugs with their keys on opposite sides, so position 1 meets position 1. A key-up to key-up adapter, called Type B, joins them with their keys on the same side, so position 1 meets position 12. That choice, together with the trunk type and the patch cords, sets the polarity of the whole channel. Our guide to MPO polarity types A, B and C maps each method fibre by fibre, so it is not repeated here. Name the adapter type next to the polarity method on the order. A correct trunk in the wrong adapter still gives a failed link.
End faces: flat PC or 8 degree APC
Multimode MPO connectors are normally polished flat for physical contact. Single-mode MPO connectors are normally angle polished at 8 degrees (APC), so light reflected at the joint leaves the core instead of returning to the laser. Some multimode MPO-16 interfaces on eight-lane optics also use an angled polish, so check the transceiver data sheet rather than assuming flat for multimode.
APC and flat MPO plugs must never be mated. The angled face meets the flat face at one edge, leaving an air gap across the fibre array, which causes high loss and can damage both ferrules. The polish also limits what can be reworked later, so decide it with the transceivers and panels in view, not cable by cable.
Housing colours and boots
MPO housings are colour coded by industry convention, broadly following the jacket colours for each fibre grade:
- Green: single-mode APC.
- Aqua: multimode OM3, and OM4 on many systems.
- Violet: OM4, where a site separates it from OM3.
- Lime green: OM5 wideband multimode.
Colour helps on site, but suppliers vary, especially for single-mode flat-polish connectors, so the label and the drawing should state the fibre type and polish.
The boot is the other choice. A standard boot suits open panels. In dense panels, a push-pull boot or pull tab lets you release one connector without reaching between its neighbours. Ask for a dust cap on every plug at dispatch, and for caps that suit the gender, since a cap for a male plug has to clear the pins.
Cleaning and inspecting MPO connectors
An MPO end face carries up to 32 fibres, and a speck on any one of them can fail that lane. The guide pins and holes also collect dust and carry it onto the mating face. Inspect every connector before mating with a scope that can view the whole array, and judge the result against the criteria in IEC 61300-3-35. Clean dry first with a cleaner made for MPO ferrules, which wipes the full row and works around the pins of a male plug, then inspect again. Our step-by-step guide on how to clean MPO connectors covers the tools and methods. Cap connectors and transceiver ports as soon as they are unplugged.
What to specify when ordering MPO assemblies
- Connector: MPO to IEC 61754-7 and TIA-604-5, or MTP where your specification names it.
- Variant at each end: MPO-8, 12, 16, 24 or 32, and the number of legs.
- Gender at each end: male (pinned) or female (unpinned).
- Polish: flat or 8 degree APC, matched to the transceivers and panels.
- Fibre type: OS2, OM3, OM4 or OM5, and the housing colour if your site uses a scheme.
- Polarity method and adapter type: Type A, B or C, with key-up to key-down or key-up to key-up adapters.
- Boot: standard or push-pull.
- Maximum insertion loss per mated pair with the test method, and a report of loss per fibre and end-face inspection results.
Radix builds MTP and MPO cable assemblies to order in Pune, India. Send the list, with a drawing if you have one, through the request a quote page.
Questions buyers ask
What is the difference between a male and female MPO connector?
A male MPO connector has two steel guide pins and a female connector has two matching holes. Every mated pair must be one male and one female. Transceiver ports are male, so the cord plugged into them is female at that end.
Can an MPO-12 connector mate with an MPO-16 connector?
No. MPO-16 uses a 16-fibre row and an offset key, so it does not fit a 12-fibre plug or adapter. Joining the two needs a conversion cord or a conversion module.
Do MPO connectors have to be APC?
No. Multimode MPO connectors are usually flat polished and single-mode MPO connectors are usually 8 degree APC. Some multimode MPO-16 optics use APC, so follow the transceiver data sheet. Never mate APC with flat.
Which standards define the MPO connector?
The connector interface is defined in IEC 61754-7 and, in North America, in TIA-604-5, also called FOCIS 5. These fix the ferrule, guide pin and key dimensions that let MPO connectors from different makers intermate. Cabling standards such as TIA-568 add the loss allowances and polarity methods.
Why does an MPO connection show high loss on only some fibres?
The usual causes are contamination on part of the array, a damaged fibre tip or a worn guide hole. Inspect the whole end face of both plugs with an MPO-capable scope, clean, and retest. If the same positions still fail, the connector needs rework or replacement.