MPO Fanout Cable: Fanout vs Breakout, Specifications, and How to Order the Right Assembly
An MPO fanout cable terminates one multi-fiber MPO connector on one end and distributes the fibers into individual legs on the other — either connectorized with LC or SC, or left unterminated for fusion splicing. It is the standard way to break an MPO trunk or MPO equipment port out into duplex links inside enclosures, ODFs, and splice trays.
This guide covers what matters before you request a quote: how fanout differs from breakout and harness assemblies, which fiber count matches your transceiver, and the exact specifications to send your supplier.
Table of Contents
- What Is an MPO Fanout Cable?
- Fanout vs Breakout vs Harness
- 8F, 12F, or 24F: Match the Fanout to Your Transceiver
- Construction Specs: Legs, Polish, Polarity, and Jackets
- Where a Fanout Belongs — and Where It Does Not
- The Fanout RFQ: Eight Fields That Prevent Re-Quotes
- FAQ
- Get a Fanout Built for Your Enclosure
What Is an MPO Fanout Cable?
An MPO fanout cable takes one MPO connector (defined in IEC 61754-7, typically 8, 12, 16, or 24 fibers) and fans the fibers out into separate legs at the opposite end. Two termination styles exist:
- Connectorized fanout — each leg ends in an LC, SC, or ST connector, ready to plug into adapter panels or transceivers. The most common configuration is MPO to LC duplex legs.
- Unterminated fanout — legs end in bare 0.9 mm buffered fiber for fusion splicing onto an ODF or splice tray pigtail. This is the standard approach in FTTH and ISP outside-plant-to-CO transitions.
Physically, the fanout point is protected by a molded breakout module or a sleeved furcation tube. From that point, each leg is an independent 0.9 mm (or 2.0 mm) cord, so individual fibers can be routed, dressed, and serviced without disturbing the rest of the assembly.
For a broader overview of MPO trunk, patch, and breakout cable types, see our MPO/MTP fiber cable guide.
Fanout vs Breakout vs Harness
The industry uses “fanout” and “breakout” loosely, and many suppliers list them as synonyms. What actually matters when you specify is where the assembly lives and how the legs are built:
| Attribute | MPO Fanout | MPO Breakout | MPO Harness |
|---|---|---|---|
| Typical legs | 0.9 mm buffered, connectorized or bare for splicing | 2.0–3.0 mm jacketed, always connectorized | Short 0.9–2.0 mm, connectorized (usually LC duplex) |
| Typical leg length | 0.3–2.0 m, often staggered | 1–3 m, uniform | 0.3–1.0 m, tightly controlled |
| Where it is used | Enclosures, ODFs, splice trays | Direct switch-to-server or rack-to-rack runs | Inside MPO-LC cassettes and high-density panels |
| Routing style | Legs dressed inside one enclosure | Legs routed like individual patch cords | Legs pre-dressed to a cassette port map |
| Main decision driver | Splice plan / panel layout | Port-to-port distance | Cassette model and port density |
Rule of thumb:
- Splicing onto an ODF or dressing legs inside a wall-mount enclosure → fanout (this page).
- Plugging an MPO port straight into four LC transceivers across the row → breakout patch cord.
- Filling an MPO cassette in a 1U panel → harness.
If a supplier’s datasheet calls the same product a “breakout fan-out cable,” use the table above — not the product name — to confirm you are buying the right construction.
8F, 12F, or 24F: Match the Fanout to Your Transceiver
The most common ordering mistake is choosing fiber count by habit (“we always buy 12F”) instead of by the transceiver the cable serves. Parallel-optic transceivers use 8 fibers (4 Tx + 4 Rx); a 12-fiber MPO fanout on an 8-fiber application leaves 4 fibers dark.
| Link | Transceiver | Fibers used | Recommended fanout |
|---|---|---|---|
| 40G to 4 × 10G | QSFP+ 40GBASE-SR4 → 4 × SFP+ | 8 | 8F MPO to 4 × LC duplex |
| 100G to 4 × 25G | QSFP28 100GBASE-SR4 → 4 × SFP28 | 8 | 8F MPO to 4 × LC duplex |
| 400G to 4 × 100G | QSFP-DD/OSFP 400G-DR4 → 4 × 100G-FR (QSFP28) | 8 | 8F MPO (APC) to 4 × LC duplex (UPC) |
| Legacy 10G aggregation | MPO cassette or trunk feed | 12 / 24 | 12F or 24F MPO to 6/12 × LC duplex |
| FTTH / OLT distribution | MPO feeder to ODF | 12 / 24 | 12F or 24F unterminated fanout for splicing |
Single-mode DR4-class links additionally require APC polish and low-loss MPO connectors to stay within the link budget — typical low-loss MPO insertion loss is ≤ 0.35 dB per mated pair, versus ≤ 0.6 dB for standard grade (TIA-568 maximum 0.75 dB). Plan the total channel budget across every mated pair in the link, not just the fanout itself.
Construction Specs: Legs, Polish, Polarity, and Jackets
| Attribute | Typical range | What drives the choice |
|---|---|---|
| Fiber count | 8, 12, 16, 24 | Transceiver mapping (see table above); 16F for 400G-SR8 / 800G-DR8 links |
| Fiber grade | OM3, OM4, OM5 multimode; OS2 single-mode | Link distance and transceiver type |
| Leg diameter | 0.9 mm buffered (splicing / tight enclosures) or 2.0 mm jacketed (ruggedized handling) | Space vs mechanical protection |
| Leg length | 0.3–2.0 m | Enclosure dimensions; leave splice slack per your tray vendor’s spec |
| Leg layout | Uniform or staggered (stepped) lengths | Staggered legs reach consecutive adapter positions without excess slack |
| Leg connectors | LC, SC, ST, or unterminated | Panel adapters; LC duplex is the default for transceiver fanout |
| Polish | Multimode: UPC. Single-mode: APC on the MPO (required on DR4-class links), UPC on LC legs | Return loss requirement; never mate UPC against APC at one connection |
| MPO polarity | Type A, B, or C | Must match the trunk/cassette polarity plan — see our MPO polarity and loss testing guide |
| Jacket | LSZH (industry default for indoor), OFNP/OFNR where code requires | Local fire code and installation space |
| Typical IL / RL | MPO ≤ 0.35 dB low-loss / ≤ 0.6 dB standard; LC ≤ 0.3 dB; single-mode RL ≥ 50 dB (UPC) / ≥ 60 dB (APC) | Link budget; request per-factory test reports |
Where a Fanout Belongs — and Where It Does Not
Use a fanout when:
- Transitioning from an MPO backbone or trunk onto an ODF or adapter panel
- Custom splice configurations where legs must be fusion-spliced to pigtails
- Working inside fiber enclosures where jacketed breakout legs are too stiff to dress
- Feeding consecutive adapter positions — staggered legs keep the panel tidy
Do not use a fanout when:
- You are plugging an MPO transceiver directly into four LC transceivers in open racks — a jacketed breakout patch cord survives handling better.
- The assembly lives permanently inside an MPO cassette — that is a harness, with legs cut to the cassette’s port map.
- The run is exposed to crush, rodents, or outdoor conditions — you need an armored assembly, not a fanout.
The Fanout RFQ: Eight Fields That Prevent Re-Quotes
Send these eight items with your RFQ and any competent factory can quote without a clarification round:
- Fiber count and grade — e.g., 8F OM4 or 12F OS2
- MPO end — male (pinned) or female (unpinned), polarity type, standard or low-loss
- Leg termination — connector type and polish, or unterminated for splicing
- Leg diameter — 0.9 mm or 2.0 mm
- Leg lengths and layout — uniform or staggered; a simple enclosure drawing with adapter positions is the fastest way to communicate this
- Jacket rating — LSZH / OFNP / OFNR
- Labeling — leg numbering, serial labels for test-report matching
- Test documentation — request per-assembly IL/RL and polarity test reports
FAQ
Is a fanout cable the same as a breakout cable?
Many suppliers use the terms interchangeably, so always check the construction rather than the name. In engineering practice, fanout usually means 0.9 mm legs — often unterminated for splicing — while breakout means fully connectorized, jacketed legs for direct equipment connections.
Can fanout legs be different lengths?
Yes. Staggered (stepped) leg lengths are common so each leg reaches its adapter or splice position without excess slack. Provide an enclosure drawing with adapter positions and the factory will set the stagger for you.
Should I order an 8-fiber or 12-fiber MPO fanout?
Match the transceiver. Parallel-optic links (40G-SR4, 100G-SR4, 400G-DR4) use exactly 8 fibers, so an 8F fanout avoids four dark fibers. Keep 12F for legacy base-12 trunks and cassette-based 10G aggregation.
What insertion loss should I expect?
Typical factory values: standard MPO ≤ 0.6 dB, low-loss MPO ≤ 0.35 dB, LC ≤ 0.3 dB per mated pair. For 100G/400G single-mode links, specify low-loss MPO with APC polish and ask for the per-assembly test report.
Can I get an MPO fanout for 400G-DR4 breakout?
Yes — this is one of the most common current uses. You need an 8F OS2 fanout with a low-loss APC MPO and four LC duplex legs. 400G-DR4 modules present an MPO-12 interface with 8 of the 12 positions live; MPO-16 belongs to 800G-DR8 modules. Confirm the interface on your module’s datasheet before ordering.
Is MTP the same as MPO on a fanout cable?
MTP® is US Conec’s branded, enhanced MPO connector; both follow the same IEC 61754-7 interface and mate with each other. A fanout built with genuine MTP connectors is interoperable with MPO infrastructure.
Can I splice an unterminated fanout to existing ODF pigtails?
Yes — that is exactly what unterminated 0.9 mm legs are for. Fusion-splice each leg to the ODF pigtail in the tray, and plan leg length and slack per your splice tray vendor’s specification.
Do I need a male or female MPO on the fanout?
Match whatever the fanout mates with. Transceiver ports (QSFP/QSFP-DD/OSFP) are pinned, so transceiver-side fanouts are female; mating to a trunk follows the trunk gender. State the mating point on your RFQ and the factory will pin it correctly.
What jacket rating do I need for an indoor fanout?
LSZH is the industry default for indoor enclosures and data halls; OFNP or OFNR only where local fire code requires. Legs inside enclosures are typically 0.9 mm regardless of jacket rating.
Get a Fanout Built for Your Enclosure
BWNFiber manufactures MPO fanout assemblies to order: 8–24 fibers, OM3/OM4/OM5/OS2, 0.9 mm or 2.0 mm legs in uniform or staggered lengths, LC/SC/ST or unterminated for splicing. Every assembly ships with an individual IL/RL and polarity test report matched to its serial label.
How to get a recommendation: send your enclosure drawing (or a photo of the panel with adapter positions marked), the transceiver or OLT ports you are connecting, and your leg-length constraints. Our engineering team replies with a proposed construction and quotation — typically within 24–48 hours.
👉 View MPO/MTP breakout & fan-out cable configurations → · Or contact our engineering team →
About the author: Marcus Chen is a Senior Fiber Optics Engineer at BWNFiber (Ningbo Bwinners Optical Tech Co., Ltd), where he designs pre-terminated MPO/MTP cabling assemblies and supports ISP, data center, and FTTH customers on link design and acceptance testing.
References & standards: TIA-568.3-E (optical fiber cabling components); IEC 61754-7 (MPO connector interface); IEEE 802.3 (40G/100G/400G Ethernet optical specifications).
