A multimode patch cord is a short fibre cable with a 50 µm or 62.5 µm core and a connector at each end, used for short links between 850 nm transceivers, patch panels and cassettes. It comes in OM1 to OM5 grades, simplex or duplex, with LC, SC, ST, FC or MPO connectors. Radix Fibrotech makes multimode cords to order in Pune and tests each one.
Multimode patch cord configurations
A multimode patch cord must match the grade of fibre in the link it joins, so the grade is the first choice on the order and the rest follows from the ports. Radix makes multimode cords to order in Pune, with each option below chosen per order line. Catalogues also list them as OM3 cable or OM4 cable, and US ones as multimode fiber patch cables.
| Grade | Core/cladding | Usual jacket colour | Typical use today |
|---|---|---|---|
| OM1 | 62.5/125 µm | Orange | Matching legacy campus plant and older equipment |
| OM2 | 50/125 µm | Orange | Matching legacy 1G links |
| OM3 | 50/125 µm | Aqua | 10G to 100G short reach, extending OM3 plant |
| OM4 | 50/125 µm | Aqua, or heather violet in some regions, mainly Europe | The usual default for new short-reach links |
| OM5 | 50/125 µm | Lime green | SWDM and other multi-wavelength optics |
| Option | Choices | Notes |
|---|---|---|
| Connectors | LC, SC, ST, FC or MPO, the same at both ends or mixed | LC for transceivers; SC and ST on older panels; MPO for parallel optics |
| Fibre count | Simplex or duplex; MPO in 8, 12, 16 or 24 fibres | Duplex cords are wired A-to-B unless the order says otherwise |
| End face | PC or UPC | Multimode MPO is normally flat polished; APC is a single-mode practice |
| Fibre | Standard or bend-insensitive multimode | Bend-insensitive fibre is compatible with standard fibre of the same grade |
| Jacket | LSZH, PVC, riser (OFNR), plenum (OFNP) or armoured | Riser and plenum are US National Electrical Code ratings |
| Diameter | 1.6, 2.0 or 3.0 mm simplex or duplex zip; round duplex | Thinner cords ease routing and airflow in full racks |
| Length | Any length to order | State a tolerance if the route is tight |
Which grade for which link
In short: OM4 is the usual default for new multimode links, OM3 suits additions to an existing OM3 plant, and OM5 earns its cost only with multi-wavelength optics. OM1 and OM2 cords are bought to match legacy equipment and cabling. For the reach of each Ethernet interface on each grade, see the OM3 vs OM4 vs OM5 guide; the multimode fibre optic cable guide covers the fibre itself.
A patch cord adds little length to a channel, but it carries a grade into it. An OM3 cord in an OM4 link means the channel should be treated as OM3. When a plant is being upgraded, order cords in the new grade so the old ones can be retired, and have the grade printed on each cord.
Mixing grades and the 62.5 vs 50 micron mismatch
OM2, OM3, OM4 and OM5 all have a 50 µm core and mate with each other at normal loss. A mixed channel is planned to the lowest grade in it.
A 62.5 µm OM1 cord in a 50 µm link is a different problem. Light passing from a 62.5 µm core into a 50 µm core overfills the smaller core and loses several decibels at the joint, while light travelling the other way loses little. A duplex link with this mismatch can read normally in one direction and fail in the other, which makes it hard to trace. Read the jacket legend before patching: OM1 and OM2 are both orange, so colour will not separate 62.5 µm from 50 µm.
Multimode and single-mode fibre are never mixed in an ordinary patch. The one exception is the mode-conditioning patch cord, which joins a single-mode transmitter to multimode fibre through an offset launch and is used with some 1000BASE-LX optics over older multimode plant. It is built differently from a standard cord, so describe the optic and the plant on the order if you need one.
850 nm SR optics, SWDM and OM5
Multimode Ethernet runs on 850 nm VCSEL optics, and the connector on the module sets the cord:
- Duplex LC. 10GBASE-SR and 25GBASE-SR, plus BiDi and SWDM modules that carry several wavelengths on two fibres.
- MPO-12. 40GBASE-SR4 and 100GBASE-SR4 use 8 of the 12 positions, four to transmit and four to receive. 400GBASE-SR4.2 uses the same 8-fibre layout with two wavelengths per fibre.
- 16 fibres. 400GBASE-SR8 uses 16 fibres; check whether the module has an MPO-16 or a 24-fibre receptacle.
OM5 is specified for wavelengths from 850 to 953 nm, so it helps only with optics that put more than one wavelength on each fibre, such as SWDM4 and SR4.2. With single-wavelength SR optics an OM5 cord performs as OM4. In a mixed room its lime green jacket marks those links clearly.
MPO multimode cords for parallel optics
Parallel optics need multi-fibre cords. An MPO cord between an SR4 module and a cassette or trunk carries the eight working fibres in one connector, and an MPO to LC breakout splits one SR4 port into four duplex 10G or 25G links. Multimode MPO connectors are normally flat polished, and the cord needs the right pin gender and polarity type for the trunk and module it joins. These cords, and MTP versions, are covered under MPO patch cords.
Testing multimode cords at 850 and 1300 nm
Radix tests each multimode cord before it ships: insertion loss on every connector at 850 nm, and at 1300 nm where the order calls for it, with end faces inspected against IEC 61300-3-35 criteria. Multimode loss readings depend on how light is launched, so reference tests use an encircled flux launch under IEC 61280-4-1. Without it, two test sets can give different results on the same cord.
| Measure | Industry reference | Source |
|---|---|---|
| Insertion loss, mated connector pair | 0.75 dB maximum for channel planning | TIA-568 |
| Cabled fibre attenuation at 850 nm | 3.0 dB/km maximum for OM3, OM4 and OM5; 3.5 dB/km for OM1 and OM2 | TIA-568.3-D |
| Cabled fibre attenuation at 1300 nm | 1.5 dB/km maximum | TIA-568 |
| Return loss, multimode connector | 20 dB minimum | TIA-568 |
Over a few metres fibre attenuation is negligible, so the loss of a cord is almost all connector loss. Put your maximum per connector on the quote with the report format you need.
Ordering checklist
Give one line per configuration, each with:
- Fibre grade, and bend-insensitive multimode if routing is tight.
- Jacket colour, if the site uses violet for OM4.
- Connector at each end, simplex or duplex; for MPO, fibre count, pin gender and polarity.
- Duplex polarity, if not A-to-B.
- Jacket rating and outer diameter.
- Length and tolerance.
- Maximum insertion loss, label text and report format.
- Quantity for that line.
Send the list through the request a quote page. Other cord families are on the fibre optic patch cords page; for older SC duplex panels, see the SC to SC patch cord page.
What sets the price of a multimode patch cord
Multimode cords are priced on request against the specification. The factors that move the figure are these:
- Grade. OM4 and OM5 fibre cost more per metre than OM3.
- Bend-insensitive fibre. It costs more than standard multimode of the same grade.
- Connectors. MPO and MTP cords cost more than duplex LC or SC.
- Jacket. Plenum and armoured constructions cost more than LSZH or PVC.
- Loss limits and reports. A tighter maximum and serialised test data add inspection and handling.
- Volume per configuration. Many identical cords cost less each than a mix of small lines.
Questions buyers ask
What is the difference between an OM3 and an OM4 patch cord?
Both have a 50 µm core and the same connectors, and they mate with each other. OM4 has higher modal bandwidth at 850 nm, so a channel built entirely in OM4 supports longer reach at 10G to 400G. Both are aqua under TIA-598, though OM4 is often violet in Europe.
Can I use an OM4 patch cord on an OM3 link?
Yes. The core size is the same and the loss at the joint is normal. The channel performs to OM3, the lowest grade in it, so the cord adds no reach, but it does no harm and suits a plant that will move to OM4 later.
Why does my link fail when I patch OM1 into OM3?
OM1 has a 62.5 µm core and OM3 a 50 µm core. Light passing from the larger core into the smaller one loses several decibels, so one direction of a duplex link can fail while the other works. Use 50 µm cords throughout a 50 µm link and check the jacket legend, since OM1 and OM2 are both orange.
Do I need OM5 patch cords?
Only if the link uses multi-wavelength multimode optics such as SWDM4 or 400GBASE-SR4.2, where OM5 extends the reach. With single-wavelength SR optics, OM5 performs the same as OM4 and costs more. Its lime green jacket keeps multi-wavelength links easy to identify.
Is OM4 cable the same as an OM4 patch cord?
Buyers use the term OM4 cable for both bulk cable and finished cords. A patch cord is a short, factory-terminated length with connectors at both ends; bulk OM4 cable is installed and then terminated or spliced on site. State which you need, and for cords give the connectors and length.