The short answer
OM3 and OM4 differ in exactly one specification: effective modal bandwidth at 850 nm, 2000 MHz·km against 4700. That is why OM4 goes further, and it is the whole story between them.
OM5 is where the confusion starts. It has the same 850 nm bandwidth as OM4 — it does not reach further on a normal SR link — but it additionally specifies bandwidth out to 953 nm so that several wavelengths can share one fibre pair. If you are not using SWDM or BiDi optics, OM5 buys you nothing and costs more. That sentence saves a lot of money.
What Is OM3?
50/125 µm laser-optimised multimode, 2000 MHz·km effective modal bandwidth at 850 nm, aqua jacket. 10GBASE-SR to 300 metres, 100GBASE-SR4 to 70 metres, 400GBASE-SR8 to 70 metres.
Enormous quantities are installed and there is no reason to replace working OM3 serving short links. For new plant the price gap to OM4 is small enough that it rarely makes sense to specify. See OM3.
What Is OM4?
The same construction held to a tighter index profile: 4700 MHz·km at 850 nm. 10GBASE-SR to 400 metres, 100GBASE-SR4 and 400GBASE-SR8 to 100 metres.
This is the default for new multimode data-centre cabling and the fibre inside most parallel-optics assemblies. The extra thirty metres over OM3 at 100G is frequently the difference between serving a row from one location or two. See OM4.
What Is OM5?
Wideband multimode, lime green jacket. Same 4700 MHz·km at 850 nm as OM4, plus specified modal bandwidth across the range to 953 nm.
The extra specification exists for SWDM and BiDi optics, which put four wavelengths on one fibre pair. On those standards OM5 reaches 150 metres where OM4 reaches 100. On everything else the two are identical. See OM5.
OM3 vs OM4 vs OM5
Read the two bandwidth rows together. The first explains OM4 against OM3; the second explains what OM5 is actually for.
| OM3 | OM4 | OM5 | |
|---|---|---|---|
| Core | 50/125 µm | 50/125 µm | 50/125 µm |
| EMB at 850 nm | 2000 MHz·km | 4700 MHz·km | 4700 MHz·km |
| Specified to 953 nm | No | No | Yes |
| Jacket colour | Aqua | Aqua or violet | Lime green |
| 10GBASE-SR | 300 m | 400 m | 400 m |
| 100GBASE-SR4 | 70 m | 100 m | 100 m |
| 400GBASE-SR8 | 70 m | 100 m | 100 m |
| 100G SWDM4 | 75 m | 100 m | 150 m |
| 400GBASE-SR4.2 BiDi | 70 m | 100 m | 150 m |
| Relative cable cost | Lowest | Slightly higher | Highest |
Notice that the OM4 and OM5 columns are identical for every single-wavelength standard and differ only on the two WDM rows. That is not an oversight in the table — it is the entire distinction between the two grades.
The other thing the table cannot show is the loss budget. At 400G the whole channel gets 1.8 dB, which is three or four mated pairs and nothing else. Multimode links usually fail on connector count rather than on distance, so check yours in the multimode reach lookup with the real number of panels in the path.
Which One Should You Choose?
New multimode cabling: OM4
Specify OM4 and stop thinking about it. The cost difference over OM3 is small, the reach difference at 100G and above is 30 per cent, and OM4 is what every parallel-optics assembly is built on by default. This covers the overwhelming majority of multimode requirements.
Existing OM3 with short links: keep it
If your longest OM3 run is under 70 metres you are inside spec for 100GBASE-SR4 and 400GBASE-SR8 and there is nothing to gain from replacing it. Spend the money on connector quality and inspection instead — that is where multimode links actually fail.
Committing to SWDM or BiDi: OM5
This is the only case where OM5 earns its price. If you have chosen SWDM or BiDi optics specifically to avoid pulling eight-fibre MPO trunk, then OM5's extra 50 metres on those standards is real and worth paying for. Decide the optics first, then the fibre — not the other way round.
Anything over 100 metres at 100G or above: none of them
This is a single-mode requirement. Multimode at these speeds is a within-the-row technology, and no grade changes that. See single-mode vs multimode.
Frequently Asked Questions
Does OM5 reach further than OM4?
Not on a standard SR link — both are 100 metres for 100GBASE-SR4 and 400GBASE-SR8. OM5 reaches further only on wideband standards such as SWDM4 and 400GBASE-SR4.2 BiDi, where it manages 150 metres against OM4's 100. If you are not running those, OM5 is a more expensive OM4.
Can I mix OM3 and OM4 in one channel?
Physically yes, and the channel is then limited by its worst segment. Two-metre OM3 cords on a 90-metre OM4 trunk hardly matter; twenty metres of OM3 in a 100-metre channel does. If the design depends on OM4 distances, keep the whole channel OM4.
Why is the loss budget so small on multimode?
Because the standard reserves most of the budget for modal and chromatic penalties rather than for your connectors, and because VCSELs launch modest power. 1.8 dB at 400G is three or four mated pairs and nothing else — which is why cassette-plus-cassette designs sometimes fail where a single harness would have worked.
Is OM1 or OM2 usable for anything modern?
OM1 62.5/125 manages 1G to 275 metres and 10G to 33. At 25G and above it is not specified at all. OM2 is little better. Legacy 62.5 plant is a replacement project rather than an upgrade path.
What jacket colour should I expect?
Aqua for OM3, aqua or violet for OM4, lime green for OM5. Colour is a convention rather than a specification, so verify the print on the jacket rather than trusting the shade — particularly with OM4, where both colours are in common use.
The Parts We Build
We build MPO trunks, harnesses, cassettes and patch cords in OM3, OM4 and OM5, measured fibre by fibre.
