Multimode fibre specified across 850–953 nm so several wavelengths can share one fibre pair — not simply 'better OM4'.
What Is OM5 Fiber?
OM5 is wideband multimode fibre. It carries the same 4700 MHz·km of effective modal bandwidth at 850 nm that OM4 does, and additionally specifies modal bandwidth across the window from 840 to 953 nm, with a floor of 2470 MHz·km at the 953 nm end.
The purpose is not more distance at one wavelength. It is the ability to put several wavelengths down one fibre pair at once and have all of them work.
What the Extra Specification Is For
SWDM places four VCSELs at 850, 880, 910 and 940 nm on a single duplex pair, so a 100G link needs two fibres instead of eight. For that to close, the fibre must have adequate modal bandwidth at all four wavelengths — and OM4 makes no promise above 850 nm. It usually behaves reasonably, but nothing in the specification says it must.
The measurable gain is one step of reach on the multi-wavelength standards: 100G-SWDM4 runs 100 m on OM4 and 150 m on OM5, and 400GBASE-SR4.2 does the same. On MPO-based parallel optics — SR4, SR8 — OM5 and OM4 reach exactly the same distance.
What OM5 Does Not Buy You
This is the most consistently oversold fibre grade on the market. If the plan is parallel optics over MPO trunks, OM5 costs more per metre, needs its own lime-green stock, and reaches not one metre further than OM4. The 850 nm bandwidth figures are identical because they are specified to be identical.
It is also worth noting what the alternative to fibre-count reduction is. Where SWDM saves eight fibres, base-8 MPO trunking and sensible grouping often saves more, for less money, and without committing the site to one optics family.
How to Choose
Buy OM5 if SWDM or BiDi transceivers are already in the design, or if the cabling has to outlive two generations of optics in a building where pulling more fibre is genuinely impractical. Otherwise buy OM4 and spend the difference on connector grade. Compare all three in OM3 vs OM4 vs OM5 and check the reach in the reach calculator.
One practical caution if you do buy it: the advantage only exists if the entire channel is OM5. An OM4 patch cord or cassette in the middle of an OM5 link re-imposes the OM4 limit on every wavelength above 850 nm, and the fault will not show on a single-wavelength test. The jackets at least differ — lime green against aqua — so a walk-down of the channel finds it quickly.
OM5 reference
| Core / cladding | 50 / 125 µm — identical to OM4 |
|---|---|
| EMB at 850 nm | 4700 MHz·km — identical to OM4 |
| EMB at 953 nm | 2470 MHz·km |
| Specified window | 840 to 953 nm |
| SWDM4 channels | 850, 880, 910, 940 nm |
| 100G-SWDM4 reach | 100 m on OM4, 150 m on OM5 |
| 400GBASE-SR4.2 reach | 100 m on OM4, 150 m on OM5 |
| Single-wavelength SR reach | the same as OM4, at every rate |
| Standards | TIA-492AAAE, ISO/IEC 11801 OM5; jacket lime green |