Why does OM4 go further?
OM4 has higher specified modal bandwidth than OM3. At 850 nm this gives the 10GBASE-SR optical signal more usable distance before modal dispersion becomes the limiting factor.
| Characteristic | OM3 | OM4 |
|---|---|---|
| 10GBASE-SR reach | 300 m | 400 m |
| Typical core | 50 µm multimode | 50 µm multimode |
| Common use | Campus/data-centre fibre | Higher-margin multimode links |
| Connector | LC duplex is common | LC duplex is common |
Can OM4 replace OM3?
OM4 can be used for a 10GBASE-SR link where the equipment supports the same SR optics. The limiting factor is the complete channel, not just the bulk cable: patch panels, connectors, splices and polarity all matter.
When OM3 is enough
If the route is comfortably below 300 m and the installed plant is already OM3, upgrading the fibre purely to gain the extra 100 m may not be useful. The value of OM4 becomes clearer when the route approaches the OM3 limit or when a new installation is intended to provide additional multimode reach margin.
When to use single-mode instead
If the route is beyond multimode reach, or the organisation wants a fibre plant suitable for much longer future links, OS2 single-mode with an appropriate optic can be a better architecture. See Multimode vs single-mode.