OM3 v OM4

I understand that OM4 is backward compatible with OM3 - but with all these things minor issues can arrise.

Does anyone know of any reason why I cannot use an short 7m OM4 cable between two OM3 compliant devices and running at just 1Gbps?

It essentially makes the link OM3 - but I'm using OM4 patch cords here with OM1 legacy fibre with no issues.

How do you mean "OM3 compliant devices"? I wasn't aware that SFPs etc. specified the cable type beyond SM/MM.

You'll be fine running it over 7m though. You could probably get away with a multimode cable with SM optics over such a short distance and low link speed.

It will be te Ubiquiti UACC-OM-MM-1G-D 1 Gbps Multi-Mode Optical Modules which they recommend using OM3.

Has to be fibre for full isolation, but routing is difficult so it needs to be a one off install and need to be sure there will not be any issues.

You will be fine with OM4.

Personally I only use single-mode but you've got the optics now.

As it’s ‘just’ a 1 GbE link over a very short distance you’d be absolutely fine with either type. They are both laser optimised cables.

The difference only really matters at the much higher data rates, driving at the full link distance (several hundred metres) where the greater spectral bandwidth of the higher grades of multimode are needed.

FS do a neat summary on their website of all the variants.

Yes, OM4 is superior to OM3 so it's fine.

It's weird that you can even buy SX 1G optics these days. Everybody I know uses 1000base-LX (Cisco call it 1000base-LH) which is compatible with both single-mode and multi-mode fibres.