@voltagex the second option is "multi-mode" fibre optic cables and optics. Traditionally, they were cheaper than "single-mode" but this is no longer true, because cheap VCSEL lasers are now capable of single-mode emission. They operate in the 850nm near-IR light band, and cables are generally constructed from 50um diameter plastic or glass cores. Because of the loose tolerance of the optics and fibre cores, their range is usually limited to 300M, and there's multiple grades of multi-mode fibre available with corresponding limitations on distance vs speed similar to copper ethernet cables. If you're buying new now, just go with OM4. OM1 cables use 62.5um diameter cores, and are only usually found in up to 1Gbit/sec applications. OM2 and later are all 50um diameter cores, but the optical transmission properties vary between generations which will limit transmission length.

You definitely don't need the fancy hybrid single-mode optics that use multi-mode cables unless you're trying to run 10GbE up the side of a building with ancient OM2 multi-mode cable plant.

@voltagex the third option is "single-mode" fibre optic cables and optics. This is where Shit Gets Real, and you do not look at energised optics with remaining good eye. Luckily, the actual cables are already so good and cheap that you just buy whatever from a reputable vendor and it'll work with any new single-mode optical devices you ever want to attach in future.

The optical devices on each end, however, are another matter entirely.

The basic consideration is the range class - typically either 10km, 20km, 40km, 80km, or 120km. Direct correlation to how much power the laser uses, and how expensive the modules is. Faster speeds may not get the 120km range class. Yes, you can have a single piece of glass 120km long to carry your signals.

And then comes the "oh wow holy shit my mind is blown" consideration of WAVELENGTH DIVISION MULTIPLEXING

@voltagex and finally the "wavelength division multiplexing" single-mode SFPs specify their wavelength, which is then optically combined into a single fibre core and transmitted to the other end, where the multiplexer uses wavelength-selective optics to split the signals back out into separate wavelengths on multiple fibres again.

Oh yeah, and there's 2 kinds of WDM, "coarse" and "fine", but they both work the same way, the only difference is how closely the wavelengths are packed together.

Almost certainly you don't need this, but you can just attach WDM MUXes to the single-mode fibres you already have whenever you want!

@jpm @voltagex oh hey Joel want to see my favourite things that render your last sentence hilariously inaccurate when it comes to weird edge cases in broadcast/AV industry?