[henrikeh]

The two other comments gave very good general answers, but I happen to have worked on this specific project, so I can give some very specific details (as far as my memory goes.)

Lab testing of this scale of transmission involves a bit of “educated simplification”. We had some hundreds of wavelength channels, 37 fiber cores and two polarizations to fill with data. That is not realistic to actually do within our budget, so instead e split the system into components where there is no interference. For example, if there is different data on all neighboring cores compared to the core-under-test, then we dare to assume that the interference is random, without considering neighbors’ neighbor etc.

This reduces our perspective to a single channel under test with known data and then at least one other channel which is just there as “noise” for the other channels. The goal is to make the channel-under-test have a realistic “background noise” from neighboring interference. This secondary signal is sometimes a time-delayed version, sometimes a completely independent (but real) data signal.

This left us with a single signal of 32 GBd (giga symbols / s). This is doable on high-performance signal generators and samplers.

[jedberg]

Ah ok so you just extrapolate the capacity of the pipe based on that, you don't actually generate petabytes of data. That makes a lot of sense, thanks!

[henrikeh]

I should clarify that we did measure every channel (polarization, wavelength and fiber core) individually. It would not be fair if we just measured one and multiplied ;)

(And yes, that took forever. A shout out to A. A. Jørgensen and D. Kong for their endurance in that.)