In the '90s we were limited by the same phenomenon known as SBS (https://en.wikipedia.org/wiki/Brillouin_scattering#Stimulated_Brillouin_scattering https://en.w

In the '90s we were limited by the same phenomenon known as SBS (https://en.wikipedia.org/wiki/Brillouin_scattering#Stimulated_Brillouin_scattering https://en.wikipedia.org/wiki/Brillouin_scattering#Stimulate...) and were working to reduce or eliminate it using predistortion. As a CATV equipment provider, our signals were typically very wide band (we said DC to daylight) so comb filters could not be used. Using a comb filter on a digital signal is a pretty common occurrence. What's truly amazing is how effective the UCSD researchers were - 12km is roughly half the circumference of the globe.