Our entire network is single mode fiber. It suffers from attenuation, loss, and dispersion, just at longer distances. All long haul fibers are single mode. The signal still has to be reconditioned though.
https://en.wikipedia.org/wiki/Non-zero_dispersion-shifted_fiber
Doped fibers:
https://en.wikipedia.org/wiki/Optical_amplifier#Doped_fibre_amplifiers
Our GPON has a 30KM limit.