It's not really the fibre that slows down the signal as much as the opto-electrical repeaters that relay the signal many times as it travels vast distances.
Light can only go a few km before it needs to be boosted
Light can only go a few km before it needs to be boosted
The speed of light in a fiber is only about 70% of speed of light in vacuum.
Modern single mode fiber has very low attenuation (less than 0.01dB/km). But more importantly you don't have to use opto-electrical repeaters to boost the signal. What you do is using purely passive dispersion control by mixing different kinds of fiber and compensate for the rest dispersion using chirped fiber bragg gratings. To boost the signal you splice in rare earth doped fibers (Erbirum, Yttrium) which acts as optically pumped optical amplifier.
/me trying to get a handle on optical development.
They're used in long haul communication for some 15 years or so. They're especially useful in submarine cables, for the sole reason, that new optical transmission schemes(modulation, wavelength multiplexing and so on) can be implemented by just replacing the equipment on either end, without the need to replace components down there on the seabed.