Tracking the exponential growth of data bandwidth?

Hi:

I've watched with interest as data bandwidth over various wires/cables keeps increasing...exponentially... over the years. I am intensely curious as to how this is possible when technologies always seem to plateau after a while and then the next step comes from a tech or scientific "breakthrough/discovery". Where can one read about the technology /engineering improvements that are making these huge improvements possible? Hopefully in layman's language.

Thanks