How does a fiber optic receiver converts the optical signal to an electrical signal
I believe that your "can't be carried by wires" notion stems from the fact that fiber optics can carry signals at data rates that would be wildly uneconomical to carry with wires -- but it could still, in theory, be done.

The frequencies involved in the modulated data cannot be higher than can be carried on a wire, because the signals are generated electronically before being modulated.

So yes, some pretty impressive high-speed photodiodes are used, and then some pretty impressive high-speed electronics.