Power in won't equal power out with a fiber optic cable.
The lazer diode used to send the signal might produce a pulse of light with an energy close to the electrical energy used to "fire" the lazer.
But once it reaches the other end, the photodiode used to "see" the light signal is just a switch. It doesn't provide any usable power. The recieving end needs its own power supply to do anything with the signal, even to "see" the signal.
