Lasers and light are indeed made from electromagnetic fields, and do radiate away from the transmission medium (the fiber). This effect is called evanescent wave coupling.
One fiber with photons travelling through it placed next to an empty fiber will generate photonic energy in the empty fiber that matches the phase/frequency/modulation of the original signal. The length of the section of the fibers next to each other determines the percentage of energy transferred. This is how optical couplers/splitters work. See
here for more info on this process.
-QMan