optical fiber eavesdropping
I believe you can eavesdrop, but not very easily at all.
==> Let's say you and your friend are talking through an optical fiber that is burried in the ground over a long distance. If I wanted to listen in, I could dig up a section of the optical fiber between you and your friend, strip it of its insulation, and then bend the fiber so that the light signal escapes the fiber through the portion that I've stripped the insulation from. Assuming I had all of the equipment to do this, I could get access to your signal, but it wouldn't be easy.