An optical ground wire (OPGW or an optical fiber composite overhead ground wire) is a type of cable that is used in overhead power lines. Such cable combines the functions of grounding and communications. It has optical fibers in it, surrounded by layers of steel and aluminum wire. Here is one example of such system installed to 110 kV high voltage power line in Finland. This is how one power line structure can also be used to carry high speed data.
OPGW is primarily used by the electric utility industry, placed in the secure topmost position of the transmission line where it “shields” the all-important conductors from lightning while providing a telecommunications path for internal as well as third party communications. OPGW must be capable of withstanding the mechanical stresses applied to overhead cables by environmental factors such as wind and ice.
OPGW as a communication medium has some advantages over buried optical fiber cable. Installation cost per kilometre is lower than a buried cable and an OPGW cable is unlikely to be damaged by excavation work, road repairs or installation of buried pipelines.
Here is one closeup how the optical ground wire is connected to a local fiber optic cable. The two fiber optic cables up from the ground wire are wired to the optical splicing box where it meets the black local fiber optic cable that most probably goes to some telecom rack some distance away.