There are several different ways to run a cable. One way is the single mode optical fiber. This fiber was created to move light completely and only through the fiber. It does not allow the light to move to other areas that are not in contact with the fiber. They use a transverse mode. There are certain modes that provide solutions to the problem. Using these modes allows the waves go through space.
There are different frequencies in regard to waves but they may have the same mode. The basic connector unit is through assembly. An optical cross connect equipment from the telephone plant to the central office. There is a cable that is considered to be the longest cable and it is the single mode fiber.