PURPOSE: To reduce the electrostatic capacity between the metal layers of the adjacent optical fibers, and to enable to a low frequency communication by providing an insulating layer composed of a foamed synthetic resin around the outer surface of the conductive metal layer which is provided on the outer circumference of the titled fiber.

CONSTITUTION: The metal layer 4 and the insulating layer 5 are provided on the outer surroundings of the quartz optical fiber 1 composed of a core 2 and a clad 3 in order from an inside of the titled fiber. The metal layer 4 is composed of a metal having an excellent conductivity such as Al, Cu, Ag, Au, Pb and a solder. The insulating layer 5 is composed of the foamed synthetic resin such as a polyethylene and a polystyrene.