PURPOSE: To provide a no-loss communication system, where intervals to an intermediate amplifier are long, and an optical fiber system for this system with respect to a relatively long-distance remote communication system.

CONSTITUTION: A glass fiber which is doped with rare earth element such as erbium with a density gradient in the longitudinal direction is used as the optical fiber 4 of a solution transmission system, and light excitation is added to obtain a optical fiber system which apparenty has no loss. The optical fibers are combined to obtain a long-distance communication system where intervals to repeaters/amplifiers are long.