INTERMEDIATE ISOLATOR TYPE OPTICAL FIBER AMPLIFIER AND OPTICAL FIBER TRANSMISSION SYSTEM

摘要

PROBLEM TO BE SOLVED: To lower light loss and to make low NF and high output possible. SOLUTION: This amplifier has a first rare earth-added optical fiber 12, a second rare earth-added optical fiber 14 and an exciting light source 10 for forming pumping light for exciting both rare earth-added optical fibers 12 and 14. The amplifier receives analog signal light and amplifies the light. The amplifier has a directional coupler 13 between the tow rare earth-added optical fibers 12 and 14. This directional coupler 13 is higher in the transmittance in the case of the propagation from the first rare earth-added optical fiber 12 to the second rare earth-added optical fiber 14 than the transmittance in the case of propagation from the second rare earth-added optical fiber 14 to the first rare earth-added optical fiber 12 with respect to the light having at least the same wavelength as the wavelength of the signal light.