Optical amplifier and transmission system

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PROBLEM TO BE SOLVED : To provide an optical amplifier and a transmission system that can reduce MDG in multi-mode transmission under an L band. SOLUTION : An optical amplifier includes N (N is an integer of 2 or more) amplification optical fibers which have different concentration distributions in the cross-section of a rare earth element added to the cores and are connected in series in a light propagation direction, and N excitation light sources for supplying excitation light to the respective amplification optical fibers. The gains of the optical amplifier and one amplification optical fiber of the transmission system vary according to each propagation mode. The addition distribution of the rare earth element in the core of each amplification optical fiber is set so that the total gain applied to light in the respective propagation modes becomes equal when the light passes through all the amplification optical fibers. SELECTED DRAWING : Figure 1 COPYRIGHT : (C)2017, JPO&INPIT