Raman amplification method, raman amplification pumping unit, and WDM optical communication system

摘要

This invention provides a Raman amplification method and the like having a structure which can properly adjust a pumping light power in accordance with a loss change in signal light and can easily flatten a gain spectrum. In the Raman amplification method according to this invention, part of Raman-amplified propagating light is branched by an optical branching device. Of the branched propagating light, at least light components having two predetermined wavelengths are demultiplexed by an optical demultiplexer. The powers of the light components having the two wavelengths are detected. The amounts of loss changes in the light components having the two wavelengths and the slope of an approximate line representing the correlation between the wavelength and the amount of loss change are obtained on the basis of these powers. The optical power of each pumping channel output from an associated one of a plurality of pumping light sources included in a Raman amplification pumping unit is adjusted on the basis of the amount of loss change and the slope of the approximate line.