On the other hand the crosstalk of the wdm signal at fan - out of demultiplexer will increase with the power difference of the each channel . therefore , the gain of optical amplifier to wdm signal must have small ripple . one of the solutions is using two or more pumps with different wavelength and power according to the range of signal light to be amplified and raman gain coefficient of the fiber 另外，各路信号光之间较大的功率差异会增加wdm信道解复用器输出端的串话，所以光放大器对wdm各路信号光的增益要满足一定的增益平坦度，解决该问题可以根据所要放大的wdm信号光的波长范围和所用光纤的拉曼增益系数谱，采用多个不同波长和功率的泵浦光源进行泵浦。
