对正向和反向抽运的L波段双通掺铒光纤放大器(EDFA)的增益改善机制进行了实验研究,比较了两种抽运方案在不同掺铒光纤(EDF)长度下的增益改善效果。结果表明,两种抽运方案的增益改善机制不同,正向抽运方案时EDF中粒子数反转度沿纵向的分布有利于信号光功率在输入输出端附近的放大,进而对抽运输入端附近的放大的自发辐射(ASE)有抑制作用;反向抽运方案则利用抽运输入端附近产生的后向C波段ASE作为辅助抽运源。反向抽运时,因反射端ASE功率过大导致了ASE引起的增益自饱和效应,使得当EDF长度较短时,其增益改善效果比正向抽运方案稍差;正向抽运方案则在EDF长度较长时出现抽运不足问题,并使得输入信号光功率较低时的增益特性变差。

The mechanisms for improving the gain properties of the forward- and backward-pumped L-band double-pass erbium-doped fiber amplifiers (EDFA) are experimentally investigated. The gain enhancements of the two EDFA are compared for different EDF lengths. The results show that,the gain improvement mechanisms of the two pumping schemes are different. With the forward-pumped scheme,the population inversion near the signal input (output) port is very high,which helps to amplify the L-band input signal quickly after entering the EDFA and boosting its power before being exited. Such high L-band signal power near the signal input port may in turn suppress the backward C-band amplified spontaneous emission (ASE) near the input pump port,and thus,improve the L-band gain properties. With the backward-pumped scheme,the backward C-band ASE generated in the pump input port may be reused as an auxiliary pump source to enhance the L-band gain. However,for the backward-pumped scheme,the reuse of the backward C-band ASE may cause the gain self-saturation effect due to the high ASE level. It is found that the gain improvements of the EDFA with forward pumping scheme is slightly better than those with backward pumping when the EDF length is 20 m,because of the gain self-saturation effect caused by the high ASE. However,when the EDF length is more than enough for pump absorption,compared with the backward-pumped scheme,the forward-pumped L-band double-pass EDFA exhibits obviously insufficient pump,deteriorating its gain improvement,especially for the relatively low input signal power.