中文摘要：

基于光纤放大器增益谱的宽带平坦化发展需要，设计了一个两段铋基掺铒光纤（Bi-EDF）级联并携带一个C波段（1530-1565nm）宽带光纤布拉格光栅（FBG）的双通结构型铋基掺铒光纤放大器（Bi．EDFA），从理论上研究了其对输入信号的放大特性。研究表明：FBG的引入可以使C和L波段（1570-1620nm）信号分别经历不同长度Bi-EDF的双向传输，各自获得高增益放大，实现增益谱的宽带平坦化。在200mw的1480nm双向对称泵浦下，第一级和第二级Bi—EDF长度分别为50cm和170cm时，对于波长间隔为2nm、每路功率为-30dBm的56路C＋L波段信号的输入，Bi-EDFA高于30dB的增益带宽达到了90nm（1530~1620nm），平均增益为35．7dB，增益起伏仅为2．3dB。同时，噪声系数得到明显改善。研究结果对于研制具有宽带、增益平坦的C＋L波段Bi-EDFA具有实际指导意义。

英文摘要：

In order to meet the developing needs of broad amplification as well as gain-flattened operation for fiber amplifier, a double-pass structure of bismuth-based erbium-doped fiber amplifier （Bi- EDFA） with the incorporation of C-band （1 530-1 565nm） broad fiber Bragg grating （FBG） in between the two cascaded segments of bismuth-based erbium-doped fiber （Bi-EDF） was designed, and the amplifying performances of Bi-EDFA were presented theoretically. The results indicate that a broad amplification and gain-flattened spectrum can be achieved with the aid of the simultaneously obtained high gain of the C-band and L-band （1 570-1 620 nm） signals due to their experiencing a different length bi-directional transmission in Bi-EDF after the incorporation of FBG. A gain bandwidth of 90 cm with average gain 35.7 dB and gain variation of approximately ±2.3 dB within the wavelength range from 1530 nm to 1620 nm are obtained under the conditions of the 1 480 nm bi-directional symmetrical pumping with pump power of 200 mW, the first and second Bi-EDF length of 50 cm and 170 cm, and 56-channel signals of C＋L band with interval of 2 nm and each power of -30 dBm are inputted simultaneously. Meanwhile, the noisefigure of Bi-EDFA is improved evidently. The theoretical studies will provide practical significance for a new design of C＋L-band Bi-EDFA with broad and flattened gain.