提出并验证了一种单-双波长可调谐掺铒光纤激光器。利用级联光纤布拉格光栅（Cascaded Fiber Bragg gratings, Cascaded FBGs)结合Sagnac环结构所产生的复合滤波效应, 实现较高精细度滤波, 并通过调节环内偏振控制器（Polarization Controller,PC), 引入双折射效应, 得到波长可调谐的光纤激光器。基于耦合模理论并使用传输矩阵法对该结构的传输特性进行了分析, 在此基础上搭建实验系统, 验证了理论分析的正确性。实验结果表明: 通过调节PC, 激光器输出激光的波长范围约为1 555.644~1 556.112 nm, 双波长间隔的可调范围约为0.108~0.452 nm, 单-双波长的边模抑制比（SMSR)均高于40 dB; 在稳定性测试中, 输出单-双波长激光的波长最大漂移量小于0.008 nm。该方法具有结构简单、调谐方便、易于实现且精细度较高的优点, 可应用于密集波分复用及全光通信系统等领域。

A tunable single-dual wavelength erbium-doped fiber laser is proposed and demonstrated. The finer filtering is generated by compound filtering effect which is produced by cascaded fiber Bragg gratings(Cascaded FBGs) combined with Sagnac loop, the birefringence effect is introduced by adjusting polarization controller(PC) in Sagnac loop, and then the tunable fiber laser is obtained. Based on the coupled mode theory and transmission matrix, the characteristics of the structure are analyzed, experimental system is established, and the correctness of theoretical analysis is verified. The experimental results show that, by adjusting PC, the adjustable laser range is about 1 555.644~1 556.112 nm, the wavelength spacing of dual-wavelength is about 0.108~0.452 nm, the side mode suppression ratio (SMSR) of single- and dual-wavelength is more than 40 dB. In the stability test, the maximum wavelength drift of single- and dual-wavelength fiber laser is less than 0.008 nm. The proposed method has the advantages of simple structure, convenient tuning, easy implementation and high fineness, which can be applied in fields such as dense wavelength division multiplexing(DWDM) and all-optical communication systems.