双折射光纤环形镜滤波器特性研究

双折射光纤环形镜具有滤波特性，将两个串联的双折射环形镜作为光学滤波器可以改善滤波特性，使其更为灵活。提出了用两个双折射光纤环形镜相串联的简单方案改善环形镜滤波特性。分析了由双折射光纤和萨尼亚克环构成的环形滤波器的透射特性，并讨论了用两个双折射光纤环形镜串联的滤波特性。从理论上模拟了双折射光纤长度比为1：2时的透射光谱形式，给出了透射光的表达式。串联后光谱中主峰的3dB带宽约为7nm，与单个环形镜相比，压缩了环形镜的3dB带宽，品质因数Q约为4．5。实验结果与理论模拟相一致，因此证实了该理论的正确性。

Study on Characteristics of Two High-Birefringence Fiber Loops Mirror Filter

Birefringence fiber loop mirror has filtering characteristics. By cascading two loops, the transmission performance can be improved and become more flexible compared with that of the single-stage one. Such a simple cascading scheme which can improve filtering characteristics of loop mirror, is proposed. The transmission characteristics of the loop mirror filter constituted by birefringence fiber and Sagnac loop have been analyzed in detail. The filtering characteristics of two cascaded birefringence fiber loop mirror are discussed. By numerical simulation, explicit expression of the transmission spectrum for the cascaded mirrors with the high-birefringence fiber (HBF) length ratio of 1∶2 is obtained. Compared with its single-stage counterpart, the 3 dB bandwidth of the two-stage filter is compressed to approximately 7 nm and its quality factor reaches about 4.5. Experimental results conform well with the theoretical calculation, thus proving the validity of this theory.