提出并实验验证了基于单模光纤基模和包层LP11模干涉耦合的可调谐光纤声光梳状滤波器,该滤波器采用普通单模光纤,通过刻蚀形成不同外径的三段光纤级联结构,通过声波调节实现调谐。说明了滤波器的结构和工作原理;并通过计算和实验结果具体说明梳状滤波谱带宽主要取决于发生声光耦合的第一、三段光纤的外径,而滤波峰间隔主要取决于用作传输的第二段光纤的长度;最后分析指出影响器件消光比的主要因素是声波的衰减和反射,优化第一、三段光纤的长度比例和采用渐变过渡的措施减小光纤外径的突变可望进一步提高器件的性能。

A novel all fiber acousto-optic tunable comb filter based on the interference between core mode and cladding mode LP11 is proposed and demonstrated. The device has cascaded 3-segment structure formed by HF etching from one piece of commercial single mode fiber. The tunable ability is realized by acoustic frequency adjustment. This paper details the structure and the working principle as well as the dependence of working bandwidth on outer diameters of the first and third segments, the dependence of peak interval on length of the second segment. The device extinction ratio may be improved by optimizing the length ratio between the first and the third segments for suppressing the acoustic attenuation and by using gradual transition between the segment-diameters to reduce the acoustic reflection.