中文摘要：

基于偏振调制器（PolM）设计并实现具有可变系数特性的可调谐微波光子滤波器，通过理论计算与实验证实了设计方案的可行性。PolM可以对输入的微波信号实现两路正交反相的相位调制，经强度调制转换后，可以拍频恢复出原来的微波信号。仅需通过调节偏振控制器（PC）控制光信号的检偏方向，即可实现恢复出的微波信号π相位变化，进而实现滤波器抽头系数的正负变化。利用偏振分束器（PBS）实现两路光信号检偏和合并的同时，能够有效地避免两路光信号之间的干涉。通过调节光路中的光可调时延线（OTDL）改变两路光信号间的时延差，能够改变滤波器的自由光谱范围（FSR），实现滤波器的可调谐。通过实验验证了时延差分别为300ps和400ps两种情况下正系数和负系数微波光子滤波器的频率响应，与理论计算值相吻合，验证了方案正确性。

英文摘要：

A tunable microwave photonic filter with variable coefficients including positive coefficients and negative coefficients is proposed, theoretically calculated and experimentally demonstrated using a polarization modulator. The polarization modulator can conjugate phase modulation in the two orthogonal polarization directions. After intensity modulation conversion,the initial microwave signal can be recovered through a photoelectric detector. The tunability of the filter tap coefficients between positive coefficients and negative coefficients is achieved only by adjusting the polarization controller to control the polarization coupling of the optical signal, which results from the π phase change of the recovered microwave sig nal. A polarization beam splitter is used for the polarization coupling and recombination of two optical signals for avoiding interference. The tunability of the microwave photonic filter is achieved by changing its free spectral range （FSR） with adjusting the optical tunable time delay line in the light path to ac quire different relative time delays. The frequency responses of the microwave photonic filter with positive and negative coefficients under different relative time delays （300 ps and 400 ps） are measured, which coincide with the theoretical calculation and confirm the correctness of this scheme.