为了设计出自由频谱区(FSR)较大和3dB带宽较小的带通滤波器，拟合级联马赫－曾德尔干涉仪(MZI)与阶梯形滤波器原理的相似性，在MZI中引入啁啾臂长差以有效扩展FSR。采用传输矩阵法建立带通滤波器的理论模型，进而分析其滤波性能(3dB带宽、FSR)与结构参数(级联级数、衍射阶数)的对应关系。结果表明，当合理选取啁啾系数，该滤波器在保持3dB带宽不变的前提下有效扩展了FSR，并且在整个FSR内具有高边模抑制比。在设计实例中，对应低于4．5nm的3dB带宽和高于100nm的FSR(要求边模抑制比高于35dB)的滤波性能，器件的级联级数、衍射阶数、最佳啁啾系数分别对应16，45和5。

The optical band-pass filter based on cascaded Mach-Zehnder interferometers with chirped path differences was designed. The filter had wide free spectral range(FSR)and narrow 3 dB bandwidth. With theoretical model established by transfer matrix method,its band-pass filtering characteristics(i.e.,3dB bandwidth and FSR)were investigated under different structure parameters(i.e.,number of stages and diffraction order). Using optimized chirp coefficient,the FSR was expanded and the 3dB bandwidth was almost fixed. Meanwhile the side-mode-suppuration-ratio(SMSR)during whole FSR was excellent. For a design example,the 3dB bandwidth was specified less than 4.5nm and the FSR was specified more than 100nm(the corresponding SMSR was required to be more than 35 dB).The derived structure parameters of filter were as follows: number of stages was 16;the diffraction order was 45;and the optimal chirp coefficient was 5(the corresponding SMSR was 65.90dB).