为构造出与理想梯形滤波器接近的滤波形状，在单级光纤马赫－曾德尔交叉复用器的基础上，引入在线滤波技术；通过增加干涉级数和调整2对干涉臂的干涉长度和耦合器的耦合比，实现了逼近宽带陡沿的滤波输出。通过与梯形滤波器傅里叶展开式的比较，计算得到了器件的最佳参数，器件的滤波性能以及温度稳定性相对于单级结构得到了明显提高。根据理论计算，成功制作出通道间隔为50GHz的样品器件。其输出为－0．5dB，带宽大于0．185nm，相邻通道隔离度大于30dB，满足了DWDM系统指标要求。

In order to generate an ideal output shape,the on-line filtering technology was introduced into fiber Mach-Zehnder interleaver. The sharp edge filtered output of approximating wideband was realized by adding interference orders,adjusting the interference length of the two pairs of interference arms and coupling ratio of the coupler. The coupling ratio should be corrected to improve the output characteristics. By comparison with Fourier function of trapezoid filter,the key parameters of Mach-Zehnder interleaver were worked out. The properties of output and the temp-stability are optimized. A sample component with the channel interval of 50 GHz was made. When its output is －0.5 dB,the band width is more than 0.185 nm and the interval between the consecutive channels is over 30 dB. The theoretical results are consistent with the experimental results and they meet the requirement of DWDM system.