分析了由光纤级联的两个相同的长周期光纤光栅形成的干涉谱。根据设计中的关键技术,利用粒子群优化算法设计了长周期光纤光栅传输损耗为50%的平坦传输损耗谱.将相同的两个优化设计的长周期光纤光栅级联,可以实现一种实用的可调谐多信道隔离滤波器.讨论了级联长周期光纤光栅对之间光纤的偏振特性对干涉谱的影响. The interference spectra formed by two identical long-period fiber gratings cascaded by the fiber are analyzed. According to the key technologies in the design, a flat transmission loss spectrum with long-period fiber grating transmission loss of 50% is designed by using Particle Swarm Optimization algorithm. By cascading the same two long-period fiber gratings with optimized design, a practical Tunable Multichannel Isolation Filter The influence of the polarization characteristics of the fiber between the cascaded long period fiber grating pair on the interference spectrum is discussed.