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基于光纤光栅的模式耦合理论,采用传输矩阵法对啁啾长周期光纤光栅(LPFG)的超宽带滤波特性进行了分析。研究表明当啁啾LPFG的纤芯模同时与同向传输的多个阶次的包层模发生耦合,且与多个不同阶次包层模对应的谐振峰交叠时,其传输谱带宽可扩展到500nm以上,可用做超宽带带阻滤波器。传输谱带宽随模式序数、啁啾系数、光栅长度、周期和折射率调制量的增加单调递增,但随光纤包层半径的增大单调递减。采用高斯折射率切趾技术抑制了传输谱旁瓣,为设计超宽带滤波器提供了新的方法。
Based on the mode coupling theory of fiber grating, the transmission matrix method is used to analyze the ultra-wideband filter characteristics of chirped long-period fiber grating (LPFG). The results show that when the core mode of chirped LPFG is coupled with multiple orders of cladding modes in the same direction and the resonant peaks of multiple LPFG modes overlap, the bandwidth of transmission spectrum can be Extended to more than 500nm, can be used as ultra-wideband band-stop filter. The bandwidth of transmission spectrum increases monotonously with the increase of mode ordinal number, chirp coefficient, grating length, period and refractive index modulation, but decreases monotonously with the increase of fiber cladding radius. Gaussian refractive index apodization is used to suppress the transmission spectrum side lobe, which provides a new method for designing UWB filters.