啁啾长周期光纤光栅的超宽带滤波特性及其切趾优化

Ultra-Wideband Filtering Characteristics of Chirped Long-Period Fiber Gratings with Apodization Optimization

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 coupled-mode theory and transfer matrix method, the ultra-wideband filtering characteristics of chirped long-period fiber gratings （LPFG） are analyzed. When the resonant peaks corresponding to different order cladding modes overlap with each other, the transmission spectral bandwidth of chirped LPFG can expand to 500 nm, so this chirped LPFG can be used as ultra-wideband band-stop filters. With the increasing of mode order, chirp coefficient, grating length, grating period and refractive index modulation, the transmission spectral bandwidth increases monotonically, but the transmission spectral bandwidth decreases with the increasing of the fiber cladding radius. The refractive index apodization is proposed to inhibit the side-lobes of the transmission spectra. It provides a new method for the design of wideband filters.