长周期光纤光栅(LPFGs)的谱结构研究

Investigation of the Spectral Structures of Long-period Fiber Gratings(LPFGs)

利用相位匹配条件,从理论和实验上研究了均匀LPFGs的谱结构特点结果表明,导模和不同包层模耦合产生的光谱特性有很大差别在模序较小时,谱宽较小;模序增加,谱宽也增加;在某一模序附近,谱宽达到最大;以后随模序增加,谱宽迅速减小给出了LPFGs中透射谱的最大损耗率及3dB带宽与包层模序、光栅周期、耦合系数和栅长的关系这些关系对设计满足特定最大损耗率和带宽的带阻滤波器或增益均衡器提供一种理论参考选用不同的包层模、耦合系数和栅长。

Long period fiber gratings (LPFGs) used in different fields of the fiber communication and sensing are required to possses different properties. The spectral characteristics of LPFGs are investigated theoretically and experimentally by using the phase matching condition. The structures of the transmission spectra are very different when the core mode is coupled to different cladding modes. For lower order cladding modes, the spectra are narrower. With the increase of the mode orders, the transmission spectra become wider. There is a critical mode order whose spectrum comes to a maximum. Then when the mode order increases,the bandwidth decreases quickly. The relationship between the maximal loss rate, 3dB bandwidth of the spectrum and the cladding mode order, grating length, coupling coefficient and period is derived. By controlling of the coupling coefficient, length, and the selection of the cladding modes, LPFGs with very wide or narrow spectrum used as gain equalizers or band rejection filter can be designed.