级联长周期光纤光栅的模式耦合与干涉机理

摘要

针对级联长周期光纤光栅(CLPFG)的光传输特性存在模式耦合和模式干涉2种不同角度的解释,基于耦合模理论和传输矩阵法,系统研究了CLPFG中的模式耦合与干涉机制,厘清参与马赫-泽德干涉的纤芯模成分,得到模式干涉的相干表达式,从而将模式耦合和干涉机制从理论本质上统一起来;同时深入分析了光栅长度L对干涉条纹结构特性的影响.结果表明:L=Lo(最佳长度)时,中心波长处条纹对比度达到最大值;L ＜Lo时,条纹整体对比度下降,在整个波长范围内无法达到最大对比度;L＞Lo时,中心波长处的对比度下降,但在中心波长两侧的2个对称波长处可达到最大的条纹对比度.该研究结果可为基于CLFG的通信和传感器件应用提供理论指导.%According to two different explanations from the view of mode coupling and mode interference for the transmission properties in cascaded long-period fiber gratings (CLPFG),based on the coupled-mode theory and transfer-matrix method,the mode coupling and interference mechanism were systematically investigated.The modal components involved in the Mach-Zehnder interference were identified and the coherent expression of the mode interference was obtained,which unified the mode coupling and interference mechanism.Furthermore,the influence of grating length on the fringe properties was analyzed.For the optimum length Lo,the fringe contrast at central wavelength reached maximum.For L ＜ Lo,the overall contrast degraded and the contrast could not reach maximum within the interested wavelength range.For L ＞ Lo,however,the contrast at central wavelength decreased,but it reached maximum at two certain wavelengths on the each side of central wavelength.The results were prospected to provide theoretical guidance for the applications of CLPFG-based communication and sensing devices.