长周期光纤光栅中纤芯导模与包层模耦合分析

基于简化的长周期光纤光栅模型 ,从理论上分析了其纤芯导模与包层模之间的耦合 ,忽略了一些弱模式耦合 ,包括轴向的模式耦合 ,包层模之间的耦合 ,及基模与偶次包层模之间的耦合 ,在特定波长处只考虑数个奇次包层模耦合 ,简化了长周期光纤光栅的模式耦合 ,从而得到解析解 ,并由此得到相应的透射光谱。与其它模型结果相比较 ,其理论结果与实验结果吻合较好 ,计算量大为减少

An analysis of the core mode coupling to the cladding mode in long-period fiber grating

The interaction between a guided core mode and the cladding modes of a long-period fiber grating filters is analyzed theoretically.Based on the modes of a step-index fiber geometry,the coupled-mode equations that describe co-propagating interactions in a long-period grating is simplified by neglecting the longitudinal coupling coefficients,and coupling among cladding modes,as well as coupling to the even cladding modes.It is show that only the interaction of several odd modes is nearly resonant at the certain wavelength.,then a closed-form solution of the coupled-mode equations can be found,and the transmission spectra are also calculated theoretically.Compare with other models,the Numerical calculations agree with the experiment results well and show the advantage of our method.