布拉格光纤光栅内部能量特性研究

Study on Energy Properities in the Bragg Fiber Grating

基于耦合模理论并结合边界条件,推导出布拉格(Bragg)光纤光栅前向波和后向波的表达式。以均匀光纤光栅为例,得出光栅内部能量分布是振荡的。在禁带内,前向波、后向波能量单调递减,其相干迭加能量振荡,振荡周期与光纤光栅周期一致;在禁带边缘及外部,前向波、后向波能量是振荡的,二者相干迭加的能量也是振荡的,且呈包络变化,迭加能量的快变周期亦与光栅周期相同;在禁带边缘及外部,前、后向波振荡周期与包络周期一致,都和入射波长有关,入射波长偏离布拉格波长的程度越大,周期越小;在禁带附近存在前向波能量振幅的极大值;能量振幅随光栅长度的增加而增大。

Employing the coupled-mode formalism,the forward and backward wave expressions are deduced under the boundary conditions.Taking up the uniformed fiber grating,it is found that the energy distribution inner the grating is oscillatory.The distributions of forward and backward waves power decay along the grating direction,yet their interference energy one is oscillatory with the period as same as that of the grating in the forbidden-gap.Beside and outerside the forbidden-gap,the distributions of the forward and backward waves energy are also oscillatory.It is the same to their interference one,but different in the period that their interference period is equal to the grating period,and interference envelope period is equal to the forward and backward ones,which varies with incident wavelength that more is the departure between incident wavelength and Bragg one,less is the period.There is maximal energy amplitude of forward wave beside the forbidden-gap.The energy amplitude becomes bigger with the longer grating.