长周期光纤光栅耦合常数的研究

长周期光纤光栅表现为前向传播的纤芯基模与同向传播的各阶次包层模式在特定波长时的模式耦合。由纤芯基模、一阶包层模式的场分布推得其功率分布 ,进一步得到两种模式的归一化常量。推导了纤芯基模与一阶各次包层模式 (HE1l/EH1l)的耦合常数。结果表明 ,纤芯基模与HE1l包层模式产生的耦合常数远大于与EH1l包层模式的耦合常数。次数低时 ,耦合常数随包层模式次数的升高而增大

Research on coupling constant of long period fiber grating

A long period fiber grating (LPFG) couples light from the forward propagating fundamental core mode into co propagating cladding modes at discrete wavelengths. Power distributions for fundamental core mode and first rank cladding modes are formulated using their field distributions. Further normalization constants for both kinds of modes are deduced. Finally coupling constants for fundamental core mode and first rank cladding modes (HE 1l /EH 1l ) are expected. Results show that coupling constant produced with HE 1l  mode is much larger than that with EH 1l  mode. Coupling constants at the lowest few coupling orders increase with the order of cladding modes.