矩形折射率分布长周期光纤光栅特性中耦合精度的分析

Analysis of coupled precision in characteristic calculation for long period fiber gratings with a rectangular index modulation

采用耦合模理论,针对光纤芯层为矩形折射率分布的长周期光纤光栅,分析不同模式间耦合对计算精度的影响。结果表明:对于一阶低次包层模式,偶次包层模式与光纤芯层基模的耦合常数要远远小于奇次包层模式与光纤芯层基模的耦合常数。因此,在不影响计算精度的情况下,可以采用忽略偶次包层模式的方法来提高计算速度。同时,根据不同的计算波长范围和计算精度的要求,可以选择合适的正弦折射率调制阶数范围来减小计算工作量。

Based on the coupled-mode theory,the influences on coupled precision in characteristic calculation for different modes in long period fiber grating are analyzed.Calculated results show that for the low order cladding mode,the longitudinal coupling constants between the odd order cladding mode and the first core mode are smaller than that between even order cladding mode and the first core mode.So we can ignore the influence of odd order cladding mode in calculation without reducing the calculation precision.At the same time,we can select the suitable orders of sinusoidal index modulation to reduce the work of calculation according to the arrangement of wavelength and calculation precision.