长周期光纤光栅模式与耦合系数的研究

从耦合模理论出发,采用三层介质光纤模型,用数值计算的方法分析了长周期光纤光栅纤芯模和包层模的有效折射率,一阶低次包层模的耦合系数随波长以及阶次的变化关系.研究发现,低次包层模的最大耦合系数对应的模次随波长增大而减小,不同光纤参数下耦合系数随波长变化的规律不同.耦合系数直接影响到光栅透射谱损耗峰峰值,这对长周期光栅的设计有一定的参考价值.

Analysis of the Modes and Coupling Coefficient of Long-period Grating

Based on the three-layer fiber model and the coupling theory,the effective refractive index of the core mode and the cladding modes were numencally calculated in Long-period grating(LPG),and the changing relation of the coupling coefficient of the cladding modes at the lowest few ones with varying wavelength were analyzed.It is revealed that the mode number of the maximum coupling coefficient of the cladding modes decreases with wavelength,the coupling coefficient with wavelength is different in different fiber parameters.These results are valuable for the design of long period grating,since the coupling coefficient directly affects the peak loss of the grating transmission spectrum.