以耦合模理论为基础，研究了两种不同结构的三芯长周期光纤光栅的模式耦合方式，推导了模式耦合方程. 分析了两种不同结构三芯光纤光栅包层模有效折射率的计算方法，并对包层模有效折射率进行了数值模拟计算. 模拟计算结果表明，不同纤芯排列方式会影响一阶奇次和偶次包层模有效折射率随波长增加而减小的程度. 研究结果为三芯长周期光纤光栅的进一步应用开发提供了潜在的理论指导.
Based on the coupled-mode theory, we study the coupling of three-core long period fiber gratings with two different structures and derive the mode coupling equations. The calculation method of cladding mode’s effective refractive index is also investigated. The rule of cladding mode’s effective refractive index
change with the wavelength is discussed by numerical simulation. The results show that, the indices of both odd and even modes reduce as the wavelength increases. Different arrangements of three cores affect the extent of the index decrease. The results of this study provide theoretical guidance to the application of three-core fiber LPFG.
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