以单轴晶体为内包层的双包层光纤偏振特性研究

Study on Polarization Characteristics of Doubly-clad Fiber Using Single Crystal as Inner Cladding

本文研究了以单轴晶体为内包层的双包层高双折射光纤的传输和偏振特性．在弱波导近似下,应用光波导理论,得出了ｏ光与ｅ光的色散方程及截止特性．通过计算机的模拟与分析,划分出了截止区、单模单偏振区、单模双偏振区及多模区;分析了单模单偏区和单模双偏区存在的条件;研究了单模双偏区两偏振模式的偏振色散特性．结果表明,几何参数Ｓ、光学参数Ｒｘ、Ｒｙ及外包层折射率η３对所划分的四个区域及所对应的偏振特性有着极为明显的影响．此结果为光纤保偏器的设计和应用高双折射单模光纤构成新型光纤传感器的设计提供了可靠的理论依据．

The characteristics of propagation and polarization are given for high-birefringence fibers with single crystal as inner cladding in this article. According to the theory of optical waveguide, the dispersion equations and the cutoff characteristics are derived for ordinary light (o light) and extraordinary light (e light) under the condition of weakly guiding fibers. Simulating on computer, we can divide the characteristics plots into four areas: cutoff area, monomode single-polarization area, monomode double-polarization area and multimode area. In the monomode double-polarization area, the polarization mode dispersion characteristics are analyzed for the two polarization modes. The existent condition of monomode single-polarization area and monomode double-polarization area is also analysed. It is found that the geometrical and optical parameters (S and Rx, Ry) and the outer cladding index n3 have great influence on the divided four areas and their polarization properties. These results provide a theory foundation for the design of fiber-optic polarizers, and suggest a new type of optical fiber sensor design using high-birefringence monomode fibers.