海水温度是海洋动力学以及海洋与大气相互作用中起关键作用的基本参数，是研究海洋现象时最重要的依据。为了实现两点海水温度的同时测量，构建了由两段椭圆高双折射光纤萨尼亚克(Sagnac)环形腔的理论模型，利用琼斯矩阵方程对该结构进行理论上的推导，获得了该模型的透射光谱，并得到了透射光谱与该结构各个部分参数的关系。通过Matlab 编程进行模型的数值模拟，研究该结构两段椭圆高双折射光纤长度的比例变化、偏转角的变化以及温度的变化对光谱的影响。计算结果表明，两段椭圆高双折射光纤的最佳长度比为1∶2，两个偏振控制器的偏转角应该分别为π/6 和π/3，温度增加时光谱向短波方向移动。得到利用光谱峰波长移动计算两段椭圆高双折射光纤温度变化的公式。另外，两段椭圆高双折射光纤之间普通单模光纤的长度以及光源的偏振特性对透射光谱的形状以及温度灵敏度没有影响。该模型可以为椭圆高双折射光纤Sagnac 环形腔海水温度传感器的实际应用提供理论支持与指导。

Seawater temperature is one of the basic parameters of ocean dynamics and it plays a key role in the interaction between the ocean and atmosphere. What′s more, seawater temperature is the most important parameter of all marine phenomenon research. In order to achieve the simultaneously measurement of seawater temperature at two points, a theoretical model of Sagnac ring with two high birefringence elliptical fibers is constructed. The transmission spectrum of the theoretical model is obtained by Jones matrix equation, and the relationship between the transmission spectra and the various parts of the structure parameters is also obtained. By the numerical simulation of the theoretical model with Matlab software, the impact of the transmission spectra is studied on the changes of two high birefringence elliptical fibers length proportion, deflection angle and temperature. The results show that the optimum length ratio of two high birefringence elliptical fibers is 1∶2. The polarization angles of the polarization controllers should be π/6 and π/3, respectively. The transmission spectra shift to shorter wavelength when the temperature increases. The formula is obtained to calculate the temperature changes of two high birefringence elliptical fibers by the wavelength shifts of spectral peaks. In addition, the length of single-mode fiber between the two high birefringence elliptical fibers has no effect on the shape of transmission spectrum and temperature sensitivity. The model can theoretically support and guide the practical application of high birefringence fiber Sagnac ring temperature sensor.