椭圆芯双模光纤干涉模斑中心间距的研究

通过弱波导近似的方法，讨论了椭圆芯双模光纤中沿光纤长轴的基模模斑半径Wx和短轴的基模模斑半径Wy尺寸，分析了它们的比值随入射光波长λ及纤芯半长轴与半短轴的比值a/b的变化规律。 针对基模LP01和第一高阶模LP11间的相位差变化，计算了双模干涉模斑的分布结构。计算结果表明，当基模LP01和第一高阶模LP11间的相位差为π/2时，两瓣干涉模斑有相同的结构特征。同时，两瓣模斑的中心间距S随Wx/Wy的的增加而变大。而且，当入射波长在0.65 μm和 1.31 μm之间变化时，结合两瓣模斑的中心间距S随Wx/Wy的变化规律，首次给出了S的计算公式。这对于实际应用如传感器和光纤耦合器件设计是很重要的。

By means of the weakly guiding approximation, the mode spot sizes W-x and W-y of the fundamental mode along the semimajor (x-direction) and semiminor (y-direction) axes of the fiber core in elliptical core two-mode fiber are discussed. The variation of their ratio value W-x/W-y with the operation wavelength lambda and the length ratio a/b between the semimajor axis and the semiminor axis of the fiber core is analyzed. Based oil this analysis, the distribution figures of two-lobe interferential mode patterns are evaluated and simulated quantitatively for different phase difference changes between LP01 and LP11even modes. The two-lobe interferential mode patterns have the same profile and distribute symmetrically when the phase difference equals pi/2. Their central distance S becomes larger when W-x/W-y augments gradually. Furthermore, the equation about the central distance S of the two-lobe interferential mode patterns is given when the operation wavelength varies between 0.65 and 1.31 mu m, which is important to applications shuch as sensors and coupling devices between different fibers.

National Basic Research Program of China [2006CB806001]