用耦合波理论求解渐变折射率光纤的传播常数和模式场

CALCULATION OF MODE FIELD AND PROPAGATION CONSTANTS FOR GRADED-INDEX OPTICAL FIBERS BY USING COUPLED MODE THEORY

本文应用耦合波理论来计算任意渐变折射李光纤的传播常数和模场分布．将无限伸展的抛物型折射率分布光纤作为一个理想波导，任意径向不均匀折射率分布光纤便可以视作该理想波导的微扰，其模场可以展开成一组完备的理想波导模的叠加．然后，模场和传播常数可以通过耦合波方程求得．进一步将一阶微分方程组形式的耦合波方程变换成线性方程组，使计算过程大大简化．文中给出了数值计算结果，并将其与准确值进行了比较．

Propagation constant and modal field distribution for guided modes of an arbitrary graded index optical fiber have been calculated by using coupled mode theory. Taking the infinitely extended parabolic profile fiber as an ideal waveguide,an arbitrary radially inhomogeneous optical fiber can be viewed as a perturbation,its modal field can be expanded in terms of a complete set of ideal waveguide modes. Eigenvalues and modal fields are then obtained from coupled mode equations which have been transformed into a set of linear equations. Numerical results have been presented and compared with exact values.