White J M, Heidrich P F
Appl Opt. 1976 Jan 1;15(1):151-5. doi: 10.1364/AO.15.000151.
The WKB approximation is used to derive simple equations that predict the shape of the index profile from measured mode indices of a planar optical waveguide. This nondestructive test is a useful tool in the study of diffused guides. The index profile is assumed either to decrease monotonically from the surface or to be symmetrical in the case of a buried guide. The approximation uses straight line segments to connect the measured points. Results are compared with mathematical solutions for exponential, Fermi, and step distributions and with other independent experimental observations of the profile in a nickel-diffused LiNbO(3) guide.
WKB近似法用于推导简单方程，这些方程可根据平面光波导的测量模式折射率预测折射率分布的形状。这种无损测试是研究扩散光波导的有用工具。对于扩散光波导，假定折射率分布从表面单调递减；对于掩埋光波导，则假定其折射率分布是对称的。该近似法使用直线段连接测量点。将结果与指数分布、费米分布和阶跃分布的数学解，以及镍扩散铌酸锂（LiNbO₃）光波导中折射率分布的其他独立实验观测结果进行了比较。
