基于GaAs/GaAlAs条形光波导的定向耦合器分析

Analysis of the Directional Coupler Based on the GaAs/GaAlAs Optical Strip Waveguide

运用基于级数展开法 (SEM)的三维光束传播法 (3D SEM BPM)分析了由GaAs/GaAlAs条形光波导构成的定向耦合器 .获得了这种定向耦合器所承载的偶模及奇模电场分布 ,其耦合长度随波导间距的增加近似指数增长 .模拟了光波在器件中的传输演变情况 ,用条形光波导的基模在给定定向耦合器的左通道激励 ,传输 2 6 2mm之后模场转移至右通道 ,获得了交叉态 (CrossState) .另外 ,3D SEM BPM最终将BPM基本方程归结为一阶常微分方程组 ,方法简单 ;导出矩阵小 ,计算效率高 .处理边界条件时 ,引入正切函数变换将无限平面映射成单位平面 。

The directional coupler based on the GaAs/GaAlAs optical strip waveguide is analyzed using three dimensional beam propagation method based on the series expansion method (3D SEM BPM).The even and odd modes supported by this coupler are obtained,respectively,and the coupling length exponentially increases with the increasing of the waveguide separation.The simulation results for the injected field through the present device are also gotten,and the excitation selected as the fundamental mode supported by the single optical strip waveguide at left channel is transferred into the right channel after propagatiny 2 62mm,thus the cross state is obtained.The 3D SEM BPM reduces the basic BPM equation to the first order normal differential equation system.Consequently,the computational program is simple.Moreover,the calculation is efficient due to the small matrix derived from the present method.In dealing with the boundary conditions,a tangent type function is applied to map the infinite space into a unit square.As a result,the boundary truncation is eliminated.