三沟道定向耦合器耦合长度的变分计算

本文提出一种用以计算三沟道定向耦合器耦合长度的精确变分方法。同时讨论一下已有的几种主要近似方法的适用范围:(1)平板波导近似(Marcatili法);(2)有效折射率法(EDC);(3)微扰论方法。可以看出,Marcatili方法得出的耦合长度偏大,而有效折射率方法给出的结果却偏小。变分法求出的传播常数则较精确,变分法与微扰法求得的耦合长度基本上一致。

Three Channel Waveguide Directional Couplers:Variational Analysis

This paper we develop an accurate variational analysis of a three channel waveguide directional coupler. We have also discussed the applicability of approaches, namely: (1) planar waveguide (Marcatili) approximation; (2)effective- index method; (3) first-order pertur- bation theory for such couplers. It is found that Marcatili's ap- proximation overestimates the coupling length, the effective-index method underestimates the coupling length, and that, while varia- tional method gives more accurate propagation constants for the modes, perturbation method gives predictions on coupling length as accurate as the predictions by variational method.