弱导多层平面光波导辐射模的自由空间模近似

FREE SPACE MODE APPROXIMATION OF RADIATION MODES FOR WEAKLY GUIDING MULTILAYER WAVEGUIDES

本文用自由空间模简化及近似表示弱导多层介质光波导的辐射模．只要辐射方向与介质界面的角度不是很小，近似程度很好．将其应用于求解光栅耦合器的辐射损耗问题，使计算公式简化，用自由空间模计算的结果与用辐射模计算的结果比较接近。

The Radiation modes of weakly guiding multilayer planar optical waveguides have been approximated and simplified as free space modes.Except a very small angle,the angle between radiation direction and the waveguide walls,the approximation is accurate.Applying this approximation of the radiation loss calculation caused by a grating assisted directional coupler,It is obtained very simple formulas.The calculated results are close to that by using exact radiation modes.Comparison with other methods have been made too.