In a practical coupling system, a cylindrical microlens is used to collimate the emission of a high power laser diode (LD) in the dimension perpendicular to the junction plane. Using passive alignment, the LD is placed in the focus of the cylindrical microlens generally, regardless of the performance of the multimode optical fiber and the LD. In this paper, a more complete analysis is arrived at by ray-tracing technique, by which the angle θ of the ray after refraction is computed as a function of the angle θ0 of the ray before refraction. The focus of the cylindrical microlens is not always the optimal position of the LD. In fact, in order to achieve a higher coupling efficiency, the optimal distance from the LD to the cylindrical microlens is dependent on not only the radius R and the index of refraction n of the cylindrical microlens, but also the divergence angle of the LD in the dimension perpendicular to the junction plane and the numerical aperture (NA) of the multimode optical fiber. The results of this discussion are in good agreement with experimental results.

本文通过采用有限差分法对描述缓变波导半导体激光器稳态特性方程组的数值分析,对InGaAsP/InP掩埋新月形激光器的阈值、波导、侧向模式进行了理论求解。结果表明,它具有良好的基横模工作特性和稳定的光场分布,与实验相符。