外腔反馈半导体激光器的损耗和阈值特性研究

通过对半导体激光器(LD)的损耗和阈值电流特性的分析，引入等效反射系数的概念，根据多光束干涉的原理，导出了在外腔反馈作用下LD的阈值电流公式。从等效反射系数的推导可以看出，外腔的反馈相当于增大了LD一个端面的反射率，减小了损耗，从而使LD激光振荡的阈值降低。该公式在外腔长度和激光波长可以比拟的情况下能够准确地分析反馈注入对阈值电流的影响，但是在外腔长度远大于激光波长情况下不再适用。针对实验中外腔长度较大的情况，使用光功率的分析简化了理论模型，得出了与实验结果相吻合的结论，即外腔反馈注入使LD出光阈值电流明显降低。

Investigation of Loss and Threshold Characteristics in the Laser Diode with External Feedback

Through the analysis of the loss and threshold characteristics of a laser diode (LD), the threshold current density of LD with external feedback is calculated, according to the theory of multi-beam interference and the definition of equivalent reflection factor. When the length of external cavity approximates to the wavelength of LD, the obtained equation can be used to analyze the influence of the external cavity to the threshold current accurately. When the length of external cavity is much longer than the wavelength of LD, it is out of work. Because in the experiment the external cavity is much longer than the wavelength, the theory model is simplified by analysis to the injected power. The threshold drive current will be reduced obviously for the external feedback. The theoretical results agree well with the experimental findings.