光纤光栅外腔半导体激光器改进模型分析

Improved Model Analysis of Fiber Bragg Grating External Cavity Semiconductor Lasers

改进了基于耦合腔激光器模型的光纤光栅外腔激光器静态分析模型,在考虑了激光器和光纤光栅之间的耦合效率后,将光从激光器耦合进光纤光栅的耦合系数η1 和从光纤光栅反馈回激光器的耦合系数η2 推导进描述耦合腔的散射矩阵元中,修正了耦合腔模型的表达式。发现两个耦合系数η1 与η2 之积的大小对增益曲线产生具体影响。分析表明短外腔及短的光纤光栅长度决定了损耗曲线最低处单纵模振荡,激光管芯与光纤端面的反射率也对阈值电流、边模抑制比产生明显影响,尤其对于激光器端面反射系数比较大的情况,可以通过仔细设计空气间隙的长度实现外腔模和法布里 珀罗(F P)模式的匹配。

A complete and precise static modal of fiber grating external cavity semiconductor laser is improved based on the coupled-cavity laser model. By taking consideration of the coupling efficiency between the laser diode and the fiber grating, the coupling coefficient η1 from the laser to the fiber grating and the coupling coefficient η2 from the fiber grating to the laser diode are both involved in the elements of scattering matrix describing the coupled-cavity model, and the analytical expression of the coupled-cavity model is modified. It is found that the product of the coupling coefficient η1 and η2 affects the gain curve. Additionally, analysis indicates that shorter external cavity and shorter fiber grating length determine the single lasing mode oscillating in the lower region of the gain curve. Diode core and fiber facets reflectivity also play important roles in the threshold current and side mode suppression ratio (SMSR), especially in the case of relatively high reflectivity. This can be solved by carefully designing the length of air gap, resulting in the match of the external cavity modes and Fabry-Perot (F-P) modes of diode. Accordingly the optimized design principle is put forward by general considering of the parameters.