A probability-amplitude transfer matrix model for distributed-feedback laser structures

Two different treatments of spontaneous emission in distributed-feedback (DFB) lasers were found in the literature, but adequate explanations for the different treatments were not found. Using an approach that allows comparison of the two different treatments of spontaneous emission, we show that the different treatments can lead to different spectral predictions. The difference in spectral predictions is negligible in Fabry-Perot lasers and index-coupled DFB lasers. However, in truncated-well gain-coupled DFB lasers, the difference between the two treatments is noticeable, and one treatment is markedly better at fitting to data. The treatment that best fits the data is also the treatment that makes sense quantum-mechanically.