Analysis of the spectral linewidth of distributed feedback laser diodes

Laser diodes with spectral linewidths as narrow as 500 kHz are required in coherent optical communication systems. 1 In this paper, we present a theoretical analysis of the spectral linewidth of distributed feedback (DFB) lasers for the first time. The numerical calculations show that DFB lasers with long cavities have an extremely narrow spectral linewidth as compared with conventional Fabry-Perot lasers.