Spectral characteristics of distributed feedback semiconductor lasers and their improvements by corrugation-pitch-modulated structure

Semiconductor lasers with stable longitudinal single-mode operation are essential for optical fiber communication systems. Distributed feedback (DFB) lasers are effective to obtain a stable longitudinal single-mode operation; however, stability is not enough mainly because of the spatial hole-burning effect. A corrugation-pitch-modulated (CPM) structure was proposed to improve the stability of longitudinal single-mode operation in distributed feedback lasers. CPM-DFB lasers have a unique corrugation structure to suppress the spatial hole-burning effect. This structure was obtained by a newly developed corrugation fabrication method, a photomask self-interference method. It is confirmed that the CPM-DFB lasers operate in a stable longitudinal single-mode by suppressing the spatial hole-burning effect. This structure is also suitable for narrowing the spectral linewidth for use in coherent optical fiber communication systems. Narrow spectral linewidth lasers with a CPM structure have achieved the narrowest spectral linewidth reported to date.