SPECTRAL CHARACTERISTICS OF DISTRIBUTED-FEEDBACK SEMICONDUCTOR-LASERSAND THEIR IMPROVEMENTS BY CORRUGATION-PITCH-MODULATED STRUCTURE

Semiconductor lasers with stable longitudinal single-mode operation ar e essential for optical fiber communication systems. Distributed feedb ack (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) stru cture was proposed to improve the stability of longitudinal single-mod e operation in distributed feedback lasers. CPM-DFB lasers have a uniq ue corrugation structure to suppress the spatial hole-burning effect. This structure was obtained by a newly developed corrugation fabricati on method, a photomask self-interference method. It is confirmed that the CPM-DFB lasers operate in a stable longitudinal single-mode by sup pressing the spatial hole-burning effect. This structure is also suita ble for narrowing the spectral linewidth for use in coherent optical f iber communication systems. Narrow spectral linewidth lasers with a CP M structure have achieved the narrowest spectral linewidth reported to date.