Effects of active section length on directly modulated 1.3 µm InGaAlAs/InP DFB lasers with a MQW-based passive DBR section

Directly modulated 1.3µm InGaAlAs/InP distributed feedback (DFB) lasers having multi-quantum well (MQW) based passive distributed Bragg reflector (DBR) section have been fabricated. In the device, the DBR and DFB sections have the same MQWs, which eases the fabrication of the device by eliminating the need for additional material growth for the DBR section. Current self-heating effects on the device performance are studied by comparing two kinds of lasers having 150 and 200 µm long DFB sections, respectively. It is found that the laser with a 150 µm long DFB section has a narrower range of current within which high side mode suppression ratio (SMSR) of optical spectra can be obtained and a smaller max modulation bandwidth than the laser with a 200 µm long DFB section. This is different from a normal single-section DFB laser and can be attributed to the larger current heating effect, which shifts the emission wavelength more quickly to a long wavelength for the 150 µm device. For the 200 µm DFB length laser, a 29 GHz direct modulation bandwidth can be obtained. 50 Gb/s nonreturn to zero (NRZ) and 4-level pulse amplitude modulation (PAM4) data transmission in up to 40 km single mode fiber have been demonstrated at both room temperature and 50 °C.