Modulation Characteristics And Optimizations Of Directly Modulated Distributed Feedback Laser

Directly Modulated Laser(DML) is a low-cost optical transmitter, widely used in the optical fiber access networks and data communications networks. Due to the booming business of the access networks and data communications recent years and their multi-use features, the need of optical transmitter in short-to-medium distance communications become huge.In addition to DML, the optical transmitter commonly used in the short-to-medium distance communications also has electro-absorption modulated laser(EML). The short-to-medium distance transmission also require low-cost devices, small power consumption and size and DML has advantage at this aspect for its simple structure. But DML generally applies to less than 10 Gb/s and a short distance access network with its limited bandwidth and chirp. However, DML has made great progress in the last 10 years and has a comparable performance with EML at a higher rate within the short-distance transmission of 20 km.This thesis focused on studying the factors which influence DML's modulation bandwidth and chirp characteristics through numerical simulation based on physical models, aimed at optimizing DML's modulation characteristics, namely, improving the modulation bandwidth and reducing the chirp to increase the transmission distance and compare with EML's performance. Finally, giving advices for selecting the optical transmitter when set up a actual optical network.The main innovations and achievements of this paper includes the following sections:(1) Established a set of simulation tools for studying the characteristics from material to device, including the one-dimensional traveling wave model to describe the light field, the free carrier model to calculate the material gain, and the Coulomb model to calculate the exciton absorption, their reliabilities have been validated by contrast the results with the literatures.(2) Optimized the bandwidth and chirp of DML from material, structure, including the differential gain, the linewidth enhancement factor, nonlinear gain saturation factor, coupling strength and etc.; Shaped the switching current to eliminate the relaxation oscillation and reduce chirp, Used our prpposed localized dual-mode model to optimize the push-pull modulated distributed feedback lasers and obtained a 60 GHz modulation bandwidth;(3) the optimized 1.5?m band DML under 10Gb/s, 25Gb/s, and 40Gb/s speeds could transmit half distances of EML, it was worth mentioning that under 10Gb/s rate and within 20 km, it can reduce the network costs by employing DML; By using the current shaping and push-pull modulation techniques, the DML's transmission capacity can be doubled.