Investigation of high power DFB lasers, operating mechanisms, electro-opto-thermal interactions

The increasing demand for higher bit rates in optical communications require the development of next generation high bit-rate optical sources. For this purpose, a new high power long-wavelength Distributed Feedback (DFB) source under industrial development for use as an externally modulated high bit rate source has been investigated through experiments and simulations in this thesis. To model modern laser sources, a new self-consistent electro-opto-thermal (EOT) DFB transfer matrix method (TMM) model for high power and complex coupled lasers has been developed. This model is the most complete longitudinal treatment of laser devices to date. The increased sophistication and broader operating range of new generation devices have made more complete and detailed models necessary. Past models have used simplifying photon density representations that have been appropriate for DFB structures. New gain-coupled devices have material gain spatial variations and complex coupling occurring at a length scale comparable and even shorter than the wavelength that invalidates the textbook theory and call for first principle detailed re-treatment of the electric field. High power and cooler-less laser operation require the thermal behaviour to be considered. These effects have been included self-consistently in this new model. Application of the EOT model to two illustrative modern devices are presented. With the model, the performance of a new Floating Grating (FG) DFB structure was characterized. In this example, the analysis has included 2-D and 3-D effects with finite element analysis. The device lacks of prior analysis because of its complexity and its unusually high injection level. Detailed experimental measurements including L-I, active region temperature with increasing bias, below and above threshold spectra and the SMSR were made to compare with the model results and show that the unoptimized FG device has retained a comparable performance to standard DFB devices while eliminating a critical process dependent uncertainty. A limitation to the FG DFB approach was greater active region heating. Using the EOT DFB TMM model and analysis from the finite element light emitting simulator (FELES) the carrier transport through the FG structure was examined. The analysis offers the first detail 2D longitudinal examination of FG structure. The model predictions were compared to the measured data for the high power FG DFB laser and showed good agreement. The model was then applied to improve the high power design. Further analysis show that by changing the FG composition alone, the output power from the FG design could be increased by 20%. As a second example, the model has been used to examine the threshold current and L-I linearity for in-phase and out-of-phase gain coupled devices by explicitly including electric field coherence resulting in the standing wave effect. The self-consistent electro-opto-thermal model developed in this thesis serves as both a useful design tool and a means for fundamental investigations into device physics providing deeper understanding of the complicated DFB device operation in the new higher power regime. While this work has focused on two particular types of laser devices, the electro-opto-thermal TMM model is readily applicable to 1-D analysis of any arbitrary structure.