GaAs-Based Distributed Feedback Lasers Based on GaAs-InGaP Regrowth Technology

This thesis describes the conceptualisation and realisation of GaAs-based self-aligned stripe (SAS) distributed feedback lasers (DFB) based on GaAs-InGaP regrowth technology, and its incorporation into the development of master oscillator power amplifier (MOPA) photonic integrated circuit (PIC). GaAs-based SAS DFB lasers operate via a single longitudinal mode and provide a robust, portable and low cost solution to enable a broad range of potential applications. Compared to other waveguides, e.g. ridge waveguide, SAS structures enable narrower active regions and demonstrate better characteristics with a lower sensitivity to temperature. In my designs, InGaP/GaAs buried gratings are formed utilising an Al-free grating sequence GaAs-InGaP-GaAs, whilst the SAS waveguides are realised via a stripe-etched n-doped InGaP optoelectronic confinement layer, where no AlGaAs is exposed during the fabrication process. Chapter 1 goes through the development of DFB lasers over almost 5 decades since its birth in 1970s, followed by discussion of the gap between present GaAs-based PIC technologies and their commercialisation. After, Chapter 2 introduces the experimental methodology involved in the research activities conducted: fundamental principles of DFB lasers and the 4-stage research process. The following 3 chapters describe the 3 main projects in this research. Chapter 3 begins with the design of 2×, 4× and 6× InGaAs QWs narrow ridge DFB lasers in, and then moved onto the conceptualisation and realisation of 2× and 4× InGaAs QWs SAS DFB lasers in Chapter 4. This SAS-DFB technology was then applied to the development of monolithically integrated 4× InGaAs QWs MOPA PIC in Chapter 5. In Chapter 6, I outline some future work to be conducted for further achievement. An optimised design of SAS-DFB-MOPA is first discussed. I then present some preparatory works for two other potential future directions: widely tunable GaAs-based sampled grating distributed Bragg reflector laser (SG-DBR) and high power ~1180nm In(Ga)As/GaAs DWELL (dot-in-a-well) SAS-DFB-MOPA.