Integration of a GaAs/AlGaAs SQW laser and a tapered waveguide coupler

Future high speed optical fiber communications and signal processing systems require the monolithic integration of a laser source and other passive as well as active devices. Key to integration is the coupling of light from the laser source to a waveguide circuit that make the light available for other optical processing functions such as modulation, switching and routing. Existing integration schemes either require complicated and costly material regrowth or impose severe design and fabrication restrictions. This dissertation studies a novel monolithic integration of a single quantum well (SQW) laser and a tapered waveguide coupler in the GaAs/AlGaAs material system. The integrated structure consists of two sections: the laser and the tapered waveguide coupler. The SQW waveguide for the laser and the multiple quantum well (MQW) waveguide as the output waveguide are vertically stacked. In the laser section, the MQWs are disordered by Zn implantation and annealing thus becoming the cladding layer of the SQW laser. In the tapered waveguide coupler section, the MQWs are gradually disordered along the waveguide by nitrogen implantation and annealing. This permits the laser output couples to the MQW waveguide for optical processing such as modulation. A groove etched between the laser and the taper sections functions as a partially transmissive mirror providing the feedback for the laser. The tapered waveguide coupler employs an adiabatic power transfer process and allows for independent optimization of individual components to be integrated. The vertical configuration of the two waveguides and the controlled impurity-induced disordering eliminate the regrowth requirements without sacrificing the device design and fabrication flexibility.; In this dissertation, the key technologies for the integration of the SQW laser and the tapered waveguide coupler have been investigated theoretically and experimentally. The MQWs in the laser section are disordered by Zn implantation and subsequent annealing. A finite difference approach has been developed to determine the concentration (Zn) dependent interdiffusion and the model leads to a prediction of a sharp reduction in threshold current density due to the disordering of the MQWs in the laser section, which agreed well with our experimental results. In addition, dependence of the lasing condition due to the groove are investigated. The fabrication techniques including the MQWs disordering by implantation and annealing and the reactive ion etching (RIE) for the groove have been developed. Utilizing these techniques, the integration of an SQW laser and a tapered waveguide coupler in the GaAs/AlGaAs material system has been accomplished.