Grating-Coupled Surface-Emitting Lasers -- Circular and Unstable-Resonator Geometries

Abstract: This thesis deals with research in the field of grating-coupled surface-emitting lasers. The emphasis has been to study the modal behavior of lasers with two different resonator geometries: circular resonators and tapered unstable-resonators. The modal behavior is dependent on drive current which is important with respect to a main aim of the work, which has been to integrate these lasers with beam forming grating outcouplers. In this work the choice has been the focusing grating outcoupler. The intensity at focus of the light emitted by the focusing outcoupler is very indicative of how the modal behavior of the laser is affected by increase in drive current. A strong theme of the work is to investigate how details in the geometry of the current injection region affect the modal behavior and its dependence on drive current. The work has included the fabrication and characterization of circular and unstable resonator lasers of different geometries and the comparison of measured results with results from simulations. In the case of the circular lasers the simulations have been on the emitted field while in the case of the unstable resonator lasers the simulations have also included the resonator and physical processes there within. We conclude that the modal performance and efficiency is strongly affected by relatively small modifications in the geometry of the injection current region for both types of lasers. The process behind this, we conclude, is carrier-field interactions. The laser performance can be improved by using a passive indentation in the circular resonator and a trumpet shaped taper for the unstable-resonator.