Effects of radiation on circular-grating DFB lasers. II. Device and pump-beam parameters

For pt.I see ibid., vol.37, no.3, p.353-64 (2001). We examine the impact of device design parameters and nonuniform gain profiles on the modes of a weakly guiding, second-order concentric-circle-grating distributed feedback laser, including the effects of radiation loss. The analysis uses near-threshold coupled-mode equations that are valid for any grating shape, and any depth for which the undepleted-bound-mode approximation is accurate. We solve these equations numerically and examine the effects of several device parameters, including coupling strengths and grating duty cycle, on mode frequencies and gain thresholds for low- and high-order radial and azimuthal modes. We further compare uniform, Gaussian, and annular optical pump-beam profiles. We find that device and pump-beam parameters can have a significant effect on the threshold gains of the laser, as well as an the azimuthal mode discrimination and total lasing linewidth it exhibits.