Formation of Transverse Modes with Y-Junction Structures in Broad-Area Oxide-Confined Vertical-Cavity Surface-Emitting Laser

We performed experimental and theoretical investigations on the transverse-mode emission behavior of a broad-area oxide-confined vertical-cavity surface-emitting laser (VCSEL). The far-field emission pattern with y-junction structures is observed in the VCSEL with a 20-µm-diameter aperture when the injection current is significantly above the thermal roll-over point. In order to provide a quantitative understanding of these emission characteristics, we present a numerical simulation to model and fit the experimental results. The numerical simulation adopts the high-order Laguerre-Gaussian mode due to the assumptions of a parabolic refractive-index profile and ring-shaped carrier distribution in the laser. From the numerical simulation results, the formation of y-junction structures is inferred to be caused by the superposition of two high-order Laguerre-Gaussian modes. The results of this numerical simulation are in good agreement with the experimental findings.