Single mode power and modal behaviour in buried vertical-cavity surface-emitting lasers

Modal behaviour in buried vertical cavity surface-emitting lasers (VCSELs) is simulated using the two-dimensional beam-propagation-method (BPM) model. For broad-area VCSELs a tapered cavity strongly enhances the modal losses of the higher order modes and increases single mode output power. However, for small-area VCSELs it reduces output power. Furthermore, passive antiguide-region structure increases modal discrimination. An optimum index difference (Δ=0.084) is needed to achieve the maximum modal discrimination in the step-profile case. A new parameter, relative modal loss difference, is introduced to describe the mode competition, which can be used to estimate single-mode operation regime. The parameter can also be used in the external cavity case. Simulations show that a carefully designed 16 μm diameter antiguide-region lasers can operate in single mode in the whole bias region