Spectral Linewidth in Oxide-confined Surface-emitting Lasers

We present a model to compute the linewidth in vertical- cavity surface-emitting lasers (VCSELs), by accounting for the 3-D structure of real devices. To this aim, we include the noise source in the field equations and treat both the noise and the structural characteristics by means of coupled-mode theory. In this way, we obtain an expression for the linewidth that is given as the standard relation, modified by two correction factors that account for spatial effects and modal dispersion of the resonator. In the numerical results, we study for oxide-confined VCSELs the transition from index to gain-guided regime, where the standard linewidth theory does not hold, and we give some guidelines for narrow-line emission devices.