High frequency current modulation of high order transverse modes in vertical-cavity surface emitting lasers

Abstract

Weakly index guided vertical cavity surface emitting lasers (VCSELs) are analyzed in the multi-transverse mode regime. An efficient dynamical model is developed that takes into account all the transverse modes (LP mn ) supported by the waveguide. Mode partition noise in a current modulated VCSEL is studied taking into account the azimuthal degree of freedom. Different transverse modes can be excited with a probability that is numerically calculated. For high injection currents modes that are not favoured in the steady state can be the ones excited with higher probability. The excitation probability is similar for azimuthally orthogonal modes. This symmetry can be broken by selecting a particular high order transverse mode by using azimuthal dependent current profiling: injection is performed where the mode has appreciable power. This selection can be achieved over current ranges larger than ten times the threshold current. The radial range of injection current to obtain this selection is shown to be wide.