Selection and modulation of high-order transverse modes invertical-cavity surface-emitting lasers

摘要

A theoretical proposal to double the pulse repetition frequency bynalternating current modulation of two orthogonal high-order transversenmodes of a vertical-cavity surface-emitting laser (VCSEL) is presented.nStatic and dynamic characteristics of weakly index-guided VCSELs in anmultitransverse mode regime are analyzed. An efficient model that takesninto account all the transverse modes supported by the waveguide isndeveloped. Mode partition noise in a current modulated VCSEL is studied,ntaking into account the azimuthal degree of freedom. Differentntransverse modes can be excited with a probability that is numericallyncalculated. For high injection currents, modes that are not favored innthe steady state can be excited with higher probability. The excitationnprobability is similar for azimuthally orthogonal modes. This symmetryncan be broken by selecting a particular high-order transverse mode bynusing azimuthal-dependent current profiling. This selection can benachieved over current ranges as wide as ten times the threshold current.nCurrent modulation of this transverse mode is then analyzed. Alternatencurrent modulation of two orthogonal high-order transverse modes is alsonstudied. Alternating modulation of these modes can double the pulsenrepetition frequency obtained by modulating just one high-orderntransverse mode, without increasing injected current density levels.nThis current-induced spatial switching leads to high-frequency beamnsteering in the laser azimuthal direction