Polarization switching in VCSELs induced by optical injection

In this paper we summarize our recent theoretical and experimental results concerning optical injection in VCSELs. First, we develop phenomenological rate equation model for the normalized photon densities of the two fundamental VCSEL modes with orthogonal linear polarization when injecting external light polarized along the direction of polarization of the nonlazing mode. We then perform a simple analytical analysis of optically induced polarization switching in VCSELs, which takes into account both the current-dependent linear dichroism and the nonlinear dichroism. We also present detailed investigation of polarization dynamics induced by optical injection using an alternative rate equation model for VCSELs which takes into account the microscopic spin-flip processes in the active medium. In particular we predict that two injection locked solutions may coexist: the first one exhibits the polarization of the master laser, while the second one corresponds to an elliptically polarized injection locking. Continuation techniques allow us to find the bifurcation scenario leading to such an elliptically locked state. We also report on our first experimental results on polarization switching and injection locking for the case of an orthogonal optical injection in VCSELs and demonstrate rich dynamical behavior. The polarization switching is accompanied by a cascade of bifurcations to timeperiodic and possibly chaotic dynamics. Our experimental results show evidence of a period doubling route to chaos.