We experimentally and numerically report on polarization switching (PS) mechanism which involves a two-mode limit
cycle dynamics in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection from a master
laser (ML). The VCSEL (slave laser, SL) emits a horizontal linearly polarized (LP) fundamental mode, without optical
injection. The VCSEL is injected by a vertically polarized light from ML. Dynamical characteristics of the VCSEL are
investigated as a function of optical injection parameters, i.e., injection strength and frequency detuning between master
and slave lasers. We experimentally resolve an injection parameter region for which, as the injection strength is
increased for fixed detunings, a limit cycle dynamics in both non-injected and injected modes is abruptly excited. For
larger injection strengths, the VCSEL switches from the two-mode to a single-mode limit cycle dynamics which
involves only the injected mode. Using continuation methods, we numerically identify two torus bifurcation
mechanisms, namely <i>TR</i><sub>1</sub> and <i>TR</i><sub>2</sub>, which support such a switching scenario. We show that both <i>TR</i><sub>1</sub> and <i>TR</i><sub>2</sub> originate
from a particular Hopf bifurcation which plays a key role in the polarization dynamics of the injected VCSEL.
Furthermore, our results reveal that the newly observed switching dynamics are generic features of VCSEL two-mode
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.
We investigate experimentally and theoretically nonlinear dynamics and polarization bistability in a vertical-cavity surface-emitting laser (VCSEL) submitted to an external optical injection with orthogonal polarization, i.e., the injected light from a master laser (ML) is linearly polarized and orthogonal to the polarization direction of the free-running VCSEL (slave laser, SL). Depending on the injection power level and the frequency detuning between ML and SL, our experimental results show that the injected VCSEL may undergo complex dynamics including subharmonic resonances and period-doubling route to chaos that are associated to polarization switching (PS). Using continuation method, we carry out a detailed bifurcation analysis and report on qualitatively different dynamics as we change the injection strength and/or the detuning. We show that PS may be strongly influenced by the presence of those dynamics. Our numerical results reveal period doubling dynamics that emerge from a Hopf bifurcation associated to an elliptical
polarized injection locking state. Pure frequency-induced polarization bistability, i.e., when the detuning is changed for
fixed injection power, is studied theoretically. Our results show that, depending on the level of the fixed injection strength, frequency induced PS may be achieved with or without hysteresis.