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International audience; We investigate the behaviour of a multimode two-color quantum dot laser subject to optical feedback. In particular, we focus on the effects of a variation of the external cavity length at the micrometer scale on the laser emission characteristics and especially on its optical spectrum. For each mode, we observe oscillations of the output power with different spectral amplitudes. No clustering or mode grouping effect is observed. Theoretically, we demonstrate a good agreement with a multimode two-color quantum dot laser model.

International audience; In this contribution, we experimentally report recurrent switching between ground and excited state emission in a quantum dot laser controlled by optical feedback. We demonstrate that changing the phase of the optical feedback can efficiently induce switching between the two emission processes of the laser. Experimentally, by using an external mirror placed on a piezo-actuator, we were able to achieve incomplete switching between ground and excited state emission, i.e. without complete extinction of the modes. The switching takes place for variations of the external cavity length at the wavelength scale, i.e. around 1.2 um. Theoretically, we successfully link this switching behaviour with the evolution of the modal gain difference between the two modes induced by the variations of the optical feedback phase.

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 TR 1 and TR 2 , which support such a switching scenario. We show that both TR 1 and TR 2 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 systems.