Experimental investigation of elliptically polarized injection-locked VCSELs

Polarization switching (PS) between linear polarizations of a vertical-cavity surface-emitting laser (VCSEL) can appear when this device is subject to orthogonal optical injection. In this type of injection the injected field has a linear polarization orthogonal to that of the free-running VCSEL. In this situation interesting nonlinear dynamics appear, one of which is the existence of an injection-locked solution for which the two linear polarized modes of the VCSEL lock to the master laser frequency. This situation has been theoretically predicted and corresponds to an elliptically polarized injection-locked (EPIL) state. In this paper we report an experimental investigation of the dynamics of a long-wavelength single-transverse mode VCSEL subject to orthogonal optical injection. The free-running VCSEL emits a linearly polarized beam in the so called “parallel” direction. The polarization of the injected light is perpendicular to this state and is termed “orthogonal” polarization. We observe the EPIL state when the frequency of the orthogonal injected light is near the frequency of the parallel polarization. The spectral feature of the EPIL state is verified and the power of each polarization is measured. The EPIL region is measured in the frequency detuning-injected power plane. As current decreases, the frequency detuning range for the EPIL to exist is narrower and shifts toward the negative frequency detuning. Periodic dynamics in which both polarizations oscillate with a frequency very close to the relaxation oscillation frequency is found above the upper boundary of the EPIL region. Below the lower boundary of the EPIL zone, periodic dynamics is found only in the parallel polarization.