Polarization Dynamics of 1550-nm VCSELs Subject to Polarization-Preserved FBG Feedback

We experimentally investigated the polarization dynamics of a 1550-nm vertical-cavity surface-emitting laser (VCSEL) subject to polarization-preserved and wavelength selective feedback, which is provided by a feedback loop composed of a variable attenuator (VA), a polarization controller, and a fiber Bragg grating. First, for given bias currents, the evolutions of the polarization behaviors with the feedback strength are inspected through adjusting the attenuation rate of the VA, and several typical evolution routes are found for different bias currents. Second, through fixing the attenuation rate of VA at minimum and continuously increasing the bias current, multiple current regions for two-mode coexistence are found, and the dominant polarization mode is multiply switched between two orthogonal linear polarization (LP) modes. Finally, the polarization-resolved dynamical characteristics of the VCSEL operating at two-mode coexistence are studied in detail, and the results demonstrate that under suitable operation parameters, both two orthogonal LP modes can simultaneously oscillate at chaotic state.