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Light polarization is an inherent property of the coherent laser output that finds applications, for example, in vision, imaging, spectroscopy, cosmology, and communications. We report here on light polarization dynamics that repeatedly switches between a stationary state of polarization and an irregularly pulsating polarization. The reported dynamics is found to result from the onset of chimeras. Chimeras in nonlinear science refer to the counterintuitive coexistence of coherent and incoherent dynamics in an initially homogeneous network of coupled nonlinear oscillators. The existence of chimera states has been evidenced only recently in carefully designed experiments using either mechanical, optomechanical, electrical, or optical oscillators. Interestingly, the chimeras reported here originate from the inherent coherent properties of a commercial laser diode. The spatial and temporal properties of the chimeras found in light polarization are controlled by the laser diode and feedback parameters, leading, e.g., to multistability between chimeras with multiple heads and to turbulent chimeras. [ABSTRACT FROM AUTHOR]

We numerically investigate the dynamics of a semiconductor laser subject to phase-conjugate optical feedback. We explore the effects of the laser model and feedback parameters for the generation of time-periodic oscillations of the output power at harmonics of the external cavity frequency, i.e., dynamical solutions that have been named external cavity modes. We point out that both the experimentally tunable and other parameters have an influence on the frequency of such dynamics. Since the delay has to exist, it is not the relevant parameter as we show that the feedback rate fixes the frequency of the periodic self-pulsations. The interaction length of the crystal and the ratio between carrier and photon lifetimes tend to filter out high frequencies as they increase. Finally, the linewidth enhancement factor unlocks high frequencies as it increases. We conclude by providing a situation which leads to periodic solutions with higher frequencies using a set of realistic values of parameters. [ABSTRACT FROM AUTHOR]

Square-wave oscillations exhibiting different plateau lengths have been observed experimentally by investigating an electro-optic oscillator. In a previous study, we analysed the model delay differential equations and determined an asymptotic approximation of the two plateaus. In this paper, we concentrate on the fast transition layers between plateaus and show how they contribute to the total period. We also investigate the bifurcation diagram of all possible stable solutions. We show that the square waves emerge from the first Hopf bifurcation of the basic steady state and that they may coexist with stable low-frequency periodic oscillations for the same value of the control parameter. [ABSTRACT FROM AUTHOR]