Investigation On The Characteristics Of Nonlinear Dynamics And Polarization Switching Of1550nm-VCSELs Under External Disturbances

As a new style of semiconductor laser, vertical cavity surface emitting lasers (VCSELs) possess lots of advantages such as low threshold current, small divergence angle, single longitudinal mode outputs, easy to integrate into two-dimensional arrays, low costs and so on. As a result, VCSELs are paid more and more attention. The researches have demonstrated that the output of a VCSEL generally consist of two perpendicular linear polarized modes due to the weak cavity and material anisotropy, which makes linear polarization mode in VCSELs unstable. The polarization mode of VCSEL with certain polarization direction could abruptly hop when some parameters of lasers are modified, and the suppressed mode turns to be dominant mode while the original dominant mode is suppressed meantime, which is defined as polarization switching (PS). Research also shows that VCSELs subject to external perturbations including optical feedback, optical injection or optoelectronic feedback, will display richer nonlinear dynamical behaviors which have potential value in optical communications, millimeter-wave and chaotic radar, etc. So far, nonlinear dynamics of VCSELs have been extensively investigated. However, relevant studies are mostly concentrated on short-wavelength (<1μm) VCSELs. Relevant studies about1550nm VCSELs especially in the long-wavelength VCSELs subject to multiple external perturbations remain relatively scarce.In this paper, based on the spin-flip model (SFM), the characteristics of nonlinear dynamics and polarization switching of1550nm-VCSELs subject to polarization-preserved optical feedback and orthogonal optical injection are theoretically investigated. The results show that, different from the case that only y linear polarization mode exists in a VCSEL with polarization-preserved optical feedback, two linear polarization modes can be simultaneously stimulated and polarization switching can be observed in a1550nm VCSEL subject to polarization-preserved optical feedback and orthogonal optical injection. Under the joint action of polarization-preserved optical feedback and orthogonal optical injection, the two linear polarization modes will exhibit rich dynamical states such as period one, period two, multi-period and chaos oscillation, and different evolution routes to chaos can be observed. Moreover, frequency detuning△f(=fm-fs, where fm and fs are the center frequencies of free-running master VCSEL and slave VCSEL, respectively) has an obvious influence on the polarization switching. Polarization switching points will shift toward larger injection strengths with the increase of the positive frequency detuning meanwhile a suitable negative frequency detuning value will make the injection strength for PS be the lowest. Therefore, the position of polarization switching and dynamics states of1550nm-VCSELs could be adjusted by changing the external perturbation parameter of VCSELs in practical applications.