Chaos synchronization in mutually coupled long-wavelength Vertical-Cavity Surface-Emitting Lasers with long delay time

We present an experimental study of the nonlinear dynamics and the chaos synchronization using an asymmetric all-fiber setup in mutually coupled but nonidentical 1550-nm VCSELs with a large total coupling delay time of 274.2 ns. The linear polarization of the two VCSELs is adjusted to be parallel to each other, i.e. to achieve parallel coupling. The results are analyzed in terms of the frequency detuning and the coupling strength between the two lasers. We define the frequency detuning as the emitting frequency difference between the solitary VCSEL 1 and VCSEL 2. For positive frequency detuning, limit cycle and period doubling have been observed. For zero and negative frequency detuning, periodic dynamics, polarization switching and chaotic behavior have been found. Novel results have been obtained for the suppressed polarization of both parallel mutually coupled VCSELs. CW emission and dynamics in the orthogonal polarization can appear for negative frequency detuning. We have analyzed the accuracy of chaos synchronization in both VCSELs given by the cross-correlation function. Good achronal chaotic synchronization is found, with a time shift that corresponds to the large coupling delay time between the lasers. The leader-laggard relationship is also investigated.