Antiphase chaotic synchronization enhancement in a vertical cavity surface emitting laser

In this paper, we demonstrate experimentally that a vertical cavity surface emitting laser (VCSEL) exhibits an enhancement of nonlinear polarization dynamics, i.e., antiphase chaos synchronization and mode hopping, with optical feedback (OF). The rotating orthogonal polarization of a VCSEL is used as an external parameter to generate a chaotic signal when it is reflected back with a fixed bias current and strong OF signal. The intensity of the two linear polarization modes of the VCSEL is measured for a range of bias current, which provides detailed insights into its dynamic dependence. The results show that the antiphase chaotic synchronization is enhanced as the angle of orthogonal polarization of the OF is increased. Polarization modes are oscillated entirely in the chaotic regime in antiphase synchronization, with no time delay at the bias currents of 1.2 (low) and 1.7 mA (high). However, the synchronization quality of the two modes completely deteriorates when the bias current is increased to 1.7 mA at a polarization angle of 70°, where power mode differences are increased. This result shows that the power mode difference affects antiphase synchronization dynamics and thus destroys the mode-computation effects. In addition, polarization switching takes place at the polarization angles of 60° and about 33° at low and high bias currents, respectively. Polarization mode hopping is also observed, which is associated with improvement of the antiphase synchronization dynamics.