Routes to broadband laser chaos with dynamics switching in a 1550-nm VCSEL laser subjected to optical feedback.

Vertical-cavity surface-emitting laser (VCSEL) has received much attention due to its high modulation response bandwidth, two linear polarization modes, and easy integration. The fundamental characteristics of lasers can be observed by simple optical feedback. Here, we experimentally investigate the dynamical characteristics in a 1550-nm VCSEL subjected to mirror optical feedback. The distribution of dynamics for different bias currents and feedback strength is in detail unveiled. Four different dynamic routes to laser chaos are observed at different bias currents. As the bias current increases, the route to chaos becomes complex. Apart from the well-known stable state, quasi-periodic state, chaotic state, and two previously reported dynamics switching phenomena, the dynamics switching between intermittently quasi-periodic state and quasi-periodic state is observed at a high bias current. Additionally, the laser chaos at different bias currents is also comparatively studied. The chaos bandwidth can reach 18 GHz. The systematic investigation provides the basis for utilizing the broadband laser chaos and understanding the nonlinear dynamics in VCSELs.