Residence time distribution and coherence resonance of optical-feedback-induced polarization mode hopping in vertical-cavity surface-emitting lasers

We report on an experimental and theoretical investigation of the residence time distribution ~RTD! of the polarization mode-hopping regime in vertical-cavity surface-emitting lasers ~VCSELs! subject to optical feedback. The RTD exhibits discontinuity and oscillations, as a result of the fast intensity oscillations at the delay time that accompany the slow mode hopping. We furthermore show numerically that an external noise source on the injection current allows observation of a coherence resonance phenomenon in VCSELs induced by time-delayed feedback.