Leader-laggard relationship of chaos synchronization in mutually coupled vertical-cavity surface-emitting lasers with time delay.

We experimentally and numerically observe synchronization of chaos in two mutually coupled vertical-cavity surface-emitting lasers (VCSELs) with time delay. We observe in-phase and antiphase synchronization of polarization-resolved chaotic temporal wave forms under the condition of wavelength matching. We investigate leader-laggard relationship between two chaotic wave forms of mutually coupled VCSELs and find that the laser with longer wavelength becomes the leader.