Square-wave switching by crossed-polarization reinjection in VCSELs

We take a VCSEL that emits stably in a linearly polarized state (X) and we make it experience crossed-polarization reinjection (XPR) of the lasing into the non-lasing linear polarization. The lasing threshold is not modified by the level of XPR. For currents close to the laser threshold the output is quite irregular, but square-wave switching develops when the current is increased however, a degradation of the square-wave switching is observed when current is further increased. Degradation of the square-wave switching is linked to the finite value of the spin-flip rate and the residual dichroism, and it occurs when the current approaches the boundaries of polarization bistability for the solitary VCSEL.