First-order Phase Transitions in the polarization switchings of vertical-cavity surface-emitting lasers

The geometry of the laser cavity of vertical-cavity surface-emitting lasers (VCSELs) is a flat cylinder, which gives an intrinsically two-dimensional isotropic freedom to the polarization states of VCSEL's emitted light. This symmetry can be broken by some residual stresses created in the manufacture processes, resulting in a linearly polarized output. Experimentally, it is often to observe the occurrence of the VCSEL's Polarization Switching (VPS) in which the polarization direction of VCSEL's output switches with the laser's current. The investigations of VPS is important for the understanding of strong photon-carrier interactions in quantum wells. Earlier studies suggested that VPS is a second-order phase transition based on some criticalities observed in the experiments. However, conventional experiments were carried out with a tuning of laser's current. Therefore, those experiments cannot clarify whether VPS is conducted by the thermal effect or by the field effect of the laser's current. This research try to distinguish VPS caused by these two effects. Experiments discovered that some VPS exhibited features of the first-order phase transitions. More results will be represented in the conference.