Spontaneously Appearing Polarization Singularities in Vertical-Cavity Lasers with Feedback

Topological states of fluids of light in nonlinear optical devices are attracting a lot of attention. Interest shifts to "fully structured light" with complex intensity, phase and polarization structure [1] . Vector vortex beams (VVB) have singularities in their director field leading to a spatially inhomogeneous polarization structure. As the simultaneous presence of different polarization states demands a high isotropy of the optical setup, their spontaneous emergence is very uncommon but they have been predicted [2] and observed [3] in vertical-cavity surface-emitting lasers (VCSEL). In Ref. [3] it was concluded that many (potentially all) different VVB exist but their mutual stability is dictated by small residual anisotropies. In this contribution, we are investigating this by introducing a controlled anisotropy via a half-wave plate (HWP).