Optically controlling the emission chirality of microlasers

Orbital angular momentum (OAM) carried by helical light beams is an unbounded degree of freedom that offers a promising platform in modern photonics. So far, integrated sources of coherent light carrying OAM are based on resonators whose design imposes a single, non-tailorable chirality of the wavefront (that is, clockwise or counterclockwise vortices). Here we propose and demonstrate the realization of an integrated microlaser where the chirality of the wavefront can be optically controlled. Importantly, the scheme that we use, based on the optical breaking of time-reversal symmetry in a semiconductor microcavity, can be extended to different laser architectures, thus paving the way to the realization of a new generation of OAM microlasers with tunable chirality. Based on optically breaking time-reversal symmetry by spin polarizing a gain medium with a circularly polarized optical pump, an integrated scheme for controlling the chirality of orbital angular momentum lasing is demonstrated.