Vortex Laser based on III-V semiconductor metasurface: direct generation of coherent Laguerre-Gauss modes carrying controlled orbital angular momentum

The generation of a coherent state, supporting a large photon number, with controlled orbital-angularmomentum L = hl (of charge l per photon) presents both fundamental and technological challenges: we demonstrate a surface-emitting laser, based on III-V semiconductor technology with an integrated metasurface, generating vortex-like coherent state in the Laguerre-Gauss basis. We use a first order phase perturbation to lift orbital degeneracy of wavefunctions, by introducing a weak anisotropy called here orbital birefringence, based on a dielectric metasurface. The azimuthal symmetry breakdown and non-linear laser dynamics create orbital gain dichroism allowing selecting vortex handedness. This coherent photonic device was characterized and studied, experimentally and theoretically. It exhibits a low divergence (< 1 degrees) diffraction limited beam, emitting 49 mW output power in the near-IR at lambda similar or equal to 1 mu m, a charge l = +/- 1,. +/- 4 (> 50 dB vortex purity), and single frequency operation in a stable low noise regime (0.1% rms). Such high performance laser opens the path to widespread new photonic applications.