The full vector nature of light provides an additional degree of freedom, namely, the angular momentum (AM) which includes both spin angular momentum (SAM) and orbital angular momentum (OAM). This full AM space holds a great promise for multi-dimensional high capacity data modulation and multiplexing in both classical and quantum regimes, confronting the exploding demands for information. The dynamical generation and control of optical vortices carrying SAM-OAM states mainly rely on tabletop optics. Vortex microlasers offer more compact and robust solution. However, the recently developed vortex microlasers either lack reconfigurability or require extremely low temperature operation environment, limiting the potential real world applications. By harnessing the properties of total angular momentum conservation, spin-orbit interaction and optically controlled non-Hermitian symmetry breaking, we demonstrate an on-chip integrated SAM-OAM-tunable vortex microlaser at room temperature, providing up to 5 different SAM-OAM states at a single telecom wavelength. Moreover, by utilizing fast transient optical gain dynamics in semiconductor materials, we experimentally demonstrate the ultrafast control of fractional OAM emission continuously from 0 to +2 in less than 100 ps. Our toolbox of flexible generation and control of vortex emission at a single wavelength provides a feasible route for the development of the next generation of multi-dimensional high capacity information system in both classical and quantum regimes.
A Weyl semimetal carries topological charges at the Weyl nodes; a light beam can also carry a topological charge, when it has an orbital angular momentum (OAM). Recently there has been a lot of interest in understanding how the spin angular momentum (SAM) of light interacts with materials to induce photocurrents (circular photogalvanic effect, CPGE), but not many studies have focused on photocurrents generated by the OAM of light. Here we report a unique orbital photogalvanic effect (OPGE) in a type-II Weyl semimetal WTe2, featured by a photocurrent winding around the axis of OAM-carrying beams, whose intensity is directly proportional to the topological winding number of the light field, and can be attributed to a discretized dynamical Hall effect. In addition to obtaining evidence of OAM induced electron excitations, our measurements show promise for on-chip detection of the phase of light.
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