Intrinsic Vortex–Antivortex Interaction of Light

Abstract The spin–orbit interaction and the extrinsic orbit–orbit interaction of light have been thoroughly studied, which have led to important phenomena including the spin Hall effect, orbital Hall effect, and spin–orbit Hall effect of light. Nevertheless, the concept of optical intrinsic orbit–orbit interaction, which is named as vortex–antivortex interaction, is scarcely known to the authors knowledge. Here, such a novel interaction process is theoretically and experimentally demonstrated, which emerges due to mutual interplays among reciprocal helicities of singular cores in a freely propagating light field. A general model describing the process is presented, which includes a linearly independent term and a nonlinearly coupling term. It is revealed that the strong coupling leads to intuitive mutual attraction between two reciprocal vortices, while the weak coupling, in contrast, results in a counterintuitive repulsive phenomenon. The vortex–antivortex interaction enables the predictions and observations of the orbital angular momentum Hall effect, as well as the stable propagation of an appropriately structured vortex arrays without nonlinear light–matter interactions. The results expand the scope of interaction processes among different forms of optical angular momenta, and open opportunities for studies of new effects using the presented coupling mechanism.