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.

Optical vortex-antivortex crystallization in free space

“…x + ∂ 2 y G, with carrier wavelength λ. The evolution initiated by the input configuration (1) can be cast in an analytical form of [16] G (x, y, z) = E (x, y, z) [F 0 (x, y, z) + F c (x, y, z)] ,…”

“…( 6) and (7). On the contrary to F 0 , the mixing term F c represents the interplay between the vortices and antivortices, which, in the framework of the linear propagation, leads to the mutual attraction, annihilation and repulsion between the vortices and antivortices, as well as the OAM Hall effect [16]. Note that the orbit-orbit coupling, emerging in the freely propagating paraxial light field, does not need the presence of any optical material, which makes this effect completely different from other photonic interactions, such as the above-mentioned spin-orbit coupling.…”

“…Specifically, lattices composed of homopolar vortices perform perturbation-induced rotation in the course of the propagation, as a direct consequence of straight motion of vortices in the transverse plane [17,18]. Furthermore, VAV pairs in the lattices demonstrate annihilation or repulsion [16,17,19,20]. The instability spontaneously transforms initially regular lattices into disordered speckles [21][22][23].…”

“…Optical vortex-antivortex (VAV) lattices, which carry OAM with positive and negative signs, i.e., opposite topological charges, are a fundamentally important concept that can find promising applications, including high-capacity optical communications [6][7][8], parallelized superresolution [9], multiparticle manipulations [10][11][12], and higher-dimensional quantum information processing [13][14][15]. However, the presence of nonlocal couplings between phase dislocations in the VAV wave front makes them strongly unstable against initial perturbations of the lattice structure [16]. Specifically, lattices composed of homopolar vortices perform perturbation-induced rotation in the course of the propagation, as a direct consequence of straight motion of vortices in the transverse plane [17,18].…”

Vortex position detection using a scanning triangular aperture in a digital micromirror device

“…Also, knowledge on vortex position has implications in controlling the direction, magnitude, and symmetry of spin shifts which opens potential applications in tunable spin-based photoelectric devices [30] and in precise measurement of step nanostructures [31,32]. Tracking the change of position of optical vortices can also be used as a proof of higher-order optical beam shifts [25] and to understand vortex dynamics including events of pair creation and annihilation [33,34], rotation of vortex clusters [35], intrinsic vortex-antivortex or orbit-orbit interaction [36], and in measuring azimuthal backflow in the superposition of helically-phased beams [37]. Optical vortices' trajectory can also provide information about correction quality of the optical elements used to generate them [38].…”