Spin-to-orbital angular momentum conversion through a coplanar converter

Spin angular momentum (SAM) and orbital angular momentum (OAM), associated with the circular polarization and helical phase front of an electromagnetic wave, respectively, have been gaining increasing interest in various fields. In this paper, a new method of SAM to OAM conversion in the microwave band is proposed. The designed coplanar structure converses the SAM to OAM, whose three electric components, E-z, E-phi, and E-rho, carry same-order OAM. The paper explains the principle of SAM to OAM conversion and provides an experimental demonstration. Both simulation and measurement results demonstrate that this conversion method from SAM to OAM is feasible. Our work could provide a promising platform to study photonic spin-orbital interaction and find applications in the near-field vortex generators.