Tailoring polarization states of multiple beams that carry different topological charges of orbital angular momentums

Generating multiple vortex beams simultaneously and independently in different directions by elaborately splicing multiple transmissive metasurfaces featuring polarization isolation

In this paper, by elaborately splicing multiple transmissive metasurfaces (MSs) featuring polarization isolation, multiple linear polarized (LP) vortex beams are generated simultaneously and independently in different directions. Specifically, by carefully optimizing the radius of the array and the distance between the MS and array, each MS generates a well-performed deflection vortex beam with a low side-lobe level and little diffraction, resulting in a minor effect on other deflection vortex beams. Subsequently, four transmissive MSs are elaborately spliced, showing the polarization isolation characteristic between the adjacent MS, and thereby each MS is only illuminated by the respective antenna array. In addition, each MS only generates the desired LP vortex beam, and the corresponding cross-polarization is suppressed. Finally, the simulation and measurement results show that multiple LP vortex beams carrying different orbital angular momentum (OAM) modes are generated simultaneously and independently in different directions, verifying the effectiveness of the proposed method.

Generating Different Polarized Multiple Vortex Beams at Different Frequencies from Laminated Meta-Surface Lenses

We demonstrate the generation of multiple orbital angular momentum (OAM) vortex beams with different radiating states at different frequencies through a laminated meta-surface lens consisting of a dual polarized meta-array interconnected with a frequency selective meta-array. The co-linearly polarized (LP) waves from the source can directly penetrate the meta-surface lens to form multiple OAM vortex beams at one frequency. On the other hand, the meta-surface lens will be capable of releasing the cross-LP counterparts at another frequency with high-efficient polarization conversions to have multiple OAM vortex radiations with different radiating directions and vortex modes. Our design, using laminated meta-surface lens to synthesize multiple OAM vortex beams with orthogonal polarizations at different frequencies, should pave the way for building up more advanced vortex beam communication system with expanded diversity of the meta-device.

Polarization induced reconfigurable multiple OAM vortex waves through a composite meta-surface beam former

We demonstrate a composite meta-surface beam former to generate reconfigurable multiple orbital angular momentum (OAM) vortex waves by integrating a polarization conversion meta-mirror with a multi-functional anisotropic meta-lens. More specifically, electromagnetic fields from the feed would be firstly reflected by the meta-mirror, and then transmit through the meta-lens to form the well converged OAM vortex waves with tailored beam numbers, radiation directions and topological charges. Especially, we show that the anisotropic characteristics of the meta-lens would create different multiple OAM vortex waves when the meta-mirror is rotated or equipped with active circuits to have different polarized illuminations on the meta-lens. Our design should pave the way for the reconfigurable design of generating multiple OAM vortex waves to further expand the communication capacity.

A Review of Orbital Angular Momentum Vortex Beams Generation: From Traditional Methods to Metasurfaces

In this paper, we review the generation of vortex beams carrying orbital angular momentum in the microwave domain. We firstly present the theory of Laguerre–Gaussian beams where it is demonstrated that they carry such type of momentum. We further provide an overview of the classical methods used to generate orbital angular momentum vortex beams, which rely on two main methods; plane wave to vortex wave conversion and direct generation using radiating antennas. Then, we present recent progress in the physics of metasurfaces devoted to the generation of vortex beams with a discussion about reflective and transmissive metasurfaces for plane wave to vortex wave conversion as well as methods to reduce the intrinsic divergence characteristics of vortex beams. Finally, we conclude on this rapidly developing research field.