Abstract
Electromagnetic waves carrying orbital angular momentum (OAM) have motivated a wealth of applications. Achromatic or broadband OAM beams are preferred in many applications and have been extensively explored in previous research endeavors. In view of the low efficiency of the previous reported broadband OAM generators, this work proposes a metasurface composed of high-refractive-index dielectric resonators to achieve broadband OAM beam generation with high efficiency. An efficient method for designing the resonators is presented, which indicates that proper adjustment of the dimensions and rotation of the dielectric resonators can render broadband and high-efficiency full phase control. A broadband high-efficiency OAM generator is engineered based on the resonators from 18 to 28 GHz as a proof-of-concept example and validated by both simulation and experiments. Above 70% polarization conversion efficiency and above 65% operation efficiency are measured throughout the entire design band. Such structure provides an alternative mechanism for realizing broadband high-efficiency microwave, millimeter-wave, terahertz or optical OAM generation and can find potential applications in high-capacity communications and imaging.
Highlights
Electromagnetic waves can carry both spin angular momentum and orbital angular momentum (OAM) [1]
The problems caused by the big divergence angle and air-dielectric mismatching inherent to the spiral phase plates OAM beam generators are significantly alleviated in the metasurface-based counterparts
A complete reflective dielectric metasurface plate consisting of 40 × 40 elements is simulated in CST (“Open” boundaries are used) to visualize the generation of broadband OAM beams
Summary
Electromagnetic waves can carry both spin angular momentum and orbital angular momentum (OAM) [1] The former pertains to polarization and the latter is associated with a helical or twisted wavefront [1]. A newly proposed technique makes use of the well-established transformation electromagnetics technique [21], [22]. Among these reported methods, the metasurface-based manner embraces obvious advantages against the other ones. As a two-dimensional version of metamaterials, the metasurface generally has a subwavelength thickness rendering the associated OAM beam generators low-profile; while the spiral phase plates, circular waveguides and the devices based on transformation electromagnetics are intrinsically bulky and high-profile structures. The problems caused by the big divergence angle and air-dielectric mismatching inherent to the spiral phase plates OAM beam generators are significantly alleviated in the metasurface-based counterparts
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