Abstract
Recently, electromagnetic (EM) waves carrying orbital angular momentum (OAM) has received considerable attention in increasingly many different realms, such as communication systems, super-resolution imaging, optical communications and quantum state manipulation. In this paper, two different kinds of two dimensional (2-D) holographic leaky-wave metasurfaces with a single OAM mode at a single frequency (18 GHz) are introduced through designs and experiments. The classic leaky-wave and a microwave holography theorem are combined to construct the holographic leaky-wave metasurfaces. The leaky wave metasurfaces-based holographic concept are implemented with isotropic artificial surface impedances and made of hexagonal metallic patches. By varying the size of the metallic patches, the effective impedances may be realized. The monopole launchers are utilized for the excitation of TM surface mode, whereby their wave functions can be approximated by the Hankel function of the second kind. The objective waves represented by the desired beams carrying different orbital angular momentum modes. Electromagnetic full-wave simulations and experimental measurements have been performed to substantiate the proposed method.
Highlights
Electromagnetic (EM) waves carrying orbital angular momentum (OAM) has received considerable attention in increasingly many different realms, such as communication systems, superresolution imaging, optical communications and quantum state manipulation
Each photon has an OAM of ±lh, where l is known as a topological charge or OAM index, which can be any integer ranging from −∞ to ∞
In 19927, Allen et al first demonstrated that light beams with an azimuthal phase distribution exp(ilφ) carries an angular momentum independent of the polarization photon state, where φ is the azimuthal angle around the propagation axis and l is the topological charge, which represents the number of twists of the wavefront
Summary
Choosing the proper reference wave is the crucial step of the design procedure of modulated metasurfaces. The color bar on the right shows the imaginary value of the patterns for the sample from minimum to maximum These interferograms are extractions of the holographic equation of surface impedance (1) and the MATLAB software. The surface impedance (comprised of different sizes of hexagonal patches) is designed to produce the desired object waves. The surface impedance depends on the incident and object waves
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