Controlling Vector Bessel Beams with Metasurfaces

Carl Pfeiffer and Anthony Grbic

Phys. Rev. Applied 2, 044012 – Published 23 October 2014

Abstract

Unprecedented control of an electromagnetic wave front is demonstrated with reflectionless metasurfaces that can manipulate vector Bessel beams: cylindrical vector beams with a Bessel profile. First, two metasurfaces are developed to convert linearly and circularly polarized Gaussian beams into vector Bessel beams. Each unit cell of the metasurfaces provides polarization and phase control with high efficiency. Next, the reciprocal process is demonstrated: an incident radially polarized Bessel beam is transformed into collimated, linearly and circularly polarized beams. In this configuration, a planar Bessel beam launcher is integrated with a collimating metasurface lens to realize a low-profile lens-antenna. The lens-antenna achieves a high directivity (exceeding 20 dB) with a subwavelength overall thickness. Finally, a metasurface providing isotropic polarization rotation is used to transform a radially polarized Bessel beam into an azimuthally polarized Bessel beam. This work demonstrates that metasurfaces can be used to generate arbitrary combinations of radial and azimuthal polarizations for applications such as focus shaping or generating tractor beams.

Received 16 July 2014

DOI:https://doi.org/10.1103/PhysRevApplied.2.044012

Authors & Affiliations

Carl Pfeiffer and Anthony Grbic^*

Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122, USA

^*To whom correspondence should be addressed. agrbic@umich.edu

Bianisotropic Metasurfaces for Optimal Polarization Control: Analysis and Synthesis

Carl Pfeiffer and Anthony Grbic

Phys. Rev. Applied 2, 044011 (2014)

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Vol. 2, Iss. 4 — October 2014

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Images

Figure 1
An inhomogeneous, anisotropic metasurface transforms a circularly polarized Gaussian beam into a vector Bessel beam with high efficiency.
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Figure 2
(a) Designed metasurface that converts a linearly polarized Gaussian beam into a vector Bessel beam. Each unit cell acts as a half-wave plate. When the incident polarization of the Gaussian beam is oriented along $\hat{x}$ and $\hat{y}$ , the transmitted Bessel beam is TM and TE polarized, respectively. (b) Designed metasurface that converts a circularly polarized Gaussian beam into a TM-polarized Bessel beam. Each unit cell acts as a quarter-wave plate. For both plots, the lines and color correspond to the orientation of the slow axis and the phase shift of the fast axis, respectively.
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Figure 3
(a) Analytic model used to design each unit cell. (b) Schematic of a typical unit cell. This particular cell acts as a half-wave plate with its fast axis oriented along $ϕ = - π / 8$ . (c) Fabricated metasurface that converts a linearly polarized Gaussian beam into a vector Bessel beam. (d) Fabricated metasurface that converts a circularly polarized Gaussian beam into a TM-polarized Bessel beam.
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Figure 4
Measurements of the fabricated metasurfaces at the operating frequency of 9.9 GHz. For all plots, the arrows point in the direction of the magnetic field, and the color corresponds to the absolute value of the magnetic or electric fields. (a),(b) Transmitted magnetic field when $x$ - and $y$ -polarized Gaussian beams are incident on the linear-to-Bessel metasurface, respectively. (c) Transmitted $z$ -directed electric field when an $x$ -polarized Gaussian beam is incident upon the linear-to-Bessel metasurface. (d),(e) Transmitted magnetic field in the $x y$ plane and $z$ -directed electric field in the $x z$ plane, respectively, when a $\hat{z}$ -propagating, left-handed-circularly-polarized Gaussian beams is incident on the circular-to-Bessel metasurface. (f) Profile of the transmitted wave front when $x$ -polarized and left-handed-circular-polarized Gaussian beams are incident upon the linear-to-Bessel and circular-to-Bessel metasurfaces, respectively. In addition, an ideal Gaussian truncated Bessel pattern is plotted as a reference.
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Figure 5
Transforming a Bessel beam into a highly collimated beam. (a) Schematic of the Bessel beam generation and its conversion to a collimated beam. (b) Measured radiation pattern of the Bessel beam launcher. (c) Experimental setup of the circular-to-Bessel metasurface placed on top of the Bessel beam launcher. A 4-mm Rohacell 31 HF foam spacer separates the Bessel beam launcher and the metasurface. (d) Measured radiation pattern of the Bessel beam launcher with the linear-to-Bessel metasurface placed on top. (e) Measured radiation pattern of the Bessel beam launcher with the circular-to-Bessel metasurface placed on top.
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Figure 6
Transforming a TM-polarized Bessel beam into a TE-polarized Bessel beam by using a polarization rotator. (a) Bottom side of the fabricated polarization rotator. (b) Schematic of a section of the polarization rotator. (c) Measured magnetic field radiated by the Bessel beam launcher. (d) Measured magnetic field after the polarization rotator is placed 4 mm from the Bessel beam launcher. Again, the arrows point in the direction of the magnetic field, and the color corresponds to the absolute value of the magnetic field.
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