Cross-polarization Conversion Research Articles

Anomalous three-dimensional refraction in the microwave region by ultra-thin high efficiency metalens with phase discontinuities in orthogonal directions

An ultrathin flat metalens that experimentally realizes three-dimensional microwave manipulation has been demonstrated as able to approach the theoretical limit of cross-polarization (cross-pol) conversion efficiency of the transmission, as predicted by Monticone et al (2013 Phys. Rev. Lett. 110 203903). The helicity-dependent phase change is introduced to the transmission and can be engineered by assembling the spatial orientation of each Pancharatnam–Berry phase element. By realizing the constant phase gradients in orthogonal directions, an anomalous non-coplanar refraction is unanimously demonstrated in the three-dimensional space under the circular-polarized incidence, and the refraction angle is well predicted with the generalized Snell’s law, derived with phase gradients in orthogonal directions. More importantly, the maximum conversion efficiency of the cross-pol transmission is as high as 24%, which approaches the upper-bound of the theoretical limit. The proposed metalens has only a single layer as thin as 0.001 λ, which massively reduces the thickness of the microwave lens along the wave propagation direction. With the great improvements in efficiency and the thickness reduction, as well as the excellent non-coplanar refraction, our design provides a promising approach to miniaturize, planarize and integrate multiple microwave components.

Tri-band transparent cross-polarization converters using a chiral metasurface

A chiral metasurface is proposed to realize a tri-band polarization angle insensitive cross-polarization converter. The unit cell of the chiral metamaterial is composed by four twisted anisotropic structure pairs in four-fold rotation symmetry. The simulation results show that this device can work at 9.824 GHz, 11.39 GHz, and 13.37 GHz with low loss and a high polarization conversion ratio (PCR) of more than 99%. The proposed design can transmit the co-polarization wave at 14.215 GHz, like a frequency selective surface. The study of the current and electric fields distributions indicates that the cross-polarization transmission is due to electric dipole coupling.

Broadband cross polarization converter using plasmon hybridizations in a ring/disk cavity

In this paper, we report on the design, fabrication and subsequent investigation of a broad band cross polarization converter based on a C2-symmetric ring/disk cavity. Different plasmon hybridization modes are excited in the ring/disk cavity and enable the polarization manipulations. The designed cross polarization converter can convert the x or y polarized incident wave to its cross polarized wave in the frequency range from 9.65 to 14.16 GHz with a bandwidth of ~38% of the central wavelength and an efficiency higher than 80%. At 9.25 GHz and 14.35 GHz, the x (y) polarized incident wave is converted to a left (right) handed and right (left) handed circularly polarized wave, respectively.

Electric toroidal metamaterial for resonant transparency and circular cross-polarization conversion

Electric toroidal dipolar response has been achieved by metamaterial based on sun-like aperture element at microwave frequency. It is confirmed numerically by scattered powers that the electric toroidal dipolar moment dominates over other moments at the corresponding resonance. This proposed metamaterial exhibits resonant transparency under linearly polarized incidence caused by destructive interference between magnetic dipole and electric toroidal dipole. Notably, it also provides circular cross-polarization conversions between left-handed circularly polarized wave and right-handed circularly polarized wave at the same frequency. These properties associated with elusive electric toroidal dipolar moment offer an avenue for various potential applications in microwave devices.

Wideband selective polarization conversion mediated by three-dimensional metamaterials

In this paper, we proposed to use ultra-thin 3D metamaterials to manipulate the polarization of the transmitted electromagnetic waves. As an example, we designed a 3D metamaterial to serve as an ultra-thin linear-polarization converter, which overcomes the defects of bulky volume and narrow bandwidth of conventional polarization converters. Polarization selectivity and polarization convertibility are achieved simultaneously in the single-layer metamaterial. The physical mechanism is analyzed using reflection matrix and transmission matrix in details. Simulated cross-polarization and co-polarization conversions for TE and TM incident waves verify the polarization selectivity and polarization convertibility.

Theoretical study on a broadband, high cross-polarization conversion efficiency metalens based on phase discontinuity

In this paper, a novel unit cell for the metalens in a microwave band based on the principle of phase discontinuity at the interface is suggested and theoretically investigated. It has a broad bandwidth of 25%, in which the cross-polarization conversion efficiency approaches the theoretical limit. The Pancharatnam–Berry phase is adopted to achieve the desired abrupt phase change for the transmitted cross-polarized wave, then an anomalous refraction metalens and a bi-functional metalens are proposed. The simulated results show that the anomalous refraction metalens can bend the transmitted cross-polarized wave with a specific angle predicted by the generalized laws of refraction, and the bi-functional metalens can diverge or converge the circularly polarized incident wave with a focal length of 10λ, determined by the helicity of the incident wave. Our designs provide a promising approach to planarize microwave components.

Polarization conversion in U-shaped chiral metamaterial with four-fold symmetry breaking

Despite chiral metamaterials being widely appreciated for their giant optical activity and negative refractive index with respect to the transmitted electromagnetic waves, little research efforts are devoted to effects occurring upon optical reflection from such metamaterials. Here, we theoretically demonstrate highly energy-efficient cross-polarization conversion for a normally incident wave reflecting from metamaterial with a broken four-fold symmetry of chiral structure. We do this by designing metamaterial that makes the polarization plane of a linearly polarized electromagnetic wave reflected from its surface almost perpendicular to the polarization plane of the incident wave. Using reflection from this metamaterial, one can also freely convert between left-handed and right-handed circular polarizations without significant energy loss. The proposed chiral metamaterial may prove useful in electromagnetic communication systems, polarization controllable antennas, and on-chip biomedical sensors.

Cross polarization converter formed by rotated-arm-square chiral metamaterial

Optical activity and cross polarization conversion (CPC) of a rotated-arm-square chiral metamaterial (CMM) is reported in this work. Proposed CMM shows strong chirality owing to the cross coupling between the induced magnetic field and incident electric field of the applied electromagnetic wave. Mechanism of CPC functionality is explained based on the surface current distribution of CMM structure. Microwave experiment is performed to reveal the CPC utility of the proposed CMM. Among various designs on the CPC converters, possibility of near 99% efficiency is revealed in the proposed CMM.

Dynamically tunable broadband mid-infrared cross polarization converter based on graphene metamaterial

We present a mid-IR highly wavelength-tunable broadband cross polarization conversion composed of a single patterned top layer with L-shaped graphene nanostructures, a dielectric spacer, and a gold plane layer. It can convert linearly polarized light to its cross polarization in the reflection mode. The polarization conversion can be dynamically tuned and realize a broadband effect by varying the Fermi energy without reoptimizing and refabricating the nanostructures. This offers a further step in developing the tunable polarizers and the polarization switchers.

Compact dual-band circular polarizer using twisted Hilbert-shaped chiral metamaterial

We propose a kind of chiral metamaterial inspired from the fractal concept. The Hilbert fractal perturbation in the twisted split ring resonator element results in compact metamaterial and breaking mirror symmetry, which readily forms chirality over triple bands. The discrepancy between co-polarization conversion and cross-polarization conversion over multiple bands can be explored for multifunctional devices. A multiband circular polarizer is then numerically and experimentally studied in the X band based on the bilayered twisted Hilbert resonator with mutual 90° rotation. The ability of transforming linearly polarized incident waves to circularly polarized waves is unambiguously demonstrated with high conversion efficiency and large polarization extinction ratio of more than 20 dB across dual bands. Moreover, exceptionally strong optical activity and circular dichroism are also observed.

One-way reciprocal spoof surface plasmons and relevant reversible diodelike beaming

One-way excitation of spoof surface plasmons (SPs) and strongly pronounced diodelike extraordinary transmission of linearly polarized waves in the beaming regime can be obtained by combining spoof SPs and cross-polarization conversion resonances. The reciprocal composite structure that is suggested to realize this mechanism consists of a symmetric metallic grating with a subwavelength slit and a metamaterial based ultrathin 90${}^{\ensuremath{\circ}}$ polarization rotator and, therefore, shows the broken spatial inversion symmetry. In contrast to the earlier studies of SP inspired transmission through subwavelength slits, asymmetric (one-way) beaming is demonstrated at normal incidence and for both $s$- and $p$-polarized incident waves. Furthermore, as an implication of Lorentz reciprocity, the studied diodelike mechanism is reversible, which manifests itself in that transmission is significant for one of the two opposite illumination directions at $s$ polarization and for the other direction at $p$ polarization. The obtained numerical and experimental results verify the general idea and enable us to select the optimal operation regimes.

Enhanced rotation of the polarization of a light beam transmitted through a silver film with an array of perforated S-shaped holes.

In this Letter, we realized an enhanced optical rotation of the zero-order transmitted light through a silver film with an array of perforated S-shaped holes. Different from the previous studies, this effect results from the contribution of both the localized surface plasmons and surface plasmon polaritons (SPPs). The rotation angle can be modulated with the thickness due to the phase retardation of the SPPs when tunneling to the emitted surface. With a sample thickness 245 nm, a near-complete cross-polarization conversion (90° optical rotation) can be achieved, representing a major advance in performance compared to the previously reported planar chiral structures.

Dual-band asymmetric transmission of linear polarization in bilayered chiral metamaterial

A bilayered chiral metamaterial is proposed and demonstrated to exhibit dual-band asymmetric transmission of linearly polarized electromagnetic waves in two opposite directions. Simulated and measured results show that the bilayered chiral metamaterial can achieve cross-polarization conversion with an efficiency of over 90% for both y- and x-polarized waves. The proposed metasurface can be regarded as an ultrathin polarization-controlled switch that is easily switched on/off by changing a linearly polarized wave to its orthogonal component.

Asymmetric electromagnetic wave transmission of linear polarization via polarization conversion through chiral metamaterial structures

In this paper a kind of chiral metamaterial structure is proposed that can achieve asymmetric transmission for forward and backward propagations of linearly polarized electromagnetic (EM) waves. We first give a theoretical analysis on a kind of bilayered metamaterial structure with specific structure asymmetry that enables the asymmetric EM wave transmission only for linear polarization. Then by constructing a proof-of-concept metamaterial sample with twisted split ring resonator patterns on both sides of a dielectric slab, we demonstrate substantial asymmetric transmission for linear polarizations, but none for circular polarizations through full-wave simulation and measurement at microwave frequency. Strong optical activity is found in the chiral metamaterial indicating that the intriguing asymmetric transmission is caused by the directional difference in cross polarization conversion. By scaling down the structure, the proposed concept could be utilized in other frequency bands, such as terahertz and optical range.

A transparent 90° polarization rotator by combining chirality and electromagnetic wave tunneling

A three-layer chiral metamaterial is constructed by using two layers of four mutually rotated resonators and a subwavelength mesh sandwiched symmetrically between these layers. The resulting structure is an ultrathin, transparent, and polarization angle independent 90° polarization rotator. Due to the electromagnetic tunneling effect exerted by the negative permittivity mesh, a cross-polarization conversion efficiency of 99% and 93% is achieved numerically and experimentally. The structure is modeled using the effective medium theory and then the transfer matrix method is applied to demonstrate the existence of the tunneling resonance theoretically.

90° polarization rotator using a bilayered chiral metamaterial with giant optical activity

A bilayered chiral metamaterial is proposed to realize a 90° polarization rotator, whose giant optical activity is due to the transverse magnetic dipole coupling among the metallic wire pairs of enantiomeric patterns. By transmission through this thin bilayered structure of less than λ/30 thick, a linearly polarized wave is converted to its cross polarization with a resonant polarization conversion efficiency of over 90%. It is demonstrated that the chirality in the propagation direction makes this efficient cross-polarization conversion possible.

Electrically and optically controlled cross-polarized wave conversion

Light wave propagation in third-order nonlinear media with applied external electric field is investigated. Interplay between the nonlinear electro-optic and all-optical effects is examined theoretically. Energy exchange between the orthogonal light polarizations, the cross polarization conversion, results. The assisting external field acts as either the effect-enhancing or functionality-controlling parameter. Various materials such as silica glass, silicon, other bulk and quantum well semiconductors, organic materials, and particle-doped nanostructures are referred to as possible candidates for device implementations. Numerical estimates of achievable parameters in a selected suitable material are discussed.

Electromagnetic‐wave diffraction by a chiral layer with a reflecting grating of dielectric‐filled grooves

AbstractA diffraction problem is solved for a plane E‐ or H‐polarized wave incident on a chiral layer placed over a reflecting grating of rectangular grooves cut in a perfectly conducting metal plane. The approach uses decomposition and generalized scattering matrix methods. The phenomenon of quasi‐complete cross‐polarization conversion of waves with large telescopicity coefficient is shown. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 462–465, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10351