Reflection Cross-polarization Research Articles

Highly sensitive dual mode dual side cross polarization converter based biosensor

—This paper investigates a dual-side, dual-mode reflective cross-polarization converter for biosensing applications. The converter consists of a polyimide substrate with a modified dumbbell-shaped resonator on one surface and its complementary slot on another. The overall volume is 8.25μm × 8.25μm × 2.47 μm with dual-band operation of 6.39268–7.311692 THz and 9.783001–23.53473 THz for PCR≥80 % for front signal incidence and two full widths at half maximum (FWHM) bands i.e. 11.71594–12.26761 THz & 19.12042–19.87691 THz for back signal incidence. The periodicity is ∼λo/6, and substrate thickness is ∼λo/19 at 6.39268 THz. This device has performance stability for incident angle (θ)≤30o. The performance of this device can be tuned from dual-band operation to single-band by varying the chemical potential of the graphene strip for signal incidence from both sides. This device can classify cancer or tuberculosis-infected cells concerning healthy cells by using the variations in their corresponding refractive indices that lead to changes in the band edge frequencies. This device can differentiate between infected and healthy cells or different refractive indices with a high sensitivity of ∼5 THz/RIU. This device has merits of dual side sensing, wide operating bandwidth, multiple frequencies for sensing purposes, and high sensitivity over previously reported sensors.

Tunable dual-functional metasurface for wideband cross-polarization conversion and wideband absorption

This work presents a tunable and wideband dual-functional metasurface (DFM) operating in the terahertz regime with highest overlap bandwidth (OBW). The structure consists of a double-split ring resonator and a meandered square ring resonator based on VO2 to achieve reflective cross-polarization conversion and absorption functionalities, respectively. When the phase changing material VO2 is in its metallic state, the metasurface acts as a perfect absorber with a peak absorption of ≥ 90% over the operating band of 2.3–4.01 THz. When VO2 is in its insulating state, the metasurface acts as a reflective cross-polarization converter over a wideband from 1–4.1 THz with high polarization conversion ratio of ≥ 90%. The proposed DFM has a stable response up to 45∘ of incidence in the polarization converter state and 60∘ of angular stability under the absorber state. Further, tunability is achieved by integrating photoconductive silicon and controlling the optical pump intensity in the double-split ring and meandered . square ring resonators. The proposed metasurface finds its applications in security, detection and THz communication systems.

Ultrabroad reflective polarization converter in terahertz based on circular-end graphene rectangles

Polarization is one of the basic properties of electromagnetic waves. Control and manipulation of polarization by devices based on metasurfaces have versatile applications in modern technologies. We propose a broadband reflective cross-polarization converter in the THz region based on an array of circular-end graphene rectangular patches. Efficient polarization conversion was accomplished through dipole graphene plasmon resonances (DGPRs), either along the long or the short axis of the graphene patches. As the width of the rectangles increased, a new longitudinal dipole mode appeared due to the circular ends of the patches. It grew strong and connected the original DGPRs, constructing an ultrabroad conversion band with efficiency over 94% from approximately 2.5 to 5.0 THz. The relative bandwidth was nearly 66%, surpassing most broadband converters reported. Such broad conversion held for a wide incident angle range as DGPRs were robust to the direction of irradiation. Due to the adjustable optical properties of graphene, the broad conversion band can be tuned. These findings are inspiring for creating broadband, compact and dynamic optoelectrical devices in the THz range.

Full-space polarization conversion of electromagnetic waves at terahertz frequency based on metasurface

In this paper, a full-space electromagnetic wave polarization converter working in the terahertz frequency was put forward, and its physical mechanism was also analyzed. The polarization converter could realize the reflection cross-polarization conversion in the frequency range of 3.16–3.75 THz, with the Polarization Conversion Rate (PCR) of more than 90%. In the frequency range of 0.43–2.15 THz, it could realize transmission cross-polarization conversion, with the PCR close to 100%. In short, the designed metasurface polarization converter has a simple structure, realizes full-space manipulation of electromagnetic waves, facilitates the miniaturization and integration of the system, and has the potential applications in antennas, imaging systems, remote sensors, and radiometers.

Wideband and Tunable Reflective Cross-Polarization Conversion Metasurface for TeraHertz Applications

An ultrathin and wideband reflective cross-polarization converter is presented in this paper. The design consists of a pair of modified dumbbell shaped resonators which are connected together with a conductive strip. The proposed single-layer THz metasurface achieved a high polarization conversion ratio (PCR) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ge$</tex-math></inline-formula> 95% in the operating frequency ranging from 1.76–4.26 THz. This wide-bandwidth cross-polarization conversion is obtained by exciting multiple closely spaced resonant frequencies at 1.98 THz, 2.61 THz, 2.95 THz, and 3.93 THz. The working mechanism of the proposed structure is analyzed and the polarizer exhibits an excellent angular stability upto 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{0}$</tex-math></inline-formula> of incidence. Further, the proposed cross-polarizer exhibits continuous tunability of PCR over the operating frequencies when photoconductive silicon (Si) is filled in the gap between pair of dumbbell-resonators. The wideband characteristics and the switchable property show that the proposed reflective cross polarizer is an excellent candidate for manipulation and control of polarization in THz communication systems.

Transmissive and reflective switchable terahertz metasurface for phase modulation based on vanadium dioxide

Metasurfaces provide a powerful ability to control electromagnetic waves, but most metasurfaces only work in transmission or reflection mode. In this paper, a transmissive and reflective switchable metasurface is designed. The unit structure consists of two split-rings and vanadium dioxide (VO2) film. Utilizing the phase change characteristics of VO2, the designed metasurface works in transmission mode at 25 °C, while works in reflection mode at 68 °C. It can transform the incident circularly polarized wave at the frequency of 0.47 THz, achieving transmission cross-polarization conversion amplitude greater than 0.8 and reflection cross-polarization conversion amplitude greater than 0.9. By rotating the split-rings, full 2π gradient phase distribution is achieved. The switchable metasurface has the potential to design multifunctional devices. To prove the concept, anomalous refraction and reflection, single-foci and dual-foci focusing metalens are designed. The proposed metasurface provides an effective method to design temperature controlled meta-devices and other systems in terahertz communications.

Reflective and transmissive cross-polarization converter for terahertz wave in a switchable metamaterial

Utilizing the phase transition characteristic of vanadium dioxide, we present a metamaterial configuration to achieve both reflective and transmissive cross-polarization converters. When vanadium dioxide is metal, the design behaves as a reflective cross-polarization converter. It consists of metallic grating, topas spacer, and vanadium dioxide film. Polarization conversion ratio is more than 90% in the frequency range from 4.80 THz to 13.13 THz. When vanadium dioxide is insulator, the design behaves as a transmissive cross-polarization converter using cascaded metallic gratings with rotation angle 45°. High-efficiency broadband cross-polarization wave conversion is achieved in the frequency band of 0.50–4.75 THz. Effect of oblique incidence is studied on polarization conversion. Results tell that cross-polarization conversion is better when incident angle is in the range of 0°–40°. The designed metamaterial may have a certain inspiration for the research of terahertz multifunctional polarization converter.

Tunable and reflective polarization converter based on single-layer vanadium dioxide-integrated metasurface in terahertz region

A single-layer and actively tunable reflective polarization converter is proposed, which is composed of periodical two-dimensional unit cell of inclined split circular ring filled into by vanadium oxide (VO2) and central rod. Through numerical simulation obtained by the CST Microwave Studio, we find that the broad bandwidth of reflective cross-polarization conversion above 90% is normally obtained from 2.03 to 5 THz at the temperature about 25 °C for both the linearly and circularly polarized wave incidence. At the same time, the polarization conversion ratio (PCR) and energy conversion ratio (ECR) have been furtherly investigated, which reflect high cross-polarization conversion efficiency with nearly no energy loss at room temperature of 25 °C. Thereafter, namely, the cross-polarization conversion can be achieved by theoretical analysis from the views on qualitative variables of polarization azimuth angle (θ), ellipticity (η) and symmetrical polarization decomposition. What is more, the device is sensitive to the incident angles which result into the split reflected frequency spectrum. Afterwards, the actively dynamic responses for reflective frequency spectrum depending on the insulator-to-metal phase transition of VO2 have been investigated. To be demonstrated, the physical mechanism of changeable polarization conversion has been discussed by the distributions of current densities. Lastly, also, the influences of structural parameter variation can be further studied. According to the interesting results, the method provides a strategy that manipulate active and passive metadevices for polarization converter, wireless communication in THz wavelength domain.

Terahertz broadband tunable reflective cross-polarization convertor based on complementary cross-shaped graphene metasurface

In this work, a broadband tunable reflective polarization convertor using a single layer complementary-cross-shaped (CCS) graphene metasurface was proposed and investigated numerically in terahertz (THz) region. The electric property of CCS graphene could be flexibly tuned through the Fermi energy level (Ef). When Ef = 0.9 eV, the proposed graphene metasurface can realize a relative high polarization conversion ratio (PCR) of over 80% from 2.15 THz to 4 THz with a relative bandwidth of 60.16%. Furthermore, the PCR peak can reach up to as high as 99%, 99.5% and 91.5% at 2.4 THz, 3.4 THz and 3.96 THz, respectively. The physical origins of this polarization conversion properties are turned out to be supported by field distributions and Fabry-Perot interference theory. Furthermore, the broadband polarization conversion properties will be regulated by varying the Fermi energy level.

Tunable broadband cross polarization converter based on a graphene sheet with a T-shaped carved-hollow array

We propose a tunable broadband reflective cross polarization converter (CPC) composed of a graphene sheet with a T-shaped carved-hollow array. In the mid-infrared region, cross polarization conversion with 5.17 THz bandwidth is achieved due to the superimposition of the two reflection components with a phase difference of nearly 180°. The polarization conversion ratio is larger than 80% in this broadband range, and the fractional bandwidth is 40%. The physical mechanism of CPC is attributed to the excitation of symmetric and antisymmetric graphene surface plasmons. The CPC broadband can always be retained when the incident angle increases from 0° to 20°, and the polarization angle increases from 40° to 50°. Also, the tunable responses of the reflective polarizer with Fermi energy and electron scattering time are discussed. Our design can be widely applied to adjustable broadband polarization conversion.

A novel ultra-wideband reflective cross-polarization converter based on anisotropic metasurface

ABSTRACT An ultra-thin and ultra-wideband anisotropic metasurface, acting as a linear polarization converter through reflection is designed and simulated in this research. The operation frequency range covers almost completely the Ku-band and the entire K- and Ka-band. The unit cell of the proposed metasurface is composed of a arrangement of concentric square metallic loops on a grounded dielectric substrate, in which a diagonal split is made, providing properties of an anisotropic material. Simulation results show that an efficient cross-polarization conversion, both for normal as well as for oblique incidence, is achieved with dB fractional bandwidth of 98.7% from 13.8 GHz to 40.7 GHz and with an average polarization conversion ratio of 97.5%. The ultra-wideband of the proposed structure results from multiple plasmonic resonances occurring at three neighboring frequencies (15.2 GHz, 25.9 GHz, and 38 GHz) resulting in a significant expansion of the operating frequency range.

Tunable mid-infrared dual-band and broadband cross-polarization converters based on U-shaped graphene metamaterials.

We propose a tunable dual-band reflective cross-polarization converter composed of periodically arranged single layer U-shaped graphene nanostructures in mid-infrared region. The proposed dual-band reflective cross-polarization converter can convert the polarization state of an incident wave from the linear polarization state to its cross polarization state at the operating frequencies of 34.67 and 44.13 THz with the high-efficiency polarization conversion ratio (PCR) approaching 100%. Furthermore, as a complementary structure, a reflective cross-polarization converter with a hollow-carved U-shaped graphene sheet shows a broadband polarization conversion performance with a bandwidth of 1 THz and the PCR over 90%. The bandwidth of this broadband converter can be further extended to 2 THz after certain geometric parameter optimization. More importantly, both the dual-band and broadband cross-polarization converters not only can dynamically tune their PCR peak frequencies and magnitudes by adjusting the chemical potential and relaxation time of graphene without changing the geometric structure but also have good angular stability with high PCR in a wide range of incident angle up to 55°. These polarization converters may have great potential applications in mid-infrared spectroscopy, radiometer, sensor, and other photonic devices.

Design and implementation of metamaterial polarization converter with the reflection and transmission polarization conversion simultaneously

In this paper, a metamaterial polarization converter which can transform linearly polarized (LP) wave into its orthogonal polarization in the microwave region is designed and realized for the simultaneous implementation of the reflection and transmission polarization conversion. The special polarization converter is composed of dielectric substrate sandwiched by the split-ring resonator and the slotted PEC ground. The simulation results demonstrate that the reflection cross-polarization of this converter has a significantly polarization conversion ratio (PCR) over 90% in the frequency bandwidths of 23.50–32.31 GHz, and the transmission cross-polarization of this converter has a high PCR over 95% at frequencies of 7.78 and 13.39 GHz for normal incident LP waves. The simulation results are in good agreement with the experimental ones. Furthermore, the property of reflection and transmission cross-polarization of this proposed converter is stable at low frequencies with incident angle up to 50°. The physical mechanisms of the proposed multifunction polarization converter can be elucidated by the electromagnetic resonant theory based on its current distribution. The proposed polarization converter can be functionalized by changing the parameters of the slotted PEC ground, which has a great potential to be used as a selective polarization filter.

Ultra-broadband linear polarization converter based on anisotropic metasurface.

Through the manipulation of co-polarized reflection and cross-polarized reflection from a periodic array of metal-dielectric-metal resonators, a plethora of unprecedented metamaterial devices have been successfully demonstrated, such as perfect absorber and polarization converter. Recently, some broadband absorbers based on anisotropic resonators have been reported, which are actually poor absorbers when the cross-polarized reflection is considered. Here, we demonstrate that an ultra-wideband and high-efficiency reflective cross-polarization convertor can be achieved by breaking the symmetry of the resonator unit of a perfect absorber. Simulation results show that the polarization conversion ratio of the proposed metasurface is above 90% in the frequency range from 6.67 to 17.1 GHz and the relative bandwidth reaches 87.7%. The experimental results are in good agreement with the simulation results. The method paves a new way for the design of broadband polarization convertor, which can also be extended to the terahertz band.

Ultra-broadband wide-angle linear polarization converter based on H-shaped metasurface

We report the design, fabrication, and measurement of an ultra-broadband wide-angle reflective cross-polarization convertor using the compact H-shaped metasurface. The significant bandwidth expansion is attributed to the four electromagnetic resonances generated in an H-shaped unit. The simulation results show that the polarization conversion ratio (PCR) of the proposed metasurface is above 90% in the frequency range from 7 to 19.5 GHz and the relative bandwidth reaches 94%. The proposed metasurface is valid for a wide range of incident angles, and the mean polarization conversion ratio remains 80% even though the incident angle reaches 41.5°. The experimental results are in good agreement with the simulation results. Compared with the previous designs, the proposed linear polarization converter has a simple geometry but an excellent performance and hence has potential applications in microwave communications, remote sensors, and imaging systems.

Dual-band high-efficiency polarization converter using an anisotropic metasurface

In this work, a dual-band and high-efficiency reflective cross-polarization converter based on an anisotropic metasurface for linearly polarized electromagnetic waves is proposed. Its unit cell is composed of an elliptical disk-ring mounted on grounded dielectric substrate, which is an anisotropic structure with a pair of mutually perpendicular symmetric axes u and v along ±45° directions with respect to y-axis direction. Both the simulation and measured results show that the polarization converter can convert x- or y-polarized incident wave to its cross polarized wave in the two frequency bands (6.99–9.18 GHz, 11.66–20.40 GHz) with the conversion efficiency higher than 90%; moreover, the higher frequency band is an ultra-wide one with a relative bandwidth of 54.5% for multiple plasmon resonances. In addition, we present a detailed analysis for the polarization conversion of the polarization converter, and derive a formula to calculate the cross- and co-polarization reflections at y-polarized incidence according to the phase differences between the two reflected coefficients at u-polarized and v-polarized incidences. The simulated, calculated, and measured results are all in agreement with the entire frequency regions.

Efficient multiband and broadband cross polarization converters based on slotted L-shaped nanoantennas.

In this paper, we presented highly efficient reflective cross polarization converters based on metamaterials operating in the infrared regime, which are composed of a dielectric spacer sandwiched between slotted L-shaped metallic nanoantennas and a ground plane. The proposed polarization converters can convert a linearly polarized wave to its cross polarized wave with high polarization conversion ratio (> 0.95) over multiple / broad frequency bands. The resulting multi-band and broadband operations are induced by the localized mode hybridizations between the slot and the original metallic nanoantenna. Furthermore, the performance of the proposed converters under different incident angles is also explored. It is found that the first broad band (or the first two resonant frequencies) of the proposed broadband (or multi-band) converters appears to be independent of the incident angle (up to 47°).