Linear Polarization Conversion Research Articles

Broadband linear polarizer with high-efficient asymmetric transmission using a chiral metasurface

Asymmetric transmission, as a peculiar electromagnetic phenomenon in electromagnetic wave transmission, has been attracted extensive attention because of its important applications in polarization control and photodiode. This wok proposes a broadband linear polarizer based on a chiral metasurface with high-efficient asymmetric transmission performance. The designed polarizer consists of double arc-shaped structures interconnected via two circular cavities, which has the capacity to achieve broadband asymmetric transmission effect at 4–15 GHz for linear polarization conversion. The polarization conversion ratio exceeds 90% at 6.8–11.9 GHz and has a relative bandwidth of 54.5%. The asymmetric transmission parameter is above 0.59 in the frequency band 7.4–11.6 GHz. The microwave experiment results show a great consistency between simulation and experiment. The physical mechanism of polarization conversion and asymmetric transmission are further studied by introducing the surface current and electric field distributions. The designed polarizer has the superiority of uncomplicated structure and easy control, and can be extended to terahertz and optical regime. We believe that it has a broad application prospect in the field of chiral metamaterial structure design.

Graphene-based tunable linear and linear-to-circular polarization converters in the THz band

A switchable and tunable reflective terahertz (THz) polarization converter based on graphene metamaterial is designed and analyzed. By changing the Fermi energy level of graphene, the converter can achieve broadband linear polarization conversion (LPC) and linear-to-circular polarization conversion (LTC-PC). At relatively low Fermi energy level, the converter can achieve dual-band (0.1–0.3 eV) and single-band (0.4–0.6 eV) LPC, respectively, with a broadband frequency range of 2.34–3.54 THz, 3.77–4.22 THz, and 3.75–4.43 THz, and maximum polarization conversion rate (PCR) exceeding 99%. At high Fermi energy level, in addition to the LPC function, the converter can also achieve LTC-PC in the frequency range of 3.34–3.59 THz and 2.89–3.34 THz by adjusting the Fermi energy level. The physical mechanisms are elucidated from the point of the surface current distribution diagram. The structure shows great potential in switchable and tunable broadband THz converters and related applications.

An effective metasurface-based linear and circular polarization converter for C- and X-band applications

In this study, a reflection-mode metasurface-based linear and circular polarization converter is designed for common microwave frequencies (C-band (5.85–8.20 GHz) and X-band (8.20–12.40 GHz)). The proposed polarization converter possesses a right-handed circular polarization (RHCP) capability in the 5.35–5.94 GHz frequency range and a left-handed circular polarization conversion (LHCP) capability in the 8.88–12.03 GHz frequency range. Besides its circular polarization converter capability, it demonstrates linear polarization transformation in the 4.61–4.85 GHz and 6.86–7.78 GHz frequency ranges with a polarization converter rate (PCR) greater than 90%. The design provides an oblique incidence performance up to 45° with 80% PCR value in linear polarization. The CST Microwave Studio (a commercial 3D electromagnetic simulator) was used to obtain simulation results of the design. For validation, the designed converter was first fabricated using the conventional circuit-board method, and then its reflection coefficient was measured by a microwave measurement setup calibrated by the thru-reflect-line method. A good agreement was observed between simulated and experimental results. Finally, the proposed converter design was compared with other converter designs in the literature to examine its effectiveness.

Design of Multi-Functional Transmitarray with Active Linear Polarization Conversion and Beam Steering Capabilities

This study designed a multi-functional reconfigurable transmitarray with switchable polarization and beam steering capabilities using only a PIN diode having ON/OFF switching ability. The simulation confirmed that the proposed architecture is capable of 2D beam scanning of up to ±45° for elevation and azimuth while maintaining or converting linear polarization when operating within the X-band. The performance was verified through a far-field beam pattern measurement using the near-field antenna measurement system by producing a transmitarray with an 8 × 8 unit cell arrangement. The maximum level of gain of the proposed architecture was confirmed to be 14.5 dBi, the sidelobe level was below 14.5 dBc, the polarization converting loss was below 1.28 dB, and the polarization isolation level was above 14.7 dB. It can be utilized for the design technique of a radar system demanding small size, weight, power, and cost (SWaP-C) characteristics based on a simplified composition.

Ultra-thin reflective linear and circular polarization converter for Ku band applications

In this study, metasurface-based ultra-thin reflective polarization converter is offered. The proposed converter acts as a hybrid converter, providing both linear and circular polarization. The design consists of periodically arranged square split ring resonator (SRR) that is made by subtracting two circular segments and a full circle. In addition, commercially more easily accessible FR-4 material was used as substrate in the design. The metasurface converter operate in Ku frequency band range from 12.05 to 17.9 GHz for both linear to linear polarization and circular to circular polarization with over 90 percent polarization conversion rate (PCR) performance under normal incidence. Oblique angle PCR performance is up to 45 degrees with 80 percent conversion ratio at the same bandwidth of the proposed design. In addition, the proposed converter provide linear to circular polarization conversion (left-handed circular polarization-LHCP) range from 11.3 GHz to 11.5 GHz. The converter has a very competitive structure with a thickness of only 1.2 mm (0.06 λ) and the performance of the design has been compared with other studies with its superior aspects in the literature.

Switchable tri-function terahertz metasurface based on polarization vanadium dioxide and photosensitive silicon.

A terahertz switchable metasurface with the function of absorption and polarization conversion is proposed. It consists of metal pattern layer - dielectric layer - VO2 layer - dielectric layer - metal pattern layer, and the photosensitive silicon is embedded in the metal pattern. When VO2 is in insulated state, the metasurface behaves as a linear polarization converter. The polarization conversion rate (PCR) is more than 90% at two frequency bands of 1.64 THz ∼ 1.91 THz and 2.35 THz ∼ 2.75 THz. The polarization converter has good asymmetric transmission ability. Moreover, the polarization conversion performance can be dynamically controlled by changing the conductivity of the photosensitive silicon. When VO2 is in metallic state, the metasurface becomes a terahertz bidirectional absorber, which exhibits different absorption properties under TE and TM waves with the maximum absorptance reaching to 100%. In addition, the absorption of TE and TM terahertz waves can be controlled at the specific frequency by changing the conductivity of photosensitive silicon. We also explore the application of dynamic control of polarization waves in the near-field image display.

Switchable Terahertz Metasurfaces Based on Patterned Vanadium Dioxide and Graphene

This paper proposes a bi-functional switchable broadband terahertz metasurface ground on U-shaped vanadium dioxide (VO2) and graphene. The proposed design can effectively switch the current working state through a two-parameter regulation mechanism. Specifically, as we fix graphene’s Fermi level at 1 eV, and VO2 is in the form of insulating, the proposed design can be seen as a broadband terahertz absorber. Shifting the Fermi level of graphene can dynamically modulate the amplitude of the broadband absorption spectrum. In other words, by arbitrarily tailoring the Fermi level of graphene, the proposed design can freely switch states, i.e., mode switching from broadband absorption to broadband reflection, in the frequency range of interest. As graphene’s Fermi level is equal to 0.01 eV, and the vanadium dioxide in the structure is in the metallic state; the designed metasurface can be seen as a broadband terahertz linear polarization converter. It can convert the incident linearly polarized terahertz wave into its orthogonal polarization. By varying the conductivity of vanadium dioxide in the simulation, the proposed design can freely tune the current operating state over the operating frequency range, similar to “ON” and “OFF”. Metasurfaces can work efficiently in different frequency ranges by changing the geometric parameters. Therefore, the designed structure has switchable and tunable functions simultaneously, providing additional options for integrated, intelligent, and miniaturized devices.

Metasurface Based Reflection Type Linear Polarization Conversion for X Band Applications

Polarization conversion describe the propagation behavior of the electric field component of the electromagnetic wave. Polarization converters are widely used to improve the performance of microwave devices. In recent years, polarization converters have been produced on a metasurface basis, as they have relatively great advantages over polarization converters produced by conventional methods. In this study, a metasurface-based reflection type polarization converter operating in the microwave X band is proposed. The proposed design has a linear polarization conversion rate (PCR) of over 90% in the 9.1 GHz-12 GHz frequency range. In addition, the proposed design provides linear polarization conversion performance over 80% up to 45 degrees under oblique angle. The design consists of metal termination, easily accessible FR4 and metasurface. In order to better understand the physical mechanism of the proposed metasurface-based polarization transducer, its analysis in the u-v axes was performed as well as the surface current behaviors at resonance frequencies. Since the proposed design shows the same behavior in both TE and TM modes under normal incidence, the converter behaves polarization independent. The Design CST was created in the Microwave Studio program and the simulation results were processed by the Matlab program. The results were compared with other X band polarization converters and it was seen that the proposed design is superior to existing metasurface polarization converters in oblique angle performance, single design, cost-effective and thickness.

Broadband Polarization Manipulation Based on W-Shaped Metasurface

We present a metasurface consisting of W-shaped resonators to realize broadband reflective linear and circular polarization conversions. We find that the cross polarization conversion ratio for normal incidence is over 0.95 from 9.2 to 18.7 GHz, covering 68.1% of the central frequency. We also show that, the conversion performance is almost insensitive to the angle of incident waves. Furthermore, by simply adjusting the geometrical parameters of the W-shaped metasurface, the broadband circular polarization conversion is also achieved. We emphasize that the bandwidth of axis ratio less than 3.0 dB covers from 10.1 to 17.7 GHz, equivalent to 54.7% relative bandwidth. Due to these broadband and high-efficiency polarization conversion features, our proposal may have a wide application prospect.

Control of Polarization Orientation Angle of Scattered Light Based on Metasurfaces: −90° to +90° Linear Variation

Metasurfaces can be used to precisely control polarization state of the scattered light. Here, we present a metasurface-based terahertz device. On the one hand, it serves as a high performance linear polarization converter in transmission of over 80% power with weak reflection. It is capable of rotating linear polarization orientation angle with respect to x-axis continuously from −90° to +90° at 0.84 THz. On the other hand, it serves as a circular polarizer. It can transform a linear polarized wave into a circular polarized wave at 2.49 THz. The transmitted and reflected field are both circular polarized with 50% power. The proposed device with dual functionalities can be applied to modulate the polarization state of the signal in THz wireless communication.

Easy‐to‐Implement Ultra‐Thin, Wide‐Band, and Multi‐Functional Polarization Converter for K and Ka Band Applications

AbstractThis article presents an ultrathin, broadband, and multipurpose polarization converter design utilizing an anisotropic metasurface for K and Ka band. The proposed polarization converter, which has a single layer F4B as a substrate material with hexagonal‐shaped metallic solid structure along with hexagonal ring with diagonal splits on its front surface and a background (a completely metallic surface) on its back, works as not only a circular polarization converter but also a linear polarization to circular polarization (LP to CP) converter. Its polarization conversion rate (PCR) is more than 90% in the frequency range from 17.87 to 43.15 GHz, covering all of the K and Ka bands with a relative bandwidth of 83% under normal incidence case. For incidence angles up to 40°, PCR is observed to be greater than 75% in almost all of the K and Ka bands (except for the frequency range between 24.72 and 27.11 GHz). Furthermore, the proposed design has LP to CP in two different frequency bands, 16.23–16.74 GHz and 48.6–48.8 GHz. The proposed polarization converter, as advantages, is low cost, ultra thin, broadband, and facile, which can be useful in linear cross polarization conversion in K and Ka band applications.

Propagation dynamics of vector vortex beams in a strongly nonlocal nonlinear medium with parity-time-symmetric potentials

We demonstrate the dynamical properties of a vector vortex optical field (VVOF) in a strongly nonlocal nonlinear medium (SNNM) with sine and cosine parity-time-symmetric potentials (SCPT) by using the coupled vector Snyder-Mitchell model. Our study shows that the shape of the optical field is chaotically distorted in different propagation distances due to the modulation of complex refractive index. Despite the distorted optical field, the VVOF reciprocally evolves in a periodic stretch and shrink behavior during propagation in the SNNM-SCPT. The reciprocal conversions between the linear and circular polarizations periodically occur during propagation. The evolution of VVOF and the linear and circular polarization conversions are strongly dependent on the modulation of the complex refractive index, the initial powers and the vortex topological charge numbers. These results can provide a new way to complexly manipulate the VVOF in a SNNM-SCPT.

Theoretical proposal of electromagnetically induced transparency with a transmissive polarization conversion based on metamaterials

The polarization of electromagnetic waves is a key feature in the research areas of modern optics and information science. How to efficiently convert the polarization directions of the EM waves remains to be a challenge in electromagnetically induced transparency (EIT). Here, we theoretically propose a double-layer metamaterial with four symmetric H-shaped resonators, which can achieve the EIT phenomenon and transmissive linear polarization conversion (LPC). The EIT effect is acquired depending on the destructive interference between the electric and magnetic resonances. It is demonstrated that electromagnetic coupling is realized by reducing the structural symmetry of the rotated H-shaped resonators. Furthermore, the value of the maximum transmission coefficient reaches up to 0.900 at 14.202 GHz. The values of the transmission dips are 0.094 at 9.913 GHz and 0.176 at 16.101 GHz, respectively. Moreover, a broad transparency window that is higher than 0.8 can be gained spanning from 11.913 GHz to 15.289 GHz, and the relative bandwidth is 24.8%. Meanwhile, the momentous capability of the LPC is also observed. The transmissive cross-polarization conversion is well observed at 9.913 GHz and 16.101 GHz, where the polarization conversion ratios respectively are 90.2% and 91.8%. In the transparent window, a slow-light effect is highlighted. The values of the maximum group delay and group index respectively approach 91 ns and 1925. The FDTD simulation had been employed to further verify the effectiveness of group delay. In particular, the surface current distributions of the H-shaped resonators are employed to explain the mechanisms of the EIT effect and the transmissive LPC. Surpassing the general EIT structures and polarization converters, the proposed metamaterial is synchronously equipped with the EIT behavior and LPC by one same structure, which has numerous potential applications in communication and antenna technologies.

Ultra-thin, wide-angle and bandwidth-enhanced linear and circular metasurface-based reflection-type polarization converter at X-band microwave frequency

In this study, a low-profile ultra-thin metasurface-based reflection-type polarization converter with enhanced bandwidth for X-band (8.2–12.4 GHz) applications is proposed. The designed converter, which has a cell topology above a substrate (FR-4) material terminated in a metal conductor with overall thickness of 1.2 mm corresponding to a thickness of in terms of wavelength (ultra-thin), indicates the cross polarization performance with a polarization converter ratio (PCR) value of 90% in a wide (9–12 GHz) frequency range (normal incidence) and linear to circular polarization performance with left-handed circular polarization between 8.44 and 8.58 GHz and between 12.74 and 13.14 GHz. It is observed that the converter has a PCR value of 80% for incidence angles up to . Simulations of the designed converter performed by a commercial electromagnetic simulation program (CST Microwave Studio) were validated by free-space measurements.

Reconfigurable multifunctional polarization converter based on asymmetric hybridized metasurfaces

In the terahertz (THz) band, it is a challenge to integrate multiple functions into a very small unit cell structure of metasurface. However, the hybrid metasurfaces composed of several controllable materials provide a solution to this problem. In this paper, two multifunctional polarization converters based on asymmetric hybrid metasurface operating in the THz band are designed. The both polarization converters are designed with double-layer resonators that embedded by photosensitive silicon (Si) and vanadium dioxide (VO2) at the appropriate positions. By controlling the optical pump intensity and the temperature of the VO2, the designed metasurface polarization converter (MPC) I can realize the identical linear polarization conversion for both forward and backward reflection modes. When the external excitation conditions are changed, the polarization conversion frequency bands of forward and backward incident waves can be switched. Moreover, the MPC II can operate in both reflection and transmission modes and realize multifunctional polarization conversion. For the forward incident THz wave, the MPC II can perform two different functions under different excitation conditions: the conversion from co-polarization to cross-polarization in the reflection mode and the conversion from linear polarization to right-handed circular polarization (RHCP) or left-handed circular polarization (LHCP) in the transmission mode. While for the backward incident THz wave, the MPC II operates in the transmission mode and converts the electromagnetic (EM) wave from co-polarization to cross-polarization one. Our designs may provide a scheme for multifunctional integrated devices operating in THz band.

Conceptual radar trap model realized via polarization conversion metasurface.

General metasurfaces (MSs) can realize low observability of radar by manipulating the polarization mode and transmission direction of the electromagnetic (EM) waves. Here, we propose the radar trap model to realize EM wave imprisonment. This three-layer model is composed of the transmission polarization converter, the connected dielectric substrate and the reflection polarization converter. Using Jones calculation as a guide, we optimized the geometric parameters of the upper and lower layers to realize specific polarization conversion functions. The middle layer is regarded as the support and matching layer. On this basis, the combined radar trap model can realize the imprisonment of EM waves between upper and lower layers, which is attributed to the cooperative effect of asymmetric transmission and polarization conversion. We further verified the feasibility and correctness of our investigations through two kinds of model designs based on linear and circular polarization conversion mechanisms. Good agreements are observed between simulation and experiment. Even though the design presents a narrow operating bandwidth, it still provides novel ideas for developing radar stealth technology.

Dual-mode terahertz broadband polarization conversion metasurface with integrated graphene-VO[formula omitted

We present a dynamically switchable broadband dual-mode polarization conversion metasurface in the terahertz (THz) regime, which consists of double-layer graphene grating, metal resonator, and gold–vanadium dioxide (VO2) alternating grating and silicon dioxide (SiO2) dielectric spacer. The phase transition capability of VO2 is utilized to realize the switching of polarization conversion between transmission mode and reflection mode, and the design of double-layer graphene grating can enhance the transmittance in transmission mode. When VO2 is in the insulating state, by increasing the Fermi level of the double-layer graphene, linear polarization conversion in transmission mode can be achieved in 0.52∼1.74 THz with the relative bandwidth of about 107.9%; when VO2 is in the metallic state and the Fermi level of graphene is 0 eV, the metasurface works in reflection mode, achieving the reflective linear polarization conversion in the range of 0.62∼1.70 THz with relative bandwidth of up to 93.1%. The PCR in the two modes can be dynamically adjusted by changing the Fermi level of graphene and the conductivity of VO2. The proposed dual-mode metasurface is a potential in the design of optical polarization control devices for spectroscopy, imaging etc.

Dynamically tunable frequency-domain multifunctional reconfigurable polarization conversion metasurface

The design of electromagnetic device with arbitrary polarization manipulation is the hot spot of the current research. Multifunctional reconfigurable electromagnetic devices have been put into wide applications in radar, satellite communication and other fields. In this work designed is a multifunctional reconfigurable polarization conversion metasurface based on two PIN diodes, which can realize linear polarization conversion, linear-circular polarization conversion and total reflection switching in the different frequency bands, and the multi-function converter can still maintain the high-efficient broadband conversion characteristics when the oblique incidence angle is less than 30 degrees. The polarization conversion and reconfigurability are mainly due to the anisotropy of the structure and the changes of coupling mode in different states of PIN diodes. In addition, the physical mechanism of polarization conversion is explained by surface current. The combined action of electric resonance and magnetic resonance results in polarization conversion. Finally, the experimental results of the sample are in good agreement with the simulation results. The device has the potential application values in polarization manipulation, frequency control, intelligent reflecting surface design, and antenna design and so on.

Optoelectronic Jointly Tuned Terahertz Polarization Converter Based on Graphene-Semiconductor Hybrid Metasurfaces

Polarization multiplexing or polarization conversion devices based on metasurfaces have been reported in various electromagnetic frequency bands, among which graphene-based electronically controlled devices and semiconductor-based optically controlled terahertz metasurfaces have unique advantages in terms of modulation depth and speed, respectively. However, both are often mutually constrained and difficult to satisfy simultaneously in a single device. In this paper, an electric-optical dual physical field modulation scheme is proposed to achieve broadband and efficient polarization transformation using metal-graphene-germanium heterostructured metasurfaces. By varying the Fermi level of graphene and the conductivity of the semiconductor, the linear polarization conversion efficiency of the device is effectively switched in a wide range of 99%-25%, and the polarization conversion characteristics are well maintained in the incident angle of 0-50 degrees. The proposed scheme provides a new idea for the design of terahertz polarization devices, which is expected to be applied to terahertz communication and imaging.

3D printing of metasurface-based dual-linear polarization converter

Three-dimensional printing using digital light processing (DLP) technology has been studied in various fields because of its ability to create complex shapes through a simple process. In this study, DLP 3D printing was employed in the implementation of the metasurface-based dual-linear polarization converter (DLPC). The unit cell of the metasurface-based DLPC for linear polarization conversion was designed consisting of the upper and lower dipole-pair antennas connected through vias and a shielding layer that electrically shields the antennas from each other, and its fabrication was based on the characterization results of the dielectric properties of the photocurable substrate materials and electrical properties of the conductive materials used for synthesizing the metasurface. The printability evaluation of dipole pairs, vias, and a shielding layer was carried out to implement the detailed structures of the DLPC in 3D printing. The electromagnetic wave transmission characteristics of the 3D-printed 8 8 array DLPC demonstrated an orthogonal polarization conversion, as predicted by the simulation results. This study confirmed that the DLP-based 3D printing technology can go beyond the existing functions of manufacturing objects and can be applied to the implementation of various electronics based on different meta-structures.