Perfect Polarization Conversion Research Articles

Polarization and Incident Angle Independent Multifunctional and Multiband Tunable THz Metasurface Based on VO2.

Aiming at the limitations of single-functionality, limited-applicability, and complex designs prevalent in current metasurfaces, we propose a terahertz multifunctional and multiband tunable metasurface utilizing a VO2-metal hybrid structure. This metasurface structure comprises a top VO2-metal resonance layer, a middle polyimide dielectric layer, and a gold film reflective layer at the bottom. This metasurface exhibits multifunctionality, operating independently of polarization and incident angle. The varying conductivity states of the VO2 layers, enabling the metasurface to achieve various terahertz functionalities, including single-band absorption, broadband THz absorption, and multiband perfect polarization conversion for linear (LP) and circularly polarized (CP) incident waves. Finally, we believe that the functional adaptability of the proposed metasurface expands the repertoire of options available for future terahertz device designs.

Bidirectional vortex beam and reflective polarization conversion terahertz metasurfaces

We design a terahertz metasurface with the functions of bidirectional vortex beams and reflection polarization conversion. The unit cell of the proposed metasurface consists of a vanadium dioxide metal mixed layer, a dielectric layer, a vanadium dioxide thin film, a dielectric layer, and a metal open ring. At room temperature, when a left-handed circularly polarized wave is incident, the metasurface generates a reflected mode vortex beam with topological charges of l=−1 and l=−2 at frequencies of 0.33 and 0.34 THz. Simultaneously, the metasurface produces transmitted mode vortex beams with topological charges of l=−1 and l=−2 at frequencies of 0.33 and 0.36 THz. When the temperature changes to 68°C and y-polarized waves are incident, the metasurface generates a reflected left-handed circularly polarized wave in the frequency bands of 0.6–0.65 THz and 1.75–1.93 THz, and a right-handed circularly polarized wave in the frequency band of 0.86–0.9 THz, achieving the function of converting linearly polarized waves into circularly polarized waves. This metasurface provides a new method for designing a single metasurface structure to achieve bidirectional multifunctional terahertz devices for transmission and reflection modes. In addition, the designed metasurface achieves a perfect polarization conversion function that can convert linearly polarized waves into circularly polarized waves.

Pseudo coherent-perfect-absorption approach toward perfect polarization conversion

Polarization is one of the essential properties of light. Thereby, its manipulation is important for numerous applications. When employing a resonance in a mirror-symmetry system to manipulate polarization, non-zero residual light in the excited polarization channel leads to the shrink in the scope of the polarization manipulation, and a perfect polarization conversion cannot occur. In this work we show that the concept of coherent perfect absorption can be applied to perfect polarization conversion for circular polarization states. We find that the only requirement to achieve a perfect polarization conversion is that the working frequency is the resonant one. More importantly, the range of the output polarization states can be efficiently enlarged, and can span the entire Poincare sphere by combining the momentum dependent radiative coupling rate driven by the bound states in the continuum (BIC) and the phase delay. When applied to realistic design, we adopt a guided mode resonance driven from the symmetry protected BICs in a dielectric photonic crystal slab. Numerical results are in good agreements with our theoretical predictions. We believe this work can deliver important benefits for a variety of applications based on the efficiently light polarization control and management.

Terahertz broadband tunable multifunctional metasurface based on VO2

A switchable multi-function terahertz metasurface employing phase transition material vanadium dioxide (VO2) is presented and investigated. By varying the temperature, the hybrid structure can switch between transmission, absorption, and reflection modes in broadband ranges. When the temperature is below 340 K and VO2 is in the insulating state, perfect polarization conversion is demonstrated. Efficient asymmetric transmission (AT) exceeding 0.7 is simultaneously achieved with an ultra-wide bandwidth of 3.6THz. When VO2 is in the metal phase, it shows different modulation characteristics for x and y-polarized waves. The structure can absorb over 90% of y-polarized waves from 3.56 THz to 7.2 THz (bandwidth, 3.64 THz), while 85% of x-polarized waves are reflected from 1 THz to 9 THz (bandwidth, 8 THz). Compared with other related published works, the designed structure makes significant progress in integrated functionalities, operating bandwidth, and working efficiency. It shows great potential for use in terahertz dynamic control and multifunctional integrated systems.

Ultra-Wide Band Polarization Converter Based on Ultra-Thin Bi-Layer Slot Structures

An ultrathin linear-to-linear polarization converter exhibiting a high polarization conversion ratio (PCR) in an ultrawide bandwidth is fabricated on a printed circuit board (PCB). It is based on a bilayer slot structure that is electrically connected by via holes. Front- and back-sided slot structures are arranged in mutually orthogonal directions and function as receivers and radiators, respectively. The via holes provide a route for the transfer of electromagnetic energy received by the front-sided slot structures to the back-sided slot structures and radiate an electromagnetic wave having polarization orthogonal to that of the input electromagnetic wave. Moreover, two slots are employed for each unit cell design, and the locations of the via holes are carefully determined to achieve broadband polarization conversion. The via-hole positions that change the surface current distribution around the slot apertures enable the control of multiple resonance frequencies. Via holes are positioned to make first and second resonance frequencies that are blue-shifted toward the third resonance frequency, which broadens the operational band of the perfect polarization conversion. The 0.8 mm thick polarization converter exhibits PCR greater than 99% in the frequency band from 24.5 to 47 GHz.

A multifunctional metasurface with asymmetric transmission and high-efficiency cross-polarization converter

A three-layer multifunctional metasurface structure is proposed to achieve polarization rotation, perfect polarization conversion, and asymmetric transmission. The design consists of mutually perpendicular rectangular patches, metal pillars, and open-slit metal sheets. By propagating the current through the metal pillars and changing the surface current direction, the dipole can be orthogonally steered to accomplish polarization conversion. The metal in the middle layer can be used to both improve the polarization conversion ratio and ensure high transmittance. The operating band of asymmetric transmission is 8.3–14.7 GHz, where the conversion ratio is above 90% in all of 9–14.2 GHz. In order to verify the proposed concept, the related parameters are designed and measured, the final experimental results match with the simulation results, and the design can be used in the radome, electromagnetic stealth.

Chiral emission from resonant metasurfaces.

Ultracompact sources of circularly polarized light are important for classical and quantum optical information processing. Conventional approaches for generating chiral emission are restricted to excitation power ranges and fail to provide high-quality radiation with perfect polarization conversion. We used the physics of chiral quasi-bound states in the continuum to demonstrate the efficient and controllable emission of circularly polarized light from resonant metasurfaces. Exploiting intrinsic chirality and giant field enhancement, we revealed how to simultaneously modify and control spectra, radiation patterns, and spin angular momentum of photoluminescence and lasing without any spin injection. The superior characteristics of chiral emission and lasing promise multiple applications in nanophotonics and quantum optics.

Chiral metasurface design with highly efficient and controllable asymmetric transmission and perfect polarization conversion of linearly polarized electromagnetic waves in the THz range

The influences of metasurfaces on the propagation of electromagnetic waves generate several important effects, such as asymmetric transmission and polarization conversion, that are highly useful in optical and microwave communication applications. However, easy method for dynamically controlling the asymmetric transmission of linearly polarized waves with perfect polarization conversion and high efficiency over a wide band in the THz range remain poorly developed. Our work addresses this issue by designing a novel metasurface structure consisting of two outer orthogonal gratings and a central lattice with an optimized chiral graphene monolayer distribution topology sandwiched between dielectric substrates. The frequency-dependent performance of the proposed metasurface is evaluated according to analyses of the asymmetric transmission coefficient, polarization conversion rate, total transmission coefficient, polarization rotation angle, ellipticity, and chirality parameter based on the results of simulations. The results demonstrate that the proposed structure provides highly efficient asymmetric transmission of linearly polarized waves and perfect polarization conversion in the high frequency range from 0.1 to 3.0 THz. The asymmetric transmission and the polarization conversion of the structure are dynamically controllable by changing the Fermi energy of graphene from 0 eV to 1 eV. The results of the analysis reveal that the observed dynamic controllability is a function of the interrelation between the special configuration of the chiral metasurface structure and the special properties of graphene.

Switchable Multi-Functional VO2-Integrated Metamaterial Devices in the Terahertz Region

In this paper, we present a multi-functional terahertz metamaterial device based on the gold and vanadium dioxide (VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). Availing of the phase transition characteristic of VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , the switchable performance between perfect absorption and broadband asymmetric transmission (AT) can be realized. When VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> acts like a metal, the proposed metamaterial device behaves as a selectively perfect absorber for linearly polarized lights. By transforming the phase of VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> into isolating state, broadband AT with high efficiencies over 90% can be achieved in the region from 1.5 THz to 2.5 THz. Moreover, perfect polarization conversion can be simultaneously realized associated with the AT effect. The Fabry-Pérot-like cavity model and the electric field distributions are employed to explain the physical mechanism of the above phenomena. Besides, the proposed metamaterial shows a high tolerance to the incident angle for achieving perfect absorption and broadband AT effect. Our designed device may provide a new avenue for developing multi-functional metamaterial devices in the THz region.

Depolarizing Chipless Tags with Polarization Insensitive Capabilities

A novel depolarizing chipless tag configuration with high angular insensitivity is presented. The basic tag comprises two dipole resonators arranged with a relative rotation of 45°. The proposed configuration improves the depolarization properties performance of a single dipole over the ground plane which provides a peak with perfect polarization conversion only if the electric field impinges at 45° with respect to the dipole resonator. The second dipole arranged at 45° compensates the cross-polar reduction which is observed when the electric field is not correctly polarized. Indeed, when the field is tilted by 90° with respect to the first dipole, it forms an angle of 45° with the second one. The proposed configuration is also analyzed for providing multiple frequency peaks. A tag with 4 angular independent frequency peaks laying between 2 GHz and 5.5 GHz is designed. Angular frequency maps are used to illustrate the peculiar frequency shifts achieved when the electric fields rotate in the plane of the dipole. Finally, a prototype of the polarization insensitive tags is fabricated and measured to confirm the simulated results.

Dual-band reflection polarization converter for circularly polarized waves based on a zigzag asymmetric split ring resonator

Polarization converters based on metasurfaces are one of the recently developed metadevices that can change the polarization state with designated modes, utilizing the sub-wavelength unit construction. In this paper, a kind of planar zigzag asymmetric split ring resonator (Z-ASRR) metasurface with dual bands is proposed to achieve nearly perfect polarization conversion for circularly polarized waves. Compared with the original prototype asymmetric resonant ring (ASRR), both magnitude and bandwidth have been remarkably improved for achieving a higher resonance, with the introduction of zigzag metallic wires. The reflection polarization conversion ratio possesses two peak values with 0.94 and 0.99 at 5.39 GHz and 9.65 GHz, respectively. It is also demonstrated that the introduction of extra gaps, which are closely linked with the multi-node standing wave characteristic, can control the number of resonant modes or modulate the relative bandwidth. Besides, an equivalent circuit model, the degree of zigzag bending, and the oblique incidence are further analyzed in detail. The experimental results agree well with the simulations, and this chiral metadevice could be applied for on-chip integration in an optical detection/laser, a chiral biosensor, and molecular spectroscopy.

Metasurface supporting broadband circular dichroism for reflected and transmitted fields simultaneously

We demonstrate significant optical activity in the near-infrared spectrum of a chiral metasurface which is designed using an array of L-shaped silver nanostructures. The far-field radiation from the plasmon-polariton surface wave currents produces combination of strong and highly dispersive orthogonal electric field components leading to the observation of broadband circular and elliptical polarization states (dichroism) for reflected and transmitted fields. Full-wave electromagnetic simulations show a linear to left hand and right hand circular polarization conversion between 200–261 THz frequency (1.15 µm–1.5 µm wavelength) range for reflected and transmitted fields. The structural chirality can be further enhanced by engraving another smaller L-dipole in nested configuration reaching near perfect polarization conversion efficiency. The nested L-dipole configuration supports circular polarization conversion between 262–306 THz frequency (980 nm–1.14 µm wavelength) range. Full-wave simulations suggest clear enhancement of the surface currents with helical orientation leading to increased optical activity. The proposed optical waveplate may be utilized in polarization control applications such as optical imaging, sensing, and display components.

Switching between the Functions of Half-Wave Plate and Quarter-Wave Plate Simply by Using a Vanadium Dioxide Film in a Terahertz Metamaterial**Supported by the Scientific and Technological Developing Scheme of Jilin Province (Grant No. 20180101281JC), “135” Research Project of Education Bureau of Jilin Province (Grant No. JJKH20190579KJ), and “111” Project of China (Grant No. D17017).

We propose a switchable THz metamaterial that can be switched between two functions of half-wave plate and quarter-wave plate. The two switchable functions can be simply achieved by inserting a VO2 film in the metamaterial design. Finite-difference time-domain (FDTD) simulation results show that the proposed metamaterial can convert x-polarized incident wave to y-polarized reflected wave when VO2 is at metal phase, and convert x-polarized wave to circularly polarized wave when VO2 is at insulator phase. The metamaterial performs well in the two functions, i.e., the same broad working frequency band and near perfect polarization conversion. The switching effect originates from the switchable Fabry–Pérot cavity length induced by the phase change of VO2. We believe that our findings provide a reference in designing switchable metamaterials.

Multifunction tunable broadband terahertz device for polarization rotation and linear asymmetric transmission based on Dirac semimetals

A three-layer complementary strip Dirac semimetal polarizer is proposed to achieve polarization rotation, perfect polarization conversion, and asymmetric transmission. This device can realize broadband polarization operation of linear polarized waves in the terahertz frequency domain. By changing the Fermi level of the Dirac semimetal, the polarization angle of linearly polarized light in the frequency range of 1.3 to 1.63 THz can be rotated from 0°to 90°, and the device has good robustness for linearly polarized light with different incident angles. When used as an asymmetric transmission device, its polarization conversion efficiency reaches more than 98% and the asymmetric transmission parameter reaches more than 50% in the range of 1.3–1.63 THz. The asymmetric transmission parameters, polarization conversion ratio, polarization rotation angle, and ellipticity are used to describe the performance of the converter.

High‐Efficiency and Tunable Circular‐Polarization Beam Splitting with a Liquid‐Filled All‐Metallic Catenary Meta‐Mirror

AbstractCircular‐polarization beam splitting is one functionality of interest in polarization control. However, current splitters suffer from limitations in either efficiency or tunability. It is theoretically and experimentally demonstrated that a meta‐mirror composed of catenary‐shaped metallic gratings can efficiently deflect left‐handed and right‐handed circularly polarized waves in opposite directions with power efficiency of over 90%. This ultrahigh efficiency is attributed to the nearly perfect polarization conversion and continuous phase profile of the metallic catenary structure. Furthermore, the meta‐mirror demonstrates high beam‐splitting tunability with ethanol injected into the catenary groove. By controlling ethanol depth, the working frequency for peak deflection can be continuously tuned from 10.5 to 8.5 GHz. It is believed that this approach can provide valuable guidance for efficient and dynamic control of electromagnetic waves for various applications.

High Efficiency Ultrathin Transmissive Metasurfaces

AbstractMetasurfaces offer unprecedented freedom to manipulate electromagnetic waves at deeply subwavelength scales. However, realizing a highly efficient metasurface, yet simple enough to conceptualize, design, and fabricate, is a challenging task. In this paper, a novel approach is proposed for designing meta‐atoms which can achieve full phase control in the range 0–2 π with high efficiency in the transmission mode. In particular, a bilayer meta‐atom is designed, exploiting nearly perfect polarization conversion of the two orthogonal transmissions, whose transmission efficiency reaches as high as 85%. The transmission phase control in the circular polarization basis is achieved with the axial rotation of the proposed meta‐atom based on Pancharatnam–Berry phase principle. These meta‐atoms are then wielded to construct metasurfaces for generating vortex beams carrying orbital angular momentum. The conversion efficiency as high as 75% and a transmission efficiency of 55% are achieved for the realized metasurfaces.

Controllable linear asymmetric transmission and perfect polarization conversion in a terahertz hybrid metal-graphene metasurface.

We propose a three layered metal-graphene-metal metasurface to investigate the controllable linear asymmetric transmission and perfect polarization conversion in THz regime, by using the finite-difference time-domain (FDTD) method. An on-to-off control of asymmetric transmission and perfect polarization conversion is achieved by changing the Fermi energy of graphene from 0.8 eV to 0 eV. We present the electric field distribution and Fabry-Perot-like cavity model to analyze the working mechanisms. By gradually shifting the Fermi energy of graphene, two functions are realized, i.e., controllable linear asymmetric transmission and controllable total transmission with near perfect polarization conversion.

Conversion between polarization states based on a metasurface

Transmission of an anisotropic metasurface is analyzed in a polar base relying on the Jones calculus, and polarization conversion from the spatial uniform polarization to the spatial nonuniform polarization is explored. Simple and compact polarization converters based on rectangular holes or cross holes etched in silver film are designed, and polarization conversions from the linear and circular polarization to the radial and azimuthal polarization are realized. Numerical simulations of three designed polarization converters consisting of rectangular holes equivalent to polarizers and quarter- and half-wave plates, exhibit the perfect polarization conversion. The experiment results consistent with the simulations verify theoretic predictions. This study is helpful for designing metasurface polarization converters and expanding the application of a metasurface in polarization manipulations.

Arbitrary linear THz wave polarization converter with cracked cross meta-surface

This Letter presents a double-layer structure combining a cracked cross meta-surface and grating surface to realize arbitrary incident linear terahertz (THz) wave polarization conversion. The arbitrary incident linear polarization THz wave will be induced with the same resonant modes in the unit cell, which results in polarization conversion insensitive to the linear polarization angle. Moreover, the zigzag-shaped resonant surface current leads to a strong magnetic resonance between the meta-surface and gratings, which enhances the conversion efficiency. The experimental results show that a more than 70% conversion rate can be achieved under arbitrary linear polarization within a wide frequency band. Moreover, around 0.89 THz nearly perfect polarization conversion is realized.

Polarization conversion based on an all-dielectric metasurface for optical fiber applications

Polarization conversion (PC) in optical fiber is a very important operation in practice. To date, however, PC in fiber is usually achieved by coupling an external bulk element, or using the birefringence results from mechanically squeezing or coiling the fiber. In this paper, we propose a distinct approach for PC in optical fiber by introducing an all-dielectric metasurface in it, which has been proven to be compact, efficient and robust. Based on this approach, nearly perfect PCs from the linear polarization fundamental mode, i.e. mode to various other polarization modes, are achieved, including the mode, left/right-handed circular polarization mode, and also vector modes with radial and azimuthal polarizations. In addition, the fabrication of this all-dielectric-based metasurface is compatible with semiconductor manufacturing technologies, which makes the PC presented here competitive against traditional ones, and may find potential applications in optical fiber elements and systems.