High Polarization Conversion Efficiency Research Articles

Flexible broadband polarization converter based on metasurface at microwave band**Project supported by the Fundamental Research Funds for the Central Universities, China (Grant No. kfjj20180401), the National Natural Science Foundation of China (Grant No. 61471368), the Aeronautical Science Foundation of China (Grant No. 20161852016), the China Postdoctoral Science Foundation (Grant No. 2016M601802), and Jiangsu Planned Projects for Postdoctoral Research Funds, China

A flexible broadband linear polarization converter is proposed based on the metasurface operating at microwave band. To achieve bandwidth extension property, long and short metallic arc wires, as well as the metallic disks placed over a ground plane, are combined into the polarizer, which can generate three neighboring resonances. Due to the combination of the first two resonances and the optimized size and thickness of the unit cell, the polarization converter can have a weak incident angle dependence. Both simulated and measured results confirm that the average polarization conversion ratio is over 85% from 11.3 GHz to 20.2 GHz within a broad range of incident angle from 0° to 45°. Moreover, the proposed polarization converter based on flexible substrates can be applied for conformal design. The simulation and experiment results demonstrate that our designed polarizer still keeps high polarization conversion efficiency, even when it adheres to convex cylindrical surfaces. The periodic metallic structure of the designed polarizer has great potential application values in the microwave, terahertz, and optic regimes.

Compact High-Efficiency Broadband Metamaterial Polarizing Reflector at Microwave Frequencies

A compact highly efficient broadband microwave polarizing reflector, employing a quasi-2-D metamaterial composed of a single layer of square split-ring resonators, is presented and its performance is reported. Numerical and experimental results show a cross-polarization average polarization conversion ratio of greater than 90% for normal incident linearly polarized waves over a frequency range of 8.2–23 GHz. Due to multiple resonances occurring over this frequency range, the polarizing reflector presents both broadband performance and high polarization conversion efficiency. Transfer matrix and equivalent surface impedance theory and modeling are discussed to explain the physical underpinnings of the reflector’s multiresonance behavior. These physical mechanisms are further analyzed by examination of simulated surface current distributions. The reflector is expected to be employed in applications where the control of the signal polarization is of central importance.

High-efficiency, broadband, and wide-angle all-dielectric quarter wave plate based on anisotropic electric and magnetic dipole resonances.

Metadevices based on dielectric nanostructure with excitation of electric and magnetic resonances have shown high efficiency for polarization control compared with conventional manipulation methods, as well as plasmonic structure metadevices. Since both the electric and magnetic dipole (MD) resonances can be precisely adjusted by optimizing geometric parameters of the resonators to meet the desired wavelength, this paper proposes an approach to implement the high transmittance metadevices operating at preferred wavelengths. By employing this method, we demonstrate an all-dielectric quarter wave plate (QWP) metasurface with high transmittance (>85%) and high polarization conversion efficiency (>0.88) in a broad telecom waveband. At the same time, conversion efficiency is nearly unaffected for incident angles within 75°. With features of high transmittance, wide angle, and invertible linear to circular polarization conversion, the all dielectric QWP can be a good replacement for plasmonic metasurface devices and offers a further step in developing polarization and phase manipulation metadevices.

Wideband Polarization Conversion with the Synergy of Waveguide and Spoof Surface Plasmon Polariton Modes

The ability to freely control the polarization of electromagnetic waves is of great significance, and state-of-the-art challenges include achieving efficient, wide-band polarization control with a relatively thin device in transmission geometry. To meet the challenge, this study combines slow waves (from spoof surface plasmon polariton modes) with fast waves (from waveguide modes) to handle orthogonal polarization components. Such a system can be quite thin, due to the strong dispersion between these two types of modes, with cancellation of the two nonlinearly dispersive modes yielding high-efficiency polarization conversion over a wide frequency range.

Design of a promising silicon slot waveguide-based ultra-short low loss efficient polarization rotator for the mid-IR

We propose design of a promising ultra-short and highly efficient mid-IR polarization rotator (PR) on silicon-on-calcium-fluoride (SOCF) platform, whose rotation section is formed from an asymmetric slot waveguide for the working wavelength of 4.47 μm by exploiting mode coupling scheme. Numerical results demonstrate that within a conversion length of just ∼18 μm, the maximum achievable polarization conversion efficiency (PCE) for both the polarizations (TE-TM and TM-TE) is as high as ∼100% with significantly low loss of ∼ 0.15 dB. Achieved polarization extinction ratios (PERs) are as high as 43.3 dB and 34.9 dB for TE-TM and TM-TE polarizations, respectively. Furthermore, over a large bandwidth of 360 nm (4.29–4.65 μm), our designed PR exhibits very high PCE (> 98%) for both the TE-TM and vice versa with an appreciable PER of ∼18 dB and relatively low loss of ∼ 0.26 dB. Study on fabrication tolerances reveals that designed PR is robust to potential imperfections in fabrication. To the best of our knowledge, our designed PR is the shortest PR reported to date for the mid-IR wavelength regime with a healthy balance/compromise between PCE, PER, bandwidth, loss and fabrication tolerance.

Broadband radar cross-section reduction using polarization conversion metasurface

AbstractA wideband and high-efficiency polarization conversion metasurface (PCM) is proposed and applied to reduce radar cross section (RCS). The proposed PCM unit is composed of two oblique asymmetry triangle split rings, which generate multiple plasmon resonances. Simulated and measured results demonstrate that it achieves polarization conversion over 90% from 9.24 to 17.64 GHz. Besides square checkerboard, the proposed PCM units and mirror units are arranged in triangle checkerboard. The mechanisms of both checkerboard PCMs are analyzed based on standard array theory, including the relationship between RCS reduction value and polarization conversion ratio value. The derived formulas provide a guideline to design checkerboard structure based on PCM. Simulated results demonstrate that both checkerboard PCMs achieve over 62% relative bandwidth of 10 dB RCS reduction under normal incidence with respect to the equal-sized metallic plate, which also means that the triangle one could be an alternative solution to reduce RCS. To verify the analyzed and simulated results, the fabricated sample and measured results of both checkerboard PCMs are presented. Good agreements are achieved between measurements, simulations and numerical analysis.

Ultrathin Planar Microlens Arrays Based on Geometric Metasurface

AbstractAscribing to the properties of two dimensional parallel focusing and imaging, low propagation loss, integration and miniaturization, microlens array has been widely used in imaging, optical communication, organic light emitting devices, adaptive optics, photolithography, biomedical and other applications. However, the existing traditional microlens array suffers from difficulty in fabrication, large‐thickness, curved surface, non‐uniformity of light spots, or requirement of additional discrete components to control the microlens. Herein, a planar microlens array is experimentally demonstrated based on the geometric metasurface. The single microlens is composed of space‐variant subwavelength metallic gratings with high polarization conversion efficiency and thus exhibits gradient phase distribution. The focused spot diameter of 22.5 μm with radius of 350 μm, focal length of 1 cm and the light spots intensity uniformity of 0.9885 (standard deviation 0.0115) at the focal plane are obtained. Moreover, the broadband property of microlens array is also confirmed. The novel design strategy for microlens array would facilitate the miniaturization of optical devices and be easily integrated in the optical interconnected devices.

Broadband reflective multi-polarization converter based on single-layer double-L-shaped metasurface

In this paper, a broadband reflective multi-polarization converter based on single-layer double-L-shaped metasurface is proposed. The proposed metasurface can effectively convert linear-polarized (TE/TM) incident wave into the reflected wave with three different polarizations within the frequency bands of 5.5–22.75 GHz. Based on the electric and magnetic resonant features of the double-L-shaped structure, the proposed metasurface can convert linearly polarized waves into cross-polarized waves at three resonant frequency bands. Furthermore, the incident linearly polarized waves can be effectively converted into left/right handed circular-polarized (LHCP and RHCP) waves at other four non-resonance frequency bands. Thus, the proposed metasurface can be regarded as a seven-band multi-polarization converter. The prototype of the proposed polarization converter is analyzed and measured. Both simulated and measured results show the 3-dB axis ratio bandwidth of circular polarization bands and the high polarization conversion efficiency of cross-polarization bands when the incident wave changes from 0° to 30° at both TE and TM modes.

Broadband and high efficiency all-dielectric metasurfaces for wavefront steering with easily obtained phase shift

All-dielectric metasurfaces for wavefront deflecting and optical vortex generating with broadband and high efficiency are demonstrated. The unit cell of the metasurfaces is optimized to function as a half wave-plate with high polarization conversion efficiency (94%) and transmittance (94.5%) at the telecommunication wavelength. Under such a condition, we can get rid of the complicated parameter sweep process for phase shift selecting. Hence, a phase coverage ranges from 0 to 2π can be easily obtained by introducing the Pancharatnam–Berry phase. Metasurfaces composed of the two pre-designed super cells are demonstrated for optical beam deflecting and vortex beam generating. It is found that the metasurfaces with more phase shift sampling points (small phase shift increment) exhibit better performance. Moreover, optical vortex beams can be generated by the designed metasurfaces within a wavelength range of 200 nm. These results will provide a viable route for designing broadband and high efficiency devices related to phase modulation.

Visible light focusing flat lenses based on hybrid dielectric-metal metasurface reflector-arrays

Conventional metasurface reflector-arrays based on metallic resonant nanoantenna to control the wavefront of light for focusing always suffer from strong ohmic loss at optical frequencies. Here, we overcome this challenge by constructing a non-resonant, hybrid dielectric-metal configuration consisting of TiO2 nanofins associated with an Ag reflector substrate that provides a broadband response and high polarization conversion efficiency in the visible range. A reflective flat lens based on this configuration shows an excellent focusing performance with the spot size close to the diffraction limit. Furthermore, by employing the superimposed phase distribution design to manipulate the wavefront of the reflected light, various functionalities, such as multifocal and achromatic focusing, are demonstrated for the flat lenses. Such a reflective flat lens will find various applications in visible light imaging and sensing systems.

Cavity-based linear-to-circular polarization converter.

This paper presents a polarization converter to convert a linearly polarized (LP) incident wave into an outgoing circularly polarized (CP) wave. It is constructed by a 2D array of thin cavities, with each cavity etched with three slots. The front slot is used to couple the LP wave into the cavity, while the backside orthogonal slots are utilized to couple the field out of the cavity with the same amplitude and 90° out-of-phase; subsequently, a CP wave is formed at the other side of the converter. As a proof-of-concept, a sample of the proposed converter is fabricated and measured in the microwave regime. Eventually, a perfect CP wave is demonstrated after the LP wave passes through the converter. The proposed linear-to-circular polarization converter features an extremely low insertion loss of around 0.1 dB and a high polarization conversion efficiency of 0.97.

A Tunable Hybrid Metamaterial Reflective Polarization Converter Based on Vanadium Oxide Film

A metamaterial reflective converter with vanadium oxide (VO2) film is investigated in this paper. The results indicate that a broadband polarization conversion ratio (PCR) above 90% is achieved from 4.95 to 9.39 THz and the PCR above 98.9% can be obtained at the three peaks. And the hybrid metamaterial converter is demonstrated for realizing temperature tuned electromagnetic properties. The different temperatures across the insulator-to-metal phase transition of the VO2 film can change the conductivity. Furthermore, the broadband and high-efficiency polarization conversion changes obviously with the temperature changing. In addition, this study demonstrates the application of different temperatures on the performance of the sensor. Moreover, surface current distributions at the resonant frequency are also discussed.

Reciprocal Circular Polarization Handedness Conversion Using Chiral Metamaterials

Chiral metamaterials (CMMs) are widely used to implement devices that transform the polarization of an incident electromagnetic wave, such as polarization rotators and linear to circular converters, but rarely used as circular polarization converters. This letter presents a CMM that changes the handedness of a circularly polarized incident wave. This structure, which presents subwavelength thickness, provides polarization conversion with independence on both the front and back directions and the handedness of the incident wave. High polarization conversion efficiency is shown by both simulations and experiments.

Middle-wave infrared and broadband polarization conversion based on metamaterial

The polarization state is one of the most important basic properties of the electromagnetic wave. Researchers have made great efforts to manipulate it. Control of the polarization state of an electromagnetic wave is a promising promotion for figuring out many practical engineering problems in infrared remote sensing, optical communication and infrared target recognition. In this paper, we propose a wide-band and high-efficient linear-polarization converter on the basis of the metamaterial, which is comprised of silicon nanorod array and subwavelength metal grating that can realize a 90 polarization converter of linearly polarized light and is composed of silicon nanorod array cascade subwavelength metal grating:on one side of design located is the cuboid silicon nanorod array, on the other side of the design the subwavelength metallic grating on the silicon substrate, and the angle between silicon nanorod array and subwavelength metal grating is 45. Because of the deference in geometrical dimension between the long axis and the short axis of the nanorod, results of the equivalent refractive index of the long axis direction and the short axis direction are different, and the anisotropic birefrigent effect is formed. Based on the Jones matrix, the feasibility of polarization converter is described. The polarization converter efficiency and polarization state of the structure are simulated and analyzed by the finite-difference time-domain method. And the variation characteristics of polarization converter transmittance are simulated under several nanorod with different heights and widths. In order to improve the contrast ratio and the transmission, the effective medium theory is used to design the metal grating for improving the transmission. According to the theory of optical thin film, we design the subwavelength metal grating with suitable duty cycle as the anti-reflection coating. The simulation results show that the structure can realize 90 rotation of linearly polarized light, the polarization converter efficiency is greater than 60% in a spectral range of 3.4-4.5 m and the contrast ratio is greater than 104 in a spectral range of 3-5 m. This structure can effectively realize the 90 polarization conversion in the spectral range of medium wave infrared and has the advantages of high conversion efficiency and high contrast ratio. In addition, the range of spectral of polarization conversion can be changed by adjusting the height and width of the nanorod. It can be applied to optical transmission control of optical network and optical information system, because of its excellent optical performance with the advantages of high polarization conversion efficiency and wide band in the mid-infrared waveband and low preparation difficulty.

Design of an Ultrabroadband and High-efficiency Reflective Linear Polarization Convertor at Optical Frequency

A simple design of an ultrabroadband and high-efficiency reflective linear polarization convertor is presented in the optical frequency region. This ultrabroadband convertor is formed from the planar anisotropic metasurface using a meander wire structure. The numerical simulation demonstrates that the polarization conversion ratio over 90% is achieved from 181 to 506 THz, which is equivalent to 94.6% relative bandwidth for y -polarized incident lights under normal incidence. Further simulation results show that the high polarization conversion efficiency can be sustained well when the incident angle increases to 45 ${}^{\circ}$ for both transverse electric (TE) and transverse magnetic (TM) modes. By taking advantage of surface current distribution, the physical mechanisms are elucidated in detail. The further theoretical calculation results based on the interference theory are good agreement with the simualtion. Our design provides a unique approach in realizing the polarization manipulation with high performances in the optical frequency region.

High-efficiency polarization conversion based on spatial dispersion modulation of spoof surface plasmon polaritons.

In this paper, we propose to achieve high-efficiency polarization conversion based on spatial dispersion modulation of spoof surface plasmon polaritons (SSPP). Different k is firstly designed in the two transverse directions by aligning an SSPP-supporting fishbone structure in y direction while maintaining free space in x direction. The orthogonal phase difference is introduced by larger k of SSPP waves for y-polarized component of incident waves. Meanwhile, to achieve high efficiency, gradient k in z-direction is designed so that the y-polarized component of incident waves can be coupled perfectly as SSPP waves. By rotating the fishbone structure with respect to the polarization direction of incident waves, different polarization states for transmitted waves can be realized. As an example, a polarization converter prototype with the central working frequency f = 8GHz was designed, fabricated, and measured. Both the simulation and experiment demonstrate the high-efficiency linear-to-circular (LTC) polarization conversion in 6.9-9.6GHz.

Microwave birefringent metamaterials for polarization conversion based on spoof surface plasmon polariton modes.

We propose the design of wideband birefringent metamaterials based on spoof surface plasmon polaritons (SSPPs). Spatial k-dispersion design of SSPP modes in metamaterials is adopted to achieve high-efficiency transmission of electromagnetic waves through the metamaterial layer. By anisotropic design, the transmission phase accumulation in metamaterials can be independently modulated for x- and y-polarized components of incident waves. Since the dispersion curve of SSPPs is nonlinear, frequency-dependent phase differences can be obtained between the two orthogonal components of transmitted waves. As an example, we demonstrate a microwave birefringent metamaterials composed of fishbone structures. The full-polarization-state conversions on the zero-longitude line of Poincaré sphere can be fulfilled twice in 6–20 GHz for both linearly polarized (LP) and circularly polarized (CP) waves incidence. Besides, at a given frequency, the full-polarization-state conversion can be achieved by changing the polarization angle of the incident LP waves. Both the simulation and experiment results verify the high-efficiency polarization conversion functions of the birefringent metamaterial, including circular-to-circular, circular-to-linear(linear-to-circular), linear-to-linear polarization conversions.

Frequency-Tunable Mid-Infrared Cross Polarization Converters Based on Graphene Metasurface

We have proposed two designs of graphene-enabled cross polarization converters, which are capable of high-efficiency polarization conversion rate and can work equally well for a wide range of incident wave angles. The first type is carefully constructed by an ellipse-shaped graphene sheet printed on a dielectric material backed up by a gold ground plane, while the second one comprises a graphene ring embedded an ellipse resonator. Numerical results demonstrate that the polarization conversion rate of the first polarizer reaches 99.38 % at 22.541 THz when the Fermi energy is fixed at 0.9 eV. The second one can simultaneously work at two frequencies with its polarization conversion rate being 96.74 and 95.88 %, respectively. Therefore, for two devices, the incident linearly polarized beams are almost completely rotated to its orthogonal counterpart after reflection in the mid-infrared spectral range. More importantly, the cross polarization amplitude and resonant frequencies can be dynamically tuned by shifting the Fermi energy without changing the nanostructure, which will exhibit enormous potential applications in photonics field.

Ultra-broadband and high-efficiency polarization conversion metasurface with multiple plasmon resonance modes**Project supported by the National Natural Science Foundation of China (Grant Nos. 61471292, 61331005, 61471388, 51277012, 41404095, and 61501365), the 111 Project, China (Grant No. B14040), the National Basic Research Program of China (Grant No. 2015CB654602), and the China Postdoctoral Science Foundation ( Grant No. 2015M580849).

In this paper, we present a novel metasurface design that achieves a high-efficiency ultra-broadband cross polarization conversion. The metasurface is composed of an array of unit resonators, each of which combines an H-shaped structure and two rectangular metallic patches. Different plasmon resonance modes are excited in unit resonators and allow the polarization states to be manipulated. The bandwidth of the cross polarization converter is 82% of the central frequency, covering the range from 15.7 GHz to 37.5 GHz. The conversion efficiency of the innovative new design is higher than 90%. At 14.43 GHz and 40.95 GHz, the linearly polarized incident wave is converted into a circularly polarized wave.

Dual-band and high-efficiency polarization converter based on metasurfaces at microwave frequencies

We present a dual-band and high-efficiency polarization converter in microwave regime. The proposed converter can convert a linearly polarized wave to its cross-polarized wave for two distinct bands: Ku (11.5–20.0 GHz) and Ka (28.8–34.0 GHz). It can also convert the linearly polarized wave to a circularly polarized wave at four other frequencies. The experimental results are in good agreement with simulation results for both frequency bands. The polarization conversion ratio is above 0.94 for the Ku-band and 0.90 for the Ka-band. Furthermore, the converter can achieve dual-band and high-efficiency polarization conversion over angles of incidence up to 45°. The converter is also polarization-selective in that only the x- and y-polarized waves can be converted. The physical mechanism of the dual-band polarization conversion effect is interpreted via decomposed electric field components that couple with different plasmon resonance modes of the structure.