Tunable wide-angle multi-band mid-infrared linear-to-linear polarization converter based on a graphene metasurface

We present a high-efficiency tunable wide-angle multi-band reflective linear-to-linear (LTL) polarization converter, which is composed of an array of two L-shaped graphene patches with different sizes. In the mid-infrared region, the proposed converter can transform x-polarized wave into y-polarized wave at four resonant frequencies. The polarization conversion ratios of the four bands reach 94.4%, 92.7%, 99.3%, and 93.1%, respectively. By carefully choosing the geometric parameter, triple-band LTL polarization conversion can also be realized. The three polarization conversion ratios reach 91.50%, 99.20%, and 97.22%, respectively. The influence of incident angle on the performances of the LTL polarization converter is investigated, and it is found that our polarization converter shows the angle insensitivity. Also, the dynamically tunable properties of the proposed polarization converter are numerically studied by changing Fermi energy. All the simulation results are conducted by finite element method.     

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.     

Dual-broadband and near-perfect polarization converter based on anisotropic metasurface

A novel dual-broadband and near-perfect reflective polarization converter based on anisotropic metasurface is presented and analyzed in this paper. The unit cell of the proposed converter is composed of a double-cut slotted metallic split-ring and a metallic ground sheet separated by an F4B-2 substrate. Both numerical analysis and measured results demonstrate that the proposed converter has five plasmon resonance frequencies, and can near-completely convert the x- or y-polarized incident wave to its orthogonal counterpart in two frequency bands (9.5–12.9 GHz, 16.1–20.2 GHz). The corresponding polarization conversion ratio is more than 98.3% in the first frequency band and 99.7% in the second one. In addition, the bandwidths and central frequencies of the two frequency bands can be effectively tuned over a wide range by adjusting the geometrical dimensions of the metasurface, while the high conversion efficiency is preserved. The proposed polarization converter may have great potentials in electromagnetic polarization control applications.     

Metamaterial polarization converter analysis: limits of performance

In this paper, we analyze the theoretical limits of a metamaterial-based converter with orthogonal linear eigenpolarizations that allow linear-to-elliptical polarization transformation with any desired ellipticity and ellipse orientation. We employ the transmission line approach providing a needed level of the design generalization. Our analysis reveals that the maximal conversion efficiency for transmission through a single metamaterial layer is 50 %, while the realistic reflection configuration can give the conversion efficiency up to 90 %. We show that a double layer transmission converter and a single layer with a ground plane can have 100 % polarization conversion efficiency. We tested our conclusions numerically reaching the designated limits of efficiency using a simple metamaterial design. Our general analysis provides useful guidelines for the metamaterial polarization converter design for virtually any frequency range of the electromagnetic waves.     

High-Efficiency Wide-Band Cross-Polarization Conversion Using Bi-layered Metal Hole Pairs

We present a polarization converter composed of bi-layered metal films perforated with rectangle hole pairs in each film. The proposed converter can convert the polarization of an incident linearly-polarized electromagnetic wave to its orthogonal direction with high efficiency and large bandwidth in the infrared or microwave regions.To make sure of the mechanism of polarization conversion, the current and electric-field distributions at different resonant frequencies are analyzed. It is found that the cross-polarized transmission is due to the near-field coupling between hole pairs in neighboring metal films. Finally, a prototype of the proposed converter is fabricated and measured in the microwave region. Good agreement between the experimental and simulated results is obtained.     

A reconfigurable terahertz polarization converter based on metal–graphene hybrid metasurface

A metal-graphene hybrid metasurface polarization converter is designed in this Letter.The unit cell of the hybrid metasurface is composed of a butterfly-shaped structure whose branches are connected by multi-layer graphene sheets.The proposed device can be reconfigured from linear-to-circular polarization to cross-polarization by changing the Fermi energy of graphene.The simulation results show that for three-layer graphene,the device acts as a linear-to-circular polarization converter when EF=0 eV and switches to a cross-polarization converter when EF=0.5 eV.Compared with single-layer graphene,the device with three-layer graphene can maintain the cross-polarization conversion performance under low Fermi energy.Furthermore,two equivalent circuits in the x and y directions are developed to understand the working mechanism of the device.     

Generation of radially polarized light beams of high quality using a step-index optical fiber

We present an experimental setup to generate radially polarized beams without using high-cost optical elements. In the setup a four-segment polarization converter is used in front of the fiber to produce a pseudo radially polarized beam. A traditional step-index fiber which supports only LP₀₁ and LP₁₁ modes is then used as a mode-cleaning device. A commercial mechanical fiber-squeezer polarization controller is applied to produce adequate pressure and twist onto the fiber. The four-segment polarization converter and the fiber squeezer polarization controller are adjusted by turns for improving the beam quality in intensity and polarization. Additionally, several methods of characterizing the polarization properties of radially polarized beams are reviewed. One of the latest methods is applied for characterizing the polarization properties of the radially polarized beams produced by using our technique. The results show the highquality of the obtained beams.     

An ultra-broadband and highly-efficient tunable terahertz polarization converter based on composite metamaterial

A near perfect, ultra-broadband and highly-efficient terahertz reflective polarization converter based on multilayer metamaterial is proposed in this paper. The hybrid metamaterial unit structure consists of a split-ring metal pattern and a metal sheet separated by a dielectric resonator spacer. The polarization conversion ratio (PCR) is above 90% from 2.06 to 4.26 THz, with an optimal range between 2.98 and 4.16 THz where the efficiency is above 98% for normal incidence. It also shows excellent performance for oblique incidences. Moreover, the working band and the optimized frequency range for the polarization conversion can be manipulated by changing the open angle between the metallic arcs and the substrate thickness, respectively. Based on this design, two types of hybrid metamaterial converters are also investigated to swith off polarization conversion altogether or modify the polarization conversion bandwidth. A polarization converter with temperature controlled PCR is realized by adding a vanadium oxide (VO₂) mask on the designed structure. In addition, by integrating photoconductive silicon islands between the split-ring and metal bar a dual-band polarization converter can be realized. Combining with a polarizer, this window can act as an active THz filter.     

Proposition of Single Molecular Orientation Determination Using polarization Controlled Beam by Liquid Crystal Spatial Light Modulators

We have proposed a method to control the three-dimensional electric field in the focus of an optical microscope using two non-twisted liquid crystal spatial light modulators, and to detect the molecular orientation of a single molecule. The three-dimensional electric field is generated by focusing the beam with two dimensional spatial distribution of polarization. The possibility of detection of three-dimensional single molecular orientation was shown by numerical calculations. © 2005 The Optical Society of Japan     

Design of a new thin-film electro-optic switch

A new thin-film electro-optic switch employing two stable states of polarization is proposed and investigated. The design can be further employed to realize a TE-TM polarization converter by constructing a Mach-Zehnder type interferometer integrated optical switch. The limitations and design procedures for electro-optic devices are also discussed.     

Nonlinear polarization conversion using microring resonators

We present a design of a polarization converter between linear, circular, and elliptic accomplished with an on-chip high-Q dielectric microring resonator. Nonlinear polarization switching can be accomplished at modest input intensities because of the high-intensity compression in the ring. We predict an optical bistability effect making the polarization of the transmitted light dependent on its spectral or intensity history.     

Three-dimensional polarization control in microscopy

We propose an approach to optical microscopy that enables full control over the three-dimensional polarization vector at the focal spot of a high-numerical-aperture lens. The input field to the lens is linearly polarized and no polarization optics are needed. This technique utilizes the azimuthal spatial degree of freedom of the input field. We find that only a small set of low-order azimuthal spatial harmonics contributes to the focused field on axis, and a simple transformation exists between the linear vector space of these harmonics and the three-dimensional polarization-vector space. Controlling the relative complex weights of these azimuthal harmonics produces any desired three-dimensional state of polarization.     

Analysis of polarization conversion in AlGaAs/GaAs electrooptic polarization converter

A numerical simulation study of the polarization conversion phenomenon in deeply etched semiconductor electrooptic polarization converter is presented. Based on a powerful and versatile finite element method, the effects of various parameters on the polarization conversion in electrooptic semiconductor polarization converter are reported.     

The Imbert-Fedorov shift of paraxial light beams

We present a solution to the problem of reflection and transmission of a polarized paraxial light beam at an interface between two homogeneous media by using a two-form amplitude and an extension matrix to represent the vectorial angular spectrum of a three-dimensional (3D) light beam. We derive general formulas for the Imbert-Fedorov (IF) shift of the reflected and transmitted beams of a polarized paraxial light beam. The IF shift of two different types of polarized beams is calculated, and the influence of the polarization state and the polarization feature of the vectorial angular spectrum on the IF shift is discussed.     

Whispering gallery mode microresonators as polarization converters

A ring resonator coupled to a waveguide can be used as a highly efficient polarization converter when the input is properly polarized. We model this phenomenon and verify the predictions with a demonstration of very efficient polarization conversion (>90%) on a silica microsphere coupled to a tapered optical fiber.     

脉冲式可控偏振态变换器及其应用

本文提出一种基于晶体双折射效应的脉冲式可控偏振态变换器,可以实现偏振光六个偏振分量的脉冲变换.将它应用于偏振型光传感信号的单光路分时检测,可以提高信号检测灵敏度和传感信号的抗干扰能力.文中给出了利用铌酸锂晶体和脉冲电场对光传感信号的X、Y线性偏振分量进行脉冲变换的实验结果.     

基于狄拉克半金属的可调谐的太赫兹宽频带纯线偏振转换器

本文基于新型材料狄拉克半金属(Dirac semimetals,DSs),设计了一款高纯度宽频带可调谐线偏振转换器,偏振转换率(PCR)超过99%的相对带宽为15.72%。在频段5.25~6.14 THz内,椭度角接近0°,偏振方位角约等于-90°。这种转换性能主要是源于顶层超表面的各向异性和局域的表面等离子体激元谐振(LSPRs)的激发。此外,通过改变费米能的大小可以使所设计的偏振转换器在不同的频带范围内实现宽频带偏振转换。最后,通过半解析的方法对偏振转换特性进行了理论分析。该设计在太赫兹通信、成像、无损检测等领域具有一定的应用价值,同时为宽频带可调谐太赫兹线偏振转换器的设计提供了新思路。     

Wideband linear-to-circular polarization conversion realized by a transmissive anisotropic metasurface

We propose a metasurface which consists of three conductive layers separated by two dielectric layers. Each conductive layer consists of a square array of square loop apertures, however, a pair of corners of each square metal patch surrounded by the square loop apertures have been truncated, so it becomes an orthotropic structure with a pair of mutually perpendicular symmetric axes u and v. The simulated results show that the metasurface can be used as a wideband transmission-type polarization converter to realize linear-to-circular polarization conversion in the frequency range from12.21 GHz to 18.39 GHz, which is corresponding to a 40.4% fractional bandwidth. Moreover, its transmission coefficients at x-and y-polarized incidences are completely equal. We have analyzed the cause of the polarization conversion, and derived several formulas which can be used to calculate the magnitudes of cross-and co-polarization transmission coefficients at y-polarized incidence, together with the phase difference between them, based on the two independent transmission coefficients at u-and v-polarized incidences. Finally, one experiment was carried out, and the experiment and simulated results are in good agreement with each other.     

Application of a fully vectorial beam propagation method

A new vectorial beam propagation method has successfully been applied to a passive polarization splitter and a passive polarization converter on InGaAsP/InP. The propagating fields are calculated and the power attenuation is evaluated. The calculated crosstalk values of the splitter are in good agreement with the realized best performance. A complete polarization conversion in the converter has also been simulated. This revised version was published online in November 2006 with corrections to the Cover Date.     

Circular polarization converters based on bi-layered asymmetrical split ring metamaterials

In this paper, a kind of bi-layered asymmetrical split ring metamaterial was proposed as a circular polarization converter. Simulations and experiments at the microwave regime showed that the proposed structures can achieve the conversions from right-handed circularly polarized electromagnetic waves to left-handed ones and the reversed conversions in the opposite propagating direction. The linear to circular polarization transmission coefficients and the surface currents were investigated to understand the mechanism of the circular polarization conversions. Moreover, we optimized the proposed metamaterials by increasing the distance between the two metal layers. The proposed circular polarization converters have applications in microwave wave plates and metamaterial antennas.