Dual-band Circular Polarizer Based on Simultaneous Anisotropy and Chirality in Planar Metamaterial

Abstract

Metamaterial of dual-square array is proposed to design a dual-band circular polarizer. The novel design of asymmetric unit cell and layout of duplicate arrays significantly enhances the coupling between electric and magnetic fields. Simulation and measurement results show that the polarizer presents wide angle circular dichroism and circular birefringence. Moreover, the polarization conversion of the proposed metamaterial changes with frequency, incident angle, and polarization of incident waves. The fundamental mechanism behind is concluded to be the angle-dependent chirality and dispersion of our novel design.In recent years, metamaterials have been studied intensively for their special electromagnetic properties which are inexistent in natural materials. Application-oriented metamaterials' effective permittivity and permeability 1,2 can be designed for some amazing functions such as invisible cloaking 3 , diffraction-limit breaking imaging 4,5 and perfect lens 6 .Recently, metamaterials have been used to manipulate polarization of electromagnetic waves 7-11 , for example, circular dichroism (CD) and circular birefringence (CB). One of the critical points behind polarization manipulation by using metamaterials is thought to be the artificial chirality. Chirality in metamaterials results in cross-coupling between electric and magnetic fields.Prominent chiral metamaterials with circularly polarized eigenmodes 12-25 include twisted U-shape split ring resonators and twisted complementary split ring resonators. However, the working bandwidth of the polarization rotator based on these metamaterials is relatively narrow. To broaden bandwidth, an infrared broadband circular polarizer with periodic gold helix structure has been proposed 12 . It is later scaled down to microwave 13 and terahertz 14 region. Unfortunately, the thickness of the polarizers studied in 12-14 is of the order of the resonant wavelength so that it is hard to integrate them. Some approaches [15][16][17][18] to miniaturize the structure to subwavelength thickness have been proposed.In this paper, metamaterial of dual-square array is proposed to design a dual-band circular polarizer. Compared with previous designs [25][26][27] , the proposed structure is simpler. It transforms incident linearly polarized wave into left/right-handed circularly polarized wave at two resonant frequencies. The differences of transformation between left-handed circular polarization (LCP) and right-handed circular polarization (RCP) waves are more than 15 dB at both resonant frequencies. Design PrincipleInspired by the original multiband chiral metamaterial of twisted arc structure 24 , a dual-band circular polarizer with two aligned identical square arrays of periodicity p separated by a dielectric slab of thickness h is proposed in this paper. Two aligned unit cells of the arrays are shown in Fig. 1 while the configuration of arrays is shown in Fig. 2. In each unit cell, a centered PEC circle of radius R and width w is broken into two arcs at angle φ 1 with an angle g...

Linear and Circular Dichroism in Graphene-Based Reflectors for Polarization Control

“…It is worth mentioning that other contemporary metasurfaces also demonstrate similar polarizationconversion capabilities in the electromagnetic spectrum [8][9][10][11]. The real strength of the proposed graphene merascreen is its property of reconfigurability, which allows the optical spectrum to be electro-optically tuned.…”

“…Therefore, there is a vital requirement for an opticalpolarization-control method to be passive (unlike Faraday rotation) and low profile, so that device integration at subwavelength scale can be achieved. Taking these practical bounds into account, electromagnetic metasurfaces have been suggested as efficient polarization-control alternatives [8][9][10][11][12][13]. Metasurfaces have also been designed at microwave, terahertz (THz), and optical frequencies for various other applications ranging from perfect absorbers [14][15][16] to sensors [17,18], thermal emitters [19], and imaging devices [20,21].…”

“…The subwavelength size of the unit cell in the case of metasurfaces is essential for neardiffraction-limit imaging and wide-angle beam-steering applications [22,23]. These thin-film metasurfaces are designed using metallic radiating elements to manipulate electromagnetic waves [9][10][11][12][13][24][25][26]. The planar twodimensional (2D) metasurface counterparts of the traditional polarizers are relatively easier to design, fabricate, and characterize.…”

Evaluation of Selected Metasurfaces’ Sensitivity to Planar Geometry Distortions

“…Various field transformations of arbitrary incident fields can be achieved [6]. Metamaterials and their planar versions (metasurfaces (MS)) can potentially find applications in telecommunications [7,8], measuring systems [9,10], selective absorbing structures [11][12][13][14], polarizers [6,15,16], surface wave control devices [6], and imaging systems (for lensing electromagnetic waves) [17][18][19], or in many others that we do not know yet.…”

Quasi-Crystal Metasurface for Simultaneous Half- and Quarter-Wave Plate Operation

“…Anisotropic metasurfaces are generally used for polarization conversion of EM waves 23 – 32 . The chiral metasurfaces achieve linear and circular polarization conversion in microwave 33 – 39 , THz 40 – 43 , and visible 44 – 46 frequency regimes. In recent years, reconfigurable metasurfaces have gained special interest because of their wide band polarization conversion and tunable operation 47 – 49 .…”