Showing papers on "Circular polarization published in 2021"
TL;DR: In this article, the authors used chiral-induced spin selectivity (CISS) to produce spin-polarized carriers and demonstrated a spin-LED that operates at room temperature without magnetic fields or ferromagnetic contacts.
Abstract: In traditional optoelectronic approaches, control over spin, charge, and light requires the use of both electrical and magnetic fields. In a spin-polarized light-emitting diode (spin-LED), charges are injected, and circularly polarized light is emitted from spin-polarized carrier pairs. Typically, the injection of carriers occurs with the application of an electric field, whereas spin polarization can be achieved using an applied magnetic field or polarized ferromagnetic contacts. We used chiral-induced spin selectivity (CISS) to produce spin-polarized carriers and demonstrate a spin-LED that operates at room temperature without magnetic fields or ferromagnetic contacts. The CISS layer consists of oriented, self-assembled small chiral molecules within a layered organic-inorganic metal-halide hybrid semiconductor framework. The spin-LED achieves ±2.6% circularly polarized electroluminescence at room temperature.
202 citations
TL;DR: In this paper, an all-in-one full Poincare sphere polarizer was designed based on perfect arbitrary polarization conversion dichroism and implemented in a monolayer all-dielectric metasurface.
Abstract: The control of polarization, an essential property of light, is of broad scientific and technological interest. Polarizers are indispensable optical elements for direct polarization generation. However, arbitrary polarization generation, except that of common linear and circular polarization, relies heavily on bulky optical components such as cascading linear polarizers and waveplates. Here, we present an effective strategy for designing all-in-one full Poincare sphere polarizers based on perfect arbitrary polarization conversion dichroism and implement it in a monolayer all-dielectric metasurface. This strategy allows preferential transmission and conversion of one polarization state located at an arbitrary position on the Poincare sphere to its handedness-flipped state while completely blocking its orthogonal state. In contrast to previous methods that were limited to only linear or circular polarization, our method manifests perfect dichroism of nearly 100% in theory and greater than 90% experimentally for arbitrary polarization states. By leveraging this attractive dichroism, our demonstration of the generation of polarization beams located at an arbitrary position on a Poincare sphere directly from unpolarized light can substantially extend the scope of meta-optics and dramatically promote state-of-the-art nanophotonic devices.
87 citations
TL;DR: In this article, a switchable bi-functional metamaterial device based on a hybrid gold-vanadium dioxide (VO2) nanostructure was proposed, which can be thermally switched for circularly polarized light in the near-infrared region.
Abstract: In this paper, we propose a switchable bi-functional metamaterial device based on a hybrid gold-vanadium dioxide (VO2) nanostructure. Utilizing the property of a metal-to-insulator transition in VO2, perfect absorption and asymmetric transmission (AT) can be thermally switched for circularly polarized light in the near-infrared region. When VO2 is in the metallic state, the designed metamaterial device behaves as a chiral-selective plasmonic perfect absorber, which can result in an optical circular dichroism (CD) response with a maximum value ∼ 0.7. When VO2 is in the insulating state, the proposed metamaterial device exhibits a dual-band AT effect. The combined hybridization model and electromagnetic field distributions are presented to explain the physical mechanisms of chiral-selective perfect absorption and AT effect, respectively. The influences of structure parameters on CD response and AT effect are also discussed. Moreover, the proposed switchable bi-functional device is robust against the incident angle for obtaining perfect absorption and strong CD response as well as the AT effect. Our work may provide a promising path for the development of multifunctional optoelectronic devices, such as thermal emitters, optical modulators, CD spectroscopy, optical isolator, etc.
78 citations
TL;DR: In this article, the state-of-the-art development of the strategies that induce the linear or circular polarization characteristics of halide perovskites is systematically reviewed, based on which the application of polarization-sensitive HPs in the field of polarization luminescence and detection are summarized, and current challenges and opportunities are discussed, and prospects of the future development in this promising field are outlined.
Abstract: While halide perovskites (HPs) have achieved enormous success in the field of optoelectronic applications, much attention has been recently drawn to the unique polarization sensitivity of HPs, either intrinsic or extrinsic, which makes HPs a potential candidate for innovative applications in directly polarized luminescence and detection. Herein, the research status in the field of polarization-sensitive HPs, including linear polarization and circular polarization, is comprehensively summarized. To evaluate the effectiveness of HPs in generating and detecting linearly or circularly polarized light, the principles and characterization methods of polarized luminescence and detection are introduced. Sequentially, the state-of-the-art development of the strategies that induce the linear or circular polarization characteristics of HPs is systematically reviewed, based on which the application of polarization-sensitive HPs in the field of polarization luminescence and detection are summarized. Moreover, the current challenges and opportunities are discussed, and prospects of the future development in this promising field are outlined.
70 citations
TL;DR: In this article, a low-profile broadband planar circularly polarized folded transmitarray antenna (CPFTA) based on well-designed top and bottom metasurfaces (MSs) is proposed.
Abstract: We propose a low-profile broadband planar circularly polarized folded transmitarray antenna (CPFTA) based on well-designed top and bottom metasurfaces (MSs). The top MS is employed to reflect the $x$ -polarized wave as a ground and, at the same time, to convert the $y$ -polarized wave into circularly polarized waves with arbitrary phase shifts in the operation band. A bottom MS is applied to reflect the incident wave and twist its polarization by 90°. The whole CPFTA, including the feeding source of microstrip antenna, and the top and bottom MSs can be fully integrated and fabricated using low-cost printed circuit board technology. Both simulated and measured results demonstrate significant advantages of the proposed antenna, including broad bandwidth, high gain, lower profile, planar geometry, and easy integration. The fabricated sample shows 3 dB axial ratio (AR) bandwidth of 23.2%, 3 dBi gain bandwidth of 11.6%, and the maximum gain of 22.8 dBi at 10.3 GHz with the antenna efficiency of 21.8%. The proposed CPFTA is promising for applications in satellite communications with circularly polarized antennas.
68 citations
TL;DR: In this article, the second harmonic generation circular dichroism (SHG-CD) was developed in bulk single crystals of chiral one-dimensional (1D) [(R/S)-3-aminopiperidine]PbI4.
Abstract: The introduction of chirality into organic-inorganic hybrid perovskites (OIHPs) is expected to achieve excellent photoelectric and nonlinear materials related to circular dichroism. Owing to the existence of asymmetric center and intrinsic chirality in the chiral OIHPs, the different efficiencies of second harmonic generation (SHG) signal occurs when the circularly polarized light (CPL) with different phases passes through the chiral crystal, which is defined as second harmonic generation circular dichroism (SHG-CD). Here, the SHG-CD effect is developed in bulk single crystals of chiral one-dimensional (1D) [(R/S)-3-aminopiperidine]PbI4 . It is the first time that CPL is distinguished using chirality-dependent SHG-CD effect in OIHPs bulk single crystals. Such SHG-CD technology extends the detection range to near infrared region (NIR). In this way, the anisotropy factor (gSHG-CD ) through SHG-CD signal is as high as 0.21.
65 citations
TL;DR: In this article, a scalable bottom-up approach to construct cross-stacked nanoparticle chain arrays that have a circular dichroism of up to 11° was described, which can be fully controlled by mechanical compression and stack rotation.
Abstract: Dynamic control of circular polarization in chiral metasurfaces is being used in many photonic applications. However, simple fabrication routes to create chiral materials with considerable and fully tunable chiroptical responses at visible and near-infrared wavelengths are scarce. Here, we describe a scalable bottom-up approach to construct cross-stacked nanoparticle chain arrays that have a circular dichroism of up to 11°. Due to their layered design, the strong superchiral fields of the inter-layer region are accessible to chiral analytes, resulting in a tenfold enhanced sensitivity in a chiral sensing proof-of-concept experiment. In situ restacking and local mechanical compression enables full control over the entire set of circular dichroism characteristics, namely sign, magnitude and spectral position. Strain-induced reconfiguration opens up an intriguing route towards actively controlled pixel arrays using local deformation, which fosters continuous polarization engineering and multi-channel detection. Stacked elastomeric arrays containing plasmonic nanoparticles show efficient chiral responses that can be fully controlled by mechanical compression and stack rotation. These simple layered materials may be useful modulators for photonic applications.
59 citations
01 Aug 2021
53 citations
TL;DR: In this paper, a plasmonic chiral metasurface absorber (CMSA) was proposed to achieve high selective absorption for right-handed and left-handed circular polarization (RCP, +, and LCP, −) lights at optical frequency.
Abstract: In this paper, we present a plasmonic chiral metasurface absorber (CMSA), which can achieve high selective absorption for right-handed and left-handed circular polarization (RCP, “+”, and LCP, “−”) lights at optical frequency. The CMSA is composed of a dielectric substrate sandwiched with bi-layer fourfold twisted semicircle metal nanostructure. The proposed CMSA has a strong selective absorption band, where absorption peaks for LCP and RCP lights occur at different resonance frequencies, reflecting the existence of a significant circular dichroism (CD) effect. It is shown that the absorbance of the CMSA can reach to 93.2% for LCP light and 91.6% for RCP light, and the maximum CD magnitude is up to 0.85 and 0.91 around 288.5 THz and 404 THz, respectively. The mechanism of the strong chiroptical response of the CMSA is illustrated by electric fields distributions of the unit-cell nanostructure. Furthermore, the influence of the geometry of the proposed CMSA on the circular polarization selective absorption characterization is studied systematically.
50 citations
TL;DR: In this paper, a general method to address broadband full-polarization properties of diffracted fields using an original superposition of circular polarization beams transmitted through metasurfaces is presented.
Abstract: Any arbitrary state of polarization of light beam can be decomposed into a linear superposition of two orthogonal oscillations, each of which has a specific amplitude of the electric field. The dispersive nature of diffractive and refractive optical components generally affects these amplitude responses over a small wavelength range, tumbling the light polarization properties. Although recent works suggest the realization of broadband nanophotonic interfaces that can mitigate frequency dispersion, their usage for arbitrary polarization control remains elusively chromatic. Here, we present a general method to address broadband full-polarization properties of diffracted fields using an original superposition of circular polarization beams transmitted through metasurfaces. The polarization-maintaining metasurfaces are applied for complex broadband wavefront shaping, including beam deflectors and white-light holograms. Eliminating chromatic dispersion and dispersive polarization response of conventional diffractive elements lead to broadband polarization-maintaining devices of interest for applications in polarization imaging, broadband-polarimetry, augmented/virtual reality imaging, full color display, etc.
42 citations
TL;DR: In this article, a mono-layer metamaterial comprising four graphenestrips and one graphene-square ring is proposed to realize triple plasmon-induced transparency (PIT), and theoretical results based on the coupled mode theory are in agreement with the simulation results obtained using the finite-difference time-domain (FDTD).
Abstract: A mono-layer metamaterial comprising four graphene-strips and one graphene-square-ring is proposed herein to realize triple plasmon-induced transparency (PIT). Theoretical results based on the coupled mode theory (CMT) are in agreement with the simulation results obtained using the finite-difference time-domain (FDTD). An optical switch is investigated based on the characteristics of graphene dynamic modulation, with modulation degrees of the amplitude of 90.1%, 80.1%, 94.5%, and 84.7% corresponding to 1.905 THz, 2.455 THz, 3.131 THz, and 4.923 THz, respectively. Moreover, the proposed metamaterial is insensitive to the change in the angle of polarized light, for which the triple-PIT is equivalent in the cases of both x- and y-polarized light. The optical switch based on the proposed structure is effective not only for the linearly polarized light in different directions but also for left circularly polarized and right circularly polarized light. As such, this work provides insight into the design of optoelectronic devices based on the polarization characteristics of the incident light field on the optical switch and PIT.
TL;DR: In this article, a tunable terahertz circular-polarization (CP) convertor based on graphene metamaterial is proposed and investigated numerically and theoretically, which is composed of a subwavelength metal grating sandwiched with bi-layered complementary-oval-shaped (COS) graphene array sheet separated by a dielectric spacer.
TL;DR: In this article, a broadband and wide-angle scanning linear polarization (LP-to-circular polarization) converter based on a dual-layer structure is presented, which can be integrated into any LP antenna system to generate CP without significantly affecting the antenna performances.
Abstract: A broadband and wide-angle scanning linear polarization (LP)-to-circular polarization (CP) converter based on a dual-layer structure is presented. The elementary cell is composed of conventional Jerusalem crosses (JCs). The design procedure is based on transmission line circuit model and on full-wave simulations. The proposed equivalent circuit has been generalized to include the oblique incidence in the model. Simulated results demonstrate a 24% axial ratio bandwidth for an incidence angle $\theta = \pm 50^{\circ }$ in both x z and y z planes. The proposed converter provides a unique combination of wide bandwidth, thin profile, and stable response with respect to the angle of incidence. It can be integrated into any LP antenna system to generate CP without significantly affecting the antenna performances.
TL;DR: The results show that the proposed CA is polarization and 3-D orientation insensitive and provides good MIMO properties, which makes it a suitable choice to transfer high data rate to an external antenna of diverse polarization.
Abstract: This article presents a first of its kind, coplanar waveguide (CPW)-fed 3-D multi-input-multi-output (MIMO) ground radiating cubic antenna (CA), implantable in the human upper arm for biotelemetry applications. The four antenna elements are circular in shape and loaded with a pair of slots to obtain circular polarization (CP). It excites diversified CP radiation in Industrial, Scientific, and Medical (ISM) band 2.45 and 5.8 GHz in orthogonal space to establish communication between the human body moving in random directions and base-station. The overall dimensions of the proposed antenna are $15\,\, {\times }\,\,15\,\, {\times }\,\,15$ mm3. Monitoring circuit PCB is placed at the top, and the bottom side of the cube and central hollow space is filled with a dry solid phantom for impedance matching. The CA is simulated in the vicinity of the canonical arm tissue model in HFSS software and examined in a realistic human model. The far-field gain is −18.5 dB with −32 dB isolation between elements. The CA is fabricated, and measurements are carried out in skin-fat-muscle phantom and minced pork. Simulated results closely match with measured results. The results show that the proposed CA is polarization and 3-D orientation insensitive and provides good MIMO properties. The low SAR value of the CA allows maximum transmit power of 5.81 mW, makes it a suitable choice to transfer high data rate (200 Mb/s) to an external antenna of diverse polarization. These features make CA an attractive solution for real-time healthcare applications.
TL;DR: In this article, a structural colored 3D shaped beetle is fabricated using molding, which reflects both left and right-handed circularly polarized light and shows reversible, temperature responsive structural color and 3D shape changes.
Abstract: Cholesteric liquid crystals (CLCs) are chiral photonic materials reflecting only circularly polarized light with the same handedness as the helical polymer structure. Concurrent shape and color changes can be achieved using CLCs, but the fabrication of CLCs with switchable 3D shape, structural color, and hyper-reflectivity, that is, reflecting both left- and right-handed circularly polarized light simultaneously, has not yet been achieved. Here, CLC elastomer (CLCE) actuators are reported to reflect equal amounts of left- and right-handed circularly polarized light. Hyper-reflectivity is achieved by uniaxially stretching the partially crosslinked film to induce helix deformation which is then fully crosslinked to fix the deformed helical structure. The shape, structural color, and hyper-reflectivity of the polymer film are switchable with temperature. At high temperatures, only right-handed circularly polarized light is reflected and the color is redshifted. The film can be shaped in three dimensions: a structural colored 3D shaped beetle is fabricated using molding, which reflects both left- and right-handed circularly polarized light and shows reversible, temperature responsive structural color and 3D shape changes. Hence, 4D engineered bioinspired multifunctional materials are fabricated, which are interesting for applications ranging from sensing actuators to switchable hyper-reflective films and objects.
TL;DR: In this article, a compact size wideband circularly polarized (CP) 2-port multiple-input-multiple-output (MIMO) antenna is designed for the fifth generation (5G) region under the sub-6 GHz band.
Abstract: A compact size wideband circularly polarized (CP) 2-port multiple-input-multiple-output (MIMO) antenna is designed for the fifth generation (5G) region under the sub-6 GHz band The presented antenna has (≤ − 10 dB) impedance bandwidth of 900 MHz (33–42 GHz) and has 100% 3-dB axial ratio bandwidth The antenna covers the potential 5G band ranging from 33 to 38 GHz having left-handed circular polarization characteristics To validate performance attributes of the MIMO antenna designed various diversity parameters such as envelope correlation coefficient (ECC), total active reflection coefficient, and diversity gain are calculated The low envelope correlation coefficient (ECC < 010) and the isolation between the antenna elements greater than 15 dB justify the acceptance of the proposed design as a MIMO antenna The proposed design exhibits good agreement between the simulated and the measured results
TL;DR: In this paper, a low profile and broadband metasurface antenna is proposed for circular polarization radiation, where two characteristic modes with the same resonant frequencies and orthogonal current distributions are chosen as operation modes.
Abstract: A low-profile and broadband metasurface antenna is proposed for circular polarization radiation. The metasurface is an array of subwavelength square patches. The modal behaviors of the proposed metasurface are investigated by using the characteristic mode theory. Two characteristic modes with the same resonant frequencies and orthogonal current distributions are chosen as operation modes. Furthermore, a hybrid feed system consisting of a cross-slot and a microstrip line is employed to excite the two orthogonal modes having a 90° phase difference to obtain circular polarization radiation. Based on these concepts, an antenna with low profile of $0.07{\lambda _0}$ ( ${\lambda _0}$ is the free-space wavelength at an operation frequency of 5.5GHz) is designed. The measurement results show that the proposed antenna has −10 dB impedance bandwidth of 4.8–6.35 GHz and 3 dB axial-ratio bandwidth of 4.85–6 GHz. Moreover, the antenna gain is 6.8–9.7 dBic in the whole axial-ratio bandwidth.
TL;DR: In this article, an anomalous nonlinear optical response of the prototypical three-dimensional topological insulator bismuth selenide through the process of high-order harmonic generation was observed.
Abstract: We report the observation of an anomalous nonlinear optical response of the prototypical three-dimensional topological insulator bismuth selenide through the process of high-order harmonic generation. We find that the generation efficiency increases as the laser polarization is changed from linear to elliptical, and it becomes maximum for circular polarization. With the aid of a microscopic theory and a detailed analysis of the measured spectra, we reveal that such anomalous enhancement encodes the characteristic topology of the band structure that originates from the interplay of strong spin-orbit coupling and time-reversal symmetry protection. The implications are in ultrafast probing of topological phase transitions, light-field driven dissipationless electronics, and quantum computation.
TL;DR: In this article, a coplanar waveguide (CPW) feed structure with a modified inverted L-shaped radiating patch is presented, and a single-layer non-uniform frequency selective surface (FSS) composed of rectangular conductive patches is designed and used with the CP antenna to improve the CP characteristics and the gain of the antenna.
Abstract: This paper presents a new ultra-wideband (UWB) antenna system with circular polarization (CP). The antenna is a coplanar waveguide (CPW) feed structure with a modified inverted L-shaped radiating patch. A single-layer non-uniform frequency selective surface (FSS) composed of rectangular conductive patches is designed and used with the CP antenna to improve the CP characteristics and the gain of the antenna. According to the measured results, the 10 dB return-loss bandwidth of the antenna with the FSS extends from 3.7 to 11.1 GHz. The 3-dB measured axial ratio (AR) bandwidth is 58.15%, covering 5 to 9.1 GHz, and the measured peak gain is 4–9.4 dBi, showing an increase of about 3 dBi compared to theantenna without the FSS.
TL;DR: In this paper, a thermally switchable terahertz metamaterial absorber consisting of an array of orthogonal coupled split-ring metal resonators involving a VO2 phase transition was designed and demonstrated.
Abstract: We design and demonstrate a thermally switchable terahertz metamaterial absorber consisting of an array of orthogonal coupled split-ring metal resonators involving a VO2 phase transition. Numerical results indicate that the active metamaterial always absorbs the TE wave in dual-band regardless of insulating and metallic VO2, while the insulator-to-metal phase transition enables a switchable effect between dual-band and broadband absorption of the TM wave with the resonant frequency tunability of 33%. Especially under the metallic VO2 state, the absorption properties are polarization-dependent and exhibit a switching effect between dual-band and broadband absorption with the increase of the polarization angle. The tunable absorption mechanism can be explained by effective impedance theory and electric energy density distributions. The proposed dual-band to broadband metamaterial switching absorber may have broad applications in sensors, imaging and emitters.
TL;DR: In this article, the authors present a 1024-element planar phased-array system with high EIRP for Ku-band satellite communication (SATCOM) mobile transmitter terminals.
Abstract: This article presents a 1024-element Ku-band phased-array transmitter for mobile satellite communications. The array is based on eight-channel transmit (TX) SiGe beamformer chips. Dual-polarized stacked-patch antennas enable the array to synthesize linear, rotated-linear, and left- and right-hand circular polarization. The array consists of four quadrants of 256-element subarrays, each of which has 64 beamformer chips and a driver chip assembled on a printed circuit board (PCB). The array achieves an effective isotropic radiated power (EIRP) of 75 dBm per polarization (78-dBm circular polarization) and scans to ±75° in all planes. This is achieved using an antenna spacing of $\lambda $ /2 at 14.4 GHz in an equilateral triangular grid. The array also results in 30-dB cross-polarization rejection up to 60° scan angles. Measured error vector magnitude (EVM) for 50-, 100-, 200-, and 500-MBd QPSK and 8 phase-shift keying (8PSK) waveforms results in at most 1.5%rms and 2.5%rms at $P_{1\textrm {dB}}$ and $P_{\mathrm{ sat}}$ , respectively, at 14 GHz over all scan angles. Also, the adjacent channel power ratio (ACPR) was measured as −32 dB for 200- and 500-MBd QPSK and 8 phase-shift keying (8PSK) waveforms at $P_{1\textrm {dB}}$ at 14 GHz. To the authors’ knowledge, this work presents a state-of-the-art planar phased-array system with high EIRP for Ku-band satellite communication (SATCOM) mobile transmitter terminals.
TL;DR: In this article, a concentric circle compound reconfigurable (frequency, polarization, and pattern) microstrip antenna for lower-S band (2.0-3.0 GHz) applications is presented.
Abstract: The article presents a concentric circle compound reconfigurable (frequency, polarization, and pattern) microstrip antenna for lower-S band (2.0 GHz-3.0 GHz) applications. Varying the capacitance of four varactor diodes from 4.15pF (0 V) to 0.94pF (6 V), the resonant frequency of the antenna can be tuned from 2.10 GHz to 2.90 GHz (34.52% tunable bandwidth). These diodes are incorporated to bridge the gap between the circle and ring of concentric geometry. The arc slots and C-shape wings are used for polarization and pattern reconfiguration, respectively. The arc slots are etched from the edge of circle geometry and loaded with RF PIN diodes to provide the different polarization states: linear polarization, left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP). Simultaneously, the pattern reconfigurability can be attained with C-shape wings, placed around the concentric circle geometry; hence, patterns are tilt at 0 ° and ± 50 ° . The pattern reconfigurability also controlled through the RF PIN diodes. The designed antenna is experimentally verified and shows the maximum gain of 4.31 dBic and 4.04 dBi in polarization and pattern reconfigurable mode, respectively. Besides, it provides an excellent axial ratio ( 3 dB) and stable radiation patterns. Therefore, the proposed compound reconfigurable antenna can be served for a future communication system and improves the signal quality without any destruction.
TL;DR: In this article, a compact low-profile reconfigurable metasurface (MTS) antenna is presented, which consists of a 3 × 3 square MTS, a ring-shaped pixel structure, a square microstrip patch, a metal ground plane and a simple feeding network.
Abstract: A compact low-profile reconfigurable metasurface (MTS) antenna is presented in this letter, occupying an overall size of 0.65λ0 × 0.65λ0 × 0.067λ0. The proposed antenna is mainly composed of a 3 × 3 square MTS, a ring-shaped pixel structure, a square microstrip patch, a metal ground plane, and a simple feeding network. Through the characteristic mode analysis, two orthogonal degenerate modes are excited to realize the reconfigurable two linear polarizations and one circular polarization (CP). Furthermore, by loading an annular pixel structure around the MTS, the designed antenna can produce the steerable beam directions of ±40° with horizontal polarization, ±20° with vertical polarization, and ±25° with CP in the yz plane. Due to the symmetry of the layout, polarization and pattern diversities can also be realized in the xz plane. The proposed reconfigurable antenna is manufactured and measured to demonstrate the proposed design. The measured results show that the designed antenna acquires polarization and pattern diversities in C -band at the center frequency of 5 GHz, and the test results generally are in consistent with the simulation ones, which demonstrates the superiority of the proposed antenna.
TL;DR: In this paper, the authors proposed that the FeClBr monolayer is a ferromagnetic semiconductor with spontaneous valley polarization owing to the combined effect of magnetic exchange interaction and spin-orbit coupling effect.
Abstract: The valley degrees of freedom of Bloch electrons provide a proper platform to realize information storage and processing. Using first principles calculations, we propose that the FeClBr monolayer is a ferromagnetic semiconductor with spontaneous valley polarization owing to the combined effect of magnetic exchange interaction and spin–orbit coupling effect. The FeClBr monolayer shows perpendicular magnetic anisotropy, a high Curie temperature of 651 K and a large valley splitting of 188 meV, which are beneficial for the practical applications in valleytronics. Then, the anomalous valley Hall effect can be realized under an in-plane electrical field due to the valley-contrasting berry curvature. According to the optical selectivity rule, the different valleys at K and K− points in momentum space can be excited by the circularly polarized light in honeycomb structures; however, the FeClBr monolayer can also respond to the linear light. Therefore, the valley degree of freedom of the FeClBr monolayer can be modulated by circularly polarized light, linear light and hole doping. Our work enriches the library of valley materials and provides a candidate for the study of spintronics and valleytronics field.
TL;DR: In this paper, a multifunctional metasurface (MFMS) based on graphene and photosensitive silicon (Si) is proposed, which integrates three functions: broadband absorption, broadband linear and circular polarization conversions in the THz band.
Abstract: With the development of metasurfaces and the improvement of manufacturing technology, it is important and imperative to design novel metasurfaces that can flexibly manipulate terahertz (THz) waves. In this paper, a multifunctional metasurface (MFMS) based on graphene and photosensitive silicon (Si) is proposed, which integrates three functions: broadband absorption, broadband linear and circular polarization conversions in THz band. For absorption mode, the MFMS can absorb above 90% energy in the frequency band of 1.74-3.52 THz with the relative bandwidth of 67.6%. For both linear-linear and circular-circular polarization conversion modes, the relative bandwidth with over 90% polarization conversion rates (PCRs) reaches 49.3% in the frequency band of 1.54-2.55 THz. The working mechanism of the MFMS is analyzed by the surface current distributions, and its properties of the absorption and polarization conversion under oblique incident angles are investigated, respectively. The proposed metasurface has promising prospects in terahertz devices such as modulators, smart switches and other terahertz devices.
TL;DR: In this article, the authors presented a Ku-band phased-array receive tile with 256 elements, which is based on 64 dual-polarized beamformer chips assembled on a printed circuit board (PCB).
Abstract: This article presents a Ku-band phased-array receive tile with 256 elements. The design is based on 64 dual-polarized beamformer chips assembled on a printed circuit board (PCB) with dual-polarized antennas and an integrated Wilkinson combiner network and can operate at any polarization (linear, rotated-linear, and circular). The 256 elements are spaced $0.52\lambda $ apart at 12.7 GHz in the $x$ - and $y$ -directions. The measured patterns show near ideal patterns with a wide beam scanning range of ±70° (V- and H-pol) and a high cross-polarization rejection of 27 dB. The array has a 3-dB instantaneous scanning bandwidth of 10.6–12.5 GHz. In circular polarization mode, the measured axial ratio (AR) is 0.5 dB at 11.75 GHz for both left- and right-hand circular polarizations. The tile design is scalable to allow large-scale phased-array construction with 1024 elements or higher. Extensive measurements are presented, showing the versatility of this approach. Also, the dual-polarization feeds can be optimized to result in very low cross-polarization for circular and slanted-linear polarizations at all scan angles. The array performance, compact size, ultralightweight of 258 g, and low profile with 3.5-mm thickness make it suitable for affordable mobile Ku-band SATCOM on the move (SOTM) terminals.
TL;DR: In this article, a dual-band dual-circularly polarized magneto-electric dipole antenna array for full-duplex communication systems is presented in this communication, which can simultaneously achieve left-hand circular polarization (LHCP) around 20 GHz with a low-loss feed network using the printed ridge gap waveguide (PRGW).
Abstract: A dual-band dual-circularly polarized magneto-electric dipole antenna array for full-duplex communication systems is presented in this communication. The proposed array can simultaneously achieve left-hand circular polarization (LHCP) around 20 GHz and right-hand circular polarization (RHCP) around 30 GHz with a low-loss feed network using the printed ridge gap waveguide (PRGW). The antenna is composed of two sets of stacked interconnected short-circuit patches operating at different frequencies and fed by the same gap. The LHCP at the 20 GHz band and RHCP at the 30 GHz band are realized by exciting the corresponding orthogonal electric-dipole mode and magnetic-dipole mode with −90°/90° phase difference. A cylindrical cavity consists of a series of metalized vias with a top metal strip used for surface wave inhibition. Using the PRGW, a four-way power divider with a low transmission loss is designed. Finally, the simulated $2 \times 2$ array was fabricated and measured. The measurement results show that the impedance bandwidths are 18.85–20.8 and 29.5–30.9 GHz. The 3 dB axial ratio bandwidths are 19.4–20.4 and 28.5–31.4 GHz, with the peak gains of 13.2 and 11.5 dBic, respectively.
TL;DR: In this article, an ultra-thin reflective metasurface is proposed for polarization conversion in the terahertz band, where each unit cell is composed of graphene ribbons lying diagonally on silicon substrate.
Abstract: In this study, an ultra-thin reflective metasurface is proposed for polarization conversion in the terahertz band. Each unit cell of metasurface is composed of graphene ribbons lying diagonally on silicon substrate. A reflective metal is also placed at the bottom of the structure. Our polarization converter works as a linear polarization converter (LPC) and linear to circular polarization converter (LTC-PC) by variation of the chemical potential of graphene, which can actively be changed by chemical doping or electrical bias of the graphene. The working bandwidth of LPC changes by adjusting the chemical potential of the graphene. The LPC structure has more than 99% polarization conversion ratio in the frequency range of 0.83-0.92 THz, even by changing the angle of incident wave up to 45°, the results are still acceptable. The LTC-PC has less than 3dB axial ratio (AR) in the frequency range of 0.6-0.67 THz for left-handed circularly polarized (LHCP) waves and 0.72-0.97 THz for right-handed circularly polarized (RHCP) waves. To verify the simulation results, an equivalent circuit model based on the structure performance is proposed. Equivalent circuit model results agree very well with the simulation results. Due to the fabrication feasibility, ultra-thin thickness, incident angle insensitive, and high efficiency, our structure has great potential in state-of-the-art technologies such as imaging, sensing, communication, and other optical applications.
TL;DR: In this article, the authors investigate the evolution of the bulk photovoltaic effect in BiFeO3 thin films with stripe-domain pattern as the polarization of light is modulated from linear to elliptical to circular.
Abstract: Multiferroic bismuth ferrite, BiFeO3, offers a vast landscape to study the interplay between different ferrroic orders. Another aspect which is equally exciting, and yet underutilized, is the possibility of large-scale ordering of domains. Along with symmetry-driven bulk photovoltaic effect, BiFeO3 presents opportunities to conceptualize novel light-based devices. In this work, we investigate the evolution of the bulk photovoltaic effect in BiFeO3 thin films with stripe-domain pattern as the polarization of light is modulated from linear to elliptical to circular. The open-circuit voltages under circularly polarized light exceed ± 25 V. The anomalous character of the effect arises from the contradiction with the analytical assessment involving tensorial analysis. The assessment highlights the need for a domain-specific interaction of light which is further analyzed with spatially-resolved Raman measurements. Appropriate positioning of electrodes allows observation of a switch-like photovoltaic effect, i.e., ON and OFF state, by changing the helicity of circularly polarized light. The authors study the evolution of the bulk photovoltaic effect in BiFeO3 thin films with stripe-domains as the polarization of light is modulated from linear to circular. A relationship between the anomalous photo-response and differential light-domain interaction is established.
TL;DR: In this paper, the design of a single point-fed, geometrically simple circularly polarized (CP) antenna for 28 GHz Ka-band applications is presented, which is based on a straight microstrip line printed on one side and coupled with the nearly square patches through a 45° inclined V-shaped slot aperture on the other side.
Abstract: This letter presents the design of a single point-fed, geometrically simple circularly polarized (CP) antenna for 28 GHz Ka-band applications. The proposed antenna is based on a straight microstrip line printed on one side and coupled with the nearly square patches through a 45° inclined V-shaped slot aperture on the other side. In order to generate circular polarization, the fundamental radiating mode is degenerated at a slightly different frequency by aligning the patch edges parallel to each arm of the V-slot with orthogonal arms. This configuration yields a relatively small size (10 mm × 27.7 mm), wideband, and high-gain right-hand CP antenna operating at 28 GHz. The impedance bandwidth of the proposed antenna is from 27.2 to 30.35 GHz and the 3 dB axial ratio (AR) bandwidth from 27.3 to 29.7 GHz with excellent directional characteristics in the broadside direction. The peak gain is approximately 11.65 dBic. The performance characteristics in terms of the impedance matching, AR, gain, and efficiency of the antenna for wearable applications are also investigated both numerically and experimentally. For practical applications, the small size of the structure allows for implementing the systems that consist of more than one antenna to account for user mobility.