Showing papers on "Circular polarization published in 2020"

Generation of spatiotemporal optical vortices with controllable transverse orbital angular momentum

Abstract: Today, it is well known that light possesses a linear momentum that is along the propagation direction. Besides, scientists also discovered that light can possess an angular momentum, a spin angular momentum (SAM) associated with circular polarization and an orbital angular momentum (OAM) owing to the azimuthally dependent phase. Even though such angular momenta are longitudinal in general, an SAM transverse to the propagation direction has opened up a variety of key applications1. In contrast, investigations of the transverse OAM are rare due to its complex nature. Here, we demonstrate a three-dimensional wave packet that is a spatiotemporal (ST) optical vortex with a controllable purely transverse OAM. Contrary to the transverse SAM, the magnitude of the transverse OAM carried by the ST vortex is scalable to a larger value by simple adjustments. Since the ST vortex carries a controllable OAM uniquely in the transverse dimension, it has strong potential for novel applications that may not be possible otherwise. The scheme reported here can be readily adapted for other spectral regimes and different wave fields, opening opportunities for the study and applications of ST vortices in a wide range of areas. By applying a spiral phase in a pulse shaper, a three-dimensional wave packet, which is a spatiotemporal optical vortex with a controllable purely transverse orbital angular momentum, is demonstrated.

Metasurfaces with Maximum Chirality Empowered by Bound States in the Continuum.

Abstract: We demonstrate that rotationally symmetric chiral metasurfaces can support sharp resonances with the maximum optical chirality determined by precise shaping of bound states in the continuum (BICs) Being uncoupled from one circular polarization of light and resonantly coupled to its counterpart, a metasurface hosting the chiral BIC resonance exhibits a narrow peak in the circular dichroism spectrum with the quality factor limited by weak dissipation losses We propose a realization of such chiral BIC metasurfaces based on pairs of dielectric bars and validate the concept of maximum chirality by numerical simulations

A Chiral Reduced-Dimension Perovskite for an Efficient Flexible Circularly Polarized Light Photodetector.

Abstract: Chiral quasi-2D perovskite single crystals (SCs) were investigated for their circular polarized light (CPL) detecting capability. Quasi-2D chiral perovskites, [(R)-β-MPA]2 MAPb2 I7 ((R)-β-MPA=(R)-(+)-β-methylphenethylamine, MA=methylammonium), have intrinsic chirality and the capability to distinguish different polarization states of CPL photons. Corresponding quasi-2D SCs CPL photodetector exhibit excellent detection performance. In particular, our device responsivity is almost one order of magnitude higher than the reported 2D perovskite CPL detectors to date. The crystallization dynamics of the film were modulated to facilitate its carrier transport. Parallel oriented perovskite films with a homogeneous energy landscape is crucial to maximize the carrier collection efficiency. The photodetector also exhibits superior mechanical flexibility and durability, representing a promising candidate for sensitive and robust CPL photodetectors.

Direct detection of circular polarized light in helical 1D perovskite-based photodiode.

Abstract: Detection of circularly polarized light (CPL) has a high potential for development of various optical technologies. Conventional photodetectors require optical polarizers on the device to detect polarized light, and this causes substantial losses of sensitivity and resolution in light detection. Here, we report direct CPL detection by a photodiode using a helical one-dimensional (1D) structure of lead halide perovskites composed of naphthylethylamine-based chiral organic cations. The 1D structure with face-sharing (PbI6)4− octahedral chains whose helicity is largely affected by chiral cations shows intense circular dichroism (CD) signals over 3000 mdeg at 395 nm with the highly anisotropy factor (gCD) of 0.04. This high CD enables photocurrent detection with effective discrimination between left-handed and right-handed CPLs. The CPL detector based on this 1D perovskite achieved the highest polarization discrimination ratio of 25.4, which largely surpasses the direct detecting CPL devices (

Dual-Band and High-Efficiency Circular Polarization Convertor Based on Anisotropic Metamaterial

Abstract: In this paper, a dual-band and high-efficiency circular polarization (CP) convertor based on anisotropic metamaterial (AMM) was proposed and investigated in microwave region. The proposed AMM based CP convertor is composed of a sub-wavelength metal grating sandwiched with bi-layered disk-split-ring (DSR) structure array, which can convert the normal incident CP wave to its orthogonal one around two adjacent frequency ranges. Based on the intrinsic anisotropic and Fabry-Perot-like cavity-enhanced effect, a high CP conversion efficiency can be achieved by applying the proposed AMM. Numerical simulation results indicate that the cross-polarization transmission coefficients can achieve maximum values of 0.84 at 4.5 GHz, and 0.92 at 7.9 GHz, respectively, which is in well agreement with experiment. In addition, the measured CP conversion efficiency is beyond 99% at resonance frequencies. The mechanism of the CP conversion properties can be explained by the electromagnetic (EM) interference model and the simulated electrical field distribution. Due to its excellent polarization conversion properties, the proposed CP convertor based on AMM structure shows potential application in such as radar, remote sensing, and satellite communication.

Giant topological longitudinal circular photo-galvanic effect in the chiral multifold semimetal CoSi

Abstract: The absence of mirror symmetry, or chirality, is behind striking natural phenomena found in systems as diverse as DNA and crystalline solids A remarkable example occurs when chiral semimetals with topologically protected band degeneracies are illuminated with circularly polarized light Under the right conditions, the part of the generated photocurrent that switches sign upon reversal of the light's polarization, known as the circular photogalvanic effect, is predicted to depend only on fundamental constants The conditions to observe quantization are non-universal, and depend on material parameters and the incident frequency In this work, we perform terahertz emission spectroscopy with tunable photon energy from 02 eV - 11 eV in the chiral topological semimetal CoSi We identify a large longitudinal photocurrent peaked at 04 eV reaching $\sim$ 550 $\mu A/V^{2}$, which is much larger than the photocurrent in any chiral crystal reported in the literature Using first-principles calculations we establish that the peak originates from topological band crossings, reaching 33$\pm$03 in units of the quantization constant Our calculations indicate that the quantized CPGE is within reach in CoSi upon doping and increase of the hot-carrier lifetime The large photo-conductivity suggests that topological semimetals could potentially be used as novel mid-infrared detectors

Metasurface-Enabled Generation of Circularly Polarized Single Photons

Abstract: Single photons carrying spin angular momentum (SAM), i.e., circularly polarized single photons generated typically by subjecting a quantum emitter (QE) to a strong magnetic field at low temperatures, are at the core of chiral quantum optics enabling nonreciprocal single-photon configurations and deterministic spin-photon interfaces. Here, a conceptually new approach to the room-temperature generation of SAM-coded single photons (SSPs) is described, which entails QE nonradiative coupling to surface plasmons being transformed, by interacting with an optical metasurface, into a collimated stream of SSPs with the designed handedness. Design, fabrication, and characterization of SSP sources, consisting of dielectric circular nanoridges with azimuthally varying widths deterministically fabricated on a dielectric-protected silver film around a nanodiamond containing a nitrogen-vacancy center, are reported. With properly engineered phases of QE-originated fields scattered by nanoridges, the outcoupled photons are characterized by a well-defined SAM (with the chirality >0.8) and high directionality (collection efficiency up to 92%).

Circularly Polarized Photoluminescence from Chiral Perovskite Thin Films at Room Temperature.

Abstract: Hybrid organic-inorganic perovskites allow the synthesis of high-quality, nanostructured semiconducting films via easily accessible solution-based techniques. This has allowed tremendous development in optoelectronic applications, primarily solar cells and light-emitting diodes. Allowed by the ease of access to nanostructure, chirality has recently been introduced in semiconducting perovskites as a promising way to obtain advanced control of charge and spin and for developing circularly polarized light sources. Circular polarization of photoluminescence (CPL) is a powerful tool to probe the electronic structure of materials. However, CPL in chiral perovskites has been scarcely investigated, and a study in bulk thin films and at room temperature is still missing. In this work, we fabricate bromine-based chiral perovskites by using a bulky chiral organic cation mixed with CsBr, resulting in Ruddlesden-Popper perovskite thin films. We measure CPL on these films at room temperature and, by using unpolarized photoexcitation, we record a degree of circular polarization of photoluminescence in the order of 10-3 and provide a full spectral characterization of CPL. Our results show that chirality is imparted on the electronic structure of the semiconductor; we hypothesize that the excess in polarization of emitted light originates from the charge in the photogenerated Wannier exciton describing an orbit in a symmetry-broken environment. Furthermore, our experiments allow the direct measurement of the magnetic dipole moment of the optical transition, which we estimate to be ≥0.1 μB. Finally, we discuss the implications of our findings on the development of chiral semiconducting perovskites as sources of circularly polarized light.

Wideband and Wide-Angle Single-Layered-Substrate Linear-to-Circular Polarization Metasurface Converter

Abstract: A wideband and wide-angle linear-to-circular polarization converter (LCPC) based on a single-layer dielectric substrate is proposed. The converter element consists of a metal strip cross backed by a strip horizontally and centrically located on the other metallic layer. The vertical arm of the strip across the whole surface performs as a high- pass filter with a wide passband above a low cutoff frequency. Meanwhile, the horizontal strip resonates at a high out-of-band frequency and also offers a wideband response below the resonant frequency. Another two short strips vertically and horizontally placed around the crosses increase the phase shift caused by the crosses and improve both the passbands. Using equivalent circuit models and ANSOFT HFSS, an example of LCPC is designed with the overall element size of only $0.11\lambda _{0}\times 0.21\lambda _{0}$ for a 90° phase difference and wide-angle stability over the wide operation band. The prototype shows the simulated / measured axial ratios (ARs) below 3 dB over the bandwidth of 69%/74% for a normal incidence wave and 54% for the oblique incident angle of 55° in yz plane, respectively. With the insertion loss of less than 3 and 2 dB, the measured 3 dB AR bandwidth keeps 70% and 55%, respectively.

Transverse spinning of unpolarized light

Abstract: It is well known that spin angular momentum of light, and therefore that of photons, is directly related to their circular polarization. Naturally, for totally unpolarized light, polarization is undefined and the spin vanishes. However, for nonparaxial light, the recently discovered transverse spin component, orthogonal to the main propagation direction, is largely independent of the polarization state of the wave. Here we demonstrate, both theoretically and experimentally, that this transverse spin survives even in nonparaxial fields (e.g., tightly focused or evanescent) generated from a totally unpolarized light source. This counterintuitive phenomenon is closely related to the fundamental difference between the degrees of polarization for 2D paraxial and 3D nonparaxial fields. Our results open an avenue for studies of spin-related phenomena and optical manipulation using unpolarized light.

An Ultra-Wideband Reflective Linear-to-Circular Polarization Converter Based on Anisotropic Metasurface

Abstract: In this work, an ultra-wideband and high-efficiency reflective linear-to-circular polarization converter based on an anisotropic metasurface is proposed, which is an orthotropic structure with a pair of mutually perpendicular symmetric axes u and v along ±45° directions with respect to the vertical y axis. The simulated and experimental results show that the polarization converter can realize ultra-wideband linear-to-circular polarization conversion at both x - and y-polarized incidences, its 3dB-axial-ratio-band is between 5.8 and 20.4 GHz, which is corresponding to a relative bandwidth of 112%; moreover, the polarization conversion efficiency (PCE) can be kept larger than 99.6% in the frequency range of 6.1-19.8GHz. In addition, to get an insight into the root cause of the LTC polarization conversion, a detailed theoretical analysis is presented, in which the conclusion is reached that in the case of neglecting the little dielectric loss, the axial ratio (AR) of the reflected wave can be completely determined by the phase difference between the two reflection coefficients at u- and v-polarized incidences, and any anisotropic metasurface can be used as an effective LTC polarization converter when the phase difference is close to ±90°.

Circularly Polarized Fabry-Perot Antenna Employing a Receiver–Transmitter Polarization Conversion Metasurface

Abstract: This study presents a linear-to-circular polarization conversion metasurface (PCM) based on a novel unit cell for a circularly polarized (CP) Fabry-Perot (FP) antenna. The unit cell consists of a bottom linear-polarization patch and a top circular-polarization patch, which are separated by a metalized plane and connected by a metalized via. The bottom patch receives the power and transfers it to the top layer through the metalized via; the top layer then transmits the power into space. The metasurface is designed to have high reflectivity and an appropriate reflection phase to compose a resonate cavity with the ground plane. The capability of linear to circular polarization conversion is provided to the PCM by adjustment of the transmission magnitude and phase. A slot coupled patch antenna is used as the feeder due to its stable broadside radiation. The linearly polarized wave emitting from the feeder resonates in the cavity and then is converted into a CP wave when it comes out of the cavity. A prototype antenna is fabricated and measured. The measurement results show that the antenna has good circular polarization performance within the band of 9.8–10.2 GHz. The maximum gain of the antenna reaches 17.8 dBic at 10 GHz, with an aperture efficiency of 53%. The proposed antenna outperforms most of the previously reported CP FP antennas due to its low profile, high gain, and relatively high efficiency.

Phase Singularities to Polarization Singularities

Abstract: Polarization singularities are superpositions of orbital angular momentum (OAM) states in orthogonal circular polarization basis. The intrinsic OAM of light beams arises due to the helical wavefronts of phase singularities. In phase singularities, circulating phase gradients and, in polarization singularities, circulating Stokes phase gradients are present. At the phase and polarization singularities, undefined quantities are the phase and Stokes phase, respectively. Conversion of circulating phase gradient into circulating Stokes phase gradient reveals the connection between phase (scalar) and polarization (vector) singularities. We demonstrate this by theoretically and experimentally generating polarization singularities using phase singularities. Furthermore, the relation between scalar fields and Stokes fields and the singularities in each of them is discussed. This paper is written as a tutorial-cum-review-type article keeping in mind the beginners and researchers in other areas, yet many of the concepts are given novel explanations by adopting different approaches from the available literature on this subject.

Vanadium dioxide-assisted broadband absorption and linear-to-circular polarization conversion based on a single metasurface design for the terahertz wave.

Abstract: Integrating tunable characteristics and multiple functions into a single metasurface has become a new scientific and technological undertaking that needs to deal with huge challenges, especially in the terahertz frequency region. The multifunctional design combining the broadband absorption and broadband polarization conversion using a single switchable metasurface is proposed in this paper. The switchable performance can be realized by treating the insulation to metal phase transition properties of vanadium dioxide (VO2). At high temperature (74 °C), the proposed metasurface can be used as a broadband absorber which consists of a VO2 square ring, polyimide (PI) spacer, and VO2 film. Simulated results show that the terahertz wave absorption can reach above 90% with the bandwidth ratio of 75% in the frequency range of 0.74 THz-1.62 THz. This absorber is insensitive to polarization resulted from the symmetry structure and also shows a good performance at large incident angles. Once the temperature is lower than the cooling phase transition temperature (about 62 °C) and VO2 is in insulation state, the metasurface can be transformed into a broadband linear-to-circular polarization converter. Numerical simulation depicts that the ellipticity reaches to -1 and the axis ratio is lower than 3 dB from 1.47 THz to 2.27 THz. The designed switchable metasurface provides the potential to be used in the fields of advanced research and intelligent applications in the terahertz frequency region.

A Scalable Ka-Band 1024-Element Transmit Dual-Circularly-Polarized Planar Phased Array for SATCOM Application

Abstract: This paper presents a scalable 1024-element transmit dual-circularly-polarized phased array for Ka-band satellite communication (SATCOM) terminal applications. The transmit array based on the CMOS beamformer and a multilayer printed circuit board (PCB) can steer up to large scan angles (±60°) with a scan loss less than 4.5 dB. With the 8-channel transmit beamformer, the array can realize dual circular polarization and the axial ratio (AR) of the array is less than 3 dB in the scanning range of ±30° in both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) mode. The effective isotropic radiated power (EIRP) of the array achieves 74 dBm from 29.5 GHz to 30 GHz. The design and measurement of the 1024-element transmit array have presented a feasible way for mass production of a low cost active phased array.

Low-Profile Circularly Polarized Array With Gain Enhancement and RCS Reduction Using Polarization Conversion EBG Structures

Abstract: A planar antenna array based on checkerboard polarization conversion electromagnetic band-gap (CPC EBG) structures with wideband circular polarization and low radar cross section (RCS) is presented. The array is formed by $2\times 2$ circularly polarized (CP) element antennas fed with a sequential feeding network. On the one hand, CP radiation is obtained due to the polarization conversion characteristic of the metamaterials. A sequentially rotated feeding network is employed for wide operating bandwidth, polarization purity, and radiation pattern symmetry. The measured results show that the array has a wide usable bandwidth of 18.4%, the common part of an impedance bandwidth of 37.3% (4.80–7.00 GHz), a 3 dB axial ratio (AR) bandwidth of 22.5% (5.00–6.27 GHz), and a 3 dB gain bandwidth of 18.4% (4.94–5.94 GHz). On the other hand, the checkerboard arrangement of the EBG structure generates both an in-band and a partial out-band RCS reduction under normal incidence for both $x$ - and $y$ -polarizations. Besides, the proposed array achieves a significant gain enhancement compared to the traditional slot array. The experimental and simulated results are in good agreement.

A Jia-shaped artistic patch antenna for dual-band circular polarization.

Abstract: This article presents a novel single-feed circularly polarized patch antenna for dual-band (2.6 and 3.4 GHz) applications. Details of the design procedure and design considerations of the proposed antenna are described. The novelties of the proposed antenna are counted by (i) a meaningful Jia-shaped patch used as the primary radiator; (ii) a 3D L-shaped feeding probe used to excite the stacked patches so that the near degenerate-modes are excited at the desired dual band; (iii) down-tilt beams achieved that are particularly suitable for wall-mount base-stations. The measured 3-dB axial-ratio bandwidths are 2.41–2.61 GHz and 3.25–3.42 GHz, where the maximum gains are recorded as 7.3 and 6.3 dBic, respectively. Methods for the adjustment of band ratio down to 1.18 are discussed. The overall antenna size is 100 × 100 × 12.8 mm3.

Broadband Spin-Decoupled Metasurface for Dual-Circularly Polarized Reflector Antenna Design

Abstract: In this article, we theoretically and experimentally demonstrate a single-layered spin-decoupled metasurface and its application to a dual-circularly polarized reflector antenna. A developed method is first analyzed to guide the design of broadband spin-decoupled metasurface. Then, a quasi-I-shaped meta-atom, which exhibits a phase coverage of $2\pi $ and high cross-polarization conversion efficiency within 12–21 GHz, is accordingly designed to actualize spin-decoupled phase change by simultaneously tuning the structural parameters and self-rotation of the element. To illustrate the independent phase control of orthogonal spins, a dual-circularly polarized multiplexing reflector antenna is designed with offset configuration. The experimentally measured results of the assembled reflector antenna are in good agreement with the simulated ones, showing a peak gain of 29.5 and 29.6 dBic, peak aperture efficiency (AE) of 53% and 54%, 3 dB gain bandwidth (BW) of 13.2–20.2 GHz (41.9%) and 13.4–20.2 GHz (40.5%), and 3 dB axial ratio (AR) BW of 11.8–21 GHz (56.1%) and 11.5–22 GHz (62.7%) for left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) radiations, respectively. The design strategy and the well-performed multiplexing reflector antenna may have promising perspective in many practical applications, for example, satellite communication system and long-distance wireless communication system.

Tunable Layer Circular Photogalvanic Effect in Twisted Bilayers.

Abstract: We develop a general theory of the layer circular photogalvanic effect (LCPGE) in quasi-two-dimensional chiral bilayers, which refers to the appearance of a polarization-dependent, out-of-plane static dipole moment induced by circularly polarized light. We elucidate the geometric origin of the LCPGE as two types of interlayer coordinate shift weighted by the quantum metric tensor and the Berry curvature, respectively. As a concrete example, we calculate the LCPGE in twisted bilayer graphene, and find that it exhibits a resonance peak whose frequency can be tuned from visible to infrared as the twisting angle varies. The LCPGE thus provides a promising route toward frequency-sensitive, circularly polarized light detection, particularly in the infrared range.

Dual-Band Circularly Polarized Transmitarray With Single Linearly Polarized Feed

Abstract: This communication proposes a novel method to design a dual-band circularly polarized (CP) transmitarray (TA) antenna with a linearly polarized (LP) feed. By using this method, a shared-aperture dual-band TA is developed, which forms independent beams with right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP) in two frequency bands with a single LP feed antenna. Four different CP TA prototypes operating at 12 and 14.2 GHz with different senses of CP and different beam directions are designed, and two of the prototypes are fabricated to validate the design concepts. A good agreement is obtained between the radiation patterns, gain curves, polarizations, and cross polarization levels measured and computed in both frequency bands. The proposed single-source dual-band CP TA design has advantages of simple structure, lightweight, easy fabrication, low cost, and high performance, making it a good candidate for varied applications.

Helicity-Preserving Optical Cavity Modes for Enhanced Sensing of Chiral Molecules

Abstract: Researchers routinely sense molecules by their infrared vibrational "fingerprint" absorption resonances. In addition, the dominant handedness of chiral molecules can be detected by circular dichroism (CD), the normalized difference between their optical response to incident left- and right- handed circularly polarized light. Here, we introduce a cavity composed of two parallel arrays of helicity-preserving silicon disks that allows one to enhance the CD signal by more than 2 orders of magnitude for a given molecule concentration and given thickness of the cell containing the molecules. The underlying principle is first-order diffraction into helicity-preserving modes with large transverse momentum and long lifetimes. In sharp contrast, in a conventional Fabry-Perot cavity, each reflection flips the handedness of light, leading to large intensity enhancements inside the cavity, yet to smaller CD signals than without the cavity.

A Frequency- and Polarization-Reconfigurable Slot Antenna Using Liquid Metal

Abstract: In this communication, a microfluidically frequency- and polarization-reconfigurable slot antenna using liquid metal (LM) is proposed. The polydimethylsiloxane (PDMS) structure with narrow-banded microchannels is loaded on the printed circuit board (PCB) of a square slot antenna, providing condition for reconfiguration. The left-hand circular polarization (LHCP), right-hand circular polarization (RHCP), and linear polarization (LP) are achieved by injecting LM into +45° and −45° channels with respect to the $x$ -axis or keeping the channels empty. Three operating frequency bands of LHCP and RHCP states can be realized by filling the microchannels with different lengths. Both states have an overall tuning 3 dB axial ratio bandwidth (ARBW) of 26.42% (2.3–3 GHz). In LP state, the proposed antenna realizes a −10 dB impedance bandwidth of 11.6% (2.03–2.28 GHz). A prototype of the proposed antenna has been fabricated and measured. Good agreement between the simulated and measured results validates the feasibility of this technique.

Orientation-Insensitive and Normalization-Free Reading Chipless RFID System Based on Circular Polarization Interrogation

Abstract: A novel normalization-free reading scheme to recover data encoded in chipless radio frequency identification (RFID) tags is presented. The proposed approach exploits the circular polarization to isolate the field scattered by the tag from that of surrounding objects. The desired polarization mismatch is achieved by exploiting the properties of high-impedance surfaces that can suitably manipulate the reflected field. A thorough analysis of the interaction between the circularly polarized (CP) interrogation and the field scattered by the chipless RFID tag as well as the hosting platform is provided. The proposed method does not require any a priori calibration if a reading antenna with a suitable axial ratio is available. More importantly, the CP-based reading approach guarantees the correct tag detection regardless of the tag orientation. The case of the tag mounted on metallic platform is also analyzed and it is demonstrated that the circular polarization reading procedure is robust under the hypothesis of a proper axial ratio of the probing antennas. The minimum requirements of axial ratio are derived by using a theoretical model. Measurements confirmed the speculations obtained through the theoretical analysis both in the case of low-scattering items as well as for metallic platforms.

Highly Efficient Inverted Circularly Polarized Organic Light-Emitting Diodes

Abstract: Circularly polarized (CP) electroluminescence has been demonstrated as a strategy to improve the performance of organic light-emitting diode (OLED) displays. CP emission can be generated from both ...

Isolation Enhancement of Closely Packed Dual Circularly Polarized MIMO Antenna Using Hybrid Technique

Abstract: Mutual coupling always seriously degrades the antenna performance in multiple-input multiple-output (MIMO) systems but this issue has been rarely investigated for antennas with circular polarization. In this paper, a planar and compact circularly polarized MIMO patch antenna with the polarization diversity is presented. Three grounded stubs and a mirrored F-shaped defected ground structure are used to achieve simultaneous matching and isolation between the two patches with offset feeding for circular polarization. The antenna elements are closely packed with the edge-to-edge distance of $0.06\lambda _{0}$ at the desired frequency of 2.5 GHz. The measured results indicate that the proposed antenna achieves the impedance matching ( $\text{S}_{11} dB), high isolation ( $\text{S}_{12} dB), and circular polarization (axial ratio< 3 dB) within the frequency band of 2.5-2.55 GHz. The radiation patterns and realized gains are measured, showing good agreement between the simulation and measurement.

A 3-D-Printed Wideband Circularly Polarized Parallel-Plate Luneburg Lens Antenna

Abstract: This communication presents a 3-D-printed wideband parallel-plate circularly polarized Luneburg lens (LL) antenna. The proposed structure of dielectric posts truncated by two metallic parallel plates serves not only as a LL, but also as a wideband linear-to-circular polarizer. The permittivity variation of the LL is realized by positioning dielectric posts with various radius (r) based on the optics theory and the effective medium theory (EMT). On the other hand, the desired circular polarization is realized by exciting two orthogonal propagating modes with different phase constants thanks to the integrated parallel plates. To verify our concept, a prototype was fabricated using 3-D-printing technology. Based on the measurement results, the proposed antenna achieves an overlapped bandwidth of 43% (21–32.5 GHz) in terms of the reflection coefficients lower than −10 dB and the axial ratios smaller than 3 dB. Good agreement between simulation and measurement is obtained.

Polarization-Reconfigurable Leaky-Wave Antenna With Continuous Beam Scanning Through Broadside

Abstract: A simple single-layer reconfigurable leaky-wave antenna (LWA) is presented that has polarization agility and beam-scanning functionality. This LWA system realizes a scanned beam that can be switched between all of its linear polarization (LP) and circular polarization (CP) states using only one dc biasing source. A slot-loaded substrate-integrated waveguide (SIW)-based LWA is first explored to attain CP performance with continuous beam scanning through broadside. This CP LWA realizes a measured CP performance with a 3 dB gain variance within 2.75–3.35 GHz for scan angles ranging from −28.6° to +31.5°. A row of shorted stubs is then incorporated into the CP LWA to obtain similar LP performance. Finally, by introducing p-i-n diodes into this LP LWA configuration to facilitate reconfigurable connections between the main patch and the shorted stubs, the radiated fields can be switched between all of its CP and LP states. The measured results of all three antennas confirm their simulated performance. It is demonstrated that the main beam of the polarization-reconfigurable LWA can be scanned from −31.5° to +17.1° with gain variations between 9.5 and 12.8 dBic in its CP state and from −34.3° to +20° with them between 7.8 and 11.7 dBi in its LP state.

Measuring the net circular polarization of the stochastic gravitational wave background with interferometers

Abstract: Parity violating interactions in the early Universe can source a stochastic gravitational wave background (SGWB) with a net circular polarization. In this paper, we study possible ways to search for circular polarization of the SGWB with interferometers. Planar detectors are unable to measure the net circular polarization of an isotropic SGWB . We discuss the possibility of using the dipolar anisotropy kinematically induced by the motion of the solar system with respect to the cosmic reference frame to measure the net circular polarization of the SGWB with planar detectors. We apply this approach to LISA, re-assessing previous analyses by means of a more detailed computation and using the most recent instrument specifications, and to the Einstein Telescope (ET), estimating for the first time its sensitivity to circular polarization. We find that both LISA and ET, despite operating at different frequencies, could detect net circular polarization with a signal-to-noise ratio of order one in a SGWB with amplitude h2 ΩGW s 10−11. We also investigate the case of a network of ground based detectors. We present fully analytical, covariant formulas for the detector overlap functions in the presence of circular polarization. Our formulas do not rely on particular choices of reference frame, and can be applied to interferometers with arbitrary angles among their arms.