Circularly Polarized Research Articles

Large Circular Dichroism and Polarization Rotation in Plasmonic Ψ-Like Structured Gold Metasurface

Large Circular Dichroism and Polarization Rotation in Plasmonic Ψ-Like Structured Gold Metasurface

A wideband circularly polarized four port microstrip MIMO antenna with high gain and enhanced isolation for 5G millimeter frequency applications

Abstract In this article, a MIMO antenna system featuring wide bandwidth, high gain, and circular polarization for 5G communication networks is presented. The proposed antenna enables high data rates, enhanced signal reliability, and improved performance in dynamic and challenging 5G environments. Wide bandwidth ensures compatibility with various 5G frequency bands, while circular polarization allows for better signal propagation and reception, particularly in non-line-of-sight scenarios. In that regard, the present endeavor exhibits an enhanced bandwidth 4-port circularly polarized MIMO antenna to encounter polarization mismatch along with high data rates. The presented MIMO antenna comprises four identical patches strategically positioned in orthogonal orientations in such a way as to provide the circular polarization direction. Meanwhile, the bandwidth is extended by inserting straightforward defected ground structure (DGS) and L slots. The MIMO antenna anticipated in this work offers an impedance bandwidth covering from 24 GHz to 28.5 GHz and an axial ratio bandwidth of 62% within the overall band. It demonstrates excellent performance with a high peak gain of approximately 14.84 dB. Additionally, it exhibits strong isolation of more than 20dB among the closely packed antennas, ensuring reliable communication and minimizing interference. The combination of these features in a MIMO antenna system is crucial for meeting the demanding requirements of 5G communication, including increased data capacity, low latency, and reliable connectivity. The simulated and measured outcomes exhibit robust concurrence, signifying a high level of accuracy. Consequently, the suggested MIMO antenna appears well-suited for encompassing the 5G bands designated for deployment in the USA (27.50–28.35 GHz) and Europe (24.25 - 27.5 GHz).

Planar Chiral Charge-Transfer Cyclophanes: Convenient Synthesis, Circularly Polarized Light-Responsive Photothermal Conversion and Supramolecular Chiral Assembly.

We report herein a series of macrocycles in which the densely π-stacked charge-transfer (CT) donor/acceptor with naphthalenediimides (NDIs) or perylene diimide (PDI) as acceptor moiety pairing various donor moieties are locked by covalent bond. The X-ray crystallography of C8BDT-NDI reveals a short intramolecular π-stacking distance around 3.4 Å and the existence of intermolecular donor/acceptor π-stacking (3.7 Å). The intramolecular CT is highly dependent on the electron-donating ability of donor moiety and replacing carbazole (C8KZ) with benzo[1,2-b:4,5-b']dithiophene (C8BDT) or dihydroindolo[3,2-b]indole (C8DN) redshift CT absorption into NIR region. Notably, both C8BDT-NDI and C8DN-NDI demonstrate excellent photothermal performance, which is a result of the active non-radiative pathways. Interestingly, the different molecular symmetry between donor and acceptor moiety in cyclophanes endow C8BDT-NDI and C8DN-NDI with intrinsic planar chirality. The enantiomeric C8BDT-NDI shows chiral selectivity for incident light, i.e., when irradiated by left-circularly polarized light, (R)-C8BDT-NDI is more sensitive and a higher maximum stable temperature is achieved. While, enantiomeric C8DN-NDI pack with different orientations forming M- and P-handedness helix, respectively, demonstrating molecular planar chirality being transferred and amplified through molecular assembly. These results provide insight into the intramolecular charge transfer in enforced D/A π-stacks in which CT interactions and planar chirality would be engineered through structural control.

Manipulation of circular polarization and mechanical waves in gyroscopic metamaterials

Manipulation of circular polarization and mechanical waves in gyroscopic metamaterials

Measuring the circular polarization of gravitational waves with pulsar timing arrays

Measuring the circular polarization of gravitational waves with pulsar timing arrays

Construction of Chiral Covalent Organic Frameworks Through a Linker Decomposition Chiral Induction Strategy for Circularly Polarized Light Detection

AbstractExploring new strategies for construction of chiral covalent organic frameworks (COFs) is of paramount importance yet remains a challenge. Herein, we report the rational design and construction of chiral COFs through a linker decomposition chiral induction (LDCI) strategy. Three pairs of azine‐linked chiral COFs are successfully synthesized by the condensation reactions of C3‐symmetric 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)tribenzaldehyde (Tz) with flexible chiral dihydrazide linkers derived from malic acid, aspartic acid and tartaric acid, respectively. Remarkably, upon complete or partial decomposition from flexible chiral dihydrazides to hydrazine during COF synthesis, the homochirality of these COFs, originating from the single‐handedness conformation of propeller‐like Tz cores, is well preserved. Such a stereoselective chiral memory realized via the LDCI strategy is confirmed by time‐dependent powder X‐ray diffraction (PXRD), Fourier transform infrared (FT‐IR) and diffuse reflectance circular dichroism (DRCD). Moreover, the resultant azine‐linked chiral COFs are used as the active materials to fabricate photodetectors to directly distinguish circularly polarized light (CPL), showing impressive recognition performances on the identification of left‐handed circularly (LHC) and right‐handed circularly (RHC) polarized lights. Notably, the residual undecomposed flexible chiral linkers within the COFs are found to be conducive to improving the polarization discrimination ratio. This work highlights LDCI as a new and effective strategy for constructing homochiral COFs with promising future in chiral optical application.

Construction of Chiral Covalent Organic Frameworks Through a Linker Decomposition Chiral Induction Strategy for Circularly Polarized Light Detection

AbstractExploring new strategies for construction of chiral covalent organic frameworks (COFs) is of paramount importance yet remains a challenge. Herein, we report the rational design and construction of chiral COFs through a linker decomposition chiral induction (LDCI) strategy. Three pairs of azine‐linked chiral COFs are successfully synthesized by the condensation reactions of C3‐symmetric 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)tribenzaldehyde (Tz) with flexible chiral dihydrazide linkers derived from malic acid, aspartic acid and tartaric acid, respectively. Remarkably, upon complete or partial decomposition from flexible chiral dihydrazides to hydrazine during COF synthesis, the homochirality of these COFs, originating from the single‐handedness conformation of propeller‐like Tz cores, is well preserved. Such a stereoselective chiral memory realized via the LDCI strategy is confirmed by time‐dependent powder X‐ray diffraction (PXRD), Fourier transform infrared (FT‐IR) and diffuse reflectance circular dichroism (DRCD). Moreover, the resultant azine‐linked chiral COFs are used as the active materials to fabricate photodetectors to directly distinguish circularly polarized light (CPL), showing impressive recognition performances on the identification of left‐handed circularly (LHC) and right‐handed circularly (RHC) polarized lights. Notably, the residual undecomposed flexible chiral linkers within the COFs are found to be conducive to improving the polarization discrimination ratio. This work highlights LDCI as a new and effective strategy for constructing homochiral COFs with promising future in chiral optical application.

Metasurface loaded twin-port microstrip antenna with circular polarization features for UHF RFID applications

Abstract This communication designs and investigates a twin-port microstrip antenna loaded with a metasurface (MS). The proposed MS works in two ways: (i) artificial ground plane for radiator and (ii) as an ideal absorber of normal incoming waves at the same time. A stair shaped slot is loaded on rectangular patch for creating circularly polarized wave in between 835–894 MHz. Antenna port slots oriented in a mirror manner increase isolation by 25 dB. To act as a validation tool, the suggested antenna was built and its executions in individually operating modes evaluated by statistical and experimental analysis. It is shown that combining the patch and absorber results in a well-matched antenna in between 710–980 MHz with improved gain (more than 3.0 dBi). The proposed antenna design effectively used for UHF (Ultra High Frequency)radio-frequency identification (RFID) applications, which is due to its ability to mitigate multipath reflection issues and incorrectRFID reading.

Chiral Rare-Earth (Ce, Eu) Metal Halides with Bright Circularly Polarized Luminescence.

Chiral metal halide materials are emerging chiroptical materials that are easy to synthesize and have a wide tunability. Rare-earth (RE) metals are desirable components to be incorporated in the hybrid regime; however, they are typically difficult to handle for solution-based halide chemistry. Here, we report two new examples of chiral RE metal halides with Ce(III) and Eu(III) with chiral alkanolammonium cations (R/S-3-hydroxyquinuclidium). These compounds crystallize in the non-centrosymmetric space group R3, where their mirror-like symmetric circular dichroism (CD) and circularly polarized luminescence (CPL) further witness the chiral nature. The superior emission properties, including the high photoluminescence quantum yield of the Ce-based materials (84-90%) and Eu-based materials (27-29%), have led to distinct and sharp symmetrical CPL in the ultraviolet and visible regions, with dissymmetry factors (glum) of ∼2 × 10-3 and ∼4 × 10-3, respectively. This work has established and expanded the materials space for chiral RE metal halides and demonstrated their potential for chiroptical and spintronic applications.

Enhanced Asymmetric Circularly Polarized Luminescence in Self-Organized Helical Superstructures Enabled by Macro-Chiral Liquid Crystal Quantum Dots.

Circularly polarized luminescent (CPL) materials have garnered considerable interest for a variety of advanced optical applications including 3D imaging, data encryption, and asymmetric catalysis. However, the development of high-performance CPL has been hindered by the absence of simple synthetic methods for chiral luminescent emitters that exhibit both high quantum yields and dissymmetry factors. In this study, we present an innovative approach for the synthesis of macro-chiral liquid crystal quantum dots (Ch-QDs/LC) and their CPL performance enhancement through doping with 4-cyano-4'-pentylbiphenyl (5CB), thus yielding a CPL-emitting generator (CEG). The Ch-QDs/LCs were synthesized, and their surfaces functionalized with a chiral mesogenic ligand, specifically cholesteryl benzoate, anchored via a lipoic acid linker. Under the regulation of chiral 2S-Zn2+ coordination complexes, the chiral LC encapsulation process promotes coordinated ligand substitution, resulting in an exceptional quantum yield of 56.3%. This is accompanied by high absorption dissymmetry factor (gabs) and luminescence dissymmetry factor (glum) values ranging from 10-3 to 10-2, surpassing most reported dissymmetry factors by at least an order of magnitude. The modular Ch-QDs/LCs demonstrate the ability to transfer chirality to the surrounding medium efficiently and manifest macro-chiral characteristics within a nematic LC matrix. Utilizing Ch-QDs/LC as an effective CPL emitter within achiral 5CB matrices enabled the system to achieve a maximum glum value of 0.35. The resultant CEG device acted as a direct CPL source, initiating enantioselective photopolymerization.

Three-Level Chirality Transfer and Amplification in Liquid Crystal Supramolecular Assembly for Achieving Full-Color and White Circularly Polarized Luminescence.

Chiral liquid crystal supramolecular assembly provides an ideal strategy for constructing excellent circularly polarized luminescence (CPL) materials. However, the chirality transfer in chiral liquid crystals normally occurs at two levels from the configurational chirality to the supramolecular phase chirality. The more precise and more levels of chirality transmission are fascinating but remain challenging. The present work reports the first success of three-level chirality transfer and amplification from configurationally point chirality of small molecules to conformationally helical chirality of helical polymers and finally to supramolecular phase chirality of cholesteric liquid crystals composed of chiral nonfluorescent polymers (P46) and nematic liquid crystals. Noticeably, the helical twisting power of P46 is five-fold larger than its monomer. Full-color and white CPL with maximum luminescence dissymmetry factor up to 1.54 and photoluminescence quantum yield up to 63.8% are realized utilizing helical supramolecular assembly combined with selective reflection mechanism. Also significantly, the electrically stimuli-responsive CPL switching device as well as anti-counterfeiting security, information encryption, and chiral logic gate applications are developed. This study deepens the understanding of chirality transfer and amplification across different hierarchical levels.

Highly Sensitive Fiber Optic Current Sensors with Integrated λ/4 Retarder

ABSTRACTFiber optic current sensors have made unprecedented contributions to the safety and security of power grids. The λ/4 retarder, as a key component for generating circular polarization, can significantly enhance the performance of fiber optic current sensors (FOCS) due to its superior characteristics. However, traditional methods of fabricating homemade λ/4 retarders have inherent flaws. This study replaced the traditional λ/4 retarder in the all‐fiber current sensor with an integrated λ/4 retarder, which is proposed to convert linearly polarized light into circularly polarized light by controlling different spin rates of the spun fiber. The current sensitivity was increased from 0.235 to 0.404 mV/mA, and the noise was suppressed.

3-D-Printed Ka-Band Circularly Polarized Monopulse Antenna Array With High Gain and Low Axial Ratio

3-D-Printed Ka-Band Circularly Polarized Monopulse Antenna Array With High Gain and Low Axial Ratio

Supramolecular Control of Helicene Circularly Polarized Luminescence Emitters in Molecular Solids and Bright Nanoparticles

AbstractCircularly polarized luminescence (CPL) from chiral molecules is attracting much attention due to its potential use in optical materials. However, formulation of CPL emitters as molecular solids typically deteriorates photophysical properties in the aggregated state leading to quenching and unpredictable changes in CPL behavior impeding materials development. To circumvent these shortcomings, a supramolecular approach can be used to isolate cationic dyes in a lattice of cyanostar‐anion complexes that suppress aggregation‐caused quenching and which we hypothesize can preserve the synthetically‐crafted chiroptical properties. Herein, we verify that supramolecular assembly of small‐molecule ionic isolation lattices (SMILES) allows translation of molecular ECD and CPL properties to solids. A series of cationic helicenes that display increasing chiroptical response is investigated. Crystal structures of three different packing motifs all show spatial isolation of dyes by the anion complexes. We observe the photophysical and chiroptical properties of all helicenes are seamlessly translated to water soluble nanoparticles by the SMILES method. Also, a DMQA helicene is used as FRET acceptor in SMILES nanoparticles of intensely absorbing rhodamine antennae to generate an 18‐fold boost in CPL brightness. These features offer promise for reliably accessing bright materials with programmable CPL properties.

Measurement of circular intensity differential scattering (CIDS) from single optically trapped biological particles

The circular intensity differential scattering (CIDS), which is the normalized Mueller matrix element -S14/S11, has been measured from single biological particles as a function of scattering angle. CIDS is valuable for its potential in detecting chiral particles that may include the helical structures of DNA or RNA molecules in biological samples, and as such is a potential method for detecting biological particles. Optical trapping is employed to levitate single particles within a custom-designed elliptical reflector for CIDS measurements. The advantage of optical levitation in light-scattering measurements is that single particles can be suspended in air with sufficient working distance to prevent interference from the suspending apparatus. To measure the phase function, the reflector is used to collect the angle-dependent scattering signals. We demonstrated that we can obtain two-dimensional angular optical scattering (TAOS) patterns that cover a wide angular range from single levitated particles. These TAOS patterns are generated using 532 nm illumination of left-handed and right-handed circular polarizations and recorded from trapped single particles (silica, English Oak, Ragweed, Mulberry, Glycine, and l-Aspartic acid).

Single layer dual wideband linear to circular polarisation converter with integrated parasitic elements

This paper presents a novel single-layer, single-sided, dual-wideband linear-to-circular (LTC) polarsation converter. The unit cell of the polarisation converter comprises two identical diagonally oriented C-shaped metallic strips arranged symmetrically and integrated with four outwardly extending diagonal parasitic strips. The LTC polarisation converter is placed on the top side of an ultra-thin substrate layer with a profile size of 0.020 λo at 11.9 GHz and 0.05 λo at 30.7 GHz. The inclusion of parasitic strips in the unit cell design is pivotal, inducing a 90º phase shift between the orthogonal wave components, thus enhancing LTC polarisation conversion. The design achieved near-equal transmission amplitudes and maintained a stable phase difference of nearly 90° across two distinct frequency bands, enabling right-hand circular polarisation in the lower frequency band and left-hand circular polarisation in the higher frequency band. Numerical and experimental results showed that the polariser can realise a wideband LTC polarisation conversion for both x- and y-polarised electromagnetic wave incidences at two distinct frequency bands of 6.78–17.08 GHz (fractional bandwidth of 86.3%) and 25.09–36.40 GHz (36.8%). The converter maintained consistent polarisation conversion performance across a broad range of incidence angles and exhibited high and uniform total transmittance in both operational frequency bands.

Design of a UWB circularly-polarized planar monopole antenna using characteristic mode analysis

This study presents a circularly-polarized (CP) planar monopole antenna designed for ultra-wideband (UWB) applications using characteristic mode analysis (CMA). Initially, a planar monopole antenna with a crescent moon-shaped radiator and a circular open-loop on an FR-4 substrate was designed to achieve wideband characteristics, however, this antenna only satisfied a 3 dB axial ratio (AR) bandwidth within the 8.78–9.4 GHz range. To enhance the AR bandwidth, a triangular slit, a shark fin-shaped stub, and an L-shaped strip were added to the ground plane, generating orthogonal modes in the desired frequency band using CMA. The overall dimensions of the proposed antenna are 30 × 24 × 1.6 mm2 (0.58 × 0.46 × 0.031 λ₀2). The − 10 dB S11 bandwidth is 5.73–10.78 GHz (61.21%) and the 3 dB AR bandwidth is 6–11.12 GHz (59.81%), achieving overlapped bandwidth from 6 to 10.78 GHz (56.9%). The proposed antenna has a realized gain 2.4–5.4 dBi and an average efficiency of 80% within the target frequency. A time-domain analysis, including group delay and system fidelity factor, is conducted to evaluate performance. The fabricated antenna demonstrates omnidirectional radiation patterns at various frequencies and performs well in both the time and frequency domains.

Complete asymmetric polarization conversion at zero-eigenvalue exceptional points of non-Hermitian metasurfaces

Abstract Non-Hermitian systems can be tuned to exhibit exceptional points, where both eigenvalues and eigenstates coalesce concurrently. The inherent adaptability of photonic non-Hermitian systems in configuring gain and loss has allowed us to observe a plethora of counterintuitive phenomena, largely as a consequence of the eigenspace reduction at these exceptional points. In this work, we propose a non-Hermitian metasurface that, through the incorporation of gain, enables complete asymmetric polarization conversion at an exceptional point with a zero eigenvalue. Specifically, we provide numerical evidence for this concept by designing a non-Hermitian metasurface that facilitates polarization conversion from right to left circular polarization, while preventing conversion in the reverse direction and co-polarized transmission. Furthermore, our investigation reveals that this specific form of complete asymmetric polarization conversion results in maximum circular dichroism in transmission, thereby eliminating the need for external chirality or three-dimensional helical structures. This non-Hermitian technique offers an intriguing approach to designing polarization-sensitive optical devices and systems, further expanding their functionalities and capabilities.

Dual band four port MIMO antenna with dual circular polarization for Wi-Fi/WiMAX applications

The planar compact four port circularly polarized printed MIMO antenna described in this article is small and intended to support Wi-Fi and WiMAX applications. Suggested four E-shaped monopole elements make up the dual circularly polarized (CP) MIMO antenna that has two left hand CP (LHCP) elements and two right hand CP (RHCP) elements. An I shaped strip is used to join separate ground planes of designed E shaped monopole antenna to have same voltage levels. A good diversity performance is achieved with an envelope correlation coefficient (ECC) of less than 0.15. The 60 mm × 60 mm antenna is designed from FR4 material, which is inexpensive and has a 1.6 mm thickness. Using a high-frequency structure simulator (HFSS), the suggested MIMO antenna is designed and optimized. The measured findings demonstrate the circular polarization, 3-dB axial ratio beamwidth, impedance bandwidth of 2.11 GHz −2.42 GHz and 3.40 GHz-3.51 GHz, adequate axial ratio bandwidth (ARBW) of the suggested MIMO antenna along with high isolation of −17 dB, gain of 3.43 and 2.09 dBic at 2.4 GHz and 3.5 GHz respectively, TARC (Total active reflection coefficient) of less than 0 dB, a CCL (Channel capacity loss) of lesser than 0.4 bits/sec/Hz, and an MEG (Mean effective gain) value of less than 3 dB.

Horizontally Stacked Inverted U-Shaped Dual-band Implantable Antenna with Circularly Polarized for Biotelemetry Application

Abstract A horizontally stacked inverted U-shaped dual-band implantable antenna is proposed for RFID and health care monitoring implantable applications. The designed antenna operates at 0.952 GHz ultrahigh frequency band (UHF; 0.951–0.956 GHz) and 2.4 GHz industrial, scientific, and medical band (ISM; 2.4–2.4835 GHz) in a suitable feeding scheme. The shorting pin is used on the radiation patch to minimize the antenna structure. The final dimension of the designed antenna size is 9 × 9 ×0.635 mm^3. The defected ground structure (DGS) helped to produce radiation with circular polarization (CP) at 2.4 GHz resonant frequency. The designed antenna achieves an axial ratio (AR) bandwidth of 20% at 2.4GHz resonant frequency. The antenna is designed on Rogers RT Duroid 6010 substrate and fabricated. The same dielectric material was used as a superstrate. At both the UHF and ISM frequency bands, the experiment was conducted using skin-mimicking gel and minced pork. The horizontally stacked inverted U-shaped antenna has a high peak gain of -27.5 dBi at 0.952 GHz. The computed maximum specific absorption ratio is within allowable bounds and complies with IEEE safety criteria.