Circularly Polarized Research Articles

Nanocellulose-Based Chiroptical Sensors for Detecting Circularly Polarized Light

Natural materials exhibit fascinating optical properties that manipulate light across multiple length scales through hierarchical photonic structures, forming a promising platform for advanced optical materials. However, developing photonic structures that are both environmentally sustainable and capable of maintaining superior optical and structural properties for use in electronic devices remains a significant challenge.In this work, we present chiroptical nanocellulose papers as flexible circularly polarized light (CPL) photodetectors. Optoelectrically activated 2D semiconducting channels are seamlessly integrated onto the nanocellulose papers, enabling high polarization-sensitive photoresponsivity that detects CPL handedness, facilitated by selective light propagation with substantial asymmetry. These flexible devices also demonstrate excellent mechanical durability while retaining their structural and chiroptical properties. We will discuss polarization-dependent optoelectronic behavior in the context of CPL sensing, with applications in next-generation bio-photonic devices.

A compact broadband circularly polarized monopulse slot array antenna based on gap waveguide technology

ABSTRACT This paper presents a circularly polarized (CP) monopulse slot array antenna based on gap waveguide (GWG) technology. The proposed monopulse antenna is composed of a 4 × 4 array antenna fed by the monopulse comparator network in a compact three-layer structure. To achieve a broad axial ratio (AR) bandwidth of right-handed circular polarization (RHCP) in the sum radiation pattern, a septum polarizer is used in the radiating aperture. Based on this approach, horizontal transition structures are used to excite the radiating array from the WR-28 waveguide to the GWG, which helps to reduce the reflection loss and expand the impedance bandwidth. Experimental results show that the impedance bandwidth is 30.5 GHz to 40 GHz, which is 27.1%. The 3 dB AR bandwidth is 31%. The measured null depth is −40 dB, and the maximum measured gain in the sum pattern is 22 dBi at 34 GHz, while the antenna efficiency is greater than 86%. The advantages of low loss, broad bandwidth, and compact structure make the proposed antenna a competitive candidate for millimeter-wave (mmWave) monopulse direction-finding applications.

Ultrathin, Dynamically Controllable Circularly Polarized Emission Laser Enabled by Resonant Chiral Metasurfaces.

We demonstrate a simple, low-cost, and ultracompact chiral resonant metasurface design, which, by strong local coupling to a quantum gain medium (quantum emitters), allows to implement an ultrathin metasurface laser, capable of generating tunable circularly polarized coherent lasing output. According to our detailed numerical investigations, the lasing emission can be transformed from linear to circular and switch from right- to left-handed circularly polarized (CP) not only by altering the metasurface chiral response but also by changing the polarization of a linearly polarized pump wave, thus enabling dynamic lasing-polarization control. Given the increasing interest for CP laser emission, our chiral metasurface laser design proves to be a versatile yet straightforward strategy to generate a strong and tailored CP emission laser, promising great potential for future applications in both photonics and materials science.

Synthesis of Chiral Au-Ag Core-Shell Nanoparticles and Their Localized Surface Plasmon Resonance Properties

Noble metal nanoparticles (NPs) such as silver (Ag), and gold (Au) exhibit localized surface plasmon resonance (LSPR) peaks in the visible light region, and their optical properties can be tuned by their size and shape. Advances in colloid chemistry enable the introduction of structural chirality to these plasmonic NPs. LSPRs of chiral metal NPs are responsive to circularly polarized light (CPL), giving them chiroptical properties. For example, Au nanoparticles prepared with L- or D-cysteines as a ligand showed almost the same shape of extinction spectra, but their CD spectra showed opposite peaks in the LSPR wavelength region, depending on the handedness of ligands.[1] Metal nanoparticles having chiral structures are expected to be applied to high-sensitivity chiral sensing. While Au nanoparticles have been extensively explored due to their high chemical stability, chiral Ag nanostructures have not been investigated in spite of the potential for a stronger LSPR-induced electric field. In this study, we report the development of a novel colloidal method to synthesize chiral Au-Ag core-shell nanoparticles via electrochemical deposition of Ag layer onto the surface of pre-synthesized chiral Au nanoparticles.Chiral Au NPs were prepared according to a previous report using L-cysteine as the ligand.[1] Thus-prepared NPs were loaded on a glassy carbon (GC) electrode. A Cu monolayer was deposited on Au NPs by the underpotential deposition (UPD) in an aqueous solution containing 1.0 mmol dm-3 CuSO4. The Cu UPD layer was replaced with Ag through galvanic replacement by immersing the electrode with the Cu-UPD Au NPs in a 10 mmol dm-3 AgNO3 aqueous solution. The amount of Ag deposition on individual Au NPs was controlled by repeating the procedures of Cu UPD and Ag replacement.Cyclic voltammograms were measured on GC electrodes loaded with chiral Au NPs in a CuSO4 solution. With a negative sweep of the electrode potential, a cathodic current peak originating from the Cu UPD was observed at ca. +0.5 V vs. RHE and a current assignable to bulk Cu deposition appeared at the potential more negative than +0.25 V vs. RHE. In contrast, a potential sweep to positive direction generated an anodic current corresponding to the oxidation of the Cu layer. Based on these results, we determined the potential of Cu UPD on chiral Au NPs.The average diameter of chiral Au NPs prepared with L-cysteine was 117 nm, and a twisted surface was confirmed by SEM measurements. Even after three cycles of the above-mentioned Ag deposition procedures, no clear change in the shape of chiral Au NPs was observed. However, the average size of particles increased to 123 nm after these cycles, indicating the deposition of Ag shell layer of ca. 1 nm thickness on Au NPs per cycle. This study successfully demonstrates the preparation of chiral Au-Ag core-shell NPs through electrochemical methods involving Cu UPD on Au NPs and subsequent galvanic replacement with Ag. References (1) K. T. Nam, et al, Nat. Commun, 11, 263 (2020).

Chiral Rotaxane‐Branched Dendrimers as Relays in Artificial Light‐Harvesting Systems with Boosted Circularly Polarized Luminescence

Chiral Rotaxane‐Branched Dendrimers as Relays in Artificial Light‐Harvesting Systems with Boosted Circularly Polarized Luminescence

Chiral Rotaxane-Branched Dendrimers as Relays in Artificial Light-Harvesting Systems with Boosted Circularly Polarized Luminescence.

Starting from AIEgen-functionalized chiral [2]rotaxane building block, we have successfully synthesized a new class of chiral rotaxane-branched dendrimers through controllable divergent strategy for the first time, based on which novel chiral artificial light-harvesting systems (LHSs) were successfully constructed in aqueous phase by sequentially introducing achiral donor and acceptor. More importantly, accompanied by the two-step Förster resonance energy transfer (FRET) process in the resultant artificial LHSs, the sequentially amplified circularly polarized luminescence (CPL) performances were achieved, highlighting that the chiral rotaxane-branched dendrimers could serve as excellent relay for both energy transfer and chirality transmission. Impressively, compared with the sole chiral rotaxane-branched dendrimers, the dissymmetry factors (glum) values of the resultant artificial LHSs were amplified by one order of magnitude up to 0.038, enabling their further applications in information storage and encryption. The proof-of concept study provides not only a feasible approach for the efficient amplification of CPL performances but also a novel platform for the construction of novel chiral luminescent materials.

Influence of resonant plasmonic nanoparticles on optically accessing the valley degree of freedom in 2D semiconductors

The valley degree of freedom in atomically thin transition metal dichalcogenides, coupled with valley-contrasting optical selection rules, holds great potential for future electronic and optoelectronic devices. Resonant optical nanostructures emerge as promising tools for controlling this degree of freedom at the nanoscale. However, their impact on the circular polarization of valley-selective emission remains poorly understood. In our study, we explore a hybrid system where valley-specific emission from a molybdenum disulfide monolayer interacts with a resonant plasmonic nanosphere. Contrary to the simple intuition that a centrosymmetric nanoresonator mostly preserves the degree of circular polarization, our cryogenic experiments reveal significant depolarization of the photoluminescence scattered by the nanoparticle. This striking effect presents an ideal platform for studying the mechanisms governing light-matter interactions in such hybrid systems. Our full-wave numerical analysis provides insights into the key physical mechanisms affecting the polarization response, offering a pathway toward designing novel valleytronic devices.

Strong-field nondipole approximation in laser-assisted thermal electron scattering

This study investigates the differential cross-section (DCS) of electrons scattered by a hydrogen molecule (H₂) under varying conditions, including temperature, momentum, laser intensity, and polarization. The objective was to understand how these parameters affect electron scattering and to compare the effects of linear and circular polarizations. Methodologically, theoretical model was developed using strong-field nondipole approximation with linear and circular polarized laser fields, examining DCS as a function of thermal electron temperature, momentum, and laser intensity. The study utilized a modified Volkov wave function model to account for thermal electron effects and analyzed DCS variations across different orbitals (n = 1, n = 2, and n = 3). Findings reveal that DCS increases with temperature due to enhanced electron oscillations, with higher orbitals (n = 3) showing greater DCS compared to lower orbitals (n = 1). Increased momentum results in decreased DCS, with higher orbitals exhibiting higher DCS values under circular polarization, contrary to linear polarization. Laser intensity decreases DCS for both polarizations, with circular polarization providing a narrower range of DCS values and generally higher DCS compared to linear polarization. This research further exploration of polarization effects on DCS in different atomic systems and extending studies to higher energy regions for a comprehensive understanding of electron scattering dynamics.

Trion sensing of a zero-field composite Fermi liquid.

The half-filled lowest Landau level is a fascinating platform for researching interacting topological phases. A celebrated example is the composite Fermi liquid, a non-Fermi liquid formed by composite fermions in strong magnetic fields1-10. Its zero-field counterpart is predicted in atwisted MoTe2 bilayer (tMoTe2)11,12-a recently discovered fractional Chern insulator exhibiting the fractional quantum anomalous Hall effect13-16. Although transport measurements at ν = -1/2 show signatures consistent with a zero-field composite Fermi liquid14, new probes are crucial to investigate the state and its elementary excitations. Here, by using the unique valley properties of tMoTe2, we report optical signatures of a zero-field composite Fermi liquid. We measured the degree of circular polarization (ρ) of trion photoluminescence versus hole doping and electric field. We found that, within the phase space showing robust ferromagnetism, ρ is near unity for Fermi liquid states. However, ρ is quenched at both integer andfractional Chern insulators, and in a holedoping range near ν = -1/2. Temperature, optical excitation power and electric-field-dependence measurements demonstrate that the quenching of ρ is a direct consequence of an energy gap (pseudogap) for electronic excitations of the Chern insulators (composite Fermi liquid): because the local spin-polarized excitations necessary to form trions are strongly suppressed, trion formation at the corresponding filling factors relies on optically generated unpolarized itinerant holes. Our work highlights a new excitonic probe of zero-field fractional Chern insulator physics, unique to tMoTe2.

Laser-Assisted Scattering With Screened Diatomic Potential

This study explores the differential cross section (DCS) for laser-assisted scattering of diatomic molecules, considering various polarization conditions (linear, circular, elliptical) and potential parameters. The primary objective is to understand how polarization, screening effects, and potential parameters influence the scattering behavior. Utilizing a model that incorporates the Morse potential with screening effects, the analysis treats the laser field classically as a time-dependent, spatially homogeneous electric field, while the electron dynamics are described quantum mechanically using the Schrödinger equation. The Volkov wavefunction is derived, and the first-Born S-matrix element is computed to evaluate the scattering process. The results show that the DCS decreases with increasing screening parameters, with linear polarization yielding higher values than circular or elliptical polarization. Specifically, at an initial momentum of 8 MeV and a final momentum of 9 MeV, the DCS for elliptical polarization is notably higher. The DCS also varies with potential strength and well width, showing a peak at 0.14 Å for potential well width. The findings suggest that linear polarization is most effective for scattering studies under varying potential strengths. It is recommended to focus on linear polarization for enhanced scattering efficiency and to carefully adjust screening parameters and potential well widths for optimal results.

Metasurface‐Loaded Twin‐Port Circularly Polarized Microstrip Array Antenna With High Gain and Isolation Features for mm‐Wave‐Based 5G Communication System

ABSTRACTIn this article, a MIMO microstrip aerial in mm‐wave regime is structured and examined. A 1 × 2 array‐based structure is designed to get directional radiation beam, which in turn provides good gain value, that is, 10.2 dBi in mm‐wave regime. The use of defected ground structure (DGS) improves the impedance matching (more than 25 dB) of the proposed radiator. Metasurface is suspended over the twin port aerial for adding two important features: (i) reduction of mutual coupling between antenna ports, that is, less than −25 dB; and (ii) conversion of the linear waves into the circular one in between 30.45 and 30.95 GHz. Experimental measurement of designed radiator confirms that designed aerial works in between 30.4 and 31.5 GHz with separation level more than 25 dB. Stable field pattern and good diversity parameter confirms its employability for mm‐wave 5G communication system.

A wideband circularly-polarized MIMO filtering array antenna using dual-layer circular patch

ABSTRACT A novel wideband circularly-polarized (CP) MIMO filtering array antenna with dual-layer circular cross-slotted patch is introduced. The presented element consists of a two-way feeding structure designed with equal amplitude and 90° phase difference, and a dual-layer circular cross-slotted patch structure. An aperture-couple-driven patch is positioned between a cross-slotted patch and a dual-feed structure. It facilitates magnetic coupling to achieve a high-frequency resonant mode and radiation null. Meanwhile, four arc-shaped patches are electrically coupled to the driver patch by surrounding it with four shorting vias to improve the bandwidth. In multiple-input multiple-output (MIMO) wireless systems, a two-port MIMO dual-CP filtering array antenna for the Sub-6 G band is proposed. The design utilizes four proposed CP antenna elements and a dual-port transmission structure. The dual-port transmission structure consists of two sets of T-junction power dividers that are 180° phase shifted with opposite polarization. The dual-CP MIMO filtering array antenna of the impedance bandwidth is 21.8% (3.1 ~ 3.9 GHz). The AR bandwidth is 13.1% (3.3 ~ 3.7 GHz), while the gain bandwidth is 20.1%. Additionally, the isolation between the antenna elements is less than −15.0 dB. The envelope correlation coefficient between its two ports is less than 0.02.

Metasurface-Assisted mutual coupling suppression in circularly polarized MIMO antenna array for Sub-6 GHz applications

A double-sided decoupling metasurface (DSDM) method is proposed to reduce the mutual coupling between very closely spaced circularly polarized (CP) MIMO antenna elements for sub-6 GHz applications. A proposed DSDM structure with a square-shaped patch layer is placed over the array to reduce mutual coupling by non-propagating evanescent waves and manipulating the polarization of propagating reflected CP waves. This decoupling mechanism relies on the DSDM’s negative electric permittivity extracted from the meta-atom. When the CP waves were incident to DSDM polarizer through the excited CP antenna of the array, the polarization states of the reflected and transmitted CP waves were changed as controlled by DSDM. In reflection mode, the negative permittivity of DSDM produce two type of the waves reflected waves generated the polarization mismatch and evanescent waves that reduce the coupling between CP antennas, while the transmission mode, controlling the radiation pattern at φ = 45° or φ = 135°. The low-profile proposed decoupling structure was fabricated and experimentally validated. The decoupling design significantly mitigated the measured mutual coupling between the CP antenna elements at 3.5 GHz by more than 15 dB and by more than 13 dB at 3.02 GHz to 3.67 GHz, compared to the reference array. The proposed design achieves less than a 3 dB axial ratio, maximum realized gain of 5.52 dBic at 3.5 GHz. An excellent agreement between the simulated and measured outcomes has been studied.

A single dual-frequency reflective metasurface for simultaneous multi-mode orbital angular momentum multiplexing

In this paper, we propose a dual-frequency reflective metasurface that utilizes geometric phase to achieve multiple modes of orbital angular momentum (OAM). The metasurface consists of two metal layers and a dielectric layer sandwiched between them, with independent control of amplitude and phase modulation at two frequency points by rotating the outer split ring and inner cross structures on the top layer of the metasurface. When circularly polarized (CP) terahertz waves impinge on the metasurface, it is possible to achieve a single-beam normal reflection, single-beam anomalous reflection, and dual-beam reflection in the form of OAM vortex beams. Specifically, for right-hand circular polarization (RCP) incidence, at the frequency of 140 GHz, its vertical reflection is the OAM beam of mode +2, and at the frequency of 200 GHz, its vertical reflection is the OAM beam of mode +1; for left-hand circular polarization (LCP) incidence, at the frequency of 140 GHz, its vertical reflection is the OAM beam of mode −2, and at the frequency of 200 GHz, the corresponding vertical reflection is the OAM beam of mode −1. Additionally, anomalously reflected OAM beams are designed, which, after RCP incidence on the metasurface, produce an OAM beam with mode −1 and a reflection angle of 17° at 140 GHz, and an OAM beam with mode +1 and a reflection angle of 12° at 200 GHz. Finally, a dual-beam OAM reflective metasurface is designed, which generates two vortex beams with mode +2 at 140 GHz and two vortex beams with mode +1 at 200 GHz under RCP incidence. Therefore, the metasurface designed in this paper has broad application prospects in multi-channel transmission for future terahertz communication systems.

Robust generation of intrinsic C points with magneto-optical bound states in the continuum.

C points, circular polarization in momentum space, play crucial roles in chiral wave manipulations. However, conventional approaches of achieving intrinsic C points using photonic crystals with broken symmetries suffer from a low Q factor and high sensitivity to structural geometry, rendering them fragile and susceptible to perturbations and disorders. We report magneto-optical (MO) bound states in the continuum (BICs) with a symmetry-preserved planar photonic crystal. We achieve intrinsic C points at Γ point that are robust against variation in both structural geometry and external magnetic field. MO coupling between two modes induces Zeeman splitting, leading to MO BICs and quasi-BICs with circular eigenstates for high-Q chiral responses. Furthermore, switchable C point handedness and circular dichroism are enabled by reversing the magnetic field. These findings unveil BICs and quasi-BICs with circular eigenstates and on-demand control of C points, paving the way for advanced chiral wave manipulation with enhanced light-matter interaction.

UGMRT Survey of EXoplanets Around M-dwarfs (GS-EXAM): Radio Observations of GJ 1151

Coherent radio emission with properties similar to planetary auroral signals has been reported from GJ 1151, a quiescent, slow-rotating mid-M star, by the LOFAR Two-meter (120–170 MHz) Sky Survey. The observed LOFAR emission is fairly bright at 0.89 mJy with 64% circular polarization, and the emission characteristics are consistent with the interaction between an Earth-sized planet with an orbital period of 1–5 days and the magnetic field of the host star. However, no short-period planet has been detected around GJ 1151. To confirm the reported radio emission caused by the putative planet around GJ 1151 and to investigate the nature of this emission, we carried out upgraded Giant Metrewave Radio Telescope observations of GJ 1151 at 150, 218, and 400 MHz over 33 hr across ten epochs. No emission was detected at any frequency. While at 150 and 218 MHz, nondetection could be due to the low sensitivity of our observations, at 400 MHz, the rms sensitivities achieved were sufficient to detect the emission observed with LOFAR at ∼20σ level. Our findings suggest that the radio emission is highly time variable, likely influenced by the star-planet system’s phase and the host star’s magnetic field. Additional observations below 170 MHz, at more frequent epochs (as the periodicity of the emission is unknown), especially during periods of high stellar magnetic field strength, are needed to confirm the emission.

Energy Transfer for Constructing Circularly Polarized Luminescence Materials: Recent Progress and Future Prospects

AbstractCircularly polarized luminescence (CPL) materials hold significant promise in multidisciplinary fields such as circularly polarized organic light‐emitting diodes, biological probes, data storage, and information encryption. However, these cutting‐edge applications also put forward higher requirements for the design of CPL materials, requiring large dissymmetry factor and high emission quality. For this purpose, diverse approaches have been explored to generate and enhance CPL emission. Among them, energy transfer (ET) strategy stands out as it can be readily implemented in a wide range of CPL materials. The present work overviews latest advances in energy transfer for generating and modulating CPL, involving small organic molecules, polymers, metal complexes, liquid crystals, as well as new‐emerging chiral luminescent materials. It is anticipated that the review article will garner increased attention toward energy transfer systems and facilitate the advancement of CPL materials.

Construction and Circularly Polarized Luminescence of Thiophene-Based Multiple Helicenes.

Thiophene-based monohelicene (TS[7]H), triple helicenes (TT[7]H), and hexapole helicenes (TH[7]H) were synthesized via oxidative photocyclization and cascade Suzuki/intramolecular cyclization as the crucial steps. The enantiomers of TS[7]H, TT[7]H-2, and TH[7]H exhibited circularly polarized luminescence (CPL), and the luminescence dissymmetry factors (glum) gradually increased from -5.1 × 10-4 to -2.0 × 10-3 with an increase in multiplicity from TS[7]H to TH[7]H. In addition, TS[7]H, TT[7]H, and TH[7]H displayed a second-level long afterglow at 77 K.

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 2.4 GHz 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.

5]Helicene Based π-Conjugated Macrocycles with Persistent Figure-Eight and Möbius Shapes: Efficient Synthesis, Chiral Resolution and Bright Circularly Polarized Luminescence.

π-Conjugated chiral shape-persistent molecular nanocarbons hold great potential as chiroptical materials, though their synthesis remains a considerable challenge. Here, we present a simple approach using Suzuki coupling of a [5]helicene building block with various aromatic units, enabling the one-pot synthesis of a series of chiral macrocycles with persistent figure-eight and Möbius shapes. Single-crystal structures of 7 compounds were solved, and 22 enantiomers were separated by preparative chiral HPLC. A notable pyrene-bridged figure-eight macrocycle, with its rigid, fully π-conjugated and overcrowded structure, exhibited pure excimer emission and outstanding circularly polarized luminescence (CPL) properties, including a large dissymmetric factor (|glum|=3.8×10-2) and significant CPL brightness (BCPL=710.5 M-1cm-1). This method provides a versatile synthetic platform for producing various chiral D2-symmetric figure-eight macrocycles and singly or triply twisted Möbius macrocycles with C2 and D3 symmetry, offering tunable chiroptical properties for CPL applications.