Optical Polarization Research Articles

Design of tunable selective light-absorbing metasurfaces driven by intrinsically chiral quasi-bound states in the continuum

Chiral metasurfaces with high quality factors (Q-factors) and strong circular dichroism (CD) are excellent platforms for studying chiral optical response. Here, a design is proposed of an intrinsic chiral silicon metasurface driven by bound states in the continuum (BIC), with ultra-high Q-factor (Q = 3722) and chirality response close to the unit CD (CD > 0.99). By breaking the in-plane and out-of-plane symmetry of the structure, the intrinsic chirality based on BIC can be precisely controlled. In addition to studying intrinsic chirality, we have also achieved extrinsic chirality by obliquely incident circularly polarized light without introducing out-of-plane asymmetry. Moreover, we introduce graphene into the intrinsically chiral metasurface to form a graphene-Si hybridized metasurface. Selective absorption of intensity-controlled right-handed/left-handed circularly polarized light (RCP/LCP) was achieved by actively tuning the Fermi level and out-of-plane tilt angle of the graphene structure based on coupled-mode theory. Our research provides another insight into the application of intrinsic optical chirality, which is expected to be widely used in the fields of optical filters, polarization detectors, and chiral imaging.

Floquet-engineered valley topotronics in Kekulé-Y bond textured graphene superlattice

The exquisite distortion in a Kekulé -Y (Kek-Y) superlattice merges the two inequivalent Dirac cones (from the K- and the K′- points) into the highest symmetric Γ-point in the hexagonal Brillouin zone. Here, we report that UV circularly polarized light not only opens up a topological gap at the Γ-point, but also lifts the valley degeneracy at that point. Endowed with Floquet dynamics and by devising a scheme of high-frequency approximation, we propose that the left/right-handedness in polarized light offers the possibility to realize valley-selective circular dichroism in a Kek-Y-shaped graphene superlattice. In addition, the non-vanishing Berry curvature and enumeration of the valley-resolved Chern number CK/CK′=+1/−1 enable us to assign two pseudospin flavors (up/down) with the two valleys. Thereby, the above observations confirm the topological transition, suggesting the ease of realizing the valley quantum anomalous Hall state within the photon-dressed Kek-Y. These findings further manifest a non-zero optical valley polarization that is maximal at the Γ-point. Our paper thus proposes an optically switchable topological valley filter, which is desired in the evolving landscape of valleytronics.

A study of gamma-ray emission from OJ 287 using Fermi-LAT from 2015-2023

We search for gamma-ray emission from OJ287 in the energy range from 0.1-300 GeV during 2015-2023, in coincidence with an extensive observing campaign to monitor the optical flux variability and polarization, as discussed in arXiv:2311.02372. We present results for eight segments in the aforementioned period, with each segment corresponding to an observing season. We report non-zero gamma-ray flux (with >10σ significance) for all the eight segments. The photon and energy flux observed during this period is and , respectively, while the SED can be fitted with a power law with a slope of 2.12±0.02. The observed luminosity is between 1045−1046 ergs/sec.

Push-pull biphenyl and tolane derivatives as novel luminescent liquid crystals: synthesis and properties

ABSTRACT Addressing the current challenge of high melting points and long π-conjugated skeletons in luminescent nematic liquid crystals (LCs), this study explores the incorporation of push-pull dyes with biphenyl and tolane skeletons to extend fluorescence emission wavelengths into the visible light region. We synthesised push-pull-type biphenyl and tolane derivatives incorporating alkylamino groups as donors and cyano groups as acceptors. The thermal behaviour was investigated using optical polarisation microscopy, differential scanning calorimetry and X-ray diffraction. Notably, some molecules exhibited a nematic phase. The photophysical properties of the solution and solid states were also investigated. Furthermore, we formulated a room-temperature luminescent LC by blending several LCs. Importantly, the fluorescence in the nematic phase exhibited a red-shift compared to that observed in the solution and solid states. This study demonstrates the efficacy of the push-pull structure in the design of luminescent LCs. The findings of this study hold considerable implications for the development of advanced optoelectronic devices, particularly those requiring luminescent materials with tailored properties.

Clues on the nature of the quasi-periodic optical outbursts of the blazar OJ 287

The fascination with the blazar OJ 287 stems not only from its status as a prominent candidate for a close supermassive black hole (SMBH) binary, but also because of the thermal bremsstrahlung origin proposed for its giant optical outbursts. These outbursts arrive as pairs, quasi-periodically every $ 12$ years, based on the unique 130-year-long, well-sampled optical light curve available for this blazar. For its three well-known, large quasi-periodic optical outbursts (QPOOs), observed in 1983, 2007 and 2015, optical photo-polarimetric monitoring has been reported in the literature. For these initially radio-undetected QPOOs, widely acclaimed as `bremsstrahlung flares', we have scrutinised the available measurements of optical polarisation and spectral index during the rising phase. Several inconsistencies of these data with the optical bremsstrahlung interpretation are noted, which point towards a synchrotron-dominated alternative interpretation for all these prominent QPOOs, just as for the optical emission observed between the outbursts. Possible reasons for the radio non-detection of the QPOOs during the initial stage are outlined.

Chip‐Scale Optically Pumped Magnetometry Enabled by Tailorable Elliptical Dichroism Metasurface

AbstractEmerging miniaturized optically pumped magnetometers (OPMs) are becoming one of the most desirable approaches for biomagnetic imaging, especially for OPM with elliptically polarized light, which promises single‐light optical pumping and detection with high sensitivity. However, conventional schemes of this kind require a set of bulk polarization optics and tedious adjustment procedures, which compromise the system's compactness and practicality. In this paper, a novel chip‐scale OPM scheme that leverages the monolithic elliptical meta‐polarizer is presented and experimentally demonstrated. The meta‐polarizer with a side length of 3 mm is laid out on a 2 × 2 cm2 glass wafer. It offers the capability to convert arbitrary incident polarization into the desired elliptical polarization and exhibits a tailorable elliptical dichroism (ED) of ≈0.77 at the wavelength of 795 nm. A 4 × 4 × 4 mm3 vapor cell containing 87Rb and N2 is combined with this elliptical meta‐polarizer to construct a miniaturized OPM. The sensitivity of this sensor reaches approximately 13 fT/Hz1/2 in a four‐layer magnetic shield with a dynamic range near zero magnetic field ≈ ±0.55 nT. By exploiting the advantages of planar integrated optics, reduced footprints and scalability are promised. And this work paves the way for the integration of emerging quantum sensors on a chip.

Dynamic control of polarization conversion based on borophene nanostructures in optical communication bands

Polarized light has a number of potential applications in the communication bands, including optical communication, polarization imaging, quantum emission, and quantum communication. Nonetheless, there is a need to enhance the dynamic tunability, broadband operation, and flexibility of polarization control. Here, a borophene structure is proposed to dynamically control the polarization state of reflected light. The coherent excitation of localized surface plasmons (LSPs) empowers the achievement of a perfect linearly-circularly polarization conversion at the commercially important communication wavelength of 1550 nm. The dynamic tunability and switching, as well as the arbitrary polarization conversion, are enabled over a wide spectral range by modulating the carrier concentration of borophene. Moreover, by deforming the borophene array and alternately stimulating the upper and lower layers of the LSPs mode, the polarization rotation direction can be flexibly switched. Finally, the process of near-field coupling between the LSPs and dipole light source positioned at a chosen hotspot is demonstrated. This coupling enables polarization-tunable spontaneous emission enhancement, with a spontaneous emission enhancement exceeding 900. The proposed design contributes to enhancing the speed and efficiency of communication within the domain of quantum communication.

Emergence of Optical Anisotropy in Moiré Superlattice via Heterointerface Engineering.

The interaction between light and moiré superlattices presents a platform for exploring unique light-matter phenomena. Tailoring these optical properties holds immense potential for advancing the utilization of moiré superlattices in photonics, optoelectronics, and valleytronics. However, the control of the optical polarization state in moiré superlattices, particularly in the presence of moiré effects, remains elusive. Here, we unveil the emergence of optical anisotropy in moiré superlattices by constructing twisted WSe2/WSe2/SiP heterostructures. We report a linear polarization degree of ∼70% for moiré excitons, attributed to the spatially nonuniform charge distribution, corroborated by first-principles calculations. Furthermore, we demonstrate the modulation of this linear polarization state via the application of a magnetic field, resulting in polarization angle rotation and a magnetic-field-dependent linear polarization degree, influenced by valley coherence and moiré potential effects. Our findings demonstrate an efficient strategy for tuning the optical polarization state of moiré superlattices using heterointerface engineering.

Testing particle acceleration in blazar jets with continuous high-cadence optical polarization observations

Variability can be the pathway to understanding the physical processes in astrophysical jets. However, the high-cadence observations required to test particle acceleration models are still missing. Here we report on the first attempt to produce continuous, $>24$ hour polarization light curves of blazars using telescopes distributed across the globe, following the rotation of the Earth, to avoid the rising Sun. Our campaign involved 16 telescopes in Asia, Europe, and North America. We observed BL Lacertae and CGRaBS J0211+1051 for a combined 685 telescope hours. We find large variations in the polarization degree and angle for both sources on sub-hour timescales as well as a $ rotation of the polarization angle in CGRaBS J0211+1051 in less than two days. We compared our high-cadence observations to particle-in-cell magnetic reconnection and turbulent plasma simulations. We find that although the state-of-the-art simulation frameworks can produce a large fraction of the polarization properties, they do not account for the entirety of the observed polarization behavior in blazar jets.

Generation of terahertz beam with longitudinally varied polarization state via coherent superposition based on metasurface.

Polarization is an important dimension in the research and applications of light waves. However, traditional polarization optics often only focus on the polarization characteristics in the transverse plane. Here, we demonstrate a new scheme for the generation of longitudinally varied polarization state in terahertz beam using all-silicon metasurface. We employ wavefront transformation designs with long-focal-depth for orthogonal circularly polarized terahertz waves, achieving varied amplitude and phase along the propagation direction in opposite spin states. Based on the principle of coherent superposition of polarized waves, different linear and elliptical polarization states are obtained in transverse planes along the propagation path, with variable ellipticity and azimuth angle. Simulation results show that a large-scale evolution of the elliptical polarization azimuth angle from 45° to -60° and ellipticity from 20° to -74° can be observed within a focal depth range of 0.45-0.8 mm. We also intuitively display the helical trajectory of the polarization state from left-hand elliptical ones to right-hand elliptical ones within the focal depth range, using the Poincaré sphere. This work expands the application of metasurface devices for multifunctional polarization devices and can be applied to polarization generation and transformation for optical imaging or terahertz communications.

Multidimensional Encryption by Chip-Integrated Metasurfaces.

Facing the challenge of information security in the current era of information technology, optical encryption based on metasurfaces presents a promising solution to this issue. However, most metasurface-based encryption techniques rely on limited decoding keys and struggle to achieve multidimensional complex encryption. It hinders the progress of optical storage capacity and puts encryption security at a disclosing risk. Here, we propose and experimentally demonstrate a multidimensional encryption system based on chip-integrated metasurfaces that successfully incorporates the simultaneous manipulation of three-dimensional optical parameters, including wavelength, direction, and polarization. Hence, up to eight-channel augmented reality (AR) holograms are concealed by near- and far-field fused encryption, which can only be extracted by correctly providing the three-dimensional decoding keys and then vividly exhibit to the authorizer with low crosstalk, high definition, and no zero-order speckle noise. We envision that the miniature chip-integrated metasurface strategy for multidimensional encryption functionalities promises a feasible route toward the encryption capacity and information security enhancement of the anticounterfeiting performance and optically cryptographic storage.

Interstellar Polarization Survey. IV. Characterizing the Magnetic Field Strength and Turbulent Dispersion Using Optical Starlight Polarization in the Diffuse Interstellar Medium

Angular dispersion functions are typically used to estimate the fluctuations in polarization angle around the mean magnetic field orientation in dense regions, such as molecular clouds. The technique provides accurate turbulent-to-regular magnetic field ratios, 〈Bt2〉1/2/Bpos , which are often underestimated by the classic Davis–Chandrasekhar–Fermi method. We assess the technique's suitability to characterize the turbulent and regular plane-of-sky magnetic field in low-density structures of the nearby interstellar medium (ISM), particularly when the turbulence outer scale, δ, is smaller than the smallest scale observed, ℓ min. We use optical polarization maps of three intermediate-latitude fields (∣b∣ ≳ 7.°5) with dimensions of 0.°3 × 0.°3, sourced from the Interstellar Polarization Survey–General ISM catalog. We decomposed the H i emission detected by the Galactic All-Sky Survey within our fields to estimate the multiphase ISM properties associated with the structure coupled to the magnetic field. We produced maps of the plane-of-sky magnetic field strength (B pos), mass density (ρ), and turbulent velocity dispersion (σ v,turb). In the regions with well-defined structures at d < 400 pc, the average B – ranges from ∼3 μG to ∼9 μ G, depending on the method and physical properties. In the region where structures extend up to 1000 pc, B pos varies from ∼1 to ∼3 μ G. The results agree with previous estimations in the local, diffuse ISM. Finally, optical starlight polarization and thermal dust polarization at 353 GHz consistently reveal a highly regular plane-of-sky magnetic field orientation unfazed by diffuse dust structures observed at 12 μm.

Research on lightning strike location by OPGW optical sensing based on extreme sliding window and wavelet

Abstract Lightning strikes usually affect the safe use and normal operation of the power grid. It is crucial to accurately identify and position the lightning strikes. The lightning current on OPGW near the lightning strike point and the modulated lightning intensity signal waveform were simulated. The polarization state signal of Faraday optical fiber will mutate when it is struck by lightning. The extreme value unit sliding window energy method was used to extract the initial time window of the signal after a lightning strike, and the three alternative windows with the maximum energy were determined. Then the maximum wavelet coefficient is determined to be the first wave time point of the struck signal. Simulation analysis and engineering field application show that the optical polarization signal characteristic of OPGW can be used to accurately locate the lightning strike point, which can meet the needs of practical engineering applications of power systems.

Is the dynamical quantum Cheshire cat detectable?

We explore how one might detect the dynamical quantum Cheshire cat proposed by Aharonov et al We show that, in practice, we need to bias the initial state by adding/subtracting a small probability amplitude (‘field’) of the orthogonal state, which travels with the disembodied property, to make the effect detectable (i.e. if our initial state is |↑z⟩ , we need to bias this with some small amount δ of state |↓z⟩ ). This biasing, which can be done either directly or via weakly entangling the state with a pointer, effectively provides a phase reference with which we can measure the evolution of the state. The outcome can then be measured as a small probability difference in detections in a mutually unbiased basis, proportional to this biasing δ. We show this is different from counterfactual communication, which provably does not require any probe field to travel between sender Bob and receiver Alice for communication. We further suggest an optical polarisation experiment where these phenomena might be demonstrated in a laboratory.

IXPE observation of PKS 2155-304 reveals the most highly polarized blazar

We report the X-ray polarization properties of the high-synchrotron-peaked (HSP) blazar PKS 2155$-$304 based on observations with the Imaging X-ray Polarimetry Explorer (IXPE). We observed the source between Oct 27 and Nov 7, 2023. We also conducted an extensive contemporaneous multiwavelength (MW) campaign. We find that during the first half ($T_1$) of the IXPE pointing, the source exhibited the highest X-ray polarization degree detected for an HSP blazar thus far, (30.7pm 2.0)&lt;!PCT!&gt;; this dropped to (15.3pm 2.1)&lt;!PCT!&gt; during the second half ($T_2$). The X-ray polarization angle remained stable during the IXPE pointing at 129.4 and 125.4 during $T_1$ and $T_2$, respectively. Meanwhile, the optical polarization degree remained stable during the IXPE pointing, with average host-galaxy-corrected values of (4.3pm 0.7)&lt;!PCT!&gt; and (3.8pm 0.9)&lt;!PCT!&gt; during the $T_1$ and $T_2$, respectively. During the IXPE pointing, the optical polarization angle changed achromatically from sim 140 to sim 90 and back to sim 130 Despite several attempts, we only detected (99.7&lt;!PCT!&gt; conf.) the radio polarization once (during $T_2$, at 225.5 GHz): with degree (1.7pm 0.4)&lt;!PCT!&gt; and angle 112.5 The direction of the broad pc-scale jet is rather ambiguous and has been found to point to the east and south at different epochs; however, on larger scales (&gt; 1.5 pc) the jet points toward the southeast (sim 135 similarly to all of the MW polarization angles. Moreover, the X-ray-to-optical polarization degree ratios of sim 7 and sim 4 during $T_1$ and $T_2$, respectively, are similar to previous IXPE results for several HSP blazars. These findings, combined with the lack of correlation of temporal variability between the MW polarization properties, agree with an energy-stratified shock-acceleration scenario in HSP blazars.

Generating complex vectorial optical fields via surface lattice resonances.

Vectorial optical fields (VOFs) with extra degrees of freedom hold promise for many photonic applications. However, current methods to generate VOFs are either bulky in size or exhibit limited functionalities. Here, we demonstrate a tunable VOF generator by exciting plasmonic surface lattice resonances (SLRs) with axial symmetry. By meticulously arranging bilayer circular arrays with opposite handedness, we achieve a high Q-factor of 103 via just a few particles despite the general belief that too small array size suppresses the SLRs. This work presents tunable complex VOFs with distinct inhomogeneous spatial polarization distributions, which may enable various applications in integrated and polarization optics.

The extreme coronal line emitter AT 2022fpx: varying optical polarization properties and late-time X-ray flare

ABSTRACT Supermassive black holes disrupt passing stars, producing outbursts called tidal disruption events (TDEs). TDEs have recently gained attention due to their unique dynamics and emission processes, which are still not fully understood. Especially, the so-called optical TDEs are of interest as they often exhibit delayed or obscured X-ray emission from the accretion disc, making the origin of the prompt emission unclear. In this paper, we present multiband optical polarization observations and optical spectrometry of a recent TDE candidate AT 2022fpx, alongside monitoring observations in optical, ultraviolet, and X-rays. The optical spectra of AT 2022fpx show Bowen fluorescence as well as highly ionized iron emission lines, which are characteristic of extreme coronal line emitters. Additionally, the source exhibits variable but low-polarized continuum emission at the outburst peak, with a clear rotation of the polarization angle. X-ray emission observed approximately 250 d after the outburst peak in the decay appear flare-like but is consistent with constant temperature blackbody emission. The overall outburst decay is slower than for typical TDEs, and resembles more the ones seen from Bowen fluorescence flares. These observations suggest that AT 2022fpx could be a key source in linking different long-lived TDE scenarios. Its unique characteristics, such as extreme coronal line emission, variable polarization, and delayed X-ray flare, can be attributed to the outer shock scenario or a clumpy torus surrounding the supermassive black hole. Further studies, especially in the context of multiwavelength observations, are crucial to fully understand the dynamics and emission mechanisms of these intriguing astrophysical events.

Investigations on the Carrier Mobility of Cs2NaFeCl6 Double Perovskites

Double perovskite materials have gradually become widely studied due to their potential applications in solar cells and other optoelectronic devices. We take Cs2NaFeCl6 as an example to investigate the carrier mobility with respect to the acoustic phonon and the optical phonon scattering mechanisms. By considering the deformation potential, carrier effective mass, and bulk modulus, the longitudinal acoustic (LA) phonon-determined mobilities for electrons and holes in Cs2NaFeCl6 are found to be μe = 2886.08 cm2 v−1 s−1 and μh = 39.09 cm2 v−1 s−1, respectively. The optical scattering mechanism involves calculating the Fröhlich coupling constant, dielectric constant, and polaron mass to determine the multiple polar optical (PO) phonon-scattering-determined mobilities, resulting in μe = 279.25 cm2 v−1 s−1 and μh = 21.29 cm2 v−1 s−1, respectively. By combining both interactions, the total electron mobility and hole mobility are determined to be 254.61 cm2 v−1 s−1 and 13.78 cm2 v−1 s−1, respectively. The findings suggest that the polarization of both electrons and ions, small coupling constant, and bulk modulus in Cs2NaFeCl6’s lattice make PO scattering a significant contribution to carrier mobility in this specific double perovskite, highlighting the importance of considering this in enhancing the optoelectronic properties of Cs2NaFeCl6 and other double perovskites.

Study on water tree resistance and self‐healing properties of multi‐monomer melt‐grafted polyethylene

AbstractIn order to suppress the damage of cable insulation caused by water tree structure formed by micro‐droplets at insulation defects in low density polyethylene (LDPE) materials under AC electric field. In this paper, the siloxane group is grafted onto LDPE by melt grafting method, and different content of comonomer styrene (St) is added to improve the grafting rate of siloxane group grafted polyethylene. The effect of St on the microscopic characteristics of LDPE grafted KH570 is studied. In order to verify the accuracy and timeliness of water tree self‐healing of grafted polymer insulation materials, the microstructure characteristics of LDPE ungrafted and grafted polymer samples are analyzed by Fourier transform infrared spectroscopy, gel content test, and differential scanning calorimeter. Second, the AC dielectric properties of LDPE ungrafted and grafted polymer samples are studied by AC breakdown experiment and space charge test. Finally, the water tree length, micropore defects, and self‐healing of the samples are observed by optical microscopy and polarization and depolarization current method, and the changes of chemical composition in the water tree area before and after aging are analyzed by infrared spectroscopy. The principle and mechanism of repairing water tree defects with grafted monomers are explained. This paper not only combines the previous research results of self‐healing materials, but also provides a new method for the preparation process of LDPE grafted polymer, which has a good research prospect in practical application.

Optical Spectropolarimetric Variability Properties in Blazars PKS 0637–75 and PKS 1510–089

Spectropolarimetry is a powerful tool to investigate the central regions of active galactic nuclei (AGNs) as polarization signatures are key to probing magnetic field structure, evolution, and the physics of particle acceleration in jets. Optical linear polarization of blazars is typically greater than a few percent, indicating the emission is dominated by nonthermal synchrotron radiation, while polarization less than a few percent is common for other type 1 AGNs. We present a spectropolarimetric study of PKS 0637–75 and PKS 1510–089 to determine how the head-on orientation of a jet and dominant emission processes influence polarimetric variations in the broad lines and continuum. Observations were obtained biweekly from the Robert Stobie Spectrograph on the Southern African Large Telescope. Variability in the continuum polarization is detected for both PKS 0637–75 and PKS 1510–089, with a total average level of 2.5% ± 0.1% and 7.5% ± 0.1%, respectively. There is no clear polarization in the broad Balmer emission lines and weak polarization in Mg ii as the average level across all observations is 0.2% ± 0.1% for Hβ, 0.2% ± 0.3% for Hγ, and 0.6% ± 0.2% for Mg ii. We find that polarization measurements confirm the conclusions drawn from spectral energy distribution modeling of the disk–jet contributions to the emission as optical polarization and time variability for PKS 0637–75 are shown to be dominated by accretion disk emission while those of PKS 1510–089 are due to both disk and jet emission, with greater jet contribution during flaring states.