Polarization Rotation Angle Research Articles

Deep neural network-enabled multifunctional switchable terahertz metamaterial devices

Under the support of deep neural networks (DNN), a multifunctional switchable terahertz metamaterial (THz MMs) device is designed and optimized. This device not only achieves ideal ultra-wideband (UWB) absorption in the THz frequency range but enables dual-functional polarization transformation over UWB. When vanadium dioxide (VO2) is in the metallic state, the device as a UWB absorber with an absorption rate exceeding 90% in the 2.43–10 THz range, with a relative bandwidth (RBW) of 145.2%, and its wideband absorption performance is insensitive to polarization. When VO2 is in the insulating state, the device can switch to a polarization converter, achieving conversions from linear to cross polarization and from linear to circular polarization in the ranges of 4.58–10 THz and 4.16–4.43 THz, respectively. Within the 4.58–10 THz range, the polarization conversion ratio approaches 100% with an RBW of 74.3%, the polarization rotation angle is near 90°. Within the 4.16–4.43 THz range, the RBW is 6.29% and the ellipticity ratio approaches 1, Moreover, the effects of incident angle and polarization angle on the operational characteristics are studied. This THz MMs due to its advantages of wide angle, broad bandwidth, and high efficiency, provides valuable references for the research of new multifunctional THz devices. It has great application potential in short-range wireless THz communication, ultrafast optical switches, high-temperature resistant switches, transient spectroscopy, and optical polarization control devices.

Multipass Faraday rotators and isolators

Faraday isolators are usually limited to Faraday materials with strong Verdet constants. We present a method to reach the 45° polarization rotation angle needed for optical isolators with materials exhibiting a weak Faraday effect. The Faraday effect is enhanced by passing the incident radiation multiple times through the Faraday medium while the rotation angle accumulates after each pass. Materials having excellent thermo-optical properties in the ultraviolet and mid-infrared range become available for optical isolators. Herriott-type multipass cells offer a simple and compact way to realize the desired propagation length in usual optical materials of standard sizes. A proof-of-principle experiment was carried out, demonstrating polarization rotation of a 532 nm laser beam by an angle of 45° in anti-reflection-coated fused silica surrounded by a standard neodymium ring magnet.

Highly sensitive terahertz polarization biosensor utilizing chiral metasurface

In order to achieve a highly sensitive biosensor with a simple structure, we propose a chiral metasurface polarization sensor. Using immunological surface plasmon resonance (SPR) detection, the antigen or antibody is fixed as a probe on the SPR metasurface to detect the corresponding antibody or antigen. Through the change of the refractive index of the analyte on the surface facial mask, the terahertz signal changes, and finally the sensing detection of avian influenza virus can be achieved. The designed metasurface adopts a hollow split sector chiral structure to generate chiral surface current, which can convert linearly polarized incident waves as elliptical polarized waves. The structure achieves the high sensitivity of 401 deg/RIU at frequency of 0.8 THz, and the avian influenza virus (H1N1, H5N2 and H9N2) with the same real part of the refractive index can also be distinguished. Influenza viruses belong to the family Orthomyxoviridae of RNA viruses, divided into three types: A, B, and C. In this article, avian influenza viruses belong to type A influenza viruses. It can clearly identify different Avian Influenza Viruses by the two polarization characteristic parameters of the reflection spectrum PEA (Polarization Ellipse Angle) and PRA (Polarization Rotation Angle). This method has a significant application prospect in the fields of biomedicine and food industries.

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.

Active Full‐Color Generation Based on a Liquid Crystal‐Integrated Plasmonic Metasurface

Structural colors based on metasurfaces outperform traditional pigments and dyes in terms of nonfading, high spatial resolution, and high stability, usually incorporating active materials for tunability. Liquid crystals (LCs) are suitable for tunable structural color design due to their large birefringence and fast modulation by external stimuli. However, most LC‐integrated structural colors focus on tailoring the polarization angle of incident light to generate two colors and their mixing. Herein, a scheme of full‐color generation based on a plasmonic metasurface integrated with LCs utilizing the combination of the polarization angle rotation effect of the twisted‐nematic LCs and the refractive index modulation through the realignment of the LCs near the metasurface is demonstrated. Based on the proposed structural color method, full‐color generation of a record color gamut of 60.7% standard Red Green Blue region, equivalent to 43% National Television Standards Committee area, in the LC‐integrated metasurface, has been numerically realized by tuning the bias voltage of the LCs in reflection. The achieved color gamut is nearly 4 times wider than the previously reported result. The proposed active full‐color generation metasurface shows great potential in applications for low‐power reflective color display, anticounterfeiting, and optical encoding.

High-precision measurements of terahertz polarization states with a fiber coupled time-domain THz spectrometer

We present a new method for high precision measurements of polarization rotation in the frequency range from 0.2 to 2.2 THz using a fiber coupled time-domain THz spectrometer. A free standing wire-grid polarizer splits THz light into orthogonal components that are then measured by two separate detectors simultaneously. We theoretically model the uncertainties introduced by optical component non-idealities and predict that we may expect to achieve accuracies of 0.8% when anti-symmetrizing the response with respect to an applied field. Anti-symmetrization improves accuracy by more than four orders of magnitude. We demonstrate this method on a 2D electron gas in magnetic field and show that we achieve a precision of 20 μrad (1.1 mdeg) for small polarization rotation angles. A detailed description of the technique and data analysis procedure is provided, demonstrating its capability to precisely measure polarization states in the 0.2 to 2.2 THz range.

Photonic generation of frequency 12‐tupling millimeter‐wave based on three cascaded‐MZMs and polarization multiplexing

SummaryOptical millimeter‐wave generation is a predominant approach for the generation of high‐quality carrier signals for future wireless transmissions. This paper proposes an optical frequency 12‐tupling millimeter‐wave generation scheme using three cascaded‐MZMs assisted by polarization multiplexing for carrier suppression. A three‐stage MZM architecture produces the desired sixth‐order sidebands along with the undesired carrier signal. The proper adjustment of polarization direction and angle of polarization rotation lead to the effective suppression of the undesired optical carrier signal. A comprehensive mathematical analysis has been accomplished to evaluate the system's performance, and the obtained results are also validated through simulation findings. The derived results demonstrate that the proposed system is capable of operating over a broad modulation index range extending from 1.5 to 4.5, thereby relaxing the stringent requirements for a constant modulation index. The proposed system generates high‐purity mm‐wave signals with an OSSR of 62.06 dB and an RFSSR of 54.79 dB at a modulation index of 2.6. Moreover, it is also validated that even if the system parameters like modulation index, polarizer rotation angle, and phase difference among RF driving signals deviate from their ideal values to a certain degree, the system performance remains acceptable. The involvement of polarization technique, omission of wavelength‐dependent devices, and a large modulation index operating range make this methodology readily appealing for implementation in radio‐over‐fiber transmissions.

The relationship between simulated sub-millimeter and near-infrared images of sagittarius A* from a magnetically arrested black hole accretion flow

Abstract Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, undergoes large-amplitude near-infrared (NIR) flares that can coincide with the continuous rotation of the NIR emission region. One promising explanation for this observed NIR behavior is a magnetic flux eruption, which occurs in three-dimensional General Relativistic Magneto-Hydrodynamic (3D GRMHD) simulations of magnetically arrested accretion flows. After running two-temperature 3D GRMHD simulations, where the electron temperature is evolved self-consistently along with the gas temperature, it is possible to calculate ray-traced images of the synchotron emission from thermal electrons in the accretion flow. Changes in the gas dominated (σ = b2/2ρ < 1) regions of the accretion flow during a magnetic flux eruption reproduce the NIR flaring and NIR emission region rotation of Sgr A* with durations consistent with observation. In this paper, we demonstrate that these models also predict that large (1.5x - 2x) size increases of the sub-millimeter (sub-mm) and millimeter (mm) emission region follow most NIR flares by 20 - 50 minutes. These size increases occur across a wide parameter space of black hole spin (a = 0.3, 0.5, −0.5, 0.9375) and initial tilt angle between the accretion flow and black hole spin axes θ0 (θ0 = 0○, 16○, 30○). We also calculate the sub-mm polarization angle rotation and the shift of the sub-mm spectral index from zero to -0.8 during a prominent NIR flare in our high spin (a = 0.9375) simulation. We show that, during a magnetic flux eruption, a large (∼10rg), magnetically dominated (σ > 1), low density, and high temperature “bubble” forms in the accretion flow. The drop in density inside the bubble and additional electron heating in accretion flow between 15 rg- 25 rg leads to a sub-mm size increase in corresponding images.

First characterization of the emission behavior of Mrk 421 from radio to very high-energy gamma rays with simultaneous X-ray polarization measurements

Aims. We have performed the first broadband study of Mrk 421 from radio to TeV gamma rays with simultaneous measurements of the X-ray polarization from IXPE. Methods. The data were collected as part of an extensive multiwavelength campaign carried out between May and June 2022 using MAGIC, Fermi-LAT, NuSTAR, XMM-Newton, Swift, and several optical and radio telescopes to complement IXPE data. Results. During the IXPE exposures, the measured 0.2–1 TeV flux was close to the quiescent state and ranged from 25% to 50% of the Crab Nebula without intra-night variability. Throughout the campaign, the very high-energy (VHE) and X-ray emission are positively correlated at a 4σ significance level. The IXPE measurements reveal an X-ray polarization degree that is a factor of 2–5 higher than in the optical/radio bands; that implies an energy-stratified jet in which the VHE photons are emitted co-spatially with the X-rays, in the vicinity of a shock front. The June 2022 observations exhibit a rotation of the X-ray polarization angle. Despite no simultaneous VHE coverage being available during a large fraction of the swing, the Swift-XRT monitoring reveals an X-ray flux increase with a clear spectral hardening. This suggests that flares in high synchrotron peaked blazars can be accompanied by a polarization angle rotation, as observed in some flat spectrum radio quasars. Finally, during the polarization angle rotation, NuSTAR data reveal two contiguous spectral hysteresis loops in opposite directions (clockwise and counterclockwise), implying important changes in the particle acceleration efficiency on approximately hour timescales.

Megahertz detection of spectroscopic polarization by a time-encoded supercontinuum vector beam.

We demonstrated a 40-MHz detection of spectroscopic polarization by a supercontinuum vector beam with a wavelength-dependent polarization state. To achieve the high-repetition-rate measurement, we detected the rotation angle of polarization and the spectrum by measuring the temporal waveform using a photodetector after expanding the pulse duration of the supercontinuum vector beam. The spectrum of the supercontinuum vector beam was measured using a spectrometer. We compared it with the temporal waveforms, confirming a good agreement of spectra between the conventional spectrometer and the temporal waveforms. The detection method is useful for many applications requiring high-repetition-rate spectroscopic-polarization measurements, such as the defect inspection of thin optical materials.

Computational polarized colorful Fourier ptychography imaging: a novel information reuse technique of polarization of scattering light field

<sec>Fourier ptychography for high-resolution imaging has been a revolutionizing technical, since it can provide abundant information about target scene by changing illumination or pupil scanning. However, many objects are covered by dynamic scattering media, such as biological tissues and mist, that disrupts the light paths and forms the scattering wall, let alone high-resolution imaging. It is worth noting that the scatting effect caused by the scattering media will reduce the correlation of scattered light field, which makes the information aliasing difficult to extract. The situation becomes worse if the image scene is in color. Typically, the wavefront shaping, optical transmission matrix, and speckle correlation technique can successfully recover hidden targets form the scattered light field. Notably, the physical model of conventional method is limited by the difficultly in extracting target information from the strong scattering environment, especially in broadband light illumination imaging. Thus, it is limited to achieve super-resolution color imaging through scattering media by utilizing the current techniques.</sec><sec>In this work, we present a computational polarized colorful Fourier ptychography imaging approach for super-resolution perspective in broadband dynamic scattering media. In order to address the challenge of current imaging methods that is limited by the width of the light spectrum, the polarization characteristics of the scattered-light-field are explored. After retrieving a series of sub-polarized images, which bring the information about different frequencies caused by the motion of scattering media and are processed by the common-mode rejection of polarization characteristic, our computational approach utilizes the iterative optimization algorithm to recover the scene. Notably, owning to the difference between the target scattering information and background scattering information of scattered light fields with different polarization rotation angles, we can obtain two images in which the target information and the background information are dominant in the scattered field. Afterwards, a series of images containing target information and background information is used to iterate the Fourier ptychographyprogram to update the target image based on the obtained image sequence until the estimation converges. During the updating procedure, the scattering effect can be removed, and the spatial-resolution is improved.</sec><sec>Compared with traditional scattering imaging model, the proposed method can perform super-resolution color imaging and descattering under various conditions, and solve the problem of color cases. Furthermore, the proposed method is easy to incorporate into a traditional Fourier Ptychography imaging system to obtain high-fidelity images with better quality and effective detail information. Therefore, the proposed method has the potential to help super-resolution imaging to obtain more practical applications.</sec>

A Faraday isolator based on fused silica in a Herriott cell

We demonstrated a multipass Faraday isolator based on fused silica. The polarization rotation angle of 45° was accumulated in a Herriott cell. The concept enables the use of magneto-optic materials with low Verdet constants in Faraday isolators.

Giant magneto-optical Kerr effect and thermoelectric properties in CeBiPt half-Heusler by DFT

The mechanical, electronic, magneto-optic and thermoelectric properties of CeBiPt compound have been calculated based on density functional theory (DFT) calculations. This compound has ground state point in the ferromagnetic phase with elastic stability by large bulk modulus of 88.565[Formula: see text]GPa. Poisson’s coefficient of 0.257 represents the ionic bonds between atoms, while the anisotropy coefficient indicates the elastic isotropic nature of this compound. Also, phonon dispersion emphasizes to the dynamic stability of this compound. By the mBJ approximation, this case exhibits ferromagnetic behavior with a magnetic moment of 0.98[Formula: see text][Formula: see text]. Based on the magnetic behavior of this crystal, the Kerr effect angles ([Formula: see text]) are 3.6∘ at 3[Formula: see text]eV and [Formula: see text] at 5.4[Formula: see text]eV, respectively, therefore, the rotation angle of the ellipse light polarization ([Formula: see text]) in the edge of ultraviolet region shows a large polarization of light in the visible region. The negative Seebeck coefficient of CeBiPt compound at low temperature refers to the hole transfer, also the magnitude of the power factor at higher temperatures indicates this compound is suitable for use in power generator applications.

Advanced Light: Liquid Crystals-Based Ultra-Broadband Polarization Rotator for Functional Smart Devices.

A novel ultra-broadband polarization rotator with advanced angular adjustability is proposed for functional devices such as displays and smart windows. The new solution offers dynamic control of light polarization across a broad range of wavelengths, encompassing the complete visible spectrum, ultraviolet and near-infrared. Moreover, it boasts a smaller footprint, faster response times, and lower dispersion compared to conventional rotators. The findings are remarkable in that they show that as the viewing angle increases, the hybrid alignment takes on a twist-like configuration, with the polarization rotation angle determined by the spatial variation in the twist angle. This intriguing behavior leads to an improved range of angular adjustability, as the effective polarization rotation depth is extended. The improved angular adjustability of reconfigurable smart devices surpasses the limitations of traditional polarization rotators, unlocking new innovative possibilities. For example, the rotator plays a crucial role in display technologies, allowing for effective control of viewing angles and minimizing reflection from disturbing external light. Similarly, in smart windows, it optimizes energy conservation by regulating direct sunlight transmission while ensuring clear visibility in normal conditions. It is believed that the proposed advanced ultra-broadband polarization rotator is a significant step forward in the development of reconfigurable smart devices.

Simultaneous measurement of polarization rotation angle and ellipticity at the quantum noise limit

An experiment has been proposed for laser polarization signal measurement, with the rotation angle and ellipticity being measured simultaneously. The proposed experiment is immune to signal-to-noise ratio degradation due to the finite extinction ratio of polarizing elements used to construct the composite polarization measurement setup. Noise analysis is carried out to show that the proposed scheme allows one to reach the quantum noise limit in the simultaneous measurement of the polarization angle and ellipticity. This work should be of great interest for experiments such as observation of vacuum magnetic birefringence, spin-orbital interaction, material characterization, polarization microscopy, or biomedical optics.

Tunable multifunctional polarization conversion inbilayer chiral metamaterials.

A chiral metamaterial composed of bilayer twisted split-ring resonators is proposed and demonstrated to realize tunable, dual-directional, and multifunctional polarization conversion for terahertz waves. Simulations show that the converter can selectively achieve linear-to-linear, linear-to-right-handed circular, or linear-to-left-handed circular polarization conversion by tuning the polarization and propagating direction of the incident waves. Stokes parameters, ellipticity, and a polarization rotation angle are introduced to determine the output polarization. The circular polarization transmission coefficients and surface current distribution are employed to demonstrate the physical mechanisms of the phenomena above. The proposed converter can find potential applications in terahertz imaging and communications.

Generation of polarization rotation function Bessel beams based on all-dielectric metasurfaces

Bessel beams have a wide range of applications in optical communications because their non-diffractive properties do not depend on the amplitude and phase distribution in the spatial frequency range. Recently, metasurfaces have been widely utilized as subwavelength materials for light manipulation, including the generation of Bessel beams. However, so far, no reports of metasurfaces generating Bessel beams with polarization rotation function have been published, which has potential applications for information encryption in optical communication. An all-dielectric metasurface based on the Pancharatnam-Berry (PB) phase is proposed to realize the generation of a Bessel beam with polarization rotation function under the incident of linearly polarized (LP) light. Furthermore, we exhibit dual Bessel beams with orthogonal polarization states through the superimposition of two Bessel beam phases onto a metasurface, with different polarization rotation angles and phase gradients. Our final demonstration illustrates Bessel beam arrays with polarization rotation, and this design concept can be extended to more channels and higher-order Bessel beams. The proposed all-dielectric metasurfaces based on polarization rotation function provides a new option for the application of Bessel beams in integrated optical systems and multiplexing.

Strong Magneto-Optical Kerr Effects in Ni-Doped ZnO Nanolaminate Structures Obtained by Atomic Layer Deposition.

The magneto-optical (MO) Kerr effects for ZnO and ZnO:Ni-doped nanolaminate structures prepared using atomic layer deposition (ALD) have been investigated. The chemical composition and corresponding structural and morphological properties were studied using XRD and XPS and compared for both nanostructures. The 2D array gradient maps of microscale variations of the Kerr angle polarization rotation were acquired by means of MO Kerr microscopy. The obtained data revealed complex behavior and broad statistical dispersion and showed distinct qualitative and quantitative differences between the undoped ZnO and ZnO:Ni-doped nanolaminates. The detected magneto-optical response is extensively inhomogeneous in ZnO:Ni films, and a giant Kerr polarization rotation angle reaching up to ~2° was established. This marks the prospects for further development of magneto-optical effects in ALD ZnO modified by transition metal oxide nanostructures.

Simple and Fast Polarization Tracking Algorithm for Continuous-Variable Quantum Key Distribution System Using Orthogonal Pilot Tone

To reduce the influence of random channel polarization variation, especially fast polarization perturbation, for continuous-variable quantum key distribution (CV-QKD) systems, a simple and fast polarization tracking algorithm is proposed and experimentally demonstrated. The algorithm is implemented by an orthogonal pilot tone scheme, one of the pilot tones is used for estimating the polarization rotation angle, and the other one is used for compensating the polarization perturbation introduced phase noise. Meanwhile, residual effects are compensated precisely with the help of a real-valued FIR filter. In this case, the excess noise introduced by polarization perturbation is effectively suppressed. Experimental results show that the polarization scrambling rate ≥12.57 krad/s can be tracked by using the proposed algorithm, and a good estimated parameters performance is achieved. Compared to conventional polarization tracking algorithms such as the constant modulus algorithm (CMA), experimental results show that the polarization tracking capability of the proposed algorithm is significantly improved. Furthermore, much faster polarization tracking performance is evaluated by digital simulations, and the simulation results show that about 188.50 Mrad/s can be tracked by the proposed algorithm. Thus, our method provides effective technology for the practical application of fiber-based CV-QKD.

Measures of non-Gaussianity in axion-string-induced CMB birefringence

The presence of axion strings in the Universe after recombination can leave an imprint on the polarization pattern of the cosmic microwave background radiation through the phenomenon of axion-string-induced birefringence via the hyperlight axion-like particle's coupling to electromagnetism. Across the sky, the polarization rotation angle is expected to display a patchwork of uniform regions with sharp boundaries that arise as the `shadow' of axion string loops. The statistics of such a birefringence sky map are therefore necessarily non-Gaussian. In this article we quantify the non-Gaussianity in axion-string-induced birefringence using two techniques, kurtosis and bispectrum, which correspond to 4- and 3-point correlation functions. If anisotropic birefringence were detected in the future, a measurement of its non-Gaussian properties would facilitate a discrimination across different new physics sources generally, and in the context of axion strings specifically, it would help to break degeneracies between the axion-photon coupling and properties of the string network.