Polarization Of Incident Light Research Articles

Weyl semimetal integrated three-unit polarimeters

The unique topology of Weyl semimetals’ band structure has been recently shown to lead to a host of novel optoelectronic properties. Among them is the prospect of polarization-dependent photocurrents, most notably the circular photogalvanic effect arising from the spin texture of the Weyl cones in the presence of symmetry breaking. Here we show that these helicity-dependent photocurrent processes can be employed to realize fully integrated polarimetric detection systems. In this respect, a TaAs-based polarimeter is demonstrated involving three pixels that can uniquely map the polarization state of light on the Poincaré sphere. Our work could enable a class of optoelectronic devices that directly respond to the polarization of incident light, while paving the way toward a better understating of light–matter interactions in Weyl semimetals.

Polarization-controlled and symmetry-dependent multiple plasmon-induced transparency in graphene-based metasurfaces.

In this paper, we theoretically and numerically demonstrate a polarization-controlled and symmetry-dependent multiple plasmon-induced transparency (PIT) in a graphene-based metasurface. The unit cell of metasurface is composed of two reversely placed U-shaped graphene nanostructures and a rectangular graphene ring stacking on a dielectric substrate. By adjusting the polarization of incident light, the number of transparency windows can be actively modulated between 1 and 2 when the nanostructure keeps a geometrical symmetry with respect to the x-axis. Especially, when the rectangular graphene ring has a displacement along the y-direction, the number of transparency windows can be arbitrarily switched between 2 and 3. The operation mechanism behind the phenomena can be attributed to the near-field coupling and electromagnetic interaction between the bright modes excited in the unit of graphene resonators. Moreover, the electromagnetic simulations obtained by finite-difference time-domain (FDTD) method agree well with the theoretical results based on the coupled modes theory (CMT). In addition, as applications of the designed nanostructure, we also study the modulation degrees of amplitude, insertion loss and group index of transmission spectra for different Fermi energies, which demonstrates an excellent synchronous switch functionality and slow light effect at multiple frequencies. Our designed metasurface may have potential applications in mid-infrared optoelectronic devices, such as optical switches, modulators, and slow-light devices, etc.

Sensitivity and reproducibility of transverse magneto-optical Kerr effect (T-MOKE) ellipsometry

We report a comprehensive experimental study to analyze the limiting factors and physical mechanisms that determine the achievable performance of transverse magneto-optical Kerr effect (T-MOKE) ellipsometry. Specifically, we explore different approaches to achieve high sensitivity and reduced acquisition times. The best sensitivity is observed for an incident light polarization with balanced s-p components. We also verify experimentally that the method’s theoretical description is accurately describing data for any s-p combination of the incoming light. Furthermore, two alternative measurement strategies are explored by using different measurement sequences for the polarization sensitive optics, which both achieve a very comparable, high quality of results. Signal-to-noise ratios and systematic deviations are measured and analyzed based on a large number of nominally identical measurement repeats, both for entire signal sequences as well as for individual Fourier components of the magneto-optical signal generated by a sinusoidal magnetic field sequence. Hereby, we observe that while higher order Fourier components have a significantly reduced signal amplitude and correspondingly exhibit reduced signal-to-noise and repeatability performance, signal-to-noise ratios always exceed values of 100 even for the lowest signal Fourier component and the lowest signal sample that we investigated, illustrating the extremely precise nature of T-MOKE ellipsometry.

Reconfigurable multifunctional metasurfaces employing hybrid phase-change plasmonic architecture

Abstract We present a hybrid device platform for creating an electrically reconfigurable metasurface formed by the integration of plasmonic nanostructures with phase-change material germanium antimony telluride (GST). By changing the phase of GST from amorphous to crystalline through Joule heating, a large range of responses from the metasurface can be achieved. Furthermore, by using the intermediate phases of GST, the metasurface can interact with the incident light in both over-coupling and under-coupling regimes, leading to an inherently broadband response. Through a detailed investigation of the nature of the fundamental modes, we demonstrate that changing the crystalline phase of the GST at the pixel-level enables an effective control over the key properties (i.e., amplitude, phase, and polarization) of incident light. This leads to the realization of a broadband electrically tunable multifunctional metadevice enabling beam switching, focusing, steering, and polarization conversion. Such a hybrid structure offers a high-speed, broadband, and nonvolatile reconfigurable paradigm for electrically programmable optical devices such as switches, holograms, and polarimeters.

Visible and Near-Infrared Broadband Absorber Based on Ti3C2Tx MXene-Wu.

A high absorption broadband absorber based on MXene and tungsten nanospheres in visible and near-infrared bands is proposed. The absorber has a maximum absorption of 100% and an average absorption of 95% in the wavelength range of 400–2500 nm. The theoretical mechanism and parameter adjustability of the absorber are analyzed by FDTD solutions. The results show that the structural parameters can effectively adjust the absorption performance. The good absorption performance is due to the action of the local surface plasmon resonance coupling with the gap surface plasmon resonance and Fabry–Perot resonance. The simulation results show that the absorber is insensitive to the polarization and oblique incidence angle of incident light, and that high absorption and broadband can be maintained when the oblique incidence angle is up to 60°.

Toward High‐Efficiency Ultrahigh Numerical Aperture Freeform Metalens: From Vector Diffraction Theory to Topology Optimization

AbstractOptical metasurface is a 2D array of subwavelength meta‐atoms that arbitrarily manipulates amplitude, polarization, and wavefront of incident light, offering great advantages in miniaturization and integration. However, the presuppositions hidden in conventional unit‐cell‐based design approach, including discrete phase sampling, local periodicity approximation, and normal response, imply that the responses and interactions of meta‐atoms are almost impossible to be accurately modeled, thus impeding the effective design of high‐efficiency ultrahigh numerical aperture (NA) metalens. Here, based on vector diffraction theory and plane wave expansion method, theoretical limitation of metalens efficiency is comprehensively investigated. It is identified that for high‐NA metalens, theoretical focusing efficiency is limited by diffraction capability of vector field, while evanescent wave attenuation dominates theoretical efficiency decline for ultrahigh‐NA metalens. It is also shown that the efficiency of conventional metalens has a huge gap from theoretical limitation, owing to imperfect diffractive focusing and impedance mismatch reflections. To fill such efficiency gap, the high‐efficiency high‐NA freeform metalens based on topology optimization is further demonstrated. Particularly, topology geometric constraints are utilized to reduce minimum feature size while keeping high efficiency. The results could shed new light on the understanding and design of ultrahigh‐NA metalens and find promising applications in optical imaging, microscopy, and lithography.

Generation of multi-channel perfect vortex beams with the controllable ring radius and the topological charge based on an all-dielectric transmission metasurface.

The perfect vortex (PV) beam, characterized by carrying orbital angular momentum and a radial electric intensity distribution independent of the topological charge, has important applications in optical communication, particle manipulation, and quantum optics. Conventional methods of generating PV beams require a series of bulky optical elements that are tightly collimated with each other, adding to the complexity of optical systems. Here, making the amplitude of transmitted co-polarized and cross-polarized components to be constant, all-dielectric transmission metasurfaces with superimposed phase profiles integrating spiral phase plate, axicon and Fourier lens are constructed based on the phase-only modulation method. Using mathematical derivation and numerical simulation, multi-channel PV beams with controllable annular ring radius and topological charge are realized for the first time under circularly polarized light incidence combining the propagation phase and geometric phase. Meanwhile, perfect vector vortex beams are produced by superposition of PV beams under the incidence of left-handed circularly polarized and right-handed circularly polarized lights, respectively. This work provides a new perspective on generating tailored PV beams, increasing design flexibility and facilitating the construction of compact, integrated, and versatile nanophotonics platforms.

Birefringence-Mediated Enhancement of the Magneto-Optical Activity in Anisotropic Magnetic Crystals

Optical anisotropy is usually treated as an unfavorable condition for the magneto-optical measurements since it is known to diminish the Faraday rotation concerning the case of the isotropic medium. Here we show that the situation could be quite opposite: a phenomenon of birefringence-mediated enhancement of the magneto-optical activity appears if the incident light polarization and angle of incidence are set properly. The present study relies on the experimental, analytical, and numerical studies of iron borate FeBO3 crystals. We demonstrate a significant increase of the magneto-optical activity resulting in nearly 100% magneto-optical light modulation magnitude. The approach applies to other types of birefringent crystals with the magneto-optical response that makes it crucial for various practical applications, including magneto-optical microscopy, pump-probe studies, and others.

Polarization-insensitive unidirectional meta-retroreflector

Extraordinary angularly asymmetric electromagnetic manipulation is desirable in angle-encoded steganography, directional display, one-side sensing and other unconventional applications, which however is challenging. Here, we build the non-Hermitian surface scattering systems by silicon nano-posts with spatially modulated loss, showing the extraordinary angular-asymmetry in the near infrared regime under different polarized light incidence. Especially a polarization-insensitive unidirectional retroreflector with non-Hermitian metasurface is first demonstrated at a fourth-order exceptional point (EP), related to the collapsed EPs of a generalized 4 × 4 non-Hermitian scattering matrix under TM and TE polarization states. Our investigations provide a new perspective for designing polarization-insensitive asymmetric photonic devices for wave manipulation and applying more generalized non-Hermitian physics to surface scattering systems.

Super-Resolved 3D Mapping of Molecular Orientation Using Vibrational Techniques.

When a sample has an anisotropic structure, it is possible to obtain additional information controlling the polarization of incident light. With their straightforward instrumentation approaches, infrared (IR) and Raman spectroscopies are widely popular in this area. Single-band-based determination of molecular in-plane orientation, typically used in materials science, is here extended by the concurrent use of two vibration bands, revealing the orientational ordering in three dimension. The concurrent analysis was applied to IR spectromicroscopic data to obtain orientation angles of a model polycaprolactone spherulite sample. The applicability of this method spans from high-resolution, diffraction-limited Fourier transform infrared (FT-IR) and Raman imaging to super-resolved optical photothermal infrared (O-PTIR) imaging. Due to the nontomographic experimental approach, no image distortion is visible and nanometer scale orientation domains can be observed. Three-dimensional (3D) bond orientation maps enable in-depth characterization and consequently precise control of the sample’s physicochemical properties and functions.

Imbert–Fedorov shift at black phosphorus-coated surfaces

In this work, the Imbert–Fedorov (IF) shift is systematically investigated when a light beam is incident on black phosphorus. Using the angular spectrum theory, we obtain the analytical expressions of IF shifts for a p-polarized and s-polarized beam. Based on the theoretical analysis, numerical calculations are performed. The results indicate that the IF shifts depend on the incident angle, polarization and frequency of incident light, as well as the optical axis angle and electron concentration of black phosphorus. These characteristics make it possible to accurately measure the physical parameters of two-dimensional atomic materials based on IF shifts.

Strong In‐Plane Anisotropy and Giant Second Harmonic Generation Response of Organic Single‐Crystalline Microwire Arrays

AbstractOrganic nonlinear optical (NLO) crystals play an indispensable role in high‐performance photonic devices due to their large nonlinear coefficient, fast response time, and low dielectric constant. However, in contrast to the strides of bulk crystals, researches on the next generation of nanophotonic devices are ignored to some extent. One of the bottlenecks is the controllable manufacturing and patterning of high‐quality organic NLO crystals with the nanometer‐scale thickness. Herein, a confined assembly method for fabricating the microwire arrays of organic NLO crystal OH1 and DAT2 with precise position, flat morphology, high crystallinity, and consistent crystallographic orientation is reported. Two strong NLO effects observed in the experiments are comprehensively studied, including second harmonic generation (SHG) and two‐photon excited fluorescence. Furthermore, it is demonstrated that the anisotropic SHG effect depends on both the polarization of incident light and the crystallographic orientation of microwire arrays. Microwire arrays can exhibit large in‐plane anisotropy with the polarization ratio up to 0.95 and second‐order nonlinear coefficient up to 55.1 pm V−1. This work provides new insights into the potential applications of organic NLO crystals in integrated optical devices.

Full-Stokes Retrieving and Configuration Optimization in a Time-Integration Imaging Polarimeter.

A time-integration imaging polarimeter with continuous rotating retarder is presented, and its full-Stokes retrieving and configuration optimization are also demonstrated. The mathematical expression between the full-Stokes vector and the time-integration light intensities is derived. As a result, the state of polarization of incident light can be retrieved by only one matrix calculation. However, the modulation matrix deviates from the initial well-conditioned status due to time integration. Thus, we re-optimize the nominal angles for the special retardance of 132° and 90° with an exposure angle of 30°, which results in a reduction of 31.8% and 16.8% of condition numbers comparing to the original configuration, respectively. We also give global optimization results under different exposure angles and retardance of retarder; as a result, the 137.7° of retardance achieves a minimal condition number of 2.0, which indicates a well-conditioned polarimeter configuration. Besides, the frame-by-frame algorithm ensures the dynamic performance of the presented polarimeter. For a general brushless DC motor with a rotating speed of over 2000 rounds per minute, the speed of polarization imaging will achieve up to 270 frames per second. High precision and excellent dynamic performance, together with features of compactness, simplicity, and low cost, may give this traditional imaging polarimeter new life and attractive prospects.

Near-infrared narrow-band minus filter based on a Mie magnetic dipole resonance.

The traditional minus filter is composed of many layers of thin films, which makes it difficult and complicated to manufacture. It is sensitive to incident light angle and polarization. Here, we propose a near-infrared narrow-band minus filter with a full width at half maximum around 5 nm made of all-dielectric Si-SiO2 structures without any ohmic loss. The stop band transmittance of the proposed filter is close to 0, while its broad pass band transmittance is as high as 90% in the work wavelength range. Theoretical analysis shows that the transmission dip originated from magnetic dipole resonance: Its position can be tuned from 1.3 µm to 1.8 µm by changing the thickness of Si structure, and the proposed structure is insensitive to changes in incident light angle and polarization angle. We further studied its potential applications as a refractive index sensor. The sensitivity of dip1 and dip2 are as high as 953.53 nm/RIU and 691.09 nm/RIU, while their figure of merit is almost unchanged: 59.59 and 115.18, respectively.

Axial Higgs mode detected by quantum pathway interference in RTe3.

The observation of the Higgs boson solidified the standard model of particle physics. However, explanations of anomalies (for example, dark matter) rely on further symmetry breaking, calling for an undiscovered axial Higgs mode1. The Higgs modewas also seen in magnetic, superconducting and charge density wave (CDW) systems2,3. Uncovering thevector properties of a low-energy mode is challenging, and requires going beyond typical spectroscopic or scattering techniques. Here we discover an axial Higgs mode in the CDW system RTe3 using the interference of quantum pathways. In RTe3 (R = La, Gd), the electronic ordering couples bands of equal or different angular momenta4-6. As such, the Raman scattering tensor associated with the Higgs mode contains both symmetric and antisymmetric components, which are excited via two distinct but degenerate pathways. This leads to constructive or destructive interference of these pathways, depending on the choice of the incident and Raman-scattered light polarization. The qualitative behaviour of the Raman spectra is well captured by an appropriate tight-binding model, including an axial Higgs mode. Elucidation of the antisymmetric component is direct evidence that the Higgs mode contains an axial vector representation (that is, a pseudo-angular momentum) and hints that the CDW is unconventional. Thus, we provide a means for measuring quantum properties of collective modes without resorting to extreme experimental conditions.

Liquid crystal lens set in augmented reality systems and virtual reality systems for rapidly varifocal images and vision correction.

The major challenges of augmented reality (AR) systems and virtual reality (VR) systems are varifocal images for vergence-accommodation conflict (VAC) and vision corrections. In this paper, we design a liquid crystal (LC) lens set consisting of three LC lenses for varifocal images and vision corrections in AR and VR. Four operating modes of such a LC lens set present three electrically tunable lens powers: 0, -0.79 diopters, -2 diopters, and -3.06 diopters by means of manipulation of polarization of incident light using electrically tunable half-wave-plates. The response time is fast(< 50 ms). We also demonstrate AR and VR systems by adopting the LC lens set to exhibit functions of varifocal images and vision corrections which enable to solve VAC as well as vision problem in AR and VR.

First-principles study of electronic and optical properties of small edge-functionalized penta-graphene quantum dots

Tailoring the optoelectronic properties of semiconductor quantum dots is essential for designing functionalized nanoscale devices. In this work, we use first-principles calculations to study the optoelectronic properties of small penta-graphene quantum dots (PGQDs) with various edge-functionalized groups, including hydrogen, halogen (fluorine, chlorine, and bromine), and hydroxyl functional groups. It is evident that these quantum dots, especially those passivated by hydrogen atoms, are thermally stable in vacuum. Moreover, the larger the quantum dots, the more negative the formation energy on stability could reach, thus forming thermodynamically more stable quantum dots. All investigated PGQDs exhibit semiconductor properties. Their bandgaps decrease with an increase in the size of the quantum dots, resulting from the hybridization of sp2 and sp3 carbon atoms and from the charge depletion or accumulation between the passivated atoms and the principal components upon interactions. Concurrently, this study aims to explain the optical absorption anisotropy induced by the edge-functionalized groups of PGQDs under multiple incident light polarizations. These results highlight the use of edge-functionalized groups to develop the next generation of optoelectronic devices.

Effect of Cr co-doping on the optical absorption and emission characteristics of Yb:YVO4 single crystals grown by OFZ technique

Cr co-doped Yb:YVO4 (Cr:Yb:YVO4) single crystals with concentrations of 1.0 and 1.5 at.% of Cr and 3.0 at.% of Yb were grown by the optical floating zone technique. X-ray diffraction analysis on the grown crystals revealed that the lattice parameters of Cr:Yb:YVO4 crystals do not depend on the Cr doping concentration. The dislocation etch pit density estimated from the etching study was found to be 103/cm2. The observed fringes of nearly uniform thickness and spacing in birefringence interferometry for [100] plate and conoscopy pattern for [001] plate indicate the compositional and optical homogeneity of the crystal. Further, the influence of the Cr doping concentration on the 2A1→2B2 transition (at ∼1100 nm) and 2A1→2E transition (at ∼640 nm) due to Cr5+ ion were analysed using two orthogonal polarized light with electric field perpendicular (π-polarization) and parallel (σ-polarization) to [001] axis. These absorption peaks of Cr ion were found to be sensitive to the polarization of incident light. The absorption transition 2A1→2B2 around 1100 nm are permitted for π-polarization and on the other hand, the absorption transition 2A1→2E at 640 nm are permitted only for σ-polarization. The characteristic broader absorption band around ∼1100 nm is of importance as it is useful for self-Q-switching in a laser gain medium. The absorption coefficient corresponding to Cr5+ ions at 1100 nm increases with the increase in Cr doping concentration. The band-gap for σ-polarized light is slightly higher than π-polarized light and decreases with Cr doping. The increase in the estimated Urbach energy (50–122 meV) with the increase in the Cr doping concentration confirms that the defect states close to the band edge increase thus decrease the band gap. Further the photoluminescence intensity is in-line with the absorption data and decreases with increase in the Cr concentration from 0 to 1.5 at.%.

High circular polarization recognition quantum well infrared photodetector based on a chiral metamaterial microcavity

Circular polarization detection has important applications in the field of infrared detection. In this paper, a chiral metamaterial microcavity is designed to enhance the recognition of circularly polarized light (CPL) by a quantum well infrared photodetector (QWIP). By sandwiching the quantum well material and GaAs electrodes between a metallic chiral metamaterial and a gold substrate to form a microcavity structure, CPL discrimination can be achieved, and inter-subband absorption in the quantum well active region can also be improved. The electric field distribution is calculated and analyzed with the finite-difference time-domain method. Under the incidence of left circularly polarized light, the metallic chiral metamaterial on the surface excites the surface plasmon polariton (SPP) effect, which enhances the electric field ( E Z ) perpendicular to the growth direction of the quantum well, and the coupling efficiency can reach 950% at 14.9 µm wavelength. The SPP resonance wavelength matches the inherent response wavelength of the quantum well, so the inter-subband absorption of the quantum well is increased to about 0.9. At right circularly polarized light incidence, the coupling efficiency is only 105%, and the inter-subband absorption is only about 0.1 because the SPP effect is not effectively excited. Since chiral metamaterials can enhance the circular dichroism of quantum wells, when our designed structure is combined with QWIP, the circular polarization extinction ratio of QWIP can be increased to nine, which is much higher than 2.5 for a typical circular polarization detector. In addition, the inter-subband absorption will also be greatly improved under the incidence of CPL in a specific rotation direction. By optimizing the structural parameters, the resonance wavelength can be matched with the QWIP of different detection bands, which provides a new idea for the improvement of the performance of a quantum well infrared circular polarization photodetector in the long wave range.

Full-range birefringence control with piezoelectric MEMS-based metasurfaces

Dynamic polarization control is crucial for emerging highly integrated photonic systems with diverse metasurfaces being explored for its realization, but efficient, fast, and broadband operation remains a cumbersome challenge. While efficient optical metasurfaces (OMSs) involving liquid crystals suffer from inherently slow responses, other OMS realizations are limited either in the operating wavelength range (due to resonances involved) or in the range of birefringence tuning. Capitalizing on our development of piezoelectric micro-electro-mechanical system (MEMS) based dynamic OMSs, we demonstrate reflective MEMS-OMS dynamic wave plates (DWPs) with high polarization conversion efficiencies (∼75%), broadband operation (∼100 nm near the operating wavelength of 800 nm), fast responses (<0.4 milliseconds) and full-range birefringence control that enables completely encircling the Poincaré sphere along trajectories determined by the incident light polarization and DWP orientation. Demonstrated complete electrical control over light polarization opens new avenues in further integration and miniaturization of optical networks and systems.