Opposite Circular Polarization Research Articles

Optical spin hall effect in exciton-polariton condensates in lead halide perovskite microcavities.

An exciton-polariton condensate is a hybrid light-matter state in the quantum fluid phase. The photonic component endows it with characters of spin, as represented by circular polarization. Spin-polarization can form stochastically for quasi-equilibrium exciton-polariton condensates at parallel momentum vector k|| ∼ 0 from bifurcation or deterministically for propagating condensates at k|| > 0 from the optical spin-Hall effect (OSHE). Here, we report deterministic spin-polarization in exciton-polariton condensates at k|| ∼ 0 in microcavities containing methylammonium lead bromide perovskite (CH3NH3PbBr3) single crystals under non-resonant and linearly polarized excitation. We observe two energetically split condensates with opposite circular polarizations and attribute this observation to the presence of strong birefringence, which introduces a large OSHE at k|| ∼ 0 and pins the condensates in a particular spin state. Such spin-polarized exciton-polariton condensates may serve not only as circularly polarized laser sources but also as effective alternatives to ultracold atom Bose-Einstein condensates in quantum simulators of many-body spin-orbit coupling processes.

Coupled circularly polarized electromagnetic soliton states in magnetized plasmas

The interaction between two co-propagating electromagnetic pulses in a magnetized plasma is considered, from first principles, relying on a fluid-Maxwell model. Two circularly polarized wavepackets by same group velocities are considered, characterized by opposite circular polarization, to be identified as left-hand- or right hand circularly polarized (i.e. LCP or RCP, respectively). A multiscale perturbative technique is adopted, leading to a pair of coupled nonlinear Schrödinger-type (NLS) equations for the modulated amplitudes of the respective vector potentials associated with the two pulses. Systematic analysis reveals the existence, in certain frequency bands, of three different types of vector soliton modes: an LCP-bright/RCP-bright coupled soliton pair state, an LCP-bright/RCP-dark soliton pair, and an LCP-dark/RCP-bright soliton pair. The value of the magnetic field plays a critical role since it determines the type of vector solitons that may occur in certain frequency bands and, on the other hand, it affects the width of those frequency bands that are characterized by a specific type of vector soliton (type). The magnetic field (strength) thus arises as an order parameter, affecting the existence conditions of each type of solution (in the form of an envelope soliton pair). An exhaustive parametric investigation is presented in terms of frequency bands and in a wide range of magnetic field (strength) values, leading to results that may be applicable in beam-plasma interaction scenarios as well as in space plasmas and in the ionosphere.

Asymmetries Caused by Nonparaxiality and Spin–Orbit Interaction during Light Propagation in a Graded-Index Medium

Spin–orbit coupling and nonparaxiality effects during the propagation of vortex vector light beams in a cylindrical graded-index waveguide are investigated by solving the full three-component field Maxwell’s equations. Symmetry-breaking effects for left- and right-handed circularly polarized vortex light beams propagating in a rotationally symmetric graded-index optical fiber are considered. The mode-group delay in a graded-index fiber due to spin–orbit interaction is demonstrated. A scheme for observing the temporal spin Hall effect is proposed. It is shown that the relative delay times between vortex pulses of opposite circular polarizations of the order of 10 ps/km can be observed in graded-index fibers for high-order topological charges.

Spin Chaos of Exciton Polaritons in a Magnetic Field

The spin properties of exciton polaritons in a micropillar cavity placed in a static magnetic field and excited by a resonant light wave are studied theoretically. Owing to the Zeeman effect, a nonlinear polariton system has two branches of optical response that are characterized by opposite circular polarizations. An indirect mechanism of polarization reversal is predicted, according to which the current state of the system undergoes a transition to dynamical chaos, and then the alternative spin state is established spontaneously. Such spin switches, mediated by a chaotic stage, proceed in both directions near the same critical excitation amplitude, so that the sign of the circular polarization of the cavity radiation is directly determined by the intensity of the optical pump.

Observation and Modulation of High-Temperature Moiré-Locale Excitons in van der Waals Heterobilayers.

Transition metal dichalcogenide heterobilayers feature strong moiré potentials with multiple local minima, which can spatially trap interlayer excitons at different locations within one moiré unit cell (dubbed moiré locales). However, current studies mainly focus on moiré excitons trapped at a single moiré locale. Exploring interlayer excitons trapped at different moiré locales is highly desirable for building polarized light-emitter arrays and studying multiorbital correlated and topological physics. Here, via enhancing the interlayer coupling and engineering the heterointerface, we report the observation and modulation of high-temperature interlayer excitons trapped at separate moiré locales in WS2/WSe2 heterobilayers. These moiré-locale excitons are identified by two emission peaks with an energy separation of ∼60 meV, exhibiting opposite circular polarizations due to their distinct local stacking registries. With the increase of temperature, two momentum-indirect moiré-locale excitons are observed, which show a distinct strain dependence with the momentum-direct one. The emission of these moiré-locale excitons can be controlled via engineering the heterointerface with different phonon scattering, while their emission energy can be further modulated via strain engineering. Our reported highly tunable interlayer excitons provide important information on understanding moiré excitonic physics, with possible applications in building high-temperature excitonic devices.

Compact Dual-Circularly Polarized Traveling-Wave Series-Fed Patch Array for Use as a Non-Linear Tag Antenna for Bio-Sensing Applications

This paper proposes a compact K-band dual-circularly polarized antenna that can be implemented on a non-linear tag based on third-order intermodulation (IM3) for bio-sensing applications. The proposed antenna has the characteristics of being low-profile and lightweight, with opposite circular polarizations (CP) between ports. The non-linear tag-based bio-sensing scenario utilizes K-band millimeter wave frequencies, which allows for compact non-linear tags for attachment to the body. Also, the proposed antenna features dual-CP, which are for the reception and re-radiation of incident transmit signals and the IM3 responses, respectively. To this end, a two-port traveling-wave series-fed patch array with coplanar proximity coupling is designed. Here, to minimize the size of the antenna, we use only four circular patch elements with a modified diamond-shaped microstrip feedline. Through simulation and measurement, we demonstrate that the proposed antenna has an axial ratio of less than 3 dB from 23.25 GHz to 24.1 GHz, with the reflection coefficients below −10 dB and port-to-port coupling below −15 dB. These results indicate the potential utility of the proposed antenna as a tag antenna for non-linear detection-based bio-sensing applications.

Argonda Dairesel Polarize Yüksek Harmonikler: Dipol ve Dipol Olmayan Etki

The interaction of the intense laser pulse, which forms the basis of the strong laser field and non-linear optical physics, with atoms, molecules, and solids leads to the High Order Harmonic Generation (HHG). There are many theoretical and experimental research related to this process defined by the Semi-Classic Model which is called the Three Step Model. In this article, the dipole and non-dipole effects specified in the theoretical Lewenstein model to be used in the Argon atom interacting with the strong circular laser field (800nm) and the resulting higher order harmonic spectrum will be investigated. We compared the results obtained using the non-collinear beams with opposite circular polarizations with those obtained using a single circularly polarized beam or a linearly polarized beam. It could be said that the circular polarization can significantly affect the HHG process in an argon atom exposed to a laser field with 800 nm wavelength and 1015 W/cm2 intensity.

Dual polarization Fourier transform processor using geometric-phase lenses.

This work presents a novel optical system for polarization image processing using geometric-phase (Pancharatnam-Berry) lenses. Such lenses are half-wave plates where the orientation of the fast (slow) axis follows a quadratic relation with the radial coordinate, and they present the same focal length but opposite sign for left and right circular polarizations. Therefore, they split an input collimated beam in a converging beam and a diverging beam with opposite circular polarizations. This coaxial polarization selectivity introduces a new degree of freedom in optical processing systems and makes it interesting for imaging and filtering applications that require polarization sensitivity. Here we profit from these properties to build an optical Fourier filter system with polarization sensitivity. A telescopic system is used to have access to two real Fourier transform planes, one for each circular polarization. A second symmetric optical system is used to recombine the two beams onto a single final image. As a result, polarization sensitive optical Fourier filtering can be applied, as demonstrated with simple bandpass filters.

Spatial mode analysis of optical beams carrying monstar disclinations

Asymmetric polarization disclinations, such as monstars, can be generated in two distinct ways: (a) by an inseparable superposition of three spatial modes bearing optical vortices with circular polarization states; (b) by using a modulated Poincaré beam, consisting of an inseparable superposition of a circularly-polarized fundamental Gaussian beam TEM00 and a second beam exhibiting an azimuthally-modulated vortex with an m-fold rotational symmetry and the opposite circular polarization. Based on the analysis of the spatial modes indirectly involved into the superposition through the latter method, we investigate its capability of spanning as many disclinations as possible, as well as its capability of enabling effective predictions about the generated patterns, such as relevant geometric features, already at the design stage.

Twist-angle-dependent momentum-space direct and indirect interlayer excitons in WSe2/WS2 heterostructure.

Interlayer excitons (ILEs) in the van der Waals (vdW) heterostructures of type-II band alignment transition metal dichalcogenides (TMDCs) have attracted significant interest owing to their unique exciton properties and potential in quantum information applications. However, the new dimension that emerges with the stacking of structures with a twist angle leads to a more complex fine structure of ILEs, presenting both an opportunity and a challenge for the regulation of the interlayer excitons. In this study, we report the evolution of interlayer excitons with the twist angle in the WSe2/WS2 heterostructure and identify the direct (indirect) interlayer excitons by combining photoluminescence (PL) and density functional theory (DFT) calculations. Two interlayer excitons with opposite circular polarization assigned to the different transition paths of K-K and Q-K were observed. The nature of the direct (indirect) interlayer exciton was confirmed by circular polarization PL measurement, excitation power-dependent PL measurement and DFT calculations. Furthermore, by applying an external electric field to regulate the band structure of the WSe2/WS2 heterostructure and control the transition path of the interlayer excitons, we could successfully realize the regulation of interlayer exciton emission. This study provides more evidence for the twist-angle-based control of heterostructure properties.

Circular polarization detector based on polarization holography.

We propose and experimentally demonstrate the generation of a circular polarization detector based on planar polarization holography. The detector is designed by constructing the interference field according to the null reconstruction effect. We create multiplexed holograms, which feature the combination of two sets of hologram patterns and operate with opposite circular polarization beams. In a few seconds, the exposure operation allows the polarization multiplexed hologram element to be generated, with functionality equivalent to a chiral hologram. We have theoretically analyzed the feasibility of our scheme and experimentally demonstrated that the right- and left-handed circularly polarized beam can be distinguished directly depending on the different output signals. This work provides a time-saving and cost-effective alternative approach for generating a circular polarization detector and opens avenues for future applications in polarization detection.

Tunable interface states between Floquet-Weyl semimetals

Weyl semimetals and nodal line semimetals are characterized by linear electronic bands touching at zero-dimensional points and one-dimensional lines, respectively. Recently, it has been predicted that nodal line semimetals can be driven into tunable Floquet-Weyl semimetals by circularly polarized light. Here, we study the occurrence of interface states between two regions of a nodal line semimetal shined by two beams of light with opposite circular polarizations. Within a minimal model, we find remarkable modifications of the energy structure by tuning the polarized light, such as the possible generation of van Hove singularities. Moreover, by adding a $\delta$-doping of magnetic impurities along the interfacial plane, we show the occurrence of a switchable and topologically non-trivial, vortex-like pseudo-spin pattern of the interface states.

Helicity exchange and symmetry breaking of in-plane phonon scattering of h-BN probed by polarized Raman spectroscopy

Due to its atomic thickness and insulating nature, hexagonal boron nitride (h-BN) is considered to be one of the most promising substrates and gate insulating materials for two-dimensional electronic devices. In this study, polarized Raman spectroscopy was employed to uncover the effects of polarized incident light on the optical properties of h-BN phonon modes. Our measured polarization-resolved Raman spectra indicate that the symmetrical nature and the broken symmetry of degenerate phonon modes from h-BN are induced by linearly and elliptically polarized light, respectively. Moreover, a helicity exchange was observed between the excitation of circularly polarized light and the resulting opposite circular polarization of scattered light from h-BN. The measured phenomena were modeled on the basis of Raman tensors and Jones calculus to eventually calculate the amplitude coefficients of two orthogonal in-plane phonon modes. Hence, our experimental study provides a holistic understanding of the vibrational modes in h-BN, which is expected to enhance the knowledge of physical mechanisms such as heat capacity and thermal and electrical conductivities of this layered material.

A 94 GHz Monopulse Duplexing Horn Antenna for a 3-D Tracking Radar

This article presents the first demonstration of a full-waveguide feed at W-band, enabling transmit–receive duplexing and 2-D tracking of targets. The proposed device is a compact unit designed to be used as feed of a 94 GHz space-borne radar. Its duplexing concept relies on a septum orthomode transducer polarizer for transmitting and receiving sum signals with opposite circular polarizations. Additionally, the first higher order mode of circular waveguide (TM01) is allowed to propagate inside the device to extract a difference signal for tracking. By comparing received sum and difference signals in amplitude and phase, both angular directions of a target position can be derived. A prototype of the duplexer was fabricated and tested: measurements at 94 GHz show return loss and isolation above 23 dB at all ports, with reasonable performance from 92 to 96 GHz. The measured monopulse characteristic enables 2-D tracking of targets deviated by less than 8.5° from boresight.

All-Dielectric Metasurface-Enabled Multiple Vortex Emissions.

On-chip integrated micro- and nanoscale vortex lasers are key elements for addressing the exponentially growing demand for information capacity. Although tunable vortex microlasers have been reported, each laser pulse still possesses one particular topological charge and requires additional multiplexing. In this study, the simultaneous generation of coherent laser arrays with different topological charges by combining metalenses with semiconductor microlasers is demonstrated. A TiO2 vortex metalens converts two orbital angular momentum beams into the same diffraction-limit spot with opposite circular polarizations through spin-to-orbital conversion. Consequently, the microlaser emission at the focal spot, which can be decomposed into two circularly polarized beams, is collimated into vortex microlaser beams with two different topological charges through a time-reversal process. This concept is extended to a 2 × 2 metalens array by introducing off-axis terms, and eight topological charges are produced simultaneously. This research is a significant step toward the on-chip integration of micro- and nanolasers.

Optical control of topological memory based on orbital magnetization

Under suitable conditions, some twisted graphene multilayers and transition-metal dichalcogenides become Chern insulators, exhibiting the anomalous quantum Hall effect and orbital magnetization due to spontaneous valley polarization. We study interaction of a Chern insulator with circularly polarized light. The interaction energy contains an antisymmetric term that couples to the helicity of incident light. For a two-band Chern insulator, this term is expressed as an integral involving the Berry curvature of the system. Taking advantage of this interaction, we propose an experimental protocol for switching topological memory based on orbital magnetization by circularly polarized light. Moreover, two laser beams of opposite circular polarization can nucleate domains of opposite magnetization and thus produce an optically configurable domain wall carrying topologically protected chiral edge modes.

Probing the rotational spin-Hall effect in a structured Gaussian beam

Spin-to-orbit conversion of light is a dynamical optical phenomenon in nonparaxial fields leading to various manifestations of the spin and orbital Hall effect. However, the effects of the spin-orbit interaction (SOI) have not been explored extensively for structured Gaussian beams carrying no intrinsic orbital angular momentum. Indeed, the SOI effects on such structured beams can be directly visualized due to azimuthal rotation of their transverse intensity profiles, a phenomenon we call the rotational spin-Hall effect. In this paper we show that for an input circularly polarized (right or left) Hermite-Gaussian $({\text{HG}}_{10})$ mode, the SOI leads to a significant azimuthal rotation of the transverse intensity distribution of both the orthogonal circularly polarized (left or right) component and the longitudinal field intensity with respect to the input intensity profile. We validate our theoretical and numerically simulated results experimentally by tightly focusing a circularly polarized ${\text{HG}}_{10}$ beam in an optical tweezers configuration and projecting out the opposite circular polarization component and the transverse distribution of the longitudinal field intensity at the output of the tweezers. We also measure the rotational shift as a function of the refractive index contrast in the path of the tightly focused light and in general observe a proportional increase. The enhanced spin-orbit conversion in these cases may lead to interesting applications in inducing complex dynamics in optically trapped birefringent particles using structured Gaussian beams with no intrinsic orbital angular momentum.

Experimental observation of transverse spin of plasmon polaritons in a single crystalline silver nanowire

We report an experimental observation of the transverse spin and associated spin-momentum locking of surface plasmon polaritons (SPPs) excited in a plasmonic single crystalline silver nanowire (AgNW). In contrast to the SPPs excited in metal films, the electromagnetic field components of the evanescent SPP mode propagating along the long axis (x axis) of the NW can decay along two longitudinal planes (x–y and x–z planes), resulting in two orthogonal transverse spin components (sz and sy). Analysis of the opposite circular polarization components of the decaying SPP mode signal in the longitudinal plane (x–y) reveals spin dependent biasing of the signal and, hence, the existence of transverse spin component (sz). The corresponding transverse spin density (s3) in the Fourier plane reveals spin-momentum locking, where the helicity of the spin is dictated by the wave-vector components of the SPP evanescent wave. Furthermore, the results are corroborated with three-dimensional numerical calculations. The presented results showcase that how a chemically prepared plasmonic AgNW can be harnessed to study optical spins in evanescent waves and can be extrapolated to explore sub-wavelength effects, including directional spin coupling and optical nano-manipulation.

42.4: Compact Stereo Waveguide Display Using a Polarization‐Multiplexed In‐coupling Metagrating

Three‐dimensional (3D) vision in augmented reality (AR) displays can enable highly immersive and realistic viewer experience, hence attracts much attention. Most current approaches create 3D visions by projecting stereoscopic images to different eyes using two separate projection systems, which are inevitably bulky for wearable devices. Here, we propose a compact stereo waveguide AR display system using a single piece of thin flat glass integrated with a polarization‐multiplexed metagrating in‐coupler and two diffractive grating out‐couplers. Incident light of opposite circular polarization states carrying stereoscopic images are first steered by the metagrating to opposite propagation directions in the flat glass waveguide, subsequently extracted by the diffractive gratings and finally received by different eyes, forming 3D stereo vision. Experimentally we fabricated a display prototype and demonstrated independent projection of two polarization‐multiplexed stereoscopic images. This work paves a novel path towards the implementation of high‐performance stereo displays with compact size, light weight, and multi‐color compatibility.

High-contrast level-crossing resonances in a small cesium vapor cell for applications in atomic magnetometry

Level-crossing (LC) resonances in alkali-metal vapors are widely used for atomic magnetometry. One of the most simple and robust techniques involves a single circularly polarized light wave, while a transverse magnetic field (Bx⊥k) is scanned around zero to observe the subnatural-linewidth resonance of electromagnetically induced transparency (EIT) in the light wave transmission. This technique allows miniaturization of the magnetic field sensor to a great extent, maintaining high sensitivity of measurements. To obtain a high quality factor of the LC resonance and, therefore, high performance of the sensor, either a high temperature (>120 °C) or an extended volume of the vapor cell (V≫1 cm3) is usually required. Here, we propose a slight modification to the commonly used configuration, which can provide high-quality LC resonances in small (≪1 cm3) vapor cells at a relatively low temperature of 60 °C or less. The modification consists in adding the second (pump) counterpropagating light wave with opposite circular polarization (σ+σ− configuration). In our experiments, the waves excite the D1-line ground-state level Fg=4 in cesium atoms in the presence of a buffer gas (Ne, 130 Torr). In the proposed scheme, a subnatural-linewidth electromagnetically induced absorption (EIA) resonance is observed. We compare parameters of the EIA resonance with those obtained in the single-wave scheme to show benefits of using the proposed σ+σ− configuration. The results have good prospects for developing a low-power miniaturized atomic magnetometer with a wide operating range.