Control Of Polarization State Research Articles

Giant magneto-optical Kerr effects governed by the quasi-bound states in the continuum

The magneto-optical Kerr effect (MOKE), as one of the magneto-optical effects, exhibits polarization change upon reflection that can be used to explore the internal information of magnetic materials with broad applications in modern information technology. However, typically, MOKE is quite weak due to the lower magneto-optical interaction. To tremendously enhance the MOKE, quasi-bound states in the continuum in a one-dimensional Ce- doped Y3Fe5O12 (CeYIG) film photonic crystal slabs (PCS) are proposed to improve the magneto-optical interaction in this work. A giant enhancement in the rotation angle and ellipticity of the longitudinal MOKE, which is about 93.4 and 136.8 times stronger than a pure uniform CeYIG, can be realized. Almost circularly polarized reflected beams with different chiralities are obtained with the CeYIG film. By tuning the geometric parameters of the PCS and the applied external magnetic field, dynamic control of polarization states of the reflected beams with different wavelengths can be realized. This magneto-optical metasurface provides a convenient way for the implementation of magneto-optical devices such as information memory devices, sensors, polarizers, and chiral devices.

Spatially distributed low-cross talk vector beams.

A spatially distributed low-cross talk vector beam refers to a vector beam that exhibits different intensities, phases, and polarization states along the propagation direction. This type of vector beam features low-cross talk between beams on different planes and finds extensive applications in optical communications and related fields. However, current technologies face challenges such as intensity interference at different imaging planes and difficulties in the precise control of phases and polarization states, which affect beam quality. In this study, we investigated the beam propagation process and employed a global optimization strategy to precisely control the intensity and phase distribution of the beam fields. This approach ensures that the beam forms the desired complex amplitude distribution in the target region while effectively suppressing cross talk in non-target regions. We utilized the method to generate two beams with complementary intensities and phases. Subsequently, through an interference optical path, we separated these two beams and converted them into orthogonal polarization states. Finally, by superimposing these two beams, we obtained a spatially varying low-cross talk vector beam. We experimentally validated the beam's different optical characteristics and low-cross talk properties on three planes. Our work opens up new prospects, to the best of our knowledge, for holographic technology with capabilities for ultra-fine depth control and polarization multiplexing.

The Design of a Multifunctional Coding Transmitarray with Independent Manipulation of the Polarization States.

Manipulating orthogonally polarized waves independently in a single metasurface is pivotal. However, independently controlling the phase shifts of orthogonally polarized waves is difficult, especially in the same frequency bands. Here, we propose a receiver-phase shift-transmitter transmitarray with independent control of arbitrary polarization states in the same frequency bands, in which transmission rates reach more than 90% in the frequency bands 4.2~4.9 GHz and 5.3~5.5 GHz. By introducing a phase-regulation structure to each element, phases covering 360° for different polarized incident waves can be independently controlled by different geometric parameters, and two-bit coding phases can be obtained. The design principle based on the two-port network's scattering matrix has been analyzed. To verify the independent tuning abilities of the proposed transmitarray for different polarization incidences in the same frequency bands, a multifunctional receive-phase shift-radiation coding transmitarray (RPRCT), which is composed of 16×16 elements, with functions of anomalous refraction (for example, orbital angular momentum wave) and focusing transmission for different polarized incident waves was simulated and measured. The measured results agree reasonably well with the simulated ones. Our findings provide a simple method for obtaining a multifunctional metasurface with orthogonal polarization in the same frequency bands, which greatly improves the capacity and spectral efficiency of communication channels.

Joint optimization of coded aperture metasurface and residual self-attention network for snapshot full-Stokes imaging

Traditional full-Stokes polarization imaging typically relies on the movements or segmentation of imaging systems, often accompanied by sacrifices in temporal or spatial resolution. Therefore, simultaneous encoding of full-Stokes vectors at the pixel scale is of great significance. Benefiting from the multi-dimensional light field control capability of metasurfaces, a coded aperture metasurface for polarization imaging is proposed in this paper, which can achieve pixel-level encoding of four Stokes vectors in a single imaging session. In addition, a Stokes residual self-attention network is designed to restore the encoded image, where the introduction of a channel-wise self-attention mechanism can effectively address the impact of intensity differences between Stokes vectors. Since the control of polarization states by metasurfaces is a differentiable physical process, the front-end metasurface encoding and back-end recovery network parameters can be jointly optimized, and this work achieves high-quality polarization imaging via such co-optimization methods. The proposed work demonstrates the flexibility and designability of metasurfaces in compact computational full-Stokes imaging systems.

Coexistence of varied intensities, phases, and polarization states along the direction of beam propagation

Polarization state, as one of the fundamental properties of light fields, has found widespread applications across various domains. The control of intensity, phase, and polarization state along the direction of beam propagation has opened up new avenues for beams. In this work, we generated a beam in which different intensities, phases, and polarization states can simultaneously appear at different positions along the direction of beam propagation. In other words, varied intensities, phases, and polarization states can coexist in the direction of beam propagation. The correctness of this method is validated through theoretical analysis and experimental results. This approach expands the application scope of light beams and provides a favorable path for exploring the optical characteristics of beams.

Research and design of metasurface antennas based on composite dielectric materials

The metasurface has the ability to regulate electromagnetic waves, which is widely used for polarization state control, impedance bandwidth expansion, vortex beam generation, and high-directional antennas. Research shows that the substrate of the metasurface has a significant impact on the performance of the antenna. The equivalent dielectric constant of composite dielectric materials is investigated by using the characteristic mode analysis (CMA). A novel metasurface with composite dielectric substrate is proposed. The composite dielectric material consists of a substrate with a dielectric constant of 3.55 and an air gap. The calculation results of the effective dielectric constant of composite dielectric materials are basically consistent with the simulation results. Based on this composite dielectric material, a metasurface antenna is designed. S11 is less than-10 dB in the frequency range of 5.22–7.87 GHz. The peak boresight gain is 10.44 dBi at 6.5 GHz.

Light-Harvesting Efficiency Cannot Depend on Optical Coherence in the Absence of Orientational Order.

The coherence of light has been proposed as a quantum-mechanical control for enhancing light-harvesting efficiency. In particular, optical coherence can be manipulated by changing either the polarization state or the spectral phase of the light. Here, we show that, in weak light, light-harvesting efficiency cannot be controlled using any form of optical coherence in molecular light-harvesting systems and, more broadly, those comprising orientationally disordered subunits and operating on longer-than-ultrafast time scales. Under those conditions, optical coherence does not affect the light-harvesting efficiency, meaning that it cannot be used for control. Specifically, polarization-state control is lost in disordered samples or when the molecules reorient on the time scales of light harvesting, and spectral-phase control is lost when the efficiency is time-averaged over a period longer than the optical coherence time. In practice, efficiency is always averaged over long times, meaning that coherent optical control is only possible through polarization and only in systems with orientational order.

Electro-tunable metasurface for tri-state dynamic polarization switching at near-infrared wavelengths

Control of polarization states of light is crucial for any photonic system. However, conventional polarization-controlling elements are typically static and bulky. Metasurfaces open a new paradigm to realize flat optical components by engineering meta-atoms at sub-wavelength scale. Tunable metasurfaces can provide enormous degrees-of-freedom to tailor electromagnetic properties of light and thus have the potential to realize dynamic polarization control in nanoscale. In this study, we propose a novel electro-tunable metasurface to enable dynamic control of polarization states of reflected light. The proposed metasurface comprises a two-dimensional array of elliptical Ag-nanopillars deposited on indium-tin-oxide (ITO)–Al2O3–Ag stack. In unbiased condition, excitation of gap-plasmon resonance in the metasurface leads to rotation of x-polarized incident light to orthogonally polarized reflected light (i.e., y-polarized) at 1.55 μm. On the other hand, by applying bias-voltage, we can alter the amplitude and phase of the electric field components of the reflected light. With 2 V applied bias, we achieved a linearly polarized reflected light with a polarization angle of −45°. Furthermore, we can tune the epsilon-near-zero wavelength of ITO at the vicinity of 1.55 μm wavelength by increasing the bias to 5 V, which reduces y-component of the electric field to a negligible amplitude, thus, resulting in an x-polarized reflected light. Thus, with an x-polarized incident wave, we can dynamically switch among the three linear polarization states of the reflected wave, allowing a tri-state polarization switching (viz. y-polarization at 0 V, −45° linear polarization at 2 V, and x-polarization at 5 V). The Stokes parameters are also calculated to show a real-time control over light polarization. Thus, the proposed device paves the way toward the realization of dynamic polarization switching in nanophotonic applications.

Continuous control of polarization state and tunable dual-channel optical communication based on highly transparent PMN-PT electro-optic ceramics

Transparent ferroelectric materials have excellent electro-optic properties, suitable to be used to develop high-performance optical communication devices. La-doped 88Pb(Mg1/3Nb2/3)O3–12PbTiO3 (88PMN-12PT) transparent ceramics with excellent comprehensive performances, including high transparency of 70.5% at near-infrared wavelength (close to its theoretical value), large quadratic electro-optic coefficient of 23.6 × 10−16 m2 V−2, low half-wave voltage (Vπ) of 146 V, and good extinction ratio of 34 dB, are successfully prepared in this paper. Based on the electro-optic effect of PMN-PT transparent ceramics, laser polarization state is transformed continuously from linear polarization to elliptical polarization, later to circularly polarization by applying electric field. Furthermore, dual-channel optical communication with a tunable laser intensity ratio is first reported here. Results indicate that PMN-PT transparent ceramic is a promising candidate for electro-optic material in polarization controller, optical switch, and information monitor in optical communication.

Nonvolatile Electrical Control and Reversible Gas Capture by Ferroelectric Polarization Switching in 2D FeI2/In2S3 van der Waals Heterostructures

Nonvolatile electrical control is the core of future magnetoelectric nanodevices. In this work, we systematically explore both the electronic structures and transport properties of multiferroic van der Waals (vdW) heterostructures consisting of a ferromagnetic FeI2 monolayer and a ferroelectric In2S3 monolayer using density functional theory and the nonequilibrium Green's function method. The results reveal that the FeI2 monolayer can be reversibly switched between semiconducting and half-metallic properties by nonvolatile control of the In2S3 ferroelectric polarization states. Correspondingly, the proof-of-concept two-probe nanodevice based on the FeI2/In2S3 vdW heterostructure exhibits a significant valving effect by modulating the ferroelectric switching. Moreover, it is also found that the preference of nitrogen-containing gases such as NH3, NO, and NO2 for adsorption on the surface of FeI2/In2S3 vdW heterostructures strongly depends on the polarization direction of the ferroelectric layer. In particular, the FeI2/In2S3 heterostructure shows reversible capture behavior for NH3. As a result, the FeI2/In2S3 vdW heterostructure-based gas sensor demonstrates high selectivity and sensitivity. These findings may open up a new route for the application of multiferroic heterostructures to spintronics, nonvolatile memories, and gas sensors.

Orbital polarization change and magnetic enhancement in rutile MnO2-δ epitaxial films

Effectively manipulating the orbital configuration is an emerging method to design quantum functional materials with novel electronic ground states. Here, we report the realization of orbital polarization change in rutile MnO2-δ epitaxial thin films by reductive treatments such as CaH2 coating annealing and hydrogen atmosphere annealing. These treated samples show significant lattice expansion due to the generation of oxygen vacancies and incorporation of H, and the mixed valence states of Mn2+ and Mn3+ are formed with the decrease in the Mn valence state. The X-ray linear dichroism results show that the electron occupied state of Mn in the treated film samples changes from 3d3z2-r2 to 3dx2-y2, which means that the deprivation of oxygen atoms in the oxygen octahedron of MnO6 causes a change of orbital polarization. The resulting high spin state in the treated MnO2-δ films greatly enhances the magnetic properties of the films. This work not only demonstrates how the oxygen atoms in the edge-shared oxygen octahedron of rutile structures are replaced by reduction but also extends the study of orbital polarization and magnetic ground state control in oxide epitaxial films.

Polarization State Preparation and Control Integration of a Quantum Communication System Based on a Field-Programmable Gate Array

Polarization State Preparation and Control Integration of a Quantum Communication System Based on a Field-Programmable Gate Array

Flexible Control of Broadband Polarization in a Spintronic Terahertz Emitter Integrated with Liquid Crystal and Metasurface.

Flexible polarization control of the terahertz wave in the wide bandwidth is crucial for numerous applications, such as terahertz communication, material characterization, imaging, and biosensing diagnosis. However, this promise is impeded by the operating bandwidth of circular polarization states, control modes, and the efficiency of the regulation. Here, we report a spintronic terahertz emitter integrated with phase complementary elements, consisting of a liquid crystal and metasurface, to achieve broadband polarization control with high flexibility. This strategy allows the broadband conversion between linear, elliptical, and circular polarization by changing the rotation angle to modulate the space-variant Pancharatnam-Berry phase. The device is characterized with a terahertz time-domain spectroscopy system, demonstrating that the ellipticity of the circular polarization state could keep greater than 0.9 in 0.60-0.99 THz. In the case of an external electro-magnetic field, further polarization modulation experiments are carried out to provide multiple conversion approaches for multi-azimuth. We first propose a method of full broadband polarization state control of the terahertz emitter based on Pancharatnam-Berry phase modulation and an external electro-magnetic field. We believe that such integrated devices with broadband working bandwidth and multiple control modes will make valuable contributions to the development and multi-scene applications of ultrafast terahertz technologies.

Broadband Design of Midinfrared Chiral Metamaterials Based on the Indium Tin Oxide Conical Helix.

This paper proposed a periodic midinfrared broadband chiral structure composed of indium tin oxide (ITO) conical helix. The simulation results show that the structure achieves a good broadband CD in the midinfrared. At the wavelength of 9.2 μm, the maximum value of CD is 0.55, the FWHM (full width half maximum) of CD is 7.2 μm, and the wavelength range is from 5.7 μm to 12.9 μm. The simulation results also show that compared with the traditional uniform spiral structure with the same radius, the conical spiral structure can achieve better broadband circular dichroism in the midinfrared band. This provides a new idea for the design of broadband polarization state control devices in the midinfrared band.

Ultra‐Broadband Terahertz Polarization Conversion Enabled by All‐Dielectric Grating Structures

Polarization control of electromagnetic waves has attracted broad interest for years. Despite meaningful efforts in the past decade, how to realize broadband transmissive polarization conversion for terahertz waves is a problem remaining unresolved. Herein, an innovative strategy of designing an all‐silicon grating is proposed, and it is experimentally demonstrated that the designed structure is capable of realizing ultra‐broadband cross‐linear and linear‐to‐circular polarization conversions in the terahertz regime. Moreover, active control of arbitrary polarization states can be accomplished by mechanically tilting the grating structure. In brief, this work promises a new approach to realizing ultra‐broadband conversion in arbitrary polarization state at terahertz frequencies, and is of great significance for terahertz wireless communication technology, polarization imaging, and emergent biochemistry research requiring dichroism light.

Polarization Fading Suppression for Optical Fiber Sensing: A Review

Optical fiber sensors are polarization sensitive and generally affected by polarization fading. This paper contributes to the optimal choice of polarization fading suppression methods for different optical fiber sensors, by means of comparative analysis of the mechanism of polarization fading, the strategy of polarization state control, and the applicability of suppression methods. The comparison results show that the polarization diversity receiving method is suitable for remote multi-channels optical fiber sensing system. The polarization orthogonal pulse pair method is only suitable for optical fiber sensing systems based on the backward scattering light. Meanwhile, the Faraday rotating mirror method is only suitable for optical fiber sensing systems based on the forward light interference. The polarization pulse coding method is suitable for sensing systems with high sensitivity and stability requirements. The polarization control method may increase the control complexity of sensing system for simultaneous variation of multiple polarization states. The full and partial polarization-maintaining fiber methods can be used to keep the polarization state of sensing light along the optical fiber, but the additional system cost limits the application. The polarization scrambler method is currently only available for sensing systems based on Brillouin scattering light. This paper provides a reference for the feasible selection of polarization fading suppression schemes for different optical fiber sensing systems.

Current-induced control of the polarization state in a polar-metal–based heterostructure SnSe/WTe2

The concept of a polar metal suggests a new approach to current-induced polarization control for ferroelectrics. We fabricate SnSe/WTe2 heterostructure to experimentally investigate charge transport between two ferroelectric van der Waals materials with different polarization directions. WTe2 is a polar metal with out-of-plane ferroelectric polarization, while SnSe ferroelectric semiconductor is polarized in-plane, so one should expect complicated polarization structure at the SnSe/WTe2 interface. We study curves, which demonstrate sharp symmetric drop to zero differential conductance at some threshold bias voltages , which are nearly symmetric with respect to the bias sign. While the gate electric field is too small to noticeably affect the carrier concentration, the positive and negative threshold positions are sensitive to the gate voltage. Also, SnSe/WTe2 heterostructure shows re-entrant transition to the low-conductive state for abrupt change of the bias voltage even below the threshold values. This behavior cannot be observed for single SnSe or WTe2 flakes, so we interpret it as a result of the SnSe/WTe2 interface coupling. In this case, some threshold value of the electric field at the SnSe/WTe2 interface is enough to drive a 90° change of the initial SnSe in-plane polarization in the overlap region. The polarization mismatch leads to the significant interface resistance contribution, analogously to the scattering of the charge carriers on the domain walls. Thus, we demonstrate polarization state control by electron transport through the SnSe/WTe2 interface.

Mechanically reconfigurable and electrically tunable active terahertz chiral metamaterials

Active and efficient control of polarization states of electromagnetic wave is highly desirable in broad optical and terahertz (THz) devices. Herein, we have proposed a type of mechanically reconfigurable and electrically tunable THz chiral metamaterials that are consisting of periodical U-shaped split ring resonators (USRRs) patterned on the graphene Miura-origami (G-Mori) structures. We demonstrate that their circular dichroism (CD) as high as 0.93 originate from the coupling effect between the proper arranged USRRs and the G-Mori structure, which can be tuned through continuous change of the folding angle and Fermi energy level of graphene origami via mechanical and electrical methods in reversible manner, respectively. Furthermore, the proposed chiral metamaterials possess ideal quarter-wave-plate behavior at the resonance which also can be controlled by combining mechanical and electrical methods. The mechanically reconfigurable and electrically tunable circular dichroism and polarization conversion properties of the chiral metamaterials will be suitable for development of various polarization-related THz devices, such as highly sensitive chiral sensors, active polarization modulators and converters.

Efficient Achromatic Broadband Focusing and Polarization Manipulation of a Novel Designed Multifunctional Metasurface Zone Plate.

In this paper, comprehensively utilizing the diffraction theory and electromagnetic resonance effect is creatively employed to design a multifunctional metasurface zone plate (MMZP) and achieve the control of polarization states, while maintaining a broadband achromatic converging property in a near-IR region. The MMZP consists of several rings with fixed width and varying heights; each ring has a number of nanofins (usually called meta-atoms). The numerical simulation method is used to analyze the intensity distribution and polarization state of the emergent light, and the results show that the designed MMZP can realize the polarization manipulation while keeping the broadband in focus. For a specific design wavelength (0.7 μm), the incident light can be converted from left circularly polarized light to right circularly polarized light after passing through the MMZP, and the focusing efficiency reaches above 35%, which is more than twice as much as reported in the literature. Moreover, the achromatic broadband focusing property of the MMZP is independent with the polarization state of the incident light. This approach broadens degrees of freedom in micro-nano optical design, and is expected to find applications in multifunctional focusing devices and polarization imaging.

Active Control of the THz Wave Polarization State by an Electronically Controlled Graphene Composite Metasurface

Active control of terahertz (THz) wave polarization state is of great significance for sensitive detection, imaging and communication. Here, a tunable THz quarter wave plate is designed by electronically controlling a composite metasurface consisting of the gold cross antennas and a monolayer graphene. The graphene composite metasurface acts as a quarter-wave plate when the chemical potential of graphene is 0 eV, by which the polarization state of the incident THz wave is converted from linear polarization to circular polarization. After the chemical potential of graphene is increased gradually, and to 0.5 eV, the transmitted polarization state of the THz wave is changed from right circular polarization to right elliptical polarization, and to linear polarization. Furthermore, the polarization state of the THz wave is able to be changed from left circular polarization to left elliptical polarization, and to linear polarization if the device is clockwise rotated by 90°. Therefore, the polarization state of THz wave could be actively controlled by the proposed tunable THz quarter wave plate. Our work will offer a new avenue for tunable THz polarization modulation devices.