Broadband Linear Polarization Research Articles

Terahertz-absorbing,dual-polarization converting supersurface structures based on the phase-change material VO2

Dynamically tunable multifunctional hypersurface structures have attracted the interest of researchers due to their good control of electromagnetic waves. Based on this, we have designed a dynamically tunable multifunctional hypersurface structure using the phase change material vanadium dioxide. By changing the state of vanadium dioxide, three functions of efficient broadband wave absorption, linear polarization conversion (LPC) and linear circular polarization conversion (LCPC) can be achieved. At room temperature, the hypersurface is used as a polarization converter to achieve broadband linear polarization conversion in the 0.903 THz range and line-circular polarization conversion with a total bandwidth of 0.608 THz in the 0.522 THz, 0.964 THz and 1.448 THz bands. When the temperature is raised to 68 °C, the hypersurface structure can be used as a broadband absorber, absorbing more than 90% of the incident wave in a wide frequency range of 1.348 THz and showing a large tolerance to variations in the angle of incidence and polarization. The electromagnetic field distribution is used to illustrate the absorption mechanism, and Stokes analysis is introduced to evaluate the polarization transition state. The designed structure can realize three electromagnetic modulation functions by changing the excitation conditions and can cover a wide range of frequency bands. Finally, we used coding to simulate the effect of loss on the wave absorption results in real applications and verified the stability of the structure. Our design provides new ideas for the development of terahertz communication and multifunctional integrated devices.

Tunable broadband absorption and broadband linear polarization converter based on vanadium dioxide

A composite dielectric metamaterial based on vanadium dioxide (VO2) is proposed to achieve flexible switching between two functions, broadband absorption, and polarization conversion, by adjusting the VO2 conductivity. The designed metamaterial functions as a broadband absorber when VO2 is in the metal phase. The absorber consists of a VO2 top structure, a silicon dioxide (SiO2) dielectric layer, and a VO2 thin film. Numerical simulation ns show that the absorber can absorb up to more than 90% in the frequency range of 3.22 ∼ 8.51 THz, and due to the symmetry of the structure, the absorber is characterized by polarization-insensitive properties and good absorption over a wider incidence angle. When VO2 is in the insulator phase, the designed metamaterial has a cross-polarization conversion function. The linear polarization converter primarily comprises an I-beam metal, a SiO2 dielectric layer, and a gold substrate layer. Numerical simulations demonstrate that the linear polarization converter accomplishes a line polarization conversion rate (PCR) greater than 90% within the 1.40 ∼ 4.11 THz frequency range, attains a close to 100% cross-polarization conversion rate (PCR) at 1.46, 1.95, 3.0, and 3.97 THz. To confirm the wave absorption mechanism of the absorber, we utilize the impedance matching theory to analyze it. The proposed switchable bifunctional metamaterials present significant potential for broader applications in future terahertz communication, imaging, stealth technology, and related fields.

Metasurface-based broadband linear polarization converter with broad angular stability for X-band applications

Metasurface-based broadband linear polarization converter with broad angular stability for X-band applications

Broadband Linear Polarization Converter Based on Slot-Line Loaded Structure for Pre-Determined Notched Band

This brief proposes a broadband linear polarization converter with pre-determined notched band. By loading a H-shaped slot line on the basis of the rectangular resonator, a pair of resonator modes as well as pre-determined polarization conversion zeros can be additionally allocated inside the band, thereby realizing broadband and band-notch characteristics, simultaneously. The multi-mode resonant mechanism to realize broadband and the conversion zero control principle for notched band are analyzed in detail. Finally, a notch-band broadband linear polarization converter is designed and fabricated, and the simulated and measured results are agreed well with each other. As the main advantage, the proposed multi-mode resonant structure realizing the notched band can achieve flexible isolation band design while hardly affecting the broadband filtering characteristics, and is especially suitable for pre-determined spectrum windows of broadband electromagnetic control devices.

A reconfigurable multifunctional polarization converter based on active metasurface

In this paper, we report a reconfigurable multifunctional polarization converter (RMPC) based on positive-intrinsic-negative (PIN) diodes, enabling to achieve different functions in different bands and states. The simulations and experiments show that when the PIN diode is off, it acts as a broadband linear polarization (LP) converter at 9.12–15.93 GHz. Simultaneously, when the PIN diode is on, the LP incident wave is converted into a left-handed circular polarization wave at 8.69–11.41 GHz and a cross-polarization wave at 13.40–14.97 GHz, whereas full reflection is obtained at 12.05–12.54 GHz. The RMPC consists of two dielectric plates and three layers of metal copper plates. Finally, a sample was fabricated and measured, the simulated and experimental results were in good agreement. Compared with other works, the RMPC has more working states and wider operating frequency bands, which has an application potential in the field of radar stealth and satellite communication.

A dynamically switchable metamaterial device with multiple functions based on vanadium dioxide

Based on the phase transition properties of vanadium dioxide (VO2), a metamaterial device is designed in this paper, which can achieve multiple switchable functions. When VO2 is in the metallic state, the proposed device can realize broadband absorption with peak absorbance more than 90 % in the frequency range of 2.40–6.73 THz and broadband linear polarization conversion (LPC) with polarization conversion ratio (PCR) greater than 90% in the range of 1.80–4.21 THz, respectively, depending on whether the incidence of terahertz (THz) electromagnetic (EM) wave is from top side or bottom side. When VO2 is in the insulated state, the proposed device can achieve LPC of half-reflection and half-transmission (HRHT) and transmissive linear-to-circular (LTC) polarization conversion. The study in this paper has guiding significance in the design of THz metamaterial devices with multiple functions.

Dual-Channel Switchable Metasurface Filters for Compact Spectral Imaging with Deep Compressive Reconstruction.

Spectral imaging technology, which aims to capture images across multiple spectral channels and create a spectral data cube, has been widely utilized in various fields. However, conventional spectral imaging systems face challenges, such as slow acquisition speed and large size. The rapid development of optical metasurfaces, capable of manipulating light fields versatilely and miniaturizing optical components into ultrathin planar devices, offers a promising solution for compact hyperspectral imaging (HSI). This study proposes a compact snapshot compressive spectral imaging (SCSI) system by leveraging the spectral modulations of metasurfaces with dual-channel switchable metasurface filters and employing a deep-learning-based reconstruction algorithm. To achieve compactness, the proposed system integrates dual-channel switchable metasurface filters using twisted nematic liquid crystals (TNLCs) and anisotropic titanium dioxide (TiO2) nanostructures. These thin metasurface filters are closely attached to the image sensor, resulting in a compact system. The TNLCs possess a broadband linear polarization conversion ability, enabling the rapid switching of the incidence polarization state between x-polarization and y-polarization by applying different voltages. This polarization conversion facilitates the generation of two groups of transmittance spectra for wavelength-encoding, providing richer information for spectral data cube reconstruction compared to that of other snapshot compressive spectral imaging techniques. In addition, instead of employing classic iterative compressive sensing (CS) algorithms, an end-to-end residual neural network (ResNet) is utilized to reconstruct the spectral data cube. This neural network leverages the 2-frame snapshot measurements of orthogonal polarization channels. The proposed hyperspectral imaging technology demonstrates superior reconstruction quality and speed compared to those of the traditional compressive hyperspectral image recovery methods. As a result, it is expected that this technology will have substantial implications in various domains, including but not limited to object detection, face recognition, food safety, biomedical imaging, agriculture surveillance, and so on.

Electrically controllable broadband reflective linear cross-polarization conversion based on liquid crystals.

This paper presents an electrically controllable reflective broadband linear polarization (LP) converter based on liquid crystals (LCs) for cross-polarization conversion (CPC) in the terahertz frequency range. The proposed structure achieves a high polarization conversion ratio (PCR) exceeding 0.9 within the frequency range of 236.8 - 269.6 GHz. A vital feature of this design is the dynamic control of polarization conversion by re-orienting the nematic liquid crystal molecules through voltage bias switching between 'on' and 'off' states, allowing for precise manipulation of cross-polarized and co-polarized reflected waves. Experimental results validate the simulation outcomes, demonstrating excellent agreement. In contrast to conventional reflective polarization converters with fixed frequency responses, the proposed electrically controllable polarization conversion offers significant potential in imaging and optical communications.

SN 2020udy: an SN Iax with strict limits on interaction consistent with a helium-star companion

ABSTRACT Early observations of transient explosions can provide vital clues to their progenitor origins. In this paper, we present the nearby Type Iax (02cx-like) supernova (SN), SN 2020udy, that was discovered within hours (∼7 h) of estimated first light. An extensive data set of ultra-violet, optical, and near-infrared observations was obtained, covering out to ∼150 d after explosion. SN 2020udy peaked at −17.86 ± 0.43 mag in the r band and evolved similarly to other ‘luminous’ SNe Iax, such as SNe 2005hk and 2012Z. Its well-sampled early light curve allows strict limits on companion interaction to be placed. Main-sequence companion stars with masses of 2 and 6 M⊙ are ruled out at all viewing angles, while a helium-star companion is allowed from a narrow range of angles (140–180° away from the companion). The spectra and light curves of SN 2020udy are in good agreement with those of the ‘N5def’ deflagration model of a near Chandrasekhar-mass carbon–oxygen white dwarf. However, as has been seen in previous studies of similar luminosity events, SN 2020udy evolves slower than the model. Broad-band linear polarization measurements taken at and after peak are consistent with no polarization, in agreement with the predictions of the companion-star configuration from the early light-curve measurements. The host galaxy environment is low metallicity and is consistent with a young stellar population. Overall, we find the most plausible explosion scenario to be the incomplete disruption of a CO white dwarf near the Chandrasekhar-mass limit, with a helium-star companion.

Vanadium dioxide based bifunctional metasurface for broadband absorption and cross-polarization conversion in THz range

Achieving switchable and reconfigurable functions based on a single metasurface has become one of the research hotspots among scholars in recent years. Based on the excellent phase transition properties of vanadium dioxide (VO2), a THz bifunctional metasurface device (BMD) is designed that can realize broadband absorption and broadband cross-polarization conversion. When VO2 behaves in the metallic state, the BMD acts as a broadband metamaterial absorber (MA), and its absorbance is larger than 90 % in the range of 1.97–4.63 THz with a relative bandwidth (RB) of 80.61 %. In addition, the MA is insensitive to the polarization angle and can maintain high absorbance over a wide range of incident angles for both y- and x-polarized THz waves. When VO2 behaves in the insulated state, the BMD will act as a broadband linear polarization converter (PC). It has a polarization conversion ratio (PCR) of greater than 90 % with a RB of 92.31 % in the frequency range of 1.54–4.18 THz. The excellent absorption and polarization conversion characteristics of the proposed BMD make it possess potential values in different THz areas with sub-wavelength device scales.

Study on a bifunctional switchable metasurface with perfect absorption and polarization conversion based on VO2 and graphene in THz region

A switchable metamaterial device with dual function (SMDDF) based on vanadium dioxide (VO2) and graphene is designed in this paper, where VO2 is a phase change material and it can transition from the insulating state to the metallic state when it is stimulated by external conditions such as heat, electricity or light. In addition, graphene is a 2D active material and its conductivity can be well controlled by adjusting its bias voltage dependent chemical potential, which makes it have the advantage of easy integration. When VO2 is in the metallic state and the chemical potential of graphene is set as 0.65 eV, the proposed SMDDF can behave as a single band absorber with the peak absorbance higher than 99.9 % at 1.8768 THz. However, when VO2 is in the insulated state, and the chemical potential of the graphene pattern layer (GPL) is set as 0 eV, the proposed SMDDF will behave as a broadband linear polarization converter. It can convert the incident linearly polarized EM waves into the cross-polarized reflected waves within the frequency range of 2.12–3.58 THz, and the polarization conversion ratio (PCR) is >90 % with the relative bandwidth (WRB) up to 51.23 %. Research results prove that the overall performances of the proposed bifunctional metamaterial device is superior to some of those reported in the literatures. Therefore, the research results of this paper may provide guidance for designing switchable multi-function terahertz devices using VO2 and graphene in variable areas of practical applications.

Broadband and high-efficiency polarization conversion with a nano-kirigami based metasurface

Nano-kirigami metasurfaces have attracted increasing attention due to their ease of three-dimension (3D) nanofabrication, versatile shape transformations, appealing manipulation capabilities and rich potential applications in nanophotonic devices. Through adding an out-of-plane degree of freedom to the double split-ring resonators (DSRR) by using nano-kirigami method, in this work we demonstrate the broadband and high-efficiency linear polarization conversion in the near-infrared wavelength band. Specifically, when the two-dimensional DSRR precursors are transformed into 3D counterparts, a polarization conversion ratio (PCR) of more than 90% is realized in wide spectral range from 1160 to 2030 nm. Furthermore, we demonstrate that the high-performance and broadband PCR can be readily tailored by deliberately deforming the vertical displacement or adjusting the structural parameters. Finally, as a proof-of-concept demonstration, the proposal is successfully verified by adopting the nano-kirigami fabrication method. The studied nano-kirigami based polymorphic DSRR mimic a sequence of discrete bulk optical components with multifunction, thereby eliminating the need for their mutual alignment and opening new possibilities.

The Potential of the Wavelength-integrated Scattering Polarization of the Hydrogen Lyα Line for Probing the Solar Chromosphere

The intensity and the linear scattering polarization profiles of the hydrogen Lyα line encode valuable information on the thermodynamic and magnetic structure of the upper layers of the solar chromosphere. The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) sounding rocket experiment provided unprecedented spectropolarimetric data of this line, as well as two-dimensional broadband images in intensity and linear polarization. We theoretically investigate the potential of the Lyα broadband polarimetric signals for probing the solar chromosphere and its magnetic fields. We analyze the synthetic Stokes profiles obtained from a series of radiative transfer (RT) calculations out of local thermodynamic equilibrium, considering semi-empirical one-dimensional models of the solar atmosphere. The wavelength-integrated linear polarization signal is found to be dominated by the contribution from the wings when considering a Gaussian weighting function with a FWHM that corresponds to the CLASP slit-jaw broadband filter. These broadband linear polarization signals are strongly sensitive to magnetic fields of strengths on the order of 50 G, via the action of magneto-optical (MO) effects, and are expected to encode information on the middle–upper chromosphere. The two-dimensional broadband intensity and linear polarization images observed by CLASP can be suitably mimicked using synthetic wavelength-integrated signals obtained considering atmospheric models and magnetic fields that are representative of solar regions with different levels of activity, provided that the impact of MO effects is taken into account. Despite the limitations of a one-dimensional RT modeling, this work illustrates the diagnostic potential of filter-polarimetric Lyα signals for probing the solar chromosphere and its magnetism.

A Nested Square Shaped Metasurface-Based Broadband Linear Polarization Converter for Ku-Band Applications

This paper presents a wideband, thin, low-cost, and easy to fabricate linear polarization (LP) converter design utilizing metasurface (MS) for Ku-band (12-18 GHz) applications (also in the 18-19 GHz part of the K-band (18-27 GHz)). The design has a topology on a 1.6 mm thick FR-4 dielectric material with copper MS on the front and an entirely copper slab on the back. The presented design shows a polarization conversion ratio (PCR) of beyond 90% within the 12-19 GHz frequency band and also over 99% in the 12.5-13.1 and 16.32-17.64 GHz frequency ranges. To further give insight into the physical structure of the suggested MS-based polarization converter (PC), both the u – v axes are analyzed, and the existing surface behaviors at resonance frequencies are investigated. We compare the performance outputs with other Ku-band PCs, and the efficiencies of the suggested strategy over current MS-based LP converters are emphasized.

Wideband linear cross-polarization conversion with 3D metamaterial configuration.

In this Letter, a broadband and wide-angle linear polarization (LP) converter based on a 3D resonator for cross-polarization conversion (CPC) is presented. The designed structure performs a CPC with a polarization conversion ratio (PCR) of more than 90% in the frequency range 16.32 to 34.12 GHz, corresponding to a relative frequency bandwidth of 70.6%. Moreover, the presented structure possesses broad angle stability and miniaturized configuration. The efficiency of CPC remains over 90% in the operational frequency band with the incident angles up to 40°, and the cell size is 0.18λ for the lowest frequency of the CPC operational band. The proposed 3D structure is fabricated using the multi-material hybrid microdroplet jetting modeling (MHMJM) technique, and the experiments agree closely with the simulated results. Compared with traditional polarization converters based on a planar resonant structure, the proposed design shows excellent bandwidth, wide-angle performance, and miniaturization advantages.

Tunable Polarization-Multiplexed Achromatic Dielectric Metalens.

Tunable metasurfaces provide a compact and efficient strategy for optical active wavefront shaping. Varifocal metalens is one of the most important applications. However, the existing tunable metalens rarely serves broadband wavelengths restricting their applications in broadband imaging and color display due to chromatic aberration. Herein, an electrically tunable polarization-multiplexed achromatic metalens integrated with twisted nematic liquid crystals (TNLCs) in the visible region is demonstrated. The phase profiles at different wavelengths under two orthogonal polarization channels are customized by the particle swarm optimization algorithm and matched with the dielectric metaunits database to achieve polarization-multiplexed achromatic performance. By combining the broadband linear polarization conversion ability of TNLC, the tunability of varifocal achromatic metalens is realized by applying different voltages. Further, the electrically tunable customized dispersion-manipulated metalens and switchable color metaholograms are demonstrated. The proposed devices will accelerate the application of metasurfaces in broadband zoom imaging, AR/VR displays and spectral detection.

Optically imprinted polarization gratings with a twisted nematic liquid crystal as a photomask

Liquid crystal Pancharatnam–Berry phase optical elements (LCPBOEs) are becoming increasingly attractive elements to be used to enhance near-eye displays or manipulate light beams, owing to their flatness and circular polarization-dependent behavior. The optical imprinting technique that is one of the commonly used methods for fabricating LCPBOEs is considered to be the most promising technique for mass production at a low cost, but the design of the photomask must be improved. In this work, a photomask that is based on a twisted nematic liquid crystal polarization grating (TNLCPG) cell, acting as a broadband linear polarization rotator, is designed. This TNLCPG cell, with a predefined alignment profile of a polarization grating, can convert linearly polarized light into a light field with spatially varying linear polarization and exhibits broadband operation over the entire visible spectrum. The designed TNLCPG photomask is used to demonstrate a liquid crystal polarization grating (LCPG) film using a white flashlight as a writing source. A high diffraction efficiency of greater than 95% is obtained. With its simple design and fabrication, the proposed TNLC-based photomask can potentially be used in the fabrication of LCPBOEs.

Graphene-based tunable linear and linear-to-circular polarization converters in the THz band

A switchable and tunable reflective terahertz (THz) polarization converter based on graphene metamaterial is designed and analyzed. By changing the Fermi energy level of graphene, the converter can achieve broadband linear polarization conversion (LPC) and linear-to-circular polarization conversion (LTC-PC). At relatively low Fermi energy level, the converter can achieve dual-band (0.1–0.3 eV) and single-band (0.4–0.6 eV) LPC, respectively, with a broadband frequency range of 2.34–3.54 THz, 3.77–4.22 THz, and 3.75–4.43 THz, and maximum polarization conversion rate (PCR) exceeding 99%. At high Fermi energy level, in addition to the LPC function, the converter can also achieve LTC-PC in the frequency range of 3.34–3.59 THz and 2.89–3.34 THz by adjusting the Fermi energy level. The physical mechanisms are elucidated from the point of the surface current distribution diagram. The structure shows great potential in switchable and tunable broadband THz converters and related applications.

Broad-band and broad-angle linear and circular polarization converting metasurface

This paper presents a broad-band and broad-angle anisotropic reflective polarization converting metasurface (PCMS) for C- and X-band applications, which is composed of square split ring resonators. Such PCMS can be used in a wide range of applications such as satellite antennas, navigation systems, and biomedical devices, to name but a few. The performance of the presented PCMS is analyzed theoretically, numerically, and experimentally. The results at normal and oblique incidences demonstrate that the PCMS achieves broad-band linear polarization (LP) transformation within an operating bandwidth of 5.3 GHz (5.3–10.6 GHz), covering the C-band and a portion of the X-band. The broad-band performance of the PCMS sustains from to . Moreover, the PCMS achieves polarization conversion for circularly polarized (CP) waves in the same bands. The polarization conversion ratio is more than for both LP and CP incident waves.

Multifunctional metasurface for broadband absorption, linear and circular polarization conversions

With the development of metasurfaces and the improvement of manufacturing technology, it is important and imperative to design novel metasurfaces that can flexibly manipulate terahertz (THz) waves. In this paper, a multifunctional metasurface (MFMS) based on graphene and photosensitive silicon (Si) is proposed, which integrates three functions: broadband absorption, broadband linear and circular polarization conversions in THz band. For absorption mode, the MFMS can absorb above 90% energy in the frequency band of 1.74-3.52 THz with the relative bandwidth of 67.6%. For both linear-linear and circular-circular polarization conversion modes, the relative bandwidth with over 90% polarization conversion rates (PCRs) reaches 49.3% in the frequency band of 1.54-2.55 THz. The working mechanism of the MFMS is analyzed by the surface current distributions, and its properties of the absorption and polarization conversion under oblique incident angles are investigated, respectively. The proposed metasurface has promising prospects in terahertz devices such as modulators, smart switches and other terahertz devices.