Polarization States Of Waves Research Articles

Reflective linear polarization converter with multimode, dual band and high efficiency

Abstract A thin, dual-band, highly efficient linear polarization converter based on a multi-mode metasurface was proposed. The high-efficiency manipulation of polarization states of electromagnetic waves in dual-band frequencies was achieved by utilizing a diagonally etched metasurface as a square joined by a ring. The metasurface transforms incident linearly polarized (LP) waves into cross-polarized LP waves at various frequencies. Numerical simulations reveal that the metasurface operates efficiently in the bands from 7.724 GHz to 8.192 GHz and 13.142 GHz to 15.95 GHz, with a polarization conversion rate (PCR) of 95% in both bands. To validate the theoretical analysis and simulation results, a model is fabricated and measured. The experimental results confirm that the proposed metasurface successfully achieves dual band-and dual-mode polarization conversion, showing reasonable consistency of theoretical and simulated findings. This converter can optimize the signal performance by clarifying polarized radio waves.

Non-Interleaved Shared-Aperture Full-Stokes Metalens via Prior-Knowledge-Driven Inverse Design.

Characterization of electromagnetic wave polarization states is critical in various applications of materials, biomedical, and imaging. The emergence of metasurfaces opens up the possibility of implementing highly integrated full-Stokes imagers. Despite rapid development, prevailing schemes on metasurface-based full-Stokes imagers require interleaved or cascaded designs, inevitably resulting in performance deterioration, bulky size, and complicating the imaging procedure due to misalignment. To overcome these challenges, a non-interleaved shared-aperture full-Stokes metalens enabled by the prior-knowledge-driven inverse design methodology is proposed. The metalens can be directly deployed into imagers, performing high-accuracy diffraction-limited full-Stokes imaging without other ancillary components, breaking intrinsic constraints of efficiency and resolution in interleaved design. To demonstrate this, the metalens is integrated into the W-band passive imaging system, as an alternative solution, to perform polarimetric imaging, which reduces the reliance on the high cost and high complexity of the ortho-mode transducer and broadband correlator in traditional polarimetric radiometers. Furthermore, with the assistance of a 3D reconstruction method, the feasibility of multi-polarization information for contactless surface slope measurements is explored. This work may open new paradigms for the full-Stokes imager designing and broaden the applications of metasurface polarimetric imaging.

Comprehensive design of all-optical logic devices utilizing polarization holography.

Polarization holography has emerged as a promising method for manipulating the amplitude, phase, and polarization states of light waves. This study proposes what we believe to be a novel design method for various all-optical logic devices, including a complete set of all-optical Boolean logic gates and a polarization-controlled 1 × 4 optical switch, utilizing polarization holography. Through the angle multiplexing technique, specially designed polarization holograms are recorded in polarization-sensitive material, transforming it into all-optical Boolean logic gates and a polarization-controlled 1 × 4 optical switch. The all-optical logic devices developed in this work function as passive diffractive optical elements, enabled by a single piece of polarization-sensitive material, eliminating the need for additional circuit control. This approach offers the advantages of a simple structure, low cost, and instantaneous response. We contend that this advancement will facilitate the expansion of the application domains of polarization holography, particularly enhancing the capabilities of all-optical information processing.

Terahertz polarization sensing for influenza A virus based on plasmonic metasurface

Terahertz metasurface sensors attract extensive attention for excellent characterisics. However, most existing sensing schemes overlooked the polarization state of electromagnetic waves. Here, we propose a plasmonic metasurface sensor based on the elliptical polarization state of reflected EM wave, which can be used for the sensing of influenza A virus. The sensor achieves the conversion from linear polarization to circular polarization within 1–3 THz. By analysing the electromagnetic field distributions of the resonances at 1.43 THz and 2.16 THz, it can be concluded that the polarization conversion originates from the magnetic dipole. Besides, the sensor can characterize the changes in the complex refractive index of the test sample based on the elliptical polarization state of the reflected wave. The electromagnetic response of the metasurface sensor shows an excellent linear relationship between the rotating direction angle of polarization ellipse and the extinction coefficient (k) of the complex RI of the analyte. Furthermore, we also demonstrate the feasibility of detecting three subtypes of Influenza A viruses (H1N1, H5N2, and H9N2) at 1.39 THz though the elliptical polarization state. This sensing approach does not rely on high-precision broadband scanning, providing an alternative perspective for THz biosensing.

Terahertz four-channel polarization-multiplexed vortex beams based on vanadium dioxide integrated metasurfaces

In recent years, vanadium dioxide (VO2) has drawn enormous attention in dynamic electromagnetic (EM) manipulation, owing to its mild phase change condition and prominent diversity of optical characteristics. In this paper, anisotropic meta-atoms integrating VO2 are proposed to obtain four polarization-multiplexing channels. The meta-atom is composed of two stacking metal–insulator–metal (MIM) structures. For the modulation of EM wavefront in desired manners, a meta-atom database composed of 256 meta-atoms is elaborately designed. Applying the meta-atom database and the degree of freedom in interfacial phase distribution, two metasurfaces are demonstrated in the verification of four-channel polarization-multiplexed vortex beams. The firstly proposed metasurface realizes the generation of four vortex beams with different topological charges. Each channel is dependent on the polarization of the incident wave and VO2 state. The further investigated metasurface achieves simultaneous control over the reflection direction, quantity, and mode of vortex beams under different VO2 states and polarization states of incident wave. In addition, designed metasurfaces exhibit wideband effect for over 100 GHz. The proposed design method enables four-channel generation of vortex beams using a single metasurface, and may have potential applications in dynamic and integrated terahertz communication.

Enhancing broadband terahertz absorption via a graphene-based metasurface absorber featuring a rectangular ring and triple crossbars

This study introduces an innovative strategy to achieve a versatile and adaptive terahertz (THz) absorber by leveraging a graphene-based metasurface. This metasurface comprises a rectangular ring, three crossbars and a grounded gold film, all separated by a thin SiO2 layer. The phenomenon of plasmonic hybridization, involving surface and cavity plasmon resonances, enables the interaction between incident THz waves and the proposed graphene-based metasurface, leading to a substantial enhancement in the absorptance bandwidth of the plasmonic system. The enhancement of absorptance can be finely adjusted by modifying the chemical potential (Fermi energy) in graphene and manipulating the structural parameters of the device. A notable feature of our design is its inherent resistance to variations in incident angles and polarization states of incoming electromagnetic waves. The proposed device achieves an absorptance exceeding 80% across a continuous spectrum, exhibiting a bandwidth of approximately 0.90 THz from 0.94 to 1.84 THz. This robust characteristic ensures consistent and reliable performance in diverse scenarios. Our findings present intriguing prospects for various applications centered on wave modulation, which encompass, but are not limited to, THz imaging, filtering, energy harvesting, and tunable sensors.

The Ellipticity of High Frequency Transionospheric Radio Waves

AbstractThe polarization state of transionospheric high frequency (HF) radio waves can be determined using the crossed‐dipole antennas of the Radio Receiver Instrument (RRI) onboard Enhanced Polar Outflow Probe (e‐POP) on the CAScade, Smallsat, and IOnospheric Polar Explorer/Swarm‐E satellite. Coordinated experiments between ground radars and RRI showed that the radio waves have high ellipticity angles (elliptical or circular polarization) for propagation direction 6°–25° from the perpendicular direction to the local geomagnetic field. However, from magnetoionic theory and a typical assumption of roughly equal power in the O‐ and X‐modes, radio waves can have high ellipticity angles only when the propagation direction is within 10° of perpendicularity. This investigation uses coordinated experiments between the Saskatoon SuperDARN radar and RRI. Magnetoionic modeling reveals that the relative strengths of the O‐ and X‐modes for the HF radio waves transmitted from the Saskatoon SuperDARN change significantly poleward of the radar. Differences in the relative power between the two wave modes were found to significantly modify the polarization state of radio waves, and govern the sense of rotation of the wave. Even a relatively modest 2–5 dB power difference in the X‐mode over the O‐mode was found to result in unexpected observations of circularly polarized radio waves at aspect angles 6°–10° from perpendicular, and unexpected elliptically polarized waves observed at aspect angles more than 10° from perpendicular. Therefore, a combination of RRI observations and modeling, which accounts for relative differences in the O‐ and X‐mode powers, was used here to better understand the unexpected observations of polarization states of transionospheric radio waves.

Cylindrical metalens for multidimensional control of terahertz waves

Metalens, consisting of planar micro/nanostructure arrays, has shown great potentials in beam steering, subwavelength focusing and high-resolution imaging. Taking the advantages of ultrathin thickness and compact design, it can be integrated with a photonic chip to improve the collection efficiency of optoelectronic systems. However, it remains challenging to realize the multidimensional control of terahertz (THz) waves by using a metalens, although the convergence properties have been widely studied. Here, we design and experimentally demonstrate a multifunctional cylindrical metalens by using a tri-layer metallic metasurface. By modulating the amplitude, phase and polarization states of terahertz waves independently, the cylindrical metalens can generate two focal lines at different positions for transmitted x- and y- polarized terahertz waves with varying amplitude distribution. Importantly, up to 64.7% focusing efficiency has been obtained at the frequency of 0.34 THz with a numerical aperture (NA) of 0.75. Our study offers a novel method for implementing multifunctional cylindrical metalens which lays the foundation of advanced integration with arrayed terahertz detection chips.

Analysis of Polarization Angle on Holographic Recording Based on PQ/PMMA.

The polarization state of light waves significantly affects the quality of holographic recordings. This paper quantitatively analyzes the impact of different polarization states of signal and reference beams on the quality of holographic recordings in PQ/PMMA photopolymer systems during the holography process. By deriving the light field distribution of the interference between two light waves of different polarization states and introducing the interference fringe contrast and the modulation of the refractive index of the photopolymer, we established the relationship between the diffraction efficiency of PQ/PMMA photopolymer holographic gratings and the angle between polarization directions. Based on this relationship, simulations and experiments were conducted. The experimental results demonstrated that as the angle between the polarization directions increased, the diffraction efficiency of the material decreased, with the efficiency dropping to 24.69% of its original value when the angle increased from 0° to 50°. When the angle increased to 60°, the influence of polarization characteristics became gradually significant, and at 90°, it was entirely dominated by polarization characteristics. The photoinduced birefringence properties of the PQ/PMMA prepared in the measurement experiment were studied, and the polarization characteristics of the reconstructed light under polarization direction angles of 0°, 60°, and 90° were investigated. The results indicated that at a polarization direction angle of 60 degrees, the material exhibited a significant response to the polarization information of the signal light. Finally, holographic recordings of objects at different polarization direction angles were conducted, and the reconstructed images were used to visually reflect the impact of the polarization direction angle on the quality of holographic recordings.

Realization of Hadamard gate with twisted magnon modes in synthetic antiferromagnets

Manipulating the polarization of spin waves highlights the potential of antiferromagnetic magnonics in encoding and handling magnon information with high fidelity. Here, we propose a flexible approach to mutually convert polarization states (i.e., Hadamard gate) by incorporating a topological degree of freedom, intrinsic orbital angular momentum (OAM), into twisted spin wave modes within synthetic antiferromagnetic nanodisks. The polarization states of spin waves and the implementation of magnonic logic operations can be electrically read out through combined spin pumping and inverse spin Hall effect, as demonstrated by numerical micromagnetic simulations for CoFeB-based synthetic antiferromagnets. Our findings present an exciting possibility of parallel magnonic computing utilizing topologically protected and magnetic damping-resistance OAM of twisted magnons.

All-dielectric terahertz metasurfaces for arbitrary linear polarization detection

The polarization state, an intrinsic property of electromagnetic waves, plays a key role in determining the mechanism of light–matter interactions. Recently, the bulky elements for evaluating polarization states have been miniaturized by using metasurfaces. However, determining arbitrary linear polarization (LP) states from vortex beams generated by metasurfaces is quite challenging. Here, a general design of all-silicon quasi-periodic arrays based on polarization multiplexing technology is proposed, which can be used for the detection of arbitrary incident LP state. By embedding independent helical phase profiles in two orthogonal LP channels, the generated interference spot at the predesigned focal plane is resolvable in a proper polarized direction. Benefiting from the establishment of a parametric theoretical model, the evolution of the incident polarization can be determined using key parameters defined on the pixelated focal plane. The proposed method can flexibly determine the polarization state of incident terahertz waves, which has great potential in remote sensing, high-resolution imaging, and data communication.

Dual-pattern broadband polarization converter in THz band based on graphene and VO2 hybrid metasurface

We propose a dual-pattern broadband polarization converter in the terahertz band using a vanadium dioxide (VO2) and graphene metasurface. The converter can be switched between transmission and reflection patterns by controlling the phase of VO2. In the insulating state of VO2 and with the Fermi energy of graphene (Ef) set to 1 eV, the converter works in transmission mode and can convert linearly polarized waves. In the metallic state of VO2 and with Ef set to = 0 eV, the converter works in reflection mode and can function as a quarter-wave plate. The proposed converter is expected to have applications in integrated devices that control the polarization state of terahertz waves.

Graphene-based metasurface for real-time control of three electromagnetic wave modes and polarization state

In various practical applications, the demand for switchable metasurfaces with versatile functionalities has grown significantly. This paper proposes a graphene-based metasurface that offers independent control over all three electromagnetic (EM) wave modes (i.e., reflection, transmission, and absorption) as well as the polarization state for both reflection and transmission modes, all achieved in real-time at terahertz frequency. The metasurface is designed with a multilayer structure, comprising quartz, gold, and graphene. Two graphene sheets are placed at the beginning and end of the structure to control specific functionalities. By dynamically adjusting the chemical potential of each graphene sheet, the proposed metasurface can manipulate all three EM wave modes and convert linear to circular polarization independently for both reflection and transmission modes. Additionally, the metasurface can switch from polarization conversion to without polarization conversion of the reflected wave by adjusting the chemical potential of graphene. Due to its numerous switchable functions and a high degree of freedom, the presented metasurface has the potential to be used in wireless communication, biomedicine, and optoelectronic devices.

Broadband polarizer using single-layer grating with ultra-high extinction ratio

Polarizers are an essential optical element for tailoring the polarization state of electromagnetic waves in a wide range of optical devices. Such polarizers, which exhibit a wide operating bandwidth and high performance, are attracting increasing attention, due to their extensive prospects for use in applications ranging from polarization imaging, to optical communications and detection, among others. However, achieving both broadband performance and ultra-high extinction ratio (ER), and that simultaneously, is still challenging in the design of effective polarizers. To tackle that demand, in this work, an Au-on-silica grating structure has been proposed as the basis of the design of a miniaturized high-efficiency polarizer that practically can cover the entire visible and near-infrared spectral ranges. The single-layer polarizer thus designed can show an ER of 60 dB in this spectral domain, and it has been shown that the geometrical parameters selected have a significant effect on the performance characteristics of the polarizer. Furthermore, an ER of ∼150 dB could be achieved merely by regulating the thickness of the grating to achieve the optimum performance. By integrating the high-performance polarizer proposed in this work with an optical fiber “meta-tip,” a refractive polarizer with a value of the ER of >45 dB, and that over the entire spectral domain considered, has been demonstrated. Such an approach offers an alternative route to achieving a broadband, powerful, and flexible processing polarizer design.

Optically controlled dielectric metasurfaces for dynamic dual-mode modulation on terahertz waves

Dynamically controlling terahertz (THz) waves with an ultracompact device is highly desired, but previously realized tunable devices are bulky in size and/or exhibit limited light-tuning functionalities. Here, we experimentally demonstrate dynamic modulation on THz waves with a dielectric metasurface in mode-selective or mode-unselective manners through pumping the system at different optical wavelengths. Quasi-normal-mode theory reveals that the physics is governed by the spatial overlap between wave functions of resonant modes and regions inside resonators perturbed by pump laser excitation at different wavelengths. We further design/fabricate a dielectric metasurface and experimentally demonstrate that it can dynamically control the polarization state of incident THz waves, dictated by the strength and wavelength of the pumping light. We finally numerically demonstrate pump wavelength-controlled optical information encryption based on a carefully designed dielectric metasurface. Our studies reveal that pump light wavelength can be a new external knob to dynamically control THz waves, which may inspire many tunable metadevices with diversified functionalities.

Design of a bifocal metalens with tunable intensity based on deep-learning-forward genetic algorithm

Metalenses, which control the amplitude, phase, and polarization state of incident waves based on metasurface to achieve focusing and imaging, have many important applications in various optical systems. We design a bifocal metalens that can independently control the focusing of right-handed circularly polarized light and left-handed circularly polarized light. Due to the demand for enormous simulations, traditional design methods are extremely time-consuming. Here, we propose a deep-learning-forward genetic algorithm to efficiently design the metalens parameters. The numerical simulation results of the metalens are in good agreement with the theoretical results. Meanwhile, it is flexible to change intensity ratio of the two foci through altering incident light ellipticity without redesigning the light intensity profile. This work provides a novel approach to multifunctional metasurface device realization.

Multichannel Airy beam generator simultaneously for linear and circular polarized waves

The Airy beam has intrigued long-held research interests and developed various striking applications attributed to the unprecedented diffraction-free, self-bending and self-healing properties. Metasurfaces with superior design freedom and small structure size open a fire-new avenue for generating efficient and broadband Airy beam. Nevertheless, most existing Airy beam generators can only respond to one polarization state of electromagnetic waves and produce the single Airy beam, which immensely limit the serviceability and utilization of the Airy beam generators. Herein, an inspiring strategy of multichannel Airy beam generator based on the multichannel amplitude and phase controlled metasurface is proposed to independently generate the Airy beams for linear polarized waves in 20–24 GHz and orthogonal circular polarized waves in 12–14 GHz and 15–17 GHz. Notably, an appealing paradigm of multichannel beam focusing can be realized by the integrated multichannel Airy beam generator, which possesses strong ability to circumvent the obstacle owing to the self-healing feature of the Airy beam. A proof-of-concept prototype is constructed to verify the feasibility of our methodology, and multitudinous simulations and experiments are in excellent accordance with our theoretical predictions. This novel design of multichannel Airy beam generator will have tremendous application potential in sensing, communication and other multifunctional metadevices.

Compact and high-performance polarization beam splitter based on triple-waveguide coupler

Polarization beam splitter (PBS) is a fundamental component of integrated photonics to manipulate wave polarization state, and most PBS devices were designed on the popular SOI. As an alternative, a PBS may be implemented on the basis of thin-film LiNbO3-on-insulator (LNOI), a promising platform for developing various compact or ultra-compact photonic active and passive devices. However, smaller modal birefringence of the LNOI waveguide makes it not easy to implement a PBS of high-performance. Here, we propose a compact, high-performance PBS on the basis of a triple-waveguide coupler consisted of two LNOI ridge waveguides and an amorphous silicon (α-Si) nanostrip assisted waveguide. By making use of the α-Si nanostrip, the PBS works in the case that the TM polarization mode meets the phase matching condition while the TE polarization mode does not. Numerical results show that the PBS is compact with a length of only 31 μm. The device can achieve an ultra-high polarization extinction ratio (>29.4 dB) and an ultra-low insertion loss (<0.066 dB) in the operating wavelength range of 1500–1600 nm for the TE polarization mode, and a polarization extinction ratio of > 20 dB and an insertion loss of < 0.16 dB over a ∼ 60 nm bandwidth from 1527 nm to 1587 nm for the TM polarization mode. Moreover, the device has a larger feature size that facilitates fabrication. Overall, this device has the advantages of compact size, higher polarization extinction ratio, lower insertion loss, and larger feature size, which is suitable for on-chip applications.

Multifunctional transmission polarization conversion metasurface based on dislocation-induced anisotropy at the terahertz frequency.

Manipulating the polarization state of terahertz waves is critical for terahertz communication systems. This study proposes a terahertz band polarization conversion metasurface based on dislocation-induced anisotropy. Numerical simulation results revealed that the polarization conversion of orthogonal linearly polarized light, orthogonal circularly polarized light, linearly polarized light to circularly polarized light, and circularly polarized light to linearly polarized light can be realized. Furthermore, the simulation revealed that multifunctional polarization conversion could be achieved by various structures of the bilayer metasurface. Thus, the proposed design can be generalized. The proposed metasurface exhibits considerable potential for applications in terahertz communications.

Polarization‐Multiplexing Bessel Vortex Beams for Polarization Detection of Continuous Terahertz Waves

AbstractDetermination of polarization states of electromagnetic waves plays a crucial role in photonic applications. However, it is very challenging to determine the polarization state of continuous terahertz (THz) waves. Here, a metasurface‐like metallic waveguide array (MWA) is proposed to address this by measuring both the phase difference and amplitude ratio of its two orthogonal components based on generation and interference of polarization‐multiplexing vortex beams. When a full‐polarized THz wave passes through the MWA, its two orthogonal components will be converted into +1st‐ and −1st‐order Bessel vortex beams, respectively. Their projection components in a proper polarized direction can interfere with each other, and their initial phase difference can be measured in real‐time owing to its linear relationship with the azimuth of the dark fringe in interference patterns. The two Bessel beams can be further collected separately using a linear polarizer to obtain their amplitude ratio. Therefore, the polarization state of incident waves can be determined with both the phase difference and amplitude ratio. The proposed method enables a convenient polarization determination of continuous THz waves and has great potential for developing polarization‐dependent investigations and applications in THz detection, communication, and sensing.