Pancharatnam-Berry Phase Principle Research Articles

Terahertz Wave Tunable Metalens Based on Phase Change Material Coded Metasurface

Based on phase change material and Pancharatnam-Berry phase principle, a tunable coded metasurface is designed to realize terahertz wave metalens. When the vanadium dioxide phase change material is reversibly converted from metal state to medium state, the lens can achieve the tunable function of reflection focusing and transmission focusing. The unique feature of our tunable metalens is that when the vanadium dioxide material is in the medium state, the silicon cuboid column plays the main role. We can rotate the silicon column structure to obtain the geometric phase coding unit. When the phase change material is in the metallic state, the vanadium dioxide metal rod structure plays the main role and rotates the element structure to obtain the reflective geometric phase coding element. In order to control the focus position of the transmission-reflection tunable metalens, we further designed non-central focusing and bifocal focusing metalens.

Free-space generation of three-dimensional tunable vector optical cages.

The generation of three-dimensional tunable vector optical cages through full polarization modulation requires complex polarization states. This paper takes the vector Airy optical cage as an example to generate a three-dimensional tunable high-quality optical cage based on the Pancharatnam-Berry phase principle. The proposed method in this paper possesses the capability of arbitrary modulation in various aspects, including the quantity of optical cages and their respective sizes as well as three-dimensional spatial positions. Moreover, the intensity of each optical cage can be modulated independently. This research will improve the capture efficiency of optical tweezers and promote further development in fields of efficient optical trapping, particle manipulation, high-resolution microscopic manipulation, and optical communication.

Broadband cross circularly polarized carpet invisibility cloak based on Pancharatnam–Berry phase reflective metasurface

We present a broadband circularly polarized reflective metasurface carpet cloak. The metasurface unit cell is composed of two crossed H-shaped metal patterns. When the incident wave is left-handed circularly polarization (LCP), the metasurface can achieve high-efficiency cross-polarization conversion in the wide frequency range. The cross-polarization reflection efficiency is higher than 94%. By using the proposed cross-polarized reflection unit cell structure, the phase gradient metasurfaces based on the Pancharatnam–Berry phase principle is proposed, and a broadband reflective metasurface invisibility cloak is constructed. The simulation results show that when the LCP light is incident vertically, the proposed carpet cloak can significantly suppress the scattering and reconstruct the wavefront in the broadband frequency range.

Ultra-Thin/Wide-Band Polarization Conversion Metasurface and Its Applications in Anomalous Reflection and RCS Reduction

In this paper, the design of an ultra-wideband polarizer based on a metasurface with high-performance is reported and demonstrated. The polarizer is composed of a dielectric substrate with double semicircular gap patches and a metal film. Multiple strong resonance points enable the design to convert the incident linearly polarized waves into cross-polarized waves in the 14.8–28.0 GHz range, with a fractional bandwidth of 61.7% and a corresponding polarization conversion rate (PCR) above 95%. Further simulated results show that the PCR remains above 87% in the 14.37–24.75 GHz range when the incident angle of the electromagnetic (EM) waves is between 0–30°, and the physical mechanism is explained by the surface current distribution. In addition, the gradient metasurface is designed according to the Pancharatnam–Berry phase principle to achieve anomalous reflection, and the 1-bit metasurface is coded to reduce the Radar Cross Section (RCS). The EM waves reach an anomalous reflection of −23° at 15 GHz normal incidence, and the RCS is reduced by 10 dB in the range of 15.3–28.0 GHz. These findings have potential application value in stealth and antenna design.

Broadband and high-efficiency ultrathin wavefront manipulation based on the Pancharatnam-Berry phase principle.

A broadband and high-efficiency metasurface is proposed based on the Pancharatnam-Berry (PB) principle. The PB phase principle is analyzed using the scattering matrix approach and proposed to achieve the abrupt phase with an equal amplitude of the transmission coefficient. The abrupt phase φ has a linear relationship with the rotation angle θ, namely, φ=±2θ. A 1-D gradient metasurface was designed, and the circular polarized waves in the frequency range 8.2-10 GHz were refracted anomalously when left-handed circular polarization or right-handed circular polarization waves were irradiated vertically on the metasurface and the refraction angle of the circular polarized waves, depending on the chirality of the incident wave. Finally, a 2-D parabolic metasurface that not only converts planar circular polarized waves into spherical circular polarized waves, but also converges the parallel wave into a focus point, was designed. The focal distance of the 2-D parabolic metasurface decreases as the frequency of the incident wave decreases, and the half-maximum at full width shows the opposite trend.

Generation of 2D Airy beams with switchable metasurfaces.

Airy beams exhibit intriguing characteristics, such as diffraction-free propagation, self-acceleration, and self-healing, which have aroused great research interest. However, the spatial light modulator that generates Airy beams has problems such as narrow operational bandwidth, high cost, poor phase discretization, and single realization function. In the visible region (λ∼532 nm), we proposed a switchable all-dielectric metasurface for generating transmissive and reflective two-dimensional (2D) Airy beams. The metasurface was mainly composed of titanium dioxide nanopillars and vanadium dioxide substrate. Based on the Pancharatnam-Berry phase principle, a high-efficient Airy beam can be generated by controlling the phase transition of vanadium dioxide and changing the polarization state of the incident light. The optimized optical intensity conversion efficiencies of the transmissive and reflective metasurfaces were as high as 97% and 70%, respectively. In the field of biomedical and applied physics, our designed switchable metasurface is expected to offer the possibility of creating compact optical and photonic platforms for efficient generation and dynamic modulation of optical beams and open up a novel path for the application of high-resolution optical imaging systems.

Omnidirectional rectangular beam steering for terahertz waves based on Pancharatnam-Berry phase encoding metasurfaces

In order to achieve efficient and flexible manipulation of transmitted beams, we propose an all-dielectric encoded particle metasurface using the Pancharatnam-Berry phase principle. After a precise analysis of the coded particle arrangement, we propose a back-shaped coded arrangement to achieve the scattering properties of a square beam. We introduce the Fourier convolution principle in digital signal processing into the coding metasurface, and perform the addition operation on the coding sequences to realize the flexible regulation of the square scattered beam. In order to achieve consistency between the numerical simulation and the theoretical analysis, we propose an error analysis theory for rectangular beams. The model is established by mathematical geometry method, the approximate error in numerical simulation is corrected, and a method to realize standard rectangular beam is theoretically given.

Broadband cross-circular polarization carpet cloaking based on a phase change material metasurface in the mid-infrared region

In view of the fact that most invisibility devices focus on linear polarization cloaking and that the characteristics of mid-infrared cloaking are rarely studied, we propose a cross-circularly polarized invisibility carpet cloaking device in the mid-infrared band. Based on the Pancharatnam-Berry phase principle, the unit cells with the cross-circular polarization gradient phase were carefully designed and constructed into a metasurface. In order to achieve tunable cross-circular polarization carpet cloaks, a phase change material is introduced into the design of the unit structure. When the phase change material is in amorphous and crystalline states, the proposed metasurface unit cells can achieve high-efficiency cross-polarization conversion, and reflection intensity can be tuned. According to the phase compensation principle of carpet cloaking, we construct a metasurface cloaking device with a phase gradient using the designed unit structure. From the near- and far-field distributions, the cross-circular polarization cloaking property is confirmed in the broadband wavelength range of 9.3–11.4 µm. The proposed cloaking device can effectively resist detection of cross-circular polarization.

Efficient Frequency Conversion with Geometric Phase Control in Optical Metasurfaces.

Metasurfaces have appeared as a versatile platform for miniaturized functional nonlinear optics due to their design freedom in tailoring wavefronts. The key factor that limits its application in functional devices is the low conversion efficiency. Recently, dielectric metasurfaces governed by either high‐quality factor modes (quasi‐bound states in the continuum) or Mie modes, enabling strong light–matter interaction, have become a prolific route to achieve high nonlinear efficiency. Here, an effective way of spatial nonlinear phase control by using the Pancharatnam–Berry phase principle with a high third harmonic conversion efficiency of 10−4 W−2 is demonstrated both numerically and experimentally. It is found that the magnetic Mie resonance appears to be the main contributor to the third harmonic response, while the contribution from the quasi‐bound states in the continuum is negligible. This is confirmed by a phenomenological model based on coupled anharmonic oscillators. Besides, the metasurface provides experimentally a high diffraction efficiency (80%–90%) in both polarization channels. A functional application of this approach is shown by experimentally reconstructing an encoded polarization‐multiplexed vortex beam array with different topological charges at the third harmonic frequency with high fidelity. The approach has the potential viability for future on‐chip nonlinear signal processing and wavefront control.

Simultaneous control of amplitude and phase via shifting isotropy to anisotropy for achieving holographic meta-mirror

Although the emerging isotropic and uniaxially anisotropic metasurfaces have been demonstrated to provide diverse ways for achieving the manipulation of electromagnetic waves, the simultaneous control of both amplitude and phase with designated spin states is still an academic challenge, especially in microwave domain. Here, a paradigm of shifting meta-atom symmetry is proposed to push the development of this difficult issue. A split-ring structure with four identical gaps is applied as a proof-of-principle. By properly arranging the relative positions of four gaps, the electromagnetic characteristics of the meta-atom can be shifted from isotropy to anisotropy. The amplitude of the cross-polarized component of reflective electromagnetic wave is smoothly changed from 0 to 1. Assisted by the Pancharatnam-Berry phase principle, the phase manipulation of anisotropic meta-atom is governed by the control of pivoting. The phase gradient metasurface with uniform amplitude modulation is used as preliminary verification. Subsequently, the complex-amplitude holographic meta-mirrors are designed to promote the proposed paradigm to the application level. Numerical simulations and experimental demonstrations are carried out to reconstruct the holographic images of “B”, “I”, and “T”. Encouragingly, the proposed paradigm may be extended in the applications of circular polarized meta-devices and on-chip systems.

Multi-focusing metalenses based on quadrangular frustum pyramid-shaped nanoantennas

This paper presents ultrathin multi-focusing metalenses that can produce several independent focusing spots, useful in imaging for light flow redistribution, even asymmetrical into many focal spots. The proposed design includes quadrangular frustum pyramids serving as individually tuned nanoantennas; their structure can be modified, facilitating wave-phase retardation tuning. Combining the propagation phase control with the Pancharatnam–Berry phase principle allows the screening of various cell structures. The specific design of the unit-cell structures makes the metalenses capable of single- and double-focusing at the required focal length. Thus, this metalens design might help in developing precision optics for micro-object manipulation. Data AvailabilityThe data that support the findings of this study are available from the corresponding author upon reasonable request.

Active circular dichroism coding meta-mirror for flexible beam-forming and dynamic amplitude control.

Equipped with the capability of simultaneous phase and amplitude modulation, the chiral metasurfaces have broken through the weak chiroptical responses of natural media, giving birth to a number of unprecedented phenomena. However, the performance of passive metasurface is inadequate to realize dynamic manipulation to fit the diverse and changeable operation requirements, which would damage their engineering applications. Here, a circular dichroism meta-mirror consisting of Archimedean spiral-based meta-atoms is proposed to achieve dynamic scattering modulation. Combining the strategy of loading active element, the chiroptical responses of a metasurface is smoothly controlled. By controlling bias voltages, continuous scattered reflection amplitude steering can be achieved for the designated spin state while the orthogonal spin state can hardly be influenced. With the assistance of Pancharatnam-Berry phase principle, the metasurface possesses the capability of tailoring waves in coded manner. We experimentally verify the proposed strategy by a 1-bit checkerboard meta-mirror for four-beam scattering pattern. Importantly, the proposed paradigm may find applications in spin-sensitive systems and adaptive camouflage.

Spin-to-orbital angular momentum conversion in symmetric dielectric nanorings

Recently, tremendous remarkable studies on spin–orbit interactions (SOIs) have attracted interest of scientists across the world in various fields. Among contemporary technologies of probing SOI, photonic metasurfaces have become a prevalent tool to guide and steer wavefront of light at the subwavelength scale. Nevertheless, the discretized nanoantennas of metasurfaces have been plagued for the shortcoming of bandwidth. In contrast to the discretized strategy, symmetric nanorings possessing a continuous phase gradient are exploited in this work. Benefiting from lossless dielectric material and nondispersive characteristic of the Pancharatnam–Berry phase principle, the designer nanorings are viable to realize high efficient spin-to-vortex conversion over a wide spectrum. The nanorings also accomplish a high purity of orbit angular momentum mode, which is of vital importance in many applications. Our findings would be beneficial to delve spin-controllable nanodevices and hold promise for applications of atomic manipulation and optical tweezers.

Ultrathin Single Layer Metasurfaces with Ultra-Wideband Operation for Both Transmission and Reflection.

Artificially engineered metasurfaces provide extraordinary wave control at the subwavelength scale. However, metasurfaces proposed so far suffer due to limited bandwidths. In this paper, extremely thin metasurfaces made of single metallic layer is experimentally presented for ultra-wideband operation from 9.3 to 32.5 GHz (with a fractional band of 112%), working at both transmission and reflection modes simultaneously. The phase control is achieved by azimuthally rotating the scatterer based on Pancharatnam-Berry phase principle. Nearly uniform efficiency (≈25%), approaching the theoretical limit of the infinitely thin metasurface, is achieved throughout the operation band. Finally, the proposed design is implemented for applications, e.g., the generation of electromagnetic waves carrying orbital angular momentums as well as anomalous reflections and refractions. The metasurfaces are characterized numerically and experimentally and the results are in good agreements.

Miniaturized Metalens Based Optical Tweezers on Liquid Crystal Droplets for Lab-on-a-Chip Optical Motors

Surfaces covered with layers of ultrathin nanoantenna structures—so called metasurfaces have recently been proven capable of completely controlling phase of light. Metalenses have emerged from the advance in the development of metasurfaces providing a new basis for recasting traditional lenses into thin, planar optical components capable of focusing light. The lens made of arrays of plasmonic gold nanorods were fabricated on a glass substrate by using electron beam lithography. A 1064 nm laser was used to create a high intensity circularly polarized light focal spot through metalens of focal length 800 µm, N.A. = 0.6 fabricated based on Pancharatnam-Berry phase principle. We demonstrated that optical rotation of birefringent nematic liquid crystal droplets trapped in the laser beam was possible through this metalens. The rotation of birefringent droplets convinced that the optical trap possesses strong enough angular momentum of light from radiation of each nanostructure acting like a local half waveplate and introducing an orientation-dependent phase to light. Here, we show the success in creating a miniaturized and robust metalens based optical tweezers system capable of rotating liquid crystals droplets to imitate an optical motor for future lab-on-a-chip applications.

High‐Efficiency Ultrathin Dual‐Wavelength Pancharatnam–Berry Metasurfaces with Complete Independent Phase Control

AbstractMetasurfaces are planar structures that can offer unprecedented freedoms to manipulate electromagnetic wavefronts at deep‐subwavelength scale. The wavelength‐dependent behavior of the metasurface could severely reduce the design freedom. Besides, realizing high‐efficiency metasurfaces with a simple design procedure and easy fabrication is of great interest. Here, a novel approach to design highly efficient meta‐atoms that can achieve full 2π phase coverage at two wavelengths independently in the transmission mode is proposed. More specifically, a bilayer meta‐atom is designed to operate at two wavelengths, the cross‐polarized transmission efficiencies of which reach more than 70% at both wavelengths. The 2π phase modulations at two wavelengths under the circularly polarized incidence can be achieved independently by varying the orientations of the two resonators constructing the meta‐atom based on Pancharatnam–Berry phase principle. As proof‐of‐concept demonstrations, three dual‐wavelength meta‐devices employing the proposed meta‐atom are numerically investigated and experimentally verified, including two metalenses (1D and 2D) with the same focusing length and a vortex beam generator carrying different orbital angular momentum modes at two operation wavelengths. Both the simulation and experimental results satisfy the design goals, which validate the proposed approach.

Broadband High-Efficiency Chiral Splitters and Holograms from Dielectric Nanoarc Metasurfaces.

Simultaneous broadband and high efficiency merits of designer metasurfaces are currently attracting widespread attention in the field of nanophotonics. However, contemporary metasurfaces rarely achieve both advantages simultaneously. For the category of transmissive metadevices, plasmonic or conventional dielectric metasurfaces are viable for either broadband operation with relatively low efficiency or high efficiency at only a selection of wavelengths. To overcome this limitation, dielectric nanoarcs are proposed as a means to accomplish two advantages. Continuous nanoarcs support different electromagnetic resonant modes at localized areas for generating phase retardation. Meanwhile, the geometric nature of nanoarc curvature endows the nanoarcs with full phase coverage of 0-2π due to the Pancharatnam-Berry phase principle. Experimentally incorporated with the chiral-detour phase principle, a few compelling functionalities are demonstrated, such as chiral beamsplitting, broadband holography, and helicity-selective holography. The continuous nanoarc metasurfaces prevail over plasmonic or dielectric discretized building block strategies and the findings lead to novel designs of spin-controllable metadevices.

High Efficiency Ultrathin Transmissive Metasurfaces

AbstractMetasurfaces offer unprecedented freedom to manipulate electromagnetic waves at deeply subwavelength scales. However, realizing a highly efficient metasurface, yet simple enough to conceptualize, design, and fabricate, is a challenging task. In this paper, a novel approach is proposed for designing meta‐atoms which can achieve full phase control in the range 0–2 π with high efficiency in the transmission mode. In particular, a bilayer meta‐atom is designed, exploiting nearly perfect polarization conversion of the two orthogonal transmissions, whose transmission efficiency reaches as high as 85%. The transmission phase control in the circular polarization basis is achieved with the axial rotation of the proposed meta‐atom based on Pancharatnam–Berry phase principle. These meta‐atoms are then wielded to construct metasurfaces for generating vortex beams carrying orbital angular momentum. The conversion efficiency as high as 75% and a transmission efficiency of 55% are achieved for the realized metasurfaces.

Wideband and low-profile transmitarray antenna using transmissive metasurface

Based on the Pancharatnam-Berry phase principle, a wideband low-profile transmissive metasurface was designed and applied to a transmitarray antenna (TA). While a full transmission phase range of 360° was achieved by rotating the proposed unit cell, the transmission coefficient was always close to 1 in the frequency range of 10.4–11.6 GHz. Hence, a TA comprised of 20 × 20 unit cells of size 180 mm × 180 mm was designed and fabricated. The simulated results agreed well with the experimental data, validating the excellent performance of the proposed metasurface structure. The measured peak gain of the TA was 21.64 dB at 11 GHz, resulting in an aperture efficiency of 34%. In addition, we attained a 12% 1-dB gain bandwidth (10.2–11.5 GHz) and an 18% 3-dB axial ratio bandwidth (10–12 GHz) for the TA. The proposed metasurface exhibits distinct performance benefits in terms of having wide bandwidth, low-profile, and high-efficiency, as well as represents a promising design option for a high-performance TA.

Broadband circularly polarized high-gain antenna design based on single-layer reflecting metasurface

According to the Pancharatnam-Berry phase principle, a single-layer reflecting element is proposed for steering the phase of the electromagnetic wave. The structure of the element is composed of metabolic cross wire and copper ground sheet, which are separated by an FR4 dielectric substrate with a thickness of 3 mm. When the incident wave is circularly polarized, different rotary angles of the element are used to achieve the co-polarization reflection with high efficiency in a broadband of 11-16 GHz. In the design of the focusing metasurface, the phase compensation for forming a constant aperture phase is provided by the individual reflected element with a different rotated angle. Remarkably, the size of the element is only 5 mm (0.230), and then it can be more accurate to control the phase of the array. The focusing metasurface is composed of 1515 elements with a focal length of 30 mm at 13.5 GHz. The designed sample is simulated in CST Microwave Studio. The results show that the incident circularly polarized plane wave is well transformed into a spherical wave in the band from 11 to 16 GHz, and the focal length is around 30 mm. For further application, a unidirectional Archimedean spiral antenna is located at the focal point of the metasurface. According to the reversibility principle of electromagnetic wave propagation, the spherical wave radiated by the feed antenna is converted into a plane wave by the reflecting metasurface, so that the antenna gain is remarkably enhanced. Through adjusting the distance between the feed antenna and the focusing metasurface, we find that 28 mm is the best distance. Finally, the feed antenna and the metasurface are fabricated, assembled and measured. Numerical and experimental results are in good agreement with each other, showing that the -1 dB gain bandwidth of the high-gain antenna is 12.5-16 GHz, and in this band the peak gains are all over 19 dBc and the axial ratio is better than 3 dB. In addition, the aperture efficiencies are more than 50% in the band from 12 to 15.5 GHz, especially the efficiency at 13 GHz reaches a highest value of 61%. The good performances indicate that the proposed high-gain antenna has a highly promising application in portable communication systems.