Artykuły w czasopismach: „Directional metasurfaces”

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Zhang, Ranran, Qiuling Zhao, Xia Wang, Kai Ming Lau, Tsz Kit Yung, Jensen Li i Wing Yim Tam. "Controlling asymmetric transmission phase in planar chiral metasurfaces". Nanophotonics 11, nr 3 (22.12.2021): 495–505. http://dx.doi.org/10.1515/nanoph-2021-0558.

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Abstract Metasurfaces with ultrathin artificial structures have attracted much attention because of their unprecedented capability in light manipulations. The recent development of metasurfaces with controllable responses opens up new opportunities in various applications. Moreover, metasurfaces composed of twisted chiral structures can generate asymmetric responses for opposite incidence, leading to more degrees of freedom in wave detections and controls. However, most past studies had focused on the amplitude responses, not to mention using bi-directional phase responses, in the characterization and light manipulation of chiral metasurfaces. Here, we report a birefringent interference approach to achieve a controllable asymmetric bi-directional transmission phase from planar chiral metasurface by tuning the orientation of the metasurface with respect to the optical axis of an add-on birefringent substrate. To demonstrate our approach, we fabricate planar Au sawtooth nanoarray metasurface and measure the asymmetric transmission phase of the metasurface placed on a birefringent sapphire crystal slab. The Au sawtooth metasurface-sapphire system exhibits large oscillatory behavior for the asymmetric transmission phase with the tuning parameter. We confirm our experimental results by Jones matrix calculations using data obtained from full-wave simulations for the metasurface. Our approach in the characterization and light manipulation of metasurfaces with controllable responses is simple and nondestructive, enabling new functionalities and potential applications in optical communication, imaging, and remote sensing.

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Aigner, Andreas, Stefan Maier i Haoran Ren. "Topological-Insulator-Based Gap-Surface Plasmon Metasurfaces". Photonics 8, nr 2 (4.02.2021): 40. http://dx.doi.org/10.3390/photonics8020040.

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Topological insulators (TIs) have unique highly conducting symmetry-protected surface states while the bulk is insulating, making them attractive for various applications in condensed matter physics. Recently, topological insulator materials have been tentatively applied for both near- and far-field wavefront manipulation of electromagnetic waves, yielding superior plasmonic properties in the ultraviolet (UV)-to-visible wavelength range. However, previous reports have only demonstrated inefficient wavefront control based on binary metasurfaces that were digitalized on a TI thin film or non-directional surface plasmon polariton (SPP) excitation. Here, we numerically demonstrated the plasmonic capabilities of the TI Bi2Te3 as a material for gap–surface plasmon (GSP) metasurfaces. By employing the principle of the geometric phase, a far-field beam-steering metasurface was designed for the visible spectrum, yielding a cross-polarization efficiency of 34% at 500 nm while suppressing the co-polarization to 0.08%. Furthermore, a birefringent GSP metasurface design was studied and found to be capable of directionally exciting SPPs depending on the incident polarization. Our work forms the basis for accurately controlling the far- and near-field responses of TI-based GSP metasurfaces in the visible spectral range.

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Li, Panyi, Jiwei Zhao, Caofei Luo, Zhicheng Pei, Hui Jin, Yitian Huang, Wei Zhou i Bin Zheng. "Self-Adaptive Intelligent Metasurface Cloak System with Integrated Sensing Units". Materials 17, nr 19 (2.10.2024): 4863. http://dx.doi.org/10.3390/ma17194863.

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Metasurfaces, which are ultrathin planar metamaterials arranged in certain global sequences, interact uniquely with the surrounding light field and exhibit unusual effects of light modulation. Many interesting applications have been discovered based on metasurfaces, particularly in invisibility cloaks. However, most invisibility cloaks are limited to working in specific directions. Achieving effectiveness in multiple directions requires the metasurface to be designed with both perception and modulation capabilities. Current multi-directional metasurface cloak systems are implemented with discrete components rather than an integrated sensing component. Here, we propose an intelligent metasurface cloak system that integrates sensing units, resulting in the cloaking effect with the help of a real-time direction sensor and an adaptive feedback control system. A reconfigurable reflective meta-atom based on phase modulation is presented. Sensing units replace parts of the meta-atoms in the designed tunable metasurface, integrating with an FPGA responsible for measuring the direction and frequency of the incident wave, constituting a closed-loop system together with the feedback parts. Experimental results demonstrate that the metasurface cloak system can recognize the different directions of the incoming wave, and can adaptively manipulate the reflected phase of EM waves to conceal objects without any human participation.

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Wu, Dong, Yang Meng i Chang Liu. "Design of Transparent Metasurfaces Based on Asymmetric Nanostructures for Directional and Selective Absorption". Materials 13, nr 17 (25.08.2020): 3751. http://dx.doi.org/10.3390/ma13173751.

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Maximizing the solar heat gain through windows in winter and minimizing the solar radiation entering the room in summer are of great significance for the energy saving of buildings. Here, we present a new idea for transparent metasurfaces, based on asymmetric metal/insulator/metal (MIM) nanostructures, which can be switched back and forth between absorbing and reflecting solar radiation by reversing the sample orientation. Owing to the fundamental mode of a low-quality-factor resonance, a selective near-infrared absorption is obtained with an absorption peak value of 90% upon front illumination. The average solar absorption (45%) is about 10% higher than that (35%) of reported transparent absorbers. The near-infrared light is also strongly and selectively reflected upon back illumination and a reflection peak value above 70% is observed. Meanwhile, the average visible transmission of the metasurface is above 60%, which is about 1.6 times that (36%) of previous transparent metasurface absorbers. In addition, Cu material can replace the noble metals in this work, which will greatly reduce the manufacturing cost. Owing to the attractive properties of directional and selective absorption, passive operation mode, and low cost of the materials, the metasurfaces have promising prospects in building energy saving or other solar applications where surface transparency is desirable.

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Zhang, Song, Yilin Wang, Pengcheng Huo i Ting Xu. "Plasmonic spin-multiplexing metasurface for controlling the generation and in-plane propagation of surface plasmon polaritons". Journal of Applied Physics 133, nr 13 (7.04.2023): 133101. http://dx.doi.org/10.1063/5.0144421.

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Surface plasmon polaritons (SPPs) are electromagnetic waves that travel along a metal–dielectric interface and are finding an ever-increasing number of applications in newly emerging nano-photonic and optoelectronic technologies. Different from the traditional approach to excite SPPs using prism or grating, metallic metasurfaces incorporating nano-slots with different orientations enable the photonic spin-dependent directional coupling of SPPs, which shows the unique spin tunability. However, the propagations of these generated SPPs are still correlative due to the conjugated phase profiles of metasurfaces for two incident orthogonal spin states. Here, we propose a plasmonic spin-multiplexing metasurface composed of nano-slots with different geometric dimensions and orientations to efficiently control the near-field generation and in-plane propagation of SPPs. By taking into account both the geometric phase and resonant phase of the nano-slots, the metasurface can generate two independent and fully decoupled SPP fields for a pair of orthogonal spin states. As proof-of-concept, we design a series of spin-multiplexing metasurfaces to numerically demonstrate different near-field optical functionalities, including spin-controlled plasmonic bi-focusing, self-accelerating beams, and vortices. We envision this approach may have potential applications in designing polarization-dependent tunable plasmonic nano-devices.

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AKRAM, Md Tausif, i Kyungjun SONG. "Advanced directional beam control via holographic acoustic metasurfaces for multibeam scanning". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 270, nr 11 (4.10.2024): 736–42. http://dx.doi.org/10.3397/in_2024_2642.

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Acoustic multi-beam leaky-wave antennas, designed with holographic metasurfaces, have great potential for beamforming by achieving directional beam control. We propose a planar holographic metasurface for beam steering using multi-beam acoustic radiation serving as high-gain acoustic leaky wave antennas. Based on the principle of holography, we designed a metasurface that adjusts its admittance in a sinusoidal pattern. This surface consists of periodic cylindrical holes with varying depth profiles. A monopole point source is positioned in the middle of the patterned surface, which generates surface waves on the modulated surface and emits acoustic leaky-wave radiation in the desired directions. The holographic admittance surface is designed to radiate an acoustic beam at a frequency of 20 kHz. Additionally, the concept was extended to generate multi-beam scanning for forward leaky-wave radiation in the holographic process. In this research, we employed 3D additive manufacturing to create acoustic holograms, manipulating surface admittance variation at a resolution smaller than the wavelength. The experimental measurements aligned well with both the theoretical and numerical analysis findings, affirming the effectiveness of the proposed technique. The methodology exhibits broad applicability across various domains, including sonar, ultrasound imaging, waveform manipulation, and acoustic communication.

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Cheng, Yang, Yongfeng Li, He Wang, Jiafu Wang, Zhe Qin i Shaobo Qu. "Circular dichroism assisted bi-directional absorbers". Journal of Physics D: Applied Physics 55, nr 9 (17.11.2021): 095101. http://dx.doi.org/10.1088/1361-6463/ac3301.

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Abstract Chirality, a geometric property that is of great importance in chemistry, biology, and medicine, has spurred many breakthroughs in the field of multi-dimensional metasurfaces that provide efficient ways of flexibly manipulating amplitude and phase of circular polarization (CP) waves. As one of the most important applications, chiral metamaterials can be used to implement novel absorbers. Herein, an ultra-thin wideband circular dichroic asymmetric metasurface was implemented via loading resistive film into chiral resonators. Opposite and reversible polarization conversion and circular dichroism (CD) were realized as being illuminated by CP waves from both sides meanwhile. Theoretical derivation and simulation verify that the polarization conversion and CD enhancement utilizing multi-layer CD metasurface. It is also found that the orientation angle of the meta-atom of each layer plays an important role in the CD enhancement, which paves a new way for CD enhancement. In addition, the coupling between the CD resonators was utilized to manipulate CD. On this basis, an ultra-thin polarization-insensitive absorber was achieved by employing a C4 2 × 2 CD resonator array, which was identical illuminating from front and back sides. Circular dichroic absorbers possess great potential in practical applications, ranging from stealth technology, antenna isolation, multi-functional microwave devices, chiral sensing, and catalysis.

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Santos, Gonzalo, Maria Losurdo, Fernando Moreno i Yael Gutiérrez. "Directional Scattering Switching from an All-Dielectric Phase Change Metasurface". Nanomaterials 13, nr 3 (26.01.2023): 496. http://dx.doi.org/10.3390/nano13030496.

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All-dielectric metasurfaces are a blooming field with a wide range of new applications spanning from enhanced imaging to structural color, holography, planar sensors, and directionality scattering. These devices are nanopatterned structures of sub-wavelength dimensions whose optical behavior (absorption, reflection, and transmission) is determined by the dielectric composition, dimensions, and environment. However, the functionality of these metasurfaces is fixed at the fabrication step by the geometry and optical properties of the dielectric materials, limiting their potential as active reconfigurable devices. Herein, a reconfigurable all-dielectric metasurface based on two high refractive index (HRI) materials like silicon (Si) and the phase-change chalcogenide antimony triselenide (Sb2Se3) for the control of scattered light is proposed. It consists of a 2D array of Si–Sb2Se3–Si sandwich disks embedded in a SiO2 matrix. The tunability of the device is provided through the amorphous-to-crystalline transition of Sb2Se3. We demonstrate that in the Sb2Se3 amorphous state, all the light can be transmitted, as it is verified using the zero-backward condition, while in the crystalline phase most of the light is reflected due to a resonance whose origin is the contribution of the electric (ED) and magnetic (MD) dipoles and the anapole (AP) of the nanodisks. By this configuration, a contrast in transmission (ΔT) of 0.81 at a wavelength of 980 nm by governing the phase of Sb2Se3 can be achieved.

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Park, Yeonsang, Hyochul Kim, Jeong-Yub Lee, Woong Ko, Kideock Bae i Kyung-Sang Cho. "Direction control of colloidal quantum dot emission using dielectric metasurfaces". Nanophotonics 9, nr 5 (2.06.2020): 1023–30. http://dx.doi.org/10.1515/nanoph-2020-0158.

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AbstractOwing to the recent developments of dielectric metasurfaces, their applications have been expanding from those pertaining to the thickness shrinkage of passive optical elements, such as lenses, polarizers, and quarter-wave plates, to applications pertaining to their integration with active optical devices, such as vertical-cavity surface-emitting lasers. Even though directional lasing and beam shaping of laser emission have been successfully demonstrated, the integration of metasurfaces with random light sources, such as light-emitting diodes, is limited because of function and efficiency issues attributed to the fact that metasurfaces are basically based on the resonance property of the nanostructure. To control the direction of emission from colloidal quantum dots, we present a dielectric metasurface deflector composed of two asymmetric TiO2 nanoposts. TiO2 deflector arrays were fabricated with a dry etching method that is adaptive to mass production and integrated with a colloidal quantum dot resonant cavity formed by sandwiching two distributed Bragg reflectors. To ensure the deflection ability of the fabricated sample, we measured the photoluminescence and far-field patterns of emission from the resonant cavity. From the obtained results, we demonstrated that the colloidal quantum dot emission transmitted through our deflector arrays was deflected by 18°, and the efficiency of deflection was 71% with respect to the emission from the resonant cavity. This integration of dielectric metasurfaces with a resonant cavity shows the possibility of expanding the application of visible metasurfaces in active devices and may help to develop next-generation active devices with novel functions.

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Liu, Zhaoyong, Kailin Ren, Gaoyu Dai i Jianhua Zhang. "A Review on Micro-LED Display Integrating Metasurface Structures". Micromachines 14, nr 7 (30.06.2023): 1354. http://dx.doi.org/10.3390/mi14071354.

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Micro-LED display technology has been considered a promising candidate for near-eye display applications owing to its superior performance, such as having high brightness, high resolution, and high contrast. However, the realization of polarized and high-efficiency light extraction from Micro-LED arrays is still a significant problem to be addressed. Recently, by exploiting the capability of metasurfaces in wavefront modulation, researchers have achieved many excellent results by integrating metasurface structures with Micro-LEDs, including improving the light extraction efficiency, controlling the emission angle to achieve directional emission, and obtaining polarized Micro-LEDs. In this paper, recent progressions on Micro-LEDs integrated with metasurface structures are reviewed in the above three aspects, and the similar applications of metasurface structures in organic LEDs, quantum dot LEDs, and perovskite LEDs are also summarized.

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Stojanoska, Katerina, i Chen Shen. "Non-Hermitian planar elastic metasurface for unidirectional focusing of flexural waves". Applied Physics Letters 120, nr 24 (13.06.2022): 241701. http://dx.doi.org/10.1063/5.0097177.

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Metasurfaces exhibiting spatially asymmetric inner structures have been shown to host unidirectional scattering effects, benefiting areas where directional control of waves is desired. In this work, we propose a non-Hermitian planar elastic metasurface to achieve unidirectional focusing of flexural waves. The unit cells are constructed by piezoelectric disks and metallic blocks that are asymmetrically loaded. A tunable material loss is then introduced by negative capacitance shunting. By suitably engineering the induced loss profile, a series of unit cells are designed, which can individually access the exceptional points manifested by unidirectional zero reflection. We then construct a planar metasurface by tuning the reflected phase to ensure constructive interference at one side of the metasurface. Unidirectional focusing of the incident waves is demonstrated, where the reflected wave energy is focused from one direction, and zero reflection is observed in the other direction. The proposed metasurface enriches the flexibility in asymmetric elastic wave manipulation as the loss and the reflected phase can be tailored independently in each unit cell.

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Guddala, S., F. Komissarenko, S. Kiriushechkina, A. Vakulenko, M. Li, V. M. Menon, A. Alù i A. B. Khanikaev. "Topological phonon-polariton funneling in midinfrared metasurfaces". Science 374, nr 6564 (8.10.2021): 225–27. http://dx.doi.org/10.1126/science.abj5488.

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Coupling light and heat Understanding of the topological features of bandgaps has provided a route for engineering optical structures that exhibit directional propagation of light and are robust to defects. Guddala et al . combined a silicon-based topological photonic crystal with an atomic monolayer of hexagonal boron nitride (hBN). The topological features of the photonic crystal are coupled to the lattice vibrations of the hBN through the formation of phonon-polaritons. Funneling of helical infrared phonons along arbitrary pathways and across sharp bends provides the possibility of realizing directional heat dissipation along topologically resilient heat sinks. —ISO

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Li, Ying, Qiang Xia, Jun Yang, Guangsheng Deng i Zhiping Yin. "High-Efficiency Multi-Channel Orbital Angular Momentum Multiplexing Enabled by the Angle-Dispersive Metasurface". Sensors 24, nr 1 (30.12.2023): 228. http://dx.doi.org/10.3390/s24010228.

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Orbital angular momentum (OAM) multiplexing of electromagnetic (EM) waves is of great significance for high-speed wireless communication and remote sensing. To achieve high-efficiency OAM multiplexing for multi-channel incident EM waves, this paper presents a novel angle-dispersive meta-atom structure, which can introduce the required anti-symmetric phase dispersion as well as high transmission efficiency for OAM multiplexing. These meta-atoms are then arranged delicately to form an angle-dispersive metasurface working at the X band, which enables three-channel OAM multiplexing by converting highly directional transverse-magnetic (TM) waves incident from 0 and ±45° to coaxial OAM beams with l = 0 and ±2 modes, respectively. The simulation and experimental results reveal that the proposed metasurface can convert a higher proportion of energy to the required OAM modes compared to the conventional OAM multiplexing metasurfaces, which can significantly improve the coaxial transmission efficiency of multi-channel OAM multiplexing.

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Agata, Kenichi, Shunsuke Murai i Katsuhisa Tanaka. "Stick-and-play metasurfaces for directional light outcoupling". Applied Physics Letters 118, nr 2 (11.01.2021): 021110. http://dx.doi.org/10.1063/5.0034115.

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Xu, Hanbo, i Zhiwei Men. "Utilizing Metasurfaces for Directional Control of LED Emission". Advances in Engineering Technology Research 11, nr 1 (18.07.2024): 606. http://dx.doi.org/10.56028/aetr.11.1.606.2024.

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This study provides a detailed modeling and analysis of four different three-dimensional GaN-based LED structures. The results reveal that incorporating DBRs effectively focuses light and enhances the light extraction efficiency (LEE). Additionally, the integration of Metasurface in the Micro-LED+DBRs+M structure allows for precise control of light emission direction and further radiation focusing. Furthermore, in the Micro-LED+DBRs+M2 structure with improved periodic nanocolumns, the light beam can be deflected simultaneously in multiple directions. These findings offer new possibilities for the advancement of LED technology.

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Jacobsen, Rasmus E., i Samel Arslanagic. "All-dielectric Cylindrical Metasurfaces for Enhanced Directional Scattering". Progress In Electromagnetics Research 183 (2025): 1–8. https://doi.org/10.2528/pier24121803.

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Yves, Simon, Yu-Gui Peng i Andrea Alù. "Topological Lifshitz transition in twisted hyperbolic acoustic metasurfaces". Applied Physics Letters 121, nr 12 (19.09.2022): 122201. http://dx.doi.org/10.1063/5.0107465.

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Acoustic metamaterials and metasurfaces have been explored in the past few years to realize a wide range of extreme responses for sound waves. As one remarkable phenomenon, extreme anisotropy and hyperbolic sound propagation are particularly challenging to realize compared to electromagnetic waves because of the scalar nature of airborne acoustics. In parallel, moiré superlattices and the rapidly expanding domain of twistronics have shown that large anisotropy combined with tailored geometrical rotations can enable tantalizing emerging phenomena, such as tailored phase transitions in metamaterials. Connecting these areas of research, here, we explore the realization of acoustic hyperbolic metasurfaces and their combination to drive topological phase transitions from hyperbolic to elliptic sound propagation. The transition point occurring at a specific rotation angle between two acoustic metasurfaces supports highly directional canalization of sound, opening exciting opportunities for twisted acoustics metasurfaces for robust surface wave guiding and steering.

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Zouhdi, Zakaria, Badreddine Ratni i Shah Nawaz Burokur. "Electronic Beam-Scanning Antenna Based on a Reconfigurable Phase-Modulated Metasurface". Sensors 22, nr 13 (1.07.2022): 4990. http://dx.doi.org/10.3390/s22134990.

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Metasurfaces (MSs) have enabled the emergence of new ideas and solutions in the design of antennas and for the control of electromagnetic waves. In this work, we propose to design a directional high-gain reconfigurable planar antenna based on a phase-modulated metasurface. Reconfigurability is achieved by integrating varactor diodes into the elementary meta-atoms composing the metasurface. As a proof of concept, a metasurface prototype that operates around 5 GHz is designed and fabricated to be tested in an antenna configuration. The metasurface is flexibly controlled by different bias voltages applied to the varactor diodes, thus allowing the user to control its phase characteristics. By assigning judiciously calculated phase profiles to the metasurface illuminated by a feeding primary source, different scenarios of far-field patterns can be considered. Different phase profiles are tested, allowing us to, firstly, achieve a highly directive boresight radiation and, secondly, to steer the main radiated beam towards an off-normal direction. The whole design process is verified by numerical simulations and is validated experimentally by far-field antenna measurements. The proposed metasurface enables the design of directive flat antennas with beam-scanning characteristics without complex feeding systems and power-consuming phase shifters, and thus provides potential interests for next generation antenna hardware.

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Ai, Huifang, Qianlong Kang, Wei Wang, Kai Guo i Zhongyi Guo. "Multi-Beam Steering for 6G Communications Based on Graphene Metasurfaces". Sensors 21, nr 14 (13.07.2021): 4784. http://dx.doi.org/10.3390/s21144784.

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As communication technology is entering the 6G era, a great demand for high-performance devices operating in the terahertz (THz) band has emerged. As an important part of 6G technology, indoor communication requires multi-beam steering and tracking to serve multi-users. In this paper, we have designed a graphene metasurface that can realize multi-beam steering for directional radiations. The designed metasurface consists of graphene ribbons, dielectric spacer, and metal substrate. By designing the graphene ribbons and controlling the applied voltage on them, we have obtained single-, double-, and triple-beam steering. In addition, we have also numerically calculated the far-field distributions of the steered multi-beam with a diffraction distance of 2 m. Our design has potential applications in future indoor directional 6G communications.

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Nye, Nicholas S., Ahmed El Halawany, Ahmed Bakry, M. A. N. Razvi, Ahmed Alshahrie, Mercedeh Khajavikhan i Demetrios N. Christodoulides. "Passive PT-Symmetric Metasurfaces With Directional Field Scattering Characteristics". IEEE Journal of Selected Topics in Quantum Electronics 22, nr 5 (wrzesień 2016): 107–14. http://dx.doi.org/10.1109/jstqe.2016.2537798.

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Babicheva, Viktoriia E. "Resonant Metasurfaces with Van Der Waals Hyperbolic Nanoantennas and Extreme Light Confinement". Nanomaterials 14, nr 18 (23.09.2024): 1539. http://dx.doi.org/10.3390/nano14181539.

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This work reports on a metasurface based on optical nanoantennas made of van der Waals material hexagonal boron nitride. The optical nanoantenna made of hyperbolic material was shown to support strong localized resonant modes stemming from the propagating high-k waves in the hyperbolic material. An analytical approach was used to determine the mode profile and type of cuboid nanoantenna resonances. An electric quadrupolar mode was demonstrated to be associated with a resonant magnetic response of the nanoantenna, which resembles the induction of resonant magnetic modes in high-refractive-index nanoantennas. The analytical model accurately predicts the modes of cuboid nanoantennas due to the strong boundary reflections of the high-k waves, a capability that does not extend to plasmonic or high-refractive-index nanoantennas, where the imperfect reflection and leakage of the mode from the cavity complicate the analysis. In the reported metasurface, excitations of the multipolar resonant modes are accompanied by directional scattering and a decrease in the metasurface reflectance to zero, which is manifested as the resonant Kerker effect. Van der Waals nanoantennas are envisioned to support localized resonances and can become an important functional element of metasurfaces and transdimensional photonic components. By designing efficient subwavelength scatterers with high-quality-factor resonances, this work demonstrates that this type of nanoantenna made of naturally occurring hyperbolic material is a viable substitute for plasmonic and all-dielectric nanoantennas in developing ultra-compact photonic components.

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Campione, Salvatore, Lorena I. Basilio, Larry K. Warne i Michael B. Sinclair. "Tailoring dielectric resonator geometries for directional scattering and Huygens’ metasurfaces". Optics Express 23, nr 3 (28.01.2015): 2293. http://dx.doi.org/10.1364/oe.23.002293.

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Algorri, José, Braulio García-Cámara, Alexander Cuadrado, José Sánchez-Pena i Ricardo Vergaz. "Selective Dielectric Metasurfaces Based on Directional Conditions of Silicon Nanopillars". Nanomaterials 7, nr 7 (7.07.2017): 177. http://dx.doi.org/10.3390/nano7070177.

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Li, Zhongyang, Edgar Palacios, Serkan Butun i Koray Aydin. "Ultrawide Angle, Directional Spectrum Splitting with Visible-Frequency Versatile Metasurfaces". Advanced Optical Materials 4, nr 6 (2.03.2016): 953–58. http://dx.doi.org/10.1002/adom.201600068.

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Yaxin, Zhang, Zeng Hongxin, Kou Wei, Wang Lan, Daniel M. Mittleman i Yang Ziqiang. "Terahertz smart dynamic and active functional electromagnetic metasurfaces and their applications". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, nr 2182 (14.09.2020): 20190609. http://dx.doi.org/10.1098/rsta.2019.0609.

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The demand for smart and multi-functional applications in the terahertz (THz) frequency band, such as for communication, imaging, spectroscopy, sensing and THz integrated circuits, motivates the development of novel active, controllable and informational devices for manipulating and controlling THz waves. Metasurfaces are planar artificial structures composed of thousands of unit cells or metallic structures, whose size is either comparable to or smaller than the wavelength of the illuminated wave, which can efficiently interact with the THz wave and exhibit additional degrees of freedom to modulate the THz wave. In the past decades, active metasurfaces have been developed by combining diode arrays, two-dimensional active materials, two-dimensional electron gases, phase transition material films and other such elements, which can overcome the limitations of conventional bulk materials and structures for applications in compact THz multi-functional antennas, diffractive devices, high-speed data transmission and high-resolution imaging. In this paper, we provide a brief overview of the development of dynamic and active functional electromagnetic metasurfaces and their applications in the THz band in recent years. Different kinds of active metasurfaces are cited and introduced. We believe that, in the future, active metasurfaces will be combined with digitalization and coding to yield more intelligent metasurfaces, which can be used to realize smart THz wave beam scanning, automatic target recognition imaging, self-adaptive directional high-speed data transmission network, biological intelligent detection and other such applications. This article is part of the theme issue ‘Advanced electromagnetic non-destructive evaluation and smart monitoring’.

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Moghaddaszadeh, Mohammadreza, Mohamed Mousa, Revant Adlakha, Mohamed Ali Attarzadeh, Amjad Aref i Mostafa Nouh. "Spatiotemporal modulations in acoustics: From nonreciprocity to mechanical computing". Journal of the Acoustical Society of America 154, nr 4_supplement (1.10.2023): A56. http://dx.doi.org/10.1121/10.0022780.

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Spatially graded materials have been a cornerstone of acoustic metamaterials for decades, enabling wave manipulation across different length scales. Likewise, structures with time-varying material properties have gained traction in wave filtering applications. Put together, systems exhibiting concurrent spatial and temporal modulations of one or more parameters (e.g., stiffness or phase) can unlock an array of new features ranging from nonreciprocal propagation to frequency-dependent wave beaming. In this talk, we will introduce the notion of dynamic phase gradients, i.e., a spatial phase shift between neighboring elements (of a metasurface) or transducers (of a phased array) which also varies in time. Through theory and experiments, we will demonstrate that the resultant systems are capable of (a) generating multiple scattered harmonics of a single input which simultaneously propagate in different directional lanes, each carrying a unique frequency footprint, and (b) exhibiting non-identical beaming patterns in transmission and reception by breaking time invariance. We will present an application of this concept in the development of a mechanical neural network via reconfigurable elastic metasurfaces, designed to perform a computational task. Since the frequency channels of a spatiotemporally-modulated metasurface are independently tunable, they can be assigned distinct tasks, thus allowing parallel operations in mechanical computing systems.

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Kan, Yinhui, Fei Ding, Changying Zhao i Sergey I. Bozhevolnyi. "Directional off-Normal Photon Streaming from Hybrid Plasmon-Emitter Coupled Metasurfaces". ACS Photonics 7, nr 5 (15.04.2020): 1111–16. http://dx.doi.org/10.1021/acsphotonics.0c00196.

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Campione, Salvatore, Lorena I. Basilio, Larry K. Warne i Michael B. Sinclair. "Tailoring dielectric resonator geometries for directional scattering and Huygens’ metasurfaces: erratum". Optics Express 25, nr 7 (24.03.2017): 7730. http://dx.doi.org/10.1364/oe.25.007730.

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Proctor, Matthew, Xiaofei Xiao, Richard V. Craster, Stefan A. Maier, Vincenzo Giannini i Paloma Arroyo Huidobro. "Near- and Far-Field Excitation of Topological Plasmonic Metasurfaces". Photonics 7, nr 4 (24.09.2020): 81. http://dx.doi.org/10.3390/photonics7040081.

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The breathing honeycomb lattice hosts a topologically non-trivial bulk phase due to the crystalline-symmetry of the system. Pseudospin-dependent edge states, which emerge at the interface between trivial and non-trivial regions, can be used for the directional propagation of energy. Using the plasmonic metasurface as an example system, we probe these states in the near- and far-field using a semi-analytical model. We provide the conditions under which directionality was observed and show that it is source position dependent. By probing with circularly-polarised magnetic dipoles out of the plane, we first characterise modes along the interface in terms of the enhancement of source emissions due to the metasurface. We then excite from the far-field with non-zero orbital angular momentum beams. The position-dependent directionality holds true for all classical wave systems with a breathing honeycomb lattice. Our results show that a metasurface in combination with a chiral two-dimensional material, could be used to guide light effectively on the nanoscale.

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30

Fang, Wei, i Yaping Yang. "Directional dipole radiations and long-range quantum entanglement mediated by hyperbolic metasurfaces". Optics Express 28, nr 22 (19.10.2020): 32955. http://dx.doi.org/10.1364/oe.401628.

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Ferry, Vivian. "(Invited, Digital Presentation) Circularly Polarized Photoluminescence from Nanostructured Arrays of Light Emitters". ECS Meeting Abstracts MA2022-01, nr 20 (7.07.2022): 1085. http://dx.doi.org/10.1149/ma2022-01201085mtgabs.

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Metasurfaces offer compact routes to spatial and polarization control of luminescence from nearby emitters. The most common integration strategy is to coat a patterned metamaterial or metasurface with a film of light emitting material. For example, structures such as arrays of Au nanorods coated with achiral light emitters exhibit circularly polarized photoluminescence at specific outcoupled angles. However, the degree of circular polarization in these systems is limited to relatively low values, and does not coincide with the angles with high photoluminescence intensity. This talk will discuss an alternative strategy, where the light emitters are patterned instead. We show that this structure offers several advantages: rather than averaging over the contributions of emitters in many different locations, this system exhibits highly directional photoluminescence with high degrees of circular polarization. Most importantly, the photoluminescence intensity is high at the same angles where the degree of circular polarization is high. These patterned light-emitting nanostructures are formed using direct-write electron beam lithography on semiconductor nanocrystals. This versatile method is capable of forming structures with aspect ratios greater than 2 and feature sizes as small as 30 nm, photoluminescence is retained after patterning, and the system is robust to multiple patterning steps.

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Gutiérrez, Yael, Dolores Ortiz, José Saiz, Francisco González, Pablo Albella i Fernando Moreno. "The Quest for Low Loss High Refractive Index Dielectric Materials for UV Photonic Applications". Applied Sciences 8, nr 11 (25.10.2018): 2065. http://dx.doi.org/10.3390/app8112065.

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Nanostructured High Refractive Index (HRI) dielectric materials, when acting as nanoantennas or metasurfaces in the near-infrared (NIR) and visible (VIS) spectral ranges, can interact with light and show interesting scattering directionality properties. Also, HRI dielectric materials with low absorption in these spectral ranges show very low heat radiation when illuminated. Up to now, most of the studies of these kind of materials have been explored in the VIS-NIR. However, to the best of our knowledge, these properties have not been extended to the ultraviolet (UV), where their application in fields like photocatalysis, biosensing, surface-enhanced spectroscopies or light guiding and trapping can be of extraordinary relevance. Here, we present a detailed numerical study of the directional scattering properties, near-field enhancement and heat generation of several materials that can be good candidates for those applications in the UV. These materials include aluminum phosphide, aluminum arsenide, aluminum nitride, diamond, cerium dioxide and titanium dioxide. In this study, we compare their performance when forming either isolated nanoparticles or dimers to build either nanoantennas or unit cells for more complex metasurfaces.

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JIANG, Wei, Zhihong WANG, Yisong HU, Jiansheng XU i Fa LUO. "Directed infrared emissions of two designed metasurfaces with ceramic arrays". Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 42, nr 5 (październik 2024): 891–94. https://doi.org/10.1051/jnwpu/20244250891.

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Two metasurfaces of ceramic arrays (A and B) were designed and the 11 μm infrared emission behaviors of them were studied. Both metasurfaces show obvious directed IR emissions. For array A, the radius of inner cylinder R1 and thickness t1 of the ceramics dominate the directional behavior of the IR emissions. The optimized structural parameters are R1=1.0 μm and t1≥1.2 μm with an effective IR emission angle θ in 0°~50 ° and emissivity ε≥0.7 achieved. For array B with Rc=1.05 μm, R1=0.1 μm, t1=0.85 μm, the IR emission is mainly constrained in θ>10°, and an obvious ϕ dependence is observed as θ>40°. The IR emission is higher at ϕ=45° or 135°(±45°) as θ>10° with ε=0.4 at θ=65°. The IR emission is affected by the thickness t1 obviously, with an effective thickness 0.3 μm≤t1≤1.7 μm at Rc=1.0 μm, R1=0.3 μm, and ϕ=0°. For array B with the optimized t1=1.2 μm (ϕ=0°), the IR emission is directed at θ~40° with the emissivity 0.7.

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34

Sakr, Enas, Deanna Dimonte i Peter Bermel. "Metasurfaces with Fano resonances for directionally selective thermal emission". MRS Advances 1, nr 49 (2016): 3307–16. http://dx.doi.org/10.1557/adv.2016.526.

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ABSTRACTThermal emission impacts a wide variety of applications, including thermophotovoltaics, photovoltaics, photon-enhanced thermionic emission, selective solar absorption, incandescent lighting, and spectroscopy. Ordinary structures generally emit a broad range of wavelengths, angles, and polarizations. However, highly selective thermal emission has potential to greatly improve performance in many of these applications. While prior work has explored a wide range of structures to provide some degree of control of one or more of these attributes, there is an ongoing challenge in combining readily-fabricated, simple structures made of appropriate (e.g., heat-resistant) materials with the desired functionality. Here, we will focus on using metasurfaces in conjunction with refractory materials as a platform for achieving selective control of emission. These structures are built from sub-wavelength elements that support localization of surface plasmon polaritons or electromagnetic resonant modes with appropriate attributes. Modeling is performed using rigorous coupled wave analysis (RCWA), plus Kirchhoff’s law of thermal radiation, which is further validated using finite-difference time domain (FDTD) simulations and coupled-mode analysis. Such structures can be considered arbitrarily directional sources that can be carefully patterned in lateral directions to yield a thermal lens with a designed focal length and/or concentration ratio; the benefit of this approach is that it can enhance the view factor between thermal emitters and receivers, without restricting the area ratio or separation distance. This design and modeling platform is then applied to exclude thermal radiation over a certain range of angles. In this work, we study the effect of controlling the angular width and direction on the view factor, and we explore angular dependence of these angular selective structures.

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35

Babicheva, V. E. "Directional scattering by the hyperbolic-medium antennas and silicon particles". MRS Advances 3, nr 33 (2018): 1913–17. http://dx.doi.org/10.1557/adv.2018.112.

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ABSTRACTOptical antennas made out of materials with hyperbolic dispersion is an alternative approach to realizing efficient subwavelength scatterers and may overcome limitations imposed by plasmonic and all-dielectric designs. Recently emerged natural hyperbolic material hexagonal boron nitride supports phonon-polariton excitations with low optical losses and high anisotropy. Here we study scattering properties of the hyperbolic-medium (HM) antennas, and in particular, we consider a combination of two types of the particles - HM bars and silicon spheres - arranged in a periodic array. We analyze excitation of electric and magnetic resonances in the particles and effect of their overlap in the array. We theoretically demonstrate that decrease of reflectance from the array can be achieved with appropriate particle dimensions where electric and magnetic resonances of different particle types overlap, and the resonance oscillations are in phase. In this case, generalized Kerker condition is satisfied, and particle dimers in the array efficiently scatter light in the forward direction. The effect can be used in designing metasurfaces based on hexagonal boron nitride scatterers with an application in mid-infrared photonics.

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Krasnok, Alexander, i Andrea Alù. "Valley-Selective Response of Nanostructures Coupled to 2D Transition-Metal Dichalcogenides". Applied Sciences 8, nr 7 (17.07.2018): 1157. http://dx.doi.org/10.3390/app8071157.

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Monolayer (1L) transition-metal dichalcogenides (TMDCs) are attractive materials for several optoelectronic applications because of their strong excitonic resonances and valley-selective response. Valley excitons in 1L-TMDCs are formed at opposite points of the Brillouin zone boundary, giving rise to a valley degree of freedom that can be treated as a pseudospin, and may be used as a platform for information transport and processing. However, short valley depolarization times and relatively short exciton lifetimes at room temperature prevent using valley pseudospins in on-chip integrated valley devices. Recently, it was demonstrated how coupling these materials to optical nanoantennas and metasurfaces can overcome this obstacle. Here, we review the state-of-the-art advances in valley-selective directional emission and exciton sorting in 1L-TMDC mediated by nanostructures and nanoantennas. We briefly discuss the optical properties of 1L-TMDCs paying special attention to their photoluminescence/absorption spectra, dynamics of valley depolarization, and the valley Hall effect. Then, we review recent works on nanostructures for valley-selective directional emission from 1L-TMDCs.

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37

Kang, Evan S. H., Shangzhi Chen, Samim Sardar, Daniel Tordera, Nerijus Armakavicius, Vanya Darakchieva, Timur Shegai i Magnus P. Jonsson. "Strong Plasmon–Exciton Coupling with Directional Absorption Features in Optically Thin Hybrid Nanohole Metasurfaces". ACS Photonics 5, nr 10 (11.09.2018): 4046–55. http://dx.doi.org/10.1021/acsphotonics.8b00679.

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Ju, Zezhao, Ming Deng, Jian Wang i Lin Chen. "Reconfigurable multifrequency and wide-angle directional beaming of light from a subwavelength metal slit with graphene metasurfaces". Optics Letters 45, nr 10 (15.05.2020): 2882. http://dx.doi.org/10.1364/ol.393812.

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Zouros, Grigorios P., Georgios D. Kolezas, Evangelos Almpanis, Konstantinos Baskourelos, Tomasz P. Stefański i Kosmas L. Tsakmakidis. "Magnetic switching of Kerker scattering in spherical microresonators". Nanophotonics 9, nr 12 (10.07.2020): 4033–41. http://dx.doi.org/10.1515/nanoph-2020-0223.

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AbstractMagneto-optical materials have become a key tool in functional nanophotonics, mainly due to their ability to offer active tuning between two different operational states in subwavelength structures. In the long-wavelength limit, such states may be considered as the directional forward- and back-scattering operations, due to the interplay between magnetic and electric dipolar modes, which act as equivalent Huygens sources. In this work, on the basis of full-wave electrodynamic calculations based on a rigorous volume integral equation (VIE) method, we demonstrate the feasibility of obtaining magnetically-tunable directionality inversion in spherical microresonators (THz antennas) coated by magneto-optical materials. In particular, our analysis reveals that when a high-index dielectric is coated with a magneto-optical material, we can switch the back-scattering of the whole particle to forward-scattering simply by turning off/on an external magnetic field bias. The validity of our calculations is confirmed by reproducing the above two-state operation, predicted by the VIE, with full-wave finite-element commercial software. Our results are of interest for the design of state-of-the-art active metasurfaces and metalenses, as well as for functional nanophotonic structures, and scattering and nanoantennas engineering.

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40

Schiattarella, Chiara, Leonardo Viti, Lucia Sichert, Valentino Pistore, Zhengtianye Wang, Stephanie Law, Oleg Mitrofanov i Miriam S. Vitiello. "Probing Dirac plasmon polaritons in bismuth selenide coupled nano-antennas by terahertz near-field microscopy". EPJ Web of Conferences 309 (2024): 05011. http://dx.doi.org/10.1051/epjconf/202430905011.

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The study of Dirac plasmon polaritons (DPPs) in two-dimensional materials has raised considerable interest in the last years for the development of tunable optical devices, plasmonic sensors, ultrafast absorbers, modulators, and switches. In particular, topological insulators (TIs) represent an ideal material platform by virtue of the plasmon polaritons sustained by the Dirac carriers in their surface states. However, tracking DPP propagation at terahertz (THz) frequencies, with wavelength much smaller than that of the free-space photons, represents a challenging task. Herein, we trace the propagation of DPPs in TI-based coupled antennas. We show how Bi2Se3 rectangular nano-antennas effectively confine DPPs propagation to one dimension, enhancing their visibility despite intrinsic attenuation. Furthermore, plasmon dispersion and loss properties of coupled antenna resonators, patterned at varying lengths and distances are experimentally determined using holographic near-field nano-imaging at different THz frequencies. Our study evidences modifications on the DPP wavelength along the single nano-antenna ascribable to the cross-talk between neighbouring elements. The results provide insights into DPPs characteristics, paving the way for the design of novel topological devices and metasurfaces by leveraging their directional propagation capabilities.

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Rikers, Marijn, Ayesheh Bashiri, Ángela Barreda, Michael Steinert, Duk-Yong Choi, Thomas Pertsch i Isabelle Staude. "Deterministic Fabrication of Fluorescent Nanostructures Featuring Distinct Optical Transitions". Nanomaterials 15, nr 3 (29.01.2025): 219. https://doi.org/10.3390/nano15030219.

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The precise and deterministic integration of fluorescent emitters with photonic nanostructures is an important challenge in nanophotonics and key to the realization of hybrid photonic systems, supporting effects such as emission enhancement, directional emission, and strong coupling. Such integration typically requires the definition or immobilization of the emitters at defined positions with nanoscale precision. While various methods were already developed for creating localized emitters, in this work we present a new method for the deterministic fabrication of fluorescent nanostructures featuring well-defined optical transitions; it works with a minimal amount of steps and is scalable. Specifically, electron-beam lithography is used to directly pattern a mixture of the negative-tone electron-beam resist with the europium complex Eu(TTA)3, which exhibits both electric and magnetic dipolar transitions. Crucially, the lithography process enables precise control over the shape and position of the resulting fluorescent structures with a feature size of approx. 100nm. We demonstrate that the Eu(TTA)3 remains fluorescent after exposure, confirming that the electron beam does not alter the structure the optical transitions. This work supports the experimental study of local density of optical states in nanophotonics. It also expands the knowledge base of fluorescent polymer materials, which can have applications in polymer-based photonic devices. Altogether, the presented fabrication method opens the door for the realization of hybrid nanophotonic systems incorporating fluorescent emitters for light-emitting dielectric metasurfaces.

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42

Chen, Ke, i Yijun Feng. "A review of recent progress on directional metasurfaces: concept, design, and application". Journal of Physics D: Applied Physics, 4.07.2022. http://dx.doi.org/10.1088/1361-6463/ac7e04.

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Abstract Metasurfaces have provided a new paradigm to control electromagnetic waves by manipulating the spatially varying distribution of subwavelength artificial structures across the interface. Directional metasurfaces, a kind of metasurface with direction-dependent properties, possess different wave functionalities upon the incidence wave coming from opposite directions. The diversified wave-manipulation capabilities of directional metasurfaces show advantages of compactness, flatness, scalability, direction dependence, etc., exhibiting promising potentials for a plethora of applications. Here, we present a review on the recent progress on directional metasurfaces, including the concept origin, the practical realization of meta-structures, the design method for direction-dependent wavefront tailoring, and the application aspects of directional metasurfaces. In the conclusion, we present possible further research directions in this field based on our own perspectives.

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43

Zhou, Yiwen, Teng Zhang, Guannan Wang, Ziqing Guo, Xiaofei Zang, Yiming Zhu, Fei Ding i Songlin Zhuang. "Directional Phase and Polarization Manipulation Using Janus Metasurfaces". Advanced Science, 9.08.2024. http://dx.doi.org/10.1002/advs.202406571.

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AbstractJanus metasurfaces, exemplifying two‐faced 2D metamaterials, have shown unprecedented capabilities in asymmetrically manipulating the wavefront of electromagnetic waves in both forward and backward propagating directions, enabling novel applications in asymmetric information processing, security, and signal multiplexing. However, current Janus metasurfaces only allow for directional phase manipulation, hindering their broader application potential. Here, the study proposes a versatile Janus metasurface platform that can directionally control the phase and polarization of terahertz waves by integrating functionalities of half‐wave plates, quarter‐wave plates, and metallic gratings within a cascaded metasurface structure. As a proof‐of‐principle, the study experimentally demonstrates Janus metasurfaces capable of independent and simultaneous control over phase and polarization, showcasing propagation direction‐encoded focusing and polarization conversion. Moreover, the directionally focused points are utilized with distinct polarization states for advanced applications in direction‐ and polarization‐sensitive detection and imaging. This unique strategy for simultaneous phase and polarization control with direction‐dependent versatility opens new avenues for designing ultra‐compact devices with significant implications in imaging, encryption, and data storage.

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Zhang, Heyi, Chunhui Zhu i Zhengyong Song. "Pancharatnam–Berry‐Phase‐Based Plasmonic Metasurfaces Enable Wavelength‐Selective Directional Focusing and Vortex". Advanced Photonics Research, 2.06.2024. http://dx.doi.org/10.1002/adpr.202400077.

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Multifoci focusing has always been a problem that researchers continue to pay attention to and urgently needs to be solved. Metasurfaces display unprecedented capabilities and flexibilities to solve this problem. In this work, Pancharatnam–Berry (PB)‐phase‐based plasmonic metasurfaces are presented to realize wavelength‐selective directional focusing on the same focal plane. Ultrathin meta‐atoms with the half‐wave plate effect have only three layers, and 360° phase modulation is obtained by axially rotating gold strip based on PB phase. Two metasurfaces are designed to verify our strategy. Above all, a wavelength‐selective directional focusing metasurface is presented to converge right‐handed circularly polarized wave with wavelengths of 187, 271, and 355 μm at different predetermined positions at 810 μm. Next, the second metasurface exhibits the function that three vortex beams carrying orbital angular momentums with different topological charges can be produced under the irradiation of incident wave at the aforementioned wavelengths. In this research, a solid step is paved toward practical applications of flat photonics.

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Ju, Fangfang, Xiao Zou, Shibei Xue i Sheng-You Qian. "Simultaneous manipulation of acoustic waves in the reflected and transmitted regions with the full space metasurface". Applied Physics Express, 10.07.2023. http://dx.doi.org/10.35848/1882-0786/ace60c.

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Abstract Acoustic metasurfaces offer great opportunities to realize exceptional functionalities and novel devices. However, most traditional metasurfaces manipulate acoustic waves either in the reflected region or in the transmitted region, leaving half of the space unexplored. Here, we propose a full space metasurface, which can simultaneously manipulate acoustic waves in the reflected and transmitted regions. As a proof of concept, three metadevices are designed and demonstrated: multi-directional scattering, asymmetric acoustic scattering and multi-focal focusing. Our proposal exhibits the full space utilization, and may offer opportunities in the capabilities of metasurfaces in sound manipulation.

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Li, Neuton, Jihua Zhang, Dragomir N. Neshev i Andrey A. Sukhorukov. "Inverse design of nonlinear metasurfaces for sum frequency generation". Nanophotonics, 5.06.2024. http://dx.doi.org/10.1515/nanoph-2024-0137.

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Abstract Sum frequency generation (SFG) has multiple applications, from optical sources to imaging, where efficient conversion requires either long interaction distances or large field concentrations in a quadratic nonlinear material. Metasurfaces provide an essential avenue to enhanced SFG due to resonance with extreme field enhancements with an integrated ultrathin platform. In this work, we formulate a general theoretical framework for multi-objective topology optimization of nanopatterned metasurfaces that facilitate high-efficiency SFG and simultaneously select the emitted direction and tailor the metasurface polarization response. Based on this framework, we present novel metasurface designs showcasing ultimate flexibility in transforming the outgoing nonlinearly generated light for applications spanning from imaging to polarimetry. For example, one of our metasurfaces produces highly polarized and directional SFG emission with an efficiency of over 0.2 cm2 GW−1 in a 10 nm signal operating bandwidth.

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Cao, Yue, Jiaqi Quan, Baoyin Sun, Xicheng Fang, Zhihong Hang, Lei Gao, Yangyang Fu i Yadong Xu. "Arbitrary multi-directional acoustic beam emission from a cylindrical metasurface with grafted topological charge". Applied Physics Letters 124, nr 13 (25.03.2024). http://dx.doi.org/10.1063/5.0197867.

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Directional sound beam emission from compact devices is highly desirable in many practical acoustic applications. Here, we present an approach for the efficient control of arbitrary multi-directional emission through a grafted metasurface that is designed by cutting and stitching two cylindrical phase-gradient metasurfaces carrying two opposite topological charges. The grafted metasurface provides a compact and robust platform for diverse multi-directional beam emission, whose beam number and azimuthal angles are precisely controlled by the topological charge. The underlying mechanism contributes to the wave interference of two opposite partial vortex waves. This scheme was verified by simulation and experimental results. Our work provides a design methodology for directional sound beam emission devices and may be useful for applications such as acoustic imaging, beam steering, and vortex detection.

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Cai, Xiaobing, Zhandong Huang, Chunguang Wang, Peipei Jia, Jun Yang i Liwen Zhang. "Acoustic Wave Manipulation by Phase Conjugate Metasurface". Journal of Vibration and Acoustics, 7.10.2022, 1–10. http://dx.doi.org/10.1115/1.4055917.

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Abstract Metasurfaces are advantageous in wavefront manipulation owing to their compact and flat nature. Particularly, ultrathin and completely smooth metasurfaces with giant phase delay and perfect impedance match are critically required for practical applications. Here we propose an ultrathin and holeless metasurface composed of simply a pair of membranes. This metasurface supports duo unity transmissions with completely conjugate phase shifts occur at two extremely close frequencies. This allows the metasurface to present giant phase delay and endow with high refractive index (n = 18) when the wave penetrates through. Such a property is employed to control the wavefront of acoustic waves to realize planar lens focusing, negative refraction, negative reflection and directional emission. The proposed design principle of acoustic metasurface provides promising avenues for acoustic wave manipulation and may enable extensive applications in beam steering, acoustic imaging, energy harvesting and surface waves.

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Naveed, Muhammad Ashar, Muhammad Afnan Ansari, Inki Kim, Trevon Badloe, Joohoon Kim, Dong Kyo Oh, Kashif Riaz i in. "Optical spin-symmetry breaking for high-efficiency directional helicity-multiplexed metaholograms". Microsystems & Nanoengineering 7, nr 1 (3.03.2021). http://dx.doi.org/10.1038/s41378-020-00226-x.

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AbstractHelicity-multiplexed metasurfaces based on symmetric spin–orbit interactions (SOIs) have practical limits because they cannot provide central-symmetric holographic imaging. Asymmetric SOIs can effectively address such limitations, with several exciting applications in various fields ranging from asymmetric data inscription in communications to dual side displays in smart mobile devices. Low-loss dielectric materials provide an excellent platform for realizing such exotic phenomena efficiently. In this paper, we demonstrate an asymmetric SOI-dependent transmission-type metasurface in the visible domain using hydrogenated amorphous silicon (a-Si:H) nanoresonators. The proposed design approach is equipped with an additional degree of freedom in designing bi-directional helicity-multiplexed metasurfaces by breaking the conventional limit imposed by the symmetric SOI in half employment of metasurfaces for one circular handedness. Two on-axis, distinct wavefronts are produced with high transmission efficiencies, demonstrating the concept of asymmetric wavefront generation in two antiparallel directions. Additionally, the CMOS compatibility of a-Si:H makes it a cost-effective alternative to gallium nitride (GaN) and titanium dioxide (TiO2) for visible light. The cost-effective fabrication and simplicity of the proposed design technique provide an excellent candidate for high-efficiency, multifunctional, and chip-integrated demonstration of various phenomena.

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Fan, Shi-Wang, Wen-Qi Wang, Jinxi Liu, Xu Liao, Jingzhe Zhang i Yue-Sheng Wang. "A single-layered elastic metasurface for switching wide-angle asymmetric transmission of flexural waves". APL Materials 11, nr 11 (1.11.2023). http://dx.doi.org/10.1063/5.0169662.

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A limitation of present elastic metasurfaces remains in their modest flexibility to meet convertible functions on demand. Here, a feasible single-layered lossless metasurface is theoretically proposed and experimentally demonstrated for adjusting the asymmetric transmission of flexural waves. The easily reconstructed unit is derived from multiple pillared resonators; then, the number of units per period can be changed depending on the desired integer parity. In addition, the asymmetric transmission is physically realized by the uneven diffraction of the ±1st orders in opposite fields of the designed metasurface. Requiring neither active modules nor passively multilayer or loss-induced strategies, our design using only a layer of lossless metasurface allows the elastic-wave behavior to switch between efficient symmetric and asymmetric transmissions. Furthermore, a high contrast ratio of transmitted energy is verified in experiments and simulations within a wide-angle range. The present work is connected with the pragmatic applications of metasurfaces in timely directional vibration control and compactly elastodynamic rectifications.

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