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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - High-Efficiency, All-Dielectric Metasurfaces Down to the Deep Ultraviolet
摘要： In recent years, researchers have demonstrated various types of high-performance, all-dielectric metasurfaces operating in the infrared (IR) and visible regimes, paving the way towards high-efficiency, multi-functional and compact photonic systems. However, there has been a conspicuous lack of research on metasurfaces designed for operation in the ultraviolet (UV) region, which is the spectral region hosting various important applications such as photolithography, spectroscopy, astronomy, medical therapy, and high-resolution imaging. Unfortunately, direct scaling of the operation frequencies of metasurfaces based on the IR and visible designs down to the UV is challenging, due to the prohibitively high optical loss of typically employed constituent materials (e.g., Si, TiO2, GaN). Here, we report on low-loss, all-dielectric metasurfaces operating at UV wavelengths down to the deep-ultraviolet range. The metasurface are based on Hafnium Oxide (HfO2), an amorphous dielectric material most commonly exploited as a high static dielectric constant (high-k) material in integrated circuit fabrication, that is characterized by a wide-bandgap (5.8 eV). We develop a unique Damascene fabrication process, involving both low-temperature atomic layer deposition (ALD) of HfO2 onto patterned resist and back etching with Argon ion milling, to achieve high-aspect-ratio HfO2 nanostructures with straight and smooth sidewall profiles (Fig. 1a). We demonstrate a variety of polarization-independent UV metasurface devices having distinct functionalities, namely diffraction-limited focusing lenses (metalenses), hologram projectors (metaholograms) and self-accelerating beam generators, operating at two near-UV wavelengths (364 and 325 nm) with efficiencies as high as 75%. As an example, the measured intensity distribution for a NA=0.6 metalens operating at 325 nm reveals lensing with a circularly symmetric focal spot (Fig. 1b), of first-dark-ring diameter close to the theoretical diffraction-limited value. Scaling down metasurface critical dimensions, we achieve metaholograms (Fig. 1c) operating with high efficiencies at a record-short, deep-UV wavelength of 266 nm. The captured image for such a metahologram operating at 266 nm (Fig. 1d) demonstrates holographic projection with a measured efficiency of 60%. Finally, we demonstrate 266-nm, spin-multiplexed metasholograms of greater degree of geometric complexities, with efficiencies up to 61%. Our work paves the way towards compact and multifunctional UV flat optical systems.
关键词： deep ultraviolet,UV wavelengths,high-efficiency,all-dielectric metasurfaces,photonic systems
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Femtosecond Laser Assisted Fabrication of Visible Wavelength All-Dielectric Nano-Membrane Metasurfaces
摘要： Metamaterials allow control and tailoring the optical response of natural materials to achieve unprecedented functionalities. These artificial electromagnetic media are engineered by structuring materials on a subwavelength scale. Metamaterials have conventionally been made out of noble plasmonic metals. Intrinsically, plasmonic metamaterials suffer from high energy dissipation due to ohmic losses at ultraviolet to visible spectral frequencies. Therefore, in recent years, all-dielectric resonant metamaterials typically made from high-index dielectrics have been explored widely as they can potentially alleviate such losses, while allowing similar functionalities. One of the factors constraining their widespread use is slow and high-cost production techniques required to achieve nanoscale structures across large areas in reasonable timescales. Here we demonstrate that laser direct writing can be used as a viable alternative to FIB and EBL for implementation of optical metasurfaces. Our proposed approach allows manufacturing all-dielectric metasurfaces with flexible geometry and high uniformity at mm2/min throughput rates. Laser direct writing relies on removing the material via irradiation with an intense light source producing a contaminant free nano-patterned surface. The patterning was performed using femtosecond laser pulses with a bandwidth centred at 515 nm (a second harmonic of the Yb:KGW laser). The laser beam was focused with a 0.6 NA objective lens producing a spot size of 430 nm. Optimized experimental conditions allowed us to fabricate arrays of holes directly in free-standing, 50 nm thick SiN membranes, which exhibit strong optical resonances in the visible spectral range. Each perforation is achieved with a single femtosecond laser pulse, providing for an area of 1×1 mm2 to be patterned within 10 minutes. Our writing technique allowed us to inscribe holes with sub-200 nm in diameter, which is well below the diffraction limit. The periods of arrays ranged from 300 to 1000 nm allowing us to achieve optical resonances in the visible with high resonance quality factors up to 46 (for a metasurface period of 520). Quality factor is defined here as Q = λR/Δλ, where λR is the reflection resonance wavelength and Δλ is the half-maximum linewidth). The asymmetry in the structure, which leads to polarization dependent resonance, stems from a linearly polarized laser beam resulting in asymmetric intensity distribution at the focal point. Although our proof of principle demonstration is limited to dielectric nanomembranes, this technique can be easily extended to fabrication of metasurfaces in semiconductors and metals due to the nonlinear character of femtosecond laser pulse interaction with materials. In conclusion, we have demonstrated feasibility and versatility of femtosecond laser processing for developing scalable optical metasurfaces.
关键词： metasurfaces,all-dielectric,optical resonances,femtosecond laser,metamaterials
更新于2025-09-12 10:27:22
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[IEEE 2018 International Applied Computational Electromagnetics Society Symposium - China (ACES) - Beijing, China (2018.7.29-2018.8.1)] 2018 International Applied Computational Electromagnetics Society Symposium - China (ACES) - Polarization-Dependent Terahertz Metasurfaces
摘要： In this paper, two kinds of polarization-dependent metasurfaces are proposed for wavefront manipulation. The results of the proposed polarization-dependent metasurfaces are illustrated while their operating principles are also briefly given.
关键词： metasurfaces,Terahertz,subwavelength structures
更新于2025-09-11 14:15:04
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Quantitatively Correlated Amplitude Holography Based on Photon Sieves
摘要： As an excellent holographic information carrier, metasurface holograms possess the advantages of subwavelength footprint, leading to large field of view and high resolution. Meanwhile, intelligent algorithms should be developed to fully exploit the flexible modulation properties provided by metasurfaces. Here, two amplitude holograms with quantitatively correlation are realized using the photon sieve as the amplitude modulation device. A new iterative algorithm is developed to obtain the amplitude profiles of the two holograms with correlation, which can make the two profiles mutually connect by simply adding/erasing dynamic pixels. Two photon sieves composed of nanoholes arrays are fabricated to demonstrate the feasibility of the scheme. This amplitude holography method can operate throughout the entire visible and near-infrared wavelength regions with polarization independence, and it is expected to achieve switchable metasurface holography with the development of materials science. Such scheme promises to be applied in compact data storage, dual pattern recognition, optical encryption, and so on.
关键词： photon sieves,metasurfaces,holographic algorithms
更新于2025-09-11 14:15:04
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Time-modulated Conducting Oxide Metasurfaces for Adaptive Multiple Access Optical Communication
摘要： We demonstrate realization of a time-modulated metasurface in near-infrared frequency regime via integration of conducting oxide layers into plasmonic stripe nanoantennas arranged in a reflectarray configuration. The permittivity of conducting oxide layers is modulated in time through modulation of carrier concentration by applying radio-frequency biasing signals which leads to generation of higher-order frequency harmonics. We rigorously characterize the electro-optical frequency conversion performance of the metasurface. We then exploit the dispersionless angle-independent phase discontinuities on the wavefront of higher-order frequency harmonics to achieve dynamic multi-wavelength multi-beam scanning across S, C, and L telecommunication bands via pixelated control over the modulation phase delay. It is established that such time-modulated metasurfaces can be utilized as reflectarray antennas for active multicasting as well as wavelength and angle multiplexing, thus improving optical communication capacity by providing multiple access and integrating several communication channels into a single antenna platform. The role of modulation waveform in the spectral diversity of harmonics is also explored. Specifically, modulation waveform is optimized to realize unicast and broadcast links. Finally, active beam-scanning performance of the time-modulated conducting oxide metasurface is compared with that of its quasi-static counterpart verifying the enhanced bandwidth as well as suppressed side lobes in the time-modulated platform.
关键词： Metasurfaces,Time-Modulation,MIMO,Multiplexing,Multicasting,Transparent Conducting Oxides
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Computational Modelling of Metasurfaces for Strongly Divergent Beams
摘要： The content of the paper discusses the computational modelling of metasurfaces for strongly divergent beams, focusing on the design and application of metasurfaces with building blocks that can efficiently control light beams with high divergence. It highlights the potential of these metasurfaces in various applications, including optical tweezers, laser beam shaping, and imaging systems. The paper also explores the challenges and limitations in designing such metasurfaces, particularly in achieving high efficiency over a broad range of angles and wavelengths.
关键词： imaging systems,computational modelling,metasurfaces,optical tweezers,divergent beams,laser beam shaping
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Complex-Birefringent and Chiral Waveplates with Metasurfaces
摘要： Metasurfaces composed of arrays of nano-resonators are a powerful tool for manipulation of polarization of light. All-dielectric metasurfaces do not suffer absorption losses and are highly transparent in contrast to metallic structures, and combined with recent advances in their design and fabrication, have enabled efficient polarization manipulation and arbitrary phase shaping. A new regime of complex-valued birefringence has been recently suggested, extending the notion of real-valued birefringence through the specially introduced polarization-sensitive loss or gain. This can enable fundamentally new possibilities for polarization control, such as amplifying the angle between polarization vectors to improve detection sensitivity. However, a practical realization of complex-valued birefringence concept was missing. In particular, the theoretical approach in Ref. [4] was based on a complicated metamaterial with loss and gain, which is challenging to fabricate and not suitable for quantum applications. Here, we report on a new conceptual approach for implementing arbitrary complex-valued birefringence with pairwise birefringent elements using high-index dielectric nanostructures. We formulate a practical design principle, which is optimal for achieving any desirable polarization transformation. While loss is inherently necessary for implementing complex birefringence, our all-dielectric metasurface design achieves the mathematically minimum required amount of loss through tailored diffraction without any material absorption.
关键词： metasurfaces,birefringence,polarization control,dielectric nanostructures
更新于2025-09-11 14:15:04
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[IEEE 2018 IEEE MTT-S International Microwave and RF Conference (IMaRC) - Kolkata, India (2018.11.28-2018.11.30)] 2018 IEEE MTT-S International Microwave and RF Conference (IMaRC) - A Graphene Based Metasurface with Wideband Absorption in the Lower Mid Infrared Region
摘要： An ultra-thin (~λ/34) graphene based metasurface exhibiting wide bandwidth in lower mid-infrared region has been discussed in this paper. The unit cell of the structure composes of graphene-based fractal geometry on the top surface depicted over amorphous silicon dioxide (SiO2) whose bottom side is completely graphene deposited. The geometrical dimensions of the deposited graphene pattern are chosen so that broadband absorption is achieved between 1.75 THz and 7.28 THz with more than 90% absorptivity. Two distinct absorption peaks have also been observed at 3 THz and 7 THz in the aforementioned broad absorption spectra. The designed prototype has been observed under different incident angles of the incoming electromagnetic wave for both TE and TM polarizations where bandwidth improved absorption has been observed upto 60o incident angles for both cases. The structure is also found to be polarization independent in nature.
关键词： polarization-insensitive,absorber,Metasurfaces,broadband,graphene
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Whispering-Gallery Resonators for Highly Integrated Plasmonic THz Circuits
摘要： Whispering-gallery resonators based on spoof plasmonic rings are presented. The resonators exhibit exceptionally high quality factors for THz metasurfaces (in excess of 240). As the resonator is coupled to two waveguides, it can serve as narrowband band-stop and band-pass filter in an integrated plasmonic circuit. The complicated mode structure shows frequency comb-like behaviour.
关键词： Whispering-gallery resonators,THz metasurfaces,integrated plasmonic circuit,high quality factors,spoof plasmonic rings
更新于2025-09-11 14:15:04
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Plasmonics || Introductory Chapter: Plasmonics
摘要： The optical interaction with nanostructures is studied by the field of plasmonics. Recently, the potential of subwavelength confinement and the enhancement of optical fields close to the appropriately designed nanoscale objects have opened a gateway to extensive investigations of plasmonic optical phenomena. Consequently, the outstanding field of plasmonics has spread over different disciplines, providing the wide avenues for the promising applications in materials science, biology, and engineering. Furthermore, the field of metamaterials has been enriched and enhanced by the plasmonic optics, for example, metasurfaces. The former concept is based on the collective electromagnetic behavior of many subwavelength inclusions and building blocks as “meta-atoms.” Doing so, novel tunable composite materials, i.e., near-zero material parameters, and extreme-value material parameters, characterized by unconventional bulk and surface properties, have been proposed and applied. Surface waves open a gateway to a wide spectrum of physical phenomena providing a fertile ground for a number of applications [1–3]. The discovery of metamaterials with tunable electric and magnetic features [4] has allowed for a rich phenomenon, i.e., expansion of the wide spectrum of structures capable of supporting surface waves. Surface plasmon polaritons (SPPs) are electromagnetic excitations occurring at the interface between a conductor and dielectric. These are evanescently confined in the perpendicular direction [5–8]. It is possible to imitate the properties of confined SPPs by geometrical-induced SPPs, named as spoof SPPs. The proposed phenomenon may take place at lower frequencies. It might be concluded that surface structure may open a gateway to spoof surface plasmons. The former serves as a perfect prototype for structured surfaces [9]. Thus, metasurfaces, a class of planar metamaterials possessing the outstanding functionality, i.e., capabilities to mold light flow, have recently attracted intensive attention. The main goal of the metasurfaces is to achieve the anticipated phase profile by designing subwavelength structures at the interface between two ordinary materials. Abilities to fully engineer the properties of the propagating waves are gained thanks to the rationally designed phase. It should be mentioned that anomalous reflection and refraction have been verified in the infrared range. Metasurface-based optical devices, such as vortex plates, waveplates, and ultra-thin focusing lenses have also been proposed for various types of incident light, i.e., linearly polarized light or vertex beams. Now is the time that the fundamental research in the field is giving rise to the first promising applications for industry. For centuries, the control of optical properties has been limited to altering material compositions, relying on light propagation through naturally occurring materials to impart phase shifts and tailor the desired wavefronts. The introduction of metamaterials allows control over optical wavefronts to deviate from the usual propagation methods and rely instead on its carefully engineered internal structure. This was first theorized 20 years ago by Pendry et al. [10], and since then, the development in the field of artificially designed materials has only accelerated. Metamaterials offer an extensive range of novel electromagnetic phenomena, which do not occur in natural materials, but whose existence is not restricted by physical laws. These artificially created “materials” are made up of a series of composite unit elements, which although are a few orders of magnitude larger than the molecular unit cells of regular materials. This allows the metamaterials to provide descriptions of its interactions with electromagnetic waves in terms of its effective “material” parameters. Metamaterials can, therefore, still be viewed as a homogenous material at their desired operational wavelengths, typically within the optical regime. With careful structuring of the elements within the metamaterial, unusual material properties such as a negative refractive index can be achieved. The refractive index η of a material is governed by its macroscopic electromagnetic permittivity e and permeability μ, where η=√eμ. The development of such negative index material could lead to novel applications especially within the optical regime, such as creating the perfect lens, which images beyond the diffraction limit, or an optical cloaking device. The initial realization of a negative refractive index metamaterial uses a pattern of metallic wires and split-ring resonators to form its unit cells, which have been experimentally demonstrated in the microwave regime and later at optical wavelengths as the elemental array is reduced into the nanoscale. Bulk metamaterials, however, are usually susceptible to high losses and strong dispersive effects due to the resonant responses of metallic structures used. Additionally, the complex structures required in a 3D metamaterial is challenging to build using the existing micro- and nanofabrication methods. Thus, recent studies have been focusing on the development of 2D metamaterials, or metasurfaces. These planar materials allow for the combined advantages of the ability to engineer electromagnetic responses with low losses associated with thin layer structures. The introduction of surfaces with subwavelength thicknesses results in minimal propagation phase; this shifts the focus from developing materials with negative permittivity and permeability to engineering surface structures to adjust surface reflection and transmissions. This is made possible by exploiting abrupt phase jumps and polarization changes from scattering effects, which can be realized and subsequently fine-tuned through designing spatially varying phase responses over the metasurface, through using either metallic or dielectric surface structures. In solid state physics, materials can be classified according to their electronic band structure. While metals have overlapping conduction and valence bands, which allows the free movement of electrons through the material, dielectric insulators have a large bandgap between the two. Both types of materials are still able to interact with incident electromagnetic fields, although through different physical methods and result in light scattering effects. Thus, both materials have, therefore, been employed in the realization of the vast potential of metasurfaces.
关键词： plasmonics,surface plasmon polaritons,spoof surface plasmons,metasurfaces,metamaterials,subwavelength confinement,optical fields
更新于2025-09-11 14:15:04