- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Nonlinear Diffraction in Asymmetric Dielectric Metasurfaces
摘要： Metasurfaces provide new and promising mechanisms to control and manipulate light at the nanoscale. While most metasurfaces are designed to operate in the linear regime, it was recently shown that such metasurfaces may also generate nonlinear signal, by manipulating the higher order susceptibility terms. As such, metasurfaces can generate additional harmonics, without the need for light propagation, as typically occur in nonlinear crystals. While such demonstrations typically rely on the nonlinear properties of metals, we hereby report the design, fabrication and experimental characterization of a resonant dielectric metasurface made of amorphous silicon to create and manipulate second harmonic light and control its diffraction patterns. As shown in the paper, the second harmonic generation of light follows selection rules which rely on the asymmetry of the meta-atom. Given the fact that silicon crystals are centrosymmetric, the generation of second harmonic signal in amorphous silicon is intriguing. In fact, second harmonic signal is generated mostly from the surface of the meta atom. It is the use of nanostructures that increases the surface to volume ratio and enables second harmonic generation. Additionally, the meta atom is designed to exploit its spectral resonances in the principal and the second harmonic frequencies for providing electromagnetic field enhancement which assist in boosting up the generation of second harmonic signal.
关键词： Metasurfaces,Nonlinear optics,Dielectric metasurfaces,Phase gradient metasurfaces
更新于2025-09-23 15:23:52
-
Manipulation of Magnetic Dipole Emission from Eu <sup>3+</sup> with Mie-Resonant Dielectric Metasurfaces
摘要： Mie-resonant high-index dielectric nanoparticles and metasurfaces have been suggested as a viable platform for enhancing both electric and magnetic dipole transitions of fluorescent emitters. While the enhancement of the electric dipole transitions by such dielectric nanoparticles has been demonstrated experimentally, the case of magnetic-dipole transitions remains largely unexplored. Here, we study the enhancement of spontaneous emission of Eu3+ ions, featuring both electric and magnetic-dominated dipole transitions, by dielectric metasurfaces composed of Mie-resonant silicon nanocylinders. By coating the metasurfaces with a layer of an Eu3+ doped polymer, we observe an enhancement of the Eu3+ emission associated with the electric (at 610 nm) and magnetic-dominated (at 590 nm) dipole transitions. The enhancement factor depends systematically on the spectral proximity of the atomic transitions to the Mie resonances as well as their multipolar order, which is controlled by the nanocylinder radius. Importantly, the branching ratio of emission via the electric or magnetic transition channel can be modified by carefully designing the metasurface, where the magnetic dipole transition is enhanced more than the electric transition for cylinders with radii of about 130 nm. We confirm our observations by numerical simulations based on the reciprocity principle. Our results open new opportunities for bright nanoscale light sources based on magnetic transitions.
关键词： Purcell enhancement,Dielectric metasurfaces,Mie resonances,Magnetic dipole emission
更新于2025-09-23 15:23:52
-
Generation of polarization-sensitive modulated optical vortices with all-dielectric metasurfaces
摘要： Optical vortices (OVs) created from helical modes of light have extensive applications in optical manipulation, imaging and optical communications. Moreover, modulated optical vortices (MOVs) with modified wavefronts could provide new opportunities for fractionating particles and actuating microelectromechanical systems. Traditional devices for generating MOVs include spatial light modulators, spiral phase plates etc. However, such bulky devices are difficult to be applied to high-level integrated optical systems. Besides, other MOV generators are typically static and polarization-insensitive. Here, we proposed an all-dielectric metasurface to generate polarization-sensitive MOVs. The intensity patterns of the OVs can be modulated by adding a tangential modulation factor in the phase profile. Independent manipulation of two orthogonal polarizations was adopted via tailoring the geometric parameters of silicon (Si) pillars. We experimentally demonstrated that the metasurface could generate a doughnut and an actinomorphic vortex beams for different polarization inputs. In addition, the intensity pattern of the MOVs can be dynamically tuned by adjusting the polarization angle. This work can benefit optical manipulation and can be further extended to visible and near-infrared bands.
关键词： propagation phase,all-dielectric metasurfaces,mid-infrared,polarizations,modulated optical vortices
更新于2025-09-23 15:22:29
-
[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) - Experimental Demonstration of Edge Detection by Dielectric Metasurfaces
摘要： Metasurfaces offer unique opportunities for optical signal processing and the design of neuromorphic optical networks for image-processing. Among different image-processing operations, edge detection is one of the essential algorithms with practical applications in microscopy or autonomous systems. The edge detection removes the plain parts of an image, to keep only the edges where the intensity changes abruptly. As such, the processed image contains just silhouettes of the object, Fig. 1a. In microscopy, edge detection helps to identify the structure of cells, while in autonomous systems, such as cars or drones, the optical edge detection can reduce the volume of data to compute on board of the vehicle, making it work faster and safer. To date, there have been several theoretical studies on metasurfaces for edge detection, however, an experimental demonstration is missing. Here we demonstrate experimentally edge detection by using the spatial dispersion of dielectric metasurfaces in the spectral vicinity of the Mie-type resonances (Fig. 1b). We show that a single ultra-thin (hundreds of nanometers) silicon metasurface can result in edge detection without any additional optical components and post computational processing.
关键词： Mie-type resonances,optical signal processing,dielectric metasurfaces,edge detection
更新于2025-09-23 15:19:57
-
Deflecting transmissive light beams with metasurfaces based on crystalline silicon high-contrast grating
摘要： Dielectric metasurfaces have emerged and expanded rapidly for their success in realizing high-efficiency wavefront control in the optical and infrared ranges. However, devices have either been demonstrated at near-infrared regime using high-index semiconductors such as silicon, or they use lower index dielectric materials such as TiO2 or Si3N4 and operate in the visible wavelength regime to avoid the optical loss of dielectric materials. It seems that dielectric metasurfaces could not achieve either high index or high device efficiency, simultaneously. Here, we provide a crystalline silicon metasurface scheme to efficiently modulate transmitted light beams at the wavelengths as short as to 532 nm. The unit cell of the metasurfaces consists of high-contrast grating (HCG), which provides full 2π phase control for circular polarized incident beams in thin film. The demonstration of HCG deflector shows that the device enables high deflecting efficiency as high as those made by transparent materials. Our results provide a paradigm to functionalize transmitted light beams based on crystalline silicon in the visible wavelength regime.
关键词： dielectric metasurfaces,high-contrast grating,diffractive optics,crystalline silicon
更新于2025-09-23 15:19:57
-
Bound States in the Continuum in Magnetophotonic Metasurfaces
摘要： We analyze the enhancement mechanisms of magneto-optical effects in all-dielectric metasurfaces caused by the bound state in the continuum resonance. In a structure under study, a square lattice of bismuth substituted yttrium iron garnet nanodisks with an air hole displaced away from the disk axis, magneto-optical polarization and intensity effects reach 0.7° and 22%, respectively.
关键词： bound state in the continuum,magneto-optical effects,all-dielectric metasurfaces,bismuth substituted yttrium iron garnet
更新于2025-09-19 17:13:59
-
Tunable Bound States in the Continuum in All-Dielectric Terahertz Metasurfaces
摘要： In this paper, a tunable terahertz dielectric metasurfaces consisting of split gap bars in the unit cell is proposed and theoretically demonstrated, where the sharp high-quality Fano resonance can be achieved through excitation of quasi-bound states in the continuum (quasi-BIC) by breaking in-plane symmetry of the unit cell structure. With the structural asymmetry parameter decreasing and vanishing, the calculated eigenmodes spectra demonstrate the resonance changes from Fano to symmetry-protected BIC mode, and the radiative quality factors obey the inverse square law. Moreover, combining with graphene monolayer and strontium titanate materials, the quasi-BIC Fano resonance can be tuned independently, where the resonance amplitude can be tuned by adjusting the Fermi level of graphene and the resonance frequency can be tuned by controlling the temperature of strontium titanate materials. The proposed structure has numerous potential applications on tunable devices including modulators, switches, and sensors.
关键词： graphene,tunable,quasi-bound states in the continuum,terahertz,dielectric metasurfaces
更新于2025-09-19 17:13:59
-
Spin-decoupled multifunctional metasurface for asymmetric polarization generation
摘要： Integrating multiple functionalities into a single device is a striking field in metasurfaces. One promising aspect is polarization-dependent meta-devices enabled by simultaneous phase control for orthogonally polarized waves. Among these, Pancharatnam-Berry (PB) metasurfaces have drawn enormous interest owing to their natural and robust phase control ability over different circularly polarized waves. However, the phase responses are locked to be opposite with each other, resulting in interrelated functionalities under the circularly-polarized incidence. Here, a generic designing method based on transmission-type dielectric metasurfaces is proposed in the terahertz regime, which breaks this relation by further incorporating dynamic phase with geometric phase, namely, spin-decoupled phase control method. We demonstrate this method by designing and characterizing an efficient multifunctional meta-grating, which splits different circularly polarized waves to asymmetric angles under normal incidences. More importantly, we promote this method by designing several multiplexed meta-gratings for applications of asymmetric polarization generation, which can convert arbitrary linearly polarized wave to two different linearly polarized waves with nearly equal strength and split them to asymmetric angles with a polarization-insensitive efficiency. The designing strategy proposed here shows an impressive robustness and a great flexibility for designing multi-functional metasurface-based devices, and opens new avenues toward modulation of polarization states and the application of metasurfaces in beam steering and polarization multiplexing systems.
关键词： multifunction,dielectric metasurfaces,asymmetric polarization generation,spin-decoupled phase control,terahertz
更新于2025-09-12 10:27:22
-
[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
-
Meta-optics and bound states in the continuum
摘要： We discuss the recent advances in meta-optics and nanophotonics associated with the physics of bound states in the continuum (BICs). Such resonant states appear due to a strong coupling between leaky modes in optical guiding structures being supported by subwavelength high-index dielectric Mie-resonant nanoantennas or all-dielectric metasurfaces. First, we review brie?y very recent developments in the BIC physics in application to isolated subwavelength particles. We pay a special attention to novel opportunities for nonlinear nanophotonics due to the large ?eld enhancement inside the particle volume creating the resonant states with high-quality (high-Q) factors, the so-called quasi-BIC, that can be supported by the subwavelength particles. Second, we discuss novel applications of the BIC physics to all-dielectric optical metasurfaces with broken-symmetry meta-atoms when tuning to the BIC conditions allows to enhance substantially the Q factor of the ?at-optics dielectric structures. We also present the original results on nonlinear high-Q metasurfaces and predict that the frequency conversion ef?ciency can be boosted dramatically by smart engineering of the asymmetry parameter of dielectric metasurfaces in the vicinity of the quasi-BIC regime.
关键词： bound states in the continuum,high-Q resonances,nanophotonics,nonlinear nanophotonics,BICs,dielectric metasurfaces,meta-optics
更新于2025-09-09 09:28:46