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Sub-decibel silicon grating couplers based on L-shaped waveguides and engineered subwavelength metamaterials
摘要： The availability of low-loss optical interfaces to couple light between standard optical fibers and high-index-contrast silicon waveguides is essential for the development of chip-integrated nanophotonics. Input and output couplers based on diffraction gratings are attractive coupling solutions. Advanced grating coupler designs, with Bragg or metal mirror underneath, low- and high-index overlays, and multi-level or multi-layer layouts, have proven less useful due to customized or complex fabrication, however. In this work, we propose a rather simpler in design of efficient off-chip fiber couplers that provide a simulated efficiency up to 95% (?0.25 dB) at a wavelength of 1.55 μm. These grating couplers are formed with an L-shaped waveguide profile and synthesized subwavelength grating metamaterials. This concept jointly provides sufficient degrees of freedom to simultaneously control the grating directionality and out-radiated field profile of the grating mode. The proposed chip-to-fiber couplers promote robust sub-decibel coupling of light, yet contain device dimensions (> 120 nm) compatible with standard lithographic technologies presently available in silicon nanophotonic foundries. Fabrication imperfections are also investigated. Dimensional offsets of ± 15 nm in shallow-etch depth and ± 10 nm in linewidth’s and mask misalignments are tolerated for a 1-dB loss penalty. The proposed concept is meant to be universal, which is an essential prerequisite for developing reliable and low-cost optical couplers. We foresee that the work on L-shaped grating couplers with sub-decibel coupling efficiencies could also be a valuable direction for silicon chip interfacing in integrated nanophotonics.
关键词： grating couplers,silicon photonics,L-shaped waveguides,subwavelength metamaterials,optical interfaces
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) - First Experimental Observation of Photonic Spin Hall Effect in Hyperbolic Metamaterials at Visible Wavelengths
摘要： The photonic spin Hall effect [1] or spin Hall effect of light [2] is the photonic analog of the spin Hall effect occurring with charge carriers in solid-state systems. Typically, this phenomenon takes place when a light beam refracts at an air-glass interface, or when it is projected onto an oblique plane, the latter effect being known as the geometric spin Hall effect of light [3]. In general, the photonic spin Hall effect leads to a polarization dependent transverse shift of a light peak intensity [3,4]. An example of the latter effect is the transverse Imbert–Federov beam shift [3], which happens for paraxial beams reflected or refracted at a sharp inhomogeneity of an isotropic optical interface. Potential applications of the photonic spin Hall effect in spin-dependent beam splitters, optical diodes [1], and surface sensors are considered in various fields in photonics, such as nanophotonics, plasmonics, metamaterials, topological optics, and quantum optics [1,2]. Here we experimentally demonstrate extreme angle sensitivity and enhancement of the spin Hall effect of light in hyperbolic metamaterials (HMMs) in the visible regime [5]. The effect is shown in transmission through a 176 nm thick HMM composed of alternating Au/Alumina layers, as illustrated in Fig.1 (a). The transverse beam shift in our HMM setting is very sensitive to the angle of incidence, drastically changing from almost no beam shift to a few hundred microns by the change of ≈0.003 rad (≈0.17°) in the incident angle, as illustrated in Fig. 1 (b). The experimental results are in extremely good agreement with the simulated values based on a theory developed by Tang et al. [6] with realistic parameters of fabricated HMMs, and taking into account beam divergence and setup errors. The large photonic spin Hall enhancement in a such thin structure and extreme angular sensitivity can be exploited in compact spin Hall devices which enable the manipulation of photons by polarization, with direct applications in quantum optics and communications.
关键词： optical diodes,photonic spin Hall effect,hyperbolic metamaterials,spin-dependent beam splitters,surface sensors,visible wavelengths
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
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A Review on Improving the Quality of Perovskite Films in Perovskite Solar Cells via the Weak Forces Induced by Additives
摘要： It is a challenge to design intelligent thermal metamaterials due to the lack of suitable theories. Here we propose a kind of intelligent thermal metamaterials by investigating a core-shell structure, where both the core and shell have an anisotropic thermal conductivity. We solve Laplace’s equation for deriving the equivalent thermal conductivity of the core-shell structure. Amazingly, the solution gives two coupling relations of conductivity tensors between the core and the shell, which cause the whole core-shell structure to counterintuitively self-?x a constant isotropic conductivity even when the area or volume fraction of the core changes within the full range in two or three dimensions. The theoretical ?ndings on fraction-independent properties are in sharp contrast with those predicted by the well-known e?ective medium theories, and they are further con?rmed by our laboratory experiments and computer simulations. This work o?ers two coupling relations for designing intelligent thermal metamaterials, and they are not only helpful for thermal stabilization or camou?age/illusion, but they also o?er hints on how to achieve similar metamaterials in other ?elds.
关键词： Laplace’s equation,intelligent thermal metamaterials,core-shell structure,anisotropic thermal conductivity,self-fixing behavior
更新于2025-09-11 14:15:04
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Bioinspired Toolkit Based on Intermolecular Encoder toward Evolutionary 4D Chiral Plasmonic Materials
摘要： Over the last two decades, nanophotonics, including plasmonics and metamaterials, have promised compelling opportunities for exotic control over light?matter interactions. The strong chiral light?matter interaction is a representative example. Three-dimensional (3D) chirality has existed naturally only in organic molecules and bio-organisms, but a negligible chiroptic effect was attained with these naturally occurring materials because of their small absorption cross sections. However, inspired by biological chirality, nanophotonic chiral materials have greatly expanded the design space of accessible chiroptic effects (e.g., pushing the chiral light?matter interaction to an exceptional regime, such as a broad-band circular polarizer, negative refractive index, and sensitive chiral sensing). Nevertheless, it is still a challenge to achieve precisely defined and dynamically reconfigurable chiral morphologies that further increase the chiroptic effect.
关键词： plasmonics,metamaterials,chiroptic effects,nanophotonics,chiral light?matter interaction,3D chirality
更新于2025-09-11 14:15:04
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Water-based Terahertz Metamaterial for Skin Cancer Detection Application
摘要： We present a highly sensitive detection of skin cancer using a novel water-based (THz) metamaterial (MM) used semiconductor film. We apply the application of terahertz pulsed imaging (TPI) in reflection geometry for the study of skin tissue and related cancers. As a refractive index (RI) sensing application of the proposed device, there will be shown with placing different sensing materials in the biosensor design, the effective RI will also change that in turn leads to measuring the sensitivity of the biosensor to detect the normal skin and Basal Cell Carcinoma (BCC). The RI FOM value of the proposed device is much higher than for the sensor using semiconductor film, to detect biomarkers in the literature. Significantly, the sensitivity increases by about 117 um/RIU and the RI FOM increases by more than 20.53. This results from a combination of size-related factors, leading to field enhancement accompanying strong field localization. We observed the resonance-frequency shift of the THz MM following the RI changing of the detected skin. The dip reflectance resonance has a blue-shift for normal skin. Finally, we suggest that this water-based MM can be used to control of the gene expression. The advantage of our design depends on two factors. Firstly, we used the MM structure, which has micro-scale, and the smaller the size of the structure, the more sensitive to the changes in the RI. Secondly, we used water in our structure, which is very well-suited to the human body and are highly bio-absorbable and inexpensive which is abundantly found in nature.
关键词： bio-absorbable metamaterials,Skin Cancer detection,THz Metamaterials,Semiconductor Biosensor,Refractive Index Sensor,control of the gene expression
更新于2025-09-10 09:29:36
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[IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Espoo, Finland (2018.8.27-2018.9.1)] 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Reduction of the beam-coupling impedance in accelerating structures using metamaterial-based absorbers
摘要： Resistive-wall impedance constitutes a significant percentage of the total beam-coupling impedance budget of an accelerator. Under extreme conditions, like large power handling and ultra-high vacuum, metamaterial-based absorbers can represent a valid alternative to other approaches for impedance mitigation in specific accelerator components, like resonant (parasitic) cavities or collimators operating along the beam line. We design sub-wavelength 2D metallic resonant structures based on split rings or on 3D hyperbolic tapered waveguide arrays that can be employed as mode dampers in accelerating structures. A number of prototypes are fabricated and then measured in a “test model” pillbox cavity.
关键词： accelerators,hyperbolic metamaterials,metamaterials,beam-coupling impedance,split-ring resonators
更新于2025-09-10 09:29:36
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Controlling Refraction Using Sub-Wavelength Resonators
摘要： We construct metamaterials from sub-wavelength nonmagnetic resonators and consider the refraction of incoming signals traveling from free space into the metamaterial. We show that the direction of the transmitted signal is a function of its center frequency and bandwidth. The directionality of the transmitted signal and its frequency dependence is shown to be explicitly controlled by sub-wavelength resonances that can be calculated from the geometry of the sub-wavelength scatters. We outline how to construct a medium with both positive and negative index properties across different frequency bands in the near infrared and optical regime.
关键词： dispersion relation,metamaterials,signal,refraction
更新于2025-09-10 09:29:36
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Photonic Microcavity-Enhanced Magnetic Plasmon Resonance of Metamaterials for Sensing Applications
摘要： We investigate photonic microcavity-enhanced magnetic plasmon (MP) resonance in metamaterials for high-quality refractive index sensing. The metamaterials are consisting of a top periodic array of U-shaped metallic split-ring resonators (SRRs), a middle dielectric layer, and a bottom metallic backed plate. The top metallic SRRs that are placed at about Bragg distance above the bottom metallic plate constitute a photonic microcavity. Because the MP resonance excited in metallic SRRs is coupled to the photonic microcavity mode supported by the photonic microcavity, the radiative damping of the MP resonance is strongly reduced and consequently its linewidth is decreased dramatically. Benefiting from the narrow linewidth, large modulation depth, and giant magnetic field enhancement at the MP resonance, the cavity-coupled metamaterial sensor has very high sensitivity (S =400 nm/RIU, S* =26/RIU) and figure of merit (FOM =33, FOM* =4215), which suggests that the proposed metamaterials have potential in applications of plasmonic biosensors.
关键词： Optical sensing and sensors,Narrow linewidth,Magnetic field enhancement,Photonic microcavity,Metamaterials
更新于2025-09-10 09:29:36
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[IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Espoo, Finland (2018.8.27-2018.9.1)] 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Vortex-sound diffusers using spiral metasurfaces
摘要： Metamaterials allow the accurate control of the acoustic scattering using subwavelength thickness panels. In this work, we report the scattering of spiral-shaped metasurfaces with practical application to sound diffusers. We analytically, numerically and experimentally show that bipolar spiral-shaped metasurfaces produce broadband non-specular reflection. We observe that the reflected energy can be scattered at higher diffraction orders and, due to the spiral geometry, the phase of the scattering field rotates producing a vortex in the near field. Thus, the specular component at normal incidence vanish. This produces a perfect correlation-scattering coefficient when comparing to a rigid flat reflector of same dimensions. In particular, the scattering of an Archimedes spiral metasurface is presented. We show that the scattering pattern corresponds to a high-order Bessel beam. The use of binary locally reacting surfaces with chiral geometry produce non-specular reflected patterns, allowing the use of these structures use as sound diffusers.
关键词： acoustic scattering,sound diffusers,metamaterials,Bessel beam,spiral-shaped metasurfaces
更新于2025-09-10 09:29:36