Metasurfaces with Multipolar Resonances and Enhanced Light–Matter Interaction

Babicheva V.E.

We investigate the resonant characteristics of planar surfaces and distinct edges of structures with the excitation of phonon-polaritons. We analyze two materials supporting phonon-polariton excitations in the mid-infrared spectrum: silicon carbide, characterized by an almost isotropic dielectric constant, and hexagonal boron nitride, notable for its pronounced anisotropy in a spectral region exhibiting hyperbolic dispersion. We formulate a theoretical framework that accurately captures the excitations of the structure involving phonon-polaritons, predicts the response in scattering-type near-field optical microscopy, and is effective for complex resonant geometries where the locations of hot spots are uncertain. We account for the tapping motion of the probe, perform analysis for different heights of the probe, and demodulate the signal using a fast Fourier transform. Using this Fourier demodulation analysis, we show that light enhancement across the entire apex is the most accurate characteristic for describing the response of all resonant excitations and hot spots. We demonstrate that computing the demodulation orders of light enhancement in the microscope probe accurately predicts its imaging.

Loulas I., Almpanis E., Kouroublakis M., Tsakmakidis K.L., Rockstuhl C., Zouros G.P.

Zhang S., An S., Dai M., Wu Q.Y., Adanan N.Q., Zhang J., Liu Y., Lee H.Y., Wong N.L., Suwardi A., Ding J., Simpson R.E., Wang Q.J., Yang J.K., Dong Z.

AbstractThermoelectric materials can be designed to support optical resonances across multiple spectral ranges to enable ultra‐wideband photodetection. For instance, antimony telluride (Sb2Te3) chalcogenide exhibits interband plasmonic resonances in the visible range and Mie resonances in the mid‐infrared (mid‐IR) range, while simultaneously possessing large thermoelectric Seebeck coefficients of 178 µV K−1. However, chalcogenide metasurfaces for achieving miniaturized and wavelength‐sensitive ultra‐wideband detectors have not been explored so far, especially with a single material platform. In this paper, Sb2Te3 metasurface devices are designed and fabricated to achieve ≈97% resonant absorption for enabling photodetectors operating across an ultra‐wideband spectrum, from visible to mid‐IR. Furthermore, relying on linear polarization‐sensitive Sb2Te3 metasurface, the thermoelectric photodetectors with linear polarization‐selectivity are demonstrated. This work provides a potential platform toward the portable ultrawide band spectrometers without requiring cryogenic cooling, for environmental sensing applications.

Brongersma M.L., Pala R.A., Altug H., Capasso F., Chen W.T., Majumdar A., Atwater H.A.

Optical metasurfaces are judiciously nanostructured thin films capable of manipulating the flow of light in a myriad of new ways. During the past two decades, we have witnessed a true revolution in the basic science that underlies their operation. As a result, these powerful optical elements can now deliver never-seen-before optical functions and transformed the way we think about light–matter interaction at the nanoscale. They also offer a favourable size, weight, power and cost metric compared to bulky optical elements such as lenses and prisms based on polished pieces of glass or moulded plastics. These valuable traits are especially relevant for use in many emerging applications, including wearable displays and sensors, autonomous navigation (robotics, automotive and aerospace), computational imaging, solar energy harvesting and radiative cooling. With the advent of advanced software and high-volume manufacturing processes, the promise of metasurfaces is becoming a practical reality and has already generated tremendous interest from industry. This Review discusses the rapid, recent advances towards transitioning metasurface science into real technologies, propelling the second metasurface revolution. Metasurface optics offer a very favourable size, weight, power and cost metric compared to bulky optical elements based on polished pieces of glass or moulded plastics, and these valuable traits are now propelling their use in many areas of technology.

Babicheva V.E., Lock E., Kim H.

We report on the structural, chemical, and optical properties of titanium sesquioxide Ti2O3 thin films on single-crystal sapphire substrates by pulsed laser deposition. The thin film of Ti2O3 on sapphire exhibits light absorption of around 25%–45% in the wavelength range of 2–10 μm. Here, we design an infrared photodetector structure based on Ti2O3, enhanced by a resonant metasurface, to improve its light absorption in mid-wave and long-wave infrared windows. We show that light absorption in the mid-wave infrared window (wavelength 3–5 μm) in the active Ti2O3 layer can be significantly enhanced from 30%–40% to more than 80% utilizing a thin resonant metasurface made of low-loss silicon, facilitating efficient scattering in the active layer. Furthermore, we compare the absorptance of the Ti2O3 layer with that of conventional semiconductors, such as InSb, InAs, and HgCdTe, operating in the infrared range with a wavelength of 2–10 μm and demonstrate that the absorption in the Ti2O3 film is significantly higher than in these conventional semiconductors due to the narrow-bandgap characteristics of Ti2O3. The proposed designs can be used to tailor the wavelengths of photodetection across the near- and mid-infrared ranges.

Zhou W., Sun G., Yuan Y., Wang Y., Burokur S.N., Wang Y., Zhang K.

AbstractBound states in the continuum (BICs) refer to nonradiative eigenmodes located within the radiation continuum, possessing infinitely high Q‐factor and enabling exceptionally strong light–matter interactions. BICs have found applications across various domains in photonics and metasurfaces, including nonlinear optical enhancement, vortex beam generation, sensor technology, microlasers, and other related areas. This work starts by classifying the phenomena of BICs and introducing the theoretical formation mechanisms and topological characteristics. Then, the current and advanced applications based on BIC‐devices are highlighted. Lastly, this work discusses the current challenges in studies related to BICs, such as structural precision, material selection, and measurement difficulties, and prospect the possible potentials in future developments. This review provides a theoretical background and application prospects of BIC‐engineered devices in optical and photonics fields, laying a solid foundation for future industrial applications.

Ramos Uña R., García Cámara B., Barreda Á.I.

The use of nanostructures to enhance the emission of single-photon sources has attracted some attention in the last decade due to the development of quantum technologies. In particular, the use of metallic and high-refractive-index dielectric materials has been proposed. However, the utility of moderate-refractive-index dielectric nanostructures to achieve more efficient single-photon sources remains unexplored. Here, a systematic comparison of various metallic, high-refractive-index and moderate-refractive-index dielectric nanostructures was performed to optimize the excitation and emission of a CdSe/ZnS single quantum dot in the visible spectral region. Several geometries were evaluated in terms of electric field enhancement and Purcell factor, considering the combination of metallic, high-refractive-index and moderate-refractive-index dielectric materials conforming to homogeneous and hybrid nanoparticle dimers. Our results demonstrate that moderate-refractive-index dielectric nanoparticles can enhance the photoluminescence signal of quantum emitters due to their broader electric and magnetic dipolar resonances compared to high-refractive-index dielectric nanoparticles. However, hybrid combinations of metallic and high-refractive-index dielectric nanostructures offer the largest intensity enhancement and Purcell factors at the excitation and emission wavelengths of the quantum emitter, respectively. The results of this work may find applications in the development of single-photon sources.

Matiushechkina M., Evlyukhin A.B., Malureanu R., Zenin V.A., Yezekyan T., Lavrinenko A., Bozhevolnyi S.I., Chichkov B.N., Heurs M.

The increasing demand for novel mirror coating designs for new generation of gravitational wave detectors is stimulating significant research interest in investigations of reflective properties of metasurfaces. Given this strong interest, this article details a systematic methodology for fabricating reflecting metasurfaces (metamirrors) designed to operate at target wavelengths of 1064 or 1550 nm. The proposed metasurfaces consist of silicon cylindrical nanoparticles placed on a sapphire substrate. First, the dimensional parameters of the structures are thoroughly selected through numerical simulations combined with material characterization. The configurations are subsequently analyzed analytically to reveal the mirror effect, which arises from the excitation of electric and magnetic dipole moments. Following this, the metasurfaces are fabricated and experimentally characterized, demonstrating reflectivity exceeding 95% around the design wavelengths, which is in good agreement with theoretical predictions. Overall, the work demonstrates the feasibility and detailed methodology for the fabrication of thin, lightweight metamirrors capable of achieving near‐perfect reflectivity at the specified target wavelengths.

Zhang X., Li W., Xie F., Wang K., Li G., Liu S., Wang M., Tang Z., Zeng L.

Metamaterials, a kind of novel materials with artificial design, have exhibited extraordinary properties that cannot be found in nature. In the past decade, remarkable achievements have been made in the field of metamaterial-based photodetectors. However, there is hardly any systematic and thorough review of the metamaterials' recent development in photodetection devices. Herein, we summarized recent advances in the metamaterial-based photodetectors according to a dual role of metamaterials: enrichment of photodetection functionalities and enhancement of photodetection performance. To start with, we presented an overview of the relevant concept of metamaterials and explore their distinctive optical characteristics. Subsequently, we delved into the work mechanism and figures of merit of metamaterial-based photodetectors. Next, we highlighted various types of metamaterials as a flexible platform for advanced photodetection technology, including metasurface, graphene-metamaterial hybrids, patterned nanostructures, and van der Waals metamaterials. Finally, the challenges and outlook associated with future developments were systematically and deeply discussed based on the current state of research. We believe that this review will offer crucial insights and valuable guidance, paving the way for future advancements and in-depth investigations in the realm of metamaterial-based photodetectors.

Babicheva V.E., Rumi M.

Chalcophosphate metasurfaces exhibit a significant electro-optic shift in multipolar resonances due to large electric-field-induced refractive index changes, obtainable with in-plane or out-of-plane biasing.

Qin H., Chen S., Zhang W., Zhang H., Pan R., Li J., Shi L., Zi J., Zhang X.

Trapping electromagnetic waves within the radiation continuum holds significant implications in the field of optical science and technology. Photonic bound states in the continuum (BICs) present a distinctive approach for achieving this functionality, offering potential applications in laser systems, sensing technologies, and other domains. However, the simultaneous achievement of high Q-factors, flat-band dispersions, and wide-angle responses in photonic BICs has not yet been reported, thereby impeding their practical performance due to laser direction deviation or sample disorder. Here, we theoretically demonstrate the construction of moiré BICs in one-dimensional photonic crystal (PhC) slabs, where high-Q resonances in the entire moiré flat band are achieved. Specifically, we numerically validate that the radiation loss of moiré BICs can be eliminated by aligning multiple topological polarization charges with all diffraction channels, enabling the strong suppression of far-field radiation from the entire moiré band. This leads to a slow decay of Q-factors away from moiré BICs in the momentum space. Moreover, it is found that Q-factors of the moiré flat band can still maintain at a high level with structural disorder. In experiments, we fabricate the designed 1D moiré PhC slab and observe both high-Q resonances and a slow decrease of Q-factors for moiré flat-band Bloch modes. Our findings hold promising implications for designing highly efficient optical devices with wide-angle responses and introduce a novel avenue for exploring BICs in moiré superlattices. Trapping electromagnetic waves within the radiation continuum has significant implications in lasers and sensing. Here the authors achieved a moiré BIC in a photonic crystal slab, demonstrating simultaneous flat-band dispersing and high-Q features within a wide-angle regime.

Jiang H., Chen Y., Guo W., Zhang Y., Zhou R., Gu M., Zhong F., Ni Z., Lu J., Qiu C., Gao W.

Light encodes multidimensional information, such as intensity, polarization, and spectrum. Traditional extraction of this light information requires discrete optical components by subdividing the detection area into many “one-to-one” functional pixels. The broadband photodetection of high-dimensional optical information with a single integrated on-chip detector is highly sought after, yet it poses significant challenges. In this study, we employ a metasurface-assisted graphene photodetector, enabling to simultaneously detect and differentiate various polarization states and wavelengths of broadband light (1-8 μm) at the wavelength prediction accuracy of 0.5 μm. The bipolar polarizability empowered by this design allows to decouple multidimensional information (encompassing polarization and wavelength), which can be achieved by encoding vectorial photocurrents with varying polarities and amplitudes. Furthermore, cooperative multiport metasurfaces are adopted and boosted by machine learning techniques. It enables precise spin-wavelength differentiation over an extremely broad wavelength range (1-8 μm). Our innovation offers a recipe for highly compact and high-dimensional spectral-polarization co-detection. The detection of light intensity, polarization, and spectral information with a single device is desired for efficient optical sensing and computing applications. Here, the authors report the realization of metasurface-assisted graphene photodetectors able to simultaneously detect polarization states and wavelengths of broadband infrared light.

Babicheva V.E.

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.

Romero A., Babicheva V.E.

Stronger light confinement can be enabled by nanoantennas in the nanostructure and result in efficient control of the directionality of the scattering. We report on an observation of the well-pronounced multipolar resonances from nickel nanoantennas originating from collective effects. We show that the collective coupling of multipolar modes from weak scatterers can substantially enhance the electric dipole and quadrupole resonances. We also demonstrate the generalized lattice Kerker effect in this nanoantenna array. Resonant multipolar excitations within nickel nanoantenna arrays can significantly enhance phenomena such as magneto-optical effects, indicating promising potential for advanced applications in the field of nanophotonics and sensing.

Babicheva V., Evlyukhin A.

Mie-resonant metaphotonics is a rapidly developing field that employs the physics of Mie resonances to control light at the nanoscale. Mie resonances are excited in high-refractive-index transparent nanoparticles and voids created in dielectric media, and they can be used to achieve a wide range of optical effects, including enhanced light–matter interaction, nonlinear optical effects, and topological photonics. Here, we review the recent advances in Mie-resonant metaphotonics, with a focus on the physics of Mie resonances and their applications in metaphotonics and metasurfaces. Through a comprehensive multipolar analysis, we demonstrate the complex interplay of electric and magnetic multipoles that govern their interaction with light. Recent advances have unveiled a diverse spectrum of scattering phenomena that can be achieved within precisely engineered structures. Within this framework, we review the underlying mechanics of the first and second Kerker conditions and describe the intricate mechanisms guiding these nanostructures’ light-scattering properties. Moreover, we cover intriguing phenomena such as the anapole and bound or quasi-bound states in the continuum. Of profound interest are the numerous practical applications that result from these revelations. Ultrafast processes, the emergence of nanolasers, and advancements in magneto-optic devices represent just a fraction of the transformative applications.