Hyperbolic Metamaterials Research Articles

Investigation on the Compressive Behavior of Hybrid Polyurethane(PU)-Foam-Filled Hyperbolic Chiral Lattice Metamaterial.

In this study, a novel hybrid metamaterial has been developed via fulfilling hyperbolic chiral lattice with polyurethane (PU) foam. Initially, both the hyperbolic and typical body-centered cubic (BCC) lattices are fabricated by 3D printing technique. These lattices are infiltrated in a thermoplastic polyurethane (TPU) solution dissolved in 1,4-Dioxane, and then freeze casting technique is applied to achieve the PU-foam-filling. Intermediate (IM) layers possessing irregular pores, are formed neighboring to the lattice-foam interface. While, the foam far from the lattice exhibits a multi-layered structure. The mechanical behavior of the hybrid lattice metamaterials has been investigated by monotonic and cyclic compressive tests. The experimental monotonic tests indicate that, the filling foam is able to soften the BCC lattice but to stiffen the hyperbolic one, further to raise the stress plateau and to accelerate the densification for both lattices. The foam hybridization also benefits the hyperbolic lattice to prohibit the property degradation under the cyclic compression. Furthermore, the failure modes of the hybrid hyperbolic lattice are identified as the interface splitting and foam collapse via microscopic analysis. Finally, a parametric study has been performed to reveal the effects of different parameters on the compressive properties of the hybrid hyperbolic lattice metamaterial.

Terahertz band range adjustable hyperbolic metamaterial refractive index sensor

Terahertz sensing has an important position in biochemical detection due to its unique advantages. In this work, we design a sensor with tunable analytes refractive index interval using graphene/dielectric multilayer structured hyperbolic metamaterials (GMHMM). We use the attenuated total reflection method to match the bulk high k waves mode in the GMHMM and derive dispersion relation of the bulk resonance mode in combination with waveguide mode analysis. By tuning the graphene Fermi energy level and incidence angle, the sensor can detect analytes with different refractive indices with a maximum sensitivity of 20.5 THz/RIU and an average sensitivity of 11.05 THz/RIU in the band of 2.4 THz. We believe that the proposed structure can be applied to biochemical molecule detection in the terahertz band and contribute to the development of hyperbolic metamaterial sensors from laboratory research to practical applications.

First-principles study of the optical properties of BaMoO[formula omitted]/SrHfO[formula omitted] hyperbolic metamaterials

The theoretical applications of hyperbolic metamaterials have generated excitement in multiple fields, particularly in super-resolution optics. In practice, however, the potential of HMMs has been limited by the shortcomings of their constituent parts. Primarily, these are high losses and instabilities in the metal component, which is typically gold or silver, and excessive thickness in both types of layers. In this paper, we use density functional theory to investigate BaMoO3-SrHfO3 metamaterials. We predict that these are hyperbolic throughout the visible range and have the potential to mitigate many of these limitations, including a significant loss reduction. We also examine the accuracy of the effective-medium theory, which is used to predict the bulk optical properties of multilayered HMMs.

Negative refraction of water waves by hyperbolic metamaterials

We study the propagation of water waves in a three-dimensional device alternating open canals and resonant canals with subwavelength resonances. The dispersion of water waves in such a medium is obtained by analysing the full three-dimensional problem and combining Bloch–Floquet analysis with an asymptotic technique. We obtain the closed forms of the dispersions for resonant canals containing one or two resonators, which depend on only two functions associated with symmetric and antisymmetric modes, and on a geometric parameter analogous to the hopping parameter in topological systems. The analysis of the complete band structure reveals frequency ranges alternating between elliptical and hyperbolic dispersions; in particular, the hyperbolic regime gives rise to a negative effective water depth with a consequent negative refraction. Throughout the course of our study, our theoretical results are validated by comparison with numerical calculations of the full three-dimensional problem.

Transverse Hypercrystals Formed by Periodically Modulated Phonon Polaritons

Photonic crystals and metamaterials are two overarching paradigms for manipulating light. By combining these approaches, hypercrystals can be created, which are hyperbolic dispersion metamaterials that undergo periodic modulation and mix photonic-crystal-like aspects with hyperbolic dispersion physics. Despite several attempts, there has been limited experimental realization of hypercrystals due to technical and design constraints. In this work, hypercrystals with nanoscale lattice constants ranging from 25 to 160 nm were created. The Bloch modes of these crystals were then measured directly using scattering near-field microscopy. The dispersion of the Bloch modes was extracted from the frequency dependence of the Bloch modes, revealing a clear switch from positive to negative group velocity. Furthermore, spectral features specific to hypercrystals were observed in the form of sharp density of states peaks, which are a result of intermodal coupling and should not appear in ordinary polaritonic crystals with an equivalent geometry. These findings are in agreement with theoretical predictions that even simple lattices can exhibit a rich hypercrystal bandstructure. This work is of both fundamental and practical interest, providing insight into nanoscale light-matter interactions and the potential to manipulate the optical density of states.

Enhanced Förster resonance energy transfer on layered metal-dielectric hyperbolic metamaterials: an excellent platform for low-threshold laser action.

Förster resonance energy transfer (FRET) is a well-known physical phenomenon, which has been widely used in a variety of fields, spanning from chemistry, and physics to optoelectronic devices. In this study, giant enhanced FRET for donor-acceptor CdSe/ZnS quantum dot (QD) pairs placed on top of Au/MoO3 multilayer hyperbolic metamaterials (HMMs) has been realized. An enhanced FRET transfer efficiency as high as 93% was achieved for the energy transfer from a blue-emitting QD to a red-emitting QD, greater than that of other QD-based FRET in previous studies. Experimental results show that the random laser action of the QD pairs is greatly increased on a hyperbolic metamaterial by the enhanced FRET effect. The lasing threshold with assistance of the FRET effect can be reduced by 33% for the mixed blue- and red-emitting as QDs compared to the pure red-emitting QDs. The underlying origins can be well understood based on the combination of several significant factors, including spectral overlap of donor emission and acceptor absorption, the formation of coherent closed loops due to multiple scatterings, an appropriate design of HMMs, and the enhanced FRET assisted by HMMs.

An array structures of nanoparticle-coupled hyperbolic metamaterials for efficient SERS sensing

Hyperbolic metamaterials (HMMs) have been employed in the field of surface-enhanced Raman scattering (SERS) for their properties to support large-wave vector bulk plasmon polariton (BPP) waves, whereas the excitation of BPP is challenging to a certain extent. In addition, with the advance of SERS, the substrate for energy utilization has aroused increasing attention. An HMM-Ag nanoparticles (Ag NPs) platform based on patterned sapphire substrate (PSS) array structure was proposed in this study. With Ag NPs as the external coupling structure, the generated large-wave vector scattered light excited the BPP in the HMM and extended the energy into the Ag NPs gap. On that basis, a hot surface with a high density of “hot spots” was formed. PSS with excellent light trapping capability was employed as a substrate, which improved the energy utilization of the platform. Furthermore, the good hydrophobicity of the nanoparticle array structure further amplified the SERS signal. Lastly, the excellent performance of the platform was experimentally verified, the detection limits of CV and R6G reached 10-10 M and 10-11 M, respectively. Accordingly, it is believed that the plasma platform has promising applications in high-sensitivity sensing and biochemical detection.

Magnetoplasmonics in confined geometries: Current challenges and future opportunities

Plasmonics represents a unique approach to confine and enhance electromagnetic radiation well below the diffraction limit, bringing a huge potential for novel applications, for instance, in energy harvesting, optoelectronics, and nanoscale biochemistry. To achieve novel functionalities, the combination of plasmonic properties with other material functions has become increasingly attractive. In this Perspective, we review the current state of the art, challenges, and future opportunities within the field of magnetoplasmonics in confined geometries, an emerging area aiming to merge magnetism and plasmonics to either control localized plasmons, confined electromagnetic-induced collective electronic excitations, using magnetic properties, or vice versa. We begin by highlighting the cornerstones of the history and principles of this research field. We then provide our vision of its future development by showcasing raising research directions in hybrid magnetoplasmonic systems to overcome radiation losses and novel materials for magnetoplasmonics, such as transparent conductive oxides and hyperbolic metamaterials. Finally, we provide an overview of recent developments in plasmon-driven magnetization dynamics, nanoscale opto-magnetism, and acousto-magnetoplasmonics. We conclude by giving our personal vision of the future of this thriving research field.

Observation of polarization-dependent optical Tamm states in heterostructures containing hyperbolic metamaterials in the near-infrared region

In the heterostructure composed of metal and one-dimensional photonic crystal (1DPC), the optical Tamm state (OTS) can be excited directly without the coupling of prism or grating, but it is strongly dependent on the photonic band gap (PBG) of the 1DPC. In particular, the PBG of the all-dielectric 1DPC as well as the corresponding OTSs shift toward shorter wavelengths for both transverse magnetic (TM) and transverse electric (TE) polarizations as the angle of incidence increases, making it impossible to achieve a high-performance polarization selection. In a heterostructure consisting of a silver layer and an ITO-based one-dimensional photonic hypercrystal (1DPHC), we experimentally observe for the first time that the OTSs are red-shifted for TM polarization and blue-shifted for TE polarization with increasing incident angle. The ITO-based 1DPHC possesses a large red-shifted PBG in the near-infrared region, which guarantees the full excitation of the OTSs at different angles. Our work provides a potential direction for improving the sensitivity, polarization selection and operating angle range of the Tamm sensor.

Integrated Optical Filters with Hyperbolic Metamaterials

The growing development of nanotechnology requires the design of new devices that integrate different functionalities at a reduced scale. For on-chip applications such as optical communications or biosensing, it is necessary to selectively transmit a portion of the electromagnetic spectrum. This function is performed by the so-called band-pass filters. While several plasmonic nanostructures of complex fabrication integrated to optical waveguides have been proposed, hyperbolic metamaterials remain almost unexplored for the design of integrated band-pass filters at optical wavelengths. By making use of the effective medium theory and finite integration technique, in this contribution we numerically study an integrated device consisting of a one-dimensional hyperbolic metamaterial placed on top of a photonic waveguide. The results show that the filling fraction, period, and number of layers modify the spectral response of the device, but not for type II and effective metal metamaterials. For the proposed Au-TiO2 multilayered system, the filter operates at a wavelength of 760 nm, spectral bandwidth of 100 nm and transmission efficiency above 40%. The designed devices open new perspectives for the development of integrated band-pass filters of small scale for on-chip integrated optics applications.

Hyperbolic Metamaterial-Based Optical Biosensor for Detecting Cancer Cells

Study was made of a hyperbolic metamaterial (HMM)-based optical biosensor in view of possible usage to detect early-stage cancerous cells. The effective medium theory was used to determine the constitutive properties of the metasurface. The reflectance was obtained under different conditions to observe shifts in spectral minima, thereby determining the status of the measurand. The sensitivity and figure-of-merit (FoM) of the structure were evaluated. Observations revealed the device showing relatively high FoM, which depends on the thickness of the HMM and sensing medium, and also, the radius of nanoholes (in HMM) and the angle of incidence of light waves.

Precise topological transition and negative refraction of a wave vector in a symmetrically arranged Al2O3/Ag/Al2O3 multilayer.

The topological transition of a symmetrically arranged Al2O3/Ag/Al2O3 multilayer is precisely estimated by the product of characteristic film matrixes instead of treating the multilayer as an anisotropic medium with effective medium approximation. The variation of the iso-frequency curve among a type I hyperbolic metamaterial, a type II hyperbolic metamaterial, a dielectric-like medium, and a metal-like medium of such a multilayer with wavelength and the filling fraction of the metal is investigated. The estimated negative refraction of wave vector in a type II hyperbolic metamaterial is demonstrated with near field simulation.

High-sensitivity Goos–Hänchen shift gas sensor based on subwavelength hyperbolic metamaterials

Optical gas sensors play an increasingly important role in many applications, particularly for the detection of toxic gases. A novel Goos–Hänchen (GH) shift optical gas sensing scheme based on subwavelength hyperbolic metamaterials (HMMs) is proposed. The GH shift intensity, direction and the critical wavelength characteristics were revealed. By virtue of the GH shift and subwavelength HMMs characteristics, we designed an ultra-sensitive gas sensor to detect helium (He), hydrogen (H2), carbon monoxide (CO) and methane (CH4). The study shows that the sensitivities of the gas sensor can reach as high as [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]. With proper surface chemical modification, this GH shift gas sensor would be a powerful tool for high-sensitive gas sensing applications.

Recyclable surface-enhanced Raman spectroscopy (SERS) platform fabricated with Ag-decorated ZnSe nanowires and metamaterial

In surface-enhanced Raman scattering (SERS), metal-semiconductor heterostructures have attracted a lot of interest because of their remarkable features. However, the use of organic substances in the fabrication of metal nanoparticles can result in contamination of the SERS substrate, which can negatively impact sensor performance. Here, we introduced new recyclable SERS substrates which include Ag-decorated ZnSe nanowires and hyperbolic metamaterial. The Ag-decorated ZnSe nanowires work as an external coupling structure for hyperbolic metamaterials, due to this structure exhibiting significant plasmonic effects as well as unique optical features. There exists overlapping and physical interaction between metal and semiconductor nanowires, as a result, both resonance energy and hot electron were transferred. Rhodamine 6G (R6G), malachite green (MG), and adenosine were used to assess the SERS performance of synthesized Ag-decorated ZnSe, which showed outstanding stability and a sensitivity limit of 10-12 M. The nanostructure's self-cleaning feature was demonstrated through photocatalytic degradation of R6G and MG molecules under visible light, enabling it to be reused multiple times and showing that it was not limited to a single organic molecule. The bifunctional structure not only offers a unique way of boosting SERS efficiency but is also considerable for photocatalytic behavior.

Highly sensitive short-range mode resonance sensor with multilayer structured hyperbolic metamaterials.

Hyperbolic metamaterial (HMM) based sensors can achieve superior sensing performance than conventional surface plasmon resonance sensors. In this work, the operator approach to effective medium approximation (OEMA) is used to characterize the HMM dielectric constant properties of metal-dielectric multilayer structures, which are classified into short-range (SR) mode and long-range (LR) mode according to the propagation length of the bulk high K waves in HMM. The dispersion relations of SR modes are derived, and a high-sensitivity refractive index sensor is designed for the near-infrared SR mode resonance. The effects of the number of periods, cell thickness, metal fill rate and incidence angle on the SR mode resonance were analyzed for the multilayer structured HMM. Our designed sensing structure achieves a maximum sensitivity of 330 µm/RIU in the near-infrared band with a quality factor of 492 RIU-1. In addition, the simulations show that the SR mode resonance wavelength is flexible and tunable. We believe that the study of HMM-based SR mode resonance sensors offers potential applications for high-sensitivity biochemical detection.

Multiplication of photonic band gaps in one-dimensional photonic crystals by using hyperbolic metamaterial in IR range

The light-slowing effect near band endpoints is frequently exploited in photonic crystals to enhance the optical transmittance. In a one-dimensional binary photonic crystal (1DPC) made of hyperbolic metamaterials (HMMs), we theoretically examined the angle-dependent omnidirectional photonic bandgap (PBG) for TM polarization. Using the transfer matrix approach, the optical characteristics of the 1DPC structure having dielectric and HMM layers were examined at the infrared range (IR). As such, we observed the existing of numerous PBGs in this operating wavelength range (IR). Meanwhile, the HMM layer is engineered by the subwavelength dielectric- nanocomposite multilayers. The filling fraction of nanoparticles have been explored to show how they affect the effective permittivity of the HMM layer. Furthermore, the transmittance properties of the suggested structure are investigated at various incident angles for transverse magnetic (TM) and transverse electric polarizations. Other parameters such as, the permittivity of the host material, the filling fraction of nanoparticles, and the thickness of the second layer (HMM) are also taken into account. Finally, we investigated the effect of these parameters on the number and the width of the (PBGs). With the optimum values of the optical parameters of the nanocomposite (NC) layer, this research could open the way for better multi-channel filter photonic crystals.

Omnidirectional defect mode in one-dimensional photonic crystal with a (chiral) hyperbolic metamaterial defect.

The wavelength of defect mode in all-dielectric photonic crystals (PCs) with a dielectric defect are blue-shifted as incident angle increases for both transverse electric and transverse magnetic (TM) polarized waves. The blue-shifted property of defect mode limits the design of some optical devices including omnidirectional optical filters and wide-angle polarization selectors. Here we introduce a hyperbolic metamaterial (HMM) layer as a defect into dielectric one-dimensional photonic crystals (1DPCs) to obtain an omnidirectional defect mode for TM polarized waves at near-infrared regimes. Since only one HMM layer is introduced, omnidirectional defect mode with transmittance as high as 71% can be realized. Because of the unusual angle-dependence of propagating phase in the HMM defect, the total phase for satisfying the resonance condition of defect mode can be unchanged in a wide-angle range at a fixed wavelength, which leads to the omnidirectional defect mode. Moreover, the manipulation of propagating phase can be generalized to the case of circularly polarized waves, and we obtain an omnidirectional defect mode for left-handed circularly polarized waves in 1DPCs with a chiral hyperbolic metamaterial defect. Nevertheless, the defect mode for right-handed circularly polarized waves is still blue-shifted. Such spin-selective omnidirectional defect mode can be utilized to greatly enhance circular dichroism in a wide-angle range up to 64.1°. Our structure facilitates the design of omnidirectional optical filters with a high transmittance and circular polarization selectors working in a wide-angle range.

A tunable wide-angle narrowband perfect absorber based on an optical cavity containing hyperbolic metamaterials.

We demonstrate that wide-angle narrowband absorption can be achieved from a microcavity where a hyperbolic metamaterial and a dielectric layer are sandwiched between two metal reflectors. As the incident angle changes, the phase-shift variation in the hyperbolic metamaterial can compensate that in the dielectric layer and, consequently, result in the angle-insensitive Fabry-Perot resonance in the proposed cavity. Silicon, indium tin oxide (ITO), and gold layers are used to construct the microcavity to produce a narrow absorption band in the near-infrared region. Our device exhibits good absorption stability over a wide angle range of incidence from 0° to 70°. Moreover, the absorption wavelength can be tuned by changing the thickness of the resonator. The presented absorber may find potential applications in the design of narrowband thermophotovoltaic emitters, sensitive detectors, filters, etc.

Transparent spacecraft smart thermal control device based on VO2 and hyperbolic metamaterials.

Effective spacecraft thermal control technologies are essential to avoid undesirable effects caused by extreme thermal conditions. In this paper, we demonstrate a transparent smart radiation device (TSRD) based on vanadium dioxide (VO2) and a hyperbolic metamaterial (HMM) structure. Using the topological transition property of HMM, high transmission in the visible band and high reflection in the infrared can be achieved simultaneously. The variable emission essentially originates from the phase change material VO2 film. Due to the high reflection of HMM in the infrared band, it can form Fabry-Pérot (FP) resonance with the VO2 film after adding the dielectric layer SiO2, which further enhances the emission modulation. Under optimized conditions, solar absorption can be reduced to 0.25, while emission modulation can reach 0.44 and visible transmission can be up to 0.7. It can be found that the TSRD can simultaneously achieve infrared variable emission, high visible transparency and low solar absorption. The HMM structure instead of traditional metal reflectors offers the possibility to achieve high transparency. In addition, the formation of FP resonance between the VO2 film and HMM structure is the key to achieving variable emission. We believe that this work can not only provide a new approach for the design of spacecraft smart thermal control devices, but also show great potential for application in spacecraft solar panels.

Unconventional organic solar cell structure based on hyperbolic metamaterial

An unconventional organic solar cell structure based on hyperbolic metamaterials (HMMs) was designed, fabricated, and demonstrated with improved performance for the first time.