Spoof Plasmon Research Articles

Anderson localized transport in non-Hermitian spoof surface plasmon polariton structures

Anderson localization, a fundamental wave phenomenon, is a challenging problem in quasiparticle transport, exacerbated in the presence of dissipation. Of late, however, a few demonstrations of Anderson localization in non-Hermitian structures have been made. In the domain of electromagnetics of structured materials, spoof surface plasmon polaritons are a very interesting concept where structured metallic surfaces sustain bound states even at very low frequencies. The metallic non-Hermiticity, in an environment of possible disorder, makes this system an interesting case-study for mesoscopic transport, although the idea of disordered structures for spoof plasmons is not commonly encountered in literature. Here, we present experimental evidence of Anderson localization in hybrid polariton–photon states within a disordered, non-Hermitian environment. Disorder is introduced by perturbing the periodic microstructure while maintaining surface confinement. Localization enhances the plasmonic intensity by about a factor of three as compared to the conventional periodic structure. We experimentally characterize the intensity distribution, dispersion properties, and generalized conductance within the Anderson localized regime. A significant decrease in both localization length and its fluctuations is observed with increasing disorder strength. The inverse participation ratio shows the anticipated linear dependency on localization length. Our results offer experimental proof of Anderson localization in hybrid polariton–photon states, showcasing the influence of disorder in boosting plasmonic intensity. This elucidates potential applications in fields requiring controlled wave transport in disordered settings.

Flexible terahertz spoof plasmonics based on graphene-assembled films

Flexible terahertz spoof plasmonics based on graphene-assembled films

Kirigami-Triggered Spoof Plasmonic Interconnects for Radiofrequency Elastronics.

The flexible and conformal interconnects for electronic systems as a potential signal transmission device have great prospects in body-worn or wearable applications. High-efficiency wave propagation and conformal structure deformation around human body at radio communication are still confronted with huge challenges due to the lack of methods to control the wave propagation and achieve the deformable structure simultaneously. Here, inspired by the kirigami technology, a new paradigm to construct spoof plasmonic interconnects (SPIs) that support radiofrequency (RF) surface plasmonic transmission is proposed, together with high elasticity, strong robustness, and multifunction performance. Leveraging the strong field-confinement characteristic of spoof surface plasmons polaritons, the Type-I SPI opens its high-efficiency transmission band after stretching from a simply connected metallic surface. Meanwhile, the broadband transmission of the kirigami-based SPI exhibits strong robustness and excellent stability undergoing complex deformations, i.e., bending, twisting, and stretching. In addition, the prepared Type-II SPI consisting of 2 different subunit cells can achieve band-stop transmission characteristics, with its center frequency dynamically tunable by stretching the buckled structure. Experimental measurements verify the on-off switching performance in kirigami interconnects triggered by stretching. Overcoming the mechanical limitation of rigid structure with kirigami technology, the designer SPIs exhibit high stretchability through out-of-plane structure deformation. Such kirigami-based interconnects can improve the elastic functionality of wearable RF electronics and offer high compatibility to large body motion in future body network systems.

Hybridization of Localized Spoof Plasmonic Skyrmions and its Application in Micro‐Displacement Sensing

AbstractPlasmon hybridization plays a crucial role in subwavelength light control, offering remarkable field enhancement. However, engineering the resonance properties becomes increasingly challenging since the field enhancement generally makes the resonance more sensitive to geometric deformation. To this end, a shape‐immuned hybridization model with localized spoof plasmonic skyrmions in the platform of ultra‐compact spoof plasmonic dimer structures is proposed. Contrary to conventional wisdom, the revealed hybrid systems exhibit shape‐independent resonance properties thanks to the topological nature of localized spoof plasmonic skyrmions. On the other hand, the strong magnetic coupling between skyrmions results in the splitting of the skyrmion resonances into two new resonances (corresponding to bonding and antibonding skyrmions, respectively). The experimental results reflect that the frequency separation of bonding and antibonding skyrmions is extremely sensitive to the coupling distance of dimer structures (with a maximum sensitivity of up to 10.875 GHz mm−1). The findings not only complete the theory of skyrmion hybridization but also apply to novel multimode topological sensors that are compact and highly sensitive to micro‐displacement.

Highly confined terahertz spoof plasmon propagation in a parallel plate corrugated waveguide

Highly confined terahertz spoof plasmon propagation in a parallel plate corrugated waveguide

Tunable non-reciprocal waveguide using spoof plasmon polariton coupling to a gaseous magnetoplasmon.

We experimentally demonstrate non-reciprocal (one-way) waveguiding in a microstrip transmission line tailored to support the propagation of spoof plasmon polaritons. Time-reversal symmetry is broken by coupling the microstrip fields to a magnetized gaseous plasma discharge column thereby exciting non-reciprocal magnetoplasmons at the interface between the plasma and a surrounding quartz envelope. The magnetic bias introduces asymmetry in the dispersion of the surface plasmon polaritons at the gaseous plasma-dielectric interface, resulting in a breaking of the bidirectionality of the wave propagation in the microstrip. The isolation generated at conditions of modest magnetic bias is measured to be nearly 60 dB, and tunable by varying the plasma density through the voltage applied to the discharge. The advantage of using magnetized gaseous plasmas to produce this unidirectional waveguide structure is that it can be turned on or off at rates limited by the production and recombination of the plasma.

Optical-to-microwave frequency conversion with Rydberg excitons

A copper-based plasmonic system is presented to provide optical-to-microwave photon conversion. The process uses highly excited levels in ${\mathrm{Cu}}_{2}\mathrm{O}$ Rydberg excitons and takes advantage of spoof plasmons, which allow for significant enhancement of the transition probability between specific excitonic energy levels. The theoretical results are verified with numerical simulations. The proposed system is very flexible, allowing for emission of microwave wavelengths from 0.1 to 10 mm.

Miniaturized Spoof Plasmonic Antennas with Good Impedance Matching.

The ability of spoof surface plasmon polaritons (SSPPs) to confine electromagnetic fields in a subwavelength regime enables the design of miniaturized antennas. However, the impedance matching scheme for miniaturized spoof plasmonic antennas has not been studied systematically. In this paper, we propose a general method in the antenna design based on SSPPs, providing a feasible solution to impedance matching at the feeding point of miniaturized spoof plasmonic antennas. To verify the method, a prototype of a planar spoof plasmonic dipole antenna is simulated, fabricated and measured, of which the dipole arm length is reduced by 35.2% as compared with the traditional dipole antenna. A peak gain level of 4.29 dBi and the radiation efficiency of about 94.5% were measured at 6 GHz. This general method can be extended to solve the impedance matching problem in the design of other spoof plasmonic devices.

Highly enhanced trace amount terahertz fingerprint spectroscopy by multiplexing surface spoof plasmon metasurfaces in a single layer

Terahertz (THz) absorption spectroscopy has a large potential for molecular label-free fingerprinting. But it should overcome barriers to effectively measure the spectra of trace-amount analysis in a real application. The popular solution is enhancing the broadband spectral signals by localizing electromagnetic fields in dielectric metagrating or metasurfaces. In this paper, we numerically demonstrate a sensing scheme based on the geometry multiplexing of metal metasurfaces in one layer steel sheet with a series of spoof surface plasmon (SSP) sharp resonances. The SSP resonances are excited by normal THz incidents. The meta device is easy to manufacture and measure. The linked resonances peaks build an enhanced absorption spectrum. The envelope curve shows a substantial absorption enhancement factor of about 104 times for the 0.1μm lactose film sample in 0.46∼0.60 THz. The proposed method offers a flexible way for the wide terahertz spectra enhancement in trace-amount chemical, organic, or biomedical materials detection.

Miniaturized microwave microfluidic sensor based on quarter-mode 2.5-D spoof plasmons

This paper proposes a miniaturized microwave microfluidic sensor based on quarter-mode 2.5-D spoof localized surface plasmons for detecting liquid permittivity. An active amplification circuit is inherited to increase the resonance quality factor and thereby improve the sensor resolution. The sensor has a double-layer structure and uses microstrip feed. The quarter-mode structure is only one quarter of the full-mode case, and the liquid amount is reduced. The introduction of 2.5-D structure can further reduce the resonator size, improve the slow-wave effect and enhance the field confinement. A polydimethylsiloxane chip with a microfluidic channel is placed directly above the resonator. The injected liquid sample flowing through the channel would induce resonant frequency shift, thus achieving the ability of detecting the liquid permittivity. The prototype is manufactured using printed circuit board technology, and the measured sensor sensitivity for characterizing water reaches 0.16% on average, which is in general agreement with the simulated result. The proposed sensor can be expected to play an important role in biomedicine, environmental monitoring, food hygiene and other fields.

Nonmagnetic Spoof Plasmonic Isolator Based on Parametric Amplification (Laser Photonics Rev. 16(4)/2022)

Magnetic-Free Plasmonic Isolation A reconfigurable non-magnetic isolator based on parametric amplification is demonstrated experimentally on an ultrathin planar spoof plasmonic platform in article number 2100578. Xinxin Gao, Jingjing Zhang, and colleagues envision this work can establish a foundation for developing magnetic-free non-reciprocal devices suitable for on-chip integration with microwave circuits, with high potential to miniaturize existing communication and radar systems.

Resolved terahertz spectroscopy of tiny molecules employing tunable spoof plasmons in an otto prism configuration

Sensitive detection of terahertz fingerprint absorption spectrum for tiny molecules is essential for bioanalysis. However, it is extremely challenging for traditional terahertz spectroscopy measurement because of the weak spectral response caused by the large mismatch between terahertz wavelengths and biomolecular dimensions. Here, we proposed a wideband-tunable metal plasmonic terahertz biosensor to detect tiny biomolecules, employing attenuated total reflection in an Otto prism configuration and tightly confined spoof surface plasmons on the grooved metal surface. Benefitting from the plasmonic electric field enhancement, such a biosensor is able to identify the molecular terahertz fingerprints. As a proof of concept, a hypothetical molecule modeled by the Lorentz model with two vibrational modes is used as the sensing analytes. Simulation results show that the absorption of two vibrational modes of analytes can be selectively enhanced up to ten times by plasmonic resonance, and their fingerprints can be resolved by sweeping incident angle in a wide waveband. Our work provides an effective approach for the highly sensitive identification of molecular fingerprints in fields of biochemical sensing for tiny analytes.

Observation of localized magnetic plasmon skyrmions

Optical skyrmions have recently been constructed by tailoring vectorial near-field distributions through the interference of multiple surface plasmon polaritons, offering promising features for advanced information processing, transport and storage. Here, we provide experimental demonstration of electromagnetic skyrmions based on magnetic localized spoof plasmons (LSP) showing large topological robustness against continuous deformations, without stringent external interference conditions. By directly measuring the spatial profile of all three vectorial magnetic fields, we reveal multiple π-twist target skyrmion configurations mapped to multi-resonant near-equidistant LSP eigenmodes. The real-space skyrmion topology is robust against deformations of the meta-structure, demonstrating flexible skyrmionic textures for arbitrary shapes. The observed magnetic LSP skyrmions pave the way to ultra-compact and robust plasmonic devices, such as flexible sensors, wearable electronics and ultra-compact antennas.

Investigation of properties of surface modes at the boundary of the DNA origami lattice

In this study, the models for the DNA origami lattice will be investigated. Our aim is to theoretically explore the ways of constructing DNA origami. To achieve this goal the DNA origami structure, consisting of nanowires embedded in a host material, will be treated from the perspective of nanowire metamaterial. Surface plasmon polaritons propagating at the interface of air and DNA metamaterial are analyzed. The dispersion relation is attained using the transfer matrix technique and employing continuity conditions of electric fields and their derivatives at the boundary separating two regions. We have concluded that with numerous nanowires into the metamaterial unit, cell frequencies of surface plasmon polaritons are altered to higher frequencies. In this study, we have studied the effect of modifications of the metamaterial, allowing for the shift of the dispersion maps toward higher frequencies. It is possible to obtain the propagation of spoof plasmons mimicking the behavior of surface waves at lower frequencies. All the properties and parameters of the inorganic metamaterials are applicable to study the phenomenon of the organic substances.

Multipole resonance and Vernier effect in compact and flexible plasmonic structures

Spoof surface plasmons in corrugated metal surfaces allow tight field confinement and guiding even at low frequencies and are promising for compact microwave photonic devices. Here, we use metal-ink printing on flexible substrates to construct compact spoof plasmon resonators. We clearly observe multipole resonances in the microwave frequencies and demonstrate that they are still maintained even under significant bending. Moreover, by combining two resonators of slightly different sizes, we demonstrate spectral filtering via the Vernier effect. We selectively address a target higher-order resonance while suppressing the other modes. Finally, we investigate the index-sensing capability of printed plasmonic resonators. In the Vernier structure, we can control the resonance amplitude and frequency by adjusting a resonance overlap between two coupled resonators. The transmission amplitude can be maximized at a target refractive index, and this can provide more functionalities and increased design flexibility. The metal-ink printing of microwave photonic structures can be applied to various flexible devices. Therefore, we expect that the compact, flexible plasmonic structures demonstrated in this study may be useful for highly functional elements that can enable tight field confinement and manipulation.

The interplay between Fano and Fabry–Pérot resonances in dual-period metagratings

We study theoretically and numerically the occurrence of Fano resonances in a metagrating made of slits with some symmetry breaking resulting in a dual period. At low frequency, a grating composed of long enough slits supports Fabry–Pérot resonances on which Fano resonances superimpose when the grating acquires dual period. The resulting spectrum exhibits flat-banded peaks interrupted by sharp dips with successions of perfect and zero transmissions. To model these scattering properties, homogenization theory is used resulting in an effective problem governing the solutions in the two, non-identical, slits, which are coupled through jump conditions at the grating interfaces. These jumps efficiently encode the effect of the evanescent field able to resonate in the radiative region due to the folding of the spoof plasmon polaritons branches. The model is validated with direct numerics and a local analysis allows us to characterize the resonant mechanisms.

Acoustic spoof surface plasmon polaritons for filtering, isolation and sensing

We study a waveguide structure supporting acoustic spoof plasmon polaritons (aSSPPs) perturbed by a defect, whose specifically tailored geometry enables controllable transmission characterized by a uniform phase distribution and very steep narrowband response. The structure is analyzed using transmission-line theory and numerical simulations, providing evidence for its use in advanced filters, isolators and sensor technology. In order to demonstrate the applicability of the aSSPP waveguide with defect, two selective narrowband filter designs are discussed and explored. Furthermore, we propose an acoustic isolator that exploits steady fluid flow to break reciprocity and provide large isolation in a narrowband region. We also propose a sensor for liquid analytes, in which the grooves of the aSSPP waveguide serve as microfluidic channels, while the sensing principle is based on the spectral shift of the transmission peak for different mixtures of water and glycerol. The sensor shows a good sensitivity and fast response, with a potential for further development for applications in water quality monitoring.

Spoof plasmon polariton coupler based on the high‐order modes of reflective metasurface

AbstractDifferent from previous phase gradient metasurfaces, in this letter we show that the spoof plasmon polariton conversion is dominated by the high‐order surface wave modes rather than the pre‐defined linear phase distribution. The latter becomes invalid due to the coupling between different metallic unit cells of the metasurface. To demonstrate this point, a metasurface, which includes six different H‐shaped structures in a super cell, is designed based on the high‐order surface wave modes with a nonlinear reflective phase distribution. The simulated and measured results support the proposed theory, that is, the designed metasurface can convert x‐ and y‐polarized incident waves into spoof plasmon polariton at 8.9, 10.6, and 11.9 GHz. The metasurface not only verifies the mechanism of spoof plasmon polariton conversion, but also shows great potential in realizing cloaks, flat antennas, and so on.

Giant Microwave Spontaneous Emission Enhancements in Planar Aperture Waveguide Structures

AbstractMicrowave interactions are an invaluable tool for probing atomic states of matter and are currently being extensively explored for the development of scalable quantum computing. However, many of the available methods for spectroscopic analysis and photonic quantum manipulations are inaccessible for microwaves due to the weak spontaneous emission of quantum emitters. In this work, a mechanism for giant resonant enhancement of spontaneous emission from magnetic dipole emitters is suggested that employs a new phenomenon of near field impedance cancellation via magnetic flux confinement. Enhancements of at least 1011are theoretically shown for structures with 100 nm features, and much greater potential enhancements are predicted with this method. Subsequently, the realization of integrated systems with enhanced quantum emitters using microwave spoof plasmon waveguides is demonstrated. Taken together, these findings will pave the way for microwave quantum photonics and microwave hybrid quantum computing.

Klein scattering of spin-1 Dirac-Weyl wave and localized surface plasmon

Localized surface plasmon and Klein tunneling resonances are two phenomena that were previously thought to be unrelated, where the former plays an important role in subwavelength optics while the latter is fundamental to relativistic quantum mechanics and physics of Dirac materials. We develop a rigorous theory for spin-1 Dirac-Weyl particles, which establishes a striking analogy between the two phenomena and unveils a deep connection between the distinct physical contexts, paving the way for gate-controlled surface plasmon mimetic electronics as well as for realizing localized spoof plasmons in a scope wider than previously thought. A possible experimental scheme is articulated.