Propagation Of Polaritons Research Articles

Near-isotropic polariton heat transport along a polar anisotropic nanofilm

SummaryThe heat transport of surface phonon-polaritons propagating along a polar uniaxial anisotropic nanofilm is studied for different orientations of its optical axis, film thicknesses, and temperatures. For an hBN nanofilm, it is shown that i) the propagation of polaritons can be described in terms of even and odd modes that generalize the transverse magnetic and transverse electrical ones that typically appear in isotropic films. ii) The frequency spectrum of polaritons can efficiently be tuned with the angle between the film optical axis and their propagation direction. iii) The polariton thermal conductivity takes higher values for a thinner or hotter nanofilm. iv) The even and odd modes have a remarkable contribution to the total polariton thermal conductivity, which takes a value higher than 5.6 Wm−1K−1 for a 25-nm-thick nanofilm at 500 K. The obtained results thus uncover some key features of the propagation and heat transport of polaritons in uniaxial nanofilms.

Tuning polaritons in van der Waals moiré superlattices with interlayer spacing

We theoretically study the interference and propagation of phonon polaritons in hexagonal boron nitride (hBN) in van der Waals heterostructures composed of hBN and twisted bilayer graphene (TBG) with different interlayer spacing in TBG. We show that varying the interlayer spacing and, hence, the interlayer coupling strength results in dramatic modifications of the local optical conductivity at the domain walls (DWs) in TBG, which leads to significant changes in the polariton interference profile near DWs. Moreover, our simulation reveals that the two-dimensional near-field interference pattern generated by polariton propagation in hBN/TBG heterostructures can be dramatically changed by interlayer spacing and the superlattice period. Our study demonstrates that combining interlayer spacing modification with moiré superlattices is a valuable route to control light at the nanoscale and design nanophotonic devices with tunable functionalities.

Multi-band propagation of spoof surface plasmon polaritons by its high-order modes

Compact dual-band and tri-band bandpass filters (BPFs) based on high-order modes of spoof surface plasmon polaritons (SSPPs) are proposed. By using the meander line technique, the electrical size of the proposed SSPP structure was reduced by 68% compared with the traditional rectangular-grating SSPP structure. The high-efficiency passbands are excited by high-order modes of SSPPs. Therefore, dual-band and tri-band BPFs are designed by using two and three high-order modes of SSPPs, respectively. In addition, a notched band is obtained by loading three complementary split-ring resonators (CSRRs) on the bottom layer of the tri-band BPF. Thus, a quad-band BPF is achieved.

On the Study of Advanced Nanostructured Semiconductor-Based Metamaterial

Tunable metamaterials belonging to the class of different reconfigurable optical devices have proved to be an excellent candidate for dynamic and efficient light control. However, due to the consistent optical response of metals, there are some limitations aiming to directly engineer electromagnetic resonances of widespread metal-based composites. The former is accomplished by altering the features or structures of substrates around the resonant unit cells only. In this regard, the adjusting of metallic composites has considerably weak performance. Herein, we make a step forward by providing deep insight into a direct tuning approach for semiconductor-based composites. The resonance behavior of their properties can be dramatically affected by manipulating the distribution of free carriers in unit cells under an applied voltage. The mentioned approach has been demonstrated in the case of semiconductor metamaterials by comparing the enhanced propagation of surface plasmon polaritons with a conventional semiconductor/air case. Theoretically, the presented approach provides a fertile ground to simplify the configuration of engineerable composites and provides a fertile ground for applications in ultrathin, linearly tunable, and on-chip integrated optical components. These include reconfigurable ultrathin lenses, nanoscale spatial light modulators, and optical cavities with switchable resonance modes.

Observation of the Wannier-Stark ladder in plasmonic waveguide arrays.

Evanescently coupled waveguides are a powerful platform to study and visualize the wave dynamics in tight-binding systems. Here, we investigate the propagation of surface plasmon polaritons in arrays of dielectric loaded surface plasmon polariton waveguides with a propagation constant gradient acting as an effective external potential. Using leakage radiation microscopy, we observe in real-space for single site excitation a periodic breathing of the wave packet and an oscillatory motion in the case of Gaussian excitation of multiple waveguides. The corresponding momentum-resolved spectra are composed of sets of equally spaced modes. We interpret these observations as the plasmonic analogs of Bloch oscillations and the Wannier-Stark ladder, respectively.

Nonscattering Photodetection in the Propagation of Unidirectional Surface Plasmon Polaritons Embedded with Graphene.

Recently, nanoscale light manipulation using surface plasmon polaritons (SPPs) has received considerable research attention. The conventional method of detecting SPPs is through light scattering or using bulky Si or Ge photodetectors. However, these bulky systems limit the application of nanophotonic circuits. In this study, the light-matter interaction between graphene and SPP was investigated. For realizing an improved integration in nanocircuits, single-layer graphene was added to asymmetric SPP nanoantenna arrays for nonscattering detection in the near field. The developed device is capable of detecting the controlled propagation of SPPs with a photoresponsivity of 15 mA/W, which paves the way for the new-generation on-chip optical communication.

Artificial Anisotropy in Ge2Sb2Te5 Thin Films after Femtosecond Laser Irradiation.

Ge2Sb2Te5 (GST225) looks to be a promising material for rewritable memory devices due to its relatively easy processing and high optical and electrophysical contrast for the crystalline and amorphous phases. In the present work, we combined the possibilities of crystallization and anisotropic structures fabrication using femtosecond laser treatment at the 1250 nm wavelength of 200 nm thin amorphous GST225 films on silicon oxide/silicon substrates. A raster treatment mode and photoexcited surface plasmon polariton generation allowed us to produce mutually orthogonal periodic structures, such as scanline tracks (the period is 120 ± 10 μm) and laser-induced gratings (the period is 1100 ± 50 nm), respectively. Alternating crystalline and amorphous phases at the irradiated surfaces were revealed according to Raman spectroscopy and optical microscopy studies for both types of structures. Such periodic modulation leads to artificial optical and electrophysical anisotropy. Reflectance spectra in the near infrared range differ for various polarizations of probing light, and this mainly results from the presence of laser-induced periodic surface structures. On the other hand, the scanline tracks cause strong conductivity anisotropy for dc measurements in the temperature range of 200–400 K. The obtained results are promising for designing new GST225-based memory devices in which anisotropy may promote increasing the information recording density.

A metamaterial sensor for detecting the location of a sub-wavelength object

A metamaterial sensor is proposed to detect the random location of a sub-wavelength metallic object. The sensor is composed of a transmission line (TL), which supports the propagation of spoof surface plasmon polaritons (SSPPs) with localized electromagnetic (EM) field, and a complementary spiral resonator (CSR) that resonates strongly at designed frequencies around 0.9 and 2.7 GHz. Based on the shift of the resonance frequencies, this sensor is able to detect the location of a sub-wavelength metallic object (whose diameter is smaller than 0.6 mm) randomly attached to the CSR. A prototype of the sensor is fabricated and tested. In practice, the CSR is excited through the EM coupling of the SSPP TL, and the location of the metallic object is obtained through the transmission coefficient (S21). To improve the accuracy, a retrieval curve for locating is generated and calibrated. It is proved that the random location of the sub-wavelength object can be accurately detected inside an area of 9π mm2 with a low error of 2‰.

Propagation length enhancement of surface plasmon polaritons in ultrafine Au nanodisk array, the role of kinky breather and periodic lump

We deal with a non-radiative approach to investigate the propagation of Surface Plasmon Polaritons (SPPs) in an Au nanodisk array in touch with an analyte medium. We obtain a nonlinear equation with solutions as in the form of kinky breather and periodic lump. The nonlinear response depends on the dielectric constant and wavenumber variation in analyte zone. It is shown that the periodic feature can guarantee the enhanced propagation length of SPPs stationary modes. Analytical results also reveal the occurrence of Fano resonance while numerical results show that the propagation length can go beyond 56 μm. On the other hand, using Kretschmann-Raether approach, we reach the Fano resonance in consequence of the interaction of dark and bright plasmon modes which is in agreement with our model and interpretation. Our nonlinear model can give a sketch for SPPs propagation especially in bio-sensing application.

Novel ELC-like and Z-shaped plasmonic waveguides to reach ultra-strong field confinements

In this paper, two novel waveguides with ELC like-shaped and Z-shaped grooves have been proposed to achieve highly efficient and strongly confined spoof surface plasmon polaritons (SSPPs) propagation. Low-dispersion bands can be realized by such structures with tight field confinement of SSPPs, resulting in size miniaturization of the proposed waveguides. Specifically, our method yields deep physical insight into the effect that the geometrically induced modifications of the supporting structure has on the dispersion properties and field confinement capabilities of SSPPs. In comparison, SSPP waveguide results presented in Aziz (2021 Results Opt. 5 100116) are given which is regarded to have stronger SSPPs field confinement as compared to previously reported different grooves shapes based SSPP waveguides. It is found that the dispersion and waveguide propagation characteristics can be directly manipulated by varying the geometrical parameters of the horizontal and slanted slits of Z-shaped and ELC-like shaped plasmonic waveguides without increasing the lateral dimension of the waveguides. Based on this waveguiding scheme, the proposed waveguides exhibit much lower asymptotic frequency of the dispersion relation and even tighter SSPPs field confinement than I-shaped plasmonic waveguide. Then, broadband transitions with a tapered metallic strip and an array of graded height ELC-like and Z-shaped units with good impedance matching and high mode conversion efficiency are designed. Fully controlled field enhancement functionality has been performed, by using such metamaterial particles in the form of grooves, decorated in SSPP waveguide. Simulated results have demonstrated that the proposed SSPP waveguides have much stronger field confinement than the highly efficient I-shaped grooves based SSPP waveguide. The proposed waveguides can be a significant contribution towards the advancement of plasmonic functional devices and integrated circuits in microwave frequencies.

Imaging Anisotropic Waveguide Exciton Polaritons in Tin Sulfide.

In recent years, novel materials supporting in-plane anisotropic polaritons have attracted a great deal of research interest due to their capability of shaping nanoscale field distributions and controlling nanophotonic energy flows. Here we report a nano-optical imaging study of waveguide exciton polaritons (EPs) in tin sulfide (SnS) in the near-infrared (near-IR) region using scattering-type scanning near-field optical microscopy (s-SNOM). With s-SNOM, we mapped in real space the propagative EPs in SnS, which show sensitive dependence on the excitation energy and sample thickness. Moreover, we found that both the polariton wavelength and propagation length are anisotropic in the sample plane. In particular, in a narrow spectral range from 1.32 to 1.44 eV, the EPs demonstrate quasi-one-dimensional propagation, which is rarely seen in natural polaritonic materials. A further analysis indicates that the observed polariton anisotropy originates from the different optical band gaps and exciton binding energies along the two principal crystal axes of SnS.

Propagation of surface plasmon polaritons at the interface of metal-free metamaterial with anisotropic semiconductor inclusions

Herein, we deal with the propagation of surface plasmon polaritons at the interface of metal-free metamaterial with anisotropic inclusions. The anisotropy effect of conventional and well-known nanostructured metamaterial combined of alternating layers is enhanced by employing anisotropic semiconductor sheets into the structure. The former provides a fertile ground for a wide range of tunability features with no needs of changing the geometry of the structure. Moreover, the current approach stands for as a perfect tool aiming to control propagation length of surface plasmon polaritons.

Compact transition enabled broadband propagation of spoof surface plasmon polaritons based on the equivalent circuit model

In this paper, a strategy to develop a compact transition of the spoof surface plasmon polariton (SSPP) transmission line (TL) is proposed. First, an equivalent distributed circuit model is employed for the theoretical analysis and optimization design of the SSPP unit. The mapping relation between the unit performance and the geometric parameters is deduced from the transmission matrix. The calculated results are compared with the numerical ones from the three-dimensional (3D) simulations for validation. Then, a compact transition (only 0.26λ g) is built with only two matching units and a tapered strip through optimizations. The optimizations are implemented with the circuit simulations based on the equivalent model, which can remarkably save time in comparison with the 3D simulations. The transition principle is also explained by quantitatively extracting the dispersion properties and impedance characteristics. Finally, a prototype of the proposed SSPP TL is fabricated and measured for demonstration. The measured operating band (0–7.7 GHz) is almost up to the cut-off frequency (about 8 GHz), which remains the inherent broadband low-pass transmission characteristics. Meanwhile, the measured in-band return loss is almost higher than 10 dB, which verifies the high-efficiency propagation. This work can pave the way for building up a new SSPP-based framework of microwave circuits.

Role of quantum-coherence dressed states on the Fresnel–Fizeau drag and optical properties of surface plasmon polaritons through asymmetric double quantum dot-metallic plasmonic interfaces

Owing to the exceptional structural-design flexibility and tunability of physical properties of quantum dots, the manipulation of light in view of surface plasmons via dots–based hybrid nanostructures and dots-metallic interfaces finds promising device applications. Hereby, we first demonstrate theoretically the role of intense laser-excited dressed states on the light propagation, optical properties, and lateral and rotary drag of surface plasmon polaritons (SPPs), via plasmon-assisted induced transparency (PIT). For this, we employed a scheme of plasmonic interface comprising an asymmetric double quantum dot molecule GaAs/AlGaAs in the Λ − type configuration embedded in gold metallic surface. In particular, using density-matrix formulation, we present a detailed analytical solution of the quantum dot system for the required eigenvalues in view of the dressed eigenstates. The dressed states played a vital role in the formation of PIT transparency and hence the manipulation of SPPs propagation, optical properties and SPPs drag, via quantum interference. The calculated theoretical results on the optical properties such as absorption and dispersion spectrum, group index, group velocity, group delay, phase delay, wave vector, propagation length and SPPs drag are further elaborated with aid of numerical simulation. The maximum calculated lateral and rotary SPPs drag was of order ± 6.0 × 10−8 m or rad, respectively. The value of SPPs propagation lengths calculated along and perpendicular to the dot-metallic interface are 3.3 × 10−7 m and 2.0 × 10−9 m, respectively.

THz pulse train generation through ultrafast development of surface plasmon-polariton modulation instability

Propagation of high-intensity electromagnetic waves in a waveguide structure could initiate nonlinear effects resulting in drastic changes of their spatial and temporal characteristics. We study the modulation instability effect induced by propagation of surface plasmon polaritons in a silver thin-film waveguide. The nonlinear Schrodinger equation for propagating surface plasmon wave is obtained. It is shown numerically that the modulation instability effect can give rise to ultrafast spatial redistribution and longitudinal localization of surface plasmon-polariton wave energy in subwavelength scale. The dependence of plasmon wave dispersion and nonlinear characteristics on metal film thickness is considered. We demonstrate that the use of films with the thickness varying along the waveguide length allows reduction of the generated pulse width and increase of frequency comb bandwidth. The proposed technique is promising for design of ultra-compact (tens of nm) optical generators delivering pulse trains with the repetition rate higher than 1 THz.

Negative refraction in twisted hyperbolic metasurfaces

Abstract Hyperbolic metasurfaces with unique dispersion properties can manipulate light–matter interactions according to the demands. However, due to their inherent physical properties, topological transitions (flat bands) exist only in the orthogonal directions, which greatly limit their application. Here, we unveil rich dispersion engineering and topological transitions in hyperbolic metasurfaces. Based on the effective medium theory, the rotation matrix is introduced into the dispersion relation to explain the distorted energy band diagrams, iso-frequency contours and higher-order multi-dipoles of the novel twisted metasurfaces, thereby forming multi-directional topological transitions and surface plasmon polariton propagation. Furthermore, we develop an integrated model to realize new dual-channel negative refraction and nondiffraction negative refraction. The phenomena observed in the experiments match well with the simulations, which proves that the designed metasurfaces make new types of negative refraction possible and will help to overcome the diffraction limit. The hyperbolic metasurfaces presented here exhibit exceptional capabilities for designing microscopes with a super lens at the molecular level, concealment of military aircraft, invisibility cloaks and other photonic devices with higher transmission efficiency.

Quantum of thermal conductance of nanofilms due to surface-phonon polaritons

Based on the Boltzmann transport equation, we demonstrate that the thermal conductance per unit width of a sufficiently thin polar nanofilm supporting the propagation of surface-phonon polaritons along its surfaces is independent of the material properties and is given by $12z(3){k}_{B}^{3}{T}^{2}/c{h}^{2}$, where ${k}_{B}$ and $h$ are the respective Boltzmann and Planck constants, while $c$ is the light speed in vacuum, $T$ is the temperature, and $z(3)$ is the Riemann zeta function. The huge propagation length of these energy carriers establishes that this quantization holds not only for temperatures much smaller than 1 K, as is the case of electrons and phonons, but also for those comparable to room temperature, which can significantly facilitate its observation and implementation in the thermal management of nanoscale electronics and photonics.

All-optical switching based on interacting exciton polaritons in self-assembled perovskite microwires.

Ultrafast all-optical switches and integrated circuits call for giant optical nonlinearity to minimize energy consumption and footprint. Exciton polaritons underpin intrinsic strong nonlinear interactions and high-speed propagation in solids, thus affording an intriguing platform for all-optical devices. However, semiconductors sustaining stable exciton polaritons at room temperature usually exhibit restricted nonlinearity and/or propagation properties. Delocalized and strongly interacting Wannier-Mott excitons in metal halide perovskites highlight their advantages in integrated nonlinear optical devices. Here, we report all-optical switching by using propagating and strongly interacting exciton-polariton fluids in self-assembled CsPbBr3 microwires. Strong polariton-polariton interactions and extended polariton fluids with a propagation length of around 25 μm have been reached. All-optical switching on/off of polariton propagation can be realized in picosecond time scale by locally blue-shifting the dispersion with interacting polaritons. The all-optical switching, together with the scalable self-assembly method, highlights promising applications of solution-processed perovskites toward integrated photonics operating in strong coupling regime.

Nonlinear TMOKE enhancement in 1D Au/Py magnetoplasmonic crystals

Resonant optical properties of the magnetoplasmonic crystals, which support propagation of surface plasmon polaritons (SPPs) accompanied by magnetooptical effects, have found success in magnetic field driven control of optical radiation. In this work we investigate the resonant magnetooptical effects in the second harmonic generation in the magnetoplasmonic crystal formed by gold/pemalloy bifilm covering dielectric grating. Strong transverse magnetooptical Kerr with the contrast up to 30% is revealed in the spectral vicinity of the SPP excitation.

Fabrication of Bloch Long Range Surface Plasmon Waveguides Integrating Counter Electrodes and Microfluidic Channels for Multimodal Biosensing

We report the fabrication of a novel multimodal biosensor combining plasmonic and electrochemical detection. The plasmonic sensors are based on monitoring the propagation of Bloch long-range surface plasmon polaritons (LRSPPs) along thin narrow Au stripes, integrating grating couplers as input/output means. The electrochemical sensors use the same Au stripes as working electrodes with nearby Pt stripes integrated on-chip as counter electrodes. The structures are fabricated on a truncated 1D photonic crystal comprised of a 15-period stack of alternating layers of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> . The Au and Pt stripes are fabricated using bilayer lift-off photolithography, and the gratings are fabricated using e-beam lithography. The structures are arranged into arrays targeting multichannel biosensing. The wafer is covered with CYTOP as the upper cladding with etched microfluidic channels providing access to the sensing surfaces and is wafer-bonded to a Borofloat silica wafer to encapsulate the fluidic channels and enable edge (in-plane) fluidic interfacing. The wavelength response of the grating-coupled plasmonic waveguide sensors is presented along with surface sensing results. Cyclic voltammetry measurements using the Au and Pt stripes as the working and counter electrodes are also presented. [2021-0103]