Polariton Modes Research Articles

Higher Light Extraction Efficiency in Organic Light-Emitting Devices by Employing 2D Periodic Corrugation.

Photons trapped in the form of waveguide (WG) modes associated with the organic–organic interface and in the form of surface plasmon polariton (SPP) modes associated with the metallic electrode–organic interface result in a large energy loss in organic light-emitting devices (OLEDs). Introducing gratings onto the metallic electrode is especially crucial for recovering the power lost to the associated SPP modes. In our research, we demonstrate the efficient outcoupling of SPP modes in TE mode by two-dimensional (2D) grating, which cannot excited in one-dimensional (1D) grating OLED. This causes a 62.5% increase in efficiency from 2D grating OLED than 1D grating OLED. The efficient outcoupling of the WG and SPP modes is verified by the numerical simulation of both the emission spectra and the field distribution.

Image polaritons in van der Waals crystals

Abstract Polaritonic modes in low-dimensional materials enable strong light–matter interactions and the manipulation of light on nanometer length scales. Very recently, a new class of polaritons has attracted considerable interest in nanophotonics: image polaritons in van der Waals crystals, manifesting when a polaritonic material is in close proximity to a highly conductive metal, so that the polaritonic mode couples with its mirror image. Image modes constitute an appealing nanophotonic platform, providing an unparalleled degree of optical field compression into nanometric volumes while exhibiting lower normalized propagation loss compared to conventional polariton modes in van der Waals crystals on nonmetallic substrates. Moreover, the ultra-compressed image modes provide access to the nonlocal regime of light–matter interaction. In this review, we systematically overview the young, yet rapidly growing, field of image polaritons. More specifically, we discuss the dispersion properties of image modes, showcase the diversity of the available polaritons in various van der Waals materials, and highlight experimental breakthroughs owing to the unique properties of image polaritons.

Spoof Surface Plasmon Polariton Endfire Antenna Possessing Bidirectional and Unidirectional Radiation Pattern

A simple approach is proposed to design a new type of endfire antenna, which simultaneously possesses bidirectional and unidirectional radiation pattern in wideband. By the dispersion engineering, different frequency bands spoof surface plasmon polariton (SPP) modes are excited at the two ports of a proposed splitter structure, and the two ports of the splitter structure are directly connected with two radiator structures, which are utilized to decouple the different frequency bands spoof SPP to free space wave by dispersion mismatching, achieving bidirectional and unidirectional radiation pattern in different frequency bands. From 8.4 to 21.6 GHz, this designed spoof SPP antenna possesses bidirectional endfire radiation pattern, and from 21.6 to 45.0 GHz, this designed spoof SPP antenna possesses unidirectional endfire radiation pattern. This designed spoof SPP antenna has an average gain over 10.6 dB in the whole working bandwidth, and the relative bandwidth of this antenna is 137%. Both the simulation and measurement results verify that the stable bidirectional and unidirectional radiation pattern of this proposed endfire spoof SPP antenna in wide bandwidth are achieved.

Mode Analyses of Subwavelength Periodic Metallic Structures With Finite Thickness

Deep-subwavelength periodic metallic structures, which are also called as plasmonic metamaterials, have received much attention due to their ability of supporting spoof surface plasmons polariton (SPP) modes. However, it is still difficult to obtain the dispersion relations of different modes for complicated plasmonic metamaterials with finite thickness. To solve the problem, we make further development of a field-network joint dispersion analysis method that was proposed recently, so that the method can be used to analyze the spoof SPP structures with certain thickness. The developed method not only allows us to predict the dispersion relations of complicated spoof SPP structures with finite thickness, but also can be used to find a series of intrinsic high-order modes of the periodic metallic structures. As an ex-ample, we present the theoretical dispersion curves of the fun-damental and high-order modes for a complicated spoof SPP structure, which have good agreements with the simulated re-sults. Meanwhile, the calculated near fields also match to the simulated and measured results well.

Exciton-polariton based WS<sub>2</sub> polarization modulator controlled by optical Stark beam

The recent era of fast optical manipulation and optical devices owe a lot to exciton-polaritons being lighter in mass, faster in speed and stronger in nonlinearity due to hybrid light-matter characteristics. The room temperature existence of polaritons in two dimensional materials opens up new avenues to the design and analysis of all optical devices and has gained the researchers attention. Here, spin-selective optical Stark effect is introduced to form a waveguide effect in uniform community of polaritons, and is used to realize polarization modulation of polaritons. The proposed device basically takes advantage of the spin-sensitive properties of optical Stark effect of polaritons inside the WS₂ microcavity so as to guide different modes and modulate polarization of polaritons. It is shown that polaritonic wavepacket of different mode profiles can be generated by changing intensity of the optical Stark beam and the polarization of polaritons can be controlled and changed periodically along the formed waveguide by introduction birefringence that is sensitive to polarization degree of the optical Stark beam.

Analysis of luminescence decay dynamics in metal-dielectric photonic structures with organic layers

Metal-dielectric photonic structures with organic materials 4,4-bis(N-carbazolyl)-1,1-biphenyl and 4,4'-bis[4-(di-ptolylamino)styryl]biphenyl) as light emitting layers were investigated. The formation of the polaritonic modes in the investigated structures was experimentally demonstrated and a correlation between theoretical and experimental dispersion was shown. Was shown, that increase in interaction between organic exciton and optical mode leads to a significant decrease in the lower polariton emission bandwidth. Keywords: light-emitting layers, exciton, luminescence.

Анализ динамики затухания люминесценции в металл-диэлектрических фотонных структурах с органическими слоями

Metal-dielectric photonic structures with organic materials 4,4-bis(N-carbazolyl)-1,1-biphenyl and 4,4′-bis[4-(di-ptolylamino)styryl] biphenyl) as light emitting layers were investigated. The formation of the polaritonic modes in the investigated structures was experimentally demonstrated and a correlation between theoretical and experimental dispersion was shown. Was shown, that increase in interaction between organic exciton and optical mode leads to a significant decrease in the lower polariton emission bandwidth.

Directional effects in plasmon excitation and transition radiation from an anisotropic 2D material induced by a fast charged particle.

We present a relativistic formulation of the energy loss of a charged particle traversing an anisotropic layer under arbitrary angle of incidence. We use a model for the conductivity tensor describing doped phosphorene, which supports plasmon polariton modes (PPMs) that exhibit a topological transition between elliptic and hyperbolic iso-frequency dispersion curves in the THz to the mid-infrared (MIR) frequency range. The total distribution of the momentum transfer and energy loss of the charged particle goes to excitation of the PPMs followed by their decay in phosphorene (Ohmic losses) and the energy that is emitted as transition radiation (TR). We show that the elliptic modes are efficiently excited in the THz range by relativistic particles, but the corresponding Ohmic distributions do not exhibit significant anisotropy. Contrastingly, hyperbolic modes are efficiently excited in the MIR range by slow particles moving under oblique incidence, producing Ohmic distributions that show strong directionality of propagation with large wavevectors associated with the asymptotes of the hyperbolic dispersion curves. The most dramatic effects of the anisotropic layer conductivity are seen in the angular spectra of the TR, with quite distinct and unexpected shapes of the radiation patterns emitted at the THz and MIR frequencies, even for a normal incidence of the charged particle. Those patterns are substantially skewed for oblique incidence, when they show a marked anisotropy relative to the principal axes of the layer. Such a rich variety of the TR spectra should be readily observable via angle-resolved measurements in a transmission electron microscope.

Поляритонный резонанс в автомодуляции асимметричного состояния сверхизлучающего лазера

Based on the numerical solution to the semiclassical Maxwell-Bloch equations in a one-dimensional model of a superradiant laser with a low-Q symmetric Fabry-Perot cavity, a comparative analysis of the spectrum of polariton modes of the linearized problem and the discrete spectrum of the of quasi-monochromatic generation with weak self-modulation under the condition of strong spontaneous mirror symmetry breaking of the counterpropagating electromagnetic waves, population inversion and polarization of an active medium is carried out. It is shown that the main frequencies of resonant self-modulation of a steady asymmetric superradiant phase state are close to the frequencies of polariton modes that are calculated in the linearized problem for the average level of the population inversion taken from the nonlinear problem and have small decay rates.

Surface Plasmon resonance implemented silver thin film PCF sensor with multiple – Hole microstructure for wide ranged refractive index detection

This paper aims to demonstrate the sensing of different materials based on their refractive indices. The Surface Plasmon Resonance(SPR) phenomenon shown by Photonic Crystal Fiber(PCF) is proving to be quite useful among the sensor markets and thus, it becomes really important to design a flexible and affordable sensor of this kind with high sensitivity. SPR based PCF sensor with plasmonic material, silver embedded on it has been designed with the implementation of the Finite element method. We have modeled SPR sensors with multiple air holes and silica is the background material. The basic principle of using the analyte is that it binds the immobile molecules of silver to its own molecules which get mobilized in presence of the incident light and finally cause the variation of the refractive index. When the refractive indices of the analyte are varied from 1.25 to 1.30, a range of variation in the loss curves is seen. The core and Surface Plasmon Polaritons modes are matched based on their phases and it is done by plotting the refractive indices of core and SPP modes against the wavelength in µm along with the confinement loss against wavelength. The sensor that is obtained is highly sensitive with a wavelength sensitivity of around 1932.09 RIU−1. The resolution of the sensor is 3 × 10-5 RIU. On comparison with the literature, it is found that the sensitivity of the sensor so achieved is highly suitable for the detection purposes in the field of pharmacy and this Ag-based photonic crystal fiber sensor proves to be a revolutionary sensor in the field of biosensors.

Low-Loss Ferrite Circulator as a Tunable Chiral Quantum System

Microwave circulators are usually treated as auxiliary, classical components in superconducting quantum computing. This study integrates the cavity-magnon polariton modes of a custom-built circulator with superconducting microwave cavities to implement a tunable nonreciprocal interaction. The apparatus is well described by a non-Hermitian Hamiltonian, yielding a theoretical framework to model other nonreciprocally coupled circuit elements on the same platform in the future. The experiment also showcases an experimental probe of the left and right eigenvectors associated with the non-Hermitian Hamiltonian.

Uniform Chiral Near‐Fields in Achiral Nanocavity Induced by Magnetic Polaritons Mode

AbstractChiral near‐fields are crucial in the analysis of chiral molecules, circularly polarized luminescence, and sensing. Under circularly polarized light illumination, left‐ and right‐handed chiral near‐fields occur around nanostructures. However, most previously reported works require structural chirality based on asymmetric 3D nanostructures. Usually, left‐ and right‐handed chiral near‐fields are difficult to separate in space, leading to low efficiency in applications. Here, achiral U‐shaped groove nanostructure arrays are proposed to generate uniform chiral near‐fields under circularly polarized light illumination. In contrast to vertical parallel plate nanostructures, a bottom layer is added below the two vertical parallel plates to design U‐shaped groove nanostructures that induce magnetic polaritons mode. In the cavity of the achiral U‐shaped groove nanostructure, chiral near‐field is induced by the excitation of electric and magnetic near‐fields with parallel components. These chiral near‐fields strongly depend on the structural parameters of the U‐shaped groove nanostructure. In addition, chiral molecules are introduced into the cavity of the U‐shaped groove nanostructure to utilize it as sensors for chiral molecular detection. Numerical results show that the circular dichroism of the molecules is enhanced remarkably. These findings pave the way toward the development of practical and scalable platforms for new chiroptical applications.

Material–structure integrated design for ultra-broadband all-dielectric metamaterial absorber

Material and structure are the essential elements of all-dielectric metamaterials. Structure design for specific dielectric materials has been studied while the contribution of material and synergistic effect of material and structure have been overlooked in the past years. Herein, we propose a material–structure integrated design (MSID) methodology for all-dielectric metamaterials, increasing the degree of freedom in the metamaterial design, to comprehensively optimize microwave absorption performance and further investigate the contribution of material and structure to absorption. A dielectric metamaterial absorber with an ultra-broadband absorption from 5.3 to 18.0 GHz is realized. Theoretical calculation and numerical simulation demonstrate that the symphony of material and structure excites multiple resonance modes encompassing quarter-wavelength interference cancellation, spoof surface plasmon polariton mode, dielectric resonance mode and grating mode, which is essential to afford the desirable absorption performance. This work highlights the superiority of coupling of material and structure and provides an effective design and optimization strategy for all-dielectric metamaterial absorbers.

Collective Phonon-Polaritonic Modes in Silicon Carbide Subarrays.

Localized surface phonon polaritons (LSPhPs) can be implemented to engineer light-matter interactions through nanoscale patterning for a range of midinfrared application spaces. However, the polar material systems studied to date have mainly focused on simple designs featuring a single element in the periodic unit cell. Increasing the complexity of the unit cell can serve to modify the resonant near-fields and intra- and inter-unit-cell coupling as well as to dictate spectral tuning in the far-field. In this work, we exploit more complicated unit-cell structures to realize LSPhP modes with additional degrees of design freedom, which are largely unexplored. Collectively excited LSPhP modes with distinctly symmetric and antisymmetric near-fields are supported in these subarray designs, which are based on nanopillars that are scaled by the number of subarray elements to ensure a constant unit-cell size. Moreover, we observe an anomalous mode-matching of the collective symmetric mode in our fabricated subarrays that is robust to changing numbers of pillars within the subarrays as well as to defects intentionally introduced in the form of missing pillars. This work therefore illustrates the hierarchical design of tailored LSPhP resonances and modal near-field profiles simultaneously for a variety of IR applications such as surface-enhanced spectroscopies and biochemical sensing.

Reservoir optics with exciton-polariton condensates

We investigate an all-optical microscale planar lensing technique based on coherent fluids of semiconductor cavity exciton-polariton condensates. Our theoretical analysis underpins the potential in using state-of-the-art spatial light modulation of nonresonant excitation beams to guide and focus polariton condensates away from their pumping region. The nonresonant excitation profile generates an excitonic reservoir that blueshifts the polariton mode and provides gain, which can be spatially tailored into lens shapes at the microscale to refract condensate waves. We propose several different avenues in controlling the condensate fluid, and demonstrate formation of highly enhanced and localized condensates away from the pumped reservoirs. This opens new perspectives in guiding quantum fluids of light and generating polariton condensates that are removed from detrimental reservoir dephasing effects.

Highly sensitive plasmonic nanorod hyperbolic metamaterial biosensor

Plasmonic sensing based on nanostructures is a powerful analytical tool for ultrasensitive label-free biomolecule detection that holds great potential in the field of clinical diagnostics and biomedical research. Here, we report the fabrication, the characterization, and the principle of operation of gold nanorod hyperbolic metamaterials (NHMMs) along with ultrasensitive bulk refractive index and label-free biomolecular detection. By combining electron-beam lithography and nanoscale electroplating, we demonstrate the fabrication of a highly ordered, height-controllable, and vertical array of nanorods. By exciting the bulk plasmon–polariton mode in the NHMM using a prism-coupling technique and integrating the sensor in microfluidics, we demonstrate that the bulk sensitivity and figure of merit of our device could reach 41,600 nm/RIU and 416 RIU-1, respectively. The physical mechanism of this high bulk sensitivity is revealed through theoretical and experimental studies. Moreover, by bio-functionalizing the surface of the NHMM sensor, monitoring the binding of streptavidin at dilute concentrations is performed in real time. We test different concentrations of streptavidin ranging from 200 to 5 µg/mL, and the NHMM biosensor exhibits a 1 nm wavelength shift for a 5 µg/mL streptavidin detection. By fitting the Hill equation of the NHMM biosensor and taking into account the level of noise (0.05 nm) as the minimum wavelength shift of the detectable limit, the limit of detection of the NHMM biosensor to streptavidin can be estimated to be 0.14 µg/mL (2.4 nm). As a direct comparison, a 0.5 nm wavelength shift for 20 µg/mL of streptavidin is reported when using a conventional gold film sensor under identical experimental conditions. The developed plasmonic NHMM sensor shows tremendous potential for highly sensitive bulk solutions and biomolecule detection and provides a promising avenue for free-label biosensing applications in the future.

Snapshot Angle-Resolved Spectroscopy and Its Application for Study of Highly Efficient Polariton OLEDs

The multifunctional snapshot angle-resolved spectroscopy (ARS) system capable of electroluminescence, photoluminescence, and reflectance measurements for thin film devices is developed based on the k-space imaging technique. Compared with the conventional goniometric ARS system, this snapshot spectroscopy system offers great advantages of rapid and simple measurement, suitable for characterizing thin film devices that are unstable or degraded under long-time or high-power driving conditions, such as OLEDs. We perform a detailed calibration of the snapshot system and show that the measured results closely match with those obtained using a goniometric system. Furthermore, we show the capabilities of the system with application in studying polariton OLEDs. The result provides comprehensive information on the polariton mode dispersion and emission distribution, and shows an effective radiative pumping of the lower polariton branch for high emission efficiency.

Phonon signatures in spectra of exciton polaritons in transition metal dichalcogenides

Embedding a monolayer of a transition metal dichalcogenide in a high-$Q$ optical cavity results in the formation of distinct exciton polariton modes. The polaritons are affected by the strong exciton-phonon interaction in the monolayer. We use a time convolutionless master equation to calculate the phonon influence on the spectra of the polaritons. We discuss the nontrivial dependence of the line shapes of both branches on temperature and detuning. The peculiar polariton dispersion relation results in a linewidth of the lower polariton being largely independent of the coupling to acoustic phonons. For the upper polariton, acoustic phonons lead to a low-energy shoulder of the resonance in the linear response. Furthermore, we analyze the influence of inhomogeneous broadening being the dominant contribution to the lower polariton linewidth at low temperatures. Our results point towards interesting phonon features in polariton spectra in transition metal dichalcogenides.

Coherence Between Different Propagating Surface Plasmon Polariton Modes Excited by Quantum Mechanical Tunnel Junctions

AbstractCoherence between different surface plasmon polariton (SPP) modes excited by inelastically tunneling electrons in biased metal–insulator–metal tunnel junctions (MIM‐TJs) is demonstrated. By employing a dedicated SPP stripe waveguide with MIM‐TJ, an effective double‐slit configuration similar to the Young's experiment is realized for an electrically biased SPP source. The spatial correlation between different SPP modes originates from a single inelastic tunneling event and leads to strong interference in the far‐field, observed as alternate bright and dark fringes in the Fourier plane. The measured fringe‐spacing inversely follows the stripe waveguide length, with upper limit dictated by the SPP propagation length, confirming the SPP mediated spatial correlation. Finite difference time domain simulations support the experimental findings. Also, the experimental and simulation results unambiguously demonstrate the two‐step plasmonic decay process in plasmonic MIM‐TJs. The results presented here provide a simple and robust demonstration of the inherent coherence existing between different decay channels (plasmons and photons) of the inelastically tunneling electrons and can be exploited for plasmonic applications with tailored spatial coherence with implications in plasmon amplification and quantum information processing.

Application of Tamm Plasmon Polaritons and Cavity Modes for Biosensing in the Combined Spectroscopic Ellipsometry and Quartz Crystal Microbalance Method.

Low-cost 1D plasmonic photonic structures supporting Tamm plasmon polaritons and cavity modes were employed for optical signal enhancement, modifying the commercially available quartz crystal microbalance with dissipation (QCM-D) sensor chip in a combinatorial spectroscopic ellipsometry and quartz microbalance method. The Tamm plasmon optical state and cavity mode (CM) for the modified mQCM-D sample obtained sensitivity of ellipsometric parameters to RIU of ΨTPP = 126.78 RIU−1 and ΔTPP = 325 RIU−1, and ΨCM = 264 RIU−1 and ΔCM = 645 RIU−1, respectively. This study shows that Tamm plasmon and cavity modes exhibit about 23 and 49 times better performance of ellipsometric parameters, respectively, for refractive index sensing than standard spectroscopic ellipsometry on a QCM-D sensor chip. It should be noted that for the optical biosensing signal readout, the sensitivity of Tamm plasmon polaritons and cavity modes are comparable with and higher than the standard QCM-D sensor chip. The different origin of Tamm plasmon polaritons (TPP) and cavity mode (CM) provides further advances and can determine whether the surface (TPP) or bulk process (CM) is dominating. The dispersion relation feature of TPP, namely the direct excitation without an additional coupler, allows the possibility to enhance the optical signal on the sensing surface. To the best of our knowledge, this is the first study and application of the TPP and CM in the combinatorial SE-QCM-D method for the enhanced readout of ellipsometric parameters.