Propagation Of Surface Plasmon Polaritons Research Articles

Surface plasmon polaritons in strained Weyl semimetals

Surface plasmon polaritons in a strained slab of a Weyl semimetal with broken time-reversal symmetry are investigated. It is found that the strain-induced axial gauge field reduces frequencies of these collective modes for intermediate values of the wave vector. Depending on the relative orientation of the separation of Weyl nodes in momentum space, the surface normal, and the direction of propagation, the dispersion relation of surface plasmon polaritons could be nonreciprocal even in a thin slab. In addition, strain-induced axial gauge fields can significantly affect the localization properties of the collective modes. These effects allow for an in situ control of the propagation of surface plasmon polaritons in Weyl semimetals and might be useful for creating nonreciprocal devices.

Optically induced crossover from weak to strong coupling regime between surface plasmon polaritons and photochromic molecules.

We demonstrate optically induced crossover from a weak to a strong coupling regime in a single photonic system consisting of propagating surface plasmon polaritons (SPPs) on a planar silver film and ultraviolet (UV)-switchable photochromic molecules. A gradual increase is observed in the vacuum Rabi splitting upon increasing UV exposure, along with intriguing behavior, where the reflectivity initially decreases due to increased losses at the weak coupling regime, and then increases due to the emergence of strongly coupled modes and the associated band gap formation at the resonance frequency of the uncoupled states. This work explicitly demonstrates the optical tunability of the degree of hybridization of the SPP and exciton modes, spanning the range from weak to intermediate and finally to the strong coupling regime.

One-Dimensional Plasmonic Sensors

Recent advances in surface plasmon sensors have significantly reduced the limitations of conventional optical sensors. With the recent development of micro- and nano-fabrication technology, miniaturized one-dimensional structures become a promising platform for surface plasmon sensors for its compactness and simple structure. In this review, we describe the generation of surface plasmon polaritons and the resonance conditions. Then we categorize surface plasmon sensors by the physical quantities they detect, elaborating their working principle, performance, and current development. Finally, we summarize both limitations and advances of various design methods to provide an outlook on future directions of this field.

Graphene-based plasmonic electro-optical SR flip-flop with an ultra-compact footprint.

In this paper, we present a new concept of electro-optical plasmonic Set-Reset flip-flops at mid-infrared frequencies. We use the 3D finite-difference time-domain (FDTD) method to simulate and evaluate our designed flip-flop. In the proposed structure, the propagation of surface plasmon polaritons is controlled by applying an electrostatic field and the switching actions occur in the electrical domain while the output signal is in the form of light. The energy consumed by each switch is 2.5 fJ/bit. In this flip-flop, the no-change state of the flip-flop is realized by using a Bias port. The time response diagram indicates that the minimum extinction ratio of the flip-flop is 14.61 dB. The probability of various errors in the flip-flop state occurring due to the lack of synchronization between the switches is also considered by the FDTD simulations and it is shown that the device has a great performance against errors. Furthermore, the structure has an ultra-compact footprint of 1.62 µm2. Our surveys show that no plasmonic flip-flop has been reported to date.

Chip‐Compatible Quantum Plasmonic Launcher

AbstractIntegrated on‐demand single‐photon sources are critical for the implementation of photonic quantum information processing systems. To enable practical quantum photonic devices, the emission rates of solid‐state quantum emitters need to be substantially enhanced and the emitted signal must be directly coupled to an on‐chip circuitry. The photon emission rate speed‐up is best achieved via coupling to plasmonic antennas, while on‐chip integration can be realized by directly coupling emitters to photonic waveguides. The realization of practical devices requires that both the emission speed‐up and efficient out‐coupling are achieved in a single architecture. Here, a novel architecture is proposed that combines chip compatibility with high radiative emission rates—a quantum plasmonic launcher. The proposed launchers contain single nitrogen‐vacancy (NV) centers in nanodiamonds as quantum emitters that offer record‐high average fluorescence lifetime shortening factors of about 7000 times. Nanodiamonds with single NVs are sandwiched between two silver films that couple more than half of the emission into in‐plane propagating surface plasmon polaritons. This simple, compact, and scalable architecture represents a crucial step toward the practical realization of high‐speed on‐chip quantum networks.

Efficient propagation of spoof surface plasmon polaritons supported by substrate integrated waveguide with bandpass features

This paper presents an effective strategy that enables the efficient propagation of spoof surface plasmon polaritons (SSPPs) based on substrate integrated waveguides (SIWs). The dispersion property of SSPPs supported by a SIW-based unit cell is firstly analyzed and compared with that of traditional SSPPs. After which transmission characteristics of SSPPs as well as the corresponding field distributions are investigated to demonstrate the predicted bandpass features. Then, parametric analysis is performed to reveal the geometrical parameter effects on the passband. A smooth transition is designed for high-efficiency excitation based on quantitative extraction of dispersion property and impedance. A prototype of a SIW integrated with arrays of uniform holes on the top layer is fabricated and tested. The design is of simple geometry which enables easy and low-cost fabrication and overcomes the restriction of the limited depth of blind via hole. The measured results show that the upper and lower cut-off frequencies are in accordance with those in the dispersion diagram. Moreover, SSPPs can be inspired and propagated with very high efficiencies (return loss almost better than −10 dB) and good bandpass features (relative bandwidth as high as 93.9%), which validates the feasibility of the proposed strategy as well.

Dynamically Modulating Plasmonic Field by Tuning the Spatial Frequency of Excitation Light.

Based on the Fourier transform (FT) of surface plasmon polaritons (SPPs), the relation between the displacement of the plasmonic field and the spatial frequency of the excitation light is theoretically established. The SPPs’ field shifts transversally or longitudinally when the spatial frequency components or are correspondingly changed. The SPPs’ focus and vortex field can be precisely located at the desired position by choosing the appropriate spatial frequency. Simulation results are in good agreement with the theoretical analyses. Dynamically tailoring the plasmonic field based on the spatial frequency modulation can find potential applications in microparticle manipulation and angular multiplexed SPP focusing and propagation.

Arrays of Plasmonic Nanostructures for Absorption Enhancement in Perovskite Thin Films.

We report optical characterization and theoretical simulation of plasmon enhanced methylammonium lead iodide (MAPbI) thin-film perovskite solar cells. Specifically, various nanohole (NH) and nanodisk (ND) arrays are fabricated on gold/MAPbI interfaces. Significant absorption enhancement is observed experimentally in 75 nm and 110 nm-thick perovskite films. As a result of increased light scattering by plasmonic concentrators, the original Fabry–Pérot thin-film cavity effects are suppressed in specific structures. However, thanks to field enhancement caused by plasmonic resonances and in-plane interference of propagating surface plasmon polaritons, the calculated overall power conversion efficiency (PCE) of the solar cell is expected to increase by up to 45.5%, compared to its flat counterpart. The role of different geometry parameters of the nanostructure arrays is further investigated using three dimensional (3D) finite-difference time-domain (FDTD) simulations, which makes it possible to identify the physical origin of the absorption enhancement as a function of wavelength and design parameters. These findings demonstrate the potential of plasmonic nanostructures in further enhancing the performance of photovoltaic devices based on thin-film perovskites.

TERAHERTZ PHOTONICS AND SPECTROSCOPY ON NOVOSIBIRSK FREE ELECTRON LASER

A review of experiments in the field of photonics and plasmonics, recently performed with the Novosibirsk free electron laser (NovoFEL) is given. Parameters of NovoFEL radiation and user workstations are described. Considerable attention was paid to the development and testing of quasi-optical elements designed for this range and to methods for the formation of powerful beams of terahertz radiation with a given mode composition. The use of terahertz radiation in the spectroscopy of gases and semiconductors, in generation and study of surface plasmon polaritons, as well as the use of the latter for the study of surfaces and in communication applications is described.

Broadband spatio-temporal propagation characteristics of Airy plasmons

We experimentally investigate the propagation of Airy surface plasmon polaritons (Airy SPPs) on a gold film by multiphoton Photoemission Electron Microscopy (PEEM) at different excitation wavelengths and compare the result with rigorous numerical simulations. The typical bent trajectories of the excited two-dimensional beams are observed and analyzed over a wide range of wavelengths. We furthermore investigate the generation bandwidth of the diffraction grating from modal overlap calculations and evaluate the possibility of creating ultrashort Airy plasmon pulses. This provides a viable route to engineer two-dimensional ultrashort non-diffracting pulsed beams in the field of ultrafast nanophotonics.

Spectroelectrochemical measurement and modulation of exciton-polaritons

Quantum emitters strongly coupled to optical cavity modes create new hybrid states called polaritons, resulting in a vacuum Rabi splitting (Ω). Strikingly, the magnitude of this splitting correlates with modified emission properties and chemical reaction rates. However, active control of this coupling strength is difficult due to the fixed properties of the coupled oscillators (both the quantum emitter and optical resonator). Here, we demonstrate active tuning of excitonic strong coupling in a system where organic dyes strongly couple to propagating surface plasmon polaritons (SPPs). After electropolymerization of a methylene blue (MB) film on a SPP-supporting Au surface, we demonstrated active control of coupling strength through reversible redox cycling of the MB film. Excitonic strong coupling was effectively cycled on and off with the electrode potential either continuously tuned (transient) or held at a fixed value (static) and was quantitatively correlated with the simultaneously measured electrochemical charge. Switching between reduced and oxidized forms of the dye resulted in Ω values tuned from ∼0 meV to ∼280 meV, i.e., ∼14% of the transition energy. The ability to control coupling strengths in a given emitter–cavity coupled system is a key capability for utilizing polaritonic states for cavity-mediated chemical reactions or optical devices.

Coherent Enhancement of Dual-Path-Excited Remote SERS.

Combining both localized surface plasmon polaritons (LSPPs) and propagating surface plasmon polaritons, remote surface-enhanced Raman scattering (SERS) emerges as a novel sensing technology in recent years, which could avoid the overlap of incident light and inelastic scattering light in SERS. Compared to traditional SERS, it has novel applications in sensors, plasmon-driven surface-catalyzed reactions, Raman optical activity, etc. However, the weak Raman intensity of remote SERS impedes its further application. In this work, we demonstrated that the remote SERS signals could be enhanced by more than 100% through the subwavelength interference in dual-path-excited Ag-branched nanowire dimer and nanowire-nanoparticle systems. Our experiment has revealed that remote SERS intensities could be modulated by polarization and phase differences of two incident lights illuminating at two separate nanowire terminals. The simulated electromagnetic field distributions through the finite-difference time-domain (FDTD) method indicate that subwavelength interference occurs in Ag nanowires, which causes the Raman intensities collected at a remote site is greatly influenced by the coherent superposition of propagating surface plasmon polaritons (PSPPs). Our work on this coherent enhancement could not only promote the application of remote SERS but also enlarge the research on light manipulating in the subwavelength.

Correlating Plasmon Polariton Propagation and Fluorescence Enhancement in Single Silver Nanowires

We observe correlation between the length of surface plasmon polariton propagation in silver nanowires and the enhancement of fluorescence intensity due to coupling with localized plasmon resonance...

Asymmetric Excitation of Surface Plasmon Polaritons via Paired Slot Antennas for Angstrom Displacement Sensing.

Optical antennas enable efficient coupling between propagating light and bonding electromagnetic waves like surface plasmon polaritons (SPPs). Under the illumination of inhomogeneous optical fields, propagating SPPs mediated by multimode antennas could be spatially asymmetric and the asymmetry strongly depends on the position of the antennas relative to the illumination field. Here we develop such asymmetric excitation of SPPs through illuminating a pair of slot antennas with the (1,0) mode Hermite-Gaussian beam. The physical scenario of the interaction between the illumination optical field and the paired slot antennas are elaborated by full-wave electromagnetic simulations. We also carry out experiments to monitor the asymmetric SPPs propagation with a back-focal plane imaging technique. By retrieving the asymmetric intensity ratio of the SPP pattern in the back-focal plane image, lateral displacement of the antennas down to angstrom level is demonstrated.

Conditions for loss compensation of surface plasmon polaritons in a metal layer surrounded by an active dielectric: an analytic solution

The propagation length of surface plasmon polaritons (SPP) is limited by the internal losses in the metal and the radiation losses due to the structure imperfections at the interface. These losses can be compensated by introducing material with optical gain (active medium) in the system. The required gain for complete loss compensation depends not only on the dissipative properties of the metal but also on the geometry of the structure. The geometry factor can weaken the gain requirements and one promising system, in this respect, is a metal layer embedded in an active medium. Here we present an analytical solution for this system, which allows to find the curves of exact loss compensation in the complex plane of the dielectric function of the gain medium. These curves determine the minimum required gain of the active medium for lossless SPP propagation. The solution is given for both modes of SPP propagation. This approach is then illustrated and discussed for silver and gold layers embedded in an active media.

Inducing LIPSS on multilayer thin metal films by femtosecond laser beam of different orientations

The occurrence of laser-induced periodic surface structures (LIPSS) has been known for a while. Multilayer thin films, like Al/Ti, are suitable for LIPSS formation and attractive for applications—due to their wearing behavior and corrosion resistance; LIPSS generation may improve their properties as well. LIPSS properties depend not only on the material but also on the beam characteristics, like wavelength, polarization and scanning directions, etc. After exposing with NIR femtosecond pulses from Coherent Mira 900 laser system in several beam exposures, we have analyzed the samples of thin metal film systems with Tescan Mira3 SEM and NTegra AFM. The formation of LIPSS is most probably due to the generation of surface plasmon polariton, through the periodic distribution of energy in the interaction zone which lead to thermal processes in layers and interfaces. Two types of LIPSS were generated, which differ in shape, orientation and in ablation pronounced or not. For consecutive interactions in the same direction, LIPSS maintained its orientation, while for orthogonal passes LIPSS with mutually orthogonal orientation were generated. LIPSS period fluctuated between 320 and 380 nm and structures with pronounced ablation have significantly smaller width. Probable mechanism is that for greater accumulated energy pronounced ablation takes place giving LIPSS in the form of trenches or grooves, while for less accumulated energy the buildup of the material—probably due to pronounced oxidation—lead to LIPSS in the form of hills or ridges.

Generating Surface Plasmon Polariton Airy Beam with Dielectric Relief Holographical Structures

Surface plasmon polariton (SPP) Airy beams are very attractive in theory and applications. We propose a new method to design dielectric relief holographical structures for controlling the SPP wave propagations and generating SPP Airy beams on metal surface. In the dielectric relief holography (DRH) method, both phase and amplitude are considered. The thickness of designed dielelctric films is proportional to the intensity of SPPs interference in holography. The films designed by the DRH method are coated on metal surface and can control SPPs propagation effectively. The complicated Airy beams can also be generated through the films designed by the method. The finite difference time domain (FDTD) method is used to test the functionalities of the designed structures and find the optimal parameters. The structures designed by the DRH method can be manufactured with traditional die or corroding methods. The investigation on the method extends SPP device manufacture methods, and therefore may open up the possibility for mass industrial manufacture of plasmonic devices.

Hybrid Electro-Optical Pumping of Active Plasmonic Nanostructures.

Surface plasmon polaritons (SPPs) offer a unique opportunity to overcome the diffraction limit of light. However, this opportunity comes at the cost of the strong absorption of the SPP field in a metal, which unavoidably limits the SPP propagation length to a few tens of micrometers in nanostructures with deep-subwavelength mode confinement. The only possibility to avoid the propagation losses is to compensate for them by optical gain in the adjacent active medium. Different approaches for surface plasmon amplification by stimulated emission of radiation have been proposed based on either optical or electrical pumping. However, each has its own disadvantages caused by the selected type of pumping scheme. Here, we study, for the first time, hybrid electro-optical pumping of active plasmonic waveguide structures, and by using comprehensive self-consistent numerical simulations, demonstrate that this hybrid approach can outperform both pure electrical pumping and pure optical pumping. The SPP modal gain is higher than under pure optical pumping, while one can precisely and locally adjust it by tuning the electric current, which allows the reduction of amplification noise and provides additional functionalities. We believe that our findings lay a solid foundation for the development of a new generation of active plasmonic devices and stimulate further research in this area.

On-chip trans-dimensional plasmonic router

Abstract Plasmons, as emerging optical diffraction-unlimited information carriers, promise the high-capacity, high-speed, and integrated photonic chips. The on-chip precise manipulations of plasmon in an arbitrary platform, whether two-dimensional (2D) or one-dimensional (1D), appears demanding but non-trivial. Here, we proposed a meta-wall, consisting of specifically designed meta-atoms, that allows the high-efficiency transformation of propagating plasmon polaritons from 2D platforms to 1D plasmonic waveguides, forming the trans-dimensional plasmonic routers. The mechanism to compensate the momentum transformation in the router can be traced via a local dynamic phase gradient of the meta-atom and reciprocal lattice vector. To demonstrate such a scheme, a directional router based on phase-gradient meta-wall is designed to couple 2D SPP to a 1D plasmonic waveguide, while a unidirectional router based on grating metawall is designed to route 2D SPP to the arbitrarily desired direction along the 1D plasmonic waveguide by changing the incident angle of 2D SPP. The on-chip routers of trans-dimensional SPP demonstrated here provide a flexible tool to manipulate propagation of surface plasmon polaritons (SPPs) and may pave the way for designing integrated plasmonic network and devices.

Duplicating Plasmonic Hotspots by Matched Nanoantenna Pairs for Remote Nanogap Enhanced Spectroscopy.

Plasmonic nanoantennas are capable of reversibly interconverting free-space radiation with localized modes at the nanoscale. However, optical access to a single nanoantenna, through a laser beam, is always accompanied by disruptive background perturbations and heating effects. Remote spectroscopy is one promising route to overcome these effects. Here, we demonstrate excitation-collection-separated enhanced spectroscopy using a matched nanoantenna pair. The receiving and transmitting antennas are geometrically separated but bridged by the propagating surface plasmon polaritons (SPPs) on the metal film. The receiving antenna, consisting of a silver nanowire on a mirror, ensures a high light-to-plasmon conversion efficiency. The transmitting antenna consists of a silver nanocube over a mirror and is impedance matched to free space photons and the propagating SPPs. As a proof-of-principle, we demonstrate remote surface-enhanced Raman scattering with a high signal-to-noise ratio. This matched nanoantenna pair may have applications for remote entanglement of quantum emitters, biochemistry detection, or optical interconnects.