Guided Surface Plasmon Polaritons Research Articles

Propagation-Invariant Space-Time Plasmonic Pulse in Subwavelength MIM Waveguide.

The metal-insulator-metal (MIM) plasmonic waveguide has been highly anticipated for confining and guiding surface plasmon polaritons (SPPs) on the subwavelength scale. However, perennial drawbacks such as a short propagation length and an unbounded transverse field have set limits on the use of the MIM waveguide in various applications. Herein, diffraction- and dispersion-free MIM modes are synthesized by using space-time wave packets (STWPs) and are therefore referred to as space-time MIM (ST-MIM) waveguide modes. Compared to a Gaussian pulse of the same duration and spectral bandwidth, the ST-MIM demonstrates enhanced propagation lengths of about 2.4 times for the symmetric mode and about 6.3 times for the antisymmetric mode. In the simulations, the ST-MIMs are confined in all transverse dimensions, thereby overriding the diffraction limits. In addition, the group velocities of the ST-MIMs can be arbitrarily designed, which makes it possible to synchronize the pulse propagation speeds of the symmetric and antisymmetric MIM modes.

Scanning Near-Field Optical Microscopy of Ultrathin Gold Films.

Ultrathin metal films are an essential platform for two-dimensional (2D) material compatible and flexible optoelectronics. Characterization of thin and ultrathin film-based devices requires a thorough consideration of the crystalline structure and local optical and electrical properties of the metal-2D material interface since they could be dramatically different from the bulk material. Recently, it was demonstrated that the growth of gold on the chemical vapor deposited monolayer MoS2 leads to a continuous metal film that preserves plasmonic optical response and conductivity even at thicknesses below 10 nm. Here, we examined the optical response and morphology of ultrathin gold films deposited on exfoliated MoS2 crystal flakes on the SiO2/Si substrate via scattering-type scanning near-field optical microscopy (s-SNOM). We demonstrate a direct relationship between the ability of thin film to support guided surface plasmon polaritons (SPP) and the s-SNOM signal intensity with a very high spatial resolution. Using this relationship, we observed the evolution of the structure of gold films grown on SiO2 and MoS2 with an increase in thickness. The continuous morphology and superior ability with respect to supporting SPPs of the ultrathin (≤10 nm) gold on MoS2 is further confirmed with scanning electron microscopy and direct observation of SPP fringes via s-SNOM. Our results establish s-SNOM as a tool for testing plasmonic films and motivate further theoretical research on the impact of the interplay between the guided modes and the local optical properties on the s-SNOM signal.

Remote two-dimensional nanometric localization of molecules by the analysis of fluorescence coupled to guided surface plasmons

The coupling between fluorescent emitters and the metal nanowire (NW) can excite the guided surface plasmon polaritons (SPPs) on the NW and can be exploited to extract the characteristic parameters of fluorescent emitters.

Three-layered nanostructured metamaterials for surface plasmon polariton guiding

A novel metamaterial (MM) to guide surface plasmon polariton (SPP) is considered. Specific example of three-layered nanostructured MM and its dispersion engineering are studied in details allowing the development of new devices. Herein we deal with the general original concept of MMs based on inclusions of the additional layers as with a promising class of materials. The metal material stands for as the limiting factor of the frequency range that SPP mode exists. It is worthwhile noting that the SPP mode at high frequency is characterized by extremely large loss. The former restriction causes serious limitations for the potential applications of SPP in the field of optical interconnection, active SPP devices and so on. The surface mode guided by dielectric/graphene/dielectric multilayers MM has been studied based on the theory of electromagnetic field aiming to extend the frequency range of SPP mode. It is demonstrated that surface mode could be supported by the MM. Moreover, the frequency range to where conventional metal SPP cannot exist is extended. Herein, it is concluded that, the MM guided SPP mode can potentially be used to enhance the plasmonic performance over traditional metal one by varying the structure parameters.

Manipulating surface plasmon polaritons with infinitely anisotropic metamaterials.

Guiding surface states through disorders recently has attracted attention of scientists from diverse backgrounds. In this work, we report a robust method to guide surface plasmon polaritons (SPPs) through arbitrary distorted metal surfaces (a kind of disorder), including slopes, bumps, and sharp corners. Almost total transmissions over a broad frequency range can be achieved by use of infinitely anisotropic metamaterials (IAMs). The SPPs are coupled into and out of the bulk modes in the IAMs, where the bulk modes are routed by altering the principle axis of the IAMs. Due to unique non-diffraction property of the IAMs, all processes are of high efficiency, which are explained from both microscopic and macroscopic perspectives. Several functional SPP devices, including adapter, cloak, and sharp bending waveguide, are presented in the simulations. Two proof-of-concept SPP devices are experimentally demonstrated, where the SPPs are mimicked by the designer SPPs at microwave frequency.

Discontinuous Tapered Surface Plasmon Polariton Waveguides with Gap.

We investigate characteristics of discontinuous tapered surface plasmon polariton waveguides with a gap (DTG-SPPWs) to control a guided surface plasmon polariton (SPP) at a telecommunication wavelength of 1.55 μm. The DTG-SPPWs are composed of an input 2 μm-wide and 10 μm-long reverse tapered IMI-W (RT-IMI-W) and a 10 μm-long tapered and output 2 μm-wide IMI-W (T-IMI-W) with the 8 μm-long gap. The width and length of the tapered regions in the RT-IMI-W and the T-IMI-W were varied from 2 to 10 μm and 1 to 8 μm, respectively. Gold is used as the metal in the insulator-metal-insulator waveguides (IMI-Ws). The thickness of the gold strips is fixed with 20 nm. A low-loss polymer is used for the 30 μm-thick upper and lower cladding layers. The coupling losses of the DTG-SPPWs are less than 0.055 dB with an 8 μm-long gap and various taper widths up to 10 μm. The normalized transmissions (NTs) of the DTG-SPPWs are less than about -0.060 dB with various taper widths up to 10 μm. The NTs of the DTG-SPPWs are less than about -0.069 dB with various taper lengths up to 8 μm. The maximum NT of about -0.042 dB was obtained using the 6 μm-wide taper width and the 3 μm-long taper length in the DTG-SPPW. The DTG-SPPWs have potential as a new plasmonic modulation device via control of the guided SPP through interaction with an applied force in the gap.

Ultrafast Plasmonics on Gold Nanowires: Confinement, Dispersion, and Pulse Propagation

We explore the potential of plasmonic nanowires for ultrafast photonics by comparing the properties of the guided surface plasmon polariton (SPP) to that of the mode guided in a silicon nanowire. For this purpose, we combine ultrafast near-field microscope measurements of gold nanowires with mode simulations to study modal properties such as mode width, propagation length, fundamental mode cutoff, group velocity dispersion, and third-order dispersion coefficients. Using this information we show that, for ultrashort-pulse propagation, plasmonic waveguides can outperform their dielectric counterparts. In particular, we demonstrate that the ohmic losses, which are unavoidable in the gold nanowire, cause less peak amplitude decay as ultrashort pulses propagate than do the high dispersion and the presence of a mode cutoff.

Electrically tunable graded index planar lens based on graphene

The realization of electrically tunable beam focusing using a properly designed conductivity pattern along a strip on a background single graphene flake with operation in the terahertz regime is proposed and numerically investigated. The strip is illuminated with a guided surface plasmon polaritons (SPP) plane wave and the physical origin of the design procedure is evaluated from the phase of effective mode index of propagating SPP wave on graphene. Upon tuning a gate voltage between the graphene sheet and the substrate, the focus tuning is achieved. Finite- difference time-domain numerical technique is employed to explore the propagation characteristic of SPP wave and the performance parameters of the lens include the focal length, full-width half-maximum, and focusing efficiency. Such a one atom thick planar lens with the capability of electrical focus tuning besides the compatibility with current planar optoelectronic systems can find valuable potential applications in the field of transformational plasmon optics.

Surface plasmon-polaritons on very thin metal tubes

A thin metal tube is proposed to guide surface plasmon-polaritons (SPPs). We derive the dispersion equation of the SPPs, and then solve the equation as a function of the tube thickness. It is indicated that both long-range (LR) SPPs and short-range (SR) SPPs can be guided by the metal tube. For the LR-SPPs the loss coefficient goes to zero as the thickness of the tube decreases, thus the propagation distance can be much longer than that of the SPPs propagating on a metal wire. For the SR-SPPs, compared with the SPPs on the wire, the mode distribution is much sharper.

Deep-Subwavelength Plasmonic Nanoresonators Exploiting Extreme Coupling

A metal-insulator-metal (MIM) waveguide is a canonical structure used in many functional plasmonic devices. Recently, research on nanoresonantors made from finite, that is, truncated, MIM waveguides attracted a considerable deal of interest motivated by the promise for many applications. However, most suggested nanoresonators do not reach a deep-subwavelength domain. With ordinary fabrication techniques the dielectric spacers usually remain fairly thick, that is, in the order of tens of nanometers. This prevents the wavevector of the guided surface plasmon polariton to strongly deviate from the light line. Here, we will show that the exploitation of an extreme coupling regime, which appears for only a few nanometers thick dielectric spacer, can lift this limitation. By taking advantage of atomic layer deposition we fabricated and characterized exemplarily deep-subwavelength perfect absorbers. Our results are fully supported by numerical simulations and analytical considerations. Our work provides impetus on many fields of nanoscience and will foster various applications in high-impact areas such as metamaterials, light harvesting, and sensing or the fabrication of quantum-plasmonic devices.

Nanosecond infrared laser-induced precipitation of silver nanoparticles in glass

We describe a novel plasmonic hybrid nanostructure based on a silver island film covered with a dielectric silica layer. The thickness of the silica layer is varied from 0 to approximately 46 nm on a single sample, thus allowing for continuous variation of the interaction strength between plasmon excitations in the metallic film and the excited states of pigments comprising photosynthetic complexes used to probe this interaction. While the largest separation between the silver film and photosynthetic complexes provides fluorescence featuring mono-exponential decay, thinner silica spacer distances show bi-exponential decay. The intensity of the fast component, which is attributed to the emission of photosynthetic complexes coupled to plasmon excitations, strongly decreases as a function of the spacer thickness. The interaction is stronger for excitation wavelengths resonant with plasmon absorption in the metallic layer. Full Text: PDF References P. Anger, P. Bharadwaj, L. Novotny, "Enhancement and Quenching of Single-Molecule Fluorescence", Phys. Rev. Lett. 96, 113002 (2006). CrossRef M.A. Noginov, G. Zhu, M. Bahoura, C.E. Small, C. Davison, J. Adegoke, V.P. Drachev, P. Nyga, V.M. Shalaev, "Enhancement of spontaneous and stimulated emission of a rhodamine 6G dye by an Ag aggregate", Phys. Rev. B 74, 184203 (2006). CrossRef K. Ray, R. Badugu, J. R. Lakowicz, "Metal-Enhanced Fluorescence from CdTe Nanocrystals:  A Single-Molecule Fluorescence Study", J. Am. Chem. Soc. 128, 8998 (2006). CrossRef W. Zhang, Y. Chen, C. Hu, Y. Zhang, X. Chen, M. Qiu Zhang, "Effective excitation and control of guided surface plasmon polaritons in a conjugated polymer–silver nanowire composite system", J. Mater. Chem. C 1, 1265 (2013). CrossRef Ł. Bujak, N. Czechowski, D. Piatkowski, R. Litvin, S. Mackowski, T.H.P. Brotosudarmo, R.J. Cogdell, S. Pichler, W. Heiss, "Fluorescence enhancement of light-harvesting complex 2 from purple bacteria coupled to spherical gold nanoparticles", Appl. Phys. Lett. 99, 173701 (2011). CrossRef J.B. Nieder, R. Bittl, M. Brecht, "Fluorescence Studies into the Effect of Plasmonic Interactions on Protein Function", Angew. Chem. Int. Ed. 49, 10217 (2010). CrossRef P. Nyga, V. P. Drachev, M.D. Thoreson, V. M. Shalaev, "Mid-IR plasmonics and photomodification with Ag films", Appl. Phys. B 93, 59 (2008). CrossRef U.K. Chettiar, P. Nyga, M.D. Thoreson, A.V. Kildishev, V.P. Drachev, V.M. Shalaev, "FDTD modeling of realistic semicontinuous metal films", Appl. Phys. B 100, 159 (2010). CrossRef V.P. Drachev, M.D. Thoreson, V. Nashine, E.N. Khaliullin, D. Ben-Amotz, V.J. Davisson, V.M. Shalaev., "Adaptive silver films for surface-enhanced Raman spectroscopy of biomolecules", J. Raman Spectroscopy 36, 648 (2005). CrossRef B. Krajnik, T. Schulte, D. Piątkowski, N. Czechowski, E. Hofmann, S. Mackowski, "SIL-based confocal fluorescence microscope for investigating individual nanostructures", Cent. Eur. J. Phys. 9, 293 (2011). CrossRef

Plasmonic Response of Bent Silver Nanowires for Nanophotonic Subwavelength Waveguiding

We have imaged, with electron energy loss spectroscopy, the plasmonic response of straight and bent silver nanowires for their potential use in nanophotonic circuits. The guided surface plasmon polaritons appear unaffected by the presence of sharp kinks and corners in the nanowires studied, shown by direct imaging of excited Fabry-Perot-type resonances. Nanoscale detection is extended down to 0.17 eV, enabling detailed measurements of the spatial extent and dispersion of guided surface plasmon polaritons at low wave numbers. The experimental measurements are in excellent agreement with calculations, and the results are relevant in the design of integrated nanophotonic circuits and devices.

Effective excitation and control of guided surface plasmon polaritons in a conjugated polymer–silver nanowire composite system

This study demonstrates a novel light-emitting conjugated polymer (PCFOz) used to initiate excitation and propagation of surface plasmon polaritons (SPPs) in silver nanowires. Excitons in the polymer optically excited in close proximity to silver nanowires directly couple to the guided SPPs, and then propagate towards the wires' ends and light up. A tunable exciton–plasmon coupling is realized by varying the distance between PCFOz and Ag nanowires. Strongly efficient excitation of SPPs appears in the case of a spacer thickness of ∼10 nm. Moreover, photobleaching of the organic system is dramatically suppressed by separating the emitter and metal with a spacer, allowing at least 20 times improvement of photostability with a spacer thickness of 25 nm. Spectral dependence of exciton–plasmon coupling indicates that the nanowires' tips contain larger amount of red components. Study of emission decay dynamics demonstrates that the emission properties of PCFOz have been significantly modified by the proximity of Ag nanowires, generating more than 9-fold enhancement of PCFOz spontaneous emission. These results are believed to be important for the development of thin-film photonic–plasmonic waveguides, single photon source and various nanoscale fluorescence sensors.

Theoretical Analysis of Long-Range Dielectric-Loaded Surface Plasmon Polariton Waveguides

A structure for guiding surface plasmon polaritons (SPPs) over millimeter distances with tight mode confinement is presented and analyzed in detail using the finite element method. The proposed long-range plasmonic waveguide consists of a dielectric ridge deposited on a narrow metal stripe supported by a dielectric buffer layer covering a low-index substrate. It is shown that such an asymmetric waveguide structure can be designed to support a long-range symmetric SPP mode, featuring a propagation length of ≈ 3.1 mm and lateral mode width of ≈ 1.6nμ m at telecom wavelengths of ~ 1.55 μm. Our analysis covers a broad spectrum of parameters: ridge dimensions, buffer layer parameters (refractive index and thickness), as well as metal stripe width, considering in detail the underlying mechanisms of SPP waveguiding in this configuration. The suggested configuration offers easy connection to electrodes enabling, e.g., thermo-optic or electro-optic control, and is technologically simple, making fabrication possible using only a few lithography steps. Additionally, a new figure of merit is introduced, which is related to a number of plasmonic components allowed for a given mode confinement and propagation loss, aiming thereby at the evaluation of the application potential of plasmonic waveguides.

Fabry-Pérot Resonances in One-Dimensional Plasmonic Nanostructures

We study the near-field optical behavior of Fabry-Pérot resonances in thin metal nanowires, also referred to as quasi one-dimensional plasmonic nanoantennas. From eigenmodes well beyond quadrupolar order we extract both, propagation constant and reflection phase of the guided surface plasmon polariton with superb accuracy. The combined symmetry breaking effects of oblique illumination and retardation allow the excitation of dipole forbidden, even order resonances. All measurements are supported by rigorous simulations of the experimental situation.

Coupled metal gap waveguides as plasmonic wavelength sorters

We propose a coupled metal gap waveguide structure for realizing plasmonic wavelength sorters. Theoretical analysis from the coupled-wave theory reveals that wavelength dependent coupling length of guided surface plasmon polaritons contributes to the routing of different wavelengths to different output ports with reasonable high extinction ratio. The analytical results are confirmed by the finite-difference time-domain numerical simulations. Our result may provide an alternative way to construct nanoscale frequency multiplexers, routers, and sorters for nanophotonic integration and optical communication.

Planar metal heterostructures for nanoplasmonic waveguides

The authors propose and numerically demonstrate a planar metal heterostructure for guiding surface plasmon polaritons (SPPs). By the analysis of the effective index method and finite-difference time-domain numerical simulations, they reveal that the planar metal heterostructure created by inlaying a Ag film, on which SPPs show a lower phase velocity, into an Al film and coating them with a uniform dielectric layer can strongly confine SPPs in the Ag region of the waveguide with 171×33nm2 cross section and 1.76μm propagation length. The planar metal heterostructures provide a way for constructing various nanoscale counterparts of conventional planar integrated devices such as splitters, resonators, sensors, optical switches, logical circuit, etc.

All-Angle Broadband Negative Refraction of Metal Waveguide Arrays in the Visible Range: Theoretical Analysis and Numerical Demonstration

In this Letter, we introduce a simple metal waveguide array for realizing all-angle wide frequency bandwidth negative refraction from the visible to infrared frequencies. Theoretical analysis from the rigorous coupled-wave theory reveals that the negative coupling constant resulting from the anomalous coupling of guided surface plasmon polariton modes contributes to the negative refraction. The analytical results are confirmed by finite-difference time-domain numerical simulations. Our result provides an alternative way to construct robust all-angle negative refractive materials operating in a wide range of frequency from the near-infrared to the visible range.