Surface Plasmon Propagation Length Research Articles

D-shaped fiber optic plasmonic sensors using planar and grating structures of silver and gold: design and analysis.

In this paper, a D-shaped optical fiber plasmonic sensor using planar and grating structures of silver and gold metals is simulated using the finite element method under the wave optics module of COMSOL Multiphysics. Performance defining parameters are based on (i) the transmittance curve, viz., resonance wavelength (λ r), shift in resonance wavelength (Δ λ r), minimum transmittance (T m i n ), and bandwidth (BW), and (ii) on electric field distribution of a surface plasmon wave, viz., penetration depth (PD) and propagation length (PL) obtained for the considered sensor structures. It is found that gold gives wider BW than silver (e.g.,at 1.39 refractive index of the sample: 480% for the planar case and 241% for the grating case), which deteriorates sensor performance by degrading detection accuracy. However, gold gives higher Δ λ r than silver (at 1.40-1.39=0.01 change in refractive index of the sample: 18.33% for the planar case and 16.39% for the grating case), which improves sensor performance and enhances sensitivity. A grating slightly increases the BW and Δ λ r for both gold and silver. Further, with respect to silver, the sensor that contains gold demonstrates higher PD (e.g.,22.32% at 1.39 refractive index of the sample for the planar case) and lower PL (e.g.,22.74% at 1.39 refractive index of sample for the planar case). A grating increases the PD (e.g.,10% for silver at 1.39 refractive index of the sample), whereas it decreases the PL (e.g.,8.73% for silver at 1.39 refractive index of the sample). Lower PL signifies the localization of the field, whereas higher PD enables the sensor to detect larger molecules. Therefore, the sensor with grating metals provides better sensitivity with reduced detection accuracy for the detection of comparatively larger molecules.

The influence of single layer MoS2 flake on the propagated surface plasmons of silver nanowire

We demonstrate enhancing the excitation and transmission efficiency of the propagated surface plasmon (SP) of an Ag nanowire (Ag NW) in hybrid Ag–MoS2 structures by contrasting the SP propagation of the Ag NW on different substrates, including SiO2 and monolayer MoS2, or partially overlapping the Ag NW on MoS2 flakes. The simulation results show that the leaky radiation of the hybrid plasmonic modes H1 and H2 can be prominently suppressed due to the high refractive index dielectric layer of MoS2, which provides an optical barrier for blocking the leaky radiation, resulting in reduced propagation loss. This paper provides a feasible and effective method to improve the SP propagation length.

A high gain and wideband on-chip hybrid plasmonic V-shaped nano-antenna

In this paper, a wideband hybrid plasmonic V-shaped nano-antenna is proposed based on coupled hybrid plasmonic waveguide (CHPW) feeding to increase the surface plasmon propagation length. The CHPW specifications are investigated analytically and numerically to obtain the dispersion relation and propagation length using the genetic algorithm and the finite element method, respectively. Moreover, the proposed V-shaped nano-antenna, with a fractional bandwidth of ∼86% and a maximum efficiency of 98%, is able to receive/transmit optical signals at three telecommunication wavelengths of 850, 1310, and 1550 nm with high realized gains of 10.5, 9.39, and 9.05 dB, respectively. The shape of the radiation pattern, with a main lobe along the antenna axis, makes this antenna appropriate for point-to-point connections in inter- or intra-chip optical wireless links and networks, which is studied comprehensively in this article. Furthermore, to obtain a high optical power signal and tune the antenna orientation, the performance of the antenna is investigated with two different types of array structure, single row and square, and its applications for energy harvesting and beam steering are studied. The fabrication feasibility of the nano-antenna is realizable based on complementary metal-oxide-semiconductor technology.

Frequency Dependent Graphene Surface Plasmon Properties on Different Dielectrics

Numerical analysis of surface plasmon behaviour is performed on graphene surface supported on different dielectric medium and with varying graphene chemical potential. The dielectric medium of graphene is varied from free standing graphene to rigid SiO2 wafer substrate to flexible PMMA polymer for diverse graphene plasmonics applications. The dispersion relation, propagation length and penetration depth of graphene surface plasmons are computed and analysed for the different dielectrics. The results show that graphene plasmonic behaviour in the various dielectrics highly depends on its chemical potential, the excitation input frequencies and produces surface plasmons with high field localization and low losses. This study of plasmonic behaviour on flexible dielectric opens up application of graphene plasmonics in the field of flexible optoelectronics.

Modulation of propagating surface plasmons

The diffraction limit of light greatly limits the development of conventional optical devices, which are difficult to be miniaturized and integrated with high density. Surface plasmons, electromagnetic modes at the metal-dielectric interface, can concentrate light into deep subwavelength dimensions, enabling the manipulation of light at the nanometer scale. Surface plasmons can be used as information carrier to transmit and process optical signals beyond the diffraction limit. Therefore, nanodevices based on surface plasmons have received much attention. By modulating surface plasmons, the modulation of optical signals at nanoscale can be realized, which is important for the development of on-chip integrated nanophotonic circuits and optical information technology. In this article, we review the modulations of propagating surface plasmons and their applications in nano-optical modulators. The wave vector of propagating surface plasmons is very sensitive to the dielectric function of the metal and the environment. By tuning the dielectric function of the metal and/or the surrounding medium, both the real and imaginary part of the wave vector of surface plasmons can be modified, leading to the modulation of the phase and propagation length of surface plasmons and thereby modulating the intensity of optical signals. We first introduce the basic principles of different types of modulations, including all-optical modulation, thermal modulation, electrical modulation, and magnetic modulation. The all-optical modulation can be achieved by modulating the polarization and phase of input light, pumping optical materials, changing the dielectric function of metal by control light, and manipulating a nanoparticle by optical force to modulate the scattering of surface plasmons. The modulation based on thermal effect depends on thermo-optic materials and phase-change materials, and the temperature change can be triggered by photothermal effect or electrical heating. For electrically controlled modulation, Pockels electro-optic effect and Kerr electro-optic effect can be employed. Electrical modulation can also be realized by controlling the carrier concentration of semiconductors or graphene, using electrochromatic materials, and nanoelectromechanical control of the waveguide. The modulation of surface plasmons by magnetic field relies on magneto-optic materials. We review recent research progresses of modulating propagating surface plasmons by these methods, and analyze the performances of different types of plasmonic modulators, including operation wavelength, modulation depth or extinction ratio, response time or modulation frequency, and insertion loss. Finally, a brief conclusion and outlook is presented.

Backward Phase Matching for Second Harmonic Generation in Negative-Index Conformal Surface Plasmonic Metamaterials.

Backward phase matching, which describes counterpropagating fundamental and harmonic waves in a negative‐index medium, is one of the most intriguing phenomena in nonlinear metamaterials. Predicted theoretically decades ago, however, it is still a challenging task to be applied for efficient second harmonic (SH) generation in a nonlinear metamaterial with ultrathin geometry and ultralow loss. Here, a negative‐index spoof plasmonic metamaterial is reported, which is composed of an ultrathin symmetrical corrugated metallic strips loaded with nonlinear active devices. The simulated and measured power spectra and surface near‐field distributions show that a peak SH signal can be generated at the backward phase‐matched frequency point in a 120° curved surface with high efficiency, thanks to the ultrathin flexible geometry, significant confinement effect, and large propagation length of the spoof surface plasmons. The results open new technological challenges from nano‐ and micro‐nonlinear photonics to science and engineering of compact, broadband, and efficient frequency‐mixing metamaterials and electromagnetic devices.

Growth of terahertz surface plasmon propagation length due to thin-layer dielectric coating

Here we consider a longstanding problem: why terahertz (THz) surface plasmons (SPs) do not run so far as the Drude theory predicts. We experimentally demonstrated that the main cause for this paradox was a drastic rise in the SP radiative losses at THz frequencies, not violation of the theory. Analysis of SPs induced with the radiation of the Novosibirsk free electron laser (λ=130 μm) showed that a thin dielectric layer (≈λ/250) on a metal surface can reduce the losses substantially and hence enlarge the SP propagation length several times. Furthermore, it was found that there was an optimal layer thickness corresponding to the minimum total SP energy losses; the cause of this phenomenon is discussed.

Coupling Emitters and Silver Nanowires to Achieve Long-Range Plasmon-Mediated Fluorescence Energy Transfer.

The development of quantum plasmonic circuitry requires efficient coupling between quantum emitters and plasmonic waveguides. A major experimental challenge is to simultaneously maximize the surface plasmon propagation length, the coupling efficiency into the plasmonic mode, and the Purcell factor. Addressing this challenge is also the key to enabling long-range energy transfer between quantum nanoemitters. Here, we use a dual-beam scanning confocal microscope to carefully investigate the interactions between fluorescent nanoparticles and surface plasmons on single-crystalline silver nanowires. By exciting the fluorescent nanoparticles via nanowire surface plasmons, we maximize the light-matter interactions and reach coupling efficiencies up to 44% together with 24× lifetime reduction and 4.1 μm propagation lengths. This improved optical performance enables the demonstration of long-range plasmon-mediated fluorescence energy transfer between two nanoparticles separated by micrometer distance. Our results provide guidelines toward practical realizations of efficient long-range fluorescence energy transfer for integrated plasmonics and quantum nano-optics.

A New Perspective on Plasmonics: Confinement and Propagation Length of Surface Plasmons for Different Materials and Geometries

Surface‐plasmon polaritons are electromagnetic waves propagating on the surface of a metal. Thanks to subwavelength confinement, they can concentrate optical energy on the micrometer or even nanometer scale, enabling new applications in bio‐sensing, optical interconnects, and nonlinear optics, where small footprint and strong field concentration are essential. The major obstacle in developing plasmonic applications is dissipative loss, which limits the propagation length of surface plasmons and broadens the bandwidth of surface‐plasmon resonances. Here, a new analysis of plasmonic materials and geometries is presented which fully considers the tradeoff between propagation length and degree of confinement. It is based on a two‐dimensional analysis of two independent figures of merit and the analysis is applied to relevant plasmonic materials, e.g., noble metals, aluminum, silicon carbide, doped semiconductors, graphene, etc. The analysis provides guidance on how to improve the performance of any particular plasmonic application and substantially eases the selection of the plasmonic material.

High resolution surface plasmon resonance imaging for single cells.

BackgroundSurface plasmon resonance imaging (SPRI) is a label-free technique that can image refractive index changes at an interface. We have previously used SPRI to study the dynamics of cell-substratum interactions. However, characterization of spatial resolution in 3 dimensions is necessary to quantitatively interpret SPR images. Spatial resolution is complicated by the asymmetric propagation length of surface plasmons in the x and y dimensions leading to image degradation in one direction. Inferring the distance of intracellular organelles and other subcellular features from the interface by SPRI is complicated by uncertainties regarding the detection of the evanescent wave decay into cells. This study provides an experimental basis for characterizing the resolution of an SPR imaging system in the lateral and distal dimensions and demonstrates a novel approach for resolving sub-micrometer cellular structures by SPRI. The SPRI resolution here is distinct in its ability to visualize subcellular structures that are in proximity to a surface, which is comparable with that of total internal reflection fluorescence (TIRF) microscopy but has the advantage of no fluorescent labels.ResultsAn SPR imaging system was designed that uses a high numerical aperture objective lens to image cells and a digital light projector to pattern the angle of the incident excitation on the sample. Cellular components such as focal adhesions, nucleus, and cellular secretions are visualized. The point spread function of polymeric nanoparticle beads indicates near-diffraction limited spatial resolution. To characterize the z-axis response, we used micrometer scale polymeric beads with a refractive index similar to cells as reference materials to determine the detection limit of the SPR field as a function of distance from the substrate. Multi-wavelength measurements of these microspheres show that it is possible to tailor the effective depth of penetration of the evanescent wave into the cellular environment.ConclusionWe describe how the use of patterned incident light provides SPRI at high spatial resolution, and we characterize a finite limit of detection for penetration depth. We demonstrate the application of a novel technique that allows unprecedented subcellular detail for SPRI, and enables a quantitative interpretation of SPRI for subcellular imaging.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2121-15-35) contains supplementary material, which is available to authorized users.

Control of the distribution of surface plasmon local field by altering the surrounding material

The field distribution of the surface plasmon (SP) around a silver nanowire greatly influences its applications for both spectrum enhancement and nano-waveguide. This paper demonstrates the change of the SP local field distribution of a silver nanowire on glass substrate with the refractive index of the covering medium by numerical simulation. The hot energy site is observed focusing on the interface between the nanowire and the surround material of larger refractive index. Moreover, we also find that the surface plasmon field becomes more confined as the refractive index between the substrate and medium has a larger gap, while a homogeneous distribution of the surrounding dielectric material around the nanowire shows a uniform local field distribution with a larger surface plasmon propagation length. The change of related parameters, such as effective index, mode area, and propagation length are also comprehensively investigated against the refractive index for nanowires with 100, 200, 300nm diameter. Considering the wide use of polymethyl methacrylate (PMMA) material, the field distribution of silver nanowire partially imbedded in PMMA against the PMMA thickness is also studied.

Leakage radiation microscope for observation of non-transparent samples

We describe a leakage radiation microscope technique that can be used to extend the leakage radiation microscopy to optically non-transparent samples. In particular, two experiments are presented, first to demonstrate that acquired images with our configuration correspond to the leakage radiation phenomenon and second, to show possible applications by directly imaging a plasmonic structure that previously could only be imaged with a near-field scanning optical microscope. It is shown that the measured surface plasmon wavelength and propagation length agree with theoretically-calculated values. This configuration opens the possibility to study important effects where samples are optically non-transparent, as in plasmonic cavities and single hole plasmonic excitation, without the use of time-consuming near-field scanning optical microscopy.

Nanoscale smoothing of plasmonic films and structures using gas cluster ion beam irradiation

We present a novel method of using gas cluster ion beam irradiation (GCIB) to flatten and widen grains in silver films and structures, while simultaneously, reducing the film thickness with nanometer precision. Ultrathin Ag films produced by GCIB have lower absorbance and better adhesion compared to as-deposited films. By applying the technique post-fabrication to plasmonic color filters, waveguides and disks, we show that an enhanced surface plasmon resonance and propagation length can be achieved.

Surface plasmons on ordered and bi-continuous spongy nanoporous gold

The dispersion relation and propagation of surface plasmons polaritons (SPPs) on nanoporous gold films is experimentally investigated and an increasing red shift of the SPPs is observed with rising porosity. This is caused by a less negative effective dielectric constant of the nanoporous metal films and is predicted by classical Bruggeman or specific two dimensional Maxwell-Garnett effective medium models. The dispersion relation data is supported with leakage radiation microscopy enabling the determination of the propagation length and losses of surface plasmons on these nanoporous films. These results demonstrate how the control of the nanoporosity of metal layers leads to designer plasmons in the visible and near infrared allowing the tuning of the SPP dispersion to match the requirements of certain applications.

Hot-electron nanoscopy using adiabatic compression of surface plasmons

Surface plasmon polaritons are a central concept in nanoplasmonics and have been exploited to develop ultrasensitive chemical detection platforms, as well as imaging and spectroscopic techniques at the nanoscale. Surface plasmons can decay to form highly energetic (or hot) electrons in a process that is usually thought to be parasitic for applications, because it limits the lifetime and propagation length of surface plasmons and therefore has an adverse influence on the functionality of nanoplasmonic devices. Recently, however, it has been shown that hot electrons produced by surface plasmon decay can be harnessed to produce useful work in photodetection, catalysis and solar energy conversion. Nevertheless, the surface-plasmon-to-hot-electron conversion efficiency has been below 1% in all cases. Here we show that adiabatic focusing of surface plasmons on a Schottky diode-terminated tapered tip of nanoscale dimensions allows for a plasmon-to-hot-electron conversion efficiency of ∼30%. We further demonstrate that, with such high efficiency, hot electrons can be used for a new nanoscopy technique based on an atomic force microscopy set-up. We show that this hot-electron nanoscopy preserves the chemical sensitivity of the scanned surface and has a spatial resolution below 50nm, with margins for improvement.

Influence of surface plasmon propagation on leakage radiation microscopy imaging

We study in this Letter, the effect of the surface plasmon (SP) propagation and coherence on the images obtained by leakage radiation microscopy. The studied system is a set of nanocrystals deposited on a thin silver film supporting surface plasmon modes. More than 70% of the emission in this typical system comes from non-local emission. The diameter of the influence circle around the detection point is of the order of magnitude of the plasmon propagation length. We also present an original method to measure the propagation length (Lspp) of surface plasmons in complex systems by a two Young's slits experiment. This method can be useful for complex systems with a very short propagation length.

Bragg-Scattered Surface Plasmon Microscopy: Theoretical Study

We present a new approach to surface plasmon microscopy with high refractive index sensitivity and spatial resolution that is not limited by the propagation length of surface plasmons. It is based on a nanostructured metallic sensor surface supporting Bragg-scattered surface plasmons. We show that these non-propagating surface plasmon modes are excellently suited for spatially resolved observations of refractive index variations on the sensor surface owing to their highly confined field profile perpendicular to as well as parallel to the metal interface. The presented theoretical study reveals that this approach enables reaching similar refractive index sensitivity as regular surface plasmon resonance (SPR) microscopy and offers the advantage of improved spatial resolution when observing dielectric features with lateral size <10 μm for the wavelength around 800 nm and gold as the SPR-active metal. This paper demonstrates the potential of Bragg-scattered surface plasmon microscopy for high-throughput SPR biosensing with high-density microarrays.

Surface plasmon and photonic mode propagation in gold nanotubes with varying wall thickness

Gold nanotube arrays are synthesized with a range of wall thicknesses (15 to &gt;140 nm) and inner diameters of \ensuremath{\sim}200 nm using a hard-template method. A red spectral shift (&gt;0.39 eV) with decreasing wall thickness is observed in dark-field spectra of nanotube arrays and single nanowire/nanotube heterostructures. Finite-difference-time-domain simulations show that nanotubes in this size regime support propagating surface plasmon modes as well as surface plasmon ring resonances at visible wavelengths (the latter is observed only for excitation directions normal to the nanotube long axis with transverse polarization). The energy of the surface plasmon modes decreases with decreasing wall thickness and is attributed to an increase in mode coupling between propagating modes in the nanotube core and outer surface and the circumference dependence of ring resonances. Surface plasmon mode propagation lengths for thicker-walled tubes increase by a factor of \ensuremath{\sim}2 at longer wavelengths (&gt;700 nm), where ohmic losses in the metal are low, but thinner-walled tubes (30 nm) exhibit a more significant increase in surface plasmon propagation length (by a factor of more than four) at longer wavelengths. Additionally, nanotubes in this size regime support a photonic mode in their core, which does not change in energy with changing wall thickness. However, photonic mode propagation length is found to decrease for optically thin walls. Finally, correlations are made between the experimentally observed changes in dark-field spectra and the changes in surface plasmon mode properties observed in simulations for the various gold nanotube wall thicknesses and excitation conditions.

LONG-RANGE SURFACE PLASMONS ON HIGHLY ANISOTROPIC DIELECTRIC SUBSTRATES

We calculate the propagation length of surface plasmons in metal-dielectric structures with anisotropic substrates. We show that the Joule losses can be minimized by appropriate orientation of the optical axis of a birefringent substrate and that the favorable orientation of the axis depends on ω. A simple Kronig-Penney model for anisotropic plasmonic crystal is also proposed.

Surface plasmon resonator: Design, construction, and observation in the farfield

We have studied the behavior of surface plasmons (SPs) in valley like structures [Schroter et al., Ultramicroscopy 68, 223 (1997)] and found that SPs traveling in both directions in such a cavity yield interference patterns in the farfield, which can be measured as specular and retroreflection. We have studied and designed the structures using finite element method in addition to a heuristic model, fabricated the devices using photolithography and experimentally verified the operation of the resonators, by observing the interference patterns of the specular and retroreflection in the farfield. We have found that the experimental results agree with the simulations, and explained the discrepancies. These structures can be useful in the study of the propagation length of SPs via observation in the farfield of the specular and the retroreflected light in laser industry and could be miniaturized to yield small biosensors.