Short-range Surface Plasmon Polaritons Research Articles

Analytical Model of Mid-Infrared Surface Plasmon Modes in a Cylindrical Long-Range Waveguide With Double-Layer Graphene

An optical waveguide for working in mid-infrared range is highly desirable. However, such a waveguide is required to yield a long propagation distance and deep subwavelength confinement. Although the graphene-based surface plasmon polariton (SPP) waveguides have exhibited some potential in this regard, their propagation lengths are currently insufficient (~100 μm). In this paper, we propose a graphene-based cylindrical long-range SPP (LRSPP) waveguide, which is composed of a cylindrical silicon nanowire core surrounded by an inner graphene layer, a silica layer, and an outer graphene layer from inside to out. First, the electromagnetic field equation and the dispersion equation of this waveguide are derived. Then, combining these derived equations with the numerical simulation, the propagation properties of the LRSPP and the short-range SPP modes are analyzed. The results show that the proposed waveguide with the LRSPP fundamental mode has a notable advantage for simultaneously achieving a larger propagation length (~10 μm) and a deep subwavelength confinement (~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the diffraction-limited mode area). This waveguide has potential for application in high-density photonic integrated circuits in the mid-infrared range.

Depolarization of a randomly distributed plasmonic meander metasurface characterized by Mueller matrix spectroscopic ellipsometry.

Metallic nanostructures offer efficient solutions in polarization control with a very low thickness. In this report, we investigate the optical properties of a nano-fabricated plasmonic pseudo-depolarizer using Mueller matrix spectroscopic ellipsometry in transmission configuration. The depolarizer is composed of 256 square cells, each containing a periodically corrugated metallic film with random orientation. The full Mueller matrix was analyzed as a function of incident angle in a range between 0 and 20° and over the whole rotation angle range. Depolarization could be achieved in two visible wavelength regions around the short-range and long-range surface plasmon polariton frequencies, respectively. Furthermore, depolarization for circularly polarized light was 2.5 times stronger than that for linearly polarized light. Our results could work as a guidance for realizing a broadband high efficiency dielectric metasurface depolarizers.

High Extinction Ratio and Short Length Surface Plasmon Polariton Polarizer

An ultrahigh extinction ratio and extremely short length resonant integrated optic TE pass polarizer are proposed, which is based on the interaction between the short range surface plasmon polaritons and the mode guided by the dielectric waveguide. It is shown that a compact very high extinction ratio and very low insertion loss TE pass polarizer can be designed by optimizing the buffer and metal layer thicknesses. The layer thicknesses and indices are chosen in a way, such that the multilayer plasmonic structure supports only asymmetric eigenmodes. It is shown that, as a result of interference (beat formation) between these asymmetric eigenmodes, a polarizer with an extinction ratio of 171 dB and insertion loss less than 0.01 dB can be designed for 49.4 $\mu \text{m}$ of its length.

Partial coherence and polarization of a two-mode surface-plasmon polariton field at a metallic nanoslab.

Rigorous electromagnetic theory is utilized to characterize the partial spatial coherence and partial polarization of a two-mode field consisting of the long-range and the short-range surface-plasmon polariton at a metallic nanofilm. By employing appropriate formulations for the spectral degrees of coherence and polarization, we examine the fundamental limits for these quantities associated with such a superposition field and explore how the degrees are influenced when the media, frequency, and slab thickness are varied. It is in particular shown that coherence lengths extending from subwavelength scales up to thousands of wavelengths are possible and their physical origins are elucidated. In addition, we demonstrate that for ultra-thin films the generally highly polarized two-mode field can be partially polarized in close vicinity of the polariton excitation region. The results could benefit cross-disciplinary electro-optical applications in which near-field interactions between plasmons and nanoparticles are exploited.

Characteristics of modified surface plasmon polaritons on double-coated metal nanofilms

The symmetrically and asymmetrically double-coated metal nanofilms are presented to transmit the modified surface plasmon polaritons. Compared with the short-range surface plasmon polaritons on single-coated metal nanofilms, the mode widths of the modified surface plasmon polaritons increase a little, but their propagation distances can increase three orders of magnitude, correspondingly their 1D figures of merit increase nearly three orders of magnitude. The long-range propagation together with the deep-subwavelength confinement of light energy makes the planar waveguides particularly useful in the fields of nanophotonics, integrated photonic circuits and nonlinear optics.

Optimization of Plasmonic Nanodipole Antenna Arrays for Sensing Applications

Nanoantennas are key optical components for several applications including biosensing. This paper presents the optimization of plasmonic nanodipole antenna arrays, operating with short-range surface plasmon polaritons, to maximize bulk sensitivity. The array is integrated on a substrate (silicon or glass) and covered by water. Using modal analysis, a full study was carried out on the dimensions of the nanodipoles at three optical wavelengths of interest, 850, 1310, and 1550 nm, and some of the results were validated using full 3D FDTD modeling. We show that nanodipoles on a glass substrate produce a greater bulk sensitivity than on a silicon substrate. The largest bulk sensitivities are produced at the longest wavelength (1550 nm) as 1000 nm/RIU on glass and 500 nm/RIU on silicon. Good performance over a wide range of nanodipole dimensions was observed, making the arrays tolerant to imperfections.

Optical f iber sensor based on the short-range surface plasmon polariton mode

An optical fiber sensor for ultrathin layer sensing based on short-range surface plasmon polariton (SRSPP) is proposed, and the sensing characteristics are theoretically analyzed. Simulation results indicate that even for a detecting layer much thinner than the vacuum wavelength, a resolution as high as 3.7\times 10-6 RIU can be obtained. Moreover, an average thickness-detection sensitivity of 6.2 dB/nm is obtained, which enables the sensor to detect the thickness variation of the ultrathin layer up to tens of nanometers. The sensitive region of thickness could be adjusted by tuning the structure parameters.

Coupled SPP Modes on 1D Plasmonic Gratings in Conical Mounting

Plasmonic nanostructures exhibit a variety of surface plasmon polariton (SPP) modes, with different characteristic properties. While a single metal dielectric interface supports a single-interface SPP mode, a thin metal film can support extended long range SPPs and strongly confined short range SPPs. When the coupling between the incident light and the SPP is provided through a diffraction grating, it is possible to azimuthally rotate the grating with respect to the scattering plane, introducing the possibility to propagate the SPP along an arbitrary direction. We present a theoretical and experimental analysis of the coupling conditions for long range and short range SPPs under this configuration. We also investigate the propagation length of the modes depending on the propagation direction with respect to the grating grooves, showing in particular that the long range SPP propagation length can be sensibly enhanced with respect to the null-azimuth case.

Grating-Assisted Excitation of Short-Range Surface Plasmon Polariton Mode

We propose an anti-symmetric grating structure for effective excitation of the short-range surface plasmon polariton (SR-SPP) mode of a metal stripe waveguide. The structure consists of two corrugated Bragg gratings offset by half of a period formed on the two sides of the metal stripe, respectively. The SR-SPP mode is excited in the backward direction by the long-range surface plasmon polariton mode launched into the waveguide. We investigate the effects of the metal stripe thickness, the grating corrugation depth, and the number of grating periods on the transmission and reflection characteristics of the grating with the finite-difference time-domain method in detail. Our numerical results show that a peak reflection of ~57% in the SR-SPP mode can be achieved with a 50-μm long grating on a 40-nm thick gold stripe.

Physical nature of volume plasmon polaritons in hyperbolic metamaterials

We investigate electromagnetic wave propagation in multilayered metal-dielectric hyperbolic metamaterials (HMMs). We demonstrate that high-k propagating waves in HMMs are volume plasmon polaritons. The volume plasmon polariton band is formed by coupling of short-range surface plasmon polariton excitations in the individual metal layers.

Integrated refractive index sensor based on hybrid coupler with short range surface plasmon polariton and dielectric waveguide

In this paper, an integrated sensor based on the vertical hybrid coupler composed of a short range surface plasmon polariton (SRSPP) waveguide and a SiNx dielectric waveguide has been studied theoretically and experimentally in detail by varying the structure parameters and the thickness of detection layer. It is demonstrated that the output power of the sensor changes significantly with the refractive index of the detection layer and the resolution is estimated to be as high as 7.3×10−6 refractive index units. The sensing range can be adjusted coarsely and delicately by varying the thickness of SRSPP waveguide and the width of the SiNx waveguide, respectively. Owing to the highly bounded mode field of SRSPP, the sensor is also applied to detect a 5nm-thick variation of detection layer with thickness detection sensitivity as high as 0.67dB/nm. Further, the sensor is used to detect the bisphenol A.

Tailoring Absorption in Metal Gratings with Resonant Ultrathin Bridges

We present a theoretical analysis of the effects of short range surface plasmon polariton excitation on sub-wavelength bridges in metal gratings. We show that localized resonances in thin metal bridges placed within the slit of a free-standing silver grating dramatically modify transmission spectra and boost absorption regardless of the periodicity of the grating. Additionally, the interference of multiple localized resonances makes it possible to tailor the absorption properties of ultrathin gratings, regardless of the apertures' geometrical size. This tunable, narrow-band, enhanced-absorption mechanism triggered by resonant, short range surface plasmon polaritons may also enhance nonlinear optical processes like harmonic generation, in view of the large third-order susceptibility of metals.

Plasmonic wave propagation in silver nanowires: guiding modes or not?

Propagation modes and single-guiding-mode conditions of one-dimensional silver nanowires based surface plasmon polariton (SPP) waveguides versus the operating wavelength (500-2000 nm) are investigated. For silver nanowires immersed in a SiO(2) matrix, both short-range SPP (SRSPP)-like modes and long-range SPP (LRSPP)-like modes can be guided. However, only the LRSPP-like modes have cutoff radii. For silver nanowires on a SiO(2) substrate, the LRSPP-like modes cannot be supported due to asymmetry. While for the SRSPP-like guiding mode, it has a cutoff radius for wavelength longer than 615 nm. For wavelength shorter than 615 nm, there is no cutoff radius for the guiding modes due to the appearance of the interface modes and thus the single-guiding-mode operation is always satisfied.

Short and long range surface plasmon polariton waveguides for xylene sensing

Nanostructured plasmonic sensors are fabricated as sinusoidal surface plasmon metallic gratings (SPGs) embedded in a functional and porous hybrid sol–gel material, phenyl-bridged polysilsesquioxane (ph-PSQ). The metal layer is in contact with the environment through the sol–gel film, which works as sensitive element, changing its dielectric properties upon interaction with aromatic hydrocarbons. The combination of sensitivity, transparency and patternability offered by ph-PSQs gives the exceptional possibility to fabricate innovative optical sensors with straightforward processes. An embedded SPG is a thin metal slab waveguide, in which the surface plasmon polaritons (SPPs) at the two metal–dielectric interfaces superpose, resulting in two physical coupled modes: the long range SPPs (LRSPPs) and the short range SPPs (SRSPPs). An extended experimental and theoretical characterization of the optical properties of the plasmonic device was performed. The sensor performance was tested against the detection of 30 ppm xylene, monitoring the influence of the target gas on the SPPs modes. A reversible red-shift of the reflectance dips of both LRSPP and SRSPP resonances in the 1.9–2.9 nm range was observed and correlated to the interaction with the analyte. An enhancement in sensitivity associated with the rotation of the grating grooves with respect to the scattering plane (azimuthal rotation) was verified within the experimental errors. Collected data are compatible with theoretical predictions assuming a variation of the film refractive index of 0.011 ± 0.005.

Integrated sensor for ultra-thin layer sensing based on hybrid coupler with short-range surface plasmon polariton and dielectric waveguide

Based on a hybrid coupler composed of short-range surface plasmon polariton (SRSPP) and dielectric waveguides, an integrated sensor for ultra-thin layer sensing has been realized. The simulation and experiment results demonstrate that the thickness variation of detection layer (polymer layer) about several nanometers could be detected. The measured thickness-detection sensitivity is as high as 0.67 dB/nm. And the sensitive region for thickness variation of polymer layer can be adjusted widely by varying the thickness of the SRSPP waveguide.

Double-Layered Metal Nano-Strip Antennas for Sensing Applications

A coupled plasmonic system based on double-layered metal nano-strips for sensing applications is investigated by means of mode analysis and two-dimensional finite-difference time-domain simulations. The nano-strips act as optical antennas through constructive interference of short-range surface plasmon polaritons, thus increasing their scattering cross-section and optical field enhancement. Near-field modulation by optical trapped metal nanoparticles (NPs) is also demonstrated. Our results reveal that the device exhibits a refractive index sensitivity of ∼200 nm/RIU, and a maximum surface-enhanced Raman scattering (SERS) factor of 109–1010 from metal NPs trapped in the near-field region. The proposed device shows reasonable figure-of-merit and is ready for integration with common optofluidic biosensors.

Pseudospectral mode solver for analyzing nonlinear optical waveguides

Numerical mode solver using a pseudospectral scheme is developed for solving various nonlinear dielectric and plasmonic waveguides with arbitrary nonlinear media. Two nonlinear iterative approaches that use this scheme are implemented; these approaches assign the mode power and effective index as extracted eigenvalues. However, to obtain the complete power dispersion curve including the stable and unstable modal solutions, assigning the mode power as an eigenvalue for a given effective index is required. Moreover, the biaxial feature of the nonlinear refractive index is considered for solving the transverse magnetic (TM) modes in materials of practical interest. Furthermore, the proposed scheme solves the problem of nonlinear surface plasmons guided by a thin metal film with nonlinear cladding, and the mode characteristics of long- and short-range surface plasmon polaritons are analyzed. We also apply the proposed scheme to a 2D strip waveguide with a nonlinear saturation substrate.

Excitation control of long-range surface plasmons by two incident beams

We demonstrate the excitation control of long-range surface plasmon polaritons (LRSPs) by experiments and simulations. We find that LRSPs and short-range surface plasmon polaritons can be selectively excited by two incident beams. This mechanism enables us to realize the excitation control of LRSPs using the phase difference or the intensity ratio between the two input signals. The excitation method analyzed here can be applied to active plasmonic devices based on LRSPs.

Refractive index sensor based on hybrid coupler with short-range surface plasmon polariton and dielectric waveguide

An integrated sensor based on a vertical hybrid coupler composed of a short-range surface plasmon polariton (SRSPP) waveguide and a SiNx dielectric waveguide has been realized. The output power of the sensor is observed to change drastically with the refractive index of the detection liquid, and the sensing region can be adjusted by varying the width of the SiNx waveguide. The resolution is estimated to be as high as 7.3 × 10−6 refractive index units. This sensor is expected to have significantly high effective sensitivity for detecting a hundred-nanometer-thick layer owing to the highly bounded field of the SRSPP mode.

Short-Range Surface Plasmon Polaritons for Extraordinary Low Transmission Through Ultra-Thin Metal Films with Nanopatterns

We provide both experimental and theoretical investigation on extraordinary low transmission through one-dimensional nanoslit and two-dimensional nanohole arrays on ultra-thin metal films. Unambiguous proofs demonstrate that short-range surface plasmon polaritons play a key role leading to this novel phenomenon, which could be useful for creating new polarization filters and other integrated plasmonic components.