Propagation Loss of Long-Range Surface Plasmon Polariton Gold Stripe Waveguides in the Thin-Film Limit

Propagation loss experienced by long-range plasmon polaritons in ultrathin gold stripe waveguides embedded in different polymer cladding materials was studied and correlated with atomic-scale characterization of the gold film structure. We identify the main sources of experimentally observed propagation loss which deviates from ideal values in the thin-film limit. Increased loss can be translated to an increased effective thickness of the ultrathin films due to incomplete surface coverage and the presence of diffuse interfaces, both of which depend significantly on the choice of cladding material. The results illustrate the importance of atomic-scale dynamics of metal film formation for the selection of optimum substrate materials for surface plasmon polariton waveguides, resonant transmission structures, and semitransparent electrical contacts.     

Tunable Multi-Port Surface Plasmon Polariton Excitation with Nanostructures

Surface plasmon polaritons (SPPs) have appealing features such as tighter spatial confinement and higher local field intensity. Manipulation of surface plasmon polaritons on metal/dielectric interface is an important aspect in the achievement of integrated plasmonic circuit beyond the diffraction limit. Here, we introduce a design of pin cushion structure and a holographic groove pattern structure for tunable multi-port SPPs excitation and focusing. Free space light is coupled into SPPs through momentum matching conditions. Both nanostructures are capable of tunably controlling of SPPs depending on the incident polarizations, while the holographic method provides more flexibility of wavelength-dependent excitations. Furthermore, a quantitative method is applied to calculate the efficiencies of excitation for both nanostructures under different conditions, including radially polarized incident beams. These results can work as a guidance and be helpful to further choice of the suitable design strategies for variable plasmonic applications such as beam splitter, on-chip spectroscopy, and plasmonic detectors.     

Coupled Mode Theory for Surface Plasmon Polariton Waveguides

In allusion to special modes supported by surface plasmon polariton (SPP) waveguides, explicit expression for mode coupling coefficient which plays a central role in coupled mode theory is firstly redefined by adding the longitudinal electric field component. The mode coupling coefficients calculated by the proposed formula improve greatly compared with the coupled mode theory suited to conventional optical waveguides, and reasonable explanations from the point of view of physics and mathematics have been given. Afterwards, the coupling lengths, the transmission lengths, the normalized power exchanges, and the cross talk performances of adjacent parallel SPP waveguides with varying waveguide separation distances D and waveguide lengths L are investigated at telecom wavelength. The results are encouraging as they indicate that the coupled mode theory is developed in a self-consistent manner by retaining the longitudinal electric field component in the derivation and neglecting it only when the waveguides structure satisfies the weakly guiding situations. As a result, the new mode coupling coefficient formula for SPP waveguides considered in this paper is an important complement in the theory of SPP waveguides.     

Highly Sensitive Refractive Index Sensing with Surface Plasmon Polariton Waveguides

Two prototypical transducer structures are proposed, including a single-waveguide (SW) and Mach–Zehnder interferometer (MZI), implemented with surface plasmon polariton waveguides. Formulas of the output power with structural parameters are deduced respectively. The sensitivities are found to be proportional to S ₁ for SW and S ₂ for MZI, which are dependent on waveguide parameters. Maximizing S ₁ or S ₂ maximizes the corresponding sensitivity, leading to optimized waveguide designs and preferred operating wavelengths. Sensitivity parameters S ₁ and S ₂ are calculated for fundamental modes of V grooves, triangular wedges, and dielectric-loaded surface plasmon polariton waveguides (DLSPPWs), as a function of measured material refractive index n _c (n _c ?=?1.3～1.6, representative refractive index of biochemical matter), at wavelength λ?=?1.55 μm. Finally, the sensitivity S ₂ is analyzed as a function of work wavelength for DLSPPWs with different ridge thickness and specific fluidic SPP waveguide for biochemical sensing is presented. The results offer foundations for application of surface plasmon polariton waveguides in biochemical sensing.     

Near-Field Coupling Method for Subwavelength Surface Plasmon Polariton Waveguides

A near-field coupling method for studying propagation properties of surface plasmon polariton (SPP) in subwavelength dielectric-loaded SPP waveguides (DLSPPWs) is presented. In this method, a tapered fiber probe is employed to generate a nanometer optical spot. When this spot is near the entrance of the DLSPPW with its polarization parallel to the waveguide, a strong guiding wave is observed by a leakage radiation microscope. For DLSPPWs with a dielectric height of about 600 nm, we observed SPP waves with zigzag propagation patterns at 650 nm wavelength. Such zigzag propagation results in a great reduction of propagation loss. In addition, the zigzag wave has a strong optical confinement. The bending loss for an L-bend DLSPPW is only about 0.4 dB.     

Three-Dimensional Manipulations of Surface Plasmon Polariton Wave Propagation

The plasmonic integrated circuit, a potential application of surface plasmon polaritons (SPPs), can manipulate an SPP wave propagating on a metal surface in a way similar to electronic circuits. Here, we propose the concept of three-dimensional (3D) SPP wave manipulation: control of an SPP wave propagating in both the horizontal direction and the vertical direction. A hole set in the film can guide an SPP wave in the vertical direction. In the horizontal direction, two holographic groove patterns are used to focus an incident SPP wave on one surface of the film to the hole and control the divergent SPP waves transmitted from the hole on the other metal surface, respectively. The holographic groove patterns are designed via the methodology of surface electromagnetic wave holography. 3D finite-difference time-domain method simulations show a good performance of the 3D manipulation via these designed holographic groove patterns.

     

On Plasmon Polariton Propagation Along Metallic Nano-Chain

The collective wave type plasmon polariton self–modes in the metallic (Au, Ag) nano-chain were determined and analyzed with respect to the nano-sphere size and chain separation parameters. At some regions for parameters, the undamped modes were identified when the interaction had been assumed as the near-field-zone dipole coupling. These modes were found on the rim of stability of the linear theory, which indicates artifact of the model of near-field coupling. Inclusion of the medium- and far-field zone contributions to dipole interaction removes, however, instability and allows for fully analytical demonstration of quenching of irradiation losses of plasmon polaritons in the chain to the level of only ohmic attenuation. The plasmon polariton dispersion and the group velocity of plasmon polariton wave packets were examined with respect to nano-sphere and chain parameters and mode polarization. Previous numerical results related to long-range plasmon polariton propagation in the chain are transparently interpreted within the analytical approach.     

Graphene Hybrid Surface Plasmon Waveguide with Low Loss Transmission

In this paper, a novel graphene hybrid surface plasmon waveguide structure is designed. Based on the finite element method, the mode characteristics, the quality factor, and the gain threshold of the waveguide structure are analyzed. The results show that the optical field constraint of the designed waveguide can reach a better level of deep sub-wavelength under the optimal parameters of 1550-nm working wavelength. The structure is applied to a laser, and the high quality factor, the low energy loss, the low threshold limit, and the ultra-small effective mode field area are obtained by adjusting waveguide design parameters. Compared with the common waveguide structure, this structure has stronger optical field limiting ability and microcavity binding ability. It provides theoretical and technical support for the development of new high-efficiency nano-laser devices and is expected to be applied to fields such as on-chip interconnects, photonic integrated circuits, optical storage, and optical signal processing.

     

Surface Plasmon Polariton Propagation at the Interface of a Metal and an Ambichiral Nanostructured Medium

The propagation of a surface plasmon polariton wave at the interface of a metal and an ambichiral nanostructured medium was theoretically investigated in the Kretschmann configuration using transfer matrix method. The dependence of optical absorption linear polarization on structural parameters was reported. The results were compared with those obtained from the interface of a metal and a chiral dielectric medium as a reference structure. We found that multiple plasmon modes are excited at the interface of metal and ambichiral dielectric medium. Our calculations revealed that there exist five plasmon modes for chiral, trigonal, and tetragonal structures; three plasmon modes for pentagonal structure; two plasmon modes for hexagonal structure; and one plasmon mode for dodecagonal structure that propagate with different phase speeds. The obtained results showed that only one plasmon mode occurs at all pitches, while other modes exist at some of the pitches of anisotropic chiral and ambichiral dielectric mediums. The time-averaged Poynting vector versus the thickness of metal film confirmed that the energy of photons of incident light is transferred to surface plasmon polariton quasiparticles and the surface plasmon polariton wave is localized at the interface of metal and ambichiral dielectric medium.     

Coupling Behaviors of Surface Plasmon Polariton and Localized Surface Plasmon with an InGaN/GaN Quantum Well

Plasmonics - Surface plasmon (SP) coupling behaviors of an InGaN/GaN quantum well (QW) with surface plasmon polariton (SPP) induced on a smooth Ag-film/GaN interface and localized surface plasmon...     

Generating Surface Plasmon Polariton Airy Beam with Dielectric Relief Holographical Structures

Plasmonics - 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...     

A Dielectric-Thickness-Adjusting Method for Manipulating Graphene Surface Plasmon Polariton

We propose and numerically investigate a dielectric-thickness-adjusting method to manipulate the graphene surface plasmon polariton (SPP). The dispersion relationships of graphene SPP at different dielectric thickness are derived by solving the analytic equations. In addition, the SPP effective index at cutoff dielectric thickness is obtained according to different dielectric permittivity and working frequencies. As a typical application, a plasmonic Bragg reflector is designed by alternately depositing dielectric gratings along the transverse direction of the SPP propagation. The performance of the Bragg reflector is analyzed at different grating thickness, and the effective index at cutoff thickness is verified by numerical simulation. The proposed method will have important potential prospects in designing graphene-based wave trapping and slow wave devices in future.     

Novel Ridge-Type Gold Film Waveguide for Surface Plasmon Polariton Laser

Plasmonics - Surface plasmon polariton lasers are the basis for photonic circuits, but their losses, thresholds, and some other problems remain thorny issues. In this study, we put forward a novel...     

Unidirectional Surface Plasmon Polariton Excitation on Single Slit with Oblique Backside Illumination

We have theoretically investigated the unidirectional surface plasmon polariton (SPP) excitation on single slits with oblique backside illumination. An aperture diffraction method is devised, from which the conditions of slit width and beam illumination angle for the unidirectional SPP excitation are formulated analytically. The derived unidirectional conditions are validated with vectorial electromagnetic simulation using the rigorous coupled wave analysis.     

Surface Plasmon Polariton Waveguide by Bottom and Top of Graphene

Semiconductor surface plasmon polariton (SPP) waveguide has unique optical properties and compatibility with existing integrated circuit manufacturing technology; thus, SPP devices of semiconductor materials have wide application potential. In this study, a new integrated graphene SPP waveguide is designed using the bottom and top roles of graphene. Moreover, a T waveguide structure is designed by InGaAs of semiconductor gain, with rectangular GaAs material on both sides. The structure adopts light to stimulate the SPP, where its local area is enhanced by the interaction between two interface layers and a semiconductor gain and where its frequency can be adjusted by the thickness of the graphene. Characteristic analysis reveals the coupling between the T semiconductor gain and the SPP mode. The propagation distance of the waveguide can reach 75 cm, the effective mode field is approximately 0.0951λ ², the minimum of gain threshold is approximately 2992.7 cm^?1, and the quality factor (FOM) can reach 180. The waveguide structure which provides stronger localization can be compatible with several optical and electronic nanoscale components. That means, it can provide light for surface plasmon circuit and also can provide a great development in the low-threshold nanolaser.     

Anticrossing Behavior of Surface Plasmon Polariton Dispersions in Metal-Insulator-Metal Structures

The anticrossing behavior of dispersion curves of the surface plasmon polaritons supported by metal-insulator-metal structures are studied experimentally and theoretically. Samples consisting of a poly(methyl methacrylate) layer sandwiched by Ag films are prepared and their angle- and wavelength-scan attenuated total reflection spectra are measured. From an analysis of the angle-scan spectrum, the coupled-mode nature of the surface plasmon polariton modes is suggested. The dispersion relations obtained from the wavelength-scan spectra exhibit clearly the anticrossing behavior that arises from the coupling of the modes. The experimental dispersion relations are in good agreement with theoretical ones.     

Direct Observation of Surface Plasmon Polariton Propagation and Interference by Time-Resolved Imaging in Normal-Incidence Two Photon Photoemission Microscopy

Plasmonics - Time-resolved imaging of the propagation and interference of isolated ultrashort surface plasmon polariton wave packets is demonstrated using two photon photoemission microscopy. The...     

Efficient Surface Plasmon Polariton Excitation with the Beam Generated by Micro Triangular Prism

The optical beam generated by a micro triangular prism is presented to excite surface plasmon polaritons (SPPs) on a single silver nano slit. The electromagnetic fields generated by the micro triangular prism and the excited surface plasmon polaritons are simulated with finite-difference time-domain method. Compared with directly normal incident beam, the efficiency of SPPs’ excitation with the beam generated by the micro triangular prism is highly improved.     

Multi-mode Hybrid Plasmonic Waveguides with Enhanced Confinement and Propagation

A hybrid waveguide, which consists of a dielectric wire above a dielectric-metal interface, has been previously proposed to achieve high confinement with low loss. By exciting this geometry with an aperture in the metal that takes advantage of the extraordinary transmission through subwavelength apertures, it is possible to strongly couple to multiple modes. The real part of the fundamental mode is in fact capable of exceeding the index of refraction of all the materials used while maintaining a manageable imaginary part, as a result of appropriate choice of materials for the dielectric wire and the metal. In addition, as the confinement of the second mode is comparable to that of the fundamental mode but has a much longer propagation length, this mode can be utilized in light-guiding applications where enhanced confinement and propagation is desired.     

Resonant Mode Analysis of the Nanoscale Surface Plasmon Polariton Waveguide Filter with Rectangle Cavity

The resonant mode characteristics of the nanoscale surface plasmon polaritons (SPP) waveguide filter with rectangle cavity are studied theoretically. By using the finite difference time domain method, both the band-stop- and band-pass-type rectangle SPP filters are analyzed. The results show that the whispering gallery mode (WGM) and the Fabry–Perot (FP) mode can be supported by the rectangle SPP resonator. Furthermore, both traveling-wave mode and standing-wave mode can be realized by the WGM, while only standing-wave mode can be introduced by the FP mode. The traveling-wave mode can only be realized by the square-shaped SPP resonator, and the traveling-wave mode is splitted into two standing-wave modes by transforming the cavity shape from square to rectangle. Also, the effects of the cavity shape, cavity size, and coupling gap size on the transmission spectra of the SPP resonators are analyzed in detail. This simple SPP waveguide filter is very promising for the high-density SPP waveguide integrations.