Plasmon Waveguide Modes Research Articles

Design and analysis of a vertical directional coupler between a three-dimensional plasmonic slot waveguide and a silicon waveguide

The design of a vertical directional coupler between a three-dimensional plasmonic slot waveguide and a silicon waveguide is theoretically investigated in detail. It consists of two steps: the design of isolated plasmonic slot waveguide and silicon waveguide and the determination of the gap between the two waveguides and the length of a coupling region. The designed structure transfers 70.8% of the power carried by the silicon waveguide mode to the plasmonic slot waveguide mode when the gap is 150 nm and the coupling length is 2.14 μm. The wavelength dependence of our vertical directional coupler is also studied. The analysis shows that the amount of the transferred power changes slightly over a very wide wavelength range between 1.40 μm and 1.61 μm. Moreover, if we employ the fabrication technology for silicon photonics, it is quite tolerant to the variation of the length of its coupling section. Finally, the vertical directional coupler is considered for a polarizer.

Surface plasmon-mediated transmission in double-layer metallic grating polarizers

We study the mechanism of polarization-selective transmission in double-layer gratings. For TM polarized light, the coupling between the surface plasmon waveguide modes of slits in the two metal layers causes most of the energy to pass the gratings. For TE polarized light, there is no surface plasmon coupling effect, and most of the energy in the photoresist waveguide is reflected back because of the cutoff of waveguide modes. In view of the characteristics of surface plasmon waveguide modes, a new polarizer with an undercut profile of the photoresist is proposed to achieve better performance by improving the coupling efficiency. At the pitch of 200nm, the TM transmissions can be over 70% in the visible spectrum and over 80% in the wavelengths from 470nm to 800nm for a bottom width w2<60nm.

Optical Forces in Hybrid Plasmonic Waveguides

We demonstrate that in a hybrid plasmonic system the optical force exerted on a dielectric waveguide by a metallic substrate is enhanced by more than 1 order of magnitude compared to the force between a photonic waveguide and a dielectric substrate. A nanoscale gap between the dielectric waveguide and the metallic substrate leads to deep subwavelength optical energy confinement with ultralow mode propagation loss and hence results in the enhanced optical forces at low input optical power, as numerically demonstrated by both Maxwell's stress tensor formalism and the coupled mode theory analysis. Moreover, the hybridization between the surface plasmon modes and waveguide modes allows efficient optical trapping of single dielectric nanoparticle with size of only several nanometers in the gap region, manifesting various optomechanical applications such as nanoscale optical tweezers.

Intercoupling of free-space radiation to s-polarized confined modes via nanocavities

The interaction of the s-polarized waveguide mode in the dielectric layer placed on a metal film with one-dimensional indentations in the metal is studied. The efficiency of the coupling to the out-of-plane radiation is considered. It is shown that varying the parameters of the cavities, the periodical array of resonant indentations can almost totally reflect back the incident waveguide mode or, on the contrary, efficiently transform it into a narrow-directional outgoing beam. An efficient waveguide mode launcher is examined on the basis of the results for Bragg mirror. The differences and similarities between scattering of surface plasmon polaritons and waveguide modes are discussed.

PlasMOStor: A Metal−Oxide−Si Field Effect Plasmonic Modulator

Realization of chip-based all-optical and optoelectronic computational networks will require ultracompact Si-compatible modulators, ideally comprising dimensions, materials, and functionality similar to electronic complementary metal-oxide-semiconductor (CMOS) components. Here we demonstrate such a modulator, based on field-effect modulation of plasmon waveguide modes in a MOS geometry. Near-infrared transmission between an optical source and drain is controlled by a gate voltage that drives the MOS into accumulation. Using the gate oxide as an optical channel, electro-optic modulation is achieved in device volumes of half of a cubic wavelength with femtojoule switching energies and the potential for gigahertz modulation frequencies.

Nonresonant enhancement of spontaneous emission in metal-dielectric-metal plasmon waveguide structures

We theoretically investigate the spontaneous emission process of an optical, dipolar emitter in metal-dielectric-metal slab and slot waveguide structures. We find that both structures exhibit strong emission enhancements at nonresonant conditions, due to the tight confinement of modes between two metallic plates. The large enhancement of surface plasmon-polariton excitation enables dipole emission to be preferentially coupled into plasmon waveguide modes. These structures find applications in creating nanoscale local light sources or in generating guided single plasmons in integrated optical circuits.

Enhancement in middle-ultraviolet emission in a surface-plasmon-assisted coaxial nanocavity

Cathodoluminescence spectrum of a single Zn–Zn2SiO4 core-shell nanocable exhibits a strong emission at 293nm accompanied with a weaker splitting peak at its long wavelength side. Experiment and ab initio calculation results indicate that the UV emissions are associated with the Zn2SiO4 surface states. Finite-difference time-domain simulations show that a surface-plasmon-assisted nanocavity can selectively confine and enhance the electric field energy of the 293nm light due to the smallest mode volume and the highest finesse among surface plasmon resonance, whispering gallery, and waveguide modes. Further temperature dependence experiment and correlative theoretical derivation suggest that the splitting is associated with a strong coupling between the nanocavity and the emitter.

Highly directional fluorescence emission from dye molecules embedded in a dielectric layer adjacent to a silver film

We report measurements on the angular radiation patterns from dye molecules embedded in a polymethyl methacrylate thin film spin-coated on a thin silver film. We systematically studied the influence of the thickness of the silver films and the thickness of the dielectric layers on the radiation pattern. We present the detailed radiation patterns over a large angular range showing highly polarized fluorescence emission coupled into the surface plasmon modes or waveguide modes. We also studied the influence of the polarization of the excitation beam on the radiation patterns. The experimental data are compared with numerical simulations using an asymptotic approach based on the Lorentz reciprocity theorem.

Grating-coupled surface plasmon polaritons and waveguide modes in a silver-dielectric-silver structure

A silver-dielectric-silver structure that supports both waveguide modes and surface plasmon polaritons is explored. The upper interface between the dielectric and the silver is periodically corrugated to allow coupling of visible photons to both types of mode. Such a metallic microcavity leads to plasmonic and waveguide self-interacting bandgaps at Brillouin zone boundaries. In addition there are found other bandgaps from mode crossings within the Brillouin zone. This results specifically in a very flat photonic band due to anticrossings between a surface plasmon polariton and waveguide modes. Characterization of the observed modes in terms of their resonant electromagnetic fields is achieved by using a multilayer, multishape differential grating theory.

Adaptive spatial resolution: application to surface plasmon waveguide modes

In order to simulate surface plasmon waveguide structures we have utilized and improved the adaptive spatial resolution technique and combined it with PML boundary conditions. Using this new technique we have developed a novel concept for an integrated surface plasmon biosensor.

Pulse delay and propagation through subwavelength metallic slits.

The transmission properties of a 2D metallic grating are investigated at optical wavelengths for an incident Gaussian pulse having pulse widths from 100 fs to 10 ps. The slits in the grating are subwavelength which can nevertheless allow significant transmission in the narrow wavelength regions where the so-called surface plasmon polariton (SPP) and waveguide mode resonances occur. The solution is obtained for each spectral component of the pulse by using the rigorous coupled wave approach and then the temporally varying output pulse is reconstructed by the standard method of taking an inverse Fourier transform. The delay of the pulse and the output pulse widths are determined by taking the first and second order moments of the Poynting vector with respect to time. It is shown that the time delay may be significant, as much as 256 fs for a pulse width of 200 fs for the SPP resonance but quite small (32 fs) for the waveguide mode resonance. The focus of the work is on demonstrating how the pulse delay evolves as the pulse propagates in the half-space beyond the grating. It is shown that the distance over which the time delay develops is much larger than the actual longitudinal dimension of the grating structure and it is approximately the same distance over which the stored energy and the vortices of the Poynting vector extend.

Optical near-field distributions of surface plasmon waveguide modes

Thin gold stripes, featuring various widths in the micrometer range, were microfabricated to obtain surface-plasmon guides on a glass substrate. Each metal stripe (MS) was excited by an incident surface-plasmon polariton which was itself launched on an extended thin gold film by the total internal reflection of a focused beam coming through the substrate. The optical near-field distributions of the surface-plasmon (sp) modes sustained by the stripes were then recorded using a photon scanning tunneling microscope (PSTM). For a fixed frequency of the incident light, these field distributions are found to depend on the widths of the stripes. We first provide an experimental study of the various order modes which arise as a function of the decreasing width. Specifically, we show that the lateral confinement of a MS surface-plasmon mode is not related to a reflection of the SP on the edges of the stripe. On the basis of PSTM images recorded over a gold thin-film step discontinuity, we show that the metal stripe plasmon modes are hybrid modes created by the coupling of interface and boundary modes. Using MSs of various thicknesses, we finally demonstrate that, similarly to the symmetric mode of an extended metal thin film bounded by different dielectric media, the field of the MS modes is mostly localized at the interface between the metal and the dielectric medium with the lowest refractive index.

Surface Plasmon Resonance Studies of Protein Binding on Plasma Polymerized Di(ethylene glycol) Monovinyl Ether Films

The attachment of fibrinogen, bovine serum albumin, and immunoglobulin on continuous wave (CW) and pulsed plasma polymerized di(ethylene glycol) monovinyl ether was studied using surface plasmon resonance (SPR) spectroscopy and waveguide mode spectroscopy (WaMS). Structural analysis of the films was carried out using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. Plasma conditions employed during depositions produced significant differences in the chemical and physical properties of the resultant polymer films. Films deposited under CW and higher plasma duty cycles showed relatively high refractive indices (n > 1.57) and essentially a constant thickness if immersed in aqueous buffer solutions and exhibited a high adsorption affinity for proteins. In contrast, films produced under lower plasma duty cycles were of lower refractive index (n < 1.4), exhibited significant swelling if immersed in aqueous buffer, and were extremely effective in preventing protein adsorption. The SPR and WaMS data suggest that the relatively non-cross-linked films produced at the lower duty cycles exhibit hydrogel-like behavior when immersed in aqueous solutions. It is believed that these hydrated films are responsible for the remarkably effective nonfouling properties of the films deposited at low duty cycles. The relationship between film structure, polymer stability in aqueous buffer, and protein binding affinities are discussed.

Continuous wave operation of ~ 19 [micro sign]m surface-plasmon quantum cascade lasers

Continuous wave laser action has been achieved in a superlattice quantum cascade device operating on surface plasmon waveguide modes. The emission wavelength λ ~ 19 µm is by far the longest ever reported for continuous wave III-V semiconductor lasers. The output power at cryogenic temperature is of the order of the mW.

Distributions of Functional Groups in Plasma Polymerized Allylamine Films by Scanning Force Microscopy Using Functionalized Probe Tips

Thin films of poly(allylamine) on silicon were prepared by polymerization of allylamine in a pulsed glow-discharge plasma reactor. The films were characterized by surface plasmon spectroscopy (SPS) and waveguide mode spectroscopy (WaMS), as well as by X-ray photoelectron spectroscopy (XPS) and FT-IR spectroscopy. It was shown that by variation of the duty cycle the film thickness as well as the content of amino and nitrile groups could be controlled. Scanning force microscopy (SFM) measurements with chemically functionalized tips led to a qualitative correlation of adhesion forces with the content of amino groups. Laterally resolved adhesion force measurements indicated the presence of a heterogeneous local environment of the amino groups, with patches exhibiting differences in hydrophobicity on a sub-50-nm scale.