Modal Analysis of Surface Plasmon Resonance Sensor Coupled to Periodic Array of Core-Shell Metallic Nanoparticles

The influence of a dielectric shell on metallic spherical nanoparticles [core-shell nanoparticles (CSNps)] in the resonant modal response of a surface plasmon resonance (SPR)-type sensor is presented. The planar multilayer sensor structure, based on the Kretschmann and surface plasmon coupled emission (SPCE) configurations, is coupled to a periodic array of these nanoparticles. In the first configuration, the CSNps are considered as a homogeneous layer with effective permittivity given by the Clausius-Mossotti mixing formula and polarizability of a core shell for a quasi-static scattering regime. In the second configuration, it performed an evaluation via the discrete complex image method (DCIM). Electromagnetic wave propagation is evaluated by the generalized reflection coefficient for multilayer structures. The analytical results are validated by numerical simulations performed via finite element method and also by experimental data. We observed that the dielectric shell thickness affects considerably the sensibility of the sensor when analyzing the change in other parameters of the CSNps array

Hybridization of Surface Plasmon Polaritons and Molecular Excitations

Starke Kopplung von Molekülen mit einem räumlich begrenzten Lichtfeld führt zur Bildung neuer polaritonischer Eigenzustände des Systems, die sowohl molekulare als auch photonische Eigenschaften erhalten und somit ein großes Potenzial für Anwendungen in der Chemie und Optoelektronik besitzen. In dieser Arbeit wird die Kopplung zwischen Oberflächenplasmonen Polaritonen (SPPs), die als das räumlich begrenzte Lichtfeld agieren, und molekularen Anregungen wie Schwingungen und polaronischen Resonanzen untersucht. Das starke Kopplungsregime zwischen einer Molekülschwingung und einem SPP wird zum ersten Mal im mittleren Infrarot unter Verwendung der Carbonylschwingung von Poly(vinylmethylketon) Polymer und Silber als Ausbreitungsmedium von SPPs demonstriert. Die neu gebildeten Hybridmoden werden durch Experimente und numerische Modellierung untersucht, wobei Messungen der abgeschwächten Totalreflexion und der thermischen Emission sowie Berechnungen mittels der Transfermatrix und der linearen Dispersionstheorie verwendet werden. Ein Anticrossing in der Dispersion der Polariton-Zweige mit einer Energieaufspaltung bis zu 15 meV, was die Hauptsignatur des starken Kopplungsregimes ist, wird beobachtet. Die starke Kopplung mit Zinkgalliumoxid, einem hochdotierten Halbleiter als Alternative zu Edelmetallen, wird auch untersucht. Experimentelle und simulierte Reflektometrie-Spektren sowie Dispersionsrelationen werden diskutiert, um Rückschlüsse auf die Eigenschaften des Systems zu ziehen. Außerdem wird ein Ansatz zur Verbesserung der Leitfähigkeit organischer Halbleiterpolymere durch starke Kopplung ihrer polaronischen Zustände an SPPs vorgestellt und Leitfähigkeitsmessungen durchgeführt. Ziel ist es, die Delokalisierung der Hybridzustände auszunutzen, um die Leitfähigkeit zu verändern. Die präsentierten Ergebnisse bieten neue Einblicke in den Nutzen der Eigenschaften der Licht-Materie-Hybridisierung, um ihr volles Potenzial für verschiedene Bereiche und Anwendungen zu erforschen.Strong coupling of molecules with a confined light field results in the formation of new polaritonic eigenstates of the system called polaritons that inherit both molecular and photonic characteristics and thus holds strong potential for applications in chemistry and optoelectronics. In this work, coupling between propagating surface plasmon polaritons (SPPs), as confined light field, and molecular excitations, such as vibrational resonances and polaronic features, is investigated. The strong coupling regime between a molecular vibration and a propagating SPP is demonstrated for the first time in the mid-infrared spectral range using the carbonyl stretch vibration of Poly(vinyl methyl ketone) polymer and silver as metallic medium for SPPs propagation. The newly formed hybrid modes are investigated through experiments and numerical modelling, employing attenuated-total-reflection and thermal emission measurements as well as transfer-matrix and linear dispersion theory calculations. An anticrossing behavior in the dispersion of the polariton branches with an energy splitting up to 15meV, which is a key signature of the strong coupling regime, is observed. Strong coupling involving zinc gallium oxide, which is a highly doped semiconductor, as an alternative to noble metals is also investigated. Experimental and simulated reflectometry spectra as well as the dispersion relations are discussed so as to draw conclusions about the properties of the system. Furthermore, an approach to enhance the conductivity of organic semiconductor polymers by strongly coupling their polaronic states to SPPs is presented and four-point probe measurements are conducted. The goal is to exploit the delocalization of the hybrid states to alter the conductivity of the organic semiconductor. The results presented in this thesis provide new insights into the profit from the properties of light-matter hybridization in order to explore its full potential for several areas and applications

Surface Plasmon Polaritons: Guided-wave Devices and Applications

The prospect of controlling the interaction of light with matter at nanoscale has been widely studied in recent years, and entails characterizing optical and optoelectronic devices at resolution higher than the diffraction limit. One technique that allows localization of light to sub-wavelength dimensions is through the use of surface plasmon polaritons (SPPs) wherein the interaction of light with free electrons on a metal surface can lead to a bound surface electromagnetic field that is confined to deep sub-wavelength dimensions. Studies based on SPPs merged with the field of nanotechnology have resulted in novel imaging technologies, nonlinear and quantum-optical devices and the ability to design materials with unusual electromagnetic properties with potential applications ranging from enhancing the efficiency of photovoltaic devices to detection of bio-molecules at ultra-small concentrations. Here we report the design of nanophotonic devices based on SPP waveguide structures that would act as a true counterpart to today’s electronic devices, providing orders of increase in data speeds while maintaining nanoscale dimensions. The devices are based on metal-dielectric-metal (MDM) waveguide structures composed of Ag/SiO2/Ag heterostructure that utilizes interference effect within multiple intersecting plasmonic waveguides. We have explored guided-wave devices such as L and T-bends, 4-way-splitters and 2x2-networked structures, wherein by altering the device geometry one can tune its operating frequency, and by changing the angle of incidence one can switch these devices between ON/OFF states. We plan to fabricate and experimentally characterize these devices for applications in color routing, directional filters and optical switches. We discuss preliminary design rules and constraints based on results obtained from finite-difference-time-domain simulations

Multiple self-healing Bloch surface wave beams generated by a two-dimensional fraxicon

Two-dimensional surface waves are a cornerstone for future integrated photonic circuits. They can also be beneficially exploited in sensing devices by offering dark-field illuminations of objects. One major problem in sensing schemes arises from the individual sensing objects: the interaction of surface waves with an object reduces the field amplitude, and the readout of other objects along the propagation path suffers from this reduced signal. Here we show in two experiments that nondiffracting and self-healing Bloch surface waves can be launched using a Fresnel axicon (i.e., fraxicon). First, we visualize the generation of an array of multiple focal spots by scanning near-field optical microscopy in the infrared. With a second device operating in the visible, we demonstrate the self-healing effect directly using a far-field readout method by placing metallic nanoantennas onto the multiple focal spots of the fraxicon. Our study extends the versatile illumination capabilities of surface wave systems

Subwavelength Surface Plasmons Based on Novel Structures and Metamaterials

With the rapid development of nanofabrication technology and powerful computational tools over the last decade, nanophotonics has enjoyed tremendous innovation and found wide applications in ultrahigh-speed data transmission, sensitive optical detection, manipulation of ultra-small objects, and visualization of nanoscale patterns. Surface plasmon-based photonics (or plasmonics) merges electronics and photonics at the nanoscale, creating the ability to combine the superior technical advantages of photonics and electronics on the same chip. Plasmonics focuses on the innovation of photonic devices by exploiting the optical property of metals. In particular, the oscillation of free electrons, when properly driven by electromagnetic waves, would form plasmon-polaritons in the vicinity of a metal surface and potentially result in extreme light confinement, which may beat the diffraction limit faced by conventional photonic devices and enable greatly enhanced light-matter interactions at the deep subwavelength scale. The objective of this dissertation is to develop subwavelength or deep subwavelength plasmonic waveguides and explore their integration on conventional dielectric platforms for multiple applications. Three novel structures (or mechanisms) are employed to develop and integrate nanoplasmonic waveguides; each consists of one part of the dissertation. The first part of this dissertation covers the design, fabrication, and demonstration of two-dimensional and three-dimensional metal-insulator-metal plasmonic couplers for mode transformation between photonic and nanoplasmonic domains on the silicon-on-insulator platform. In particular, deep subwavelength plasmonic modes under 100-nm are achieved via end-fire coupling and adiabatic mode transformation at telecom wavelengths. The second part studies metallic gratings as spoof plasmonic waveguides hosting deep subwavelength surface propagation modes. Metallic gratings under different dielectric coatings are numerically investigated for terahertz and gigahertz regions. The third part proposes, explores, and experimentally demonstrates the metametal for super surface wave excitation based on multilayered metal-insulator stacks, where the dispersion of the supported surface modes can be engineered by insulator dopant films in a given metal. The final part discusses the potential applications of active plasmonics for optical sensing, modulation and photovoltaics

Effects of relief gratings, light characteristics and material properties to the emission resonance region

We present numerical simulations in order to investigate the coupling of the incident radiation to Surface Plasmon polaritons (SPPs) by metallic relief gratings. When the frequency of the SPPs is coincident with the electromagnetic waves, there is a strong absorption of the electromagnetic waves. This phenomenon is called surface Plasmon resonance (SPR). The effects of surface materials, characteristics of incident light and the geometrical shapes on the SPR are studied by using the rigorous coupled-wave algorithm (RCWA). The results reveal that a peak of high emissivity is obtained for Au compared with W, Cu and Al. This explained that the gold is the best transition metal used for the excitation of SPPs. At the resonance the absorption of light by the (Au) grating is greater for grazing than normal incident light. Every considered transition material has the particular wavelength emission region and the period emission region. The influence of gratings geometric parameters on the SPR is also presented

Performance analysis of higher mode spoof surface plasmon polariton for terahertz sensing

We investigated the spoof surface plasmon polaritons (SSPPs) on 1D grooved metal surface for terahertz sensing of refractive index of the filling analyte through a prism-coupling attenuated total reflection setup. From the dispersion relation analysis and the finite element method-based simulation, we revealed that the dispersion curve of SSPP got suppressed as the filling refractive index increased, which cause the coupling resonance frequency redshifting in the reflection spectrum. The simulated results for testing various refractive indexes demonstrated that the incident angle of terahertz radiation has a great effect on the performance of sensing. Smaller incident angle will result in a higher sensitive sensing with a narrower detection range. In the meanwhile, the higher order mode SSPP-based sensing has a higher sensitivity with a narrower detection range. The maximum sensitivity is 2.57 THz/RIU for the second-order mode sensing at 45° internal incident angle. The proposed SSPP-based method has great potential for high sensitive terahertz sensing