Manipulation of light via subwavelength nanostructures is currently a subject of intense research interest, and is enabling the development of nanostructured photonic crystal, metamaterials and metasurfaces that provide a variety of new optical and electromagnetic functionalities, or that enable existing functionalities to be realized in new and often extremely compact form factors. This dissertation will include wide-angle wavelength-selective metasurface, omnidirectional enhancement in photovoltaic performance via subwavelength gradient anti-reflection coating, and applications of birefringent nanocylinders for single-molecule spectroscopy. In wide-angle wavelength-selective metasurface, high and broad reflectance (~95%) with low absorption (<5%) are shown to be achieved with multilayer metasurface structures. These characteristics are shown to be independent of interlayer misalignment and defects within individual layers. Interactions between different metasurface layers due to Fabry-Perot resonance are also examined with analytical models and numerical simulations. Wavelength-selective focusing at optical wavelengths which is enabled by large-area nanosphere lithography on a flexible substrate is demonstrated. In omnidirectional enhancement in photovoltaic performance via subwavelength gradient anti-reflection coating, large-area "moth-eye" structure fabricated on a flexible substrate is shown to have high transmittance (>85%) at large angle of incidences (>70°) and insensitivity to polarizations. Integration of the "moth-eye" anti-reflection coating together with nanostructured gradient A1₂O₃/TiO₂ on a GaAs solar cell shows significant improvements on external quantum efficiency (EQE) and short circuit current over all angle of incidences compared with conventional thin film anti-reflection coating. Detailed design, simulation, and fabrication of these nanostructured anti-reflection coating for reducing the discontinuity in refractive index profile will also be discussed. In application of birefringent nanocylinders for single-molecule spectroscopy, the design and fabrication method for large quantity of subwavelength birefringent nanoparticle are also discussed. These birefringent nanoparticles are shown to be stably trapped in an optical torque wrench setup, and enable observation of the dynamical response of a double-stranded DNA under torsional and extensional forces. / text

Coupling of light to charges in a metallic nanoparticle leads to hybrid light-matter states, localised surface plasmon polaritons. They are characterised by very strong field intensities in vicinity of the nanoparticle. This field enhancement can be exploited by coupling the nanoparticles to quantum emitters, e.g. molecules or quantum dots. Many new applications are based on fabrication of arrays of metallic nanoparticles. Significant spatial coherence in such systems is caused by electromagnetic interaction between the nanoparticles. In this work, we study the possibilities of quantum-mechanical description of metallic nanoparticles and the interactions between them. Using the principles of molecular quantum electrodynamics and quantisation of quasistatic normal modes of charge oscillations, we propose a quantum model of interaction between dipole quasistatic oscillation modes and the electromagnetic field. This model is then applied to estimate how presence of another nanoparticle influences the spontaneous radiative decay rate of dipole charge oscillation mode using the third-order perturbation theory. Powered by TCPDF (www.tcpdf.org)

This thesis focuses on the study of the electromagnetic properties of active spinplasmonic artificial materials. Artificial materials are composites having a macroscopic electromagnetic response that arises due to electromagnetic and electronic interactions between subwavelength sized elements. They are of practical engineering interest due to the wide range of free parameters such as the size, shape, density, and orientation of the individual elements, among others, thus providing the means to produce highly customizable photonic components. The thesis work can be categorized into four major sections: the design and construction of an advanced terahertz system capable of probing the electromagnetic response of such materials, the development of a class of artificial materials that permits the active, spin-dependent tuning of the position dependent phase accumulation of terahertz radiation, the study of spintronic-plasmonic artificial materials, and the discovery of a loss reduction mechanism for terahertz pulses transmitted through dense ensembles of bimetallic particles.

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The aim of this thesis is to establish a platform for implementing nanoscale plasmonic slot waveguide (PSW) devices that can interface with dielectric technology for hybrid silicon-plasmonic interconnect applications. For waveguide excitation, an orthogonal junction coupler that operates based on momentum matching is analyzed and then experimentally demonstrated to have coupling efficiency of 50 +/- 2 % between 450 nm wide silicon waveguide and 50 nm wide PSW across a 200 nm bandwidth. Next, for designing scalable optical components with multiple-input multiple-output capability and high fabrication tolerance, two dimensional PSW mesh structure that utilizes simultaneous power distribution and interference within a network of intersecting PSW junctions is introduced. Finally, a closed-form model for PSW mesh structures is derived by incorporating the characteristic impedance model into the scattering matrix formalism. The model can handle arbitrary combination of junctions and has less than 5 % discrepancy when compared to Finite-Difference Time-Domain results.

The aim of this thesis is to establish a platform for implementing nanoscale plasmonic slot waveguide (PSW) devices that can interface with dielectric technology for hybrid silicon-plasmonic interconnect applications. For waveguide excitation, an orthogonal junction coupler that operates based on momentum matching is analyzed and then experimentally demonstrated to have coupling efficiency of 50 +/- 2 % between 450 nm wide silicon waveguide and 50 nm wide PSW across a 200 nm bandwidth. Next, for designing scalable optical components with multiple-input multiple-output capability and high fabrication tolerance, two dimensional PSW mesh structure that utilizes simultaneous power distribution and interference within a network of intersecting PSW junctions is introduced. Finally, a closed-form model for PSW mesh structures is derived by incorporating the characteristic impedance model into the scattering matrix formalism. The model can handle arbitrary combination of junctions and has less than 5 % discrepancy when compared to Finite-Difference Time-Domain results.

Photonic circuits can transmit data signals in a much higher speed thanconventional electronic circuits. However, miniaturization of photonic circuitsand devices is hindered by the existence of light diffraction limit. A promisingsolution to this problem is by exploiting plasmonic systems for guiding andmanipulating signals at optical frequencies. Plasmonic devices are generallycomposed of noble metals and dielectrics, whose interfaces can confine surfaceplasmon polaritons, a hybrid wave that is free of diffraction limit. Plasmonicwaveguides and devices are serious contenders for achieving next-generationphotonic integrated circuits with a density comparable to the electronic counterpart. This thesis addresses the design issues of passive plasmonic devices whichare critical for realization of photonic integration, including plasmonic waveguides,splitters, couplers, and resonators, investigated with both the finitedifferencetime-domain method and the finite-element method. In particularwe present, firstly, a coupler which efficiently couples light between a silicondielectric waveguide and a hybrid plasmonic (HP) waveguide. A coupling efficiencyas high as 70% is realized with a HP taper as short as 0.4μm. Theexperimental result agrees well with the numerical simulation. Secondly, wenumerically investigate and optimize the performances of 1×2 and 1×3 HPmultimode interferometers (MMIs), which split light from a silicon waveguideto multiple HP waveguides. Total transmission over 75% can be achieved inboth cases. Thirdly, we study the coupling and crosstalk issues in plasmonicwaveguide systems. Several methods for crosstalk reduction are proposed.Finally, HP nanodisk micro-cavities are designed and are numerically characterized.With a radius of 1μm, a high quality factor of 819 and a highPurcell factor of 1827 can be simultaneously achieved, which can be useful forrealizing efficient nano-lasers. / QC 20110523

Plasmonic nanostructures, like noble metal, have gained large attention due to their plasmonic properties so they can reach areas like electronics, photo-catalysis, biomedicine, and sensing. Plasmonic nanomaterials are known for their local surface plasmon resonance and enhanced electromagnetic field and wavelength dependence. The higher the electromagnetic field at the surface of the nanoparticles can interact with nearby molecules, the bigger the influence is on the intensity of the molecule signals. This phenomenon is called surface-enhanced Raman scattering (SERS) and plasmonic enhanced fluorescence (PEF), which enable the plasmonic nanomaterials as a signal amplifier. By using these plasmonic nanostructures as a signal amplifier, SERS and PEF have become ultrasensitive methods in biomedicine and biosensing. Plasmonic biosensing is fast and label-free detection of biologically relevant analytes in real time. The objective of my doctoral dissertation focusses on developing new plasmonic nanostructures for detecting biomarkers related to cancers and some other diseases based on hybrid platforms. In this work, a newly spiky nanostructure was developed, internal standard Raman molecules were embedded into the nanostructure for quantitative SERS detection of polycyclic aromatic hydrocarbons molecules. Then the morphology and dispersity of this nanostructure were optimized to get an approximately fusiform shape, which showed a stable, reproducible and high SERS signals. This nanostructure was furtherly functionalized by double strand DNA and aptamer, showing a good performance in drug delivery and detecting circulating tumor cells. Inspired by the mechanism of SERS, a SERS and PEF dual model sensor based on plasmonic nanostructures and newly synthesized probe molecules was developed. This dual model sensor combined the advantages of SERS and PEF and exhibited a lower limit of detection of γ-glutamyl transferase in living cells. This dissertation contains the fabrication of newly plasmonic nanostructures and utilizing them in bioanalysis.

Electrochromic smart windows offer a viable route to reducing the consumption of buildings energy, which represents about 30% of the worldwide energy consumption. Smart windows are far more compelling than current static windows in that they can dynamically modulate the solar spectrum depending on climate and lighting conditions or simply to meet personal preferences. The latest generation of smart windows relies on nominally transparent metal oxide nanocrystal materials whose chromism can be electrochemically controlled using the plasmonic effect. Plasmonic electrochromic materials selectively control the near infrared (NIR) region of the solar spectrum, responsible for solar heat, without affecting the visible transparency. This is in contrast to conventional electrochromic materials which block both the visible and NIR and thus enables electrochromic devices to reduce the energy consumption of a building or a greenhouse in warm climate regions due to enhancements of both visible lighting and heat blocking. Despite this edge, this technology can benefit from important developments, including low-cost solution-based manufacturing on flexible substrates while maintaining durability and coloration efficiency, demonstration of independent control in the NIR and visible spectra, and demonstration of self-powering capabilities. This thesis is focused on developing low-temperature and all-solution processed plasmonic electrochromic devices and dual-band electrochromic devices. We demonstrate new device fabrication approaches in terms of materials and processes which enhance electrochromic performance all the while maintaining low processing temperatures. Scalable fabrication methods are used to highlight compatibility with high throughput, continuous roll-to-roll fabrication on flexible substrates. In addition, a dualband plasmonic electrochromic device was developed by combining the plasmonic layer with a conventional electrochromic ion storage layer. This enables independent control of the transmittance of NIR and visible spectra and is done without time- and energyintensive synthesis and processing methods. We have fabricated self-powered smart windows by integrating the plasmonic and dual-band devices with organic photovoltaic mini-modules and introduced static color bias with the help of photonic crystals to explore a few possibilities of multi-platform building integration.

As visual display technologies move closer to producing true three dimensional displays, pixel technologies need to be ever smaller and more functional to keep pushing the boundaries. Plasmonic metasurfaces have been shown to control the phase, amplitude and/or polarisation of incoming electromagnetic radiation. Nano-fabrication advancements have resulted in the fabrication of the building blocks of such metasurfaces at nano-scale dimensions, allowing the surfaces to interact with visible light, opening up applications in visual displays. As pixel sizes shrink, smaller colour filters will be required. The excitation of plasmonic resonances in metallic nano-structure arrays have resulted in colour filters an order of magnitude smaller than what is currently commercially available. As colour filters, plasmonic metasurfaces offer numerous advantages over pigment-based colour filters used in modern commercial liquid crystal (LC) displays, including environmental, size and longevity factors. Furthermore, exploiting the wavelength and polarisation dependant scattering of nano-structures, optical components, including lenses, waveplates and holograms containing sub-wavelength pixels have been demonstrated in the visible wavelength spectrum. The metasurfaces are able to mould optical wavefronts into arbitrary shapes with sub-wavelength resolution by introducing spatial variations in the optical response of the light scatterers. The applications demonstrated so far are, on the whole, static devices, that is to say their optical properties may not be altered post fabrication. To realise the full potential of plasmonic metasurfaces to visual applications the devices must be made active. By activating structural colour surfaces, not only may pixel densities potentially be increased simply by removing the need for separate red, green and blue filters, but a new class of high definition ultra-thin display devices may be accessible, whilst the dynamic manipulation of the wavelength and polarisation properties of nano-scattering elements would open up the possibilities to create sub-wavelength holographic pixels. This thesis investigates ways to activate static metasurfaces for colour, flat optic, and holographic applications. First, methods of dynamic control of the structural colour of plasmonic nano-hole arrays are investigated. By combining nano-hole arrays with liquid crystals, transmissive electrically tunable LC-nanohole pixels operating across the visible spectrum with un-polarised input light are experimentally demonstrated. An output analyser in combination with a nematic LC layer enables pixel colour to be electronically controlled through an applied voltage across the device, where LC re-orientation leads to tunable mixing of the relative contributions from the plasmonic colour input. Furthermore, exploiting the strong surface anchoring effects between an aluminium surface and LC molecules a twisted nematic LC cell, using a metallic grating as a combined colour filter, electrode and alignment layer, was shown to act a variable amplitude colour filter. The colour of these pixels was improved greatly utilising a grating-insulator-grating structure unique to this work. Second, a new process for fabricating aluminium nano-rod structures embedded in an elastomeric medium, with high spatial accuracy, is presented. The process is used to create nano-rod plasmonic resonator arrays whose optical properties may be altered by mechanical deformation. The pattern transfer process is further utilised to create dynamic optical elements, including nano-rod arrays for colour filters, tunable focal length Fresnel zone plates and photon sieves, and stretchable holograms with dynamic replay fields.