Plasmonics is a promising field of nanophotonics dealing with light interaction with metallic nanostructures. In such material systems, hybridizationof photons and collective free-electron oscillation can result in sub-wavelength light confinement. The strong light-matter interaction can be harnessed for,among many applications, high-density photonic integration, metamaterial design, enhanced nonlinear optics, sensing etc. In the current thesis work, we focus on experimental fabrication and characterization of planar plasmonic metamaterials and waveguide structures. The samples are fabricated based on the generic electron beam lithography and characterizations are done with our home-made setups. Mastering and refinement of fabrication techniques as well as setting up the characterization tools have constituted as a majorpart of the thesis work. In particular, we experimentally realized a plasmonic absorber based on a 2D honeycomb array of gold nano-disks sitting on top of a reflector through a dielectric spacer. The absorber not only exhibits an absorption peak which is owing to localized surface plasmon resonance and is insensitive to incidence’s angle or polarization, but also possesses an angle- and polarization-sensitive high-order absorption peak with a narrow bandwidth. We also demonstrated that the strong light absorption in such plasmonic absorbers can be utilized to photothermally re-condition the geometry of gold nanoparticles. The nearly perfect absorption capability of our absorbers promises a wide range of potential applications, including thermal emitter, infrared detectors, and sensors etc. We also fabricated a plasmonic strip waveguide in a similar metal-insulator-metal structure. The strip waveguide has a modal confinement slightly exceeding that of the so-called plasmonic slot waveguide. We further thermally annealed the waveguide. It is observed that the propagation loss at 980 nm has been decreased significantly,which can be attributed to the improvement in gold quality after thermal annealing. / <p>QC 20140203</p>

Tailoring surface plasmon (SP) resonances using metallic nanostructures for optical manipulation has been widely investigated in recent years; and there are many puzzles yet to be solved in this relatively new area. This thesis covers the study of the interaction of light with SP-supporting planar/patterned metallo-dielectric multilayer structures. Two separate, but closely related subjects were investigated using such structures, which are: SP-assisted optical transmission and optical metamaterials. The physical mechanisms of the SP-assisted transmission phenomenon were studied using planar/grating and planar/hole-array multilayer structures. Extraordinary light transmission has been demonstrated through experimental work and simulations for both arrangements; and the effects of different structural parameters on the transmission efficiencies of the structures were analyzed systematically. The interplays of the surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) in the extraordinary optical transmission (EOT) phenomenon were identified. The potential of the planar/hole-array multilayer structures as optical magnetic metamaterials was evaluated using two independent electromagnetic simulation techniques. The ability of such structures to produce strong magnetic resonances from infrared down to visible side of spectrum was revealed. The methods of tuning the magnetic response of the structures were suggested. A novel design of optical metamaterial based on high-order multipolar resonances in a single-layer plasmonic structure was also proposed. Numerical results from two different computation methods indicate that a simultaneously negative permittivity and permeability can be achieved in such a structure.

Terahertz range of frequency has found a fast growing number of applications in material characterization and sensing, imaging and extreme bandwidth communication. Different structures have been proposed for sensing at these frequencies. Surface plasmon waves have successfully been applied to ultra-high precision sensing at optical frequencies, because of their strong field confinement and enhancement. These waves are not as confined in THz due to metal properties over this range of frequencies. However, it has been shown that surface waves on properly designed periodic metallic structure have behavior very similar to plasmonic waves in optical range. These surface wave modes are called surface plasmon-like waves. Here we consider several periodic metallic structures, which support these surface plasmon-like modes, for THz sensing applications. The first one is a two dimensional array of metallic rods which is excited by prism. Many existing plasmonic sensing configurations use prism for plasmonic wave excitation. However, prism is too bulky for integration. Interests in integrated surface plasmonic devices at optical frequencies have been growing recently. As compared with free space configuration, integrated structures have distinct advantages such as small size and multi-channel sensing capabilities. An integrated sensing configuration using plasmonic-like wave is proposed. The new configuration uses a metallic grating that acts as a THz waveguide with a stop-band with a sharp transition edge. Excitation of such metallic grating waveguide through a dielectric waveguide will be described and analyzed. Moreover, it will be shown that the frequency of the transition edge between pass-band and stop-band is highly sensitive to the refractive index of the surrounding medium, and therefore it can be used for dielectric sensing. The excitation requirements of the proposed sensor and its sensitivity will be presented.

An SOI-based platform designed for wideband coupling of light from optical fibers to a 50 nm wide plasmonic slot waveguide is described in this thesis. The device is based on a newly proposed orthogonal junction with coupling efficiencies above 70% near the telecom wavelength. To construct the coupling platform, two such junctions are utilized for input and output, where Si wires are place 90 degree with respect to each of the two ends of a plasmonic section. Analytic studies and FDTD simulations have demonstrated attractive properties such as a smooth micron-wide transmission spectrum that can be spectrally shifted with the design parameters, and the natural phase-matching between the dielectric and plasmonic sections consequent of the waveguide orientations. Fabrication procedures and proof-of-concept characterization work are also presented. The experimentally-tested platform with its unique features would enable applications in on-chip sensing and plasmonic slot-based waveguiding at the 50 nm scale.

An SOI-based platform designed for wideband coupling of light from optical fibers to a 50 nm wide plasmonic slot waveguide is described in this thesis. The device is based on a newly proposed orthogonal junction with coupling efficiencies above 70% near the telecom wavelength. To construct the coupling platform, two such junctions are utilized for input and output, where Si wires are place 90 degree with respect to each of the two ends of a plasmonic section. Analytic studies and FDTD simulations have demonstrated attractive properties such as a smooth micron-wide transmission spectrum that can be spectrally shifted with the design parameters, and the natural phase-matching between the dielectric and plasmonic sections consequent of the waveguide orientations. Fabrication procedures and proof-of-concept characterization work are also presented. The experimentally-tested platform with its unique features would enable applications in on-chip sensing and plasmonic slot-based waveguiding at the 50 nm scale.

No description available.

The ability to understand and control the propagation of electromagnetic radiation underpins a vast array of modern technologies, including: communication, navigation and information technology. Therefore, there has been much work to understand the interaction between electromagnetic waves and metal surfaces, and in particular to design materials the characteristics of which can be tailored to produce a desired response to microwave radiation. It is the objective of this thesis to demonstrate that patterning metal surfaces with sub-wavelength apertures can afford hitherto unrealised control over the reflection and transmission characteristics of materials which are an order of magnitude thinner than those employed historically. The work presented herein aims to establish ultra thin cavity structures as novel materials for the selective absorption and transmission of microwave radiation. Experimental and theoretical approaches are used to elucidate the mechanism that allows such structures to produce highly efficient absorption via the excitation of standing wave modes in structures that are two orders of magnitude thinner than the operating wavelength. Also considered is how this same mechanism mediates transmission of selected frequencies through similarly thin structures. Later chapters focus on ultra thin cavity structures which, through higher-order rotational symmetry, exhibit resonant absorption which is almost completely independent of incident and azimuthal angle and polarisation state. A detailed studied of the absorption bandwidth of these devices is also presented in the context of fundamental theoretical limitations arising from the thickness and magnetic permeability of the structure.

This thesis presents novel results in the field of plasmonics and optoelectronics application. Plasmonics is the rapidly expanding branch of photonics. It opens up capabilities of electronic and photonic device implementation within the same integrated circuits as well as enhances the limit of detection for chemical and biological-based sensors. The first finding lies in solving the dilemma in search of ultimate plasmonics materials for plasmonics application. It is well known that Cu and Ag are metals that have incredible electric and optic properties. However, they are easily oxidized in contact with air. Both experimental and theoretical findings demonstrate that application of a mono or bilayer graphene protects Cu and Ag from oxidation and degradation of its plasmonic properties. The performance of each metal is evaluated based on the quality factor Q and the minima in amplitude of reflection intensity Rmin of the Surface plasmon-polariton (SPP) curve. The second novelty of this thesis comprises the fabrication of low loss, high efficient broadband, as well as narrowband, graphene-based electro-absorption modulators. The studied graphene-based modulators made use of Fabry-Perot resonator geometries. It has been shown that high-k dielectric hafnium dioxide (HfO2) provides solid state “supercapacitor” effects and allows to observe light modulation from the near-infrared to shorter wavelengths close to the visible spectrum with remarkably low gate voltages (~4 V). The electro-absorption modulators based on Fabry-Perot resonator geometry reached the modulation depth in transmission mode of 28% at a wavelength of 1.1 Âμm.

Optical trapping is an important tool for studying and manipulating nanoscale objects. Recent experiments have shown that subwavelength control of nanoparticles is possible by using patterned plasmonic nanostructures, rather than using a laser directly, to generate the electric fields necessary for particle trapping. In this thesis we present a theoretical model and experimental evidence for plasmonic optical trapping in nanoscale metal junctions. Further, we examine the use of the resultant devices as ultrasmall photodectors. Electromigrated nanojunctions, or “nanogaps”, have a well-established plasmon resonance in the near-IR, leading to electric field enhancements large enough for single-molecule sensitivity in Surface-Enhance Raman (SERS) measurements. While molecule-based devices have been carefully studied, optically and electrically probing individual quantum dots in nanoscale metal junctions remains relatively unexplored. Plasmon-based optical trapping of quantum dots into prefabricated structures could allow for inexpensive, scalable luminescent devices which are fully integrable into established silicon-based fabrication techniques. Additionally, these metal-nanocrystal-metal structures are ideal candidates to study optoelectronics in ultrasmall nanocrystals-based structures, as well as more exotic nanoscale phenomena such as blinking, plasmon-exciton interactions, and surface-enhanced fluorescence (SEF). We present experimental data supporting plasmon-based optical trapping in the nanogap geometry, and a corresponding numerical model of the electric field-generated forces in the nanogap geometry. Further, we give proof-of-concept measurements of photoconductance in the resultant quantum dot-based devices, as well as challenges and improvements moving forward.

This thesis presents a novel micron-sized trapezoidal plasmonic waveguide design, called an Interface Plasmon Polariton waveguide. The guiding mechanism is explained using an effective index method and validated by simulations. The mode cut-off conditions and single-mode guiding properties are both determined using simulation and experimentally demonstrated. The waveguides have a long 1 mm propagation distance at 1550 nm wavelengths. Using this IPP waveguide, novel dielectric rib, dielectric varying-density hole-array, and metal-groove Bragg grating $\emph{in vitro}$ sensors are designed, fabricated, and characterized. The devices have a 1100 nm/RIU sensitivity and 0.006 RIU sensing resolution obtained from measurements and are validated by theory. The IPP sensors developed in this thesis not only offer competitive plasmonic sensitivity, sensing resolution, signal to noise ratio, result reproducibility, and reusability, they are also easy to fabricate and simple to package. Therefore, these new sensor designs are an enabler for lab-on-a-chip platforms to adapt plasmonic technology.