Chapter Photonic Crystals for Plasmonics: From Fundamentals to Superhydrophobic Devices

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Photonic Crystals for Plasmonics: From Fundamentals to Superhydrophobic Devices

Production engineerin

Plasmonic Nanostructures for Biosensor Applications

Improving the sensitivity of existing biosensors is an active research topic that cuts across several disciplines, including engineering and biology. Optical biosensors are the one of the most diverse class of biosensors which can be broadly categorized into two types based on the detection scheme: label-based and label-free detection. In label-based detection, the target bio-molecules are labeled with dyes or tags that fluoresce upon excitation, indicating the presence of target molecules. Label-based detection is highly-sensitive, capable of single molecule detection depending on the detector type used. One method of improving the sensitivity of label-based fluorescence detection is by enhancement of the emission of the labels by coupling them with metal nanostructures. This approach is referred as plasmon-enhanced fluorescence (PEF). PEF is achieved by increasing the electric field around the nano metal structures through plasmonics. This increased electric field improves the enhancement from the fluorophores which in turn improves the photon emission from the fluorophores which, in turn, improves the limit of detection. Biosensors taking advantage of the plasmonic properties of metal films and nanostructures have emerged an alternative, low-cost, high sensitivity method for detecting labeled DNA. Localized surface plasmon resonance (LSPR) sensors employing noble metal nanostructures have recently attracted considerable attention as a new class of plasmonic nanosensors.;In this work, the design, fabrication and characterization of plasmonic nanostructures is carried out. Finite difference time domain (FDTD) simulations were performed using software from Lumerical Inc. to design a novel LSPR structure that exhibit resonance overlapping with the absorption and emission wavelengths of quantum dots (QD). Simulations of a composite Au/SiO2 nanopillars on silicon substrate were performed using FDTD software to show peak plasmonic enhancement at QD emission wavelength (560nm). A multi-step fabrication process was developed to create plasmonic nanostructures, and the optical characterization of emission enhancement was performed

Nanophotonic and nanoplasmonic couplers: Analysis and fabrication

Mode mismatch between waveguides of different geometries and propagation mechanisms causes radiation and back reflection, which results in significant loss of optical power. This is considered one of the obstacles that prevents multiple applications of the optical integrated circuits. In this dissertation, we design, fabricate, and experimentally demonstrate four novel photonic couplers that achieve mode matching between hybrid waveguides. These hybrid waveguides include conventional optical waveguides, photonic crystal (PC) waveguides, and plasmonic waveguides. First, we propose a novel method to enhance the coupling efficiency between a dielectric waveguide and a planar PC. This method is based on introducing structural imperfections that cause a change in the mode size and shape inside the taper to match that of the PC line-defect waveguide. These imperfections are introduced by changing the size and position of the inner taper rods. Our results show that introducing the structural imperfections increases the coupling to 96% without affecting the transmission spectrum of the structure. Second, we demonstrate through numerical simulations and experiments that low crosstalk between two crossed line-defect waveguides formed in a square lattice PC structure can be achieved by using a resonant cavity at the intersection area. The PC resonator consists of cubic air-holes in silicon. The theoretical and experimental crosstalk values are approximately -40 dB and -20 dB, respectively. Third, we introduce a novel silicon microring vertical coupler that efficiently couples light into a silicon-on-insulator (SOI) waveguide. A specific mode is excited to match the effective index of the SOI guided mode by oblique incidence. The vertical leakage from the microring forms gradual coupling into the SOI slab. Coupling efficiency up to 91% is demonstrated numerically. The coupler is fabricated and tested to confirm the analytical results. Fourth, we present a novel design, analysis, and fabrication of an ultracompact coupler and a 1 × 2 splitter based on plasmonic waveguides. In addition, we present two nano-scale plasmonic devices: a directional coupler and a Mach-Zehnder interferometer. The devices are embedded between two dielectric waveguides. Our simulation results show a coupling efficiency of 88% for the coupler, 45% for each splitter\u27s branch, 37% for a 2 × 2 directional coupler switch, and above 50% for the proposed designs of the Mach-Zehnder interferometer. In order to confirm the analytical results, the plasmonic air-slot coupler and splitter are fabricated and tested

Parametric Optimization of Visible Wavelength Gold Lattice Geometries for Improved Plasmon-Enhanced Fluorescence Spectroscopy

The exploitation of spectro-plasmonics will allow for innovations in optical instrumentation development and the realization of more efficient optical biodetection components. Biosensors have been shown to improve the overall quality of life through real-time detection of various antibody-antigen reactions, biomarkers, infectious diseases, pathogens, toxins, viruses, etc. has led to increased interest in the research and development of these devices. Further advancements in modern biosensor development will be realized through novel electrochemical, electromechanical, bioelectrical, and/or optical transduction methods aimed at reducing the size, cost, and limit of detection (LOD) of these sensor systems. One such method of optical transduction involves the exploitation of the plasmonic resonance of noble metal nanostructures. This thesis presents the optimization of the electric (E) field enhancement granted from localized surface plasmon resonance (LSPR) via parametric variation of periodic gold lattice geometries using finite difference time domain (FDTD) software. Comprehensive analyses of cylindrical, square, star, and triangular lattice feature geometries were performed to determine the largest surface E-field enhancement resulting from LSPR for reducing the LOD of plasmon-enhanced fluorescence (PEF). The design of an optical transducer engineered to yield peak E-field enhancement and, therefore, peak excitation enhancement of fluorescent labels would enable for improved emission enhancement of these labels. The methodology presented in this thesis details the optimization of plasmonic lattice geometries for improving current visible wavelength fluorescence spectroscopy

Design and Fabrication of 1-D, 2-D Photonic Crystals and Metasurface Based Perfect Light Absorbers

Perfect light absorbers are devices which absorb all the light that is incident up on it at a particular frequency. Perfect light absorbers find applications in designing efficient solar absobers, thermophotovoltaic energy conversion systems and stealth technologies. Two methods to realize prefect light absorbers are investigated in this thesis; one using 2-D metallic photonic crystals and using metasurface based absorbers. Photonic crystals have periodic variation of dielectric constant at a subwavelength scale of the light. These periodic variation of dielectric constant lead to the formation of photonic band gaps in these materials. The two dimensional metallic photonic crystal consist of square array of cylindrical cavities on a tantalum metal surface. These cavities on the metal surface couple to the incident electromagnetic radiation and lead to enhanced absorption. The effect of design parameters namely choice of metal, radius, depth and period of the cylinders on the absorption of light is studied and then an optimum design providing peak emissivity at 3.5 µm is arrived at and fabricated. Metasurface based aborbers on the other hand are composite materials with artifical permeability and permitivity. A qualitative picture for creating the artificial permitivity and permeability formation in this material is given in this thesis, with a contrast to the atomic scale resonance to explain the optical properties of these materials. We show how by controlling the design of the electric ring resonator and split ring resonators we can create perfect light absorption in these metasurface absorbers. We then discuss the equivalence of the complimentary electric ring resonators

Design and Fabrication of 1-D, 2-D Photonic Crystals and Metasurface Based Perfect Light Absorbers

Perfect light absorbers are devices which absorb all the light that is incident up on it at a particular frequency. Perfect light absorbers find applications in designing efficient solar absobers, thermophotovoltaic energy conversion systems and stealth technologies. Two methods to realize prefect light absorbers are investigated in this thesis; one using 2-D metallic photonic crystals and using metasurface based absorbers. Photonic crystals have periodic variation of dielectric constant at a subwavelength scale of the light. These periodic variation of dielectric constant lead to the formation of photonic band gaps in these materials. The two dimensional metallic photonic crystal consist of square array of cylindrical cavities on a tantalum metal surface. These cavities on the metal surface couple to the incident electromagnetic radiation and lead to enhanced absorption. The effect of design parameters namely choice of metal, radius, depth and period of the cylinders on the absorption of light is studied and then an optimum design providing peak emissivity at 3.5 µm is arrived at and fabricated. Metasurface based aborbers on the other hand are composite materials with artifical permeability and permitivity. A qualitative picture for creating the artificial permitivity and permeability formation in this material is given in this thesis, with a contrast to the atomic scale resonance to explain the optical properties of these materials. We show how by controlling the design of the electric ring resonator and split ring resonators we can create perfect light absorption in these metasurface absorbers. We then discuss the equivalence of the complimentary electric ring resonators