Due to the increased demand for high-operating-speed systems and ultra-compact optical devices, nanophotonic waveguides such as plasmonic waveguides have been a subject of intense interest over the past few years. The ability of plasmonic waveguides to guide light within nano-scale structures beyond the diffraction limit has driven researchers in different fields to exploit their unique features. Even though plasmonic waveguides have shown a strong mode confinement at nano-scale dimensions, they have high propagation loss. Consequently, many geometries and structures have been proposed to investigate ways to reduce this loss. The most recent type of plasmonic waveguide that shows high mode confinement and low propagation loss compared with the other types is the hybrid plasmonic waveguide (HPW). An HPW consists of a low-index dielectric layer sandwiched between a high-index dielectric material and a metal layer; the mode is predominantly confined within the low-index layer. This thesis addresses the use of HPWs for nonlinear applications such as optical switching devices based on the nonlinear phenomenon known as the Kerr effect, where the sub-wavelength dielectric layer has a pronounced nonlinear response. Using Finite Element Method analysis, the nonlinear hybrid plasmonic waveguide (NLHPW) is modeled, and the performance of the NLHPW has been investigated by using appropriate figures of merit to measure the Kerr nonlinearity of the NLHPW with and without the linear loss of the waveguide. These are shown to compare favourably with those of alternate waveguiding geometries. Moreover, the NLHPW has been shown a good balance between mode confinement and loss; small effective mode areas of 0.04 – 0.15 µm2 at a wavelength of λ=1.55 µm and relatively long propagation lengths of 30 to 160 µm can be realized, which make NLHPWs promising candidates for nonlinear applications. As a result, a nonlinear ring resonator with a radius of 1 µm based on the NLHPW is designed and investigated numerically by using frequency domain simulations. It is found that the field intensity in the ring is enhanced four times higher than the field intensity in the input waveguide, and that a nonlinear resonance shift is realized when changing the intensity of the data signal.

Due to the increased demand for high-operating-speed systems and ultra-compact optical devices, nanophotonic waveguides such as plasmonic waveguides have been a subject of intense interest over the past few years. The ability of plasmonic waveguides to guide light within nano-scale structures beyond the diffraction limit has driven researchers in different fields to exploit their unique features. Even though plasmonic waveguides have shown a strong mode confinement at nano-scale dimensions, they have high propagation loss. Consequently, many geometries and structures have been proposed to investigate ways to reduce this loss. The most recent type of plasmonic waveguide that shows high mode confinement and low propagation loss compared with the other types is the hybrid plasmonic waveguide (HPW). An HPW consists of a low-index dielectric layer sandwiched between a high-index dielectric material and a metal layer; the mode is predominantly confined within the low-index layer. This thesis addresses the use of HPWs for nonlinear applications such as optical switching devices based on the nonlinear phenomenon known as the Kerr effect, where the sub-wavelength dielectric layer has a pronounced nonlinear response. Using Finite Element Method analysis, the nonlinear hybrid plasmonic waveguide (NLHPW) is modeled, and the performance of the NLHPW has been investigated by using appropriate figures of merit to measure the Kerr nonlinearity of the NLHPW with and without the linear loss of the waveguide. These are shown to compare favourably with those of alternate waveguiding geometries. Moreover, the NLHPW has been shown a good balance between mode confinement and loss; small effective mode areas of 0.04 – 0.15 µm2 at a wavelength of λ=1.55 µm and relatively long propagation lengths of 30 to 160 µm can be realized, which make NLHPWs promising candidates for nonlinear applications. As a result, a nonlinear ring resonator with a radius of 1 µm based on the NLHPW is designed and investigated numerically by using frequency domain simulations. It is found that the field intensity in the ring is enhanced four times higher than the field intensity in the input waveguide, and that a nonlinear resonance shift is realized when changing the intensity of the data signal.

Optical sensors based on Surface-enhanced Raman scattering (SERS) effect are among the most versatile sensors due to their ability to characterize samples in various states of matter. The appeal of the SERS sensors lies in the molecular “fingerprint” specificity, sensitivity, and the non-invasive nature of the analysis. Although the current state of art SERS sensors have advanced toward ultrasensitivity with single-molecule detection limit, ultrafast analysis at femtosecond and sub-nanometer resolution, the application of these innovations in the industrial settings is still limited by the complexity of the substrate fabrication and the reproducibility of the SERS measurements. In this context, a study on the SERS sensors fabrication strategies and reliability of the SERS analysis is essential. This dissertation investigates various hybrids of noble metal and semiconductor materials and surface modifications to improve the stability and reliability of SERS measurement. Different industrial applications, including detection of petrochemical organic compounds and sensitive biochemical samples, were conducted to evaluate the performance of different SERS sensor designs. Evaluation of the morphology and surface functionalization of the substrate was accomplished to optimize the performance and stability of the collected signal. Together with the separately performed studies on Raman signal processing and interpretation, the proposed SERS sensor fabrication and signal analysis approach was successfully applied to detect and quantify organic isomers compounds and mutation point in peptides. The findings presented in this thesis offer rational SERS substrate designs and detection approaches that can advance the future commercialization of SERS sensors.

This dissertation contains two different research topics. One is a ‘Nano Scale Device for Plasmonic Nanolithography – Optical Antenna’ and the other is a ‘Nano Scale Device for Rapid Sensing of Bacteria – SEPTIC’. Since these two different research topics have little analogy to each other, they were divided into different chapters throughout the whole dissertation. The ‘Optical Antenna’ and ‘Nanowell / Microwell / ISFET Sensor’ represent the device names of each topic ‘Plasmonic Nanolithography’ and ‘Rapid Sensing of Bacteria’, respectively. For plasmonic nanolithography, we demonstrated a novel photonic device - Optical Antenna (OA) - that works as a nano scale object lens. It consists of a number of sub-wavelength features in a metal film coated on a quartz substrate. The device focuses the incident light to form a narrow beam in the near-field and even far-field region. The narrow beam lasts for up to several wavelengths before it diverges. We demonstrated that the OA was able to focus a subwavelength spot with a working distance (also the focal length) of several µm, theoretically and experimentally. The highest imaging resolution (90-nm spots) is more than a 100% improvement of the diffraction limit (FWHM = 210 nm) in conventional optics. A model and 3D electromagnetic simulation results were also studied. Given its small footprint and subwavelength resolution, the PL holds great promise in direct-writing and scanning microscopy. Collaborative work demonstrated a Nanowell (or Microwell) device which enables a rapid and specific detection of bacteria using nano (or micro) scale probe to monitor the electric field fluctuations caused by ion leakage from the bacteria. When a bacteriophage infects a bacterium and injects its DNA into the host cell, a massive and transitory ion efflux from the host cell occurs. SEPTIC (SEnsing of Phage-Triggered Ion Cascade) technology developed by collaboration uses a nanowell device to detect the nano-scale electric field fluctuations caused by this ion efflux. The SEPTIC provides fast (within several minutes), effective (living cell only), phage specific (simple and less malfunction), cheap, compact and robust method for bacteria sensing. We fabricated a number of devices, including ‘Nanowell’, ‘Microwell’, and ‘ISFET (Ion Selective Field Effect Transistor)’, which detect bacteria-phage reactions in frequency domain and time domain. In the frequency domain, detected noise spectrum is characterized by β f / 1 . The positive reaction showed much higher 1 ≅ β than that of background noise or negative reaction ( 0 ≅ β ). For the time domain, we observed abnormal pulses (> σ 8 ) lasting 0.1 ~ 0.3 s which match the duration of ion flux reported by prior literatures. And the ISFET showed the phage-infection-triggered pulse in the form of the deviated drain current. Given the size of nanowell (or microwell, ISFET) and the simplified detection electronics, the cost of bacteria sensing is significantly reduced and the robustness is well improved, indicating very promising applications in clinical diagnosis and bio-defense.

This dissertation contains two different research topics. One is a "Nano Scale Device for Plasmonic Nanolithography - Optical Antenna' and the other is a 'Nano Scale Device for Rapid Sensing of Bacteria - SEPTIC'. Since these two different research topics have little analogy to each other, they were divided into different chapters throughout the whole dissertation. The 'Optical Antenna' and 'Nanowell / Microwell / ISFET Sensor' represent the device names of each topic 'Plasmonic Nanolithography' and 'Rapid Sensing of Bacteria' respectively. For plasmonic nanolithography, we demonstrated a novel photonic device - Optical Antenna (OA) - that works as a nano scale object lens. It consists of a number of sub-wavelength features in a metal film coated on a quartz substrate. The device focuses the incident light to form a narrow beam in the near-field and even far-field region. The narrow beam lasts for up to several wavelengths before it diverges. We demonstrated that the OA was able to focus a subwavelength spot with a working distance (also the focal length) of several µm, theoretically and experimentally. The highest imaging resolution (90-nm spots) is more than a 100% improvement of the diffraction limit (FWHM = 210 nm) in conventional optics. A model and 3D electromagnetic simulation results were also studied. Given its small footprint and subwavelength resolution, the PL holds great promise in direct-writing and scanning microscopy. Collaborative work demonstrated a Nanowell (or Microwell) device which enables a rapid and specific detection of bacteria using nano (or micro) scale probe to monitor the electric field fluctuations caused by ion leakage from the bacteria. When a bacteriophage infects a bacterium and injects its DNA into the host cell, a massive and transitory ion efflux from the host cell occurs. SEPTIC (SEnsing of Phage-Triggered Ion Cascade) technology developed by collaboration uses a nanowell device to detect the nano-scale electric field fluctuations caused by this ion efflux. The SEPTIC provides fast (within several minutes), effective (living cell only), phage specific (simple and less malfunction), cheap, compact and robust method for bacteria sensing. We fabricated a number of devices, including 'Nanowell', 'Microwell' and 'ISFET (Ion Selective Field Effect Transistor)', which detect bacteria-phage reactions in frequency domain and time domain. In the frequency domain, detected noise spectrum is characterized by 1/f[beta]. The positive reaction showed much higher [beta] =̃1 than that of background noise or negative reaction ( [beta] =̃0). For the time domain, we observed abnormal pulses (> 8[omega] ) lasting 0.1 ~ 0.3 s which match the duration of ion flux reported by prior literatures. And the ISFET showed the phage-infection-triggered pulse in the form of the deviated drain current. Given the size of nanowell (or microwell, ISFET) and the simplified detection electronics, the cost of bacteria sensing is significantly reduced and the robustness is well improved, indicating very promising applications in clinical diagnosis and bio-defense.

Plasmons can be generated in the two dimensional electron gas (2DEG) of grating-gated high electron mobility transistors (HEMTs). The grating-gate serves dual purposes, namely to provide the required wavevector to compensate for the momentum mismatch between the free-space radiation and 2D-plasmons, and to tune the 2DEG sheet charge density. Since the plasmon frequency at a given wavevector depends on the sheet charge density, a gate bias can shift the plasmon resonance. In some cases, plasmon generation results in a resonant change in channel conductance which allows a properly designed grating-gated HEMT to be used as a voltage-tunable resonant detector or filter. Such devices may find applications as chip-scale tunable detectors in airborne multispectral detection and target tracking. Reported here are investigations of InGaAs/InP-based HEMT devices for potential tunable resonant sub-THz and THz detectors. The HEMTs were fabricated from a commercial double-quantum well HEMT wafer by depositing source, drain, and semi-transparent gate contacts using standard photolithography processes. Devices were fabricated with metalized transmission gratings with multiple periods and duty cycles. For sub-THz devices, grating period and duty cycle were chosen to be 9 ?m and 22%, respectively; while they were chosen to be 0.5 ?m and 80% for the THz device. The gratings were fabricated on top of the gate region with dimensions of 250 ?m x 195 ?m. The resonant photoresponse of the larger grating-period HEMT was investigated in the sub-THz frequency range of around 100 GHz. The free space radiation was generated by an ultra-stable Backward Wave Oscillator (BWO) and utilized in either frequency modulation (FM), or amplitude modulation (AM) experiments. The photoresponse was measured at 4K sample temperature as the voltage drop across a load resistor connected to the drain while constant source-drain voltages of different values, VSD, were applied. The dependence of such optoelectrical effect to polarization of the incident light, and applied VSD is studied. The results of AM and FM measurements are compared and found to be in agreement with the calculations of the 2D-plasmon absorption theory, however, a nonlinear behavior is observed in the amplitude and the line-shape of the photoresponse for AM experiments. For detection application, the minimum noise-equivalent-power (NEP) of the detector was determined to be 235 and 113 pW/Hz1/2 for FM and AM experiments, respectively. The maximum responsivity of the detector was also estimated to be ~ 200 V/W for the two experiments. The far-IR transmission spectra of the device with nanometer scale period was measured at 4 K sample temperature for different applied gate voltages to investigate the excitation of 2D-plasmon modes. Such plasmon resonances were observed, but their gate bias dependence agreed poorly with expectations.

Miniaturization of electronic circuits and systems continue to pose great difficulties in meeting the demand and anticipated growth for information services and their associated electronics. Of the several information processing techniques under consideration for devices of the future, optical systems are considered to offer significant advantages in terms of speed and bandwidth. Unfortunately, at the dimensions of contemporary electronics, optical waveguides will fail to assist significantly due to the fact that standard optical waveguides will have dimensions below the diffraction limit and hence optical waveguiding at such scales will be impractical. In order to circumvent this, recent work in the area of using nano-sized protrusions to guide light below the diffraction limit has been receiving a decent amount of attention. Such systems have typically involved using electron beam lithography to create these perturbations on metallic surfaces called plasmonic waveguides. While these waveguides are fairly efficient, in the amounts required to make real circuits this method would be impractically slow and prohibitively expensive. However, such waveguides could be made much more cheaply if means could be found to arrange colloidal nanoparticles on suitable substrates. In this project, nanoscale self-assembly has been investigated with the aim of achieving such ends. Colloidal nanoparticles have been synthesized and self-assembled onto substrates such that they show near field interactions necessary for plasmonic waveguiding without any aggregation. Absorption peak shifts, which were obtained during the experimental phase of this project confirmed that such nanoparticle assemblies can be achieved and that they do demonstrate some plasmonic waveguiding action. With this first step, it is hoped that films like these may find use for quick and cheap plasmonic waveguiding sometime in the near future. / Master of Science

Strong light matter interactions in metallic nanoparticles (NPs), especially those made of noble metals such as Gold and Silver is at the heart of much ongoing research in nanoplasmonics. Individual NPs can support collective excitations (Plasmon’s) of the electron plasma at certain wavelengths, known as the localized surface Plasmon resonance (LSPR) which provides a powerful platform for various sensing, imaging and therapeutic applications. For a collection of NPs their optical properties can be signify cannily different from isolated particles, an effect which originates in the electromagnetic interactions between the localised Plasmon modes. An interesting aspect of such interactions is their strong dependence on the geometry of NP collection and accordingly new optical properties can arise. While this problem has been well considered in one and two dimensions with periodic as well as with random arrays of NPs, three dimensional systems are yet to be fully explored. In particular, there are challenges in the successful de-sign and fabrication of three dimensional (3D) plasmonic metamaterials at optical frequencies. In the work presented in this thesis we present a detail investigation of the theoretical and experimental aspects of plasmonic interactions in two geometrically different three dimensional plasmonic nanostructured systems - a chiral system consisting of achiral plasmonic nanoparticles arranged in a helical geometry and an achiral system consisting of achiral plasmonic nanoparticle arrays stacked vertically into three dimensional geometry. The helical arrangement of achiral plasmonic nanoparticles were realised using a wafer scale technique known as Glancing Angle Deposition (GLAD). The measured chiro-optical response which arises solely from the interactions of the individual achiral plasmonic NPs was found to be one of the largest reported value in the visible. Semi analytical calculation based on couple dipole approximation was able to model the experimental chiro-optical response including all the variabilities present in the experimental system. Various strategies based on antiparticle spacing, oriented elliptical nanoparticles, dielectric constant value of the dielectric template were explored such as to engineer a strong and tunable chiro-optical response. A key point of the experimental system despite the presence of variabilities, was that the measured chiro-optical response showed less than 10 % variability along the sample surface. Additionally we could exploit the strong near held interactions of the plasmonic nanoparticles to achieve a strongly nonlinear circular differential response of two photon photoluminescent from the helically arranged nanoparticles. In addition to these plasmonic chiral systems, our study also includes investigation of light matter interactions in purely dielectric chiral systems of solid and core shell helical geometry. The chiro-optical response was found to be similar for both the systems and depend strongly on their helical geometry. A core-shell helical geometry provides an easy route for tuning the chiro-optical response over the entire visible and near IR range by simply changing the shell thickness as well as shell material. The measured response of the samples was found to be very large and very uniform over the sample surface. Since the material system is based entirely on dielectrics, losses are minimal and hence could possibly serve as an alternative to conventional plasmonic chiro-optical materials. Finally we demonstrated the used of an achiral three dimensional plasmonic nanostructure as a SERS (surface enhance Raman spectroscopy) substrate. The structure consisted of porous 3D metallic NP arrays that are held in place by dielectric rods. For practically important applications, the enhancement factor, as well as the spatial density of the metallic NPs within the laser illumination volume, arranged in a porous 3D array needs to be large, such that any molecule in the vicinity of the metal NP gives rise to an enhanced Raman signal. Having a large number of metallic NPs within the laser illumination volume, increases the probability of a target molecule to come in the vicinity of the metal NPs. This has been achieved in the structures reported here, where high enhancement factor (EF) in conjunction with large surface area available in a three dimensional structure, makes the 3D NP arrays attractive candidates as SERS substrates.

Lab-on-chip systems have been developed for various applications like point of care diagnostics and compact imaging systems. Compact, on-chip imaging systems face a challenge in the integration of multicolor light sources on-chip. This is because of the unavailability of compact, individually addressable, multicolor light sources on a single planar substrate. Colloidal Quantum Dot based Light Emitting Diodes (QDLEDs), which have found wide appeal, due to their unique properties like their tunable and narrow emission bandwidth and easy fabrication, are ideal for lab-on-chip integration. Among different types of QDLED structures implemented, inorganic QDLEDs have shown great promise. We have demonstrated designs and fabrication strategies for creating QDLEDs with enhanced performance. In particular: (I) We introduce a sandwich structure with a spin coated inorganic hole transporting layer of nickel oxide underlying the QD layer and with a spin coated zinc oxide electron transporting layer, with patterning of anode and cathode on the substrate. Compared to the use of sputtered thin films, solution processed charge transporting layers (CTLs) improve robustness of the device, as crystalline ZnO shows low CB and VB edge energy levels, efficiently suppressing hole leakage current resulting in LEDs with longer lifetimes. We also use Atomic Layer Deposition to deposit an additional hole injecting layer to protect the QDs from direct contact with the anode. With this device design, we demonstrate a working lifetime of more than 12 hours and a shelf-life of more than 240 days for the devices. Our solution based process is applicable to micro-contact printed and also spin-coated QD films. QDLEDs with spin-coated CTLs show a lifetime increase of more than three orders of magnitude compared to devices made using sputtered CTLs. (II) We implement strategies of the enhancement of light extraction from the fabricated QDLEDs. We discuss the integration of a two dimensional grating structure based on a metal-dielectric-metal plasmonic waveguide with the metal electrode of a QDLED, with the aim of enhancing the light intensity by resonant suppression of transmitted light. The grating structure reflects the light coupled with the metal electrode in the QDLED and we found an increase of 34.72% in the electroluminescence intensity from the area of the pattern and an increase of 32.63% from photoluminescence of QDs deposited on a metal surface. (III) We demonstrate the capability of our fabricated devices as a light source by measuring intensity across stained cells with QDLEDs of two different wavelengths and show the correlation as expected with the absorption profile of the fluorescent dye. We measure the absorption from the biological samples using QDLEDs fabricated with various design modifications, as a quantification of the improvements in device performance, directly affecting to our target application. / text

Optical nanoantennas have raised much interest during the past decade for their vast potential in photonics applications. This thesis investigates the response of periodic arrays of nanomonopoles and nanodipoles on a silicon substrate, covered by water, to variations of antenna dimensions. These arrays are illuminated by a plane wave source located inside the silicon substrate. Modal analysis was performed and the mode in the nanoantennas was identified. By characterizing the properties of this mode certain response behaviours of the system were explained. Expressions are offered to predict approximately the resonant length of nanomonopoles and nanodipoles, by accounting for the fringing fields at the antenna ends and the effects of the gap in dipoles. These expressions enable one to predict the resonant length of nanomonopoles within 20% and nanodipoles within 10% error, which significantly facilitates the design of such antennas for specific applications.