The progressive blooming of silicon photonics technology (SiP) has indicated that optical interconnects may substitute the electrical wires for data movement over short distances in the future. Silicon Photonics platform has been the subject of intensive research for more than a decade now and its prospects continue to emerge as it enjoys the maturity of CMOS manufacturing industry. SiP foundries all over the world and particularly in the US (AIM Photonics) have been developing reliable photonic design kits (PDKs) that include fundamental SiP building blocks such as wavelength selective modulators and tunable filters. Microring resonators (MRR) are hailed as the most compact devices that can perform both modulation and demodulation in a wavelength division multiplexed (WDM) transceiver design. Although the use of WDM can reduce the number of fibers carrying data, it also makes the design of transceivers challenging. It is probably acceptable to achieve compactness at the expense of somewhat higher transceiver cost and power consumption. Nevertheless, these two metrics should remain close to their roadmap values for Datacom applications. An increase of an order of magnitude is clearly not acceptable. For example costs relative to bandwidth for an optical link in a data center interconnect will have to decrease from the current $5/Gbps down to <$1/Gbps. Additionally, the transceiver itself must remain compact. The optical properties of SiP devices are subject to various design considerations, operation conditions, and optimization procedures. In this thesis, the general goal is to develop mathematical models that can accurately describe the thermo-optical and electro-optical behavior of individual SiP devices and then use these models to perform optimization on the parameters of such devices to maximize the capabilities of photonic links or photonic switch fabrics for datacom applications. In Chapter 1, Introduction, we first provide an overview of the current state of the optical transceivers for data centers and datacom applications. Four main categories for optical interfaces (Pluggable transceivers, On-board optics, Co-packaged optics, monolithic integration) are briefly discussed. The structure of a silicon photonic link is also briefly introduced. Then the direction is shifted towards optical switching technologies where various technologies such as free space MEMS, liquid crystal on silicon (LCOS), SOA-based switches, and silicon-based switches are explored. In Chapter 2, Silicon Photonic Waveguides, we present an extensive study of the silicon-on-insulator (SOI) waveguides that are the basic building blocks of all of the SiP devices. The dispersion of Si and SiO2 is modeled with Sellmiere equation for the wavelength range 1500–1600 nm and then is used to calculate the TE and TM modes of a 2D slab waveguide. There are two reasons that 2D waveguides are studied: first, the modes of these waveguides have closed form solutions and the modes of 3D waveguides can be approximated from 2D waveguides based on the effective index method. Second, when the coupling of waveguides is studied and the concept of curvature function of coupling is developed, the coupled modes of 2D waveguides are used to show that this approach has some inherent small error due to the discretization of the nonuniform coupling. This chapter finishes by describing the coefficients of the sensitivity of optical modes of the waveguides to the geometrical and material parameters. Perturbation theory is briefly presented as a way to analytically examine the impact of small perturbations on the effective index of the modes. In Chapter 3, Compact Modeling Approach, the concept of scattering matrix of a multi-port silicon photonic device is presented. The elements of the S-matrix are complex numbers that relate the amplitude and phase relationships of the optical models in the input and output ports. Based on the scattering matrix modeling of silicon photonics devices, two methods of solving photonic circuits are developed: the first one is based on the iteration for linear circuits. The second approach is based on the construction of an equivalent signal flow graph (SFG) for the circuit. We show that the SFG approach is very efficient for circuits involving microring resonator structures. Not only SFG can provide the solution for the transmission, it also provides the signal paths and the closed-form solution based on the Mason’s graph formula. We also show how the SFG method can be utilized to formulate the backscattering effects inside a ring resonator. In Chapter 4, Scalability of Silicon Photonic Switch Fabrics, we develop the models for electro-optic Mach-Zehnder switch elements (2×2). For the electro-optic properties, the empirical Soref’s equations are used to characterize how the loss and index of silicon changes when the charge carrier density is changed. We then use our photonic circuit solver based on the iteration method to find accurate result of light propagation in large-scale switch topologies (e.g. 4×4, and 8×8). The concept of advanced path mapping based on physical layer evaluation of the switch fabric is introduced and used to develop the optimum routing tables for 4×4 and 8×8 Benes switch topologies. In Chapter 5, Design space of Microring Resonators, we introduce the concept of curvature function of coupling to mathematically characterize the coupling coefficient of a ring resonator to a waveguide as a function of the geometrical parameters (ring radius, coupling gap, width and height of waveguides) and the wavelength. Extensive 2D and 3D FDTD simulations are carried out to validate our modeling approach. Experimental demonstrations are also used to not only further validate our modeling of coupling, but also to extract an empirical power-law model for the bending loss of the ring resonators as a function the radius. By combining these models, we for the first time present a full characterization of the design space of microring resonators. Moreover, the value of this discussion will be further apparent when the scalability of a silicon photonic link is studied. We will show that the FSR of the rings determines the optical bandwidth but it also impacts the properties of the ring resonators. In Chapter 6, Thermo-optic Efficiency of Microheaters, we develop analytical models for the thermo-optic properties of SiP waveguides. For the thermo-optic properties, the concept of thermal impulse response is mathematically developed for integrated micro-heaters. The thermal impulse response is a key function that determines the tradeoff between heating efficiency and heating speed (thermal bandwidth), as well as allows us to predict the pulse-width-modulation (PWM) optical response of the heater-waveguide system. One of the motivations behind this study was to find the highest possible efficiency for thermal tuning of microring resonators to use it in the evaluation of the energy consumption of a photonic link. The results indicate 2 nm/mW which is in agreement with the trends that we see in the literature. In Chapter 7, Crosstalk Penalty, we theoretically and experimentally investigate the optical crosstalk effects in microring-based silicon photonic interconnects. Both inter-channel crosstalk and intra-channel crosstalk are investigated and approximate equations are developed for their corresponding power penalties. Inclusion of the inter-channel crosstalk is an important part of our final analysis of a silicon photonic link. In Chapter 8, Scalability of Silicon Photonic Links, we present the analysis of a WDM silicon photonics point-to-point link based on microring modulators and microring wavelength filters. Our approach is based on the power penalty analysis of non-return-to-zero (NRZ) signals and Gaussian noise statistics. All the necessary equations for the optical power penalty calculations are presented for microring modulators and filters. The first part of the analysis is based on various ideal assumptions which lead to a maximum capacity of 2.1 Tb/s for the link. The second part of the analysis is carried out with more realistic assumptions on the photonic elements in the link, culminating in a maximum throughput of 800 Gb/s. We also provide estimations of the energy/bit metric of such links based on the optimized models of electronic circuits in 65 nm CMOS technology.

近年在矽光子學方面的研究日漸增多，主要原因是在高效能電腦，低成本通訊接取網絡及集成光學感應器等各方面有很大的潛在應用。以矽為原材料的各種光學器件已經被廣泛研究，包括電光調制器，光感應器和各式各樣主動及被動器件。但是由於矽是一種間接能隙的物質，即是由電子激發的電子電洞的結合是屬於非輻射躍遷，所以不可以得到光放大和激光器的效果。為了製作集成激光器，已經有很多不同的研究方案，例如在矽波導上摻雜鉺或是混合集成矽和-族半導體。在這篇論文中，我們提出並且論証了一個創新的方案去製作由光纖和矽波導混合而成的激光器，大大簡化了設計和生產過程。 / 在論文中，我們會集中討論選取光波長的器件及整體結構的設計。在首次的結構設計上，我們利用了分佈在矽波導兩側的布拉格反射鏡作為選取光波長的器件和一小段以鉺摻雜的光纖作為放大器。我們將會詳細形容該器件的設計、模擬效果和實驗結果。我們已經透過實驗証明了單波長的光纖－矽波導混合激光器，其側模抑制超過35分貝。 / 另一方面，為了製作多波長的光纖－矽波導混合激光器，我們利用微環諧震器來取代分佈在矽波導兩側的布拉格反射鏡作為選取光波長的器件。我們將會討論微環諧震器的設計以及達到穩定多波長的光纖和矽波導混合激光器的設計要求。 / Motivated by potential applications for optical interconnects in high performance computing, low cost optical access networks in telecommunications and integrated optical sensors, there has been much research in recent years on silicon photonics. Different silicon-based photonic devices have been studied, including optical modulators, detectors and various types of active and passive components. However, since the bandgap of silicon is indirect, the recombination of carriers injected by electrical pumping is dominated by non-radiative transitions and thus it is not possible to get optical gain via current injection into silicon diodes. / To implement integrated laser, different approaches such as erbium doping on silicon waveguide and hybrid integration of III-V semiconductors on silicon have been investigated. In this thesis, we propose and demonstrate a novel approach for making a hybrid fiber-silicon laser to simplify the design and fabrication processes. We propose the use of Erbium-doped fiber (EDF) to provide gain and silicon devices to provide all the other functionalities needed for a modulated laser. / The thesis focuses on the design of wavelength selective element and the structure of hybrid fiber-silicon laser. The first design includes a silicon waveguide side-cladding distributed Bragg reflector (WSC-DBR) as the wavelength selective component on silicon-on-insulator (SOI) wafer and a short length of EDF as the gain medium. The details of design, simulation and experimental results of the WSC-DBR will be described. Single wavelength WSC-DBR hybrid fiber-silicon laser is demonstrated with a side mode suppression ratio (SMSR) of over 35dB. / We also investigate the use of a micro-ring resonator to replace WSC-DBR for selecting multiple wavelengths. Details of the micro-ring resonator are given and we discuss the requirement and design criteria to achieve stable multi-wavelength lasing. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Fung, Ka Yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / ABSTRACTOF THESIS ENTITLED: --- p.ii / ACKNOWLEDGEMENT --- p.v / TABLE OF CONTENT --- p.vii / Chapter 1 --- INTRODUCTION --- p.10 / Chapter 1.1 --- Photonic Integrated Circuits --- p.10 / Chapter 1.2 --- Silicon Photonics --- p.13 / Chapter 1.3 --- Lasers in Silicon --- p.20 / Chapter 1.4 --- Motivation --- p.27 / Chapter 1.5 --- References --- p.29 / Chapter 2 --- ERBIUM DOPED FIEBR AND FIBER LASERS --- p.34 / Chapter 2.1 --- Erbium doped fiber --- p.34 / Chapter 2.2 --- Multi-wavelength lasers --- p.45 / Chapter 2.3 --- References --- p.54 / Chapter 3 --- SINGLE CHANNEL HYBRID FIBER-SILICON LASER --- p.59 / Chapter 3.1 --- Introduction of Distributed Bragg reflector --- p.60 / Chapter 3.2 --- Design of waveguide side-cladding distributed Bragg reflector --- p.63 / Chapter 3.3 --- Simulation results of waveguide side-cladding distributed Bragg reflector --- p.66 / Chapter 3.4 --- Device fabrication --- p.69 / Chapter 3.5 --- Experimental results of waveguide side-cladding distributed Bragg reflector --- p.71 / Chapter 3.6 --- Experimental results of hybrid fiber-silicon laser --- p.77 / Chapter 3.7 --- Introduction of micro-ring resonator --- p.81 / Chapter 3.8 --- Design of race track micro-ring resonator --- p.85 / Chapter 3.9 --- Experimental results of race track micro-ring resonator --- p.88 / Chapter 3.10 --- Experimental results of hybrid fiber-silicon laser with ring resonator --- p.95 / Chapter 3.11 --- Summary --- p.99 / Chapter 3.12 --- References --- p.101 / Chapter 4 --- DUAL WAVELENGTH HYBRID FIBER SILICON LASER --- p.102 / Chapter 4.1 --- Design of micro-ring resonator for dual wavelength --- p.103 / Chapter 4.2 --- Experimental results of micro-ring resonator --- p.104 / Chapter 4.3 --- Experimental results of dual wavelength hybrid fiber-silicon laser --- p.108 / Chapter 4.4 --- Summary --- p.119 / Chapter 4.5 --- References --- p.121 / Chapter 5 --- DUAL WAVELENGTH VERTICAL GRATING COUPLER --- p.123 / Chapter 5.1 --- Introduction of grating coupler --- p.123 / Chapter 5.2 --- Design of dual wavelength vertical grating coupler --- p.125 / Chapter 5.3 --- Simulation of dual wavelength vertical grating coupler --- p.127 / Chapter 5.4 --- Experimental results of dual wavelength vertical grating coupler --- p.135 / Chapter 5.5 --- Summary --- p.138 / Chapter 5.6 --- References --- p.139 / Chapter 6 --- CONCLUSION AND FUTURE WORK --- p.141 / Chapter 6.1 --- Conclusion --- p.141 / Chapter 6.2 --- Future work --- p.144 / Chapter 6.3 --- References --- p.146 / Chapter APPENDIX A: --- PUBLICATION LIST --- p.147 / Chapter APPENDIX B: --- LIST OF TABLES --- p.149 / Chapter APPENDIX C: --- LIST OF FIGURES --- p.150 / Chapter APPENDIX D: --- METHODS OF LINEWIDTH MEASUREMENT --- p.155 / Chapter APPENDIX E: --- EQUIPMENT INFORMATION --- p.164

The rapid growth in data communication technologies is at the heart of enriching the digital experiences for people around the world. Encoding high bandwidth data to the optical domain has drastically changed the bandwidth-distance trade-off imposed by electrical media. Silicon photonics, sharing the technological maturity of the semiconductor industry, is a platform poised to make optical interconnect components more robust, manufacturable, and ubiquitous. One of the most prominent device classes enabled by the silicon photonics platform is photonic switching, which describes the direct routing of optical signal carriers without the optical-electrical-optical conversions. While theoretical designs and prototypes of monolithic silicon photonic switch devices have been studied, realizing high-performance and feasible switch systems requires explorations of all design aspects from basic building blocks to control systems. This thesis provides a holistic collection of studies on silicon photonic switching in topics of novel switching element designs, multi-stage switch architectures, device calibration, topology scalability, smart routing strategies, and performance-aware control plane. First, component designs for assembling a silicon photonic switch device are presented. Structures that perform 2×2 optical switching functions are introduced. To realize switching granularities in both spatial and spectral domains, a resonator-assisted Mach-Zehnder interferometer design is demonstrated with high performance and design robustness. Next, multi-stage monolithic switching devices with microring resonator-based switching elements are investigated. An 8×8 switch device with dual-microring switching elements is presented with a well-balanced set of performance metrics in extinction ratio, crosstalk suppression, and optical bandwidth. Continued scaling in the switch port count requires both an economic increase in the number of switching elements integrated in a device and the preservation of signal quality through the switch fabric. A highly scalable switch architecture based on Clos network with microring switch-and-select sub-switches is presented as a solution to reach high switch radices while addressing key factors of insertion loss, crosstalk, and optical passband to ensure end-to-end switching performance. The thesis then explores calibration techniques to acquire and optimize system-wide control points for integrated silicon switch devices. Applicable to common rearrangeably non-blocking switch topologies, automated procedures are developed to calibrate entire switch devices without the need for built-in power monitors. Using Mach-Zehnder interferometer-based switching elements as a demonstration, calibration techniques for optimal control points are introduced to achieve balanced push-pull drive scheme and reduced crosstalk in switching operations. Furthermore, smart routing strategies are developed based on optical penalty estimations enabled by expedited lightpath characterization procedures. Leveraging configuration redundancies in the switch fabric, the routing strategies are capable of avoiding the worst penalty optical paths and effectively elevate the bottom-line performance of the switch device. Additional works are also presented on enhancing optical system control planes with machine learning techniques to accurately characterize complex systems and identify critical control parameters. Using flexgrid networks as a case study, light-weight machine learning workflows are tailored to devise control strategies for improving spectral power stability during wavelength assignment and defragmentation. This work affirms the efficacy of intelligent control planes to predict system dynamics and drive performance optimizations for optical interconnect systems.

The continuous growth of electronic compute and memory nodes in terms of the number of I/O pins, bandwidth, and areal throughput poses major integration and packaging challenges associated with offloading multi-Tbit/s data rates within the few pJ/bit targets. While integrated photonics are already deployed in long and short distances such as inter and intra data centers communications, the promising characteristics of the silicon photonic platform set it as the future technology for optical interconnects in ultra short inter-chip distances. The high index contrast between the waveguide and the cladding together with strong thermo-optic and carrier effects in silicon allows developing a wide range of micro-scale and low power optical devices compatible with the CMOS fabrication processes. Furthermore, the availability of photonic foundries and new electrical and optical co-packaging techniques further pushes this platform for the next steps of commercial deployment. The work in this dissertation presents the current trends in high-performance memory and processor nodes and gives motivation for disaggregated and reconfigurable inter-chip network enabled with the silicon photonic layer. A dense WDM transceiver and broadband switch architectures are discussed to support a bi-directional network of ten hybrid-memory cubes (HMC) interconnected to ten processor nodes with an overall aggregated bandwidth of 9.6Tbit/s. Latency and energy consumption are key performance parameters in a processor to primary memory nodes connectivity. The transceiver design is based on energy-efficient micro-ring resonators, and the broadband switch is constructed with 2x2 Mach-Zehnder elements for nano-second reconfiguration. Each transceiver is based on hundreds of micro-rings to convert the native HMC electrical protocol to the optical domain and the switch is based on tens of hundreds of 2x2 elements to achieve non-blocking all-to-all connectivity. The next chapters focus on developing methods for controlling and monitoring such complex and highly integrated silicon photonic subsystems. The thermo-optic effect is characterized and we show experimentally that the phase of the optical carrier can be reliably controlled with pulse-width modulation (PWM) signal, ultimately relaxing the need for hundreds of digital to analog converters (DACs). We further show that doped waveguide heaters can be utilized as \textit{in-line} optical power monitors by measuring photo-conductance current, which is an alternative for the conventional tapping and integration of photo-diodes. The next part concerned with a common cascaded micro-ring resonator in a WDM transceiver design. We develop on an FPGA control algorithm that abstracts the physical layer and takes user-defined inputs to set the resonances to the desired wavelength in a unicast and multicast transmission modes. The associated sensitivities of these silicon ring resonators are presented and addressed with three closed-loop solutions. We first show a closed-loop operation based on tapping the error signal from the drop port of the micro-ring. The second solution presents a resonance wavelength locking with a single digital I/O for control and feedback signals. Lastly, we leverage the photo-conductance effect and demonstrate the locking procedure using only the doped heater for both control and feedback purposes. To achieve the inter-chip reconfigurability we discuss recent advances of high-port-count SiP broadband switches for reconfigurable inter-chip networks. To ensure optimal operation in terms of low insertion loss, low cross-talk and high signal integrity per routing path, hundreds of 2x2 Mach-Zehnder elements need to be biased precisely for the cross and bar states. We address this challenge with a tapless and a design agnostic calibration approach based on the photo-conductance effect. The automated algorithm returns a look-up table for all for each 2x2 element and the associated calibrated biases. Each routing scenario is then tested for insertion loss, crosstalk and bit-error rate of 25Gbit/s 4-level pulse amplitude modulation signals. The last part utilizes the Mach-Zehnder interferometers in WDM transceiver applications. We demonstrate a polarization insensitive four-channel WDM receiver with 40Gbit/s per channel and a transmitter design generating 8-level pulse amplitude modulation signals at 30Gbit/s.

No description available.

Animals have evolved diverse strategies to control solar and thermal radiations so that they can better adapt to their natural habitats. Structured materials utilized by these animals to control electromagnetic waves often surpass analogous man-made optical materials in both sophistication and efficiency. Understanding the physical mechanism behind these structured materials of nature inspires one to create novel materials and technologies. Our optical and thermodynamic measurements of insects (Saharan silver ants and cocoons of the Madagascar comet moth) living in harsh thermal environments showed their unique ability to simultaneously enhance solar reflectivity and thermal emissivity, and to maintain a cool body temperature. Saharan silver ants, Cataglyphis bombycina, forage on the desert surface during the middle of the day. The ants’ conspicuous silvery glance is caused by a coating of hairs with unique triangular cross-sections. The hair coating enhances not only the reflectivity of the ant’s body surface in the visible and near-infrared range of the spectrum, where solar radiation culminates, but also the emissivity of the ant in the mid-infrared. The latter effect enables the animals to efficiently dissipate heat back to the surroundings via blackbody radiation under full daylight conditions. The fibers produced by the wild comet moth, Argema mittrei, are populated with a high density of air voids that have a random distribution in the fiber cross-section but are invariant along the fiber. These filamentary air voids strongly back-scatter light in the solar spectrum, which, in combination with the fibers’ intrinsic high emissivity in the mid-infrared, enables the cocoon to function as an efficient radiative-cooling device, preventing the pupa inside from overheating. The reduced dimensionality of the random voids leads to strong optical scattering in the transverse direction of the cocoon fibers. This enables tightly confined optical modes to propagate along the fibers via transverse Anderson localization. We made the first observation of transverse Anderson localization in a natural fiber and further demonstrated light focusing and image transport in the fibers. This discovery opens up the possibility to use wild silk fibers as a biocompatible and bioresorbable material for transporting optical signals and images. Drawing inspirations from these discoveries, we designed and developed high-throughput fabrication processes to create coatings and fibers with passive radiative-cooling properties. The radiative-cooling coatings consist of various nanoparticles imbedded within a silicone thin film. The sizes and materials of the nanoparticles were chosen to provide simultaneously high solar reflectivity and thermal emissivity. The coating has been implemented in two site studies on real roofs and has demonstrated reduced roof temperature by up to 30oC in the summer and associated reduction of electricity usage by up to 30%. We also made biomimetic fibers from regenerated silk fibroin and a thermoplastic using wet spinning. Spectroscopic measurements showed that these man-made fibers exhibit exceptional optical properties for radiative-cooling applications.

<p dir="ltr">Quantum photonics is one of the leading platforms to realize quantum information technologies. Quantum emitters embedded in host materials which can readily form photonic circuitry elements have received significant research interest in recent years for on-chip quantum information processing applications. In this work, we report on the discovery of bright, stable, and linearly polarized quantum emitters in SiN films with room temperature single photon generation. We suggest that the emission originates from a specific defect center in SiN because of the narrow wavelength distribution of the observed luminescence peak.</p><p dir="ltr">We further probe these emitters’ fundamental photophysical properties through measurements of optical transition wavelengths, linewidths, and photon antibunching as a function of temperature. Important insight into the potential for lifetime-limited linewidths is provided through measurements of inhomogeneous and temperature-dependent broadening of the zero-phonon lines. At 4.2K, spectral diffusion was found to be the main broadening mechanism, while spectroscopy time series revealed zero-phonon lines with instrument-limited linewidths.</p><p dir="ltr">Along with the optical properties of the quantum emitters, we study their formation mechanisms by investigating the effects of sample composition and thermal annealing parameters. From these measurements, we gain critical insight into the fundamental nature of the quantum emitters in SiN, as well as the dependence of their photophysical properties on the changes in the host material. Additionally, we explore alternative SiN fabrication approaches and the optical properties of the SiN films developed with these techniques. We then investigate quantum emitter formation and hypothesize why the optical properties of the defects in each type of film differ.</p><p dir="ltr">Finally, we begin preliminary investigations into the possible existence of near-infrared (NIR) emitting defects in SiN, as well as single-photon electroluminescence from thin SiN-on-silica films embedded in p-n heterojunctions.</p><p dir="ltr">The single-photon emitters in SiN we have studied extensively in this work have the potential to enable scalable and low-loss integration of quantum light sources with a mature on-chip photonics platform.</p>

Photonic band gap materials, commonly referred to as photonic crystals (PCs), have been a topic of great interest for almost two decades due to their promise of unprecedented control over the propagation and generation of light. We report investigations of the optical properties of a new PC structure based upon a triangular lattice in which adjacent [i, j] rows of holes possess different properties, creating a superlattice (SL) periodicity. Symmetry arguments predicted and quot;band folding and quot; and band splitting behaviors, both of which are direct consequences of the new basis that converts the Brillouin zone from hexagonal (six-fold) to rectangular (two-fold). Plane wave expansion and finite-difference time-domain (FDTD) numerical calculations were used to explore the effects of the new structure on the photonic dispersion relationship of the SL PC. Electron beam lithography and inductively coupled plasma dry etching were used to fabricate 1 mm2 PC areas (lattice constant, a =358 nm and 480 nm) with hole radius ratios ranging from 1.0 (triangular) to 0.585 (r2/r1 = 73.26 nm/125.26 nm) on Silicon-on-insulator wafers. The effects of modifying structural parameters (such as hole size, lattice constant, and SL strength) were measured using the coupled resonant band technique, confirming the SL symmetry arguments and corroborating the band structure calculations. Analysis of the dispersion contours of the static SL (SSL) PC predicted both giant refraction (change in beam propagation angle of 110 for an 8 change in incident angle) and superprism behavior (change in beam propagation angle of 108 for a 12% change in normalized frequency) in these structures. Dynamic control of these refraction effects was also investigated by incorporating electro-optic and nonlinear materials into the SSL PC structure. Wave vector analyses on these structures predicted a change in beam propagation angle and gt;96 when the refractive index inside of the holes of the structure changed from n=1.5 to 1.7. Through this investigation, the first successful measurement of the band folding effect in multidimensional PCs as well as the first explicit measurement of the dielectric band of a 2D PC were reported. In addition, the SL PCs impact on new opto-electronic devices was explored.

In the past few years, the solution-processed organic based solar cells gained more importance by meeting the demands for cost effective photovoltaic devices. To date, the focus of the organic photovoltaic devices has been on the optimization of the processing the materials to improve photo conversion efficiency and also by modifying the active components of the organic materials. Recently, it has been recognized that the deposition techniques also plays a major role in enhancing the power conversion efficiencies. Currently, though the most common deposition technique for organic solar cells is spin coating, which does not allow scaling up of the large device area. As an alternative method, a simple airbrush spray deposition technique has been developed to fabricate the test devices. The film thickness of the layers was characterized under scanning electron microscope. Devices with different thickness (1000 nm, 500 nm, 240 nm) of poly(3,4-ethylenedioxythipohene) polystyrene sulfonate (PEDOT.PSS) and active layers are prepared and their photovoltaic performances have been evaluated and compared by plotting the IV curves with respect to each thickness. Maintaining the distance between the substrate and the airbrush nozzle the thickness of the layers was controlled. From the results, we found that the test devices with 500 nm thickness of PEDOT.PSS and active layers shows the best device performance with highest current density of 3.97 mA/cm2, open circuit voltage of 1.3 V and power conversion efficiency of 2.34%. As a control experiment, devices were also developed using the standard poly(3- hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) system, but the power conversion efficiencies of these devices were not promising with respect to the literature results. Future studies of this project will focus on improving the power conversion efficiency of poly(3-hexylthiophene-2,5-diyl)/perylenediimide bridged system (P3HT/PDIB) by developing a new device architecture called “tandem solar cells” which consists of multiple layers of different donor and acceptor blends with inorganic transition metal oxides such as zinc oxide and molybdenum oxides.

Although the study of the interaction of acoustic and elastic waves with periodic surfaces and structures has a rich history dating back to Lord Rayleigh, it has recently been attracting new research efforts due to its value in the study of phononic crystals and in methods for ultrasonic non-destructive evaluation (NDE). The objective of the research described in this thesis is to provide new numerical and experimental tools capable of capturing important features that occur due to the diffraction of ultrasound on periodic solid surfaces. This thesis is divided into four main parts. First, the Rayleigh-Fourier (R-F) method will be used to simulate diffracted fields generated by structures containing multiple periodic surfaces and/or multiple solid layers. The second part of this thesis examines diffraction effects and compares ultrasonic NDE techniques for surfaces with imperfect periodicities. The third portion of this thesis focuses on one unusual phenomenon that has been observed on periodic surfaces, namely the lateral backward displacement of a bounded ultrasonic beam along the surface. This effect is currently understood to occur due to backward propagating surface waves that result from diffraction and mode conversion on the surface. The fourth and final part of this thesis describes the diffraction of bulk ultrasonic waves that can occur on the surfaces of phononic crystals.