Theses and Dissertations from UMD
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Item SILICON NITRIDE INTEGRATED PHOTONIC DEVICES AND THEIR APPLICATIONS IN ASTRONOMY AND QUANTUM PHYSICS(2022) Zhan, Jiahao; Dagenais, Mario; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The photonics technology has revolutionized the telecommunication industry in the past 40 years with the deployment of the undersea fiber-optic network. Nowadays, with the maturity of silicon photonics technology, the integrated photonic platform is enabling more and more cutting-edge technologies, such as optical transceivers for data center connectivity, automotive LiDARs for self-driving vehicles, the next-generation astronomical instrumentation and nearterm photonic quantum computers, to name a few. In recent years, silicon nitride (Si3N4) material has attracted a significant amount of attention mainly due to the ultra-low loss that can be achieved. Compared to silicon, Si3N4 has a much wider transparency window, and does not suffer from two-photon absorption and free-carrier absorption over the telecommunication band. The relatively low refractive index of Si3N4 also means less sensitivity of optical modes to the waveguide sidewall roughness, therefore reducing the scattering loss. In this dissertation, I will first give an introduction of integrated photonics, and a brief overview of some novel applications and current trends. Next I will graphically show our methods for device fabrication and characterization, and then demonstrate a few integrated photonic devices implemented on the Si3N4 material platform, including Bragg gratings, multimode interferometers, polarization beam splitters, and polarization rotators, with an in-depth discussion of their potentialapplications, principles of operation, simulation and experimental results. I will then embark on a new chapter on arrayed waveguide gratings (AWGs), with emphasis on its application in integrated astronomical spectrometers. To obtain a continuous two-dimensional spectrum, cleaving at the output focal plane of the AWGis required. I will discuss and demonstrate a three-stigmatic-point AWG, which provides an elegant solution to the non-flat focal plane issue in traditional Rowland AWGs. This work is a critical step towards the development of an efficientand miniaturized astronomical spectrograph for the upcoming extremely-large telescopes. Next, I will introduce a one-dimensional nanobeam cavity enabled by a slow-light waveguide. A cubic relation between the quality factor and the length of the cavity will be derived and experimental verification will be demonstrated. The current progress towards the investigation of the Purcell effect of this nanobeam cavity will be discussed, including the platform and the loss characterization of the deposited amorphous silicon material. In the final chapter, I will first summarize the major conclusions from the previous chapters. Then I will briefly discuss some future research directions extending the work in this thesis, including ultra-broadband polarization beam splitter, the development of an on-chip Bell state analyzer, and the design of a polarization-insensitive flat-focal-field spectrometer.Item INTEGRATED QUANTUM PHOTONIC CIRCUITS WITH QUANTUM DOTS(2019) Aghaeimeibodi, Shahriar; Waks, Edo; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Scalable quantum photonics require efficient single-photon emitters as well as low-loss reconfigurable photonic platforms that connect and manipulate these single photons. Quantum dots are excellent sources of on-demand single photons and can act as stable quantum memories. Therefore, integration of quantum dots with photonic platforms is crucial for many applications in quantum information processing. In this thesis, we first describe hybrid integration of InAs quantum dots hosted in InP to silicon photonic waveguides. We demonstrate an efficient transition of quantum emission to silicon. Quantum nature of the emission is confirmed through photon correlation measurements. Secondly, we present a micro-disk resonator device based on silicon photonics that enables on-chip filtering and routing of single photons generated by quantum dots. The tunability of silicon photonics decreases at low temperatures due to “carrier freeze-out”. Because of a strong electro-optic effect in lithium niobate, this material is the ideal platform for reconfigurable photonics, even at cryogenic temperatures. To this end, we demonstrate integration of quantum dots with thin-film lithium niobate photonics promising for active switching and modulating of single photons. More complex quantum photonic devices require multiple identical single-photon emitters on the chip. However, the transition wavelength of quantum dots varies because of the slightly different shape and size of each dot. To address this hurdle, we propose and characterize a quantum dot device located in an electrostatic field. The resonance wavelength of the quantum dot emission is tuned up to 8 nm, more than one order of magnitude greater than the transition linewidth, opening the possibility of tuning multiple quantum dots in resonance with each other. Finally, we discuss the application of a single quantum dot strongly coupled to a nanophotonic cavity as an efficient medium for non-linear phenomenon of optical amplification. Presence of a strong pump laser inverses the population of the quantum dot and leads to stimulated emission from the cavity-coupled quantum dot. Using this platform, we observe an optical gain of ~ 16%, significantly increased compared to previous demonstrations of gain in single solid-state quantum emitters without cavities or weakly coupled to cavities. These demonstrations are significant steps toward robust control of single photons using linear and non-linear photonic platforms.Item Metals and Metallic Alloys for Energy Harvesting and Storage(2018) Gong, Chen; Leite, Marina S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Metals have been widely used for harvesting and storing energy in devices such as superabsorbers and Li-ion batteries. However, incorporating metals into a wider range of energy applications is severely limited by their intrinsic optical and electrochemical properties. Therefore, in this thesis, we provide a new class of metallic materials by forming binary mixtures of Ag, Au, Cu, and Al with novel physical properties for photonics, and a comprehensive understanding of the fundamental electrochemistry in Al and Si anode all-solid-state batteries for energy storage. The first part of my thesis focuses on developing metallic alloys with a tunable optical response. We realize a new family of metallic materials by alloying Ag, Au, and Cu with on-demand dielectric functions, which can be used in superabsorbers and hot carrier devices. We design and fabricate alloyed nanostructures with engineered optical response and spatially resolve the electric field distribution at the nanoscale by utilizing near-field scanning optical microscopy, which can potentially enhance the performance of optoelectronic devices. To understand the physical origin of the optical response of the alloys, we measure the valence band spectra and calculate the band structures of Ag-Au alloys, providing direct evidence that the change in the electronic bands is responsible for its optical property. Further, we obtain a photonic device with superior performance using metallic alloys. Specifically, an Al-Cu/Si bilayer superabsorber is reached in a lithography-free manner with maximum absorption > 99%, which can be used for energy harvesting. The second part of my thesis highlights the importance of understanding the reactions and ion distribution in energy storage devices. We inspect how the Al electrode surface changes upon cycling and directly map the Li distribution in 3-dimensions within all-solid-state batteries by implementing time-of-flight secondary ion mass spectroscopy. This research indicates that undesired chemical reactions, including the formation of an insulating layer on the Al anode surface and the trapping of Li ions at the interfaces, hinder the cycling performance of the devices. Overall, our results will contribute to the design of energy storage devices with enhanced electrochemical performance.Item Novel Organic Polymeric and Molecular Thin-Film Devices for Photonic Applications(2006-12-08) Kim, Younggu; Lee, Chi H.; Herman, Warren N.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The primary objective of this thesis is to explore the functionalities of new classes of novel organic materials and investigate their technological feasibilities for becoming novel photonic components. First, we discuss the unique polarization properties of optical chiral waveguides. Through a detailed experimental polarization analysis on planar waveguides, we show that eigenmodes in planar chiral-core waveguides are indeed elliptically polarized and demonstrate waveguides having modes with polarization eccentricity of 0.25, which agrees very well with recent theory. This is, to the best of our knowledge, the first experimental demonstration of the mode ellipticities of the chiral-core optical waveguides. In addition, we also examine organic magneto-optic materials. Verdet constants are measured using balanced homodyne detection, and we demonstrate organic materials with Verdet constants of 10.4 and 4.2 rad/T · m at 1300 nm and 1550 nm, respectively. Second, we present low-loss waveguides and microring resonators fabricated from perfluorocyclobutyl copolymer. Design, fabrication and characterization of these devices are addressed. We demonstrate straight waveguides with propagation losses of 0.3 dB/cm and 1.1 dB/cm for a buried channel and pedestal structures, respectively, and a microring resonator with a maximum extinction ratio of 4.87 dB, quality factor Q = 8554, and finesse F = 55. In addition, from a microring-loaded Mach-Zehnder interferometer, we demonstrate a modulation response width of 30 ps and a maximum modulation depth of 3.8 dB from an optical pump with a pulse duration of 100 fs and a pulse energy of 500 pJ when the signal wavelength is initially tuned close to one of the ring resonances. Finally, we investigate a highly efficient organic bulk heterojunction photodetector fabricated from a blend of P3HT and C60. The effect of multilayer thin film interference on the external quantum efficiency is discussed based on numerical modeling. We experimentally demonstrate an external quantum efficiency ηEQE=87±2% under an applied bias voltage V = −10 V, leading to an internal quantum efficiency ηIQE≈97%. These results show that the charge collection efficiency across the intervening energy barriers can indeed reach near 100% under a strong electric field.