Nano-structures, such as photonic crystal cavities and metallic antennas, allow one to focus and store optical energy into very small volumes, greatly increasing light-matter interactions. These structures produce resonances which are typically characterized by how well they confine energy both temporally (quality factor–Q) and spatially (mode volume–V). In order to observe non-linear effects, modified spontaneous emission (e.g. Purcell enhancement), or quantum effects (e.g. vacuum Rabi splitting), one needs to maximize the ratio of Q/V while also maximizing the coupling between the resonance and the active medium. In this dissertation I will discuss several projects related by the goal of controlling light-matter interactions using such nano-structures. In the first portion of this dissertation I will discuss the deterministic placement of self-assembled InAs quantum dots, which would allow one to precisely position an optically-active material, for maximum interaction, inside of a photonic crystal cavity. Additionally, I will discuss the use of atomic layer deposition to tune and improve both the resonance wavelength and quality factor of silicon based photonic crystal cavities. Moving from dielectric materials to metals allows one to achieve mode-volumes well below the diffraction limit. The quality factor of these resonators is severely limited by Ohmic loss in the metal; however, the small mode-volume still allows for greatly enhanced light-matter interaction. In the second portion of this dissertation I will investigate the coupling between an array of metallic resonators (antennas) and a nearby semiconductor quantum well. Using time-resolved pump-probe measurements I study the properties of the coupled system and compare the results to a model which allows one to quantitatively compare various antenna geometries.

Silicon Nanowires (SiNWs) with ability to confine carriers and photons in two directions while allowing propagation in third dimension offer interesting modified optical properties such as increased material absorption and optical non-linearities with regard to that of bulk silicon. Enhanced optical properties in SiNWs open a window not only to improve the performance of existing devices but also to realize novel structures. As such, I chose to investigate SiNWs for their applications in photonics, especially for sensing and non-linear devices. My goal was to conduct fundamental research on the optical properties of these SiNWs, and then develop an integration platform to realize practical devices. The platform should be compatible with IC manufacturing. Electron Beam Lithography (EBL) using a Poly Methyl Methacrylate (PMMA) resist followed by Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) is used for SiNWs fabrication. Now we are able to fabricate nanowires as small as 15 nm in diameter with the smallest separation of 50 nm. In addition, the interface between SiNWs and Si substrate is optically smooth enabling us to fundamentally understand optical properties of these structures. During the course of this project, I have contributed new fundamental knowledge about SiNWs. For example, Second Harmonic Generation (SHG) is demonstrated in SiNWs, which is absent in bulk silicon. This is achieved by self-straining the nanowires and is the first demonstration of this kind. Second-order non-linearities are more efficient for optical signal processing than third-order ones (which have been used for silicon photonics devices so far). Therefore, these results open a new area of research in silicon. In addition to second order nonlinearity, high enhancement of Raman scattering is achieved in SiNWs fabricated on Silicon on Insulator (SOI) substrate. This can find promising applications in sensing and nonlinear based devices such as optical switches and logic gates. Further, polarization resolved reflections from these nanowire arrays were measured and significant differences were observed for the reflection characteristics for the sand p-polarized beams. In order to understand these reflections, an effective index model is proposed based on calculations using Finite Difference Time Domain (FDTD) method. Results of this analysis provide useful information for designing of many optical devices using SiNWs such as solar cells and photodetectors. As another part of this thesis, vivid colors in mutually coupled SiNWs is demonstrated where nanowire diameters range from 105 nm to 345 nm. A simple sensor is demonstrated by observing the change in the reflected color with changing refractive index of the surrounding medium. A refractive index resolution of 5×10−5 is achieved using a simple charge coupled device (CCD) camera. Although, there were some paradigm shifting results during my fundamental studies, it became very apparent that SiNWs suffer from a major issue inhibiting their use in photonics devices. Below the diameter of 100 nm where these enhanced material properties were observed, SiNW is a poor optical waveguide with less than 1 % of light confined. The low confinement factor means that though the intrinsic properties of SiNWs increase, the overall device performance is not significantly enhanced. To overcome this issue, a new platform technology is invented, called Silicon Nanowire Optical Waveguide (SNOW). It combines the material advantages of nanostructures with the optical properties of conventional waveguides, and consists of arrays of nanowires in close proximity. It is shown that such a structure can guide an optical mode using the FDTD method. This waveguide structure can be used as a versatile platform to manufacture various devices such as sensors, switches, modulators, grating, and delay lines. For instance, a novel bio-sensor is proposed and designed whose sensitivity is enhanced by a factor of 20, compared to conventional silicon-wire waveguides.

Silicon Nanowires (SiNWs) with ability to confine carriers and photons in two directions while allowing propagation in third dimension offer interesting modified optical properties such as increased material absorption and optical non-linearities with regard to that of bulk silicon. Enhanced optical properties in SiNWs open a window not only to improve the performance of existing devices but also to realize novel structures. As such, I chose to investigate SiNWs for their applications in photonics, especially for sensing and non-linear devices. My goal was to conduct fundamental research on the optical properties of these SiNWs, and then develop an integration platform to realize practical devices. The platform should be compatible with IC manufacturing. Electron Beam Lithography (EBL) using a Poly Methyl Methacrylate (PMMA) resist followed by Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) is used for SiNWs fabrication. Now we are able to fabricate nanowires as small as 15 nm in diameter with the smallest separation of 50 nm. In addition, the interface between SiNWs and Si substrate is optically smooth enabling us to fundamentally understand optical properties of these structures. During the course of this project, I have contributed new fundamental knowledge about SiNWs. For example, Second Harmonic Generation (SHG) is demonstrated in SiNWs, which is absent in bulk silicon. This is achieved by self-straining the nanowires and is the first demonstration of this kind. Second-order non-linearities are more efficient for optical signal processing than third-order ones (which have been used for silicon photonics devices so far). Therefore, these results open a new area of research in silicon. In addition to second order nonlinearity, high enhancement of Raman scattering is achieved in SiNWs fabricated on Silicon on Insulator (SOI) substrate. This can find promising applications in sensing and nonlinear based devices such as optical switches and logic gates. Further, polarization resolved reflections from these nanowire arrays were measured and significant differences were observed for the reflection characteristics for the sand p-polarized beams. In order to understand these reflections, an effective index model is proposed based on calculations using Finite Difference Time Domain (FDTD) method. Results of this analysis provide useful information for designing of many optical devices using SiNWs such as solar cells and photodetectors. As another part of this thesis, vivid colors in mutually coupled SiNWs is demonstrated where nanowire diameters range from 105 nm to 345 nm. A simple sensor is demonstrated by observing the change in the reflected color with changing refractive index of the surrounding medium. A refractive index resolution of 5×10−5 is achieved using a simple charge coupled device (CCD) camera. Although, there were some paradigm shifting results during my fundamental studies, it became very apparent that SiNWs suffer from a major issue inhibiting their use in photonics devices. Below the diameter of 100 nm where these enhanced material properties were observed, SiNW is a poor optical waveguide with less than 1 % of light confined. The low confinement factor means that though the intrinsic properties of SiNWs increase, the overall device performance is not significantly enhanced. To overcome this issue, a new platform technology is invented, called Silicon Nanowire Optical Waveguide (SNOW). It combines the material advantages of nanostructures with the optical properties of conventional waveguides, and consists of arrays of nanowires in close proximity. It is shown that such a structure can guide an optical mode using the FDTD method. This waveguide structure can be used as a versatile platform to manufacture various devices such as sensors, switches, modulators, grating, and delay lines. For instance, a novel bio-sensor is proposed and designed whose sensitivity is enhanced by a factor of 20, compared to conventional silicon-wire waveguides.

This thesis investigates the security of optical fiber communication and demonstrates the feasibility of eavesdropping using different tapping methods and superconducting nanowire single-photon detectors (SNSPDs). Methods for surveillance against fiber intrusion are also investigated. The setups were built from mainly commercially available components and a 3D-printed sculpture and data analysis was done using open-source software. By the use of a clip-on coupler, classical systems were tapped. Transmission loss and tapping efficiency was measured to 42% and 1.5% respectively. Continuous system monitoring for tap detection using an SNSPD was performed showing that photon backscattering increased by a factor of 6 when the tap was applied. A qualitative investigation on tapping light via fiber bending was performed with signal loss/coupling efficiency registered with regards to bending diameter. Loss in a light conducting fiber and detection events in the tapping fiber increased with decreasing bend diameter. It is also shown that keeping a constant bend diameter while increasing the number of turns of the tapping fiber can increase amount of tapped light while keeping signal loss constant. Lastly, optical routers were tapped, the tapped light was analysed through a spectrum analyser yielding the lights wavelength and signal-to-noise ratio. The tapped light was then connected to a SNSPD and photon detection events was registered. / Denna avhandling undersöker säkerheten för optisk fiberkommunikation inom telekomområdet och genomförbarheten av avlyssing med olika avlyssningsmetoder samt superconducting nanowire single-photon detectors (SNSPDer). Även metoder för att övervaka mot avlyssing undeersöks. Utrustningarna byggdes med kommersiellt tillgängliga komponenter och en 3D-utskriven skulptur och dataanalysen utfördes med hjälp av öppen källkodsprogramvara. Genom användning av en Clip-On-Coupler avlyssnades klassiska system. Överföringsförlusten och avlyssningseffektiviteten mättes till 42% respektive 1,5%. Kontinuerlig systemövervakning för att upptäcka avlyssning med hjälp av en SNSPD utfördes och visade att antalet bakreflekterade fotoner ökade med en faktor på 6 när avlyssningen applicerades. En kvalitativ undersökning av att avlyssna ljus genom att böja fiber utfördes, där signalförlust och kopplingseffektivitet registrerades med avseende på böjningsdiameter. Förlusten i en ljusledande fiber och fotonförekomst i avlyssningsfibern ökade med minskande böjningsdiameter. Det visas också att genom att behålla en konstant böjningsdiameter samtidigt som antalet varv på avlyssningsfibern ökas kan mängden avlyssnat ljus öka samtidigt som signalförlusten hålls konstant. Slutligen avlyssnades optiska routrar, det avlyssnade ljuset analyserades med hjälp av en spektrumanalysator som utvann ljusets våglängd och signal-brusförhållande. Det avlyssnade ljuset kopplades sedan till en SNSPD och fotonförekomst registrerades.

Thanks to their capability of transmitting light with low loss, optical fibers have found a wide range of applications in illumination, imaging, and telecommunication. However, since the light guided in a regular optical fiber is well confined in the core and effectively isolated from the environment, the fiber does not allow the interactions between the light and matters around it, which are critical for many sensing and actuation applications. Specially shaped optical fibers endow the guided light in optical fibers with the capability of interacting with the environment by modifying part of the fiber into a special shape, while still preserving the regular fiber’s benefit of low-loss light delivering. However, the existing specially shaped fibers have the following limitations: 1) limited light coupling efficiency between the regular optical fiber and the specially shaped optical fiber, 2) lack special shape designs that can facilitate the light-matter interactions, 3) inadequate material selections for different applications, 4) the existing fabrication setups for the specially shaped fibers have poor accessibility, repeatability, and controllability. The overall goal of this dissertation is to further the fundamental understanding of specially shaped fibers and to develop novel specially shaped fibers for different applications. In addition, the final part of this dissertation work proposed a microfluidic platform that can potentially improve the light-matter interactions of the specially shaped fibers in fluidic environments. The contributions of this dissertation work are summarized as follows: 1) An enhanced fiber tapering system for highly repeatable adiabatic tapered fiber fabrications. An enhanced fiber tapering system based on a novel heat source and an innovative monitoring method have been developed. The novel heat source is a low-cost ceramic housed electric furnace (CHEF). The innovative monitoring method is based on the frequency-domain optical transmission signal from the fiber that is being tapered. The enhanced fiber tapering system can allow highly repeatable fabrication of adiabatically tapered fibers. 2) A lossy mode resonance (LMR) sensor enabled by SnO2 coating on a novel specially shaped fiber design has been developed. The developed LMR sensor has a D-shape fiber tip with SnO2 coating. It has the capability of relative humidity and moisture sensing. The fiber-tip form factor can allow the sensor to be used like a probe and be inserted into/removed from a tight space. 3) Specially shaped tapered fibers with novel designs have been developed for integrated photonic and microfluidic applications. Two novel specially tapered fibers, the tapered fiber loop and the tapered fiber helix have been developed. The tapered fiber loop developed in this work has two superiority that differentiated itself from previous works: a) the mechanical stability of the tapered fiber loop in this work is significantly better. b) the tapered fiber loops in this work can achieve a diameter as small as 15 ?m while still have a high intrinsic optical quality factor of 32,500. The tapered fiber helix developed in this work has a 3D structure that allows it to efficiently deliver light to locations out of the plane defined by its two regular fiber arms. Applications of the tapered fiber helices in both integrated photonic device characterizations and microparticle manipulations have been demonstrated. 4) Developed an acrylic-tape hybrid microfluidic platform that can allow function reconfiguration and optical fiber integration. A low-cost, versatile microfluidic platform based on reconfigurable acrylic-tape hybrid microfluidic devices has been developed. To the best of the author’s knowledge, this is the first time that the fabrication method of sealing the acrylic channel with a reconfigurable functional tape has been demonstrated. The tape-sealing method is compatible with specially shaped fiber integrations.

Thanks to their capability of transmitting light with low loss, optical fibers have found a wide range of applications in illumination, imaging, and telecommunication. However, since the light guided in a regular optical fiber is well confined in the core and effectively isolated from the environment, the fiber does not allow the interactions between the light and matters around it, which are critical for many sensing and actuation applications. Specially shaped optical fibers endow the guided light in optical fibers with the capability of interacting with the environment by modifying part of the fiber into a special shape, while still preserving the regular fiber’s benefit of low-loss light delivering. However, the existing specially shaped fibers have the following limitations: 1) limited light coupling efficiency between the regular optical fiber and the specially shaped optical fiber, 2) lack special shape designs that can facilitate the light-matter interactions, 3) inadequate material selections for different applications, 4) the existing fabrication setups for the specially shaped fibers have poor accessibility, repeatability, and controllability. The overall goal of this dissertation is to further the fundamental understanding of specially shaped fibers and to develop novel specially shaped fibers for different applications. In addition, the final part of this dissertation work proposed a microfluidic platform that can potentially improve the light-matter interactions of the specially shaped fibers in fluidic environments. The contributions of this dissertation work are summarized as follows: 1) An enhanced fiber tapering system for highly repeatable adiabatic tapered fiber fabrications. An enhanced fiber tapering system based on a novel heat source and an innovative monitoring method have been developed. The novel heat source is a low-cost ceramic housed electric furnace (CHEF). The innovative monitoring method is based on the frequency-domain optical transmission signal from the fiber that is being tapered. The enhanced fiber tapering system can allow highly repeatable fabrication of adiabatically tapered fibers. 2) A lossy mode resonance (LMR) sensor enabled by SnO2 coating on a novel specially shaped fiber design has been developed. The developed LMR sensor has a D-shape fiber tip with SnO2 coating. It has the capability of relative humidity and moisture sensing. The fiber-tip form factor can allow the sensor to be used like a probe and be inserted into/removed from a tight space. 3) Specially shaped tapered fibers with novel designs have been developed for integrated photonic and microfluidic applications. Two novel specially tapered fibers, the tapered fiber loop and the tapered fiber helix have been developed. The tapered fiber loop developed in this work has two superiority that differentiated itself from previous works: a) the mechanical stability of the tapered fiber loop in this work is significantly better. b) the tapered fiber loops in this work can achieve a diameter as small as 15 ?m while still have a high intrinsic optical quality factor of 32,500. The tapered fiber helix developed in this work has a 3D structure that allows it to efficiently deliver light to locations out of the plane defined by its two regular fiber arms. Applications of the tapered fiber helices in both integrated photonic device characterizations and microparticle manipulations have been demonstrated. 4) Developed an acrylic-tape hybrid microfluidic platform that can allow function reconfiguration and optical fiber integration. A low-cost, versatile microfluidic platform based on reconfigurable acrylic-tape hybrid microfluidic devices has been developed. To the best of the author’s knowledge, this is the first time that the fabrication method of sealing the acrylic channel with a reconfigurable functional tape has been demonstrated. The tape-sealing method is compatible with specially shaped fiber integrations.

No description available.

Quantentechnologien sind im Begriff sich von Laborversuchen zu effizienten Anwendungen zu entwickeln. Die Quantenzustände einzelner Photonen spielen dabei die Rolle als Bindeglied zwischen stationären Quantensystemen. Ein hybrider Ansatz wird verfolgt, um die Wechselwirkung gezielt zwischen im Wellenleiter geleiteten Photonen und gekoppelten Quantenemittern zu erreichen. Die Dissertation untersucht zwei zentrale Aspekte solcher hybriden photonischen Quantentechnologien: die effiziente Erzeugung von Photonen und die Optimierung von photonischen Strukturen. Der erste Teil dieser Arbeit behandelt die Entwicklung einer optischen Mikrotechnology. Integrierte nano-photonische Wellenleiter aus Siliziumnitrid wurden für die Kopplung zu Quantenemittern entworfen, optimiert und optisch untersucht. Das finale Design wurde erfolgreich in Kopplungsexperimenten verwendet, bei denen 42 % der Fluoreszenz eines einzelnen Moleküls an einen Wellenleiter gekoppelt wurde. Der zweite Teil der Arbeit untersucht zwei Einzelphotonenquellen. Zunächst wurde ein neuartiger Einzelphotonenemitter basierend auf Defektzentren in Zinkoxid optisch bei tiefen Temperaturen untersucht. Es konnte im Zuge dieser Arbeit erstmals gezeigt werden, dass die Photonen von nano-strukturiertem Zinkoxid sehr schmalbandige Emission aufweisen. Im letzten Teil, wird eine Einzelphotonenquelle bestehend aus einem organischen Molekül untersucht. Bei kryogenen Temperaturen wurden Lebenszeit-limitierte Linienbreiten auf den Molekülproben detektiert. Die Rabi-Oszillationen zwischen den Molekülzuständen konnten akkurat durch eine quantenmechanische Theorie beschrieben werden, wodurch die Vermessung der Dephasierung des Quantensystems durch die nanoskopische Umgebung präzise studiert werden konnte. Die Ergebnisse dieser Arbeit zur Kopplung von Einzelphotonenquellen stellen die Grundlage für weitere Anwendungen durch eine photonische Quantentechnologie dar. / Quantum technologies are on the verge to transition from laboratory experiments to efficient integrated applications. The quantum states of photons are the connecting link between individual stationary quantum systems. A hybrid approach is employed to tailor the interaction of routed photons with optically coupled quantum systems. The thesis investigates two core aspects of a hybrid photonic quantum technology: efficient single photon generation and optimized photonic micro-structures, suitable to form a hybrid system. In the first part of this work, nano-photonic integrated structures were optimized for efficient coupling to quantum emitters. Optical waveguides based on silicon nitride (SiN) were designed, fabricated, and optically characterized. The final design was successfully employed in coupling experiments, where up to 42% of the fluorescence from a single molecule was coupled to a waveguide. In the second part of this thesis two single photon sources are investigated towards their implementation into a hybrid photonic system. First, a novel single photon source based on a defect center in zinc oxide was optically investigated at room-temperature and cryogenic temperature. Spectrally narrow zero-phonon lines of the fluorescence from nano-structured zinc oxide were measured for the first time during this work. A second emitter system, based on an organic dye molecule was investigated in the final part of this research. At cryogenic temperatures, single molecules showed lifetime-limited linewidths of <50MHz. A resonant laser source drives Rabi oscillations, which are accurately described by the quantum mechanical theory of a two-level system. The system's decoherence was mapped, illustrating the quantum sensing capabilities of the system. The results presented in this thesis on coupling efficiencies and single emitter performance provide the necessary background of the elements composing a future hybrid technology.

Size reduction is a key issue in the development of contemporary integrated photonics. This thesis is mainly devoted to study some integrated photonic components in sub-wavelength or nanometric scales, both theoretically and experimentally. The possible approaches to reduce the sizes or to increase the functionalities of photonic components are discussed, including waveguides and devices based on silicon nanowires, photonic crystals, surface plasmons, and some near-field plasmonic components. First, some numerical methods, including the finite-difference time-domain method and the full-vectorial finite-difference mode solver, are introduced. The finite-difference time-domain method can be used to investigate the interaction of light fields with virtually arbitrary structures. The full-vectorial finite-difference mode solver is mainly used for calculating the eigenmodes of a waveguide structure. The fabrication and characterization technologies for nano-photonic components are reviewed. The fabrications are mainly based on semiconductor cleanroom facilities, which include thin film deposition, electron beam lithography, and etching. The characterization setups with the end-fire coupling and the vertical grating coupling are also described. Silicon nanowire waveguides and related devices are studied. Arrayed waveguide gratings with 11nm and 1.6nm channel spacing are fabricated and characterized. The dimension of these arrayed waveguide gratings is around 100 μm, which is 1--2 order of magnitude smaller than conventional silica based arrayed waveguide gratings. A compact polarization beam splitter employing positive/negative refraction based on a photonic crystal of silicon pillars is designed and demonstrated. Extinction ratio of ~15dB is achieved experimentally in a wide wavelength range. Surface plasmon waveguides and devices are analyzed theoretically. With surface plasmons the light field can be confined in a sub-wavelength dimension. Some related photonic devices, e.g., directional couplers and ring resonators, are studied. We also show that some ideas and principles of microwave devices, e.g., a branch-line coupler, can be borrowed for building corresponding surface plasmon based devices. Near-field plasmonic components, including near-field scanning optical microscope probes and left handed material slab lenses, are also analyzed. Some novel designs are introduced to enhance the corresponding systems. / QC 20100908