Universiẗat, Diss.--Paderborn, 1994.

University, Diss., 2005--Jena.

Chemnitz, Techn. Univ., Studienarb., 2002.

In this work, functional plasmonic nanocircuitry is examined as a key of revolutionizing state-of-the-art electronic and photonic circuitry in terms of integration density and transmission bandwidth. In this context, numerical simulations enable the design of dedicated devices, which allow fundamental control of photon flow at the nanometer scale via single or multiple plasmonic eigenmodes. The deterministic synthesis and in situ analysis of these eigenmodes is demonstrated and constitutes an indispensable requirement for the practical use of any device. By exploiting the existence of multiple eigenmodes and coherence - both not accessible in classical electronics - a nanoscale directional coupler for the ultrafast spatial and spatiotemporal coherent control of plasmon propagation is conceived. Future widespread application of plasmonic nanocircuitry in quantum technologies is boosted by the promising demonstrations of spin-optical and quantum plasmonic nanocircuitry. / In dieser Arbeit werden funktionelle plasmonische Schaltkreise als Schlüssel zur Revolutionierung modernster elektronischer und photonischer Schaltkreise in Bezug auf deren Integrationsdichte und Übertragungsbandbreite untersucht. Mit Hilfe numerischer Simulationen werden Bauelemente speziell für die Steuerung des Photonenflusses im Nanometerbereich mittels einzelner bzw. mehrerer plasmonischer Eigenmoden konzipiert. Die deterministische Synthese und Analyse solcher Eigenmoden wird aufgezeigt und stellt eine unverzichtbare Voraussetzung für die praktische Anwendung eines jeden Nanoschaltkreises dar. Durch die Existenz mehrerer Eigenmoden und Kohärenz - beide in der klassischen Elektronik nicht zugänglich - lässt sich ein nanoskaliger Richtkoppler für die ultraschnelle räumliche und räumlich-zeitliche kohärente Kontrolle der Plasmonenausbreitung entwerfen. Künftig werden plasmonische Schaltkreise aufgrund der vielversprechenden Demonstrationen von spinoptischen und quantenplasmonischen Schaltkreisen in Quantentechnologien weite Verbreitung finden.

A major focus is on integrated Silicon-based optoelectronics for the creation of low-cost photonics for mass-market applications. Especially, the growing demand for sensitive and portable optical sensors in the environmental control and medicine follows in the development of integrated high resolution sensors [1]. In particular, since 2013 the quick onsite verification of pathogens, like legionella in drinking water pipes, is becoming increasingly important [2, 3]. The essential questions regarding the establishment of portable biochemical sensors are the incorporation of electronic and optical devices as well as the implementations of fundamental cross-innovations between biotechnology and microelectronics. This thesis describes the design, fabrication and analysis of high-refractive-index-contrast photonic structures. Besides silicon nitride (Si3N4) strip waveguides, lateral tapers, bended waveguides, two-dimensional photonic crystals (PhCs) the focus lies on monolithically integrated waveguide butt-coupled Silicon-based light emitting devices (Sibased LEDs) [4, 5] for use as bioanalytical sensor components. Firstly, the design and performance characteristics as single mode regime, confinement factor and propagation losses due to the geometry and operation wavelength (1550 nm, 541 nm) of single mode (SM), multi mode (MM) waveguides and bends are studied and simulated. As a result, SM operation is obtained for 1550 nm by limiting the waveguide cross-section to 0.5 μm x 1 μm resulting in modal confinement factors of 87 %. In contrast, for shorter wavelengths as 541 nm SM propagation is excluded if the core height is not further decreased. Moreover, the obtained theoretical propagation losses for the lowestorder TE/TM mode are in the range of 0.3 - 1.3 dB/cm for an interface roughness of 1 nm. The lower silicon dioxide (SiO2) waveguide cladding should be at least 1 μm to avoid substrate radiations. These results are in a good correlation to the known values for common dielectric structures. In the case of bended waveguides, an idealized device with a radius of 10 μm was developed which shows a reflection minimum (S11 = - 22 dB) at 1550 nm resulting in almost perfect transmission of the signal. Additionally, tapered waveguides were investigated for an optimized light coupling between high-aspect-ratio devices. Here, adiabatic down-tapered waveguides were designed for the elimination of higher-order modes and perfect signal transmission. Secondly, fabrication lines including Electron-beam (E-beam) lithography and reactive ion etching (RIE) with an Aluminum (Al) mask were developed and lead to well fabricated optical devices in the (sub)micrometer range. The usage of focused ion beam (FIB) milling is invented for smoother front faces which were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). As a result, the anisotropy of the RIE process was increased, but the obtained surface roughness parameters are still too high (10 – 20 nm) demonstrating a more advanced lithography technique is needed for higher quality structures. Moreover, this study presents an alternative fabrication pathway for novel designed waveguides with free-edge overlapping endfaces for improving fiber-chipcoupling. Thirdly, the main focus lies on the development of a monolithic integration circuit consisting of the Si-based LED coupled to an integrated waveguide. The light propagation between high-aspect-ratio devices is enabled through low-loss adiabatic tapers. This study shows, that the usage of CMOS-related fabrication technologies result in a monolithic manufacturing pathway for the successful implementation of fully integrated Si-based photonic circuits. Fourth, transmission loss measurements of the fabricated photonic structures as well as the waveguide butt-coupled Si-based LEDs were performed with a generated setup. As a result, free-edge overlapping MM waveguides show propagation loss coefficients of ~ 65 dB/cm in the range of the telecommunication wavelength. The high surface roughness parameters (~ 150 nm) and the modal dispersion in the core are one of the key driving factors. These facts clearly underline the improvement potential of the used fabrication processes. However, electroluminescence (EL) measurements of waveguide butt-coupled Si-based LEDs due to the implanted rare earth (RE) ion (Tb3+, Er3+) and the host material (SiO2/SiNx) were carried out. The detected transmission spectra of the coupled Tb:SiO2 systems show a weak EL signal at the main transition line of the Tb3+-ion (538 nm). A second emission line was detected in the red region of the spectrum either corresponding to a further optical transition of Tb3+ or a Non Bridging Oxygen Hole Center (NBOHC) in SiO2. Unfortunately, no light emission in the infrared range was established for the Er3+-doped photonic circuits caused by the low external quantum efficiencies (EQE) of the Er3+ implanted Si-based LEDs. Nevertheless, transmission measurements between 450 nm – 800 nm lead again to the result that an emission at 650 nm is either caused by an optical transition of the Er3+-ion or initialized by the NBOHC in the host. Overall, it is difficult to assess whether or not these EL signals are generated from the implanted ions, thus detailed statements about the coupling efficiency between the LED and the integrated waveguide are quite inadequate. Nevertheless, the principle of a fully monolithically integrated photonic circuit consisting of a Si-based LED and a waveguide has been successfully proven in this study.

Zugl.: Hannover, Univ., Diss., 2008

University, Diss., 1999--Osnabrück.

A major focus is on integrated Silicon-based optoelectronics for the creation of low-cost photonics for mass-market applications. Especially, the growing demand for sensitive and portable optical sensors in the environmental control and medicine follows in the development of integrated high resolution sensors [1]. In particular, since 2013 the quick onsite verification of pathogens, like legionella in drinking water pipes, is becoming increasingly important [2, 3]. The essential questions regarding the establishment of portable biochemical sensors are the incorporation of electronic and optical devices as well as the implementations of fundamental cross-innovations between biotechnology and microelectronics. This thesis describes the design, fabrication and analysis of high-refractive-index-contrast photonic structures. Besides silicon nitride (Si3N4) strip waveguides, lateral tapers, bended waveguides, two-dimensional photonic crystals (PhCs) the focus lies on monolithically integrated waveguide butt-coupled Silicon-based light emitting devices (Sibased LEDs) [4, 5] for use as bioanalytical sensor components. Firstly, the design and performance characteristics as single mode regime, confinement factor and propagation losses due to the geometry and operation wavelength (1550 nm, 541 nm) of single mode (SM), multi mode (MM) waveguides and bends are studied and simulated. As a result, SM operation is obtained for 1550 nm by limiting the waveguide cross-section to 0.5 μm x 1 μm resulting in modal confinement factors of 87 %. In contrast, for shorter wavelengths as 541 nm SM propagation is excluded if the core height is not further decreased. Moreover, the obtained theoretical propagation losses for the lowestorder TE/TM mode are in the range of 0.3 - 1.3 dB/cm for an interface roughness of 1 nm. The lower silicon dioxide (SiO2) waveguide cladding should be at least 1 μm to avoid substrate radiations. These results are in a good correlation to the known values for common dielectric structures. In the case of bended waveguides, an idealized device with a radius of 10 μm was developed which shows a reflection minimum (S11 = - 22 dB) at 1550 nm resulting in almost perfect transmission of the signal. Additionally, tapered waveguides were investigated for an optimized light coupling between high-aspect-ratio devices. Here, adiabatic down-tapered waveguides were designed for the elimination of higher-order modes and perfect signal transmission. Secondly, fabrication lines including Electron-beam (E-beam) lithography and reactive ion etching (RIE) with an Aluminum (Al) mask were developed and lead to well fabricated optical devices in the (sub)micrometer range. The usage of focused ion beam (FIB) milling is invented for smoother front faces which were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). As a result, the anisotropy of the RIE process was increased, but the obtained surface roughness parameters are still too high (10 – 20 nm) demonstrating a more advanced lithography technique is needed for higher quality structures. Moreover, this study presents an alternative fabrication pathway for novel designed waveguides with free-edge overlapping endfaces for improving fiber-chipcoupling. Thirdly, the main focus lies on the development of a monolithic integration circuit consisting of the Si-based LED coupled to an integrated waveguide. The light propagation between high-aspect-ratio devices is enabled through low-loss adiabatic tapers. This study shows, that the usage of CMOS-related fabrication technologies result in a monolithic manufacturing pathway for the successful implementation of fully integrated Si-based photonic circuits. Fourth, transmission loss measurements of the fabricated photonic structures as well as the waveguide butt-coupled Si-based LEDs were performed with a generated setup. As a result, free-edge overlapping MM waveguides show propagation loss coefficients of ~ 65 dB/cm in the range of the telecommunication wavelength. The high surface roughness parameters (~ 150 nm) and the modal dispersion in the core are one of the key driving factors. These facts clearly underline the improvement potential of the used fabrication processes. However, electroluminescence (EL) measurements of waveguide butt-coupled Si-based LEDs due to the implanted rare earth (RE) ion (Tb3+, Er3+) and the host material (SiO2/SiNx) were carried out. The detected transmission spectra of the coupled Tb:SiO2 systems show a weak EL signal at the main transition line of the Tb3+-ion (538 nm). A second emission line was detected in the red region of the spectrum either corresponding to a further optical transition of Tb3+ or a Non Bridging Oxygen Hole Center (NBOHC) in SiO2. Unfortunately, no light emission in the infrared range was established for the Er3+-doped photonic circuits caused by the low external quantum efficiencies (EQE) of the Er3+ implanted Si-based LEDs. Nevertheless, transmission measurements between 450 nm – 800 nm lead again to the result that an emission at 650 nm is either caused by an optical transition of the Er3+-ion or initialized by the NBOHC in the host. Overall, it is difficult to assess whether or not these EL signals are generated from the implanted ions, thus detailed statements about the coupling efficiency between the LED and the integrated waveguide are quite inadequate. Nevertheless, the principle of a fully monolithically integrated photonic circuit consisting of a Si-based LED and a waveguide has been successfully proven in this study.

Metallic nano-optical systems allow to confine and guide light at the nanoscale, a fascinating ability which has motivated a wide range of fundamental as well as applied research over the last two decades. While optical antennas provide a link between visible radiation and localized energy, plasmonic waveguides route light in predefined pathways. So far, however, most experimental demonstrations are limited to purely optical excitations, i.e. isolated structures are illuminated by external lasers. Driving such systems electrically and generating light at the nanoscale, would greatly reduce the device footprint and pave the road for integrated optical nanocircuitry. Yet, the light emission mechanism as well as connecting delicate nanostructures to external electrodes pose key challenges and require sophisticated fabrication techniques. This work presents various electrically connected nano-optical systems and outlines a comprehensive production line, thus significantly advancing the state of the art. Importantly, the electrical connection is not just used to generate light, but also offers new strategies for device assembly. In a first example, nanoelectrodes are selectively functionalized with self-assembled monolayers by charging a specific electrode. This allows to tailor the surface properties of nanoscale objects, introducing an additional degree of freedom to the development of metal-organic nanodevices. In addition, the electrical connection enables the bottom-up fabrication of tunnel junctions by feedback-controlled dielectrophoresis. The resulting tunnel barriers are then used to generate light in different nano-optical systems via inelastic electron tunneling. Two structures are discussed in particular: optical Yagi-Uda antennas and plasmonic waveguides. Their refined geometries, accurately fabricated via focused ion beam milling of single-crystalline gold platelets, determine the properties of the emitted light. It is shown experimentally, that Yagi-Uda antennas radiate light in a specific direction with unprecedented directionality, while plasmonic waveguides allow to switch between the excitation of two propagating modes with orthogonal near-field symmetry. The presented devices nicely demonstrate the potential of electrically connected nano-optical systems, and the fabrication scheme including dielectrophoresis as well as site-selective functionalization will inspire more research in the field of nano-optoelectronics. In this context, different future experiments are discussed, ranging from the control of molecular machinery to optical antenna communication. / Nano-optische Systeme ermöglichen es, Licht auf der Nanoskala zu fokussieren und zu leiten - eine faszinierende Fähigkeit, die in den letzten zwei Jahrzehnten ein breites Spektrum an Grundlagen- und angewandter Forschung motiviert hat. Während optische Antennen lokalisierte Energie mit sichtbarer Strahlung verknüpfen, leiten plasmonische Wellenleiter das Licht in vordefinierte Bahnen. Bislang jedoch beschränken sich die meisten Experimente auf isolierte Strukturen, die durch externe Lichtquellen angeregt werden. Die elektrisch getriebene Lichterzeugung auf der Nanoskala reduziert den Platzbedarf dieser Systeme erheblich und ebnet so den Weg für optische Nano-Schaltkreise. Allerdings stellen sowohl die Lichtemission als auch die Kontaktierung der Nanostrukturen erhebliche Herausforderungen dar. In dieser Arbeit werden verschiedene elektrisch kontaktierte nano-optische Systeme vorgestellt. Eine zentrale Rolle spielt dabei die Kontaktierung - nicht nur für die Lichterzeugung, sondern auch für die Fabrikation der jeweiligen Strukturen. In einem ersten Beispiel werden Nanoelektroden durch Anlegen einer Spannung selektiv mit molekularen Monolagen beschichtet. Dadurch können die chemischen und elektronischen Oberflächeneigenschaften von Nanoobjekten maßgeschneidert werden, was einen zusätzlichen Freiheitsgrad bei der Entwicklung von optoelektronischen Nanosystemen darstellt. Darüber hinaus ermöglicht die elektrische Kontaktierung die Herstellung von Tunnelbarrieren mittels Dielektrophorese, was die Lichterzeugung in verschiedenen nano-optischen Systemen durch inelastisches Elektronentunneln ermöglicht. Hier werden zwei Strukturen diskutiert: optische Yagi-Uda-Antennen und plasmonische Wellenleiter. Ihre ausgeklügelten Geometrien, hergestellt aus einkristallinen Goldflocken mittels fokussiertem Ionenstrahl, bestimmen die Eigenschaften des emittierten Lichts. Es wird gezeigt, dass Yagi-Uda-Antennen das Licht gezielt in eine bestimmte Richtung abstrahlen, während plasmonische Wellenleiter das Schalten zwischen zwei propagierenden Moden ermöglichen. Damit demonstriert diese Arbeit das Potenzial von elektrisch kontaktierten nano-optischen Systemen und wird - in Kombination mit Dielektrophorese und selektiver Funktionalisierung - weitere Forschungen auf dem Gebiet der Nano-Optoelektronik anregen. In diesem Zusammenhang werden verschiedene zukünftige Experimente, von der Steuerung molekularer Maschinen bis zur optischen Antennenkommunikation, diskutiert.

The work provides an overview of different integrated optical amplifiers. Semiconductor optical amplifiers and fiber amplifiers are described, as well as devices that utilize non-linear effects, nanocrystalline materials, or photonic crystals. Dielectric materials that are doped with rare-earth ions are considered more thoroughly. After a review of the principles of their optical activity the general mechanisms of excitation and emission are described. Materials aspects regarding the spectral range, their fabrication and the solubility of the dopants follow. An erbium-doped alumina waveguide amplifier, reported earlier in the literature, is chosen as an example to demonstrate the feasibility of such components. A theoretical model of the population densities of the energy levels is derived for the simulation. By numerical methods the non-linear system of the rate equations is solved and the stability of the steady state is shown. The simulation of the amplifier demonstrates the dependence of the gain of both the excitation energy and the z-coordinate. Moreover, the superiority of an excitation wavelength of 980 nm compared to 1530 nm is shown. With the model the literature data could be reproduced. / Die Arbeit gibt einen Überblick über verschiedene Möglichkeiten der Realisierung integriert-optischer Wellenleiterverstärker. Ausgehend von optischen Halbleiter- und Faserverstärkern werden einführend ebenso Anordnungen beschrieben, die nichtlineare Effekte sowie nanokristalline Materialien und photonische Kristalle nutzen. Besondere Bedeutung kommt dielektrischen Materialien zu, die mit optisch aktiven Dotanden, bevorzugt Seltenerdionen, versehen sind. Hierbei werden die Ursachen für die optische Aktivität der Lanthanide sowie die generellen Mechanismen der Anregungs- und Emissionsprozesse beschrieben. Aspekte der Materialauswahl, vor allem hinsichtlich des verwendeten Spektralbereiches sowie bezüglich ihrer Herstellung und der Löslichkeit der Dotanden schließen sich an. Anhand eines Literaturbeispiels wird die Realisierbarkeit eines erbiumdotierten Aluminiumoxid-Wellenleiterverstärkers demonstriert. Hierfür wird ein Modell zur Simulation der Besetzungsdichten der angeregten Energieniveaus abgeleitet und mittels numerischer Methoden das sich ergebende, nichtlineare System der Ratengleichungen gelöst, wobei besonders die Stabilität des stationären Besetzungszustandes herausgearbeitet wird. Die Simulation der Verstärkeranordnung zeigt zum einen die Abhängigkeit der Verstärkung von der z-Koordinate sowie der Pumpleistung; zum anderen wird deutlich, dass die Anregung bei 980 nm der Variante bei 1530 nm überlegen ist. Mit dem verwendeten Modell konnten die Literaturdaten reproduziert werden.