1,721,581 research outputs found
Integrated Optical Sensors utilizing Slow-light Propagation in Grated-Waveguide Cavities
Full text linkAbstract Integrated Optical Sensors utilizing Slow-light Propagation in Grated-waveguide Cavities Owing to the small size of integrated optical (IO) devices many basic functions can be integrated on one single IO chip. IO sensors are suitable candidates for accurate detection of small changes of physical or chemical parameters. The integration offers advantages such as enabling a high density of functionalities, automatic and stable alignment of elements, a high potential for mass production with in principle low production costs, and the possibility for the realization of sensor arrays for multi-parameter detection. The main goal of this PhD project is firstly to design, fabricate and demonstrate functioning IO devices based on grated waveguides for sensing applications. A grated waveguide (GWG) is a waveguide with a finite-length grated section, being a structure with a periodic variation of the dielectric constant. Such a structure acts as both a 1-dimensional photonic crystal (PhC) and, owing to modal reflections at the waveguide-GWG transitions, an optical resonator, as evidenced by fringes in the transmission spectrum. In particular near the band edge these fringes can be extremely sharp, which is related to both the near band edge shape of the dispersion curve, corresponding to slow light propagation, and high modal reflectance due to mode mismatch between WG and GWG modes. Both effects lead to strong light-matter interaction, which can be exploited for sensing applications. In this thesis, we demonstrate the versatility of a silicon nitride GWG optical cavity as a compact IO sensor for bulk-index concentration sensing, label-free protein sensing and mechano-optical gas sensing. For concentration sensing, the sensing principle is based on the bulk index change of the GWG top cladding. The principle of the label-free protein sensing relies on the growth and measurement of an ad-layer on the GWG surface, owing to the antigen-antibody interaction. The mechano-optical gas sensing is based on stress-induced deflections of a microcantilever (μCL) suspended above the GWG, which are due to H2 gas absorption by the palladium receptor layer coated on the μCL surface. In the first chapter of this thesis an overview is given of bio- and gas-sensors. In chapter 2, the background of slow light propagation in GWGs and its utilization for sensing applications are discussed. In chapter 3, results related to the first 2 sensing applications (concentration sensing and label-free protein sensing) are presented; here, sensitivity and limit of detection of the sensors are analyzed in detail. The design and fabrication of the GWG-CL integrated readout, and the demonstration of the integrated mechano-optical sensor for gas sensing, are presented in chapter 4 and chapter 5, respectively. Results of an optimization study of the integrated mechano-optical readout principle, on the basis of numerical calculations, is presented in chapter 6. In chapter 7, conclusions and outlook, based on the results presented in this thesis, are given
Epitaxial growth and optical characterization of BaSO4:Mn6+ layers for novel coherent light sources
No full textBecause of the strong electron-phonon coupling of the emitting 3d orbital in transition-metal (TM) ions, 3d systems exhibit luminescence with typically several hundred nm of spectral bandwidth. TM-ion-doped materials are, therefore, of high interest for applications as tunable and short-pulse lasers. Whereas many TM-ion-doped systems suffer from excited-state absorption (ESA), systems with a d1 electron configuration possess only one excited 3d level and ESA into higher-lying 3d levels is impossible. However, ESA can occur owing to transitions into the conduction band and conduction-band-related energy levels. Mn6+ is a promising ion for a tunable laser system, and near-infrared emission from Mn6+ was observed in several host lattices. In BaSO4, the room-temperature stimulated-emission cross section is larger than the ESA cross section in the spectral range 920-1600 nm [bru97II]. Therefore, as a laser material BaSO4:Mn6+ can offer a broad tuning range. The fabrication of Mn6+-doped BaSO4 layers requires a particular growth method at low temperatures, since the Mn6+ ions tend to reduce to Mn4+ at T ≥ 600°C. Moreover, this reduction is also time-dependent. The Mn6+-doped BaSO4 layers have been grown at low temperatures using liquid-phase epitaxy (LPE). The eutectic CsCl-KCl-NaCl served as solvent for the LPE of BaSO4:Mn6+ with a low eutectic temperature of 480°C in order to keep the temperatures well below 600°C to prevent chemical reduction of Mn6+. The initial Mn6+ concentration was up to 1 mol% with respect to S6+. In contrast, the Mn6+ concentration in the layers was maximum 20% of the initial Mn6+ concentration. High quality layers with thickness of up to 580 μm, lack of large-size inclusions, and low defect concentration were achieved [ehr02]. The etch-pit density for the (011) face was 103 cm-2. The Mn6+-doped BaSO4 layers were investigated spectroscopically by absorption and emission measurements at room temperature and the incorporation of manganese solely in its hexavalent oxidation state into the layers was confirmed [ehr02]. The Mn6+ absorption bands are 2E —> 2T2 at 700-900 nm and a ligand-to-metal charge-transfer band at 500-650 nm. Excitation into these bands leads to broadband Mn6+ emission between 850 and 1600 nm. The fluorescence lifetime was measured to be 0.56μs [ehr02]. A relatively small reabsorption from the ground state is visible in the region of the fluorescence emission. With the measured spectroscopic data, analytical and numerical simulations in order to investigate the future laser potential of BaSO4:Mn6+ was performed. Since reabsorption at the laser wavelength from the ground state especially in the wings of the pump absorption may play a significant role in such a ground-state laser system, the rate equations for the excited-state population density and the photon density in the cavity were solved. The pump and laser wavelengths, the dopant concentration, and the length of the active medium were optimized with respect to minimize the laser threshold. Pumping around 800 nm and providing high reflectivity of the cavity mirrors at 1150 nm cannot enable laser emission, because the ratio of 3:1 between pump absorption cross-section and laser reabsorption cross-section is too small to allow for sufficient pump absorption and simultaneously avoid significant reabsorption of the oscillating laser light. In contrast, when pumping at 532 nm and providing high reflectivity at 1500 nm, this ratio becomes 143:1. In conclusion, laser oscillation of BaSO4:Mn6+ at 1500 nm is more likely. The damage threshold was evaluated for the pump wavelengths of 532 and 1064 nm, 1.6 × 106 W cm-2 and 5.2 × 108 W cm-2, respectively. The damage threshold and the laser threshold are similar for pumping at 532 nm and 5% Losses in the crystal. References [bru97II] T.C. Brunold, H.U. Güdel, S. Kück, G. Huber, J. Opt. Soc. Am. B 14 (1997) 2373. [ehr02] D. Ehrentraut, M. Pollnau, S. Kück, Appl. Phys. B 75 (2002) 59
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Neodymium-doped waveguide amplifiers and lasers for integrated optical applications
Full text linkAbstract: In this thesis neodymium-doped polymer and amorphous aluminum oxide waveguide amplifiers and lasers for integrated optical applications have been realized. Nd3+-complex-doped, photo-defined polymer channel waveguides were realized on thermally oxidized silicon wafers with a simple and reproducible fabrication procedure by dividing the functionalities of photo-definition and active doping over two different polymers. Waveguides had very low loss in the visible and near-infrared wavelength range below 1.1 µm. A high internal net gain of 5.7 dB/cm has been demonstrated at 1064 nm. In the wavelength range between 865 and 930 nm, internal net optical gain with up to 2.8 dB gain was obtained at 873 nm by optimization of the Nd3+ concentration and channel waveguide length. Laser experiments of polymer channel waveguides have resulted in lasers operating at the four-level as well as the quasi-three-level transition near 1060.2 nm and 878 nm, respectively. These lasers exhibit remarkable lifetime stability, as they can withstand at least two hours of uninterrupted operation when pumping with up to 150 mW. The maximum output power of the polymer laser was ~1 mW. This is the first demonstration of a rare-earth-ion-doped polymer waveguide laser as well as a CW solid polymer laser. The thermally more stable amorphous aluminum oxide was investigated as a host material. Al2O3:Nd3+ films were deposited on thermally oxidized silicon wafers using reactive co-sputtering, and reactive-ion-etch was applied to realize low-loss waveguide structures in the films. High-gain waveguide amplifiers have been demonstrated. At the investigated signal wavelengths of 880 nm, 1064 nm, and 1330 nm small-signal gain of 1.57 dB/cm, 6.30 dB/cm, and 1.93 dB/cm, respectively, has been measured for individually optimized Nd3+ concentrations. The feasibility of using Al2O3:Nd3+ channel waveguides as amplifiers between polymer waveguides in optical backplanes has been investigated. Al2O3:Nd3+ channel waveguides with a PECVD SiO2 layer as an upper cladding were placed in between polymer waveguide samples to achieve optical amplification in optical waveguides on backplanes. A maximum of 0.42 dB internal net gain has been demonstrated in a polymer waveguide coupled to an Al2O3:Nd3+ waveguide. Therefore, a solution for compensating optical loss in optical interconnects has been provided
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Yb:KYW planar waveguide laser Q-switched by evanescent-field interaction with carbon nanotubes
Full text linkWe report Q-switched operation of a planar waveguide laser by evanescent-field interaction with single-walled carbon nanotubes deposited on top of the waveguide. The saturable-absorber-integrated gain medium, which operates based on evanescent-field interaction, enables the realization of a diode-pumped 2.5-cm-long Q-switched Yb:KYW waveguide laser emitting at 1030 nm. With such a compact cavity design, we achieve maximumoutput powers of up to 30 mW, corresponding to a single-pulse energy of 124 nJ, at 241 kHz repetition rate. The shortest pulse duration of 433 ns is generated at a repetition rate of 231 kHz
Al2O3:Er3+ as a gain platform for integrated optics
Full text linkThis thesis revolves around the development of fabrication technologies for waveguides and their use towards demonstrating new active devices and applications
Embedded Micro-Mirrors for Compact Routing of Multimode Polymer Waveguides
Full text linkThe limited scalability of high-speed electrical interconnects drives research on optical interconnect technologies. This work is concerned with compact polymer waveguide routing schemes for optical printed circuit boards (PCB). The developed embedded micro-mirrors are an integral part of the waveguide layer. The micro-structures that make up their bodies are fabricated directly onto the lower cladding of the waveguide by means of UV-laser patterning of a photosensitive resin. Vertical and 45°-tilted micro-structures are eventually used as in-plane and out-of-plane micro-mirrors, respectively. A wet-chemical deposition process is developed to apply the reflective metal layer selectively on the micro-structures. The fabrication processes are compatible to polymer waveguide and PCB manufacturing equipment. An electro-optical flex board is designed as basis for an optical transceiver module. Therein implemented are mechanical fiducial markers for adjustment-free alignment of the optical connector and the embedded out-of-plane micro-mirrors. The latter will vertically couple the light path from the laser- or detector-array to the polymer waveguide array. In a second part, an experimental approach to characterize the modal power coupling of light propagating in polymer waveguides is investigated. A modal power coupling matrix is thereby used to describe the relation between the input and output modal power distribution of a waveguide. The specific mode launch, required to control the input modal power distribution, is realized by an intensity- and a phase-controlling spatial light modulator (SLM). The modal power distribution at the end facet of the waveguide is analyzed by an approach based on optical Fourier transformation
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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