This thesis consist of a theoretical study of propagation effects in optical waveguides, fibres and photonic crystals, with some comparison with experiment.¶ Chapter 1 gives a brief introduction with the current view of optical components in photonic integrated circuits and issues related to the loss mechanism.¶ In Chapter 2 the characteristics of single-mode propagation and transient effects in practical square- and rectangular-core buried channel planar waveguides are quantified, assuming a cladding which is unbounded in one transverse dimension and bounded in the other. The wavelength cut-off condition for the fundamental mode is determined when the cladding index is asymmetric and composed of step-wise, uniform index regions.¶ In Chapter 3, the application of segmented reflection gratings in planar devices that can function as either a single- or two-wavelength add/drop filter is investigated and a numerical technique developed in Chapter 2 is applied to the waveguides with high extinction ratio. The role of the segmented gratings is analogous to that of a blazed grating, but they can provide a higher reflectivity level at the Bragg wavelength, eliminate back reflection into the fundamental mode and provide arbitrarily small channel spacing in the two-wavelength case.¶ Chapters 4 address the problem of bend loss in a single-mode slab waveguide. A new theoretical strategy for reducing bend loss is presented and compared to existing designs. The results obtained in this chapter are the basis for the following two chapters.¶ Chapter 5 deals with bend loss in single-mode buried channel waveguides and demonstrates that the new strategy can lead to significant bend loss reduction when compared to other strategies, and, conversely, can be used to enhance bend loss for a fixed bend radius for application to devices such as optical attenuators.¶ In Chapter 6, a novel design of a variable optical attenuator based on a bent channel waveguide is proposed, realized by applying a new strategy for bend loss control in a polymer buried channel waveguide.¶ Chapter 7 investigates effects of the additional rings in a single mode step-index fibre on bend loss. It is supported with the experimental results of Ron Bailey from Optical the Fibre Technology Centre, University in Sydney.¶ In Chapter 8, bend loss of a one-dimensional photonic crystal is quantified and compared to bend loss of a standard single-mode slab waveguide and a bend-resistant waveguide.¶

<p>Nedgångar i världsekonomin med påföljande likviditetsproblem hos företag har medfört negativa konsekvenser för banker, vilket skapade behov av effektiv kreditriskhantering. För att förhindra stora kreditförluster försöker banker ständigt minimera sina risker vid kreditgivning genom att identifiera fallgropar.</p><p>Syftet är att undersöka vilka faktorer som bidrar till kreditförluster och belysa hur Nordea kan minimera risker vid kreditgivning utifrån dessa faktorer.</p><p>Datainsamling skedde via granskning av litteratur och en fallstudie. Studieobjektet var affärsbanken Nordea där det genomfördes flera intervjuer med kreditansvariga på en regional nivå. För att ta reda på utvecklingen av kreditvolym inom Sverige sammanställdes data utifrån kreditgivningsstatistik från Nordea Hypotek AB.</p><p>Enligt teorin är kreditförluster beroende av direkta och indirekta faktorer. Medan de direkta faktorerna kan påverkas av en kreditanalytiker ligger de indirekta faktorer utanför dennes inflytande. Det kan konstateras att Nordea har lyckats minimera kreditrisker i avsevärd grad med reservation för vissa förbättringar och att de faktorer som förorsakar förluster har banken klarat av att hålla under kontroll.</p><p>Bankens grundläggande strategi i riskhanteringen är att använda sig av förnuftig kreditgivning. Samtliga respondenter har betonat vikten av att göra grundliga utredningar vid nya kreditansökningar samt frekventa uppföljningar vid en föraning på betalsvårigheter hos befintliga kredittagare. Genom dessa rutiner kan banken fånga upp problematiska affärstransaktioner och förebygga uppkomsten av kreditförluster.</p> / <p>Turbulence in the world economy with following liquidity problem in enterprises has lead to negative consequences for banks that creates a need for effective credit risk management. To prevent significant credit losses, banks tries constantly to minimize their risks in credit granting through identifying pitfalls.</p><p>The purpose is to investigate the factors that contribute to the credit losses and illustrate how Nordea can minimize risks in credit granting.</p><p>Data were gathered from the literature review and a case study. The object of study is the Swedish Business Bank Nordea where several credit managers has been interviewed at the regional level. To obtain a volume of credit development in Sweden, gathered the credit granting statistics of the source of Nordea Hypotek AB.</p><p>According to the theory credit losses are depending on direct and indirect factors. While direct factors can be affected by a credit analyst, indirect factors are outside of his influence. It can be stated that Nordea has been succeed in minimizing of risks at the considerable degree, with reservation for some improvements, and that some factors that cause losses the bank manage to keep under control.</p><p>Bank´s fundamental strategy in risk management is to use reasonable credit granting. All of respondents have stressed the importance of thorough inquiry on new credit application and frequent following up suspicions of payment difficulties with existing borrowers. Through these routines can bank capture problematic business transactions and prevent appearance of credit losses.</p>

Bragg grating reflectors etched in amorphous silicon overlay films have been integrated with Ti:LiNbO3 optical waveguides. With a 12.5 mm long grating segment and an etch depth of ~ 93 nm in a 105 nm-thick silicon film, a narrow (0.05 nm) spectral bandwidth with a record high transmission dip (> 20 dB) was achieved at a wavelength of ~1542 nm for TE polarization on an x-cut, y-propagating substrate. The reflectance in the channel waveguides is found to be strongly dependent on the depth of the etched grating. The 3-dB bandwidth of 0.05 nm obtained for all tested samples is the smallest reported for waveguides in LiNbO3. The effect of the Bragg waveguide loss factor on the transmittance and reflectance spectra is investigated using a model for contra-directional coupling that includes an attenuation coefficient. The Bragg grating spectral characteristics are exploited to fabricate distributed Bragg feedback modulators (DBFM) and Bragg reflector Fabry-Perot modulators (BFPM). The sharp cut-off in transmission and reflection spectra, which is an inherent characteristic of Bragg grating, was tuned by applying voltage via the linear electrooptic effect, to produce intensity modulation. The Bragg grating based modulators consume less electric power compared to polarization intensity modulators (PIMs). The DBFM demonstrates 1/1.6 times the modulating voltage of a PIM with identical waveguide and electrode structure. The BFPM shows 1/3.3 times the modulating voltage of the PIM. No difference in the frequency response is observed among the three modulators. Comparison of the modulation sensitivity in the linear region indicates that the Bragg grating based modulators provide better sensitivity than that of the PIM with identical waveguide and electrode structure. These results indicate the potential advantage of the Bragg grating based modulators for enhanced modulation efficiency over conventional modulators. Further improvements can be expected from the optimization of the electrode design.

Ein neuentwickeltes azobenzenhaltiges Material, das auf einem supramolekularen Konzept basiert, wird bezüglich seiner Strukturbildung während einer holografischen Belichtung bei 488 nm untersucht. Im Mittelpunkt stehen dabei eindimensionale, sinusförmige Reliefs mit Periodizitäten kleiner 500 nm. Es wird gezeigt, wie der Grad der Vernetzung der photosensitiven Schicht die Strukturbildung in diesem Größenbereich beeinflusst. Zur Maximierung der Strukturtiefe werden gezielt Prozessparameter der Belichtung sowie Materialparameter variiert. Unter Standardbedingungen und moderaten Belichtungsintensitäten von ca. 200 mW/cm² bilden sich innerhalb weniger Minuten bei einer Periode von 400 nm Strukturtiefen von bis zu 80nm aus. Durch die Beeinflussung von Materialparametern, wie Oberflächenspannung und Viskosität, wird die maximale Strukturtiefe auf 160nm verdoppelt. Durch Mehrfachbelichtungen wird auch die Bildung von zweidimensionalen Gittern untersucht. Die Originalstrukturen werden in einem Abformverfahren kopiert und in Schichten von unter UV-Licht aushärtenden Polymeren übertragen. Durch das Abformen kommt es zu einer geringfügigen Verschlechterung der Oberflächenqualität sowie Abnahme der Strukturtiefe. Dieser Verlust wird durch eine Verringerung der Prozesstemperatur verringert. Mithilfe kopierter Oberflächengitter werden organische Distributed Feedback-(DFB)-Laser zweiter Ordnung hergestellt, um den Einfluss von Gitterparametern auf die Emissionseigenschaften dieser Laser zu untersuchen. Dazu erfolgt zunächst die Charakterisierung der optischen Verstärkungseigenschaften ausgewählter organischer Emittermaterialien mittels der Variablen Strichlängenmethode. Das mit dem Laserfarbstoff Pyrromthen567 (PM567) dotierte Polystyrol (PS) zeigt dabei trotz konzentrationsbedingter geringer Absorption eine vergleichsweise geringe Gewinnschwelle von 50µJ/cm² bei ca. 575 nm. Das aktive Gast-Wirt-System der konjugierten Polymere MEH-PPV und F8BT* weist eine hohe Absorption und eine kleine Gewinnschwelle von 2,5 µJ/cm² bei 630 nm auf. Dieses Verhalten spiegelt sich auch in den Emissionseigenschaften der damit hergestellten DFB-Laser wieder. Die Dicke der aktiven Schichten liegen im Bereich hunderter Nanometer und wird so eingestellt, dass sich nur die transversalen Grundmoden im Wellenleiter ausbreiten können. Die Gitterperiode sind so gewählt, dass ein Lichtmode im Verstärkungsbereich des Emittermaterials liegt. Die Emissionslinien der Laser sind mit FWHM-Werten von bis zu 0,3 nm spektral sehr schmalbandig und weisen auf eine sehr gute Gitterqualität hin. Die Untersuchungen liefern minimale Laserschwellen und maximale differentielle Effizienzen von 4,0µJ/cm² und 8,4% für MEH-PPV in F8BT* (bei ca. 640nm) sowie 80 µJ/cm² und 0,9% für PM567 in PS (bei ca. 575 nm). Die Vergrößerung der Strukturtiefe von 40nm auf 80nm in mit MEH-PPV dotierten F8BT*-Lasern zu einem deutlichen Anstieg der ausgekoppelten Energie sowie der differentiellen Effizienz und einem geringen Absinken der Laserschwelle. Dies ist ein Resultat der erhöhten Kopplung von Lasermode und Gitter. Die Emission von DFB-Lasern mit zweidimensionalen Oberflächengittern zeigen eine Verringerung der Divergenz aber kein Einfluss auf die Laserschwelle. Abschließend erfolgt eine Vermessung der Photostabilität von DFB-Lasern unter verschiedenen Bedingungen. Das Einbringen eines konjugierten Polymers in eine aktive Matrix sowie der Betrieb in einer Stickstoffatmosphäre führen dabei zu einer Erhöhung der Lebensdauer auf über eine Million Pulse. Durch die Kombination von Oberflächengittern in PDMS-Filmen mit elektroaktiven Substraten wird eine elektrisch steuerbare Deformation des Beugungsgitters erreicht und auf einen DFB-Laser übertragen. Die spannungsinduzierte Verformung wird zunächst in Beugungsexperimenten charakterisiert und ein optimaler Arbeitspunkt bestimmt. Mit den beiden Elastomeren SEBS12 und VHB4910 werden in den Gittern maximale Periodenänderungen von 1,3% bzw. 3,4% bei einer Steuerspannung von 2 kV erreicht. Der Unterschied resultiert aus den verschiedenen Elastizitätsmoduln der Materialien. Übertragen auf DFB-Laser resultiert eine Variation der Gitterperiode senkrecht zu den Gitterlinien in einer kontinuierlichen Verschiebung der Emissionswellenlänge. Mit einem Spannungssignal von 3,25 kV wird die schmalbandige Emission eines elastischen DFB-Lasers kontinuierlich um fast 50nm von 604 nm zu 557 nm hin verschoben. Aus dem Deformationsverhalten sowohl der reinen Beugungsgitter als auch der Laser werden Rückschlüsse auf die Elastizität der verwendeten Materialien gezogen und erlauben Verbesserungen der Bauteile. / The photoinduced surface relief formation in a newly developed azobenzene containing material is investigated. A photosensitive film based on a supramolecular material concept is illuminated in a holographic setup with light at 488 nm leading to sinusoidal surface structures. It can be shown how the degree of network formation within the material influences structure formation at periods below 500nm. Different material and process parameters are varied to determine maximum possible structure amplitude. At moderate recording conditions and illumination intensities of 200 mW/cm² maximum structure amplitudes of 80 nm are formed within several minutes at periods of approximately 400 nm. Changing material parameters like surface tension and viscosity leads to an increase of maximum amplitude to 160 nm. Additionally, twodimensional structures are fabricated by multiple recording steps. Original surface structures are copied by soft lithography methods into films of UV cured polymers. This replication leads to a decrease of structure contrast and increase of surface roughness. It is shown that structure contrast is preserved by reduction of process temperature. Organic second order distributed feedback (DFB) lasers are prepared with the help of replicated surface gratings covered with organic active layers with thicknesses of several hundred nanometers. The lasers are investigated regarding the influence of grating amplitude on laser threshold and slope efficiency. For this, the optical gain of two green/red emitter materials, polystyrene (PS) doped with laser dye pyrromethene567 (PM567) and active guest host system of conjugated polymers MEH-PPV and F8BT*, is measured. PS doped with PM567 shows relatively low gain threshold of 50 µJ/cm² at 575 nm caused by the low dye concentration while F8BT* doped with MEH-PPV shows threshold gain of 2.5 µJ/cm² at 630 nm. Similar behavior is observed during laser action. Following Bragg-condition grating periods at approximately 400nm lead to laser emission within the gain spectra of the materials. DFB lasers show single mode narrow line emission with FWHMs of down to 0.3nm. This is a result of high grating quality. Lasers based on MEH-PPV-F8BT* exhibit laser thresholds and slope efficiencies of 4.0µJ/cm² and 8.4%, respectively. PM567-PS lasers exhibit 80 µJ/cm² and 0.9%. An increase of grating amplitude of a MEH-PPV-F8BT*-DFB laser from 40nm to 80nm leads to a considerable increase of energy output and a slight decrease of laser threshold. This is a result of an increase of coupling between light mode and grating which relates to an increase of reflectivity. The use of a two dimensional grating leads to a decrease of divergence angle of laser emission but shows no influence on laser threshold. Finally, laser lifetime is observed under different conditions. Doping the conjugated polymer MEH-PPV in an active matrix in combination with the allocation of nitrogen atmosphere leads to an prolongation of half life time to several million pulses. The combination of elastic surface relief gratings with electro active substrates enables electrical controlled deformation of the surface structure. This deformation is characterized by diffraction measurements. At optimal working conditions electro active substrates based on elastomers SEBS12 and VHB4910 show maximum grating deformation of 1.3% und 3.4% at actuation voltages of 2kV, respectively. The different results are caused by the different elastic modulus of the elastomer materials. The transfer of deformation principle to elastic DFB lasers leads to a continuously shift of emission wavelength. At an actuation voltage of 3.25kV an elastic DFB laser based on polyvinylacetate doped with PM567 shows a shift of nearly 50 nm, from 604 nm to 557 nm. Deformation behavior of grating and laser allow to draw conclusions on elasticity of the material and with this is tool for the improvement of the device.

The role played by azobenzene polymers in the modern photonic, electronic and opto-mechanical applications cannot be underestimated. These polymers are successfully used to produce alignment layers for liquid crystalline fluorescent polymers in the display and semiconductor technology, to build waveguides and waveguide couplers, as data storage media and as labels in quality product protection. A very hot topic in modern research are light-driven artificial muscles based on azobenzene elastomers. The incorporation of azobenzene chromophores into polymer systems via covalent bonding or even by blending gives rise to a number of unusual effects under visible (VIS) and ultraviolet light irradiation. The most amazing effect is the inscription of surface relief gratings (SRGs) onto thin azobenzene polymer films. At least seven models have been proposed to explain the origin of the inscribing force but none of them describes satisfactorily the light induced material transport on the molecular level. In most models, to explain the mass transport over micrometer distances during irradiation at room temperature, it is necessary to assume a considerable degree of photoinduced softening, at least comparable with that at the glass transition. Contrary to this assumption, we have gathered a convincing evidence that there is no considerable softening of the azobenzene layers under illumination. Presently we can surely say that light induced softening is a very weak accompanying effect rather than a necessary condition for the formation of SRGs. This means that the inscribing force should be above the yield point of the azobenzene polymer. Hence, an appropriate approach to describe the formation and relaxation of SRGs is a viscoplastic theory. It was used to reproduce pulse-like inscription of SRGs as measured by VIS light scattering. At longer inscription times the VIS scattering pattern exhibits some peculiarities which can be explained by the appearance of a density grating that will be shown to arise due to the final compressibility of the polymer film. As a logical consequence of the aforementioned research, a thermodynamic theory explaining the light-induced deformation of free standing films and the formation of SRGs is proposed. The basic idea of this theory is that under homogeneous illumination an initially isotropic sample should stretch itself along the polarization direction to compensate the entropy decrease produced by the photoinduced reorientation of azobenzene chromophores. Finally, some ideas about further development of this controversial topic will be discussed. / Azobenzenhaltige Polymere sind in modernen photonischen, elektronischen und opto-mechanischen Anwendungen nicht mehr wegzudenken. Diese Polymere werden erfolgreich in der Bildschirm- und Halbleitertechnologie eingesetzt, um Ausrichtungsschichten für flüssig-kristalline fluoreszierende Polymere zu produzieren sowie Wellenleiter und Wellenleiterkoppler herzustellen. Auch dienen sie als Medien für Datenspeicher oder der Sicherung von Qualitätsprodukten. Ein wichtiges Thema in der modernen Forschung sind lichtgetriebene künstliche Muskeln basierend auf azobenzenhaltigen Elastomeren. Die Inkorporation von Azobenzene in Polymersysteme durch kovalente Bindungen oder durch Vermischung resultiert in einer Anzahl ungewöhnlicher Effekte, welche unter Bestrahlung mit sichtbarem und ultraviolettem Licht auftreten. Der erstaunlichste Effekt ist das Erzeugen von Oberflächengittern (Surface Relief Gratings - SRGs) auf dünnen azobenzenhaltigen Polymerfilmen. Es wurden mindestens sieben Modelle zur Erklärung der Herkunft der dieses Gitter erzeugenden Kraft vorgeschlagen aber keines von diesen kann befriedigend den lichtinduzierten Massetransport auf molekularem Niveau beschreiben. Um einen Massetransport über Mikrometerabstände zu erklären, ist es in den meisten Modellen notwendig, eine deutliche lichtinduzierte Erweichung, die mit der Erweichung bei dem Glasübergang vergleichbar ist, anzunehmen. Entgegen dieser Annahme wurden in dieser Arbeit überzeugende Beweise gesammelt, dass es keine signifikante Erweichung in azobenzenhaltigen Schichten bei homogener Bestrahlung gibt. Deshalb kann man davon ausgehen, dass die lichtinduzierte Erweichung eher ein schwacher begleitender Effekt als eine notwendige Voraussetzung für die Bildung derartiger Oberflächengitter ist. Aus dieser Beobachtung muss geschlussfolgert werden, dass die erzeugende Kraft oberhalb der Fließgrenze azobenzenhaltiger Polymer liegt. Deshalb ist die viskoplastische Theorie ein geeigneter Ansatz zur Beschreibung der Formation von Oberflächengittern und deren Relaxation. Dieser Ansatz wurde genutzt, um die beim pulsartigen Erzeugen von Oberflächengittern gemessene Lichtstreuung mit einem Modell zu beschreiben. Bei längeren Bestrahlungszeiten weist das Streumuster einige Besonderheiten auf, die durch die Bildung eines Dichtegitters erklärt werden können. Dieses Gitter entsteht infolge der begrenzten Kompressibilität des Polymerfilms. Als logische Konsequenz der oben genannten Erkenntnisse wird eine thermodynamische Theorie, die die lichtinduzierte Deformation des freistehenden Filmes und die Oberflächen-gitterbildung wiedergeben kann, vorgeschlagen. Die Hauptidee ist, dass eine ursprünglich isotrope Probe sich unter homogener Bestrahlung entlang der Polarisationsrichtung ausdehnen muss, um die Entropieabnahme, die durch die lichtinduzierte Reorientierung der Azobenzene entstanden ist, zu kompensieren. In der Folge werden einige Ideen über die weitere Entwicklung dieses interessanten Themas diskutiert.

This thesis concerns various aspects of the durability offibre optic sensors embedded in composite. Since repair orreplacement of embedded sensors is not generally possible, thefunctional reliability of embedded sensors is one of the mostimportant prerequisites for successful use. The main researchobjective was to investigate the interaction between the sensorand the composite, and how this is affecting the mechanical andoptical sensor response. Fibre optic sensors embedded incomposite structures induce local stress concentrations whenthe composite is subjected to mechanical loads andenvironmental changes such as temperature and moisture. Acomplex transfer of stresses through the interfaces between theembedded sensor and the composite occurs and can result inlarge local stresses in the composite and a significant changein the response of the embedded sensor. These stressconcentrations make the interfaces susceptible todebonding. The sensor performance was studied experimentally andnumerically. Some basic results were generated for the EFPI andBragg grating sensors. The phase-strain response was determinedduring static and fatigue loading. The results showed that thesensors were more reliable in compression than in tensilestatic and fatigue loading. Generally, the sensor reliabilityduring loading was significantly improved for the Bragg gratingsensors over that of the EFPI sensor, as an effect of thesensor geometry. This was also demonstrated in theinvestigations on impacts. Impacts do not necessarily result indamage in the composite, but might cause debonding or otherfailure modes in the sensor area. Large, local stressconcentrations occur at several positions in the EFPI sensor,which pointed out that this sensor type was not suitable forembedded applications. The shift in focus from the sensor concept based on the EFPIsensor to that based on the Bragg grating sensor manifesteditself in several studies. The calculated deformation fieldaround an embedded optical fibre was verified in experimentsusing a high-resolution moiré interferometric technique.Furthermore, the improvement in the coating technology wasverified. A significant higher interfacial strength wasobtained with the silane-treated glass surface. The resultsindicated that at least a twofold improvement of the shearstrength was obtained. To simultaneously measure the in-plane strain components andthe temperature change, embedded Bragg grating sensors werearranged in a rosette configuration. The relationship betweenthe optical response from each sensor and the strains in thelaminate was numerically and analytically established. Damage lead to stress redistribution in the sensor region,which may influence the output from the embedded Bragg gratingsensor. The effect was numerically evaluated for interfacialdamage, and was compared to that of a sensor with undamagedinterface. The results showed that debonding might have asignificant influence, in particular for combined thermal andmechanical loading. <b>Keywords</b>: composites, fibre optic sensor, embedded, EFPIsensor, Bragg grating sensor, durability, fatigue, impact,strain measurement, interface, stress analysis

Nedgångar i världsekonomin med påföljande likviditetsproblem hos företag har medfört negativa konsekvenser för banker, vilket skapade behov av effektiv kreditriskhantering. För att förhindra stora kreditförluster försöker banker ständigt minimera sina risker vid kreditgivning genom att identifiera fallgropar. Syftet är att undersöka vilka faktorer som bidrar till kreditförluster och belysa hur Nordea kan minimera risker vid kreditgivning utifrån dessa faktorer. Datainsamling skedde via granskning av litteratur och en fallstudie. Studieobjektet var affärsbanken Nordea där det genomfördes flera intervjuer med kreditansvariga på en regional nivå. För att ta reda på utvecklingen av kreditvolym inom Sverige sammanställdes data utifrån kreditgivningsstatistik från Nordea Hypotek AB. Enligt teorin är kreditförluster beroende av direkta och indirekta faktorer. Medan de direkta faktorerna kan påverkas av en kreditanalytiker ligger de indirekta faktorer utanför dennes inflytande. Det kan konstateras att Nordea har lyckats minimera kreditrisker i avsevärd grad med reservation för vissa förbättringar och att de faktorer som förorsakar förluster har banken klarat av att hålla under kontroll. Bankens grundläggande strategi i riskhanteringen är att använda sig av förnuftig kreditgivning. Samtliga respondenter har betonat vikten av att göra grundliga utredningar vid nya kreditansökningar samt frekventa uppföljningar vid en föraning på betalsvårigheter hos befintliga kredittagare. Genom dessa rutiner kan banken fånga upp problematiska affärstransaktioner och förebygga uppkomsten av kreditförluster. / Turbulence in the world economy with following liquidity problem in enterprises has lead to negative consequences for banks that creates a need for effective credit risk management. To prevent significant credit losses, banks tries constantly to minimize their risks in credit granting through identifying pitfalls. The purpose is to investigate the factors that contribute to the credit losses and illustrate how Nordea can minimize risks in credit granting. Data were gathered from the literature review and a case study. The object of study is the Swedish Business Bank Nordea where several credit managers has been interviewed at the regional level. To obtain a volume of credit development in Sweden, gathered the credit granting statistics of the source of Nordea Hypotek AB. According to the theory credit losses are depending on direct and indirect factors. While direct factors can be affected by a credit analyst, indirect factors are outside of his influence. It can be stated that Nordea has been succeed in minimizing of risks at the considerable degree, with reservation for some improvements, and that some factors that cause losses the bank manage to keep under control. Bank´s fundamental strategy in risk management is to use reasonable credit granting. All of respondents have stressed the importance of thorough inquiry on new credit application and frequent following up suspicions of payment difficulties with existing borrowers. Through these routines can bank capture problematic business transactions and prevent appearance of credit losses.

The research work presented in this thesis deals with modelling, design and characterisation of passive and active optical waveguide devices. The rst part of the thesis is related to algorithm development and numerical modelling of planar optical waveguides and gratings using the Method of Lines (MoL). The basic three-point central-di erence approximation of the δ2=δx2 operator used in the Helmholtz equation is extended to a new ve-point and seven-point approximation with appropriate interface conditions for the TE and TM elds. Di erent structures such as a high-contrast waveguide and a TM surface plasmon mode waveguide are simulated, and improved numerical accuracy for calculating the optical mode and propagation constant is demonstrated. A new fast and stable non-paraxial bi-directional beam propagation method, called Cascading and Doubling algorithm, is derived to model deep gratings with many periods. This algorithm is applied to model a quasi-guided multi-layer anti-resonant reecting optical waveguide (ARROW) grating polarizing structure. In the second part of the thesis, our focus is on active optical devices such as vertical-cavity and edge-emitting lasers. With a view to improve the bandwidth of directly modulated laser, an InGaAsP quantum well with InGaAlAs barrier is studied due to its favorable band o set for hole injection as well as for electron con nement. Quantum wells with di erent barrier bandgap are grown and direct carrier transport measurements are done using time and wavelength resolved photoluminescence upconversion. Semi-insulating regrown Fabry-Perot lasers are manufactured and experimentally evaluated for light-current, optical gain, chirp and small-signal performance. It is shown that the lasers having MQW with shallow bandgap InGaAlAs barrier have improved carrier transport properties, better T0, higher di erential gain and lower chirp. For lateral current injection laser scheme, it is shown that a narrow mesa is important for gain uniformity across the active region. High speed directly modulated DBR lasers are evaluated for analog performance and a record high spurious free dynamic range of 103 dB Hz2=3 for frequencies in the range of 1-19 GHz is demonstrated. Large signal transmission experiment is performed at 40 Gb/s and error free transmission for back-to-back and through 1 km standard single mode ber is achieved. / QC 20100827

The characteristics of a silicon-on-insulator (SOI) rib waveguide, including the bending loss of a multimode bent waveguide and the birefringence of a rib waveguide, are analyzed by using a finite-difference method (FDM). Based on a detailed analysis for a multimode bent waveguide, an appropriately designed multimode bent waveguide for reducing effectively the bending loss of the fundamental mode is realized. The slab height and the rib width of an SOI rib waveguide are normalized with the total height of the silicon layer and a general relation between these two normalized parameters for a nonbirefringent SOI rib waveguide is established. Using this general relation, one can easily design a nonbirefringent SOI rib waveguide. The issue of multimode effect in the SOI-based microphotonic devices such as arrayed-waveguide gratings (AWGs), etched diffraction gratings (EDGs), and multimode interference (MMI) couplers is discussed in detail. Two kinds of taper structures are proposed for reducing the multimode effects in EDGs or MMI couplers. A bi-level taper is introduced to eliminate effectively the multimode effects in an EDG or an MMI coupler. The bi-level taper is very appropriate for an EDG demultiplexer since the Si layer is etched through simultaneously for both the grating and the bottom taper structure, and thus no additional fabrication process is required. For the simulation of an AWG demultiplexer, a fast simulation method based on the Gaussian approximation is proposed and two kinds of effective and accurate three-dimensional (3D) simulation modeling are developed. The first 3D model is based on Kirchhoff-Huygens diffraction formula. To improve the computational speed, the 3D model is reduced to a two-dimensional (2D) one by integrating the corresponding field distributions in the AWG demultiplexer along the vertical direction under an assumption that the power coupled to the higher order modes in the free propagation region (FPR) is negligibly small. The equivalent 2D model has an almost the same accuracy as the original 3D model. Furthermore, a reciprocity theory is introduced for the optimal designof a special structure used for flattening the spectral response of an AWG demultiplexer. In the second 3D simulation method, we combine a beam propagation method (BPM) and the Kirchhoff-Huygens diffraction formula. In this method, a 3D BPM in a polar coordinate system is used for calculating the light propagation in the region connecting the first FPR and the arrayed waveguides, and thus the coupling coefficient of each arrayed waveguide is calculated conveniently and accurately. In the simulation of the second FPR, due to the uniform arrangement of arrayed waveguides, only several arrayed waveguides are needed in the BPM window and thus the computational efficiency is improved. / QC 20101004

The primary objective of the presented research is to develop a class of integrated compact silicon diffractive sensors (CSDS) based on in-plane diffraction gratings. This class of sensors uses a silicon-on-insulator (SOI) substrate to limit costs, exploit established fabrication processes, enable integration of supporting electronics, and use the well-understood telecommunications wavelength of 1.55µm. Sensing is achieved by combining constant-diffraction-efficiency and highly-angularly-selective in-plane resonance-domain diffraction gratings. Detection is based on the diffraction efficiency of the highly angularly selective grating. In this research, the design processes for the constant-diffraction-efficiency and the highly angularly selective gratings are detailed. Grating designs are optimized with rigorous coupled-wave analysis (RCWA) and simulated with finite-difference time-domain (FDTD) analysis. Fabrication results are presented for the CSDS gratings. An inductively coupled plasma (ICP) Bosch etch process enables grating fabrication to within one percent of designed values with nearly vertical sidewalls. Experimental results are presented for individual CSDS gratings, the prototype sensor, and a prototype linear sensor array. The results agree well with simulation. The linear sensor array prototype demonstrates the intrinsic splitting mechanism and forms the basis of a 2-D sensor array. Finally, a toluene sensor was functionally demonstrated. The proof-of-concept device includes a polymer immobilization layer and microfluidic delivery of toluene. Toluene concentrations as low as 100ppm are measured, corresponding to a refractive index change of 3x10⁻⁴ RIU.