Ο ταλαντωτής αποτελεί σημαντικό κομμάτι κάθε τηλεπικοινωνιακού συστήματος. Το σημαντικότερο στοιχείο της απόδοσής του είναι ο θόρυβος φάσης. Για τη βελτίωσή του χρησιμοποιείται η μέθοδος του injection locking. Με αυτή τη μέθοδο ένα σήμα αναφοράς με καλά χαρακτηριστικά θορύβου χρησιμοποιείται για να βελτιώσει την έξοδο του ταλαντωτή. Χρησιμοποιείται μια τοπολογία τροποποιημένου ταλαντωτή Colpitts, ο οποίος εξομοιώνεται και υλοποιείται. Με τις μετρήσεις που ακολουθούν επιβεβαιώνεται η καλύτερη συμπεριφορά θορύβου που επιτυγχάνει η μέθοδος του injection locking. / Oscillators form an integral part of all communication systems. Their most crucial element regarding performance is phase noise. To improve it we use the method of injection locking. With this method, a reference signal with good noise characteristics is used to improve the output of the oscillator. A modified Colpitts oscillator topology is used which is both simulated and implemented as a circuit board. Measurements confirmed that injection locking improved the characteristics of phase noise.

No description available.

The objective of this thesis was to explore the usefulness of all-fiber modulators for laser applications. The modulators were all based on refractive index change achieved in the core of the studied fiber- components, exploiting either the elasto-optic effect or the electro-optic effect. This was realized with the aid of electrodes inside the fiber cladding close to the core that provided either thermal stress in the core, or an electric field across the core. The electrodes consisted of low melting-point alloys, such as BiSn and AuSn, which were pushed into the hole-fiber, in the liquid state, which then solidified to form solid electrodes filling the entire hole. Together with an analyzer such as a polarizer or an interferometer the achieved refractive index modulation in the core could then be translated into an amplitude modulation of the guided light, which was subsequently utilized for switching fiber-lasers to generate cavity dumped, Q-switched, or mode-locked pulses. The fast rise/fall-time of a few nanoseconds for the elasto-optic devices was due to the fast thermal expansion of the electrodes. The maximum repetition rate, however, was limited to a few tens of kHz, due to the slow thermal processes for dissipation of the applied energy. The electro-optic fiber components, which displayed similar rise/fall-times on the other hand, showed a much higher cut-off frequency of 16 MHz. The electro-optic, all-fiber switch was also employed to select single pulses at 1 MHz repetition rate out of a 7 MHz train of pulses. Additionally, simulations using the finite element method were performed in order to gain insight and to explain the underlying processes of the observed response of a long-period grating written in a 2-hole fiber with electrodes, when applying HV-pulses to one of these. The thesis shows that the studied fiber-components show great potential of becoming complementary devices with high damage threshold for all-fiber laser applications in the future. / <p>QC 20121129</p>

A large number of bone fractures are treated with stabilisation devices that utilise metal wires or screws, which traverse the bone and are connected to an external frame or internal plate. Clinically, fixation devices are required to be able to: sustain loads; minimise patient discomfort and possible implant loosening; and promote healing. In the recent years locking plates have become increasingly popular for osteoporotic or complex fractures, which can be difficult to manage. It, however, remains unclear as to how these devices need to be configured for optimum clinical performance. This thesis investigates the mechanics of locking plates, factors that influence their performance and provides guidance to optimise the placement of screws. Finite element simulation and analytical models were developed and validated using lab-based experimental models. The local behaviour around the screw-bone interface is considered and the implications of different modelling assumptions assessed. A novel method of simulating the effect of radial interference due to pilot-hole size is proposed. Different screw types are evaluated: osteoporotic bone is found to be particularly susceptible to the screw tightening preload used in compression screws; far-cortical locking screws are found to slightly reduce device stiffness but substantially increase strain levels around screw holes. Finite element simulations show that many of the local effects, such as preloads and contact modelling, can profoundly influence the prediction of strains around screws but do not generally influence the global load-displacement behaviour; the screw-plate connection and bone/plate material and geometric properties are found to have an influence on global stiffness predictions. The key determinants of load-displacement behaviour evaluated through models are the loading and restraint conditions, which explain the huge range of stiffness predictions in the literature (three orders of magnitude). An analytical model based on 7 bone-plate construct parameters is developed. Despite its simplicity, the model is found to be able to predict the axial stiffness for experimental tests conducted and for 16 other cases from five previous studies with an average error of 20%. The manner of load application, not considered in the literature, is shown to dramatically alter predictions of plate stress, strains within the bone and conclusions regarding screw placement. Even with the inclusion of muscles forces, the choice of restraint condition dominates the mechanical behaviour. Using the models, the influence of screw position is systematically evaluated in varying bone qualities under axial loading and torsion and guidance for optimising fixation is developed.

The main objective of the thesis is to understand the parameters that contribute in limiting the pulse energy and spectral bandwidth of the mode-locked femtosecond fiber lasers. I have focused on studying the impact of the parameters of the saturable absorber and the bandwidth of the lumped spectral filter on the temporal and spectral profiles of the pulse. Therefore, I developed two models that can help us to optimize the pulse characteristics such as the pulse energy, spectral bandwidth and de-chirped pulse width. I also introduce two techniques that result in increasing the pulse peak power and spectral bandwidth. The nonlinear transmission coefficient of the saturable absorber is one of the main limitations to achieving high-energy pulses. Throughout my research, I have used two types of saturable absorbers. The first is a lumped semiconductor saturable absorber mirror (SESAM) and the second is based on the nonlinear polarization rotation (NPR) that is considered an artificial saturable absorber with distributed effect. The first model introduced in this thesis is an analytical model, which provides closed form relations for the pulse characteristics of all-normal dispersion fiber laser. It shows how the spectral bandwidth of the lumped filter inserted inside the cavity affects the pulse characteristics. Also, it illustrates the influence of the saturable absorber parameters on the pulse characteristics. I show that increasing the small signal saturable absorber loss and decreasing the saturation power leads to the increase in pulse energy and spectral bandwidth. Numerical simulation and experimental results are in agreement with the results of the analytical models. The second model, which is called the semi-vector model, is applicable to all-normal dispersion mode-locked fiber laser with high output coupling ratio. Nonlinear polarization rotation is employed for mode-locking. The model shows the relationship between the location of the overdriving point of the saturable absorber and the output pulse energy. The results of this model are in agreement with those of the full-vector model, but with a much reduced simulation time. In addition, the experimental results show the accuracy of the proposed model. In this thesis, I mitigate the peak power limitation, caused by the accumulated nonlinear phase shift, by replacing the short high-doped Yb3+ fiber with a long low-doped one. This results in an increase of the peak power by a factor that depends on the ratio between the gain coefficient of the high- and low-doped Yb3+ fiber. The length of the nonlinear section is kept unchanged by reducing the length of the single mode fiber after the long low-doped Yb3+ fiber. Numerical simulation and experimental results validate the idea. The location of narrow bandwidth lumped spectral filter, in an active Similariton laser, has proved to have a distinct effect on the pulse energy, spectral bandwidth and de-chirped pulse width and peak power. The proximity of the spectral filter to the input of the Yb3+-doped fiber leads to increasing the pulse spectral bandwidth and peak power of the de-chirped pulse as well as shortening the de-chirped pulse, but at the expense of reducing the pulse energy.

Autor no autoriza el acceso a texto completo de su documento hasta el 15/4/2020. / Ingeniero Civil Industrial / Boxeway es una empresa de tecnología que soluciona el problema de la logística de última milla mediante el uso de lockers inteligentes (eLockers), complementados con una plataforma online. Esta solución permite realizar transacciones de objetos o documentos entre distintos actores mediante intercambios automáticos y asincrónicos. Las aplicaciones son tan vastas, desde empresas de retail, e-commerce u operadores logísticos hasta edificios corporativos y habitacionales que requieran gestionar objetos. El potencial es inmenso: Boxeway tendrá una red de eLockers ubicados en distintos puntos de la ciudad para que cualquiera, empresas o personas naturales puedan utilizar la plataforma para realizar intercambios. La propuesta de valor de Boxeway es hacer más cómodo, práctico y barato el intercambio de objetos entre distintas partes. En los últimos años el crecimiento de 20% anual del comercio electrónico ha traído consigo todas las dificultades que implica la logística de despachos, provocando un alza en la cantidad de reclamos realizados al SERNAC. Estos han llegado a más de 12.000 reclamos en 2014. Los beneficios que trae tener menos puntos de entrega, no tener que coincidir con un morador, buscar una dirección, trae consigo una disminución en el costo de despacho de última milla, que según datos entregados por los mismos clientes, puede llegar a ser el 50% del total. La competencia se clasificó en proveedor tecnológico dentro y fuera de Chile y red pública (red de eLockers de Boxeway de uso público). El estudio validó las hipótesis propuestas en el Método Canvas para los distintos segmentos de clientes. Algunas conclusiones son que las personas están dispuestas a usar un eLocker son muy sensibles al precio de despacho, valoran que les llegue una alerta cuando el producto ya está en el eLocker y que les importa las ubicaciones de estos. Se definieron 3 productos (Pick Up, Corporativo y Front Desk) y dos modelos de pricing. Un modelo de precio de arriendo de eLockers fijo y otro que combina un valor fijo menor más un variable en función del número de operaciones realizadas al mes. La inversión necesaria para cumplir con los objetivos comerciales de instalar una red de 400 eLockers al cabo de 5 años es de 1,2 MM CLP, obteniéndose una TIR de 57,6% y un IR de 0,6.

The goal of this research was to study the polarization effect on the achievability of mode locked laser signal in accordance to polarization dependency. Polarization characterization was studied in prior to mode locking to determine semiconductor optical amplifiers (SOA) polarization dependency. It was found that per SOA manufacturer a variation of dependency was recognized. Two setups were suggested based on dissipative soliton resonance (DSR) schemes, the external DSR with regenerative feedback and the total internal reflection (TIR) DSR. The laser operated at 1530nm for multiple SOA manufacturers and was capable of generating ultrashort pulses with different durations as listed in Table (3.2.3) and Table (3.3.2). For the external mode-lock, the maximum achieved average output power of 3.40mW corresponding to ~77.15fJ of output pulse energy through continuous pumping by gain modulation of an SOA used as the active medium. While the TIR mode-lock the maximum achieved average output power for mode-locked signal of 5.25mW corresponding to ~23.73fJ of output pulse energy.It was concluded that the output pulse of the external DSR setup showed polarization dependency for two SOAs A and C and provided mode locked signals with pulse width ranging between 1200ps and 1000ps with repetition rate approximately of 35MHz and 101MHz respectively. The TIR DSR had a variation in results also to be polarization related. While SOA D did not provide mode-locked signal output. The least polarization dependent SOAs E and X did not provide distinctive stable mode-locked signal. While increased sensitivity towards polarization however resulted in stronger mode locked signal for SOAs A and C with FWHM between 200ps and 350ps and a repetition rate of approximately 20MHz. For future work, it is recommended to adjust the setup length in addition to fine tuning polarizer and filters to improve pulse stability and eliminate the noise effect.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22843号 / 工博第4783号 / 新制||工||1748(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 篠原 真毅, 教授 大村 善治, 准教授 後藤 康仁 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

No description available.

The fundamental advantages of applying Isogeometric Analysis (IGA) to shell analysis have been extensively demonstrated across a wide range of problems and formulations. However, a phenomenon called numerical locking is still a major challenge in IGA shell analysis, which can lead to dramatically deteriorated analysis accuracy. Additionally, for complex thin-walled structures, a simple and robust coupling technique is desired to sew together models composed of multiple patches. This dissertation focuses on addressing these challenges of IGA shell analysis. First, an isogeometric dual mortar method is developed for multi-patch coupling. This method is based on Be ?zier extraction and projection and can be employed during the creation and editing of geometry through properly modified extraction operators. It is applicable to any spline space which has a representation in Be ?zier form. The error in the method can be adaptively controlled, in some cases recovering optimal higher-order rates of convergence, by leveraging the exact refineability of the proposed dual spline basis without introducing any additional degrees-of-freedom into the linear system. This method can be used not only for shell elements but also for heat transfer and solid elements, etc. Next, a mixed formulation for IGA shell analysis is proposed that addresses both shear and membrane locking and improves the quality of computed stresses. The starting point of the formulation is the modified Hellinger-Reissner variational principle with independent displacement, membrane, and shear strains as the unknown fields. To overcome locking, the strain variables are interpolated with lower-order spline bases while the variations of the strain variables are interpolated with the proposed dual spline bases. As a result, the strain variables can be condensed out of the system with only a slight increase in the bandwidth of the resulting linear system and the condensed approach preserves the accuracy of the non-condensed mixed approach but with fewer degrees-of-freedom. Finally, as an alternative, new quadrature rules are developed to release membrane and shear locking. These quadrature rules asymptotically only require one point for Reissner-Mindlin (RM) shell elements and two points for Kirchhoff-Love (KL) shell elements in B-spline and NURBS-based isogeometric shell analysis, independent of the polynomial order p of the elements. The quadrature points are Greville abscissae and the quadrature weights are calculated by solving a linear moment fitting problem in each parametric direction. These quadrature rules are free of spurious zero-energy modes and any spurious finite-energy modes in membrane stiffness can be easily stabilized by using a higher-order Greville rule.