Relevant bibliographies by topics / Coherence technique / Dissertations / Theses
To see the other types of publications on this topic, follow the link: Coherence technique.

Dissertations / Theses on the topic 'Coherence technique'

Author: Grafiati
Published: 21 December 2024

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles

Select a source type:

Consult the top 50 dissertations / theses for your research on the topic 'Coherence technique.'

Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.

You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.

Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.

1

Chau, Alexandra H. (Alexandra Hung) 1980. "Elastography using optical coherence tomography : development and validation of a novel technique." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/91380.

Full text
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.<br>Includes bibliographical references (p. 161-167).<br>Atherosclerosis is an inflammatory disease characterized by an accumulation of lipid and fibrous tissue in the arterial wall. Postmortem studies have characterized rupture-prone atherosclerotic plaques by the presence of a large lipid-rich core covered by a thin fibrous cap. Studies employing finite element analysis (FEA) based on ex vivo plaque geometry have found that most plaques rupture at sites of high circumferential stress, thus diagnosis of plaque vulnerability may be enhanced by probing the mechanical behavior of individual plaques. Elastography is a method of strain imaging in which an image sequence of the artery undergoing deformation is acquired, pixel motion is estimated between each frame, and the resulting velocity field is used to calculate strain. In this thesis, optical coherence tomography (OCT), a high-resolution optical imaging modality, is investigated as a basis for FEA and elastography of atherosclerotic plaques. FEA was performed using plaque geometries derived from both histology and OCT images of the same plaque. Patterns of mechanical stress and strain distributions computed from OCT-based models were compared with those from histology-based models, the current gold standard for FEA. The results indicate that the vascular structure and composition determined by OCT provides an adequate basis for investigating the biomechanical factors relevant to atherosclerosis. A new variational algorithm was developed for OCT elastography that improves upon the conventional algorithm by incorporating strain smoothness and incompressibility constraints into the estimation algorithm.<br>(cont.) In simulated OCT images, the variational algorithm offers significant improvement in velocity and strain accuracy over the conventional algorithm, particularly in the presence of image noise. Polyvinyl alcohol (PVA) phantoms of homogeneous and heterogeneous elastic modulus distribution were developed for further testing of the variational algorithm. Testing with the phantoms indicated that motion- and strain-induced decorrelation between images presents a practical challenge to the implementation of OCT elastography. Analysis of the experimental results led to the identification of potential improvements to the elastography algorithm that may increase accuracy. These improvements may include relaxation of the strain smoothness constraint to incorporate strain discontinuities at boundaries of elastic modulus in heterogeneous regions, and enforcement of geometry compatibility to prevent the estimation of non-physical velocity fields.<br>by Alexandra H. Chau.<br>S.M.
APA, Harvard, Vancouver, ISO, and other styles
2

Kinnunen, M. (Matti). "Comparison of optical coherence tomography, the pulsed photoacoustic technique, and the time-of-flight technique in glucose measurements in vitro." Doctoral thesis, University of Oulu, 2006. http://urn.fi/urn:isbn:9514281462.

Full text
Abstract:
Abstract The development of a non-invasive glucose monitoring technique is very important because it would tremendously diminish the need to puncture the skin when taking blood samples and help diabetic patients in controlling their blood glucose levels and in treating Diabetes Mellitus. The focus of this thesis is on measuring the effect of glucose on the light scattering properties of a tissue-simulating phantom and biological tissues in vitro. Optical coherence tomography (OCT), the pulsed photoacoustic (PA) technique, and the time-of-flight (TOF) technique are used in the measurements and their capabilities for detecting changes in the scattering properties are evaluated and compared with each other. The theoretical background of the techniques, light propagation and PA wave generation are briefly explained. The glucose-induced changes in light scattering are also reviewed. The measurement results with the OCT and the PA technique from Intralipid, pig whole blood, and mouse skin tissue samples show that the glucose-induced changes are larger in the biological tissues than in the Intralipid phantom. The PA measurements show that although the PA signals are stronger at a wavelength of 532 nm than at 1064 nm, the glucose-induced change in the peak-to-peak value of the PA signal measured from pig whole blood is larger at a wavelength of 1064 nm than at 532 nm. The TOF measurements with a streak camera show that the scattering-related changes in the registered pulse shapes occur mainly in the rising part of the pulses. The utilization of fiber-optic measurement heads enabled the detection of back-scattered photons at different distances from the emitting fiber. Although all the techniques are able to detect changes induced by large glucose concentrations (0–5000 mg/dl) in Intralipid, the effect of glucose on the scattering properties of Intralipid is so weak that the techniques failed to detect changes with lower (50–500 mg/dl) concentrations. The measurements of biological samples with the PA technique and with the OCT also demonstrate capabilities to measure glucose concentrations in the physiologically relevant range (18–450 mg/dl) as well. The results compare well with earlier literature and also confirm some earlier findings.
APA, Harvard, Vancouver, ISO, and other styles
3

Hollington, Barnaby Paul. "Chordal roots, Klangverwandtschaft, euphony and coherence : an approach to ostensibly 'atonal', 'non-tonal' or 'post-tonal' harmonic technique." Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/75394/.

Full text
Abstract:
My harmonic approach is founded on two premises, pertaining especially to chordal spacing. First, that for each of the 4,096 possible sets of pitch-classes within equal temperament, without exception, certain spacing principles and techniques, if consistently applied, will generate clear, or relatively clear chordal roots. Typically, the resulting sonorities will possess more than one root – that is, be heard as polychords. Second, that one may control the level of inherent sensory dissonance of any given set of pitch-classes, presented as a chord, through register. These two factors combine to induce both harmonic coherence and euphony. For most listeners, rightly or wrongly, these are not qualities normally associated with music written using the 4,096 – that is, ostensibly ‘atonal', ‘non-tonal' or ‘post-tonal' music. Through my harmonic method, since chordal roots are consistently clarified, one may compose progressions of chordal roots – an asset on which the coherence of diatonic tonality also fundamentally depends. Within a non-diatonic context, the expressive and technical consequences are far-reaching. The following textual commentary demonstrates all of the above, supported by analyses of numerous musical extracts. These are drawn primarily from four of the compositions included in the portfolio – Madame de Meuron, The Art of Thinking Clearly, Velvet Revolution and Nevermore.
APA, Harvard, Vancouver, ISO, and other styles
4

Pfeffer, Nathalie. "Connaissances expertes, propagation de contraintes et maintien de coherence pour l'aide a la conception. Application a la conception d'equipements electroniques de satellites : le systeme smack." Paris 11, 1992. http://www.theses.fr/1992PA112278.

Full text
Abstract:
L'activite de conception donne naissance a tous les objets qui nous entourent: les voitures, les batiments, les ordinateurs. . . Cette these vise l'automatisation du processus de conception preliminaire d'objets industriels (artefacts). Le modele computationnel de conception par assemblage que nous avons elabore s'execute en trois phases. La premiere analyse l'ensemble des specifications pour y detecter les points delicats et completer les valeurs manquantes. La seconde phase applique un modele de decomposition/combinaison pour construire un artefact de performances proches des specifications. La troisieme phase applique un modele de reconception transformationnelle pour l'ameliorer en vue d'obtenir un artefact repondant aux specifications. Nous proposons dans cette these de combiner trois types de techniques d'intelligence artificielle: (1) un systeme expert pour conseiller des pistes de solution, (2) un systeme de propagation de contraintes pour expliciter leurs consequences afin d'anticiper les conflits et de tirer parti d'interactions entre parties de la solution, et (3) un systeme de maintien de coherence pour resoudre les conflits au sein de la solution dus a l'incoherence et/ou incompletude des connaissances expertes. Ces principes sont mis en uvre dans le systeme smack d'aide a la conception preliminaire d'equipements electroniques de satellites
APA, Harvard, Vancouver, ISO, and other styles
5

Gerges, Awad Samir. "Novel fibre-optic-based interferometric sensors exploiting coherent and low-coherence signal processing techniques." Thesis, University of Kent, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236854.

Full text
APA, Harvard, Vancouver, ISO, and other styles
6

Wu, Jigang Yang Changhuei Yang Changhuei. "Coherence domain optical imaging techniques /." Diss., Pasadena, Calif. : Caltech, 2009. http://resolver.caltech.edu/CaltechETD:etd-12112008-102138.

Full text
APA, Harvard, Vancouver, ISO, and other styles
7

Albezzawy, Muhammad Nabil Mustafa. "Advanced signal processing methods for source identification using references." Electronic Thesis or Diss., Lyon, INSA, 2024. http://www.theses.fr/2024ISAL0074.

Full text
Abstract:
Les techniques de référence à rang réduit sont couramment employées pour résoudre les problèmes d’extraction de source et de resynchronisation de champs physiques, lorsque le nombre de références dépasse celui des sources incohérentes. Dans ce cas, la matrice croisée-spectrale devient mal conditionnée, rendant la solution des moindres carrés invalide. Bien que la décomposition en valeurs singulières tronquée (DVST) soit utilisée pour résoudre ce problème, elle n'est valable que pour un bruit scalaire sur les références. De plus, il est difficile de définir un seuil de troncature lorsque les valeurs singulières diminuent progressivement. Cette thèse propose une solution nommée technique de référence maximale-coherent (RMC), basée sur la recherche d’un ensemble de références virtuelles maximales correlées avec les mesures de champ. Cette technique est optimale, surtout en présence d’un bruit corrélé sur la référence. Cependant, elle nécessite également une troncature des valeurs propres, exigeant la connaissance ou l’estimation préalable du nombre de sources incohérentes, un problème inverse mal posé et peu étudié. La thèse présente trois méthodes d’énumération de sources applicables à toutes les techniques de référence : un test du rapport de vraisemblance contre le modèle saturé, une technique de bootstrap paramétrique et une approche de validation croisée. Une étude comparative basée sur des données numériques et expérimentales montre deux résultats importants. D'abord, le nombre de fenêtres spectrales utilisées affecte grandement la performance des trois méthodes, qui se comportent différemment selon ce nombre. Ensuite, le bootstrap paramétrique s’avère être la meilleure méthode en termes de précision et de robustesse par rapport au nombre de fenêtres utilisées. Enfin, la technique RMC accompagnée de bootstrap a été utilisée pour l’extraction de source et la resynchronisation de données réelles provenant d’expériences en laboratoire et d’un moteur électrique, fournissant de meilleurs résultats que la solution des moindres carrés et la DVST dans les mêmes conditions<br>Rank-reduced reference/coherence techniques based on the use of references, i.e. fixed sensors, are widely used to solve the two equivalent problems of source extraction and resynchronization encountered during remote sensing of physical fields, when the number of references surpasses the number of incoherent sources. In such case, the cross-spectral matrix (CSM) becomes ill-conditioned, resulting in the invalidity of the least squares LS solution. Although the truncated singular value decomposition (TSVD) was successfully applied in the literature to solve this problem, its validity is limited only to the case of scalar noise on the references. It is also very difficult to define a threshold, for truncation, when the singular values are gradually decreasing. This thesis proposes a solution based on finding a set of virtual references that is maximally correlated with the field measurements, named the maximally-coherent reference (MCR) Technique. This solution is optimal, especially, in the case of correlated noise on the reference, where TSVD fails. However the technique also includes an eigenvalue truncation step, similar to the one required for the TSVD, which necessitates a priori knowledge or the estimation of the number of incoherent sources, i.e. source enumeration, which is an ill-posed inverse problem, insufficiently investigated in the literature within the framework of reference techniques. In this thesis, after providing a unified formalism for all the reference techniques in the literature, three alternative source enumeration methods, applicable to all the reference techniques, were presented namely; a direct likelihood ratio test (LRT) against the saturated model, a parametric bootstrap technique and a cross-validation approach. A comparative study is performed among the three methods, based on simulated numerical data, real sound experimental data, and real electrical motor data. The results showed two important outcomes. The first is that the number of snapshots (spectral windows), used in the spectral analysis, greatly affects the performance of the three methods, and that, they behave differently for the same number of used snapshots. The second is that parametric bootstrapping turned out to be the best method in terms of both estimation accuracy and robustness with regard to the used number of snapshots. Finally, the MCR technique accompanied with bootstrapping was employed for source extraction and resynchronization of real data from laboratory experiments, and an e-motor, and it returned better results than the LS solution and the TSVD when employed for the same purpose
APA, Harvard, Vancouver, ISO, and other styles
8

Zhu, Kai. "Coherent and non-coherent techniques for cooperative communications." Thesis, University of York, 2014. http://etheses.whiterose.ac.uk/6852/.

Full text
Abstract:
Future wireless network may consist of a cluster of low-complexity battery-powered nodes or mobile stations (MS). Information is propagated from one location in the network to another by cooperation and relaying. Due to the channel fading or node failure, one or more relaying links could become unreliable during multiple-hop relaying. Inspired by conventional multiple-input multiple-output (MIMO) techniques exploiting multiple co-located transmit antennas to introduce temporal and spatial diversity, the error performance and robustness against channel fading of a multiple-hop cooperative network could be significantly improved by creating a virtual antenna array (VAA) with various distributed MIMO techniques. In this thesis, we concentrate on the low-complexity distributed MIMO designed for both coherent and non-coherent diversity signal reception at the destination node. Further improvement on the network throughput as well as spectral efficiency could be achieved by extending the concept of unidirectional relaying to bidirectional cooperative communication. Physical-layer network coding (PLNC) assisted distributed space-time block coding (STBC) scheme as well as non-coherent PLNC aided distributed differential STBC system are proposed. It is confirmed by the theoretical analysis that both approaches have the potential for offering full spatial diversity gain. 　　 Furthermore, differential encoding and non-coherent detection techniques are generally associated with performance degradation due to the doubled noise variance. More importantly, conventional differential schemes suffer from the incapability of recovering the source information in time-varying channels owing to the assumption of static channel model used in the derivation of non-coherent detection algorithm. Several low-complexity solutions are proposed and studied in this thesis, which are able to compensate the performance loss caused by non-coherent detection and guarantee the reliable recovery of information in applications with high mobility. A substantial amount of iteration gain is achieved by combining the differential encoding with error-correction code and sufficient interleaving, which allows iterative possessing at the receiver.
APA, Harvard, Vancouver, ISO, and other styles
9

Dunsby, Christopher William. "Wide-field coherence-gated imaging techniques including photorefractive holography." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407465.

Full text
APA, Harvard, Vancouver, ISO, and other styles
10

Méteau, Jérémy. "Instrumentation optique pour la caractérisation des tissus : analyse de la complémentarité et des limites techniques de fluorescence hyperspectrale et de Tomographie Optique Cohérente en vue de leur intégration multimodale." Thesis, Besançon, 2014. http://www.theses.fr/2014BESA2041/document.

Full text
Abstract:
L'objectif de ce travail de recherche est le développement d'un système fibré d'imagerie point par point d'auto fluorescence multi-excitation, de tissus biologiques en utilisant la technique de fluorescence hyperspectrale et l'étude d'un système de tomographie optique cohérente comme possible modalité supplémentaire. La première partie de ce rapport présente les propriétés optique des tissus biologiques et les fluorophores pertinents pour la détection de tumeurs cancéreuses. La deuxième partie présente l'instrumentation du système d'imagerie de fluorescence et l'analyse hyperspectrale des résultats obtenus in vitro.Il est démontré la pertinence de ce type d'analyse qui permet de déterminer la concentration de certains fluorophores. La troisième partie présente le système de tomographie optique cohérente appelé "scan free" OCT car il permet de réaliser des images sans déplacement d'éléments optiques. Ce système est caractérisé et présente des fonctionnalités intéressantes comme la compensation de la dispersion dépendante de la profondeur. Les divers résultats obtenus montrent que ces deux techniques sont complémentaires car elles apportent des informations de nature différentes. La première technique donne de se informations sur la composition biochimique des tissus, la seconde donne des information sur la structure<br>The aim of this activity is the development of a mono point imaging fiber system which uses hyperspectral multi-excitation auto fluorescence technique for biological tissues and the study of an Optical Coherence Tomography system like another modality. At first, this report presents the optical properties of biological tissues and the relevant fluorophores for cancerous tumors detection. Secondly, the fluorescence imaging system instrumentation and hyperspectral analysis are presented with in vitro results. The third part presents the "scan free" optical coherence tomography system which is able to image without optical displacement. It's characterized and have interesting functionality like depth dependant dispersion compensation. These both techniques are complementary because they get different kind of information. The information of the first one is about biochemical composition of the tissues and the information of the second one is about the stucture
APA, Harvard, Vancouver, ISO, and other styles
11

Rodriguez, Solimar Reyes. "Optical coherence tomography and microwave imaging diagnostic techniques for osteoporosis /." Diss., Connect to online resource - MSU authorized users, 2008.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
12

Fatadin, M. I. A. "DSP techniques for optical coherent receivers." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1306182/.

Full text
Abstract:
The design of modern optical communication systems seeks a solution to the optimisation of bandwidth utilisation. Despite the inherent simplicity offered by intensity modulation direct detection (IM-DD), it is evident that this conventional binary scheme cannot fully explore in full the theoretical achievable capacity of optical systems. A lot of research activity is directing towards coherent detection techniques, already investigated in the early nineties, but then abandoned because of IM-DD cost efficiency and technological ease with erbium-doped fibre amplifiers. Coherent techniques require a more complex receiver architecture, but allow higher receiver sensitivity and more spectrally efficient modulation formats. With these advanced modulation formats it is possible to better exploit the wide bandwidth offered by the optical channel so that the total bit rate can be increased keeping affordable baud rates. Coherent detection is therefore a promising candidate that will most likely represent the future of optical communication systems. The aim of this thesis is to investigate coherent detection algorithms empowered by advanced digital signal processing (DSP) techniques for multilevel modulation formats to improve the performance of coherent systems. We first review the basic concepts of coherent detection. Algorithms for the compensation of imperfections in the receiver front-end are investigated. Characterisation of time-interleaved ADCs is presented and it is shown that the imperfections can be mitigated using DSP. The digital compensation of quadrature imbalance due to imperfections in a digital coherent receiver is then discussed. Blind equalisation techniques for the 16-QAM modulation format are also presented. Next, algorithms to compensate for frequency offset and laser phase noise for a 16-QAM coherent system are discussed. We consider a second-order recursive digital loop to track frequency offset from the transmitter laser and the LO. Finally, the thesis examines the interaction between the LO phase noise and electronically-compensated chromatic dispersion.
APA, Harvard, Vancouver, ISO, and other styles
13

Cuesta, Sáez Blas Antonio. "Efficient techniques to provide scalability for token-based cache coherence protocols." Doctoral thesis, Universitat Politècnica de València, 2009. http://hdl.handle.net/10251/6024.

Full text
Abstract:
Cache coherence protocols based on tokens can provide low latency without relying on non-scalable interconnects thanks to the use of efficient requests that are unordered. However, when these unordered requests contend for the same memory block, they may cause protocols races. To resolve the races and ensure the completion of all the cache misses, token protocols use a starvation prevention mechanism that is inefficient and non-scalable in terms of required storage structures and generated traffic. Besides, token protocols use non-silent invalidations which increase the latency of write misses proportionally to the system size. All these problems make token protocols non-scalable. To overcome the main problems of token protocols and increase their scalability, we propose a new starvation prevention mechanism named Priority Requests. This mechanism resolves contention by an efficient, elegant, and flexible method based on ordered requests. Furthermore, thanks to Priority Requests, efficient techniques can be applied to limit the storage requirements of the starvation prevention mechanism, to reduce the total traffic generated for managing protocol races, and to reduce the latency of write misses. Thus, the main problems of token protocols can be solved, which, in turn, contributes to wide their efficiency and scalability.<br>Cuesta Sáez, BA. (2009). Efficient techniques to provide scalability for token-based cache coherence protocols [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/6024<br>Palancia
APA, Harvard, Vancouver, ISO, and other styles
14

Holmes, R. D. "Coherent optical detection techniques in surface metrology." Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294698.

Full text
APA, Harvard, Vancouver, ISO, and other styles
15

Baines, Darwin Tarry. "Accelerated Ray Traced Animations Exploiting Temporal Coherence." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd915.baines.

Full text
APA, Harvard, Vancouver, ISO, and other styles
16

Russell, Christopher David. "Study of interference effects and signal processing techniques in optical coherence tomography." Thesis, University of Liverpool, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.406628.

Full text
APA, Harvard, Vancouver, ISO, and other styles
17

Zhang, Hao, Robert Kuschmierz, and Jürgen Czarske. "3D interferometric shape measurement technique using coherent fiber bundles." SPIE, 2017. https://tud.qucosa.de/id/qucosa%3A34957.

Full text
Abstract:
In-situ 3-D shape measurements with submicron shape uncertainty of fast rotating objects in a cutting lathe are expected, which can be achieved by simultaneous distance and velocity measurements. Conventional tactile methods, coordinate measurement machines, only support ex-situ measurements. Optical measurement techniques such as triangulation and conoscopic holography offer only the distance, so that the absolute diameter cannot be retrieved directly. In comparison, laser Doppler distance sensors (P-LDD sensor) enable simultaneous and in-situ distance and velocity measurements for monitoring the cutting process in a lathe. In order to achieve shape measurement uncertainties below 1 µm, a P-LDD sensor with a dual camera based scattered light detection has been investigated. Coherent fiber bundles (CFB) are employed to forward the scattered light towards cameras. This enables a compact and passive sensor head in the future. Compared with a photo detector based sensor, the dual camera based sensor allows to decrease the measurement uncertainty by the order of one magnitude. As a result, the total shape uncertainty of absolute 3-D shape measurements can be reduced to about 100 nm.
APA, Harvard, Vancouver, ISO, and other styles
18

Ribeiro, H. "Symmetry and proportion : how these issues guide, inform and add coherence to musical composition." Thesis, Canterbury Christ Church University, 2011. http://create.canterbury.ac.uk/10823/.

Full text
Abstract:
The central subject of this thesis is the application of the concepts of symmetry and proportion in music and how these can be used to generate original compositions. Information about the musical application regarding concepts of symmetry and proportion both in the twentieth-century and earlier is provided. The first section also offers additional information about the construction of symmetrical harmony and its common usage; here too, principles of intervallic proportion are explained based on the compositional thinking of English composer Christopher Bochmann. The second section presents seven original compositions, each supported by their own commentary. Each work features a variety of instrumental forces ranging from solo to orchestral. Lending a separate emphasis (in analysis) to each composition helps to provide a broad picture of the potential that the ideas of symmetry and proportion bring to contemporary composition.
APA, Harvard, Vancouver, ISO, and other styles
19

Adler, Desmond Christopher 1978. "Digital signal processing techniques for optical coherence tomography : OCT and OCT image enhancement." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28486.

Full text
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.<br>Includes bibliographical references (p. 132-135).<br>Digital signal processing (DSP) techniques were developed to improve the flexibility, functionality, and image quality of ultrahigh resolution optical coherence tomography (OCT) systems. To reduce the dependence of OCT research systems on fixed analog electronics and to improve overall system flexibility, a digital demodulation scheme implemented entirely in software was developed. This improvement allowed rapid reconfiguration of the OCT imaging speed and source center wavelength without having to construct new analog filters and demodulators. This demodulation scheme produced a highly accurate envelope and was immune to local variations in carrier frequency. To provide an alternative contrast modality to conventional intensity-based OCT imaging, spectroscopic OCT technology was investigated. Preliminary studies on animal models were carried out, with the ultimate goal of enabling the early detection of dysplastic lesions in epithelial tissue through spectroscopic changes not visible with conventional OCT. Various spectral analysis techniques were investigated and evaluated for their ability to provide enhanced contrast of specific tissue types. Areas of concern such as red-shifting of the spectrum with increasing imaging depth, Doppler shifts induced by the optical path length scanner, and determination of an optimal spectroscopic metric were addressed. To improve the quality of ultrahigh resolution OCT images, wavelet processing techniques for speckle noise reduction were investigated. Spatially adaptive wavelet denoising techniques were compared to basic wavelet denoising techniques and time domain filtering. By using a set of image quality metrics, it was possible to quantify the effectiveness of the various filtering methods and determine an optimal<br>(cont.) process for removing speckle noise while maintaining feature sharpness.<br>by Desmond Christopher Adler.<br>S.M.
APA, Harvard, Vancouver, ISO, and other styles
20

Laurain, Alexandre. "Sources laser à semiconducteur à émission verticale de haute cohérence et de forte puissance dans le proche et le moyen infrarouge." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2010. http://tel.archives-ouvertes.fr/tel-00613743.

Full text
Abstract:
Le développement de sources lasers monomodes et accordables constitue un enjeu important dans plusieurs domaines en fort développement telle que la métrologie, les senseurs optiques, la spectroscopie, le traitement optique de l'information ou la médecine. Dans cette thèse nous faisons le point sur les limites des technologies actuelles, puis nous montrons comment les surpasser à travers la conception et l'étude physique de lasers à semiconducteur de haute cohérence émettant dans l'infrarouge. Nous nous intéressons particulièrement aux VECSEL dans le but d'obtenir un fonctionnement monofréquence accordables et robustes. Nous traitons de la conception et de la caractérisation de ces lasers, depuis l'optimisation du milieu à gain jusqu'à l'élaboration de prototypes laser fonctionnels. Nous effectuons ensuite une étude approfondie des propriétés physiques de la source. Les différents sujets abordés traitent de nombreux aspects de l'optoélectronique tels que la physique du solide, l'optique traditionnelle et quantique, la technologie des matériaux, la thermique, ect. Les travaux présentés ici ouvrent la voie à de nombreux développements liés aux VECSEL et à leurs applications.
APA, Harvard, Vancouver, ISO, and other styles
21

Goldfarb, Gilad. "DIGITAL SIGNAL PROCESSING TECHNIQUES FOR COHERENT OPTICAL COMMUNICATION." Doctoral diss., University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2893.

Full text
Abstract:
Coherent detection with subsequent digital signal processing (DSP) is developed, analyzed theoretically and numerically and experimentally demonstrated in various fiber‐optic transmission scenarios. The use of DSP in conjunction with coherent detection unleashes the benefits of coherent detection which rely on the preservation of full information of the incoming field. These benefits include high receiver sensitivity, the ability to achieve high spectral‐efficiency and the use of advanced modulation formats. With the immense advancements in DSP speeds, many of the problems hindering the use of coherent detection in optical transmission systems have been eliminated. Most notably, DSP alleviates the need for hardware phase‐locking and polarization tracking, which can now be achieved in the digital domain. The complexity previously associated with coherent detection is hence significantly diminished and coherent detection is once again considered a feasible detection alternative. In this thesis, several aspects of coherent detection (with or without subsequent DSP) are addressed. Coherent detection is presented as a means to extend the dispersion limit of a duobinary signal using an analog decision‐directed phase‐lock loop. Analytical bit‐error ratio estimation for quadrature phase‐shift keying signals is derived. To validate the promise for high spectral efficiency, the orthogonal‐wavelength‐division multiplexing scheme is suggested. In this scheme the WDM channels are spaced at the symbol rate, thus achieving the spectral efficiency limit. Theory, simulation and experimental results demonstrate the feasibility of this approach. Infinite impulse response filtering is shown to be an efficient alternative to finite impulse response filtering for chromatic dispersion compensation. Theory, design considerations, simulation and experimental results relating to this topic are presented. Interaction between fiber dispersion and nonlinearity remains the last major challenge deterministic effects pose for long‐haul optical data transmission. Experimental results which demonstrate the possibility to digitally mitigate both dispersion and nonlinearity are presented. Impairment compensation is achieved using backward propagation by implementing the split‐step method. Efficient realizations of the dispersion compensation operator used in this implementation are considered. Infinite‐impulse response and wavelet‐based filtering are both investigated as a means to reduce the required computational load associated with signal backward‐propagation. Possible future research directions conclude this dissertation.<br>Ph.D.<br>Optics and Photonics<br>Optics and Photonics<br>Optics PhD
APA, Harvard, Vancouver, ISO, and other styles
22

Alwafi, Reem. "Development of optical coherence tomography endoscopy for gynaecological and gastrointestinal studies and peritoneal membrane imaging." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/development-of-optical-coherence-tomography-endoscopy-for-gynaecological-and-gastrointestinal-studies-and-peritoneal-membrane-imaging(8254ec5d-549d-413a-a048-7d773e28dc79).html.

Full text
Abstract:
In the medical field, the detection and diagnosis of diseases continue to improve. Developments in diagnostic techniques have helped to improve treatment in the early stages and avoid many risks to patients. One relatively new diagnostic technique is optical coherence tomography (OCT), which is used in many medical applications to perform internal microstructure imaging of the human body at high resolution (typically 10 micro metre), at high speed and in real time. OCT is non-invasive and can be used as a contact or non-contact technique to obtain an image. In medicine, there are many applications that involve OCT, such as in ophthalmology, gastroenterology, cardiology and oncology. This work demonstrates the design, development and implementation of a high resolution swept laser OCT system for the imaging and diagnosis of tissues in laboratory and clinical experiments. It reports an investigation to measure the thickness of the peritoneal membrane and the use of optical imaging contrast agents such as gold nanorods. There is also an account of the design of an endoscope-catheter fast scanning OCT system for biomedical studies of the gastrointestinal tract and gynaecological areas. These results were achieved by using a swept tuneable laser source with a very high tuning speed of 16 kHz over a wide range of wavelengths: 1260 nm to 1390 nm. The laser sweeps across 110 nm at a 16 kHz repetition rate. The real axial line speed is limited by the source that is used in the OCT system. The axial resolution of the system is 7 µm and its transverse resolution is 15 µm. The bandwidth of the source is up to DeltaGamma = 110 nm, centred at Gamma0 = 1325 nm, and the coherent length is 7 µm. On the sample arm of the interferometer, the swept laser OCT technique is combined with an optical probe and endoscope in order to develop a novel diagnostic imaging device to visualize tissue in vivo for animal and human experimental trials.
APA, Harvard, Vancouver, ISO, and other styles
23

Meadway, Alexander. "Combinations of techniques for the advancement of scanning laser ophthalmology and optical coherence tomography." Thesis, University of Kent, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.653049.

Full text
Abstract:
In this thesis methods of eye imaging are investigated, primarily optical coherence tomography (OCT) and scanning laser ophthalmology (SLO). These are two well established technologies. This thesis investigates the combination of techniques to improve resolution, sensitivity and the amount of information that can be extracted from a device. There are three systems presented in the thesis. The first generates on-axis and off axis confocal retinal images simultaneously by way of a drilled mirror. Off-axis imaging provides greater depth penetration, but at the cost of resolution. The second system combines three technologies; SLO, time domain (TD) OCT and adaptive optics (AO). The system is able to generate simultaneous en-face SLO and OCT images, whilst the AO closed loop corrects for aberrations enhancing the intensity and resolution of the images in both modes. This system is used in several investigative directions; the effect of deformable mirror dynamics on the acquired image; the OCT channel is used to investigate the confocal profile; the performance of the deformable mirror with regards to its focus control is investigated; the focus control is used to generate 3D confocal images. Finally, the system is converted to a balanced Fourier domain (FD) OCT system. It has previously been assumed that excess photon noise (that balanced detection is used to remove) is not significant due to the limitations of the CCD camera used in an FD system's spectrometers, however, CCD cameras have since been developed, with increased depths of quantum wells and balanced detection offers other advantages, such as the removal of auto correlation terms from an image. The third system investigated is a TD-OCT system that spectrally separates the broadband source into discrete channels at detection. It can be viewed as a hybrid system, combining TD and FD OCT. A system such as this may be used to reduce the shot noise of a time domain system, or it may be used to make spectroscopic measurements. Both are investigated in this thesis, dispersion was measured as well as absorption profiles and a preliminary investigation into the noise reduction is also presented.
APA, Harvard, Vancouver, ISO, and other styles
24

Gómez, Casco David. "Non-Coherent Acquisition Techniques for High-Sensitivity GNSS Receivers." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/665404.

Full text
Abstract:
Los sistemas de radionavegación por satélite (GNSSs) se han convertido en una herramienta indispensable de la vida diaria, ya que nos ofrecen la posibilidad de conocer de manera precisa nuestra ubicación en tiempo real y en entornos al aire libre. Desde la aparición de estos sistemas, han surgido una gran cantidad de exitosas aplicaciones de GNSS. Algunos ejemplos de estas aplicaciones son los siguientes: navegación para automóviles, rastreo de vuelos, seguimiento de actividad deportiva y juegos de realidad aumentada. Debido al éxito alcanzado por los sistemas de GNSS, un gran interés está surgiendo para extender sus servicios a entornos más complicados tales como cañones urbanos e interiores. No obstante, en estos entornos los receptores de GNSS tienen grandes dificultades para poder detectar las señales recibidas desde los satélites, las cuales son muy débiles ya que sufren una severa atenuación a causa de la presencia de obstáculos en el camino de propagación entre los satélites y el receptor. Esta tesis aborda varios problemas del procesamiento de señales de GNSS débiles como la detección en la etapa de adquisición, la determinación de la calidad de la señal y las estimaciones de la frecuencia Doppler y el tiempo de retraso. Para ello, se emplean las herramientas de detección y estimación de la señal, que se basan en teoría de probabilidad y estadística. Para poder emplear estas herramientas es necesario tener un conocimiento sobre la arquitectura y las señales que transmiten los sistemas de GNSS. Por este motivo, la primera parte de la tesis se centra en describir las principales características de dos de los sistemas de GNSS más conocidos el americano GPS y el europeo Galileo. Además, tratamos los fundamentos de los receptores y analizamos las señales que están implementadas actualmente en estos sistemas. Después, se explican los fundamentos de teoría de detección requeridos, que son el Neyman-pearson criterion, el Generalized likelihood Ratio Test y el Bayesian approach. Más adelante, se realiza una revisión del estado del arte sobre la detección de señales de GNSS. Las principales contribuciones de esta tesis ocupan lugar en la segunda parte, las cuales tratan de derivar los detectores óptimos para adquirir las señales de GNSS débiles. Hemos encontrado que el detector óptimo depende de las características de la señal trasmitida por el satélite, que puede variar dependiendo de la constelación seleccionada. Los resultados teóricos y simulados demuestran que los detectores propuestos en esta tesis superan claramente el rendimiento de los detectores utilizados en la práctica actualmente. Además, se concluye en qué condiciones es mejor utilizar un detector u otro. También, en esta tesis se aborda el problema de estimar la relación portadora a ruido de las señales de GNSS débiles. Esta relación aporta información esencial ya que se utiliza en todas las etapas de los receptores de GNSS. En esta tesis proponemos nuevos estimadores de la relación portadora a ruido, que son muy sencillos de implementar en receptores de alta sensibilidad de GNSS y ofrecen una mejora de precisión con respecto a los estimadores propuestos en la literatura. Finalmente, la última parte de la tesis se centra en las binary offset carrier (BOC) de alto orden, un tipo de señal que está implementada en el sistema Galileo. Más precisamente, esta parte está dedicada a proponer estimadores precisos de tiempo de retardo y frecuencia Doppler. Estos estimadores mejoran la precisión del método generalmente aplicado en la práctica para estimar estos parámetros.<br>Global Navigation Satellite Systems (GNSSs) have become an indispensable tool of daily life, since they offer us the possibility of accurately knowing our location in real time and in open-sky environments. Since the advent of these systems, a large number of successful GNSS applications have emerged. Some examples of these applications are: car navigation, flight tracking, sport activity tracking and augmented reality games. Due to the success achieved by GNSS, a great interest is emerging to extend its services to harsher environments such as urban canyons and indoor scenarios. However, in these environments GNSS receivers face great difficulties to detect the signals received from the satellites, which are very weak since they suffer from severe attenuation due to the presence of obstacles in the propagation path between satellites and the receiver. This thesis addresses several problems of processing weak GNSS signals, such as the detection at the acquisition stage, the determination of their signal quality and the time delay and Doppler frequency estimations. To do so, detection and estimation tools are used, which are based on the probability theory and statistics. In order to use these tools, it is necessary to understand the architecture and the signals that GNSSs transmit. For this reason, the first part of the thesis focuses on describing the main features of two of the best-known GNSSs, the American GPS and the European Galileo. In addition, we describe the fundamentals of the receivers and analyze the signals that are implemented in these systems. After that, we explain the required fundamentals of detection theory, namely the Neyman-pearson criterion, the Generalized Likelihood Ratio Test and the Bayesian approach. Then, a review of the state of the art in the detection of GNSS signals is carried out. The main contribution of this thesis is provided in the second part, which tackles the problem of deriving optimal detectors to acquire weak GNSS signals. We have found that the optimal detector depends on the characteristics of the signal transmitted by the satellite, which is different depending on the selected constellation. The theoretical and simulated results show that the detectors proposed in this thesis clearly outperform the detectors currently used in practice. In addition, we conclude when it is better to apply each detector. Moreover, this thesis addresses the problem of estimating the carrier-to-noise ratio of weak GNSS signals. This parameter provides essential information since it is used in all stages of GNSS receivers. In this thesis, we propose new estimators of the carrier-to-noise ratio, which are very simple to implement in high-sensitivity GNSS receivers and offer an enhanced accuracy with respect to the estimators proposed in the literature. Finally, the last part of the thesis focuses on the so-called high-order binary offset carrier (BOC) signals, a kind of signal that is implemented in the Galileo system. More precisely, this part is devoted to proposing accurate estimators of time delay and Doppler frequency. These estimators improve the accuracy of the method usually applied in practice to estimate these parameters.
APA, Harvard, Vancouver, ISO, and other styles
25

Molter, Daniel [Verfasser]. "Novel approaches in coherent terahertz measurement techniques / Daniel Molter." München : Verlag Dr. Hut, 2011. http://d-nb.info/1018982531/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
26

He, Qubao. "Coherent power combining on spacecraft via wavefront Multiplexing techniques." Thesis, California State University, Long Beach, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1527380.

Full text
Abstract:
<p> A novel orthogonal wavefront (WF) Multiplexing (Muxing) and De-Multiplexing (Demuxing) scheme is proposed for uplink from antenna array elements to multiple spacecraft (S/C). By using an adaptive equalization at the receiver of S/C, the phase deviation due to different near field distances of the uplink from antenna array elements to S/C is compensated via the WF Demuxing method on S/C. This scheme allows power combining from antenna array elements to S/C. Besides, this scheme can be extended and applied to multiple S/C. Simulations verify that the proposed scheme achieves the same bit error rate (BER) performance as the theoretical BER in additive white Gaussian noise (AWGN) channels and one path flat fading channel. Furthermore, although the radiated signals among the multiple radiating antenna array elements are non-coherent, the coherent power combining of the radiations of multiple radiating antenna array elements is accomplished on the S/C receiver in the proposed techniques. </p>
APA, Harvard, Vancouver, ISO, and other styles
27

Mann, Berenice Ann. "Novel coherent laser spectroscopic techniques for minor species combustion diagnostics." Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304258.

Full text
APA, Harvard, Vancouver, ISO, and other styles
28

Lee, Kyehun. "Coherent Mitigation of Radio Frequency Interference in 10-100 MHz." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28929.

Full text
Abstract:
This dissertation describes methods of mitigating radio frequency interference(RFI) in the frequency range 10-100 MHz, developing and evaluating coherent methods with which RFI is subtracted from the afflicted data, nominally resulting in no distortion of the underlying signals. This approach is of interest in weak signal applications such as radio astronomy, where the signal of interest may have interference-to-noise ratio much less than one, and so can be easily distorted by other methods. Environmental noise in this band is strong and non-white, so a realistic noise model is developed, with which we characterize the performance of signal parameter estimation, a key component of the proposed algorithms. Two classes of methods are considered: "generic" parameter estimation/subtraction (PE/S) and a modulation-specific form known as demodulation-remodulation ("demod--remod") PE/S. It is demonstrated for RFI in the form of narrowband FM and Broadcast FM that generic PE/S has the problem of severely distorting underlying signals of interest and demod-remod PE/S is less prone to this problem. Demod-remod PE/S is also applied and evaluated for RFI in the form of Digital TV signals. In both cases, we compare the performance of the demod-remod PE/S with that of a traditional adaptive canceling method employing a reference antenna, and propose a hybrid method to further improve performance. A new metric for "toxicity" is defined and employed to determine the degree to which RFI mitigation damages the underlying signal of interest.<br>Ph. D.
APA, Harvard, Vancouver, ISO, and other styles
29

Ambarkutuk, Murat. "A Grid based Indoor Radiolocation Technique Based on Spatially Coherent Path Loss Model." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/80405.

Full text
Abstract:
This thesis presents a grid-based indoor radiolocation technique based on a Spatially Coherent Path Loss Model (SCPL). SCPL is a path loss model which characterizes the radio wave propagation in an environment by solely using Received Signal Strength (RSS) fingerprints. The propagation of the radio waves is characterized by uniformly dividing the environment into grid cells, followed by the estimation of the propagation parameters for each grid cell individually. By using SCPL and RSS fingerprints acquired at an unknown location, the distance between an agent and all the access point in an indoor environment can be determined. A least-squares based trilateration is then used as the global fix of location the agent in the environment. The result of the trilateration is then represented in a probability distribution function over the grid cells induced by SCPL. Since the proposed technique is able to locally model the propagation accounting for attenuation of non-uniform environmental irregularities, the characterization of the path loss in the indoor environment and radiolocation technique might yield improved results. The efficacy of the proposed technique was investigated with an experiment comparing SCPL and an indoor radiolocation technique based on a conventional path loss model.<br>Master of Science<br>This thesis presents a technique uses radio waves to localize an agent in an indoor environment. By characterizing the difference between transmitted and received power of the radio waves, the agent can determine how far it is away from the transmitting antennas, i.e. access points, placed in the environment. Since the power difference mainly results from obstructions in the environment, the attenuation profile of the environment carries a significant importance in radiolocation techniques. The proposed technique, called Spatially Coherent Path Loss Model (SCPL), characterizes the radio wave propagation, i.e. the attenuation, separately for different regions of the environment, unlike the conventional techniques employing global attenuation profiles. The localization environment is represented with grid-cell structure and the parameters of SCPL model describing the extent of the attenuation of the environment are estimated individually. After creating an attenuation profile of the environment, the agent localizes itself in the localization environment by using SCPL with signal powers received from the access points. This scheme of attenuation profiling constitutes the main contribution of the proposed technique. The efficacy and validity of the proposed technique was investigated with an experiment comparing SCPL and an indoor radiolocation technique based on a conventional path loss model.
APA, Harvard, Vancouver, ISO, and other styles
30

Boone, Marc. "High-definition optical coherence tomography: Contribution to the non-invasive near infrared optical imaging techniques of the skin." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/232235.

Full text
Abstract:
Background. The development of non-invasive imaging techniques has been stimulated by the shortcomings of histopathology. Currently the only valid diagnostic technique in dermatology is skin biopsy which remains a painful, invasive intervention for the patient. Moreover, this approach is not always convenient for monitoring and follow-up of a skin disease. Optical imaging technologies could solve these shortcomings as they are fast, precise, repeatable and painless. There are four established non-invasive skin imaging techniques used in daily practice: dermoscopy, high-frequency ultrasound, reflectance confocal microscopy (RCM) and conventional optical coherence tomography (C-OCT). In imaging there is a trade-off between resolution and penetration depth. The former permits the visualization of cells, if the resolution is at least 3 µm. The latter enables the recognition of patterns and structures in deeper layers of the skin if the penetration depth is deeper than 150 µm. New non-invasive techniques using infrared light sources have been developed recently. The technique used in this work is a high-definition optical coherence tomography (HD-OCT).Objectives. The overall aims of this thesis were the feasibility of HD-OCT to visualize in/ex vivo, in real time and in 3-D the cellular and structural morphology of the skin, secondly the assessment of the capability of this technology to measure in vivo and real time the cutaneous optical properties, and finally the determination of the contribution of this technique to the non-invasive near-infrared imaging technologies. Five specific objectives have been established: i) could cells be observed in their 3-D microenvironment in normal and diseased skin, ii) could we describe morphologic features of cells and structures in normal and diseased skin (m_HD-OCT), iii) could these morphologic features be quantified by optical property analysis (o_HD-OCT), iv) was it possible to perform accurate thickness measurements in normal and diseased skin, and finally v) what was the diagnostic potential of this technique?Methodology. HD-OCT uses a combination of parallel time-domain interferometry, high power tungsten lamp (with Gaussian filter, very low lateral coherence and ultra-high bandwidth (1300 nm +/- 100 nm)), and last but not least, full field illumination with real time focus tracking. A constant homogeneous resolution of 3 µm resolution in all three dimensions is obtained up to a depth of 570 µm. Hence, the system is capable of capturing real time full 3-D images. Moreover, the in vivo assessment of optical properties of the skin is only applicable to OCT when operating in focus-tracking mode, which is the case for HD-OCT. The means to obtain answers to the five specific questions were the comparison of en face HD-OCT images with RCM and HD-OCT cross-sectional images with histopathology and C-OCT. Results. At least 160 line pares were observed by imaging a high resolution phantom with HD-OCT. This suggested a 3 µm lateral resolution. The presence of cells such as keratinocytes, melanocytes, inflammatory cells, fibroblasts and melanophages in their 3-D cutaneous microenvironment in vivo as well as ex vivo has been demonstrated .A qualitative description of structures and patterns in normal and diseased skin could be performed by HD-OCT. Clear structural changes of the epidermis, dermo-epidermal junction, papillary dermis and reticular dermis related to intrinsic skin ageing could be observed. Lobulated structures, surrounded by stretched stromal fibers and arborizing vessels, could be demonstrated in nodular basal cell carcinoma (BCC). The o_HD-OCT of normal and diseased skin could be assessed in vivo. This approach permitted the quantitative assessment of the OCT signal attenuation profiles of normal healthy skin, actinic keratosis (AK) and squamous cell carcinoma (SCC). Differences in signal attenuation profiles could be demonstrated between these three groups. These differences were also observed between BCC subtypes. The slope of the exponential attenuation of the signal in the upper part of the epidermis was very high in benign nevi. The more malignant the lesion the lower the slope. Thickness measurements of epidermis and papillary dermis could be performed by m_HD-OCT, based on a cross-sectional images and their corresponding en face image. More accurate measurements of epidermal and papillary dermal thickness could be performed based on the optical analysis of a skin volume by o_HD-OCT. The diagnostic potential of HD-OCT in comparison with dermoscopy, RCM and C-OCT could be assessed regarding i) melanoma, ii) BCC differentiation from BCC imitators and BCC sub-differentiation and iii) SCC differentiation from AK. A much higher diagnostic potential could be demonstrated for o_HD-OCT in comparison with m_HD-OCT concerning melanoma detection. The diagnostic potential of HD-OCT to discriminate BCC from clinical BCC imitators was moderate. However, HD-OCT seemed to have high potential in sub-differentiation of BCC subtypes: i) it seemed to be the best technique to include and exclude a superficial BCC, ii) the technique appeared to be the best approach to exclude nodular BCC, and iii) HD-OCT looked to be the best technique to include an infiltrative BCC. Finally, HD-OCT has proven to be a powerful method to discriminate AK from SCC.Conclusions. HD-OCT is able to capture real time 3-D imaging with a sufficiently high optical resolution and penetration depth to allow the visualization of cells in and ex vivo in their micro-architectural context. At the same time, HD-OCT permits the recognition of patterns and structures in a sufficiently large volume of skin (1.5 mm³). HD-OCT closes therefore the gap between RCM with a high resolution but low penetration depth and C-OCT with a low resolution but high penetration depth. Moreover, HD-OCT permits, in contrast to RCM and C-OCT, the real time in vivo analysis of optical properties of the skin. HD-OCT seems to be a promising tool for early diagnosis of melanoma, BCC sub-differentiation and differentiation between SCC and AK.Future perspectives. Multicenter validation studies are needed to determine the diagnostic performance of this promising new technology, especially in other clinical settings combining both morphological and optical property analysis. This combined analysis could be a valuable method not only for diagnosis, monitoring and therapeutic guidance of dermatologic diseases but it could also be helpful in the management of non-dermatologic conditions such as diabetic micro-angiopathy, infantile cystinosis or even osteoporosis.<br>Doctorat en Sciences médicales (Santé Publique)<br>info:eu-repo/semantics/nonPublished
APA, Harvard, Vancouver, ISO, and other styles
31

Ng, Wing Chau. "Digital signal processing algorithms in single-carrier optical coherent communications." Doctoral thesis, Université Laval, 2015. http://hdl.handle.net/20.500.11794/26102.

Full text
Abstract:
Des systèmes de détection cohérente avec traitement numérique du signal (DSP) sont présentement déployés pour la transmission optique de longue portée. La modulation par déplacement de phase en quadrature à deux polarisations (DP-QPSK) est une forme de modulation appropriée pour la transmission optique sur de longues distances (1000 km ou plus). Une autre forme de modulation, le DP-16-QAM (modulation d’amplitude en quadrature) a été récemment utilisée pour les communications métropolitaines (entre 100 et 1000 km). L’extension de la distance maximum de transmission du DP-16-QAM est un domaine de recherche actif. Déterminer si l’utilisation de la détection cohérente pour les transmissions à courtes distances (moins de 100 km) en justifieraient les coûts demeure cependant une question ouverte. Dans cette thèse, nous nous intéresserons principalement au recouvrement de phase et au démultiplexage en polarisation dans les récepteurs numériques cohérents pour les applications à courte distance. La réalisation de systèmes optiques gigabauds cohérents en temps-réel utilisant des formats de modulation à monoporteuse plus complexes, comme le 64-QAM, dépend fortement du recouvrement de phase. Pour le traitement numérique hors-ligne, la récupération de phase utilisant les résultats de décisions (decision-directed phase recovery (DD-PR)) permet d’obtenir, au débit des symboles, les meilleures performances, et ce avec un effort computationnel moindre que celui des meilleurs algorithmes connus. L’implémentation en temps-réel de systèmes gigabauds requiert un haut degré de parallélisation qui dégrade de manière significative les performances de cet algorithme. La parallélisation matérielle et le délais de pipelinage sur la boucle de rétroaction imposent des contraintes strictes sur la largeur spectrale du laser, ainsi que sur le niveau de bruit spectral des sources laser. C’est pourquoi on retrouve peu de démonstrations de recouvrement de phase en temps-réel pour les modulations 64-QAM ou plus complexes. Nous avons analysé expérimentalement l’impact des lasers avec filtres optiques sur le recouvrement de phase realisé en pipeline sur un système cohérent à monoporteuse 64-QAM à 5 Gbaud. Pour les niveaux de parallélisation plus grands que 24, le laser avec filtres optiques a permis une amélioration de 2 dB du ratio signal-à-bruit optique, en comparaison avec le même laser sans filtre optique. La parallélisation du recouvrement de phase entraîne non seulement une plus grande sensibilité au bruit de phase du laser, mais aussi une plus grande sensibilité aux fréquences résiduelles induites par la présence de tonalités sinusoïdales dans la source. La modulation de fréquences sinusoïdales peut être intentionnelle, pour des raisons de contrôle, ou accidentelles, dues à l’électronique ou aux fluctuations environnementales. Nous avons étudié expérimentalement l’impact du bruit sinusoïdal de phase du laser sur le système parallèle de recouvrement de phase dans un système 64-QAM à 5 Gbauds, en tenant compte des effets de la compensation du décalage de fréquence et de l’égalisation. De nos jours, les filtres MIMO (multi-input multi-output) à réponse finie (FIR) sont couramment utilisés pour le démultiplexage en polarisation dans les systèmes cohérents. Cependant, ces filtres souffrent de divers problèmes durant l’acquisition, tels la singularité (les mêmes données apparaissent dans les deux canaux de polarisation) et la longue durée de convergence de certaines combinaisons d’états de polarisation (SOP). Pour réduire la consommation d’énergie exigée dans les systèmes cohérents pour les applications à courtes distances où le délais de groupe différentiel n’est pas important, nous proposons une architecture DSP originale. Notre approche introduit une pré-rotation de la polarisation, avant le MIMO, basée sur une estimation grossière de l’état de polarisation qui n’utilise qu’un seul paramètre Stokes (s1). Cette méthode élimine les problèmes de singularité et de convergence du MIMO classique, tout en réduisant le nombre de filtres MIMO croisés, responsables de l’annulation de la diaphonie de polarisation. Nous présentons expérimentalement un compromis entre la réduction de matériel et la dégradation des performances en présence de dispersion chromatique résiduelle, afin de permettre la réalisation d’applications à courtes distances. Finalement, nous améliorons notre méthode d’estimation à l’aveugle par un filtre Kalman étendu (EKF) à temps discret de faible complexité, afin de réduire la consommation de mémoire et les calculs redondants apparus dans la méthode précédante. Nous démontrons expérimentalement que la pré-rotation de polarisation basée sur le EKF operé au taux ASIC (Application-Specific Integrated Circuits) permet de récupérer la puissance de fréquence d’horloge du signal multiplexé en polarisation ainsi que d’améliorer la performance du taux d’erreur sur les bits (BER) en utilisant un MIMO de complexité réduite.<br>Coherent detection with digital signal processing (DSP) is currently being deployed in longhaul optical communications. Dual-polarization (DP) quadrature phase shift keying (QPSK) is a modulation format suitable for long-haul transmission (1000 km or above). Another modulation, DP-16-QAM (quadrature amplitude modulation) has been deployed recently in metro regions (between 100 and 1000 km). Extending the reach of DP-16QAM is an active research area. For short-reach transmission (shorter than 100 km), there is still an open question as to when the technology will be mature enough to meet cost pressures for this distance. In this dissertation, we address mainly on phase recovery and polarization demultiplexing in digital coherent receivers for short-reach applications. Implementation of real-time Gbaud (Gsymbol per second) optical coherent systems for singlecarrier higher-level modulation formats such as 64-QAM depends heavily on phase tracking. For offline DSP, decision-directed phase recovery is performed at the symbol rate with the best performance and the least computational effort compared to best-known algorithms. Real-time implementations at Gbaud requires significant parallelizing that greatly degrades performance of this algorithm. Hardware parallelization and pipelining delay on the feedback path impose stringent requirements on the laser linewidth, or the frequency noise spectral level of laser sources. This leads to the paucity of experiments demonstrating real-time phase tracking for 64- or higher QAM. We experimentally investigated the impact of opticallyfiltered lasers on parallel and pipelined phase tracking in a single-carrier 5 Gbaud 64-QAM back-to-back coherent system. For parallelization levels higher than 24, the optically-filtered laser shows more than 2 dB improvement in optical signal-to-noise ratio penalty compared to that of the same laser without optical filtering. In addition to laser phase noise, parallelized phase recovery also creates greater sensitivity to residual frequency offset induced by the presence of sinusoidal tones in the source. Sinusoidal frequency modulation may be intentional for control purposes, or incidental due to electronics and environmental fluctuations. We experimentally investigated the impact of sinusoidal laser phase noise on parallel decision-directed phase recovery in a 5 Gb 64-QAM system, including the effects of frequency offset compensation and equalization. MIMO (multi-input multi-output) FIR (finite-impulse response) filters are conventionally used for polarization demultiplexing in coherent communication systems. However, MIMO FIRs suffer from acquisition problems such as singularity and long convergence for a certain polarization rotations. To reduce the chip power consumption required in short-reach coherent systems where differential group delay is not prominent, we proposed a novel parallelizable DSP architecture. Our approach introduces a polarization pre-rotation before MIMO, based on a very-coarse blind SOP (state of polarization) estimation using only a single Stokes parameter (s1). This method eliminates the convergence and singularity problems of conventional MIMO, and reduces the number of MIMO cross taps responsible for cancelling the polarization crosstalk. We experimentally presented a tradeoff between hardware reduction and performance degradation in the presence of residual chromatic dispersion for short-reach applications. Finally, we extended the previous blind SOP estimation method by using a low-complexity discrete-time extended Kalman filter in order to reduce the memory depth and redundant computations of the previous design. We experimentally verified that our extended Kalman filter-based polarization prerotation at ASIC rates enhances the clock tone of polarization-multiplexed signals as well as the bit-error rate performance of using reduced-complexity MIMO for polarization demultiplexing.
APA, Harvard, Vancouver, ISO, and other styles
32

Olsson, Andreas. "Target recognition by vibrometry with a coherent laser radar." Thesis, Linköping University, Department of Electrical Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-1730.

Full text
Abstract:
<p>Laser vibration sensing can be used to classify military targets by its unique vibration signature. A coherent laser radar receives the target´s rapidly oscillating surface vibrations and by using proper demodulation and Doppler technique, stationary, radially moving and even accelerating targets can be taken care of. </p><p>A frequency demodulation method developed at the former FOA, is for the first time validated against real data with turbulence, scattering, rain etc. The issue is to find a robust and reliable system for target recognition and its performance is therefore compared with some frequency distribution methods. The time frequency distributions have got a crucial drawback, they are affected by interference between the frequency and amplitude modulated multicomponent signals. The system requirements are believed to be fulfilled by combining the FOA method with the new statistical method proposed here, the combination being suggested as aimpoint for future investigations.</p>
APA, Harvard, Vancouver, ISO, and other styles
33

Iqbal, Md Asif. "Advanced Raman amplification techniques for high capacity and broadband coherent optical transmission systems." Thesis, Aston University, 2018. http://publications.aston.ac.uk/37651/.

Full text
Abstract:
This thesis presents a detailed study of different advanced Raman fibre laser (RFL) based amplification schemes and the development of novel broadband distributed and discrete Raman amplifiers in order to improve the transmission performance of modern high capacity, long-haul coherent optical systems. The numerical modelling of different Raman amplifier techniques including power distribution of signal, pump and noise components, RIN transfer from pump to signal, broadband gain optimization and so on have been described in details. The RIN and noise performances of RFL based distributed Raman amplifiers (DRAs) with different span lengths, forward pump powers and input reflection levels have been characterized experimentally. It has been shown through coherent transmission experiment that, in order to improve pump power efficiency, a low level of input reflection up to ~10% can be allowed without increasing the Q factor penalty > 1dB due to additional signal RIN penalty. A novel broadband (>10nm) first order Raman pump is developed for use as a forward pump in long-haul transmission experiment. Significant signal RIN mitigation up to 10dB compared with conventional low RIN, narrowband sources was obtained for bidirectional DRA schemes. Long-haul coherent transmission experiments with 10×120Gb/s DP-QPSK system were carried out in are circulating loop setup using the proposed broadband pump in bidirectional and backward only pumping configurations. The maximum transmission reach up to ~8330km was reported with first order broadband pumped bidirectional DRA, with transmission reach extensions of 1250km and1667km compared with conventional backward only and first order semiconductor pumped bidirectional pumping scheme respectively. Finally, a novel design of bidirectional broadband distributed DRA is proposed to reduce the noise figure tilt and improve the WDM transmission performances. Furthermore, broadband discrete Raman amplifier schemes in dual stage configuration are also shown for high gain, high output power, low noise and low nonlinear performances.
APA, Harvard, Vancouver, ISO, and other styles
34

Zhang, Bo. "Experimental Studies of Quantum Dynamics and Coherent Control in Homonuclear Alkali Diatomic Molecules." Doctoral thesis, KTH, Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3420.

Full text
Abstract:
<p>The main theme covered in this thesis is experimentalstudies of quantum dynamics and coherent control in homonuclearalkali diatomic molecules by ultrafast laser spectroscopy iththe implementation of pump-probe techniques.</p><p>A series of experiments have been performed on the Rb2molecules in a molecular beam as well as in a thermal oven. Thereal-time molecular quantum dynamics of the predissociatingelectronically excited D(3)<sup>1</sup>Πu state of Rb<sub>2</sub>, which couples to/intersects several otherneighbouring states, is investigated using wavepackets. Thepredissociation of the D state, explored by this wavepacketmethod, arises from two independent states, the (4)<sup>3</sup>Σ<sub>u</sub><sup>+</sup>and (1)<sup>3</sup>∆<sub>u</sub>, for which the second corresponds to a much fasterdecay channel above a sharp energy threshold around 430 nm. Thelifetime of the D state above the energy threshold is obtained,τ ≈ 5 ps, by measuring the decay time of thewavepacket in a thermal oven. Further experimentalinvestigation performed in a molecular beam together withquantum calculations of wavepacket dynamics on the D state haveexplored new probe channels of wavepacket evolution: theD′(3)1Σu+ channel, which exhibits vibrational motionin a shelf state and the (4)<sup>3</sup>Σu+ channel, where direct build-up of thewavefunction is observed due to its spin-orbit oupling to the Dstate.</p><p>The real-time quantum dynamics of wavepackets confined totwo bound states, A<sup>1</sup>Σ<sub>u</sub><sup>+</sup>(0<sub>u</sub><sup>+</sup>) and b<sup>3</sup>Π<sub>u</sub>(0<sub>u</sub><sup>+</sup>), have been studied by experiment andcalculations. It is shown that these two states are fullycoupled by spin-orbit interaction, characterised by itsintermediate strength. The intermediate character of thedynamics is established by complicated wavepacket oscillationatterns and a value of 75 cm<sup>-1</sup>is estimated for the coupling strength at thestate crossing.</p><p>The experiments on the Li<sub>2</sub>molecule are performed by coherent control ofrovibrational molecular wavepackets. First, the Deutsch-Jozsaalgorithm is experimentally demonstrated for three-qubitfunctions using a pure coherent superposition of Li<sub>2</sub>rovibrational eigenstates. The function’scharacter, either constant or balanced, is evaluated by firstimprinting the function, using a phase-tailored femtosecond(fs) pulse, on a coherent superposition of the molecularstates, and then projecting the superposition onto an ionicfinal state using a second fs pulse at a specific delay time.Furthermore, an amplitude-tailored fs pulse is used to exciteselected rovibrational eigenstates and collision induceddephasing of the wavepacket signal, due to Li<sub>2</sub>-Ar collisions, is studied experimentally. Theintensities of quantum beats decaying with the delay time aremeasured under various pressures and the collisional crosssections are calculated for each well-defined rovibrationalquantum beat, which set the upper limitsfor ure dephasingcross sections.</p><p><b>Keywords:</b>Ultrafast laser spectroscopy, pump-probetechnique, predissociation, wavepacket, pin-orbit interaction,coherent control, (pure) dephasing</p>
APA, Harvard, Vancouver, ISO, and other styles
35

Tongning, Robert-christopher. "Ralentir le déphasage des états de superposition atomiques dans un cristal de Tm3+ : YAG." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01011160.

Full text
Abstract:
Ce travail se place dans le contexte des recherches sur les mémoires quantiques pour la lumière. L'information quantique est stockée dans un état de superposition atomique, dont la durée de vie détermine le temps maximum de stockage.On s'intéresse particulièrement aux matériaux capables de capturer la lumière par excitation résonnante d'une raie d'absorption, puis de conserver l'information quantique dans un état de superposition du fondamental électronique.Dans Tm3+:YAG, l'information est enregistrée dans un état de spin nucléaire. Cependant le champ magnétique qui lève la dégénérescence nucléaire entraîne les différents spins à des vitesses de précession différentes, ce qui tend à détruire l'aimantation initiale, porteuse de l'information.Une étude quantique du cristal est réalisée lors du premier chapitre de ce manuscrit. Les trois chapitres suivants traitent des différents mécanismes conduisant au déphasage des spins nucléaires. On y trouvera différente analyses théoriques qui seront confirmées par un ensemble de résultats expérimentaux, ainsi qu'une description détaillée du dispositif expérimental. Enfin le dernier chapitre, prospectif, exploite les outils développés au cours de la thèse pour préserver les cohérences optiques. Il présente quelques résultats expérimentaux prometteurs sur l'allongement du temps de vie de ces cohérences optiques.
APA, Harvard, Vancouver, ISO, and other styles
36

Lau, Alan Pak Tao. "Signal processing techniques for coherent fiber-optic communication systems in presence of Kerr nonlinearity /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

Full text
APA, Harvard, Vancouver, ISO, and other styles
37

FRANCESCHINI, PAOLO. "NOVEL SCHEMES FOR ULTRAFAST MANIPULATION OF QUANTUM MATERIALS." Doctoral thesis, Università Cattolica del Sacro Cuore, 2022. http://hdl.handle.net/10280/111822.

Full text
Abstract:
La possibilità di controllare le proprietà elettroniche on-demand su una scala di tempo ultraveloce rappresenta una delle sfide più intriganti verso la realizzazione di dispositivi fotonici ed elettronici di nuova generazione. Stimolata da questo, negli ultimi decenni la ricerca scientifica ha concentrato la propria attenzione su diverse piattaforme a stato solido. Tra tutte, nanostrutture dielettriche (e metamateriali) e materiali correlati si presentano come i più promettenti candidati per la realizzazione di dispositivi dotati di nuove funzionalità. Al di là delle caratteristiche specifiche che rendono i dielettrici più adatti ad applicazioni in fotonica e i materiali correlati ai dispositivi elettronici, entrambe le categorie manifestano nuove funzionalità se soggetti ad uno stimolo esterno sotto forma di impulsi di luce con durata più breve della scala di tempo caratteristica del rilassamento dei gradi di libertà interni al sistema. Infatti, lo stato fuori equilibrio raggiunto a seguito di una foto-eccitazione presenta proprietà elettroniche ed ottiche di gran lunga differenti da quelle all'equilibrio. Pertanto, l'obiettivo di questo lavoro di tesi consiste nello sviluppo di nuovi metodi ed approcci sperimentali in grado di indurre, misurare e controllare nuove funzionalità in materiali complessi su una scala di tempo ultraveloce.<br>The possibility to control the electronic properties on-demand on an ultrafast time scale represents one of the most exciting challenges towards the realization of new generation photonic and electronic devices. Triggered by this, in the last decades the research activity focused its attention to different solid-state platforms. Among all, dielectric nanostructures (and metamaterials) and correlated materials represent the most promising candidate for the implementation of devices endowed by new functionalities. Apart from the specific features making dielectrics more suitable for photonic applications and correlated materials for electronic devices, both categories exhibit new functionalities if subjected to an external stimulus in the form of excitation light pulses shorter than the relaxation timescale of the internal degrees of freedom of the system. Indeed, the out-of-equilibrium state achieved upon photoexcitation exhibits electronic and optical properties highly different from those at equilibrium. Therefore, the aim of this thesis work consists in the development of new methods and experimental approaches capable to induce, measure, and control new functionalities in complex materials on an ultrafast time scale.
APA, Harvard, Vancouver, ISO, and other styles
38

Muhammad, Rashed D. B. "Assessment of new real-time in-situ optical coherence tomography instrumentation and techniques for diagnosing and monitoring oral and cutaneous lesions." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1471556/.

Full text
Abstract:
Head and neck cancer is the sixth most common cancer worldwide, with 686,328 new cases per year. Most head and neck cancers are squamous cell carcinomas of the oral cavity and oropharynx, and are burdened by high mortality (50% at 5 years from diagnosis), notwithstanding recent progress in treatment methods. The vast majority of oro-pharyngeal cancers are late diagnosed, with significant adverse effects on cure, morbidity and prognosis. There is general consensus that earlier diagnosis contributes to better outcome measures. Current diagnostic standards consist of clinical examination and surgical biopsy, which are associated with delayed presentation, diagnosis and greater mortality. There is an unmet need for effective diagnostic techniques to aid early identification of cancers. Optical coherence tomography (OCT) is one of a number of non-invasive real-time imaging systems, introduced during the last two decades aiming to provide tissue information similar to conventional histopathological examination. The technique is similar to a B-mode ultrasound section, but employs a scanning near infrared light source rather than ultrasound waves, generating cross-sectional images of the sample tissue in an X-Z orientation. In this study, I investigated a modified OCT oral instrument (VivoSight® Michelson Diagnostics Ltd, Orpington, Kent, UK) with adapted probe for intraoral use. The new oral instrument was not CE marked, was uncalibrated and consequently a non-standard instrument. Therefore, prior to clinical application, the new instrument required calibration and comparison with the conventional instrument to assess and confirm performance in image quality and resolution in X, Y, and Z-planes. A series of laboratory engineering standards were created and compared by scanning with both instruments in X, Y & Z planes. A second series of experiments were conducted using porcine tissue as models for human tissue, confirming the similarities of fact and artefact observable when the two instruments were applied to challenging imaging scenarios, in particular, the effects of dissimilar target tissue refractive indices on the OCT image. The effects (tissue dimensional changes) of fixing samples in formal-incontaining media and tissue processing were also then investigated using this non-invasive measuring technique.
APA, Harvard, Vancouver, ISO, and other styles
39

Fornieri, Antonio. "Coherent manipulation of electronic heat currents in superconducting quantum circuits." Doctoral thesis, Scuola Normale Superiore, 2017. http://hdl.handle.net/11384/85898.

Full text
APA, Harvard, Vancouver, ISO, and other styles
40

Hanna, Sherif Fayez. "Electronic resonance enhanced coherent anti-Stokes Raman scattering technique for detection of combustion species and biological molecules." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4379.

Full text
Abstract:
The application of electronic-resonance enhanced (ERE) coherent anti-Stokes Raman scattering (CARS) for the detection of nitric oxide (NO) and acetylene (C2H2) is experimentally demonstrated and the effects of various parameters on the ERE CARS signal investigated. In addition, the detection of dipicolinic acid (DPA) using “normal” CARS is demonstrated. For NO detection, the frequency difference between a visible Raman pump beam and Stokes beam is tuned to a vibrational Q-branch Raman resonance of the No molecule to create a Raman polarization in the medium. The second pump beam is tuned into resonance with the rotational transitions in the (1,0) band of the A2Σ+-X2Π electronic transition at 236 nm, and the CARS signal is thus resonant with transitions in the (0,0) band. A NO gas cell was used for the experiment to detect NO at various pressure levels. A significant resonant enhancement of the NO CARS signal was observed and good agreement between calculated and experimental data was obtained. For C2H2 detection, ERE CARS experiments were performed in a roomtemperature gas cell using mixtures of 5000 ppm C2H2 in N2. Visible pump and Stokes beams were used, with the frequency difference between the pump and Stokes tuned to the 1974 cm-1 Ϡ2 Raman transition of C2H2. An ultraviolet probe beam with the wavelengths ranging from 232 nm to 242 nm is scattered from the induced Raman polarization to generate the ERE CARS signal. The effects of probe wavelength and pressure on signal generation are discussed. CARS was used to detect the 998 cm-1 vibrational Raman transition from a sample of polycrystalline DPA. The transition is the breathing ring vibration in the pyridine ring structure in the DPA molecule. The DPA 998 cm-1 transition is detected with excellent signal-to-noise ratio and the full-width-at-half-maximum is very narrow, approximately 4 cm-1.
APA, Harvard, Vancouver, ISO, and other styles
41

PLANTEY, JOSIANE. "Reseaux de capteurs a fibres optiques pour materiaux composites : analyse et developpement des techniques de reflectometrie frequentielle et de multiplexage de coherence." Nice, 1991. http://www.theses.fr/1991NICE4520.

Full text
Abstract:
Dans le cadre du projet ostic, des experts et utilisateurs de materiaux composites ont exprime le besoin de doter les pieces fabriquees de capteurs susceptibles de les informer sur l'etat de contraintes et de temperature affectant celles-ci, lors des phases de cuisson et/ou d'utilisation. Les capteurs proposes sont des capteurs a fibres optiques dont le nombre lie a la finesse de la resolution spatiale requise (quelques centimetres), et par la-meme au nombre de points de mesure, a exige une mise en reseau de ceux-ci. Deux systemes ont ete, ici, presentes: pour le premier, la gestion du reseau est confiee a la methode de multiplexage frequentiel (f. M. C. W. ) par un adressage des capteurs en parallele (10 capteurs multiplexables). Le second systeme est fonde sur la technique de multiplexage de coherence (10 capteurs multiplexables) completee par une mesure de type polarimetrique pour la quantification des champs de temperature et de contraintes. Chacun des deux systemes a fait l'objet d'une analyse theorique suivie de tests experimentaux permettant de souligner l'adequation des resultats au cahier des charges etabli, lequel exige une gamme de temperature s'etendant de 150 k a 400 k et des mesures de contraintes jusqu'au point de rupture. La precision requise pour la mesure de la temperature (5 k) et de contraintes (50 m/m) est aisement obtenue dans chacun des deux cas
APA, Harvard, Vancouver, ISO, and other styles
42

Fickers, Jessica. "Modulation formats and digital signal processing for fiber-optic communications with coherent detection." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209204.

Full text
Abstract:
A débit de données élevé, typiquement supérieur à 10 Gsymboles/s, les lignes de<p>télécommunication optique à fibre monomode souffrent de façon accrue des distorsions<p>inhérentes à la fibre et à l’architecture de transmission. Nous pouvons classer les<p>effets de fibre en plusieurs catégories:<p>– Les effets linéaires. La dispersion chromatique est entraînée par la dépendance en<p>fréquence de l’indice de réfraction de la fibre. Il en résulte un élargissement des<p>bits optiques. La dispersion des modes de polarisation prend son origine dans<p>la biréfringence de la fibre. La modélisation de cet effet est compliquée par son<p>caractère stochastique et variable dans le temps.<p>– Les effets non linéaires prennent leur origine dans un indice de réfraction de<p>fibre qui dépend du champ optique. Ces effets peuvent être classés en deux<p>catégories. Premièrement, les effets intérieurs à un canal dont le plus influant<p>est l’automodulation de phase qui découle de l’effet Kerr optique :l’intensité<p>d’une impulsion lumineuse influence sa propre propagation. Deuxièmement, il<p>existe des conséquences de l’effet Kerr par lesquelles les différents canaux, se<p>propageant au sein de la même fibre, s’influencent mutuellement. Le phénomène<p>le plus influent parmi ces derniers est la modulation de phase croisée :l’intensité<p>d’un canal influence la propagation dans un canal voisin.<p>– Les pertes par diffusion Rayleigh sont compensées par les amplificateurs distribués<p>le long de la ligne de transmission. L’amplification optique par l’intermédiaire<p>d’émission stimulée dans des dispositifs dopés aux ions Erbium est<p>accompagnée d’émission spontanée amplifiée. Ceci entraîne la présence d’un<p>bruit blanc gaussien se superposant au signal à transmettre.<p>– La gestion des canaux dans le réseau optique implique la présence dans les noeuds<p>du réseau de filtres de sélection, des multiplexeurs et démultiplexeurs.<p>Nous examinerons aussi les effets de ligne non inhérents à la fibre mais à l’architecture<p>de transmission. Les modèles de l’émetteur et du récepteur représentent les imperfections<p>d’implémentation des composants optiques et électroniques.<p>Un premier objectif est de définir et évaluer un format de modulation robuste aux<p>imperfections introduites sur le signal par la fibre optique et par l’émetteur/récepteur.<p>Deux caractéristiques fondamentales du format de modulation, determinants pour la<p>performance du système, sont étudiés dans ce travail :<p>– La forme d’ onde. Les symboles complexes d’information sont mis en forme par<p>un filtre passe-bas dont le profil influence la robustesse du signal vis-à-vis des<p>effets de ligne.<p>– La distribution des fréquences porteuses. Les canaux de communication sont<p>disposés sur une grille fréquentielle qui peut être définie de manière électronique<p>par traitement de signal, de manière optique ou dans une configuration hybride.<p>Lorsque des porteuses optiques sont utilisées, le bruit de phase relatif entre lasers<p>entraîne des effets d’ influence croisée entre canaux. En revanche, les limites des<p>implémentations électroniques sont données par la puissance des architectures<p>numériques.<p>Le deuxième objectif est de concevoir des techniques de traitement numérique du<p>signal implémentées après échantillonnage au récepteur afin de retrouver l’information<p>transmise. Les fonctions suivantes seront implémentées au récepteur :<p>– Les techniques d’estimation et d’égalisation des effets linéaires introduits par la<p>fibre optique et par l’émetteur et le récepteur. Le principe de l’égalisation dans<p>le domaine fréquentiel est de transformer le canal convolutif dans le domaine<p>temporel en un canal multiplicatif qui peut dès lors être compensé à une faible<p>complexité de calcul par des multiplications scalaires. Les blocs de symboles<p>émis doivent être rendus cycliques par l’ajout de redondance sous la forme d’un<p>préfixe cyclique ou d’une séquence d’apprentissage. Les techniques d’égalisation<p>seront comparées en termes de performance (taux d’erreurs binaires, efficacité<p>spectrale) et en termes de complexité de calcul. Ce dernier aspect est particulièrement<p>crucial en vue de l’optimisation de la consommation énergétique du<p>système conçu.<p>– Les techniques de synchronisation des signaux en temps/fréquence. Avant de<p>pouvoir égaliser les effets linéaires introduits dans la fibre, le signal reçu devra<p>être synchronisé en temps et en fréquence sur le signal envoyé. La synchronisation<p>est généralement accomplie en deux étapes principales :l’acquisition réalisée<p>avant de recevoir les symboles d’information don’t l’objectif est une première<p>estimation/compensation des effets de manière "grossière", le tracking réalisé en<p>parallèle à l’estimation des symboles d’information dont l’objectif est l’estimation<p>/compensation des effets de manière "fine". Les algorithmes d’acquisition et<p>de tracking peuvent nécessiter l’envoi d’informations connues du récepteur.<p>– Les techniques d’estimation et de compensation des imperfections de fonctionnement<p>de l’émetteur et du récepteur. Une structure de compensation des effets<p>introduits par les composants optiques et électroniques sera développée afin de<p>relâcher les contraintes d’implémentation de l’émetteur et du récepteur.<p>Etant donné la très haute cadence à laquelle les échantillons du signal sont produits<p>(plusieurs dizaines de Gech/s), une attention particulière est portée à la complexité de<p>calcul des algorithmes proposés.<br>Doctorat en Sciences de l'ingénieur<br>info:eu-repo/semantics/nonPublished
APA, Harvard, Vancouver, ISO, and other styles
43

Parks, Daniel. "X-ray Scattering Techniques for Coherent Imaging in Reflection Geometry, Measurement of Mutual Intensity, and Symmetry Determination in Disordered Materials." Thesis, University of Oregon, 2013. http://hdl.handle.net/1794/13221.

Full text
Abstract:
The advent of highly-coherent x-ray light sources, such as those now available world-wide in modern third-generation synchrotrons and increasingly available in free-electron lasers, is driving the need for improved analytical and experimental techniques which exploit the coherency of the generated light. As the light illuminating a sample approaches full coherence, a simple Fourier transform describes the diffraction pattern generated by the scattered light in the far field; because the Fourier transform of an object is unique, coherent scattering can directly probe local structure in the scattering object instead of bulk properties. In this dissertation, we exploit the coherence of Advanced Light Source beamline 12.0.2 to build three types of novel coherent scattering microscopes. First, we extend the techniques of coherent diffractive imaging and Fourier transform holography, which uses iterative computational methods to invert oversampled coherent speckle patterns, into reflection geometry. This proof-of-principle experiment demonstrates a method by which reflection Bragg peaks, such as those from the orbitally-ordered phase of complex metal oxides, might eventually be imaged. Second, we apply a similar imaging method to the x-ray beam itself to directly image the mutual coherence function with only a single diffraction pattern. This technique supersedes the double-slit experiments commonly seen in the scattering literature to measure the mutual intensity function by using a set of apertures which effectively contains all possible double slit geometries. Third, we show how to evaluate the speckle patterns taken from a labyrinthine domain pattern for "hidden" rotational symmetries. For this measurement, we modify the iterative algorithms used to invert speckle patterns to generate a large number of domain configurations with the same incoherent scattering profile as the candidate pattern and then use these simulations as the basis for a statistical inference of the degree of ordering in the domain configuration. We propose extending this measurement to position-resolved speckle patterns, creating a symmetry-sensitive microscope. The three new techniques described herein may be employed at current and future light sources.
APA, Harvard, Vancouver, ISO, and other styles
44

Fiege, Daniel Pascal [Verfasser]. "Development and application of multiple-quantum coherence techniques for in vivo sodium MRI at high and ultra-high field strengths / Daniel Pascal Fiege." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2014. http://d-nb.info/1052254756/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
45

Corradini, Marina. "Reconstruction of the earthquake rupture process through coherent teleseismic imaging and statistical modeling." Thesis, Université de Paris (2019-....), 2019. https://theses.md.univ-paris-diderot.fr/CORRADINI_Marina_va1.pdf.

Full text
Abstract:
De nombreuses études ont tenté d’éclairer la complexité de la rupture sismique de grands séismes en utilisant des techniques d’imagerie cohérente telles que la back- projection (BP). Dans une étude récente, Fukahata et al. (2013) ont suggéré que, d’un point de vue théorique, l’image BP de la rupture sismique est liée au glissement ou à la vitesse de glissement sur la faille. Cependant, la relation quantitative entre les images BP et les propriétés physiques du processus de rupture reste encore peu connue. Cette thèse vise à clarifier comment les images BP du champ d’ondes rayonné peuvent être utilisées pour déduire les hétérogénéités spatiales en glissement et en vitesse de rupture le long de la faille. Nous réalisons des simulations de différents processus de rupture à l’aide d’un modèle de source linéaire. Pour chaque modèle de rupture, nous calculons les sismogrammes synthétiques à trois réseaux télésismiques et nous appliquons la technique de BP afin d’identifier les sources de rayonnement haute fréquence (HF). Cette procédure permet de comparer les images BP avec le modèle de rupture originaire et d’interpréter les émissions HF en fonction des trois paramètres cinématiques: le temps de montée, la valeur du glissement final, la vitesse de rupture. Nos résultats montrent que les pics HF extraits avec l’analyse BP sont le plus étroitement associés aux hétérogénéités spatio-temporelles de l’accélération du glissement. Nous vérifions nos observations sur deux grands séismes survenus dans la faille de Swan Islands à neuf ans d’intervalle: le séisme du 2009 (Mw 7.3) et celui du 2018 (Mw 7.5) au nord du Honduras. Les deux événements montrent une géométrie linéaire, ce qui les rend comparables à notre approche synthétique. Malgré la géométrie simple, les deux séismes sont caractérisés par un taux de glissement complexe, avec plusieurs sous-événements. Nos résultats préliminaires montrent que l’image BP des émissions HF permet d’estimer une longueur et une vitesse de rupture compatibles avec d’autres études et qu’un fort rayonnement HF pourrait correspondre aux zones de forte variabilité du taux de glissement. En conclusion, nous utilisons une méthode de réseau de neurones afin de prédire les paramètres cinématiques d’une rupture sismique à partir de son image BP. Le réseau s’appuie sur un grand nombre de processus de rupture synthétiques et leurs images BP, dans le but d’identifier le lien statistique entre le rayonnement HF et les paramètres cinématiques. Nos résultats montrent que le réseau de neurones appliqué à l’image BP du séisme est capable de prédire les valeurs du temps de montée et de la vitesse de rupture le long de la faille, ainsi que la position moyenne de l’hétérogénéité. Par contre, le réseau de neurones n’arrive pas à récupérer les valeurs du glissement final, auquel l’approche BP est relativement insensible. Notre étude permet de mieux comprendre l’écart qui existe actuellement entre la description théorique de la génération de rayonnements HF et les observations d’émissions HF obtenues par des techniques d’imagerie cohérentes, en s’appuyant aux pistes d’action possibles et en suggérant de nouvelles perspectives<br>Many studies have attempted to illuminate rupture complexities of large earthquakes through the use of coherent imaging techniques such as back-projection (BP). Recently, Fukahata et al. (2013) suggested that, from a theoretical point of view, the BP image of the rupture is related to the slip motion on the fault. However, the quantitative relationship between the BP images and the physical properties of the earthquake rupture process still remains unclear.Our work aims at clarifying how BP images of the radiated wavefield can be used to infer spatial heterogeneities in slip and rupture velocity along the fault. We simulate different rupture processes using a line source model. For each rupture model, we calculate synthetic seismograms at three teleseismic arrays and we apply the BP technique to identify the sources of high-frequency (HF) radiation. This procedure allows for the comparison of the BP images with the originating rupture model, and thus the interpretation of HF emissions in terms of along-fault variation of the three kinematic parameters: rise time, final slip, rupture velocity. Our results show that the HF peaks retrieved from BP analysis are most closely associated with space-time heterogeneities of slip acceleration. We verify our findings on two major earthquakes that occurred 9 years apart on the strike-slip Swan Islands fault: the Mw 7.3 2009 and the Mw 7.5 2018 North of Hondurasearthquakes. Both events followed a simple linear geometry, making them suitable for comparison with our synthetic approach. Despite the simple geometry, both slip-rate functions are complex, with several subevents. Our preliminary results show that the BP image of HF emissions allows to estimate a rupture length and velocity which are compatible with other studies and that strong HF radiation corresponds to the areas of large variability of the moment-rate function. An outstanding question is whether one can use the BP image of the earthquake to retrieve the kinematic parameters along the fault. We build on the findings obtained in the synthetic examples by training a neural network model to directly predict the kinematic parameters along the fault, given an input BP image. We train the network on a large number of different synthetic rupture processes and their BP images, with the goal of identifying the statistical link between HF radiation and rupture kinematic parameters. Our results show that the neural network applied to the BP image of the earthquake is able to predict the values of rise time and rupture velocity along the fault, as well as thecentral position of the heterogeneity, but not the absolute slip values, to which the HF BP approach is relatively insensitive. Our work sheds some light on the gap currently existing between the theoretical description of the generation of HF radiation and the observations of HF emissions obtained by coherent imaging techniques, tackling possible courses of action and suggesting new perspectives
APA, Harvard, Vancouver, ISO, and other styles
46

Zhao, Qing. "Advanced Synchronization Techniques for Continuous Phase Modulation." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10486.

Full text
Abstract:
The objective of this research work is to develop reliable and power-efficient synchronization algorithms for continuous phase modulation (CPM). CPM is a bandwidth and power efficient signaling scheme suitable for wireless and mobile communications. Binary CPM schemes have been widely used in many commercial and military systems. CPM with multilevel symbol inputs, i.e., M-ary CPM, can achieve a higher data rate than binary CPM. However, the use of M-ary CPM has been limited due to receiver complexity and synchronization problems. In the last decade, serially concatenated CPM (SCCPM) has drawn more attention since this turbo-like coded scheme can achieve near Shannon-limit performance by performing iterative demodulation/decoding. Note that SCCPM typically operates at a low signal-to-noise ratio, which makes reliable and power-efficient synchronization more challenging. In this thesis, we propose a novel timing and phase recovery technique for CPM. Compared to existing maximum-likelihood estimators, the proposed data-aided synchronizer can achieve a better acquisition performance when a preamble is short or channel model errors are present. We also propose a novel adaptive soft-input soft-output (A-SISO) module for iterative detection with parameter uncertainty. In contrast to the existing A-SISO algorithms using linear prediction, the parameter estimation in the proposed structure is performed in a more general least-squares sense. Based on this scheme, a family of fixed-interval A-SISO algorithms are utilized to implement blind iterative phase synchronization for SCCPM. Moreover, the convergence characteristics of iterative phase synchronization and detection are analyzed by means of density evolution. Particularly, an oscillatory convergence behavior is observed when cycle slips occur during phase tracking. In order to reduce performance degradation due to this convergence fluctuation, design issues, including delay depth of the proposed algorithms, iteration-stopping criteria and interleaver size, are also discussed. Finally, for completeness of the study on phase synchronization, we investigate the error probability performance of noncoherently detected full-response CPM, which does not require channel (or phase) estimation.
APA, Harvard, Vancouver, ISO, and other styles
47

Ingels, Alexandre. "Développement de techniques d’imageries pour le diagnostic et le pronostic des tumeurs du rein." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS451/document.

Full text
Abstract:
Le but du projet est le développement de nouvelles techniques d’imagerie pour le diagnostic et le traitement du cancer du rein. Nous avons évalué différentes techniques comprenant la tomographie en cohérence optique et l’imagerie moléculaire. Nous avons évalué différents marqueurs potentiels pour l’imagerie moléculaire en étudiant l’expression de différents marqueurs dans le cancer du rein et leur association avec le pronostic de la maladie. Enfin, nous avons évalué deux techniques d’imagerie moléculaire sur des modèles précliniques : l’Imagerie par Résonnance Magnétique moléculaire et l’échographie moléculaire<br>The aim of this project is the development of new imaging techniques for renal cancer diagnostic and treatment.We have assessed several techniques including optical coherence tomography and molecular imaging. We assessed a series of potential markers for molecular imaging by measuring some pre-defined markers expressions by immunohistochemistry in renal cell carcinoma and their association with disease’s prognostic. Finally, we assessed two molecular imaging techniques in pre-clinical models: Molecular Magnetic Resonance Imaging and Molecular Ultrasound Imaging
APA, Harvard, Vancouver, ISO, and other styles
48

Barnhart, Samuel. "Design and Development of a Coherent Detection Rayleigh Doppler Lidar System for Use as an Alternative Velocimetry Technique in Wind Tunnels." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1595276402371536.

Full text
APA, Harvard, Vancouver, ISO, and other styles
49

Alhumaidi, Mouhammad [Verfasser], Abdelhak M. [Akademischer Betreuer] Zoubir, and Harald [Akademischer Betreuer] Klingbeil. "Statistical Signal Processing Techniques for Coherent Transversal Beam Dynamics in Synchrotrons / Mouhammad Alhumaidi. Betreuer: Abdelhak M. Zoubir ; Harald Klingbeil." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2015. http://d-nb.info/1111112657/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
50

Parks, Daniel H. "X-ray scattering techniques for coherent imaging in reflection geometry, measurement of mutual intensity, and symmetry determination in disordered materials." Thesis, University of Oregon, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3589544.

Full text
Abstract:
<p> The advent of highly-coherent x-ray light sources, such as those now available world-wide in modern third-generation synchrotrons and increasingly available in free-electron lasers, is driving the need for improved analytical and experimental techniques which exploit the coherency of the generated light. As the light illuminating a sample approaches full coherence, a simple Fourier transform describes the diffraction pattern generated by the scattered light in the far field; because the Fourier transform of an object is unique, coherent scattering can directly probe local structure in the scattering object instead of bulk properties.</p><p> In this dissertation, we exploit the coherence of Advanced Light Source beamline 12.0.2 to build three types of novel coherent scattering microscopes. First, we extend the techniques of coherent diffractive imaging and Fourier transform holography, which uses iterative computational methods to invert oversampled coherent speckle patterns, into reflection geometry. This proof-of-principle experiment demonstrates a method by which reflection Bragg peaks, such as those from the orbitally-ordered phase of complex metal oxides, might eventually be imaged. Second, we apply a similar imaging method to the x-ray beam itself to directly image the mutual coherence function with only a single diffraction pattern.</p><p> This technique supersedes the double-slit experiments commonly seen in the scattering literature to measure the mutual intensity function by using a set of apertures which effectively contains all possible double slit geometries. Third, we show how to evaluate the speckle patterns taken from a labyrinthine domain pattern for "hidden" rotational symmetries. For this measurement, we modify the iterative algorithms used to invert speckle patterns to generate a large number of domain configurations with the same incoherent scattering profile as the candidate pattern and then use these simulations as the basis for a statistical inference of the degree of ordering in the domain configuration. We propose extending this measurement to position-resolved speckle patterns, creating a symmetry-sensitive microscope. The three new techniques described herein may be employed at current and future light sources.</p>
APA, Harvard, Vancouver, ISO, and other styles
We offer discounts on all premium plans for authors whose works are included in thematic literature selections. Contact us to get a unique promo code!

To the bibliography