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The movement of a soluble material during the washing of a bed of packed solids.Sherman, William Roger 01 January 1962 (has links)
No description available.
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Tjänsteutbud i stadsnät : Vilka faktorer påverkar utbudet?Kaloczy, Erik, Häggström, Daniel January 2006 (has links)
<p>Under IT-boomen i början av 2000-talet släpptes regeringens IT-proposition som bland annat behandlade svenska folkets tillgång till bredband med hög överföringskapacitet. Kommunerna fick i uppdrag att bygga en infrastruktur för bredband baserad på fiber genom så kallade stadsnät. Förhållningen från staten var att näten skulle byggas enligt en öppen modell som skulle stimulera fri konkurrens och operatörsneutralitet. Detta skulle i slutändan resultera i ökad valfrihet för kunden och ett ökat tjänsteutbud.</p><p>I denna magisteruppsats har vi undersökt hur affärsmodellen som stadsnät ar-betar efter inverkar på tjänsteutbudet. Vi har även identifierat andra faktorer som påverkar tjänsteutvecklingen. Resultatet av denna undersökning har utvecklats till en modell som beskriver intressentstrukturen och vilka krafter som verkar mellan dessa intressenter samt de faktorer som påverkar tillväxten på tjänstesidan.</p><p>För att erhålla en djup förståelse för det studerade ämnet har en undersökning genomförts med hjälp av en webbenkät innehållande såväl kvantitativa som kvalitativa inslag. Webbenkäten har skickats till 90 stadsnät i Sverige och vi erhöll en svarsfrekvens på 71 %.</p><p>Magisteruppsatsen visar att stadsnäten i vårt urval kan delas in i två grupper; stadsnät där det råder fri konkurrens och neutralitet samt stadsnät som inte lyckats attrahera några kommersiella tjänsteleverantörer. Bristen på externa tjänsteleverantörer har lett till att stadsnätsägare har tvingats erbjuda tjänster i egen regi. För litet kundunderlag anses vara en bidragande orsak till tjänsteleverantörernas ointresse.</p> / <p>During the IT-era in the beginning of the 21st century high speed Internet connection for all citizens was on the top of the agenda. The Swedish government proposed a government bill stating that all Swedish citizens should have access to a broadband connection. The local municipalities were given the mission to build this new fiber-optic IT-infrastructure. The municipalities should adopt an open access network enabling all service providers to connect themselves to the network. The network should encourage competitive advantage and impartiality towards service providers resulting in increased service options for the citizens.</p><p>This master thesis investigates how the chosen business model affects the service offerings. We have also identified other factors that influence the development of service offerings. The result of this investigation concludes with a model that describes which factors that influences the growth of services in the municipal fiber network.</p><p>To get a deeper understanding of the studied subject have the authors conducted a web survey including qualitative and quantitative elements. The survey was sent to 90 municipal fiber networks. 71 % of these networks answered the questionnaire.</p><p>The result of this master thesis shows that the municipal fiber networks could be divided into two different groups. The first groups containing networks where the open access network is working and the other group where there is a lack of interest from the service providers. The lack of interest from service providers results in that municipal fiber network operators are forced to offer services themselves. The reason for this is often caused by an insufficient customer base.</p>
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SESAM Q-switched fiber laser at 1.2 mu mWang, Yuchen, Zhu, Xiushan, Zong, Jie, Wiersma, Kort, Chavez-Pirson, Arturo, Norwood, Robert A., Peyghambarian, N. 06 1900 (has links)
Q-switched operation of a holmium-doped fluoride fiber laser at 1.2 mu m wavelength induced by a semiconductor saturable absorber mirror (SESAM) is reported. 650 ns pulses with 0.13 mu J pulse energy at a repetition rate of 260 kHz were obtained.
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Tjänsteutbud i stadsnät : Vilka faktorer påverkar utbudet?Kaloczy, Erik, Häggström, Daniel January 2006 (has links)
Under IT-boomen i början av 2000-talet släpptes regeringens IT-proposition som bland annat behandlade svenska folkets tillgång till bredband med hög överföringskapacitet. Kommunerna fick i uppdrag att bygga en infrastruktur för bredband baserad på fiber genom så kallade stadsnät. Förhållningen från staten var att näten skulle byggas enligt en öppen modell som skulle stimulera fri konkurrens och operatörsneutralitet. Detta skulle i slutändan resultera i ökad valfrihet för kunden och ett ökat tjänsteutbud. I denna magisteruppsats har vi undersökt hur affärsmodellen som stadsnät ar-betar efter inverkar på tjänsteutbudet. Vi har även identifierat andra faktorer som påverkar tjänsteutvecklingen. Resultatet av denna undersökning har utvecklats till en modell som beskriver intressentstrukturen och vilka krafter som verkar mellan dessa intressenter samt de faktorer som påverkar tillväxten på tjänstesidan. För att erhålla en djup förståelse för det studerade ämnet har en undersökning genomförts med hjälp av en webbenkät innehållande såväl kvantitativa som kvalitativa inslag. Webbenkäten har skickats till 90 stadsnät i Sverige och vi erhöll en svarsfrekvens på 71 %. Magisteruppsatsen visar att stadsnäten i vårt urval kan delas in i två grupper; stadsnät där det råder fri konkurrens och neutralitet samt stadsnät som inte lyckats attrahera några kommersiella tjänsteleverantörer. Bristen på externa tjänsteleverantörer har lett till att stadsnätsägare har tvingats erbjuda tjänster i egen regi. För litet kundunderlag anses vara en bidragande orsak till tjänsteleverantörernas ointresse. / During the IT-era in the beginning of the 21st century high speed Internet connection for all citizens was on the top of the agenda. The Swedish government proposed a government bill stating that all Swedish citizens should have access to a broadband connection. The local municipalities were given the mission to build this new fiber-optic IT-infrastructure. The municipalities should adopt an open access network enabling all service providers to connect themselves to the network. The network should encourage competitive advantage and impartiality towards service providers resulting in increased service options for the citizens. This master thesis investigates how the chosen business model affects the service offerings. We have also identified other factors that influence the development of service offerings. The result of this investigation concludes with a model that describes which factors that influences the growth of services in the municipal fiber network. To get a deeper understanding of the studied subject have the authors conducted a web survey including qualitative and quantitative elements. The survey was sent to 90 municipal fiber networks. 71 % of these networks answered the questionnaire. The result of this master thesis shows that the municipal fiber networks could be divided into two different groups. The first groups containing networks where the open access network is working and the other group where there is a lack of interest from the service providers. The lack of interest from service providers results in that municipal fiber network operators are forced to offer services themselves. The reason for this is often caused by an insufficient customer base.
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Comportement unilatéral dans les milieux fibreux / Unilateral constitutive law in fibrous mediaMahmood, Omar Ateeq 01 April 2016 (has links)
Dans cette thèse, on s'intéresse au comportement effectif non linéaire issu de l'homogénéisation d'un milieu désordonné de fibres dans le plan. A partir d'une hypothèse de déformation homogène, on obtient une loi de comportement non linéaire isotrope par intégration sur les orientations de fibres. La particularité du modèle réside dans la représentation du flambement des fibres par une loi de comportement de type ressort avec raideurs asymétriques en traction/compression. Dans un premier temps, la limite d'une raideur nulle en compression est étudiée numériquement par éléments finis sur des géométries planes fissurées. On montre que le champ de contrainte solution est constitué d'un ensemble de graphe de force de traction en équilibre avec le chargement. En particulier, le caractère unilatéral révèle une interaction forte des fissures : la raideur en traction d'une éprouvette fissuré peut-être nulle quand bien même la percolation des fissures n'est pas atteinte. Par ailleurs, on montre que le champ de contrainte est partitionné en régions auto-équilibrées et libres de contrainte Pour finir, on propose une application au calcul des bornes énergétiques de la solution élastique d'un problème aux limites. En perspective, on met en évidence le caractère bi-module d'un voile de fibres de verre avec des mesures de champs de déplacement par corrélations d'images. Un dispositif d'Arcan est mis en place pour exercer un chargement anisotrope sur le voile. Les champs de déplacement mesurés sont utilisés pour identifier une loi de comportement du matériau. Un résultats préliminaire montre que le caractère unilatéral du voile est d'autant plus prononcé que sa densité est faible. / An homogenized non linear mechanical behavior of a 2D disordered fiber mats is considered. Under the homogeneous strain assumptions, a continuum description of an isotropic non linear media is derived by integration over all fibers orientations. The fiber non linearity due to buckling is featured by a lower spring constant in compression than in traction. First, the response of a sheet containing multiple cracks with different geometries is explored numerically in the case of a tension-field material, corresponding to the singular limit where the compressive spring constants goes to zero. It is reported that the stress solution is composed of a set of pattern built from tensile branches in equilibrium with the boundary conditions. In particular, the unilateral feature reveal a strong interaction between multiple cracks : the tensile stiffness of a cracked sheet can be zero even though the sheet is made up of a single piece. Besides the pattern of tensile branches, it is reported a partitioning of the stress into self-equilibrated and stress free regions. Finally, an application is proposed to find good estimates of the energetic bounds of the boundary value problem. As an experimental perspective to this work, it is proposed to estimates the bi-modulus feature of a manufactured fiber glass veil using digital image correlations. An Arcan device is set up to enforce an anisotropic loading on the veil. Measured displacement fields are used to identify a material constitutive law. As a preliminary results, it is reported that the unilateral feature is noticeable in light weight fiber glass veil.
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Systèmes optiques dédiés à la 5° génération de réseaux sans fils (5G) / Optical systems for next wireless standard (5G) generation deliveryHallak Elwan, Hamza 07 September 2017 (has links)
Cette thèse concerne le développement de futurs appareils, systèmes et réseaux prenant en charge l’internet haute vitesse, sans fil 5éme g´enération (5G). La demande de débit très élevé nécessite une bande passante suffisante, et ainsi la bande de fréquence millimetrique (mm-wave) a beaucoup d’intérêt. Un certain nombre de technologies devront converger, coexister et interagir, et surtout, coopérer, si cette vision doit être efficace et rentable. Le concept principal de cette de 5G est l’intégration de réseaux de fibre optique et Les réseaux radio grâce à la technologie Radio-sur-Fibre (RoF) aux fréquences d’onde millimetriques, pour fournir des services à large bande passante et permettre des réseaux évolutifs et gérables sans structure d’interface très complexe et multiples protocoles superposés.Dans cette thèse, les systèmes de communication RoF à ondes millimetriques sont théoriquement étudiés et démontrés expérimentalement pour étudier les altérations du système. Le travail présenté dans cette thèse est axé sur le bruit optique représenté par le bruit de phase et d’intensité induit par la source optique et la dispersion chromatique introduite par la fibre optique. Le bruit optique est analysé et mesuré pour différentes techniques de génération optique. Deux dispositifs différents de conversion, un mélangeur et un détecteur d’enveloppe sont, appliqués pour le traitement du signal et pour décorréler la phase et le bruit d’intensité. Nous souhaitons souligner que cette étude et le modèle peuvent s’appliquer à tout type de système de génération optique hétérodyne et à toute gamme de fréquences. La corrélation entre les modes optiques en peigne à fréquence optique est examinée pour montrer l’impact de la dispersion chromatique. Cette thèse présente la distribution d’énergie des ondes millimetriques et son influence sur la portée des fibres et la façon dont l’effet de dispersion chromatique sur le réseau RoF depend des paramètres de dispersion. Ensuite, cette thèse démontre comment la décorrélation de la phase optique induite par la dispersion chromatique entraîne un bruit de partition de modes dans les réseaux de communication RoF à ondes millimétriques.Lors de la transmission de certains types de données sur le système, les résultats démontrent l’impact du bruit optique et de la dispersion chromatique sur le qualité du signal. Les résultats de simulation sont présentés et sont en très bon accord avec les résultats expérimentaux. La grandeur du vecteur d’erreur evaluée par en processus en ligne montre l’impact des altèrations du système sur les performances du système. Le débit de données et l’évolution du système présentée sont en conformité avec les normes de communication comme à ondes millimétriques. / This thesis is for the development of future devices, systems and networks supporting the 5th Generation (5G) high-speed wireless internet. The demand for very high bit rate requires a sufficient large bandwidth, and therefore Millimeter-Wave (mm-wave) frequency band has a lot of interest. Several number of technologies will need to converge, co-exist and interoperate, and most importantly, cooperate, if this vision is to be efficiently and cost-effectively realized. The main concept within this next 5G is the integration of optical fiber networks and radio networks through Radio-over-Fiber (RoF) technology at mm-wave frequencies, to provide high-bandwidth front/backhaul services and enable scalable and manageable networks without a highly complex interface structure and multiple overlaid protocols.In this thesis, the mm-wave RoF communication systems are theoretically studied and experimentally demonstrated to investigate the system impairments. The work presented in this thesis is focused on optical noise represented by phase and intensity noise induced by optical source and chromatic dispersion introduced by optical fiber. The optical noise is analyzed and measured for different optical generation techniques. Two different down-conversion stages, mixer and envelope detector, are applied for signal processing and to decorrelate phase and intensity noise. We would like to highlight that this study and the model can be applicable toany kind of optical heterodyne generation system and any frequency range. The correlation among optical modes in optical frequency comb is examined to show the impact of chromatic dispersion. This thesis also exhibits the mm-wave power distribution over fiber span and how the chromatic dispersion effect on the RoF network is modified by varying dispersion parameters. Then, this thesis demonstrates how the optical phase decorrelation induced by chromatic dispersion results in mode partition noise at mm-wave RoF communication networks.When transmitting some types of data over the system, the results demonstrate the impact of optical noise and chromatic dispersion on the signal quality. The simulation results are presented and are in very good agreement with experimental results. The error vector magnitudethrough online process shows the impact of the system impairments on the system performance. The data rate and system evolution are compliance with communication standards at mm-wave.
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A dynamic behavior of pulp floc and fibers in the papermaking processPark, Chang Shin 03 1900 (has links)
No description available.
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Etude système de diodes lasers à verrouillage de modes pour la radio-sur-fibre en bande millimétrique / Millimeter-wave Radio-over-fiber Links based on Mode-Locked Laser DiodesBrendel, Friederike Cornelia 23 January 2013 (has links)
Ce travail de thèse s’inscrit dans la recherche des solutions économiquementviables pour des réseaux personnels à hauts débits (plusieurs Gbps à plusieursdizaines de Gbps) opérationnels en bande millimétrique autour de 60 GHz. Aucas où ces réseaux servent un nombre élevé d’utilisateurs, ils comprendront unemultitude d’antennes afin d’assurer l’accès sans fil rapide. Afin de réduire aumaximum le coût d’un module d’antenne, les réseaux doivent fournir un signalanalogue à des porteuses millimetriques. Une solution prometteuse pour les systèmesde distribution qui correspond à ces besoins sont des structures à fibreoptique, laquelle permet une transmission à faibles pertes et à haute bande passante.On parle de l’approche "radio-sur-fibre" (en anglais, radio-over-fiber). Laproblématique est de pouvoir générer et moduler un signal aux fréquences millimétriqueslors de la transmission optique - et ce avec des composant bas coûts.La technique utilisée dans le cadre de cette thèse est l’emploi des diodes laser àverrouillage de modes. Ces derniers vont pouvoir générer des hautes fréquencestout en ne nécessitant qu’une alimentation continue, et ils peuvent être modulésde manière directe ou externe. Les lasers à semi-conducteurs employés ici sontd’une génération encore à l’état d’étude puisqu’il s’agit des lasers à boites (ouîlots) quantiques. Ces lasers ont montrés de très bonnes capacités à générer dessignaux électriques aux fréquences autour de 60 GHz, bien qu’ayant encore, pourl’instant, à une stabilité de fréquence (ou de phase) limitée. Dans le cadre des systèmesde communication opto/micro-ondes, peu de travaux approfondis ont étémenés sur ces structures.Au cours de cette thèse, plusieurs études ont été effectuées. La première portesur les propriétés générales d’un système construit à partir de ce type de laser(puissances disponibles, figure de bruit, linéarité etc.). Une deuxième étude aété consacrée aux effets de la propagation des signaux dans les systèmes baséssur les lasers à verrouillage de modes, notamment de la dispersion chromatiquelaquelle a un effet considérable sur les distances de transmission. Les deux étudesmettent en avant l’importance d’une limitation du nombre de modes générés parla diode laser afin d’optimiser non seulement le gain du lien et la puissance RFrécupérée, mais aussi la figure de bruit du système. Lors d’une troisième étude, lastabilité en fréquence/phase s’est révélée critique, car le bruit de fréquence/phaselimite la qualité de la transmission en introduisant un plancher d’erreur mêmepour des rapports signal-a-bruit très élevés. Des différentes générations de lasersà boites (îlots) quantiques et à verrouillage de modes ont été testées. Le problèmedu bruit de fréquence et de phase persiste et ne peut pas être résolu en utilisantles techniques classiques comme les boucles à verrouillage de phase conventionnelles.Une solution pour ce problème a été développée pour les systèmes detransmission; elle permet simultanément un ajustement de fréquence supérieure(précision de quelques Hz à quelques kHz) à celle donnée par le processus de fabricationdes diodes lasers (précision de quelques GHz), ainsi qu’une stabilisationde fréquence et de phase. / This dissertation is related to the search for an economically sustainable solutionfor high data rate (several Gbps to several tens of Gbps) personal area networksoperating in the millimeter-wave region around 60 GHz. If such networks supplya large number of users, they need to encompass a multitude of antenna pointsin order to assure wireless access to the network. With the aim of reducing thecost of an antenna module, the networks should at best provide quasi "readyto-radiate" signals to the modules, i.e. at millimeter-wave carrier frequencies.Thanks to their low transmission loss and their high bandwidth, optical fiber distributionarchitectures represent a promising solution. The technique is referredto as the so-called "radio-over-fiber" approach whereby the analog radio signalwill be transported to the access point by an optical wave. The challenge herebyis the generation and modulation of an optical signal by a millimeter-wave radiosignal using preferably cost-efficient system components. The technique proposedherein is based on the use of mode-locked laser diodes which can generatesignals at very high frequencies under the condition of continuous current supply.Mode-locked laser diodes can be modulated both directly and externally. Thediodes employed in this work are based on so-called quantum dots (or quantumdashes); these are material structures which are themselves still subject to intensivephysical research. Signals at millimeter-wave frequencies (around 60 GHz)can easily be generated by such lasers. However, their frequency and phase stabilityis as yet limited. In the context of radio-over-fiber communication systems,these structures have not yet been studied in detail.In the course of this dissertation, several aspects are considered. A first systemstudy treats the basic properties of a system built from this type of laser source(available signal power, system noise figure, linearity etc.). A second study isdevoted to an investigation of propagation effects like dispersion, which considerablyinfluence the attainable transmission distances. An essential result of bothstudies is the importance of limiting the laser spectrum to a small number of lasermodes for an optimization of link gain, generated RF power, and system noisefigure. A third study deals with the limited frequency and phase stability whichturn out to be critical factors for transmission quality. The study of several generationsof quantum dot/dash lasers has revealed that the problems of frequencyand phase noise persist and cannot be solved using classical techniques involvinge.g. conventional phase-locked loops. In this dissertation, a solution is presentedwhich not only allows a more precise adjustment of the laser frequency (precisionin the order of Hz to kHz) than that given by the manufacturing process of thelaser (precision in the order of GHz), but also enables a stabilization of frequencyand phase. / Die vorliegende Dissertation steht im Zusammenhang mit der Suche nach wirtschaftlichtragfähigen Lösungen zum Aufbau hochdatenratiger Heimnetzwerke(einige Gbps bis einige zehn Gbps), so genannter Personal area-Netzwerke imMillimeterwellenbereich um 60 GHz. Sollen diese Netze eine große Anzahl vonNutzern versorgen, wird eine Vielzahl von Zugangspunkten - also Antennenmodulen- benötigt, um den drahtlosen Netzanschluss zu ermöglichen. Um dieKosten eines Antennenmoduls soweit wie möglich zu senken, sollen die Netzequasi "abstrahlfertige" Signale an die Module liefern, d. h. auf Trägerfrequenzenim Millimeterwellenbereich. Glasfaserbasierte Verteilsysteme werden dankihrer geringen Leitungsverluste und ihrer hohen Bandbreite diesem Anspruchgerecht. Man spricht hier vom so genannten Radio-over-fiber-Ansatz, wobei dasanaloge Signal von einer optischen Welle zum Zugangspunkt transportiert wird.Die Herausforderung liegt hierbei in der Generierung und Modulation eines optischenSignals mit einem Nutzsignal imMillimeterwellenbereich - und das unterVerwendung möglichst kostengünstiger Komponenten. Die hier vorgeschlageneTechnik basiert auf der Nutzung von modengekoppelten Laserdioden, welcheallein bei Gleichstromversorgung Signale bei hohen Frequenzen erzeugen undsowohl direkt als auch extern moduliert werden können. Die Dioden, welche hierzur Verwendung kommen, basieren auf so genannten Quantenpunkten (englisch:quantum dot/quantum dash); es sind Strukturen, die selbst noch Gegenstand intensiverphysikalischer Forschung sind. Signale bei Frequenzen um 60 GHz könnenleicht von diesen Lasern erzeugt werden, wenn auch bisher nur bei begrenzterFrequenz- und Phasenstabilität. Im Kontext von Radio-over-fiber-Systemenwurden diese Strukturen noch nicht untersucht.Im Rahmen dieser Dissertation wurden mehrere Aspekte betrachtet. Eine ersteSystemstudie behandelt die grundlegendenEigenschaften eines Systems, welchesauf dieser Art von Lasern basiert (verfügbare Leistung, Rauschzahl, Linearitätusw.). Eine zweite Untersuchung ist der Erforschung von Ausbreitungseffektenwie etwa Dispersion gewidmet, welche die erreichbaren Entfernungen maßgeblichbeeinflusst. Ein wesentliches Ergebnis beider Studien ist die Relevanzeiner Begrenzung des Laserspektrums auf wenige Moden zur Optimierung vonGewinn, Hochfrequenz-Leistung und Rauschzahl. Eine dritte Studie untersuchtdie Frequenz-und die Phasenstabilität, welche sich als kritisch für die Übertragungsqualitäterweisen. Die Untersuchung von mehreren Generationen von modengekoppeltenQuantenpunktlasern hat ergeben, dass das Problem des FrequenzundPhasenrauschens fortbesteht und nicht auf konventionellem Weg wie z.B.durch die Verwendung von klassischen Phasenregelkreisen gelöst werden kann.Im Rahmen der Arbeit wurde eine Lösung für dieses Problem gefunden, welcheerstens eine bessere Feineinstellung der Frequenz erlaubt (Genauigkeit von Hzbis kHz), als sie durch den Laserfertigungsprozess gegeben ist (Genauigkeit vonGHz), und zweitens eine Stabilisierung von Frequenz und Phase ermöglicht.
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Optical WDM Systems for Multi-point Distribution of Hybrid Signals in Phased Array Radar ApplicationsMeena, D January 2015 (has links) (PDF)
Photonics and Optical techniques have advanced recently by a great extend to play an important role in Microwave and Radar applications. Antenna array of modern active phased array radars consist of multiple low power transmit and receive mod- ules. This demands distribution of the various Local Oscillator(LO) signals for up conversion of transmit signals and down conversion of receive signals during various modes of operation of a radar system. Additionally, these receivers require control and clock signals which are digital and low frequency analog, for the synchronization between receive modules.
This is normally achieved through RF cables with complex distribution networks which add significantly higher additional weight to the arrays. During radar operations, radio frequency (RF) transmit signal needs to be distributed through the same modules which will in turn get distributed to all antenna elements of the array using RF cables. This makes the system bulky and these large number of cables are prone to Electromagnetic Interference (EMI) and need additional shielding. Therefore it is very desirable to distribute a combination of these RF, analog and digital signals using a distribution network that is less complex, light in weight and immune to EMI.
Advancements in Optical and Microwave photonics area have enabled carrying of higher datarate signals on a single fiber due to its higher bandwidth capability including RF signals. This is achieved by employing Wavelength Division Multi- plexing (WDM) that combine high speed channels at different wavelengths. This work proposes, characterizes and evaluates an optical Wavelength Division Multiplexed(WDM) distribution network that will overcome the above mentioned problems in a phased array radar application. The work carries out a feasibility analysis supported with experimental measurements of various physical parameters like am- plitude, delay, frequency and phase variation for various radar waveforms over WDM links.
Different configurations of optical distribution network are analyzed for multipoint distribution of both digital and RF signals. These network configurations are modeled and evaluated against various parameters that include power level, loss, cost and component count. A configuration which optimizes these parameters based on the application requirements is investigated. Considerable attention is paid to choose a configuration which does not provide excess loss, which is economically viable, compact and can be realized with minimum component count.
After analysing the link configuration, multiplexing density of the WDM link is considered. In this work, since the number of signals to be distributed in radar systems are small, a coarse WDM(CWDM) scheme is considered for evaluation. A comparative study is also performed between coarse and dense WDM (DWDM) links for selection of a suitable multiplexing scheme. These configurations are modeled and evaluated with power budgeting. Even though CWDM scheme does not permit the utilisation of the available bandwidth to the fullest extent, these links have the advantage of having less hardware complexity and easiness of implementation.
As the application requires signal distribution to thousands of transmit-receive modules, amplifiers are necessary to compensate for the reduction of signal level due to the high splitting ratio. Introduction of commonly available optical amplifiers like Erbium Doped Fiber Amplifier (EDFA), affect the CWDM channel output powers adversely due to their non-flat gain spectrum. Unlike DWDM systems, the channel separation of CWDM systems are much larger causing significantly high channel gain differences at the EDFA output. So an analysis is carried out for the selection of a suitable wavelength for CWDM channels to minimize the EDFA output power variation. If the gain difference is still significant, separate techniques needs to be implemented to flatten the output power at the antenna end. A CWDM configuration using C-band and L-band EDFAs is proposed and is supported with a feasibility analysis.
As a part of evaluation of these links for radar applications, a mathematical model of the WDM link is developed by considering both the RF and digital sig- nals. A generic CWDM system consisting of transmitters, receivers, amplifiers, multiplexers/ demultiplexers and detectors are considered for the modeling. For RF signal transmission, the transmitters with external modulators are considered. Mod- eling is done based on a bottom-top approach where individual component models are initially modeled as a function of input current/power and later cascaded to obtain the link model. These models are then extended to obtain the wavelength dependent model ( spectral response) of the hybrid signal distribution link
Further mathematical analysis of the developed link model revealed its variable separable nature in terms of the input power and wavelength. This led to significant reduction in the link equation complexity and development of some approximation techniques to easily represent the link behavior. The reduced form of the link spectral model was very essential as the initially developed wavelength model had a lot
of parametric dependency on the component models. This mathematical reduction
process led to simplification of the spectral model into a product of two independent
functions, the input current and wavelength. It is also noticed that the total link
power within specific wavelength range can be obtained by the integrating these
functions over a specific link input power.
After the mathematical modelling, an experimental prototype physical link is
set up and characterized using various radar signals like continuous wave (CW) RF,
pulsed RF, non linear frequency modulated signal (NLFM) etc. Additionally a proof
of concept Radio-Over-Fiber (RoF) link is established to prove the superior transmission
of microwave signal through an optical link. The analysis is supported with
measurements on amplitude, delay, frequency and phase variations. The NLFM
waveforms transmissions are further analysed using a matched _ltering process to
confirm the side lobe requirement. Further a prototype WDM link is built to study
the performance when digitally modulated channels are also multiplexed into the
link. The link is again validated for signal levels, delay, frequency and phase parameters.
Since amplitude and delay are deterministic, it is proposed that these parameter variations can be compensated by using suitable components either in the electrical or the optical domain.
Radar systems use low frequency digital signals of different duty-cycles for synchronization and control across various transmit-receive modules. In the proposed
link, these digital signals also modulate a WDM channel and hence the link is called
a hybrid system. As the proposed link has EDFA to compensate for the splitting
losses, there are chances of transient effects at the EDFA output for these low bitrate channels. Owing to the long carrier lifetime, low bitrate digital channels are prone
to EDFA transient effects under specific signal and pump power conditions. Additionally, the synchronization signals used in radar application vary the duty-cycle
over time, which is found to introduce variations in transient output. This practical challenge is further studied and the thesis for the first time, includes an analysis of EDFA transient e_ects for variable duty-cycle pulsed signals. The analysis is carried out for various parameters like bitrate, input power, pump power and duty-cycle.
Investigations on EDFA transients on variable duty-cycle signals help in proposing
a viable method to predict the lower duty-cycle transients from higher duty-cycle
transients. The predicted transients were again validated against simulated transients
and experimental results. As these transient effects are not desirable for radar
signals, we propose a novel transient suppression techniques in optical and electrical domain which are validated with simulation and experimental measures.
One suppression technique tries to avoid transient effect by keeping the optical input to EDFA always constant by feeding an inverted version of the original pulse into the EDFA along with the actual pulse. It is observed that as the wavelength of the
inverted pulse is closer to the original input pulse, the transient effect settles faster.
These EDFA transients are evaluated with WDM link configurations, where both
high and low bitrate signals are co-propagated.
Another challenging aspect of the link operation is the non-at gain spectrum
of EDFA. i.e., EDFA provides unequal power level for various signals at WDM
link output. This is especially true in the case of local oscillator signals, where
it is preferable to have the same amplitude signals before feeding it to the mixer
stages. But in the radar applications, this will require additional hardware circuits
to equalize the signal level within a phased array antenna. This work also proposes
some of the power equalization methods that can be used along with the WDM links.
This part of the work is also supported with simulation model and experimental
results.
The analytical and experimental study of this thesis aids the evaluation process
of a suitable optical Wavelength Division Multiplexed(WDM) distribution network
that can be used for the distribution of both RF and digital signals. The optical
WDM links being superior with its light weight, less loss and EMI/ EMC immunity
provides a better solution to future class of radars.
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