The performance of fused fiber couplers is wavelength dependent. Wavelength spectral compensation is a technique to decrease the effect of the wavelength dependence, which is an essential task for many applications in fiber optic communication systems. Fiber devices such as wavelength-flattened couplers (WFCs) can be fabricated using wavelength spectral compensation methods. In this dissertation, wavelength spectral compensation techniques in fused biconical taper (FBT) couplers including both multimode and single-mode fiber couplers are studied in detail. In multimode fiber coupler operation, a novel theoretical model based on frustrated total internal reflection (FTIR) has been developed to effectively describe the power coupling and loss mechanism. Experimental results support the theoretical predictions. In single-mode fiber couplers, the conventional technique of fabricating WFCs is discussed. An alternative analytical model has been developed based upon coupled mode theory, which provides a relatively simple and mathematically sound explanation to the wavelength spectral compensation. Aiming to simplify WFC fabrication, a new way of constructing WFCs is proposed and demonstrated by connecting regular single-mode fiber couplers, some of which serve as wavelength spectral compensators. WFCs of various structures including 2x2, 1x3, 1x2ᴺ, and 4x4 have been developed, and the experimental data agree with theoretical predictions of performance. Potential applications and future research directions in wavelength spectral compensation are also presented. / Ph. D.

The growing demand for faster connection to the Internet service and wireless multimedia applications has motivated the development of broadband wireless access technologies in recent years. WiMAX has enabled convergence of mobile and fixed broadband networks through a common wide-area radio-access technology and flexible network architecture. Scheduling is a fundamental component in resource management in WiMAX networks and plays the main role in meeting QoS requirements such as delay, throughput and packet loss for different classes of service. In this dissertation work, the performance of uplink schedulers at the fixed WiMAX MAC layer has been considered, we proposed an Adaptive Hierarchical Weighted Fair Queuing Scheduling algorithm, the new scheduling algorithm adapts to changes in traffic, at the same time; it is able to heuristically enhance the performance of WiMAX network under most circumstances. The heuristic nature of this scheduling algorithm enables the MAC layer to meet the QoS requirements of the users. The performance of this adaptive WiMAX Uplink algorithm has been evaluated by simulation using MATLAB. Results indicate that the algorithm is efficient in scheduling the Base Stations’ traffic loads, and improves QoS. The utilization of relay stations is studied and simulation results are compared with the case without using relay stations. The results show that the proposed scheduling algorithm improves Quality of Service of WiMAX system. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Gee-Kung Chang; Committee Co-Chair: Jianjun Yu; Committee Member: John A. Buck; Committee Member: Joy Laskar; Committee Member: Umakishore Ramachandran; Committee Member: Ye Li

No description available.

Orientador: Yuzo Iano / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-24T09:55:18Z (GMT). No. of bitstreams: 1 Mesquita_OdairdosSantos_M.pdf: 8376051 bytes, checksum: 11a0307915c4b7e7e94393ba4f65c532 (MD5) Previous issue date: 2013 / Resumo: Nos últimos anos houve uma evolução das redes de telecomunicações no Brasil. A implantação de redes de fibra óptica tornou-se uma realidade dos centros urbanos bem como nas áreas rurais. Com a expansão dessas redes observa-se o surgimento e a necessidade de normatização das redes ópticas passivas. Entre essas redes passivas destaca-se a EPON (Ethernet Passive Optical Network) e a GPON (Gigabit-Capable Passive Optical Network). Com a expansão de redes de banda larga e de novos serviços ligados a ela, torna-se necessário a realização de estudos detalhados sobre a viabilidade técnica econômica e de aplicabilidade dessas redes. É por isso que desenvolvemos nesse trabalho um modelamento econômico financeiro sobre essas novas tecnologias. Esse modelamento permite escolher a tecnologia economicamente mais viável na implantação de projetos envolvendo as tecnologias GPON e/ou EPON. Esse projeto é baseado em um estudo de caso para um município do interior de São Paulo, Brasil. Durante o estudo realizamos um planejamento técnico econômico detalhado visando uma eventual implantação de uma dessas redes. Foi feita uma apresentação completa dessas tecnologias baseada no estudo de caso. Foi discutida a possibilidade de implantar esse projeto na cidade escolhida do interior de São Paulo ou em qualquer outra cidade brasileira / Abstract: In recent years there has been an evolution of telecommunications networks in Brazil. The implementation of fiber-optic networks has become a reality of urban centers and rural areas. With the expansion of these networks, we observed the emergence and the need for standardization of these passive optical networks. Among these networks, there are the EPON (Ethernet Passive Optical Network) and GPON (Gigabit-Capable Passive Optical Network). With the expansion of broadband networks and new services linked to them, it becomes necessary to conduct detailed studies of the technical and economic applicability of these networks. We developed in this project a careful financial economic modeling on these new technologies. This modeling technique allows choosing the best of these technologies (GEPON/EPON) and the one that is economically feasible. This project is based on a case study for the city of São Paulo, Brazil. During the study, we performed a detailed techno-economic planning aimed an eventual implementation of any of these networks. A complete presentation of these technologies was done based on this case study. It was also discussed the possibility of implementing this project in the chosen city of São Paulo or any other Brazilian city / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

While the capacity of multiple-input multiple-output (MIMO) systems has been explored in considerable detail, virtually all literature on this topic ignores electromagnetic considerations. This dissertation explores electromagnetic effects on the capacity performance of these multi-antenna architectures. Specifically, it examines the impact of superdirectivity for compact antenna arrays, the effect of antenna mutual coupling, and MIMO performance of multi-mode optical fiber with non-linear detection. Superdirectivity can lead to abnormally large capacity bounds in a MIMO communication system, especially when the antennas are placed close together. Because superdirective behavior is difficult to achieve in practice, this work formulates an approach for limiting the impact of superdirectivity by introducing finite ohmic loss into the capacity expressions. Results show that even a small amount of ohmic loss significantly affects the achievable system capacity and suppresses superdirective solutions. This formulation allows a more detailed examination of the capacity of MIMO systems for compact arrays. For channels which do not vary in time, placing antennas closer together generally reduces the system capacity. However, recent work has demonstrated that for a MIMO system operating in a fast fading environment where the transmitter and receiver know the channel covariance information, the capacity increases as antennas are placed near each other due to an increase in spatial correlation. Analysis of this behavior illustrates that when these capacity gains (due to closely spaced antennas) are observed the radiated power is also increased. Constraining the radiated power leads to superdirective solutions in which the ohmic loss constraint developed must be used to properly determine the capacity behavior of this system. Application of this constraint then leads to an optimum antenna spacing in contrast to the findings of previous research which indicate that antennas should be as close together as possible. Additionally, this section provides an analysis regarding the number of spatial modes that can be used for various system configurations. Recent research has shown that it is possible for MIMO communication techniques to be used with multimode optical fibers to increase the available distance-bandwidth. However, implementation of traditional MIMO schemes requires the use of coherent optical detection which can lead to high system complexity and cost. This dissertation proposes a multimode fiber MIMO system architecture which allows simultaneous transmission of unique streams to different users on the same fiber while using incoherent detection with amplitude and phase modulation at the transmitter. The resulting capacity scales nearly linearly with the number of transmitters and receivers. Because the architecture requires channel state information at the transmitter, a training scheme appropriate for use with optical intensity detection is also discussed.

Optical packet switching (OPS) is one of the more promising solutions for meeting the diverse needs of broadband networking applications of the future. By virtue of its small data traffic granularity as well as its nanoseconds switching speed, OPS can be used to provide connection-oriented or connectionless services for different groups of users with very different networking requirements. The optical buffer and the switch fabric are two of the most important components in an OPS router. In this research, novel designs for the optical buffer and switch fabric are proposed and experimentally demonstrated. In particular, an optical buffer that is based on a folded-path delay-line tree architecture will be discussed. This buffer is the most compact non-recirculating optical delay line buffer to date, and it uses an array of high-speed ON-OFF optical reflectors to dynamically reconfigure its delay within several nanoseconds. A major part of this research is devoted to the design and performance optimization of these high-speed reflectors. Simulations and measurements are used to compare different reflector designs as well as to determine their optimal operating conditions. Another important component in the OPS router is the switch fabric, and it is used to perform space switching for the optical packets. Optical switch fabrics are used to overcome the limitations imposed by conventional electronic switch fabrics: high power consumption and dependency on the modulation format and bit-rate of the signals. Currently, only those fabrics that are based on the broadcast-and-select architecture can provide truly non-blocking multicast services to all input ports. However, a major drawback of these fabrics is that they are implemented using a large number of optical gates based on semiconductor optical amplifiers (SOA). This results in large component count and high energy consumption. In this research, a new multicast-capable switch fabric which does not require any SOA gates is proposed. This fabric relies on a passive all-optical gate that is based on the Four-wave mixing (FWM) wavelength conversion process in a highly-nonlinear fiber. By using this new switch architecture, a significant reduction in component count can be expected.

The central objective of this thesis is to suggest and develop one simple, unified method for communication over optical fiber networks, valid for all values of dispersion and nonlinearity parameters, and for a single-user channel or a multiple-user network. The method is based on the nonlinear Fourier transform (NFT), a powerful tool in soliton theory and exactly solvable models for solving integrable partial differential equations governing wave propagation in certain nonlinear media. The NFT decorrelates signal degrees of freedom in such models, in much the same way that the Fourier transform does for linear systems. In this thesis, this observation is exploited for data transmission over integrable channels such as optical fibers, where pulse propagation is governed by the nonlinear Schr\"odinger (NLS) equation. In this transmission scheme, which can be viewed as a nonlinear analogue of orthogonal frequency-division multiplexing commonly used in linear channels, information is encoded in the nonlinear spectrum of the signal. Just as the (ordinary) Fourier transform converts a linear convolutional channel into a number of parallel scalar channels, the nonlinear Fourier transform converts a nonlinear dispersive channel described by a \emph{Lax convolution} into a number of parallel scalar channels. Since, in the spectral coordinates the NLS equation is multiplicative, users of a network can operate in independent nonlinear frequency bands with no deterministic inter-channel interference. Unlike most other fiber-optic transmission schemes, this technique deals with both dispersion and nonlinearity directly and unconditionally without the need for dispersion or nonlinearity compensation methods. This thesis lays the foundations of such a nonlinear frequency-division multiplexing system.

The central objective of this thesis is to suggest and develop one simple, unified method for communication over optical fiber networks, valid for all values of dispersion and nonlinearity parameters, and for a single-user channel or a multiple-user network. The method is based on the nonlinear Fourier transform (NFT), a powerful tool in soliton theory and exactly solvable models for solving integrable partial differential equations governing wave propagation in certain nonlinear media. The NFT decorrelates signal degrees of freedom in such models, in much the same way that the Fourier transform does for linear systems. In this thesis, this observation is exploited for data transmission over integrable channels such as optical fibers, where pulse propagation is governed by the nonlinear Schr\"odinger (NLS) equation. In this transmission scheme, which can be viewed as a nonlinear analogue of orthogonal frequency-division multiplexing commonly used in linear channels, information is encoded in the nonlinear spectrum of the signal. Just as the (ordinary) Fourier transform converts a linear convolutional channel into a number of parallel scalar channels, the nonlinear Fourier transform converts a nonlinear dispersive channel described by a \emph{Lax convolution} into a number of parallel scalar channels. Since, in the spectral coordinates the NLS equation is multiplicative, users of a network can operate in independent nonlinear frequency bands with no deterministic inter-channel interference. Unlike most other fiber-optic transmission schemes, this technique deals with both dispersion and nonlinearity directly and unconditionally without the need for dispersion or nonlinearity compensation methods. This thesis lays the foundations of such a nonlinear frequency-division multiplexing system.

Three 40/60-GHz optical-wireless bidirectional architectures are designed with a centralized light source in the central office based on wavelength reuse. Three super-broadband access networks are proposed and experimentally demonstrated for simultaneously delivering wired and wireless services over an optical fiber and an air link in a single transport platform. The transport feasibility in metro and wide-area access networks with multiple reconfigurable optical add-drop multiplexers (ROADMs) nodes is explored for 40-GHz and 60-GHz optical millimeter-wave signals. Additionally, the optical-wireless systems using the orthogonal frequency division multiplexing (OFDM) modulation format are analytically and experimentally demonstrated to mitigate the chromatic dispersion in optical fiber. This thesis also successfully implements the testbed trial for the delivery of uncompressed 270-Mb/s standard-definition television (SDTV) and 1.485-Gb/s high-definition television (HDTV) video signals over optical fiber and air links. The demonstration represents the first ever reported real applications over hybrid wired and wireless access networks, showing that our developed up-conversion schemes and designed architectures are highly suitable for super-broadband applications in next-generation optical-wireless access networks.