Dissertations / Theses on the topic 'Fiber-optic communication system'

In this dissertation the performance of a novel variant of a return-to-zero (RZ) modulation format, based on square-wave phase modulation and filtering of a continuous-wave (CW) signal, is investigated and compared with various modulation formats considered in the literature. We call this modulation format continuous-wave square-wave (CWSW). With CWSW an RZ pulse train is generated by phase modulating the CW signal by a periodic square-wave phase function having an amplitude of and frequency of half the bit rate, and then filtering the signal. The filter performs phase-to-amplitude conversion, resulting in an alternate-sign RZ pulse train, which is shown to be resistant to fiber dispersion. The alternate-sign RZ pulse train is then amplitude modulated with the data before the transmission. Alternate signs between adjacent pulses makes this signal format robust to impairments caused by the optical fiber, similar to a conventional alternate-sign RZ signal format. However, the unique property of the CWSW signal format is that individual pulses can induce peak intensity enhancement (PIE), a phenomenon by which the peak of a pulse increases during the initial propagation in the presence of dispersion. The PIE in effect delays the decrease in the pulse peak, which represents the signal level for bit 1. Thus, the eye opening at the receiver is improved. An analytically tractable model is developed to explain the occurrence of the PIE, which cannot be achieved with a conventional pulse shape. The sources of performance degradations for different modulation formats in single-channel 40 Gb/s systems are also discussed in this dissertation. Various transmission system configurations of practical interest are considered and the performance of CWSW is compared with alternative modulation formats. It is found that the CWSW signal format performs significantly better than the other considered modulation formats in systems not employing dispersion compensation and is comparable to the others in dispersion-managed systems. Furthermore, the transmitter configuration of the CWSW signal format is simpler than the other approaches.
Ph. D.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 2004.
Thesis advisor(s): Gamani Karunasiri, Xiaoping Yun. Includes bibliographical references (p. 47-50). Also available online.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California
This paper discusses the conversion of an existing telemetry system to the use of fiber optic communications. The change was implemented to provide expanded capabilities of existing capital assets with a minimum of investment. The paper reviews the design constraints and options considered for a specific flight test program. The different options, such as fiber type, connector type, wavelength, bit rate, and encoding method, are compared and discussed as to their applicability, reliability, and cost effectiveness in a telemetry environment. The paper discusses the solution selected and the capabilities of the final design, as compared to the initial system.

Doutoramento em Fisica
In this thesis we perform a detailed analysis of the state of polarization (SOP) of light scattering process using a concatenation of ber-coil based polarization controllers (PCs). We propose a polarization-mode dispersion (PMD) emulator, built through the concatenation of bercoil based PCs and polarization-maintaining bers (PMFs), capable of generate accurate rst- and second-order PMD statistics. We analyze the co-propagation of two optical waves inside a highbirefringence ber. The evolution along the ber of the relative SOP between the two signals is modeled by the de nition of the degree of co-polarization parameter. We validate the model for the degree of co-polarization experimentally, exploring the polarization dependence of the four-wave mixing e ect into a ber with high birefringence. We also study the interaction between signal and noise mediated by Kerr e ect in optical bers. A model accurately describing ampli ed spontaneous emission noise in systems with distributed Raman gain is derived. We show that the noise statistics depends on the propagation distance and on the signal power, and that for distances longer than 120 km and signal powers higher than 6 mW it deviates signi catively from the Gaussian distribution. We explore the all-optical polarization control process based on the stimulated Raman scattering e ect. Mapping parameters like the degree of polarization (DOP), we show that the preferred ampli cation of one particular polarization component of the signal allows a polarization pulling over a wavelength range of 60 nm. The e ciency of the process is higher close to the maximum Raman gain wavelength, where the DOP is roughly constant for a wavelength range of 15 nm. Finally, we study the polarization control in quantum key distribution (QKD) systems with polarization encoding. A model for the quantum bit error rate estimation in QKD systems with time-division multiplexing and wavelength-division multiplexing based polarization control schemes is derived.
Nesta tese realizamos uma análise detalhada do processo de espalhamento do estado de polarização (SOP) da luz, obtido através da concatenação de vários controladores de polarização (PCs) baseados no enrolamento de fibra ótica. E proposto um emulador de dispersão dos modos de polarização (PMD), construído através da concatenação de PCs e fibras que mantêm a polarização, capaz de gerar corretamente a estatística da PMD de primeira e segunda ordens. Analisamos ainda a copropagação de dois feixes de luz em fibras de elevada birrefringencia. A evolução ao longo da fibra do SOP relativo entre os dois feixes de luz é modelada através da definição do parâmetro grau de copolarização. O modelo e validado experimentalmente, explorando a dependência na polarização do efeito de mistura de quatro ondas em fibras de elevada birrefringência. Estudamos também a interação sinal ruído mediada pelo efeito de Kerr em fibras óticas. É derivado um modelo que descreve o ruído gerado pela emissão espontânea amplificada em sistemas com ganho de Raman distribuído. Mostramos que a estatística do ruído varia com a distância de propagação e com a potencia do sinal, e que para distâncias superiores a 120 km e potências do sinal maiores que 6 mW esta deixa de ser descrita por uma distribuição Gaussiana. Analisamos o processo de controlo totalmente ótico da polarização baseado no efeito de espalhamento de Raman estimulado. Através do mapeamento do grau de polarização (DOP), mostramos que a amplificação preferencial de uma componente do sinal permite uma atração do SOP num intervalo de comprimentos de onda igual a 60 nm. A eficiência do processo é mais elevada em torno do comprimento de onda de ganho de Raman máximo, onde existe um intervalo de 15 nm para o qual o DOP tem valores praticamente constantes. Finalmente, fazemos um estudo do controlo do SOP em sistemas de distribuição de chaves quânticas (QKD) com codificação na polarização. E derivado um modelo que permite estimar a taxa de erro quântica em sistemas de QKD com esquemas de controlo do SOP baseados na multiplexagem no comprimento de onda e na multiplexagem no domínio temporal.

The presence of low frequency cutoffs in the forward path of the information signal leads to inter-symbol interference (ISI) and degradation of the signal to noise ratio at the sampling instant in digital on-off keying (OOK) systems. The low frequency cutoffs occur as a result of the presence of power separation filters in a line wire system and gain instability of APDâ s to D.C. in fiber optic systems. Also, it is easier to design amplifiers that do not extend to D.C. The ISI which manifests itself in the form of baseline wander can cause appreciable degradation in the signal to noise ratio. This thesis investigates two ways of combating the baseline wander problem. They are quantized feedback and line coding schemes. A detailed performance evaluation of quantized feedback scheme is performed. An overview of line coding schemes is given and some specific codes are evaluated in terms of S/N degradation at the receiver.
Master of Science

Future parallel computer systems for embedded real-time applications,where each node in itself can be a parallel computer, are predicted to havevery high bandwidth demands on the interconnection network. Otherimportant properties are time-deterministic latency and guarantees to meetdeadlines. In this thesis, a fiber-optic passive optical star network with amedium access protocol for packet switched communication in distributedreal-time systems is proposed. By using WDM (Wavelength DivisionMultiplexing), multiple channels, each with a capacity of several Gb/s, areobtained.

A number of protocols for WDM star networks have recently been proposed.However, the area of real-time protocols for these networks is quiteunexplored. The protocol proposed in this thesis is based on TDMA (TimeDivision Multiple Access) and uses a new distributed slot-allocationalgorithm with real-time properties. Services for both guarantee-seekingmessages and best-effort messages are supported for single destination,multicast, and broadcast transmission. Slot reserving can be used toincrease the time-deterministic bandwidth, while still having an efficientbandwidth utilization due to a simple slot release method.

By connecting several clusters of the proposed WDM star network by abackbone star, thus forming a star-of-stars network, we get a modular andscalable high-bandwidth network. The deterministic properties of thenetwork are theoretically analyzed for both intra-cluster and inter-clustercommunication, and computer simulations of intra-cluster communicationare reported. Also, an overview of high-performance fiber-opticcommunication systems is presented.

Parallel and distributed computing systems become more and more powerful and hence place increasingly higher demands on the networks that interconnect their processors or processing nodes. Many of the applications running on such systems, especially embedded systems applications, have real-time requirements and, with increasing application demands, high-performance networks are the hearts of these systems. Fiber-optic networks are good candidates for use in such systems in the future. This thesis contributes to the relatively unexplored area of fiber-optic networks for parallel and distributed real-time computer systems and  suggests and evaluates several fiber-optic networks and protocols. Two different technologies are used in the networks, WDM (Wavelength Division Multiplexing) and fiber-ribbon point-to-point links. WDM offers multiple channels, each with a capacity of several Gbit/s. A WDM star network in which protocols and services are efficiently integrated to support different kinds of real-time demands, especially hard ones, has been developed. The star-of-stars topology can be chosen to offer better network scalability. The WDM star architecture is attractive but its future success depends on components becoming more commercially mature. Fiber-ribbon links, offering instead an aggregated bandwidth of several Gbit/s, have already reached the market with a promising price/performance ratio. This has motivated the development and investigation of two new ring networks based on fiber-ribbon links. The networks take advantage of spatial bandwidth reuse, which can greatly enhance performance in applications with a significant amount of nearest downstream neighbor communication. One of the ring networks is control channel based and not only has support for real-time services like the WDM star network but also low level support for, e.g., group communication. The approach has been to develop network protocols with support for dynamic real-time services, out of time-deterministic static TDMA systems. The focus has been on functionality more than pure performance figures, mostly on real-time features but also on other types of functionality for parallel and distributed systems. Worst-case analyses, some simulations, and case studies are reported for the networks. The focus has been on embedded supercomputer applications, where each node itself can be a parallel computer, and it is shown that the networks are well suited for use in the radar signal processing systems studied. Other application examples in which these kinds of networks are valuable are distributed multimedia systems, satellite imaging and other image processing applications.
Technical report / School of Electrical and Computer Engineering, Chalmers University of Technology, Göteborg, Sweden, 0282-5406 ; 379

In this thesis, the optical communication systems for millimeter-scale sensing and communication devises known as "Smart Dust" are described and analyzed. A smart dust element is a self-contained sensing and communication system that can be combined into roughly a cubic-millimeter mote to perform integrated, massively distributed sensor networks. The suitable passive optical and fiber-optic communication systems will be selected for the further performance design and analysis based on the requirements for implementing these systems. Based on the communication link designs of the free-space passive optical and fiber-optic communication systems, the simulations for link performance will be performed.
Master of Science

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.
Includes bibliographical references (leaves 64-66). Also available in electronic version. Access restricted to campus users.

High-performance embedded systems communicating heterogeneous traffic with high bandwidth and strict timing requirements are in need of more efficient communication solutions. This thesis proposes two multi-wavelength passive optical networks able to meet these demands. The networks are based upon a single-hop star topology with an Arrayed Waveguide Grating (AWG) placed in the centre. The intended application areas for the two networks are short range embedded communication systems like System Area Networks (SANs) and router architectures with electronic queuing. The AWG’s attractive property of spatial wavelength reuse, as well as the combination of fixed-tuned and tuneable transceivers in the end nodes, enables simultaneous control and data traffic transmission. This, in turn, makes it possible to support heterogeneous traffic with both hard and soft real-time constraints.

Additionally, two Medium Access Control (MAC) protocols, one for each network solution, are developed. Traffic scheduling is centrally controlled by a node, the protocol processor, residing together with the AWG in a hub. All nodes use Earliest Deadline First (EDF) scheduling and communicate with the protocol processor through physical control channels. A case study, including simulations, in the field of Radar Signal Processing (RSP) and simulations using periodic real-time traffic are conducted for the two application areas respectively, showing very good results. Further, a deterministic real-time analysis is conducted to provide throughput and delay guarantees for hard real-time traffic and an increase in guaranteed traffic is achieved through an analysis of existing traffic dependencies in a multichannel network. Simulation results incorporating the traffic dependency analysis indicate a considerable increase in the possible guaranteed throughput of hard real-time traffic.

The purpose of this thesis is to investigate the effect of dispersion on a spectrum-sliced WDM (SS-WDM) system, specifically a system employing a single-mode optical fiber. The system performance is expressed in term of the receiver sensitivity defined as the average number of photon per bit N_p required for a given probability of bit error P_e. The receiver sensitivity is expressed in terms of two normalized parameters: the ratio of the optical bandwidth per channel and the bit rate m=B₀/R_b=B₀T, and the transmission distance normalized by the dispersion distance z/L_D. The former represents the effect of the excess beat noise caused by the signal fluctuation. The latter represents the effect of dispersion. The excess beat noise can be reduced by increasing the value of m (increasing the optical bandwidth B₀ for a given bit rate R_b). However, a large m implies that the degradation due to the dispersion is severe in a system employing a single-mode fiber. Therefore, there should be an optimum m resulting from the two effects. The theoretical results obtained from our analysis have confirmed this prediction. It is also shown that the optimum m (m_opt) decreases with an increase in the normalized distance. This suggests that the dispersion strongly affects the system performance. The increase in the excess beat noise is traded for the decrease in the dispersion effect. Additionally, the maximum transmission distance is relatively short, compared to that in a laser-based system. This suggests that the SS-WDM systems with single-mode fibers are suitable for short-haul systems, such as high-speed local-access network where the operating bit rate is high but the transmission distance is relatively short.
Master of Science

In this dissertation we present the research findings around two important hot topics of modern and future fiber-optic communication systems: 100 Gbit/s transmission and alloptical processing of received phase-modulated signals. The findings are discussed in the same chronological order they were obtained. Each topic is summarized in two chapters that correspond to one selected journal and one conference publications. The first and second chapters are dedicated to the simulation and numerical analysis of 100 Gbit/s systems. In chapter one, we present a thorough investigation of the best 100 Gbit/s serial modulation format. Seven different modulation formats are considered and are compared in terms of tolerance to dispersion and maximum reach for a 10⁻⁹ bit error rate target. In chapter two, the behavior of chapter one’s best candidate is analyzed in a realistic environment. The influence of the existing lower data rate neighboring channels is discussed in particular. The results of these two chapters were obtained in collaboration with engineers from the Deutsche Telekom Technology Center in Darmstadt, Germany. They served as a theoretical basis for a field trial carried out by this same company. Chapter three and four focus on the use of semiconductor optical amplifiers for all-optical processing applications. Impaired phased-modulated signals are under particular interest in this study. The novelty in this work resides in the counter-propagating configuration that the semiconductor optical amplifier is operated in. In chapter three we give a detailed description of the experimental results. The complete setup is explained and the improvement in Q-factor and bit error rate for the received signal is proven. Furthermore, two novel concepts (Photonic Balancing and Saturated Asymmetric Filtering) that explain the observed improvements are developed and discussed for the first time to the best of our knowledge. Finally, chapter four aims at optimizing numerically the experimental setup for the saturated asymmetric filtering technique. The required detuned filter after the saturated semiconductor optical amplifier is optimized in terms of both off set and bandwidth.

In this dissertation I investigated a multi-channel and multi-bit rate all-optical clock recovery device. This device, a birefringent Fabry-Perot resonator, had previously been demonstrated to simultaneously recover the clock signal from 10 wavelength channels operating at 10 Gb/s and one channel at 40 Gb/s. Similar to clock signals recovered from a conventional Fabry-Perot resonator, the clock signal from the birefringent resonator suffers from a bit pattern effect. I investigated this bit pattern effect for birefringent resonators numerically and experimentally and found that the bit pattern effect is less prominent than for clock signals from a conventional Fabry-Perot resonator.I also demonstrated photonic balancing which is an all-optical alternative to electrical balanced detection for phase shift keyed signals. An RZ-DPSK data signal was demodulated using a delay interferometer. The two logically opposite outputs from the delay interferometer then counter-propagated in a saturated SOA. This process created a differential signal which used all the signal power present in two consecutive symbols. I showed that this scheme could provide an optical alternative to electrical balanced detection by reducing the required OSNR by 3 dB.I also show how this method can provide amplitude regeneration to a signal after modulation format conversion. In this case an RZ-DPSK signal was converted to an amplitude modulation signal by the delay interferometer. The resulting amplitude modulated signal is degraded by both the amplitude noise and the phase noise of the original signal. The two logically opposite outputs from the delay interferometer again counter-propagated in a saturated SOA. Through limiting amplification and noise modulation this scheme provided amplitude regeneration and improved the Q-factor of the demodulated signal by 3.5 dB.Finally I investigated how SPM provided by the SOA can provide a method to reduce the in-band noise of a communication signal. The marks, which represented data, experienced a spectral shift due to SPM while the spaces, which consisted of noise, did not. A bandpass filter placed after the SOA then selected the signal and filtered out what was originally in-band noise. The receiver sensitivity was improved by 3 dB.

This dissertation investigates the design and performance issues of a recently demonstrated technique, termed as spectrum-slicing, for implementing wavelength-division-multiplexing (WDM) in optical fiber systems. Conventional WDM systems employ laser diodes operating at discrete wavelengths as carriers for the different data channels that are to be multiplexed. Spectrum-slicing provides an attractive low-cost alternative to the use of multiple coherent lasers for such WDM applications by utilizing spectral slices of a broadband noise source for the different data channels. The principal broadband noise source considered is the amplified spontaneous emission (ASE) noise from an optical amplifier. Each slice of the spectrum is actually a burst of noise that is modulated individually for a high capacity WDM system. The stochastic nature of the broadband source gives rise to excess intensity noise which results in a power penalty at the receiver. One way to minimize this penalty, as proposed and analyzed for the first time in this work, is to use an optical preamplifier receiver. It is shown that when an optical preamplifier receiver is used, there exists an optimum filter bandwidth which optimizes the detection sensitivity (minimizes the average number of photons/bit) for a given error probability. Moreover the evaluated detection sensitivity represents an order of magnitude ( > 10 dB) improvement over conventional PIN receiver-based detection techniques for such spectrum-sliced communication systems. The optimum is a consequence of signal energy fluctuations dominating at low values of the signal time bandwidth product (m), and the preamplifier ASE noise dominating at high values of m. Operation at the optimum bandwidth renders the channel error probability to be a strong function of the optical bandwidth, thus providing motivation for the use of forward error correction coding (FEC). System capacity (for BER = ) is shown to be 23 Gb/s without coding, and 75 Gb/s with a (255,239) Reed Solomon code. The effect of non-rectangular spectra on receiver sensitivity is investigated for both OOK and FSK transmission, assuming the system (de)multiplexer filters to be N'th order Butterworth bandpass. Although narrower filters are recommended for improving power budget, it is shown that system penalty due to filter shape may be kept < 1 dB by employing filters with N > 2. Moreover spectrum-sliced FSK systems using optical preamplifier receivers are shown, for the first time, to perform better in a peak optical power limited environment. Performance-optimized spectrum-sliced WDM systems have potential use in both local loop and long-distance fiber communication systems which require low-cost WDM equipment for high data rate applications.
Ph. D.

In recent years, a growing number of diagnostic examinations in a hospital are being generated by digitally formatted imaging modalities. The evolution of these systems has led to the development of a totally digitized imaging system, which is called Picture Archiving and Communication System (PACS). A high speed computer network plays a very important role in the design of a Picture Archiving and Communication System. The computer network must not only offer a high data rate, but also it must be structured to satisfy the PACS requirements efficiently. In this dissertation, a computer network, called PACnet, is proposed for PACS. The PACnet is designed to carry image, voice, image pointing overlay, and intermittent data over a 200 Mbps dual fiber optic ring network. The PACnet provides a data packet channel and image and voice channels based on Time Division Multiple Access (TDMA) technique. The intermittent data is transmitted over a data packet channel using a modified token passing scheme. The voice and image pointing overlay are transferred between two stations in real-time to support the consultive nature of a radiology department using circuit switching techniques. Typical 50 mega-bit images are transmitted over the image channel in less than a second using circuit switching techniques. A technique, called adaptive variable frame size, is developed for PACnet to achieve high network utilization and short response time. This technique allows the data packet traffic to use any residual voice or image traffic momentarily available due to variation in voice traffic or absence of images. To achieve optimal design parameters for network and interfaces, the PACnet is also simulated under different conditions.

The ever-increasing demands for transmission capacity are the cause for the quick evolution of optical communication systems. Channel transmission at 100 Gb/s is already being considered by network operators. The major transmission impairments at these high rates are intra-channel and inter-channel nonlinearities, nonlinear phase noise, and polarization mode dispersion. By implementing LDPC-coded modulation schemes with soft decoding and Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm for equalization we have demonstrated significant improvements in system performance experiencing several impairments simultaneously. The new turbo-equalization scheme is used as a mean to simultaneously mitigate both linear and nonlinear impairments. This approach is general and applicable to both direct and coherent detection.We provide comprehensive study of LDPC codes suitable for implementation in high-speed optical transmission systems. We determine channel capacity based on the forward step of the BCJR algorithm and show that by using LDPC codes we can closely approach the maximum transmission capacity that is possible. We propose the multilevel maximum a posteriori probability (MAP) turbo equalization scheme based on multilevel BCJR algorithm and an LDPC decoder, which considers independent symbols transmitted over both polarizations as two dimensional super-symbols. The use of multilevel modulation schemes provide higher spectral efficiency, while all related signal processing is performed at lower symbol rates, where dealing with PMD compensation and fiber nonlinearities mitigation is more manageable. We show significant improvement in system performance over a system employing an equalizer that considers symbols transmitted in different polarizations as independent.

A evolução das redes ópticas para atender o crescimento da demanda por largura de banda tem estimulado a busca por uma maior eficiência na utilização da largura de faixa disponível. O sucesso da implementação prática da técnica de acesso múltiplo por divisão de código (CDMA) em sistemas de comunicações móveis também despertou o interesse por aplicações em redes ópticas (OCDMA). Atributos únicos tais como capacidade flexível sob demanda, segurança na comunicação e alta escalabilidade, incentivaram significativamente as pesquisas. Neste contexto, este trabalho apresenta, primeiramente, uma revisão de várias configurações OCDMA propostas na literatura para qualificar e quantificar códigos válidos, com ênfase nas propriedades de correlação. Em seguida, realiza uma modelagem de sistema óptico abrangendo os subsistemas principais de geração, transmissão e recepção de sinal. O impacto das degradações, referentes à fibra óptica e aos diversos dispositivos que constituem o sistema, é então avaliado e sua influência sobre o desempenho de algumas configurações de codificação é investigado. O conhecimento da forma e das condições de manifestação destas degradações poderá servir de base ao processamento de sinal óptico à luz dos esquemas de codificação. Uma discussão sobre qualidade de serviço (QoS) e sobre flexibilização da aplicação OCDMA em sistemas de comunicação óptica também são também abordadas.
The evolution of optical networks verified in the last few years has been characterized by the search for better bandwidth utilization efficiency. The successful implementation of practical code division for multiple access techniques (CDMA) in mobile communications systems has stimulated new investigations on this topic, particularly in the optical domain (optical CDMA). This is justified due to some remarkable attributes of this technology, such flexibility in code design, capacity on demand, safety, and high scalability. In this context, this dissertation presents, initially, a comprehensive review of several code configurations for OCDMA proposed in the literature, with emphasis particularly on the correlation and users availability properties. Next, it describes the modeling of an optical system consisting of the following three subsystems: generation, transmission, and signal detection. The penalties imposed to the optical codes by the propagating medium, as well as by the devices employed in the system, are accounted for and their influence on the performance of some coding configurations is investigated. The knowledge of how and when these penalties will affect the system is crucial in optical signal processing based on codification schemes. Finally, this work also addresses some aspects related to quality of service (QoS) and flexibility of the OCDMA technology in optical communications systems.

碩士
國防大學中正理工學院
應用物理研究所
90
Because of the properties of high speed and capacity, low cost and loss, free from electromagnetic interference, and privacy protected efficiently, fiber optics is becoming a new star in wired communication systems. Today, as demand for faster data transfer speeds soars, traditional fiber optics systems, which have their own limitations fail to meet the need. The scientists have to seek new technologies for increasing the transmissive ability of fiber optic communication system. There are two key technical developments that are pushing it forward: one is the Impulse Bandwidth and the other is “wavelength division multiplexing”; the latter is the focus of this dissertation. “Dense wavelength division multiplexing” (DWDM) is a main stream to develop wavelength division multiplexing for the future. It is to narrow down the channel interval (less than 2 nm), so the current fiber optics can transmit wave band in maximum capacity. The studying methods of this dissertation are to search and collect articles related to DWDM, understand the recent technological developments, discuss and confront the probably problems that DWDM might occur, and then analyze them and compare with every possible solutions in order to catch on the evolution in the future.

碩士
國立臺灣師範大學
光電科技研究所
93
In this thesis, we provide a simple but novel solution for WDM/PolSK fiber-optic communication system. We use a 1.3 μm SOA, 1×4 channel WDM MUX/DeMUX, 90:10 2×2 fiber couplers, and 50:50 1×2 fiber couplers to form a WDM symmetric resonator laser. By combining the resonator laser and phase modulators together, we can provide a well performance multi-level WDM/PolSK light source. Besides, we design a multi-channel Stokes receiver as the polarization-state measured WDM/PolSK receiver to track the changes of the SOPs of the WDM/PolSK lightwave. By using the multi-channel Stokes receiver, we can easily observe and analysis the changes of the SOPs. Moreover, we set up a WDM/PolSK fiber-optic transmission experiment with 1Gbps signal. In this experiment, we track the SOP variation by using the multi-channel Stokes receiver. Moreover, we compare the received signal with the initial signal to see the performance of our WDM/PolSK transmission system and check the practicalities of our homemade components in the WDM/PolSK fiber-optic communication system. The proposed design of our WDM/PolSK fiber-optic transmission system can serve as another possibility for PolSK signaling for high spectral efficiency and low symbol-rate systems. We can validate this WDM/PolSK scheme as a potential solution for future high-speed modulation format.

碩士
國立臺灣大學
電子工程學研究所
92
The exploring increasing of data rate in optical networks in recent years has created a major challenge for electronic circuits used at the interface of the optical physical layer links. Historically, the optical fiber used to be considered as a perfect channel. However, as the data rate increases above Gb/s, intersymbol interference (ISI) becomes an essential issue in digital communications, limiting the achievable transmission speed and distance over fibers. Optical techniques can be used to compensate the impairments of optical fibers, with the advantage of requiring no high-speed electronic circuits. Nevertheless, electronic compensation is more flexible and economical, and may be a better choice. As to electronic compensation, digital or analog equalizers can be used. Digital (DSP based) equalization offers more accurate and higher performance comparing with analog counterpart. But the design of digital equalization has a bottleneck on the implementation of high-speed ADCs, which need large area and high power consumption. Consequently, pure analog equalizer is a more efficient solution. Among different sub-standards of 10 Gigabit Ethernet (IEEE 802.3ae), 10GBASE-LX4 particularly attracts us. Its low-cost property has a substantially economical advantage on short-haul applications such as LANs. The use of WDM and 8B/10B coding scheme on 10GBASE-LX4 leads to a data rate of 3.125 Gb/s. In this thesis, a 4-tap fractionally spaced analog FIR filter designed for 10GBASE-LX4 fiber-optic communication performs channel equalization. The continuous-time tap delay line is realized by a lumped LC ladder, providing linear and wideband characteristics. Fabricated in a standard 0.18-μm CMOS technology, the analog equalizer can successfully recover the 3.125- Gb/s random data transmitted over MMF channels while dissipating 2.3 mW from a 1.8-V power supply. Furthermore, an additional DLL is proposed to lock the tap delay time of the FIR filter, operating at 1.5625 GHz. The die sizes of two prototypes are 1.77 × 0.64 mm2 and 1.12 × 0.99 mm2, respectively.

Optical signal processing plays a key role in a high capacity all-optical communication network. Rapid advances in the processing technology offers new solutions to enhance fiber communications. This thesis focuses on the development of new components and techniques for optical signal processing.
The application of optical nonlinearities in fibers and in semiconductor devices is of great importance in different fields of research. In this thesis, we report our findings in the development of new techniques for photonic signal processing. Two different approaches for extinction ratio enhancement of an amplitude-shift keying (ASK) signal have been demonstrated using self-phase modulation in a highly nonlinear bismuth oxide fiber. The differential phase-shift keying (DPSK) modulation format is also receiving much attention owing to its improved receiver sensitivity and its higher tolerance to signal degradation by undesired fiber nonlinearities. We demonstrated all-optical processing of DPSK signals using different nonlinear phenomena in a semiconductor optical amplifiers, a dispersion-flattened highly nonlinear photonic crystal fiber, and a highly nonlinear bismuth oxide fiber. Various application areas including extinction ratio enhancement, amplitude noise reduction, phase noise reduction, wavelength conversion and wavelength multicasting have been realized using four-wave mixing, self-phase modulation, and cross-phase modulation in the optical elements. (Abstract shortened by UMI.)
The birefringent comb filter is an important element in the processing of microwave and optical signals. To increase the flexibility in its operation, it is desirable for the filter to be tunable in both the spectral position and the spacing of the comb. By incorporating an electro-optic phase modulator to control the overall birefringence, the output comb can be rapidly modulated in the spectral domain. We also introduced a new architecture of a dual-pass Lyot filter that offers the highest tunability of the comb spacing at a given number of birefringent fiber elements. Selectivity of the spacing is based on different alignments between the fiber axes in our cascadable scheme. We applied the birefringent comb filter to multi-wavelength laser source generation using either a semiconductor or a fiber-based gain element. By electrical tuning of the birefringence inside a semiconductor optical amplifier ring laser, a waveband switchable multi-wavelength source has been obtained. In an erbium-doped fiber (EDF) laser, multi-wavelength lasing is inhibited at room temperature owing to the homogeneously broadened gain medium. To address this problem, two different types of fiber nonlinearities, stimulated Brillouin scattering and four-wave mixing, are incorporated separately to the EDF laser to provide self-stabilization of the multi-wavelength oscillation. In addition to multi-wavelength source generation, we further applied the birefringent comb filter to multiply the repetition rate of a high-speed pulsed source using the spectral elimination approach. Repetition rate multiplication from 10 to 40 GHz has been simultaneously achieved for four ITU-grid laser sources around 1550 nm, resulting in an aggregate pulse rate of 160 GHz. The phase coherence of the output pulses is also preserved.
Fok, Mei Po Mable.
"August 2007."
Adviser: Chester Shu.
Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1198.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2007.
Includes bibliographical references.
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract in English and Chinese.
School code: 1307.

博士
國立臺灣大學
電信工程學研究所
89
This thesis investigates code division multiple access (CDMA) techniques for direct-detection fiber-optic communication systems. We propose five countermeasures to alleviate the adverse impact of multiple access interference (MAI). Avalanche photodiode (APD) is utilized for photodetection. We take account of the MAI, thermal noise, and APD noise to analyze system performance. The first approach uses PPM (pulse position modulation) signaling scheme and double optical hard-limiters placed before and after optical correlator. Such scheme is an interference-limited system, and system performance can be further improved if we increase the multiplicity M. The second method employs three kinds of interference cancellation schemes, which can completely eliminate the error floor via increasing power. Multirate optical CDMA system via spatial channel diversity is proposed. We employ the essence of the parallel transmission of spatial channels to perform error control, which considerably enhance performance. This novel scheme requires only one laser diode, optical sequence encoder, and product-coded encoder/decoder. Another system using coding method is also proposed. Applying the orthogonality of the shifted versions of optical orthogonal code, trellis-coded scheme can greatly reduce error and also increase aggregate capacity. Finally, ternary line coding scheme is discussed for optical CDMA system. We combine equal weight orthogonal (EWO) scheme and line coding technique to further improve system performance and also avoid a long sequence with null characters.

This thesis aims to develop a software, Fiber Optic Planning Tool (FOPT) that is an efficient and modern software pack developed for planning of telecommunication systems for point-to-point fiber optic links. The system planning is divided into two parts: the transport network and the access network, and the route is chosen by using Google Maps (GM) that is integrated in the FOPT. This tool contains a very interesting didactic component for graduation and post-graduation telecommunications students and, on the other hand for telecommunications engineers that need to make a technical-economic project guided by fiber optic as a communication system. The tool allows you to choose components and equipment that exist in the market (it considers several suppliers) according with the network type. This allows to obtain the partial and total project costs. The user can also add new components to the database. The tool is built by several blocks that the user must fill sequentially to obtain the best solution for the planning. The results given by the tool are compared with the requirements of ITU-T recommendations, showing whether the obtained values reach the established standards. This tool is efficient, modern, very user friendly and it might simplify the techno-economic project of fiber-optic networks. This tool was developed in Java, a rich and versatile programming language capable of interacting with other languages and softwares. It was necessary to use several integrated libraries of Java for graphing, for managing the data in the database and for the execution of mathematical operations. For the insertion and management of data in the database was used Structured Query Language (SQL) and Hypertext Preprocessor (PHP).
Esta dissertação visa o desenvolvimento de um software, Fiber Optic Planning Tool (FOPT). Este é um software moderno e eficiente desenvolvido para o planeamento de sistemas de telecomunicações guiados por fibra ótica, mais especificamente para ligações ponto-a-ponto. O planeamento do sistema divide-se em duas partes: a rede de transporte e a rede de acesso, sendo o percurso escolhido através da integração do Google Maps (GM). Esta ferramenta contém uma forte componente didática para alunos e profissionais de engenharia de telecomunicações que têm a necessidade de fazer um projeto técnico-económico de sistemas de comunicação guiados, que utilizam fibras óticas. Esta permite a escolha dos componentes e equipamentos (considerando vários fornecedores) de acordo com o tipo de rede ou mesmo adicionar novos equipamentos à base de dados. Também permite obter o custo parcial e total do projecto. A ferramenta é composta por diversos blocos que o utilizador deve preencher de forma sequencial. Os resultados devolvidos pela ferramenta, de acordo com os inputs introduzidos, são comparados com as normas da ITU-T Recommendations, sendo que a ferramenta indica se os valores calculados cumprem com as normas estabelecidas. Esta ferramenta é bastante eficiente, moderna e é de fácil compreensão para o utilizador e simplifica o planeamento de projectos técnico-económicos de fibras óticas. Para o desenvolvimento do software foi utilizada a linguagem Java, uma linguagem de programação bastante versátil. Foi necessário recorrer a várias bibliotecas integradas do Java para a construção de gráficos, para a gestão dos dados na base de dados e para a realização de operações analíticas, que envolvem a resolução de equações. Para a inserção de dados na base de dados foi utilizada a linguagem Structured Query Language (SQL) e Hypertext Preprocessor (PHP).

博士
國立臺灣大學
電機工程學研究所
88
Several issues on the design and performance analysis of differential polarization modulation fiber-optic systems are addressed. To reduce the system complexity and the phase-noise sensitive property of the conventional 4-Quadrature (4Q) system, we design a differential 4Q system which possesses simpler system structure and does not need the absolute phase information of the received signals at the receiver. On the other hand, we solve the performance analysis problem in the conventional Double Differential Polarization Shift Keying (DDPolSK) system. The exact distribution of the received information parameters is derived first time. The saddle point method is applied to obtain the approximated Bit Error Rate (BER) values which agree with simulation data very well. Furthermore, the Gram-Schmidt Differential Polarization Shift Keying (GDPolSK), which generalizes the constellation design concept of the conventional DDPolSK, is proposed to construct the reference frame based on the Gram-Schmidt algorithm. The idea is to take the relative position of consecutive three symbols as an information symbol and design the constellation of the information symbol directly instead of applying the conventional n-vertex polyhedron method. This system not only provides more design flexibility in the symbol constellation but also performs much better than the conventional DDPolSK. At last, a novel differential coding method is proposed to further improve the performance of Differential Polarization Shift Keying (DPolSK) systems. The optimal constellation for the system is symmetric and easy to find. So it is named Symmetrically DPolSK (SDPolSK). The SDPolSK system constructs the noisy reference frame at the receiver more accurately than the Gram-Schmidt algorithm such that it has the best performance among all DPolSK systems presented so far.

Multimode devices play an increasingly important role in both communication and sensing systems. Mode division multiplexing (MDM) in multimode fiber (MMF) is becoming a promising method to further increase the capacity of optical transmission link with a controllable mode coupler. Similarly, optic sensors based on core-cladding-mode interference can be widely used in measurement of refractive index (RI), temperature and strain. Fiber Bragg gratings (FBGs) in single mode operation have been extensively studied as in-line optical components for both communication and sensing applications. In recent years, research has been extended to FBGs in few-mode operation as mode couplers in MDM applications. Experimentally, mode conversion from fundamental linear polarization (LP) mode LP01 to higher order LP11 mode in two-mode FBG (TMFBG) has been observed. Index asymmetry and electric field distortion induced by ultraviolet (UV) side illumination in fabrication of FBG make the two modes no longer orthogonal. However, its spectrum analysis mainly depends on experimental data and software simulation using the complex finite element method (FEM). Here a simpler theoretical model based on coupled mode theory (CMT) and Runge-Kutta method (RKM) is proposed. An analytical expression of the mode coupling coefficient is derived and the modeling results match very well with experimental data. Abrupt fiber tapers allow power transfer between core and cladding modes and show promise as RI sensing components when two abrupt tapers are cascaded into an in-line Mach-Zehnder interferometer (MZI). The main advantage of the MZI taper sensor is its low manufacturing cost. However, the optical spectrum analyzer (OSA) used as the receiver and demodulation device in the conventional setup is still expensive. Three simplified schemes of fiber taper MZI RI sensor systems are designed and demonstrated experimentally. The transmitter and the demodulation devices for the three schemes are a single wavelength laser and a photodetector (PD), two modulated lasers and a PD together with data acquisition and processing module, and a broadband source (BBS) and a PD together with matched MZI, respectively. In all those implementations OSA is not required, which significantly lowers the cost and leads to easy integration. Although extra modulation/demodulation devices are required, the second implementation has the best performance. Automatic operation is realized by LabVIEW programming. High sensitivity (2371 mV/RI unit (RIU)) and high stability are achieved experimentally. Those new schemes have great potential to be applied to other interferometric optic sensor systems.
Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2014-05-09 11:44:44.837

Polarization division multiplexing (PolDM) is a promising way to improve the spectral efficiency of fiber-optic communication systems. However, PolDM systems suffer greatly from polarization mode dispersion (PMD), especially in long-haul systems. PMD is time-varying and is intrinsically hard to compensate. Current PMD compensators are complicated and expensive to build, adding to the cost and complexity of practical PolDM systems. We propose a new differential polarization time coding scheme combined with controlled polarization rotation to increase the system tolerance to PMD. An encoding algorithm, a differential receiver design, and a decoding algorithm are described in detail. Controlled polarization rotation is achievable using conventional Mach-Zehnder interferometers that are used to modulate the signal. Simulation results show that significant improvement in PMD tolerance can be achieved with little added complexity. Given a certain transmission distance, our proposed system can also increase the achievable data rate compared to a PolDM differential quadrature phase shift keying system.

碩士
國立中央大學
通訊工程研究所
93
The implementation of fiber optic link with single wavelength is studied in this thesis. When a system was built, many employed components should be verified. Based on this purpose, the measuring benches of optoelectronic and radio frequency (RF) devices must be constructed for getting real parameters. In the following topic, the standards of synchronous optical network (SONET) and global system for mobile communications (GSM) with Gaussian minimum shift keying (GMSK) modulation are described, because the implemented single wavelength fiber optic systems which operated in hybrid mode need a monitoring basis. Using the verified components and standing on the standards of digital and modulated RF signals, a subcarrier modulation (SCM) system which comforted to SONET and GSM is implemented. The known broadband in spectrum of digital signal and the narrowband of carried GSM signal by RF tone are adopted, so how the microwave techniques applied to this system is our study goal. The estimating method of link which contains the electrical domains of transmitter and receiver, the electrical to optical (EO) conversion, the fiber channel, and the optical to electrical (OE) conversion, based on purely electrical simulator was also built in this topic. Next, a Mach-Zehnder electrical to optical modulator (MZ-EOM or MZM) was analyzed. An analysis of electrical small signal model with varying optical large signal model was processed. According to this innovating definition, a double optical modulation (DOM) technique applied to implementation of SCM was proposed. The digital signal in optical domain and the modulated GMSK RF tone in electrical domain were directly combined by a MZ-EOM and simultaneously propagated through a fiber channel in a single wavelength window.

博士
國立臺北科技大學
光電工程系研究所
102
The high transmission capacity and bandwidth are increasingly required due to the booming of the applications of wireless and wire-line communications. Therefore, the next generation communication systems must provide higher transmission rates and higher bandwidth services to meet the needs of users. Since the optical fiber has the advantages of low loss, high bandwidth, high transmission capacity, and anti-electromagnetic interference, it gradually replacing the traditional twisted pair and coaxial cable as the signal transmission medium. Because of the rapid development of wavelength division multiplexing (WDM) technology, the all optical transport network concepts are driven further by this technology. The all-optical transport network is based on the optical fiber technology for the transmission network, the exchange network and the access network. Therefore, for the improvements in the performance of these basic networks effectively, it will become a key point for building a successful next generation communication networks. In this dissertation, three parts that (1) using optical feedback method for all-optical gain-clamping optical amplifier module, (2) optical pulse signal generated by gain-switching self-injection technique, and (3) optical frequency quadrupling radio-over-fiber transport system are studied. Of optical amplifier gain clamping modules and optical pulse signal generator module are based on the use of the optical self-injection, an additional injection light source can be omitted. The more stable effects of dynamic gain were achieved for all-optical gain-clamping optical amplifier module and the quality of optical pulse signal was also better than external injection for generator module. In the part of optical frequency quadrupling radio-over-fiber transport system, using two low-speed intensity modulators by cascade way to produce optical frequency quadrupling signal without excessive expensive optical filters for bidirectional transport systems is demonstrated. Therefore, the proposed bidirectional transport systems were more flexible that previous reported due to their greater tolerance for wavelength fluctuation. Optical feedback self-injection and optical frequency quadrupling techniques will enhance the operational effectiveness of all-optical fiber network in fiber-optic communication systems. The studied results can be a contribution for the next generation communication system.

Interferometer Fiber Optic Gyroscope (IFOG) has established as critical sensor for advance navigation systems. Sensor coil is known to be heart of IFOG. The bias drift and scale factor performance of IFOG depend on the sensor coil. The environmental perturbations like vibration, shock, temperature and magnetic field can affect the measured phase difference between the counter propagating beams, thereby introducing a bias error resulting in degradation of IFOG performance. In general these factors are both time varying and unevenly distributed throughout the coil producing a net undesirable phase shift due to variations in the optical light path, which is undistinguishable from the rotation induced signal. The development of sensor coil for high performance includes selection of optical fiber, spool material, coil winding technique and potting adhesive. In the thesis, the effects of various perturbations like temperature, vibration and magnetic field on the sensor coil are analysed, which degrades the gyro performance. The effect of temperature and vibration can be reduced by proper selection of spool material, winding method and by applying adhesive during the winding of sensor coil. The effect of magnetic field can be reduced by using the high birefringence polarization maintaining fiber with shorter beat length, shielding the sensor coil and reducing the number of twist during the winding. Design and fabrication of the sensor coil is done for control grade & navigation grade FOG with fiber length of 100 m and 1000 m respectively with the polarization maintaining fiber of two different manufacturer Fiber Core, UK and Nufern, USA selected based upon the beat length and Numerical Aperture so that sensor coil has minimum effect of magnetic field and the bending of fiber. Presently the spool material used is Aluminium alloy (HE15) for the ease of fabrication and easily availability of material. The Quadrupolar winding is done to reduce the thermal gradient effects. The indigenously developed special adhesive is applied layer by layer to reduce the environmental effects. In order to study the lifetime of sensor coil accelerated aging test (85°C, RH 85 %) for 30 days is also carried out.

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.

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.