Design and applications of advanced optical modulation formats for optical metro/access transmission systems.

光纖通信技術與光網絡在過去三十年間極大地改變了人們的生活。雖然整個光通信行業因為2000年互聯網泡沫的破滅受到了影響，但近年來由於高清電視，移動多媒體和社交網絡的興盛，互聯網對通信網絡傳輸帶寬的需求達到了前所未有的高度，進而推動了光通信行業的再一次興盛。站在行業的高度來看，寬帶接入網無疑是推動行業發展的最主要領域。而實現寬帶接入網的最主要技術則是無源光網絡技術。無源光網絡的本質是一個樹型拓撲的光網絡，其主要的傳輸光纖可被多用戶共享，且在中央基站和用戶之間無任何有源器件，從而大大降低了網絡的成本。然而，在具體實踐中，仍然有許多的技術難題需要解決，例如：無色光網絡單元、突發性傳輸、全雙工傳輸、長距離無源光網絡和網絡功能集成等。這些技術需求亦反應了市場對通信技術發展的要求，及“更快，更便宜，更灵活“。為滿足無源光網絡的技術要求，研究者們從不同的角度提出了各種解決方案，研究領域囊括光傳輸技術、新型器件、系統結構、網絡協議等等。本論文研究從傳輸碼型的角度來解決上述一項或幾項問題。研究碼型包括雙二進制反歸零碼，雙二進制曼切斯特碼，還有常規曼切斯特碼。研究內容則包括上述碼型的產生、接收、傳輸特性和系統應用等等。論文首貳章為概要和背景技術介紹，其餘幾章則按照不同的碼型分類討論。本論文第一項研究課題為雙二進制反歸零碼。相比傳統的歸零碼和反歸零碼，雙二進制反歸零碼具有更大的色散容限，且每個傳輸符號均有能量。我們先研究了它的優勢，調製/解調方法，而後研究了該碼型在無源光網絡中的具體應用，包括10‐Gb/s 全光組播系統和基於重調製的80 公里長距離波分複用無源光網絡系統。第二項研究課題為雙二進制曼切斯特碼型，該碼型的優勢包括較大的時鐘分量，窄帶寬，無直流分量等。我們提出了一種基於直接調製的雙二進制曼切斯特碼產生方法。該方法具有高效，低價，高輸出功率等特點。基於該雙二進制曼切斯特碼發射機，我們實現了70 公里雙向傳輸的波分複用無源光網絡。該系統下行傳輸採用雙二進制曼切斯特碼型，上行傳輸採用直接調製的反射式半導體激光器，所以系統成本大大降低。最後，我們研究了電色散補償技術對於傳統曼切斯特碼型的傳輸性能的改善。所使用的電均衡技術包括前向均衡器、判決反饋均衡器和極大似然估計均衡器。通過離線處理的方法，我們對曼切斯特碼型在三種均衡器下的傳輸性能進行了實驗驗證。研究內容包括前向均衡器和判決反饋均衡器抽頭數的優化、不同採樣率下系統性能、極大似然估計中狀態機個數的影響和不同的曼切斯特接收機的影響等等。The increasing demands for bandwidth have aroused a myriad of industry and academic activities in developing high-speed and cost-effective optical networks,among which optical broad band access networks was the main driving force for such growth in recent years. The most promising solution to optical broadband access network is the passive optical network (PON), which is a point-to-multipoint tree-topology network that connects optical line terminal (OLT) with many optical network units (ONUs) via a long fiber feeder and many short distribution fibers. Promising the concept it is, it raises many detailed technical challenges, such as colorless ONUs, burst mode transmission, bi-directional transmission with mitigated backscattering noise, long-reach PON, and integrating network functionalities. All of the technical requirements are motivated by the “original requirements“ of telecommunication -- faster, cheaper, and more robust.To fulfill the technical requirements, different researchers take different angles to design system and to study the enabling technologies. For example, devices, system architectures, network protocols, etc. In this thesis research, we have tried to deal with one or multiple problems by employing advanced modulation formats for the optical signals. In particular, we have studied IRZ-duobinary, Manchester-duobinary, and Manchester formats, including the modulation/demodulation techniques, transmission properties, and system applications. The research topics are classified according to the type of modulation formats.In the first topic, IRZ-duobinary format is proposed for optical signal transmission. It has desirable properties of large dispersion tolerance (as compared to conventional RZ/IRZ) and finite optical power in each bit. In this study, we firstly show the advantages of IRZ-duobinary and the corresponding modulation techniques. Then, we demonstrate a 10-Gb/s per channel optical multicast overlay scheme and an 80-km-reach system with re-modulated ONU, both in wavelength division multiplexing (WDM) PON.In the second topic, Manchester-duobinary format, which has the advantages including easy clock/level recovery, compressed bandwidth, and zero DC component, is studied. We propose an efficient and cost-effective Manchester-duobinary transmitter by properly modulating a chirp managed laser (CML) with electrical Manchester signal. Then, a cost-effective CLS 70-km-Reach full-duplex WDM-PON with downstream 10-Gb/s Manchester-duobinary signal and upstream 1.25-Gb/s re-modulated NRZ-OOK signal is proposed and experimentally demonstrated. This design simultaneously solves the problems of colorless ONU, bi-directional transmission, and long-reach, using cost-effective system design and devices.Finally, we investigate the performance of electronic dispersion compensation (EDC) technique on 10-Gb/s Manchester coded optical signal, so as to further improve its dispersion tolerance and may enables its applications in long-reach PON. In this study, feed forward equalizer (FFE), decision feedback equalizer (DFE), and maximum-likelihood sequence estimation (MLSE) are employed as the equalizers Utilizing off-line signal processing, the performance of different equalizers with different parameters (number of taps, sampling rates, number of states, etc.) under both cases of single-ended and balanced detection are studied and compared. Experimental results show that the transmission distance of Manchester coded signal can be increased by a factor of three with four-sample-per-symbol FFE-DFE.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Liu, Zhixin.Thesis (Ph.D.)--Chinese University of Hong Kong, 2012.Includes bibliographical references (leaves 128-148).Abstract also in Chinese.Acknowledgement --- p.1Abstract --- p.3摘要 --- p.5Table of contents --- p.7List of figures and tables --- p.13Chapter Chapter 1. --- IntroductionChapter 1.1 --- Optical Broadband Access --- p.18Chapter 1.1.1 --- Bandwidth requirement --- p.19Chapter 1.1.2 --- Passive optical networks --- p.22Chapter 1.2 --- Research Challenge of Next-Generation Optical Access Network --- p.25Chapter 1.2.1 --- Colorless ONU --- p.25Chapter 1.2.2 --- Burst Mode Transmission --- p.27Chapter 1.2.3 --- Backscattering Noise in PON --- p.28Chapter 1.2.4 --- Long-Reach Access Network --- p.30Chapter 1.2.5 --- Enriching Network Functionalities --- p.31Chapter 1.3 --- Major contribution of this thesis --- p.32Chapter 1.3.1 --- IRZ-duobinary transmitter and application --- p.32Chapter 1.3.2 --- Manchester-duobinary transmitter and application --- p.33Chapter 1.3.3 --- Receiver with electronic equalizer for Manchester signal --- p.34Chapter 1.4 --- Outline of this Thesis --- p.35Chapter Chapter 2. --- Optical Modulation Technique and Transmission ImpairmentsChapter 2.1 --- Optical Modulation techniques --- p.38Chapter 2.1.1 --- Chirp managed laser --- p.38Chapter 2.1.2 --- Mach-Zehnder modulator --- p.41Chapter 2.2 --- Transmission Impairments --- p.47Chapter 2.2.1 --- Noise --- p.47Chapter 2.2.2 --- Chromatic dispersion --- p.49Chapter 2.2.3 --- Fiber nonlinearity --- p.50Chapter 2.3 --- Impairment Mitigation Techniques --- p.51Chapter 2.3.1 --- In-line compensation techniques --- p.51Chapter 2.3.2 --- Post-compensation techniques --- p.52Chapter Chapter 3. --- Optical Multicast and Re-modulation Based on Inverse-RZ-duobinary TransmitterChapter 3.1 --- Introduction --- p.53Chapter 3.2 --- IRZ-duobinary transmitter --- p.55Chapter 3.2.1 --- Generation of IRZ-duobinary format --- p.55Chapter 3.2.2 --- Comparison of different configurations of IRZ-duobinary generation --- p.56Chapter 3.3 --- IRZ-duobinary format for optical multicast in WDM-PON --- p.60Chapter 3.3.1 --- Optical multicast in WDM-PON --- p.60Chapter 3.3.2 --- Proposed system architecture --- p.61Chapter 3.3.3 --- Experimental demonstration of the proposed optical multicast system --- p.65Chapter 3.4 --- IRZ-duobinary for long-reach PON --- p.68Chapter 3.4.1 --- Long-reach PON using DI based IRZ-duobinary transmitter --- p.69Chapter 3.4.2 --- Long-reach PON using CML based IRZ-duobinary transmitter --- p.75Chapter 3.5 --- Summary --- p.81Chapter Chapter 4. --- Manchester-duobinary Transmitter for Bi-directional WDM-PONChapter 4.1 --- Introduction --- p.83Chapter 4.2 --- Manchester-duobinary transmitter --- p.85Chapter 4.2.1 --- Mach-Zehnder modulator based Manchester-duobinary transmitter --- p.85Chapter 4.2.2 --- Chirp managed laser based Manchester-duobinary transmitter --- p.87Chapter 4.3 --- Rayleigh noise mitigated bi-directional WDM-PON based on Manchester-duobinary transmitter --- p.94Chapter 4.3.1 --- CLS Bi-directional long-reach WDM-PON. --- p.94Chapter 4.3.2 --- Proposed system architecture --- p.97Chapter 4.3.3 --- Experimental demonstration --- p.99Chapter 4.4 --- Summary --- p.102Chapter Chapter 5. --- Electronic Equalizer for Manchester Coded SignalChapter 5.1 --- Introduction --- p.103Chapter 5.2 --- Electronic equalizer for CD compensation --- p.104Chapter 5.2.1 --- Channel model --- p.104Chapter 5.2.2 --- FFE-DFE --- p.106Chapter 5.2.3 --- MLSE --- p.107Chapter 5.3 --- FFE-DFE for Manchester signal --- p.109Chapter 5.3.1 --- Experimental setup for CD compensation of Manchester signal using FFE-DFE --- p.110Chapter 5.3.2 --- Results and discussion --- p.112Chapter 5.4 --- MLSE equalizer for Manchester signal --- p.121Chapter 5.4.1 --- Experimental setup for CD compensation of Manchester format using MLSE --- p.121Chapter 5.4.1 --- Results and discussion --- p.122Chapter 5.5 --- Summary --- p.124Chapter Chapter 6. --- ConclusionChapter 6.1 --- Summary of this thesis --- p.125Chapter 6.2 --- Future work --- p.127References --- p.128Chapter Appendix: --- p.149Chapter A. --- List of abbreviations --- p.149Chapter B. --- List of publications --- p.15

Phase estimation receiver for full-field detection: a novel receiver structure for electronic dispersion compensation of metropolitan area networks

The development of ultra high speed (~20 Gsamples/s) analogue to digital converters (ADCs), and the delayed deployment of 40 Gbit/s transmission due to the economic downturn, has stimulated the investigation of digital signal processing (DSP) techniques for compensation of optical transmission impairments. In the future, DSP will offer an entire suite of tools to compensate for optical impairments and facilitate the use of advanced modulation formats. Chromatic dispersion is a very significant impairment for high speed optical transmission. This thesis investigates a novel electronic method of dispersion compensation which allows for cost-effective accurate detection of the amplitude and phase of the optical field into the radio frequency domain. The first electronic dispersion compensation (EDC) schemes accessed only the amplitude information using square law detection and achieved an increase in transmission distances. This thesis presents a method by using a frequency sensitive filter to estimate the phase of the received optical field and, in conjunction with the amplitude information, the entire field can be digitised using ADCs. This allows DSP technologies to take the next step in optical communications without requiring complex coherent detection. This is of particular of interest in metropolitan area networks. The full-field receiver investigated requires only an additional asymmetrical Mach-Zehnder interferometer and balanced photodiode to achieve a 50% increase in EDC reach compared to amplitude only detection

Time and frequency offsets in all optical OFDM systems

Ultra-high-speed data transmission (terabit-per-second per channel) is urgently required in optical communication systems to fulfill the emerging demands of 3D multimedia applications, cloud computing, and bandwidth-hungry applications. In one way by using singlecarrier optical communication systems for the data transmission rates 1 Tb/s, we need the high baud rate and/or the high-order modulation formats (i.e. 512-QAM, 1024-QAM). Another way is to group the data carrying subcarriers without a guard bands (tightly spaced) to form a superchannel which gives increase in channel capacity. In a superchannel, the requirements of high-order modulation formats and high baud rates are relaxed. In an alloptical orthogonal frequency division multiplexing (AO-OFDM) system, the subcarriers are orthogonal and closely packed which gives more suitability to form superchannel. This thesis focuses on the time and frequency offsets in AO-OFDM systems. A theoretical model to investigate the performance of on-off-keying (OOK) modulated AO-OFDM system is developed for analytical simulation. The analytical (statistical) model considers the random characteristics of time and frequency offsets in adjacent subcarriers as well as the common noise sources such as shot and thermal noises to calculate the interference variances for evaluating the BER performance. The effects of time and frequency offsets on the BER performance of AO-OFDM system is evaluated with the number of optical subcarriers (NSC), receiver bandwidth (BWRX), and cyclic prefix (CP) We further develop an analytical model to evaluate the performance of AO-OFDM system with advanced modulation format (M-QAM) in the presence of time and frequency offsets, and the performance is compared with numerical simulations of other emulation setups (oddand- even subcarriers and decorrelated systems). The performance is investigated with NSC, BWRX, and CP in AO-OFDM system. A delay-line interferometer based all-optical method to reduce the effects of time and frequency offsets is proposed and evaluated. Finally, performance of demultiplexed subcarriers from an optical discrete Fourier transform (O-DFT) in AO-OFDM system in the presence of chromatic dispersion and limited modulation bandwidth is evaluated. The fiber Bragg grating (FBG) based passive device is proposed to reduce the interference and the results are compared with existing method using sampling gates. The proposed method using FBG for interference reduction provides a cost-effective design of AO-OFDM system

Techniques émergentes de codage espace-temps pour les systèmes de communications optiques

Research in the field of optical fiber communications is advancing at a rapid pace in order to meet the growing needs for higher data rates. The main driving forces behind these advancements are the availability of multiple degrees of freedom in the optical fiber allowing for multiplexing more data: amplitude, phase and polarization state of the optical field, along with time and wavelength are already used in the deployed optical transmission systems. Yet, these systems are approaching their theoretical capacity limits and an extra dimension "space" is investigated to achieve the next capacity leap. However, packing several data channels in the same medium brings with it differential impairments and crosstalk that can seriously deteriorate the performance of the system. In this thesis, we focus on recent optical MIMO schemes based on polarization division multiplexing (PDM) and space division multiplexing (SDM). In both, we assess the performance penalties induced by non-unitary crosstalk and loss disparities among the channels arising from imperfections in the used optical components (fibers, amplifiers, multiplexers...), and suggest novel MIMO coding techniques known as Space-Time (ST) codes, initially designed for wireless multi-antenna channels, to mitigate them.La recherche dans le domaine des communications sur fibres optiques avance à un rythme rapide afin de satisfaire des demandes croissantes de communications à débits élevés. Les principaux moteurs de ces avancements sont la multitude de degrés de liberté offerts par la fibre permettant ainsi la transmission de plus de données: l'amplitude, la phase et l'état de polarisation du champ optique, ainsi que le temps et la longueur d'onde sont déjà utilisés dans les systèmes de transmission optique déployés. Pourtant, ces systèmes s'approchent de leur limite fondamentale de capacité et un degré supplémentaire: "la dimension spatiale" est étudié pour réaliser un saut qualitatif majeur en termes de capacité de transmission. Cependant, l'insertion de plusieurs flux de données dans le même canal de propagation induit également des pertes différentielles et de la diaphonie entre les flux, ce qui peut fortement réduire la qualité du système de transmission. Dans cette thèse, nous nous concentrons sur les systèmes de transmission optique de type MIMO basés sur un multiplexage en polarisation ou en modes de propagation. Dans les deux cas, nous évaluons la dégradation de la performance provoquée par une interférence inter-canaux non-unitaire et des disparités de gain entre les canaux engendrées par des imperfections dans les composants optiques utilisés (fibres, amplificateurs, multiplexeurs...), et proposons pour les combattre, de nouvelles techniques de codage pour les systèmes MIMO nommées "codes Spatio-Temporels" (ST), préalablement conçues pour les systèmes radios multi-antennaires

Optical Communication

Optical communication is very much useful in telecommunication systems, data processing and networking. It consists of a transmitter that encodes a message into an optical signal, a channel that carries the signal to its desired destination, and a receiver that reproduces the message from the received optical signal. It presents up to date results on communication systems, along with the explanations of their relevance, from leading researchers in this field. The chapters cover general concepts of optical communication, components, systems, networks, signal processing and MIMO systems. In recent years, optical components and other enhanced signal processing functions are also considered in depth for optical communications systems. The researcher has also concentrated on optical devices, networking, signal processing, and MIMO systems and other enhanced functions for optical communication. This book is targeted at research, development and design engineers from the teams in manufacturing industry, academia and telecommunication industries

Advanced performance monitoring in all-optical networks.

This thesis investigates advanced optical performance monitoring approaches for future all-optical networks using the synchronous sampling technique. This allows for improved signal quality estimation, fault management and resource allocation through improved control of transmission at the physical layer level. Because of the increased transparency in next generation networks, it is not possible to verify the quality of the signal at each node because of the limited number of optical-electrical-optical conversions, and therefore new non-intrusive mechanisms to achieve signal quality monitoring are needed. The synchronous sampling technique can be deployed to estimate the bit error rate, considered an important quality measure, and hence can be utilised to certify service level agreements between operators and customers. This method also has fault identification capabilities by analysing the shapes of the obtained histograms. Each impairment affects the histogram in a specific way, giving it a unique shape that can be used for root cause analysis. However, chromatic dispersion and polarisation mode dispersion (PMD) can have similar signatures on the histograms obtained at decision times. A novel technique to unambiguously discriminate between these two sources of degradation is proposed in this work. It consists of varying the decision times so that sampling also occurs at both edges of the eye diagram. This approach is referred to as three-section eye sampling technique. In addition, it is shown that this method can be used to accurately assess first order polarisation mode dispersion and can simultaneously estimate the differential group delay (DGD) and the power splitting ratio between the two states of polarisation. Since synchronous sampling is employed, the effect of PMD on the sampling times is also investigated. For the first time, closed form relationship between the shift in sampling time, the DGD and the power splitting ratio between the polarisation states is obtained. Three types of high-Q filter based clock recovery circuits are considered: without pre-processing circuits that can be used for RZ format and with an edge detector or a squarer pre-processing circuits suitable for NRZ format. Moreover, this technique can be used to monitor chromatic dispersion and a large monitoring range of more than 1750ps/nm is experimentally demonstrated at 10Gbit/s. Since it can monitor PMD and dispersion, this method can be deployed to control dynamic PMD or dispersion compensators. Furthermore, this technique offers easy and quick inline eye mask testing and timing jitter assessment

Hybrid fibre and free-space optical solutions in optical access networks

This thesis evaluates the potentials of hybrid fibre and free space optical (FSO) communications access networks in providing a possible solution to an all optical access network. In such network architectures, the FSO link can extend the system to areas where an optical fibre link is not feasible, and/or provide limited mobility for indoor coverage. The performance of hybrid fibre and FSO (HFFSO) networks based on digital pulse position modulation (DPPM), for both the indoor and outdoor environments of the optical access network, are compared with the performance of such a network that is based on conventional on-off keying non-return-to-zero (OOK NRZ) modulation using results obtained through computational and analytical modelling. Wavelength division multiplexing (WDM) and/or code division multiple access (CDMA) are incorporated into the network for high speed transmission and/or network scalability. The impacts of optical scintillation, beam spreading and coupling losses, multiple access interference (MAI), linear optical crosstalk and amplified spontaneous emission noise (ASE) on the performance of hybrid fibre and FSO (HFFSO) access networks are analysed, using performance evaluation methods based on simple Gaussian approximation (GA) and more complex techniques based on moment generating function (MGF), including the Chernoff bound (CB), modified Chernoff bound (MCB) and saddlepoint approximation (SPA). Results in the form of bit error rate (BER), power penalty, required optical power and outage probability are presented, and both the CB and MCB, which are upper bounds, are suggested as safer methods of assessing the performance of practical systems. The possibility of using a CDMA-based HFFSO network to provide high speed optical transmission coverage in an indoor environment is investigated. The results show a reduction in transmit power of mobile devices of about 9 – 20 dB (depending on number of active users) when an optical amplifier is used in the system compared to a non-amplified system, and up to 2.8 dB improvement over OOK NRZ receiver sensitivity is provided by a DPPM system using integrate and compare circuitry for maximum likelihood detection, and at coding level of two, for minimum bandwidth utilization. Outdoor HFFSO networks using only WDM, and incorporating CDMA with WDM, are also investigated. In the presence of atmospheric scintillations, an OOK system is required (for optimum performance) to continuously adapt its decision threshold to the fluctuating instantaneous irradiance. This challenge is overcome by using the maximum likelihood detection DPPM system, and necessitated the derivation of an interchannel crosstalk model for WDM DPPM systems. It is found that optical scintillation worsens the effect of interchannel crosstalk in outdoor HFFSO WDM systems, and results in error floors particularly in the upstream transmission, which are raised when CDMA is incorporated into the system, because of MAI. In both outdoor HFFSO networks (with WDM only and with WDM incorporating CDMA), the optical amplifier is found necessary in achieving acceptable BER, and with a feeder fibre of 20 km and distributive FSO link length of 1500 m, high speed broadband services can be provided to users at safe transmit power at all turbulence levels in clear air atmosphere