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

High-speed WDM-PON using CW injection-locked Fabry-Pérot laser diodes

2006-2007 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

An efficient optimization scheme for WDM/TDM PON network planning

With the growing popularity of bandwidth demanding services such as HDTV, VoD, and video conferencing applications, there is an increasing demand on broadband access. To meet this demand, the access networks are evolving from the traditional DSL (xDSL more recently) and cable techniques to a new generation of fiber-based access techniques. While EPONs and GPONs have been the most studied passive optical access networks (PONs), WDM-PON is now clearly seen as the next generation trend with an hybrid set of switching equipment. We propose here an original optimization scheme for the deployment of greenfield PON networks where we minimize the overall deployment cost. Given the geographical location of ONUs and their incoming/outgoing traffic demands, the newly proposed scheme optimizes the placement of splitters/AWGs in a PON and the link dimensioning in order to provision the overall demand. The optimization scheme proceeds in three phases. In the first phase, we generate several potential equipment hierarchies, where each equipment hierarchy is associated with an ONU partition such that a switching equipment is associated with each cluster, each ONU belongs to a single cluster, and the splitting ratio of the equipment corresponds to the number of ONUs in the cluster. In the second phase, for each equipment hierarchy, we make use of a column generation (CG) mathematical model to select the type and location of the switching equipment that leads to the minimum cost multi-stage equipment topology which accommodates all the traffic demand. The third phase selects the best hierarchy among all the generated and dimensioned hierarchies. The optimization model encompasses the particular cases where all switching equipment are either splitters and AWGs, and outputs the location of the switching equipment together with the dimensioning of the PON network. We performed numerical experiments on various data sets in order to evaluate the performance of the optimization model, and to analyze the type of equipment hierarchies which are generated depending on the traffic and the location of the ONUs

Dynamically reconfigurable optical access network

This dissertation presents the research results on a fiber-optic high-bitrate access network which enables dynamic bandwidth allocation as a response to varying subscribers' demands and bandwidth needs of emerging services. The motivation of the research is given in Chapter 1 "Introduction" together with a brief comparative discussion on currently available and future access networks. The idea of wavelength reconfigurability in the last-mile networks is described as a solution for more efficient bandwidth utilization and a subject of the Broadband Photonics project. Chapter 2 "Wavelength-flexible WDM/TDM access network - architecture" provides a comprehensive description of the proposed solution with each network element being analyzed in terms of its functionalities. This includes a colorless optical network unit and a reconfigurable optical add/drop multiplexer. An estimation of power budget is followed by the choice of wavelength set and network control and management layer overview. In Chapter 3 "Reflective transceiver module for ONU" after discussing different communication schemes and modulation formats three approaches to a colorless high-bitrate transmitter are analyzed in detail. This includes experiment and simulation results on a reflective semiconductor optical amplifier, reflective electro-absorption modulator and a Michelson-interferometer modulator. The Chapter is concluded with a comparative discussion. Chapter 4 "Reconfigurable optical add/drop multiplexer" discusses another key element in the proposed network architecture which is an integrated structure of micro-ring resonators providing wavelength reconfigurability. The measured characteristics assess the applicability of the device able to support unicast and multicast transmission. A range of possible sources of signal degradation in the access links are analyzed in Chapter 5 "Transmission and network impairments in the access network". An estimation of potential power penalties resulting from such impairments in the proposed system follow afterwards. Special attention is paid to optical in-band crosstalk penalties and improvement methods in Chapter 6 "Interferometric crosstalk in the access network with an RSOA". This subject is treated extensively with the support of mathematical considerations and experimental results. Proof-of-concept experiments of the proposed network architecture are presented in Chapter 7 "Reconfigurable WDM/TDM access network - experiments". The results of bidirectional transmission of high-bitrate WDM signals in different wavelength allocation schemes are discussed in detail. From there, by means of simulations the behavior of a full-scale network is assessed. In Chapter 8 "Migration towards WDM/TDM access network" the migration scenario from currently deployed fiber-optic access networks towards the novel solution is proposed. Afterwards, a short dispute on the economics of last-mile fiber technologies is included. Finally, the work is concluded and potential future research ideas based on this thesis are given in Chapter 9 "Conclusions and further work"

Dynamically reconfigurable optical access network

This dissertation presents the research results on a fiber-optic high-bitrate access network which enables dynamic bandwidth allocation as a response to varying subscribers' demands and bandwidth needs of emerging services. The motivation of the research is given in Chapter 1 "Introduction" together with a brief comparative discussion on currently available and future access networks. The idea of wavelength reconfigurability in the last-mile networks is described as a solution for more efficient bandwidth utilization and a subject of the Broadband Photonics project. Chapter 2 "Wavelength-flexible WDM/TDM access network - architecture" provides a comprehensive description of the proposed solution with each network element being analyzed in terms of its functionalities. This includes a colorless optical network unit and a reconfigurable optical add/drop multiplexer. An estimation of power budget is followed by the choice of wavelength set and network control and management layer overview. In Chapter 3 "Reflective transceiver module for ONU" after discussing different communication schemes and modulation formats three approaches to a colorless high-bitrate transmitter are analyzed in detail. This includes experiment and simulation results on a reflective semiconductor optical amplifier, reflective electro-absorption modulator and a Michelson-interferometer modulator. The Chapter is concluded with a comparative discussion. Chapter 4 "Reconfigurable optical add/drop multiplexer" discusses another key element in the proposed network architecture which is an integrated structure of micro-ring resonators providing wavelength reconfigurability. The measured characteristics assess the applicability of the device able to support unicast and multicast transmission. A range of possible sources of signal degradation in the access links are analyzed in Chapter 5 "Transmission and network impairments in the access network". An estimation of potential power penalties resulting from such impairments in the proposed system follow afterwards. Special attention is paid to optical in-band crosstalk penalties and improvement methods in Chapter 6 "Interferometric crosstalk in the access network with an RSOA". This subject is treated extensively with the support of mathematical considerations and experimental results. Proof-of-concept experiments of the proposed network architecture are presented in Chapter 7 "Reconfigurable WDM/TDM access network - experiments". The results of bidirectional transmission of high-bitrate WDM signals in different wavelength allocation schemes are discussed in detail. From there, by means of simulations the behavior of a full-scale network is assessed. In Chapter 8 "Migration towards WDM/TDM access network" the migration scenario from currently deployed fiber-optic access networks towards the novel solution is proposed. Afterwards, a short dispute on the economics of last-mile fiber technologies is included. Finally, the work is concluded and potential future research ideas based on this thesis are given in Chapter 9 "Conclusions and further work"

Optical Network Design, Modelling and Performance Evaluation for the Upgraded LHC at CERN

This thesis considers how advances in optical network and optoelectronic technologies may be utilised in particle physics applications. The research is carried out within a certain framework; CERN's Large Hadron Collider (LHC) upgrade. The focus is on the upgrade of the "last-tier" data links, those residing between the last information-processing stage and the accelerator. For that purpose, different network architectures, based on the Passive Optical Network (PON) architectural paradigm, are designed and evaluated. Firstly, a Time-Division Multiplexed (TDM) PON targeting timing, trigger and control applications is designed. The bi-directional, point-to-multipoint nature of the architecture leads to infrastructure efficiency increase. A custom protocol is developed and implemented using FPGAs. It is experimentally verified that the network design can deliver significantly higher data rate than the current infrastructure and meet the stringent latency requirements of the targeted application. Consequently, the design of a network that can be utilised to transmit all types of information at the upgraded LHC, the High-Luminosity LHC (HL-LHC) is discussed. The most challenging requirement is that of the high upstream data rate. As WDM offers virtual point-to-point connectivity, the possibility of using a Wavelength-Division Multiplexed (WDM) PON is theoretically investigated. The shortcomings of this solution are identified; these include high cost and complexity, therefore a simpler architecture is designed. This is also based on the PON paradigm and features the use of Reflective Electroabsorption Modulators (REAM) at the front-end (close to the particle collision point). Its performance is experimentally investigated and shown to meet the requirements of a unified architecture at the HL-LHC from a networking perspective. Finally, since the radiation resistance of optoelectronic components used at the front-end is of major importance, the REAM radiation hardness is experimentally investigated. Their radiation resistance limits are established, while new insights into the radiation damage mechanism are gained

WDM/TDM PON bidirectional networks single-fiber/wavelength RSOA-based ONUs layer 1/2 optimization

This Thesis proposes the design and the optimization of a hybrid WDM/TDM PON at the L1 (PHY) and L2 (MAC) layers, in terms of minimum deployment cost and enhanced performance for Greenfield NGPON. The particular case of RSOA-based ONUs and ODN using a single-fibre/single-wavelength is deeply analysed. In this WDM/TDM PON relevant parameters are optimized. Special attention has been given at the main noise impairment in this type of networks: the Rayleigh Backscattering effect, which cannot be prevented. To understand its behaviour and mitigate its effects, a novel mathematical model for the Rayleigh Backscattering in burst mode transmission is presented for the first time, and it has been used to optimize the WDM/TDM RSOA based PON. Also, a cost-effective, simple design SCM WDM/TDM PON with rSOA-based ONU, was optimized and implemented. This prototype was successfully tested showing high performance, robustness, versatility and reliability. So, the system is able to give coverage up to 1280 users at 2.5 Gb/s / 1.25 Gb/s downstream/upstream, over 20 Km, and being compatible with the GPON ITU-T recommendation. This precedent has enabled the SARDANA network to extend the design, architecture and capabilities of a WDM/TDM PON for a long reach metro-access network (100 km). A proposal for an agile Transmission Convergence sub-layer is presented as another relevant contribution of this work. It is based on the optimization of the standards GPON and XG-PON (for compatibility), but applied to a long reach metro-access TDM/WDM PON rSOA-based network with higher client count. Finally, a proposal of physical implementation for the SARDANA layer 2 and possible configurations for SARDANA internetworking, with the metro network and core transport network, are presented

Switching Equipment Location/Allocation in hybrid PONs

Our research goal is to investigate the FTTX (Fiber-to-the Home/Premises/Curb) passive optical network (PON) for the deployment of BISAN (Broadband Internet Subscriber Access Network) to exploit the opportunities of optical fiber enabled technologies as well as of passive switching equipment. Indeed, the deployment of FTTX PON is the most OPEX-friendly scenario, because it allows for completely passive access networks through minimizing the number of active components in the network. Previously, most FTTX PON architectures are designed based on the principle of either time division multiplexing (TDM) technology or wavelength division multiplexing (WDM) technology. We focus on designing the best possible architectures of FTTX PON, specifically hybrid PONs, which embraces both TDM and WDM technology. A hybrid PON architecture is very efficient as it is not limited to any specific PON technology, rather it is flexible enough to deploy TDM/WDM technology depending on the type (i.e unicast/multicast) and amount of traffic demand of the end-users. The advantages of a hybrid PON are of two folds: (i) it can offer increased data rate to each user by employing WDM technology, (ii) it can provide flexible bandwidth utilization by employing TDM technology. In this thesis, we concentrate on determining the optimized covering of a geographical area by a set of cost-effective hybrid PONs. We also focus on the greenfield deployment of a single hybrid PON. It should be worthy to mention that while investigating the deployment of hybrid PONs, the research community around the world considers the specifications of either the physical layer or the optical layer. But an efficient planning for PON deployment should take into account the constraints of the physical and optical layers in order that both layers can work together harmoniously. We concentrate our research on the network dimensioning and the selection as well as the placement of the switching equipment in hybrid PONs with the intention of considering the constraints of both physical and optical layers. We determine the layout of an optimized PON architecture while provisioning wavelengths in a hybrid PON. We also propose to select the switching equipment depending on the type (unicast/multicast) of traffic demand. Finally, we determine the best set of hybrid PONs along with their cascading architecture, type and location of their switching equipment while satisfying the network design constraints such as the number of output ports of the switching equipment and maximum allowed signal power loss experienced at each end user’s premises. In this thesis, we propose two novel schemes for the greenfield deployment of a single hybrid PON. The first scheme consists of two phases in which a heuristic algorithm and a novel column generation (CG) based integer linear programming (ILP) optimization model are proposed in the 1st and 2nd phase respectively. In the second scheme, a novel integrated CG based ILP cross layer optimization model is proposed for the designing of a single hybrid PON. We also propose two novel schemes to deal with the greenfield deployment of multiple hybrid PONs in a given geographical area. These two schemes determine the best set of cost-effective hybrid PONs in order to serve all the end users in a given neighborhood. The first scheme executes in four phases in which two heuristic algorithms, a CG based ILP model and an ILP optimization model are proposed in the 1st, 2nd, 3rd and 4th phase respectively. In the second scheme, an ILP model as well as a CG based ILP model, another ILP model as well as another CG based ILP model, a CG based ILP model and an ILP optimization model are proposed during four consecutive phases. Our proposed scheme can optimize the design of a set of hybrid PONs covering a given geographic area as well as the selection of the best cascading architecture 1/2/mixedstage) for each selected PON. It minimizes the overall network deployment cost based on the location of the OLT and the ONUs while granting all traffic demands. The scheme emphasizes on the optimum placement of equipment in a hybrid PON infrastructure due to the critical dependency between the network performances and a proper deployment of its equipment, which, in turn depends on the locations of the users. It is a quite powerful scheme as it can handle data instances with up to several thousands ONUs. On the basis of the computational results, the proposed scheme leads to an efficient automated tool for network design, planning, and performance evaluation which can be beneficial for the network designers

Optical frequency comb source for next generation access networks

The exponential growth of converged telecommunication services and the increasing demands for video rich multimedia applications have triggered the vast development of optical access technology to resolve the capacity bottleneck at metropolitan-access aggregations. To further enhance overall performance, next generation optical access networks will require highly efficient wavelength division multiplexing (WDM) technology beyond the capability of current standard time division multiplexed (TDM) systems. The successful implementation of future-proof WDM access networks depends on advancements in high performance transmission schemes as well as economical and practical electronic/photonic devices. This thesis focuses on an investigation of the use of optical frequency comb sources, and spectrally efficient modulation formats, in high capacity WDM based optical access networks. A novel injected gain switched comb generation technique which deliver simplicity, reliability, and cost effectiveness has been proposed and verified through experimental work. In addition, a detailed characterization of the optical comb source has been undertaken with special attention on the phase noise property of the comb lines. The potential of the injected gain switched comb source is then demonstrated in a digital coherent receiver based long reach WDM access scenario, which intends to facilitate 10 - 40 Gbit/s data delivery per channel . Furthermore, an optical scalar transmission scheme enabling the direct detection of higher order modulation format signals has been proposed and experimentally investigated