Performance analysis and centralised optical processing in next generation access networks

The Next Generation Passive Optical Network (NG-PON) is currently being standardised and developed, with a goal to achieve higher bandwidth at 10Gb/s, greater capacity at thousands of users and longer backhaul reach at 60km or 100km. The aim is to provide cost effective solutions for telecom operators to vastly deploy optical access networks, enabling customers with the benefit of the greater bandwidth and wider range of services. This thesis presents research that has identified and addressed various design issues relating to next generation access networks. Interferometric noise may be present in future, ring based, access networks which utilise WDM and OADMs. Simulation and experiment results are presented which studies the performance tolerance to not-precisely-defined wavelength, in the presence of interferometric noise. The impact of receiver electrical filtering was also investigated. The next generation access network will, in the upstream direction, use burst transmission and are likely to need a large tolerance to wavelength drift due to the low cost equipment used at the customer’s premises. A demonstration of optical burst equalisation was presented, based on SOAs. This study also explores the possibility of reducing the SOA saturation induced non-linear distortions through simulations and experiments. As an extension to the optical burst equaliser and to remedy the saturation induced distortions, an intermediate site optical processing system was proposed. This solution not only performs burst-mode wavelength conversion at 10 Gb/s, but also pre-chirps the signal to allow long-reach transmission and suppressed level fluctuation to ease the requirements on the burst-mode receiver. As a result, a proof of concept 10Gb/s Wavelength Converting Optical Access Network (WCOAN) with up to 62km DWDM backhaul is experimentally demonstrate. It is designed to consolidate drifting wavelengths, generated with an uncooled laser in the upstream direction, into a stable wavelength channel for DWDM long backhaul transmission

Applications of Ring Resonators and fiber delay lines for sensors and WDM Networks

En esta tesis doctoral, se presentan diversas aportaciones científicas en el ámbito de las aplicaciones de la fibra óptica y de las comunicaciones ópticas. En primer lugar, la tesis doctoral describe nuevas técnicas de medida remota y multiplexación en longitud de onda (WDM), a través de fibra óptica monomodo, para sensores ópticos. Las técnicas de medida están orientadas a sensores de intensidad óptica y se basan en configuraciones ópticas implementadas mediante redes de Bragg en fibra y líneas de retardo en fibra recirculantes (anillo resonante) y no recirculantes. En el documento se describen matemáticamente dichas técnicas y se presentan medidas experimentales que verifican los modelos teóricos. En segundo lugar, la tesis contiene diversas contribuciones novedosas al diseño y simulación por ordenador de filtros fotónicos compuestos basados en el anillo resonante con interferómetro Sagnac, para la compensación de la dispersión cromática en enlaces de transmisión digital con fibra óptica. Por último, el documento incluye un listado de todas las referencias empleadas, un listado de los acrónimos empleados, así como las publicaciones y patentes obtenidas por el autor hasta la fecha.Los proyectos de la Comisión Interministerial de Ciencia y Tecnología (CICYT): TIC2003-03783 (DISFOTON) y TEC2006-13273-C03-03-MIC (FOTOCOMIN). El programa de I+D+i de la Comunidad Autónoma de Madrid: FACTOTEM-CM (S-0505/ESP/000417). La Acción Integrada Hispano-Portuguesa del Plan Nacional de I+D+i 2004-2007: Self-referenced fibre optic intensity configurations for single and multi-sensors (HP2007-0093). El proyecto cofinanciado por la Universidad Carlos III de Madrid y la Comunidad Autónoma de Madrid: Fotónica en visualización, comunicaciones y sensores (CCG06-UC3M/TIC-0619). Las ayudas a la movilidad de investigadores en formación que me concedió la Universidad Carlos III de Madrid en 2006 y 2007. La Red Temática Europea SAMPA (HPRN-CT-2002-00202) del 5º Programa Marco de la Unión Europea. La Acción Europea FIDES (COST Action 299) del 6º Programa Marco de la Unión Europea. Y las Redes de Excelencia Europea ePhoton/ONe+ (FP6-IST-027497) y BONE (FP7-ICT-216863), del 6º y 7º Programa Marco de la Unión Europea, respectivamente

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"

Coupled-resonator-induced-transparency concept for wavelength routing applications

The presence of coupled resonators induced transparency (CRIT) effects in side-coupled integrated spaced sequence of resonators (SCISSOR) of different radii has been studied. By controlling the rings radii and their center to center distance, it is possible to form transmission channels within the SCISSOR stop-band. Two different methods to exploit the CRIT effect in add/drop filters are proposed. Their performances, e. g. linewidth, crosstalk and losses, are examined also for random variations in the structural parameters. Finally, few examples of high performances mux/demux structures and 2 × 2 routers based on these modified SCISSOR are presented. CRIT based SCISSOR optical devices are particularly promising for ultra-dense wavelength division multiplexing applications

Bidirectional 4-PAM to Double Per-Fiber Capacity in 2-km Intra-Datacenter Links

This paper presents an experimental demonstration of bidirectional 4-PAM transmission for intra-datacenter links using a pair of SMF fibers. In the proposed architecture, each transceiver laser feeds both fibers, which are thus used bidirectionally to double the capacity per used fiber, wavelength, and laser. Besides the experimental demonstration, we also report a theoretical and simulative investigation on the penalty induced in this architecture by spurious connector back-reflections. We show that the resulting penalty can be kept under control for typical realistic connector reflection values, provided that each pair of lasers in both directions are separated by at least twice the system symbol rate

Green radio communication networks applying radio-over-fibre technology for wireless access

Wireless communication increasingly is becoming the first choice link to enter into the global information society. It is an essential part of broadband communication networks, due to its capacity to cover the end-user domain, outdoors or indoors. The use of mobile phones and broadband has already exceeded the one of the fixed telephones and has caused tremendous changes in peoples life, as not only to be recognised in the current political overthrows. The all-around presence of wireless communication links combined with functions that support mobility will make a roaming person-bound communication network possible in the near future. This idea of a personal network, in which a user has his own communication environment available everywhere, necessitates immense numbers of radio access points to maintain the wireless links and support mobility. The progress towards “all-around wireless” needs budget and easily maintainable radio access points, with simplified signal processing and consolidation of the radio network functions in a central station. The RF energy consumption in mobile base stations is one of the main problems in the wireless communication system, which has led to the worldwide research in so called green communication, which offers an environmentally friendly and cost-effective solution. In order to extend networks and mobility support, the simplification of antenna stations and broadband communication capacity becomes an increasingly urgent demand, also the extension of the wireless signal transmission distance to consolidate the signal processing in a centralised site. Radio-over-Fibre technology (RoF) was considered and found to be the most promising solution to achieve effective delivery of wireless and baseband signals, also to reduce RF energy consumption. The overall aim of this research project was to simulate the transmission of wireless and baseband RF signals via fibre for a long distance in high quality, consuming a low-power budget. Therefore, this thesis demonstrated a green radio communication network and the advantage of transmitting signals via fibre rather than via air. The contributions of this research work were described in the follows: Firstly, a comparison of the power consumption in WiMAX via air and fibre is presented. As shown in the simulation results, the power budget for the transmission of 64 QAM WiMAX IEEE 802.16-2005 via air for a distance of 5km lies at -189.67 dB, whereas for the transmission via RoF for a distance of 140km, the power consumption ranges at 65dB. Through the deployment of a triple symmetrical compensator technique, consisting of SMF, DCF and FBG, the transmission distance of the 54 Mbps WiMAX signal can be increased to 410km without increasing the power budget of 65dB. An amendment of the triple compensator technique to SMF, DCF and CFBG allows a 120Mbps WiMAX signal transmission with a clear RF spectrum of 3.5 GHz and constellation diagram over a fibre length of 792km using a power budget of 192dB. Secondly, the thesis demonstrates a simulation setup for the deployment of more than one wireless system, namely 64 QAM WiMAX IEEE 802.16-2005 and LTE, for a data bit rate of 1Gbps via Wavelength Division Multiplexing (WDM) RoF over a transmission distance of 1800km. The RoF system includes two triple symmetrical compensator techniques - DCF, SMF, and CFBG - to obtain a large bandwidth, power budget of 393.6dB and a high signal quality for the long transmission distance. Finally, the thesis proposed a high data bit rate and energy efficient simulation architecture, applying a passive optical component for a transmission span up to 600km. A Gigabit Optical Passive Network (GPON) based on RoF downlink 2.5 Gbps and uplink 1.25Gbps is employed to carry LTE and WiMAX, also 18 digital channels by utilising Coarse Wavelength Division Multiplexing (CWDM). The setup achieved high data speed, a low-power budget of 151.2dB, and an increased service length of up to 600km

Feed-forward linearisation of a directly modulated semiconductor laser and broadband millimetre-wave wireless over fibre systems.

This thesis is concerned with reduction of non-linear distortion in a directly modulated uncooled semiconductor laser using feed-forward compensation and investigating the performance of broadband millimetre-wave wireless over fibre systems. One of the key elements that determine the performance in a fibre optic link is the linearity of the optical source. Direct modulation of an uncooled semiconductor laser diode is a simple and cost effective solution. However, the distortion and noise generated by the laser limit the achievable dynamic range and performance in a system. Feed-forward linearisation is demonstrated at 5 GHz, the highest operating frequency reported, with 26 dB third order intermodulation distortion suppression and simultaneous noise reduction leading to enhanced spurious free dynamic range of 107 dB (1Hz). The effectiveness of feed-forward in a multi-channel system is investigated. Laser non-linearity can cause spectral re-growth and interchannel distortion that can completely mask the adjacent channel. A significant 11 dB interchannel distortion suppression and 10.5 dB power advantage is obtained compared to the non-linearised case. These results suggest that feed-forward linearisation arrangement can make a practical multi-channel or multi-operator wireless over fibre system. In the second part of this thesis the first experimental transmission of wireless data over fibre with remote millimetre-wave local oscillator delivery using a bi-directional semiconductor optical amplifier in a full duplex system with 2.2 km coarse wavelength division multiplexing fibre ring architecture is demonstrated. The use of bi-directional SOAs in place of unidirectional erbium doped fibre amplifier or unidirectional SOAs, together with the use of CWDM and optical distribution of the local oscillator signal allow substantial reduction in overall complexity and cost. Successful transmission of data over 12.8 km fibre is achieved with clear and well defined constellations and eye diagrams as well as 10.5% and 7.8 % error vector magnitude values for the downlink and uplink directions, respectively. The thesis also presents an implementation and performance of a millimetre-wave gigabit wireless over fibre system. CWDM devices such as uncooled laser diodes and passive components are used for the first time in a gigabit system allowing cost savings compared to dense WDM. This makes such solutions more attractive for millimetre-wave access systems. Optically modulated gigabit wireless data signals to and from the base stations are distributed at 5 GHz and up-converted using a remotely delivered LO source. Eye diagrams and bit error rate are measured to assess the system performance

A direct temporal domain approach for ultrafast optical signal processing and its implementation using planar lightwave circuits /

Ultrafast optical signal processing, which shares the same fundamental principles of electrical signal processing, can realize numerous important functionalities required in both academic research and industry. Due to the extremely fast processing speed, all-optical signal processing and pulse shaping have been widely used in ultrafast telecommunication networks, photonically-assisted RFlmicro-meter waveform generation, microscopy, biophotonics, and studies on transient and nonlinear properties of atoms and molecules. In this thesis, we investigate two types of optical spectrally-periodic (SP) filters that can be fabricated on planar lightwave circuits (PLC) to perform pulse repetition rate multiplication (PRRM) and arbitrary optical waveform generation (AOWG).First, we present a direct temporal domain approach for PRRM using SP filters. We show that the repetition rate of an input pulse train can be multiplied by a factor N using an optical filter with a free spectral range that does not need to be constrained to an integer multiple of N. Furthermore, the amplitude of each individual output pulse can be manipulated separately to form an arbitrary envelope at the output by optimizing the impulse response of the filter.Next, we use lattice-form Mach-Zehnder interferometers (LF-MZI) to implement the temporal domain approach for PRRM. The simulation results show that PRRM with uniform profiles, binary-code profiles and triangular profiles can be achieved. Three silica based LF-MZIs are designed and fabricated, which incorporate multi-mode interference (MMI) couplers and phase shifters. The experimental results show that 40 GHz pulse trains with a uniform envelope pattern, a binary code pattern "1011" and a binary code pattern "1101" are generated from a 10 GHz input pulse train.Finally, we investigate 2D ring resonator arrays (RRA) for ultraf ast optical signal processing. We design 2D RRAs to generate a pair of pulse trains with different binary-code patterns simultaneously from a single pulse train at a low repetition rate. We also design 2D RRAs for AOWG using the modified direct temporal domain approach. To demonstrate the approach, we provide numerical examples to illustrate the generation of two very different waveforms (square waveform and triangular waveform) from the same hyperbolic secant input pulse train. This powerful technique based on SP filters can be very useful for ultrafast optical signal processing and pulse shaping