All-optical router with PPM header processing in high speed photonic packet switching networks

Rapidly growing internet traffic volume is the major driving force behind the development of optically-transparent and ultra high-capacity photonic packet-switching networks. In such networks, the packet routing decision at each router is made by sequentially correlating an incoming packet header address with addresses in all entries of the router's look-up routing table. The routing task is achieved in the optical domain using all-optical logic gates and optical correlator technologies which have been predominantly replacing the existing low-speed electronic processing devices. Nevertheless when a network is expanded, a larger routing table is required thus exponentially increasing header processing time, which results in the increases in routing latency and complexity. This research aims to significantly reduce the size of the routing table and the number of optical devices required in a router by mapping both the packet header address and the look-up routing table entries into the pulse-position-modulation format, where more than one address could be located in a single entry of a new pulse-position routing table. By simply carrying out a single correlation of the packet header address with pulse- position routing table entries, the router can instantly obtain the routing decision, thus significantly reducing the processing time and neglecting the gain recovery time in existing optical logic gates. The structure of the pulse-position routing table also offers flexibility in the transmission mode including unicast, multicast or broadcast embedded in the optical (physical) layer. In the thesis, a new router based on the pulse-position¬modulation scheme will be introduced. Essential router modules including high on-off contrast-ratio clock extraction, pulse position routing table, header processing and optical switch are proposed and analysed. In addition, the thesis investigates and improves the switching window profile and residual crosstalk performance of the all- optical Mach-Zelmder switches as a building block for the implementation of the above router modules. A number of new variants of Mach-Zehnder-based switches are also introduced to enhance switching inter-output contrast ratio and reduce the complexity in multiple-channel OTDM demultiplexing

All-optical flip flop based on a symmetric Mach-Zehnder switch with a feed-back loop and multiple forward set/reset signals

The paper proposed an improved performance for optical flip-flop using symmetric Mach-Zehnder interformeter with a feedback and multiple forward configurations. At the optimum operating condition for the optical flip-flop, high contrast ratio of 22 dB can be achieved. The findings in the paper will have an impact on the design of future optical flip-flop and other optical logic gates such as exclusive OR and NAND gates. A PhD research (Le-Minh) funded by the University Studentship, completed in 200

BER performance analysis of 100 and 200 Gbit/s all-optical OTDM node using symmetric Mach-Zehnder switches

New insight to the feasibility of all-optical ultra speed switching up to 200 Gb/s. The technique will reduce the dependency and bottleneck on the electronic-to-optical-to-electronic conversion. Current conversion speed is up to 40 Gb/s in laboratories. The novel clock extraction technique proposed shows the potential of an all-optical switch. The research results are directly relevant to the access technology where optical fibre and RF is competing to be the solution. The growing demands of bandwidth will exceed RF capability while the optical fibre will be the optimum solution. A PhD project (Le-Minh) funded by the University Studentship, completed in 2007

Indoor gigabit optical wireless communications: challenges and possibilities

Indoor Gigabit optical wireless communication systems have the potential to offer multiple high-speed data services that can be delivered to homes via an optical fibre cable in the near future. In this paper we will discuss the challenges involved in the design of such systems and future possible advances. Results from a recent cellular Gigabit prototype link will also be presented and discussed

High speed short range optical wireless ground-to-train communications

There is a huge demand for seamless high-speed communications in fast moving trains. People want broadband services while on board as in their home or in the workplace. This demand drives the motivation for a high speed dedicated optical wireless link. Here we propose a free space optical ground-to-train communications system which consists of optical transceivers placed on the train and along the railway track. A mathematical model for three different scenarios when the train is moving has been developed. The optical link analysis, results as well as a simple proof of concept are also presented

Power distribution investigation of a hexagonal diffused cellular indoor visible light communications system

This paper presents a three dimensions (3D) model of optical power distribution in a diffused cellular indoor visible light communication (VLC) system. To achieve an ideal system which has a maximum coverage area with a minimum power consumption, both hexagon geometric structure and holographic light shaping diffuser (LSD) are employed. We analysed the mathematical models for both square and hexagonal structures with and without using LSD. In addition, the practical system consisting of a (Luxeon Star/O) royal blue LED as a transmitter is used to verify and evaluate the system performance. The system operates at a date rate of 5 Mb/s using the on-off keying non-return-to-zero (OOK-NRZ) modulation format. The simulation results show that using hexagon geometry and a 30o holographic LSD diffuser, the received optical power distribution becomes uniform. The coverage area of the cellular link is therefore significantly extended by 343%. In addition the experimental results for a single cell system are also presented

All optical fog-sensor for determining the fog visibility range in optical wireless communication links

The goal of this research work is to use an all optical based fog sensor to study the atmospheric visibility of fog and its constituents on the optical wireless communication (OWC) links in a controlled laboratory test-bid. The fog sensor measures the transmittance of the Infrared (IR) radiations which is used to determine the link visibility. Experimental results obtained show that using the fog sensor the visibility range from 0.37 – 1 km and above with respect to different fog density can be predicted

Deterministic scheduling for energy efficient and reliable communication in heterogeneous sensing environments in industrial wireless sensor networks

The present-day industries incorporate many applications, and complex processes, hence, a large number of sensors with dissimilar process deadlines and sensor update frequencies will be in place. This paper presents a scheduling algorithm, which takes into account the varying deadlines of the sensors connected to the cluster-head, and formulates a static schedule for Time Division Multiple Access (TDMA) based communication. The scheme uses IEEE802.15.4e superframe as a baseline and proposes a new superframe structure. For evaluation purposes the update frequencies of different industrial processes are considered. The scheduling algorithm is evaluated under varying network loads by increasing the number of nodes affiliated to a cluster-head. The static schedule generated by the scheduling algorithm offers reduced energy consumption, improved reliability, efficient network load management and improved information to control bits ratio