Digital signal processing optical receivers for the mitigation of physical layer impairments in dynamic opticaludnetworks

摘要

IT IS generally believed by the research community that the introduction of complexudnetwork functions—such as routing—in the optical domain will allow a better networkudutilisation, lower cost and footprint, and a more efficiency in energy usage. The new opticaludcomponents and sub-systems intended for dynamic optical networking introduceudnew kinds of physical layer impairments in the optical signal, and it is of paramountudimportance to overcome this problem if dynamic optical networks should become audreality. Thus, the aim of this thesis was to first identify and characterise the physicaludlayer impairments of dynamic optical networks, and then digital signal processingudtechniques were developed to mitigate them.udThe initial focus of this work was the design and characterisation of digital opticaludreceivers for dynamic core optical networks. Digital receiver techniques allow for complexudalgorithms to be implemented in the digital domain, which usually outperformudtheir analogue counterparts in performance and flexibility. An AC-coupled digital receiverudfor core networks—consisting of a standard PIN photodiode and a digitiser thatudtakes samples at twice the Nyquist rate—was characterised in terms of both bit-errorudrate and packet-error rate, and it is shown that the packet-error rate can be optimised byudappropriately setting the preamble length. Also, a realistic model of a digital receiverudthat includes the quantisation impairments was developed. Finally, the influence ofudthe network load and the traffic sparsity on the packet-error rate performance of theudreceiver was investigated.udDigital receiver technologies can be equally applied to optical access networks,udwhich share many traits with dynamic core networks. A dual-rate digital receiver, capableudof detecting optical packets at 10 and 1.25 Gb/s, was developed and characterised.udThe receiver dynamic range was extended by means of DC-coupling and non-linearudsignal clipping, and it is shown that the receiver performance is limited by digitiserudnoise for low received power and non-linear clipping for high received power.