Electrical and Electronic Engineering - Theses
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ItemOptical add-drop multiplexers and amplifier placement methods for metropolitan WDM ring network( 2002)The tremendous growth in broadband communication services, brought about by the phenomenal expansion of the Internet, has triggered an unprecedented demand for bandwidth in telecommunication networks. Optical fibre communication technology has kept up with the growing bandwidth demand by exploiting wavelength division multiplexing (WDM) technology. WDM is now beginning to expand from a network core technology towards the metropolitan and access networks with the goal of bringing the benefit of cost and network efficiencies of the optical networking revolution to the end users. The advent of metropolitan WDM networks has motivated the work in this thesis to develop new devices and design methods in order to reduce cost and improve network performance. This thesis explores the design of new optical add-drop multiplexers (OADMs), which are critical devices enabling the realisation of metropolitan WDM ring networks. Three types of OADMs are investigated corresponding to different network requirements, namely fixed, reconfigurable, and bidirectional OADMs. Three new fixed single-channel OADMs are proposed and demonstrated. The devices use a multi-port optical circulator (OC) and one or two fibre Bragg gratings (FBGs), depending on crosstalk requirements. The OADMs have a simple and compact configuration, low insertion loss, and excellent crosstalk performance. Two new reconfigurable multi-channel OADMs (RM-OADMs) are also proposed and demonstrated in this thesis. The devices employ multi-port OCs, FBGs, and optical switches (OSWs). By effectively using 8- port OCs, the new RM-OADMs significantly reduce component count and insertion loss, and achieve good crosstalk characteristics. One of the new RM-OADMs potentially has the lowest insertion loss among existing RM-OADMs. This thesis also presents a new bidirectional OADM (BOADM) with gain for use in single-fibre bidirectional networks. With the use of multi-port OCs, FBGs, and a single amplifier element, the new structure can add and/or drop channels in both directions and achieves more than 16 dB of bidirectional gain. The BOADM utilises FBGs and light absorbers to remove Rayleigh backscattered and reflected light. All of the proposed OADMs have the potential to be commercially deployed in metropolitan WDM networks. This thesis also investigates new amplifier placement methods to reduce the number of amplifiers in metropolitan WDM rings. Two amplifier placement methods for single-fibre ring networks are developed based on integer programming techniques. The first method describes the amplifier placement problem exactly and uses a nonlinear programming solver to obtain a solution. The second method approximates some requirements in the problem and employs a linear programming solver to derive the amplifier placement solution. Both logical-meshed and logical-hubbed ring networks are investigated. A new amplifier placement method for self-healing WDM rings is also developed in this thesis. The new method is based on iteratively solving an amplifier placement problem for a ring network under different link failure scenarios. The solution provides a minimum number of amplifiers required to operate the self-healing ring under a normal, or any single link or single node failure conditions. Amplifier placement solutions for different network architectures including logical-hubbed unidirectional, logical-meshed unidirectional, and bidirectional self-healing rings are presented.