published_or_final_version / abstract / toc / Computer Science / Doctoral / Doctor of Philosophy

Electro-optic (EO) beam deflectors are voltage-controlled devices widely used for scanning and switching applications. For example, high-speed, low-loss optical switches aimed at future optical networks can be built on EO deflectors. Novel EO deflectors distinguish themselves with a much-improved steering performance, high-speed response and simple fabrication requirements. Patterned ferroelectric crystals such as LiTaO3 are first poled to provide the required prism shaped domain structures. The application of an electrical field across the entire crystal can then be used to drive the trajectory of the beam as it travels through the poled wafer. The electric field induces an index change of opposite magnitude on the adjacent domain regions in the EO device, causing the optical beam to refract at the interfaces. / Although rectangular geometry is extensively employed in EO devices, nonrectangular scanners have demonstrated better deflection performance. Two new nonrectangular geometries capable of further enhancing the deflection performance of EO beam scanners, proposed in this dissertation, were constructed. Their parabola and half-horn geometries provide 2-3 degrees of steering, which is 2-3 times greater than the steering provided by rectangular deflectors. / EO deflectors based on the parabola and the half-horn geometries, which can provide larger deflection angles, were built. These devices demonstrated a deflection angle of 3.1°, less than 5 dB of insertion loss from fiber to fiber, and -40 dB of crosstalk. / Two packaged optical switches using rectangular EO deflectors were demonstrated. By combining these EO deflectors with fiber collimators and high voltage packaging, high speed optical switches were built and characterized. The switch design was based on a 500mum z-cut LiTaO3 single crystal wafer fabricated using the domain inversion method. The 1x2 switch had a maximum deflection angle of 1.22° with an applied voltage of 1.1 kV and the 1x4 switch had a maximum deviation angle of 2.14°, with an applied voltage of 1 kV. The average insertion loss and crosstalk figures were 2.36 dB and -36 dB, respectively. The worst case switching time was 86 ns.

Submitted in partial fulfillment for the Masters in Engineering Degree: Electrical Engineering, Department of Electrical Engineering, Durban University of Technology, Durban, South Africa, 2017. / All-optical networks (AON) based optical burst switching (OBS) promise to be the ultimate backbone network technology solution for next generation( NG) as well as fu­ ture generation (FG)networks because of their relatively higher resources utilization, great flexibility at lower cost and potential massive bandwidth capacities both at trans­ mission and switching levels. By design, buffering is not provisioned in interior nodes. End users exchange data with one another through end-to-end light channels, called lightpaths in which wavelength continuity is maintained. In practice, their establish­ ing, in a cost effective manner remains an inescapable challenge. The routing and wave­ length assignment (RWA) problem entices successful establishment of a physical route for each lightpath connection request, assigning a wavelength to each route and at the same time ensm·ing end to end continuity, subject to the limited number of wave­ lengths. The wavelengths must be assigned such that no lightpaths can share the same wavelength simultaneously on a given fibre, or else contentions may occur. Some data bursts may be discarded whenever contention occurs among multiple bursts that arrive simultaneously at any interior node using the same wavelength and are intended for the same output port. Because of the buffer-less nature of OBS networks, conten­ tion/congestion in the core network can quickly lead to degradation in overall network performance at moderate to high traffic levels due to heavy burst loses. In this disser­ tation we propose and evaluate a congestion management approach we refer to as '"en­ hanced congestion management" which gears towards rendering and guaranteeing a consistent QoS as well as rational and fair use of available network links. Simulation results show that the scheme can effectively minimize both contention and congestion and at the same time improving both throughput and effective utilization under mod­ erate to high network traffic loads / M

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A single user deconcentrator is designed for a circuit switched digital switching system which emphasizes mass conferencing. The switching system consists of distributed concentrators which include a first level of conferencing and a broadcast bus which includes a second level of conferencing. The deconcentrator features volume adjustment of individual conferences as well as a third and last level of conferencing- a conference of the individual conferences obtained from the broadcast bus. The design identifies the MSI and SSI components of the deconcentrator and provides an estimate of timing and board size. An alternative volume adjustment algorithm and the extension of a single user deconcentrator to a multi-user deconcentrator is discussed.

Data link control, multiple access, and flow control for data communication have at last advanced to the state that it is possible for applications that require combining these techniques to be carried out. Therefore, research efforts are now beginning to focus on the performance of these applications, rather than the previous trend of carrying out the performance of each scheme separately. This study analyses the performance of a Very Small Aperture Terminal (VSAT) satellite star network. The network uses roll-call polling as its multiple access scheme, High-level Data Link Control or HDLC, and go-back-N Automatic Repeat Request, for error control. The network is a VSAT packet-switched network, that carries out its communications task on a Time Division Multiplexing (TDM) satellite channel. This research consists of three major parts. First, the performance analysis of the single-hop star architecture network is carried out. This includes the study of a polling communication system for the inbound, VSAT-to-Hub line. The time delay of a packet using the inbound line is evaluated. Secondly, the performance analysis of the TDM outbound Hub-to-VSAT line is represented. The throughput of the multiplexed system for the outbound Hub-to-VSAT line, as well as the average time delay of a packet are determined. Thirdly, both the analysis of the inbound, and outbound lines are combined to provide the performance of the double-hop architecture of the network. The time delay of a VSAT-to-VSAT packet is found. / Master of Science

by Kit-man Chan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 82-86). / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Overview of Integrated Service Digital Networks --- p.1 / Chapter 1.2 --- Multirate Loss Networks --- p.5 / Chapter 1.3 --- Previous Work --- p.7 / Chapter 1.4 --- Organization --- p.11 / Chapter 1.5 --- Publications --- p.12 / Chapter 2 --- Call Admission in Multirate Loss Networks --- p.13 / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.2 --- Two Adaptive Routing Rules --- p.15 / Chapter 2.3 --- Call Admission Policies --- p.17 / Chapter 2.4 --- Analysis of Call Admission Policies --- p.25 / Chapter 2.4.1 --- "The CS, LO, GB and the EB Policies" --- p.25 / Chapter 2.4.2 --- The DP Policy --- p.29 / Chapter 2.5 --- Performance Comparisons --- p.32 / Chapter 2.6 --- Concluding Remarks --- p.35 / Chapter 3 --- Least Congestion Routing in Multirate Loss Networks --- p.41 / Chapter 3.1 --- Introduction --- p.41 / Chapter 3.2 --- The M2 and MTB Routings --- p.42 / Chapter 3.2.1 --- M2 Routing --- p.43 / Chapter 3.2.2 --- MTB Routing --- p.43 / Chapter 3.3 --- Bandwidth Sharing Policies and State Aggregation --- p.45 / Chapter 3.4 --- Analysis of M2 Routing --- p.47 / Chapter 3.5 --- Analysis of MTB Routing --- p.50 / Chapter 3.6 --- Numerical Results and Discussions --- p.53 / Chapter 3.7 --- Concluding Remarks --- p.56 / Chapter 4 --- The Least Congestion Routing in WDM Lightwave Networks --- p.60 / Chapter 4.1 --- Introduction --- p.60 / Chapter 4.2 --- Architecture and Some Design Issues --- p.62 / Chapter 4.3 --- The Routing Rule --- p.66 / Chapter 4.4 --- Analysis of the LC Routing Rule --- p.67 / Chapter 4.4.1 --- Fixed Point Model --- p.67 / Chapter 4.4.2 --- Without Direct-link Priority --- p.68 / Chapter 4.4.3 --- With Direct-link Priority --- p.72 / Chapter 4.5 --- Performance Comparisons --- p.73 / Chapter 4.6 --- Concluding Remarks --- p.75 / Chapter 5 --- Conclusions and Future Work --- p.79 / Chapter 5.1 --- Future Work --- p.80

by Kwok Siu Yu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 48-49). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background of switching networks --- p.1 / Chapter 1.2 --- Nonblocking properties of 3-stage networks --- p.5 / Chapter 1.3 --- Wide-sense nonblocking networks --- p.10 / Chapter 1.4 --- Routing algorithms by packing --- p.12 / Chapter 2 --- The Concept of the Upper Ideals --- p.15 / Chapter 3 --- "Routing algorithm over the network [6x10, 3x3, 10x6]" --- p.26 / Chapter 4 --- Simulation Program (SP) --- p.30 / Chapter 5 --- "Nonexistence of routing algorithm over the network [5x8, 3x3, 8x5]" --- p.35 / Chapter 6 --- Packing algorithms --- p.42 / Chapter 7 --- Summary and directions of further study --- p.47

Yang Qin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves [65]-[67]). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Thesis Overview --- p.7 / Chapter 2 --- Storage Area Network(SAN) --- p.9 / Chapter 2.1 --- Fibre Channel Protocol --- p.11 / Chapter 2.2 --- Switched Fibre Channel SAN --- p.16 / Chapter 2.2.1 --- Cascaded Topology --- p.17 / Chapter 2.2.2 --- Meshed Topology --- p.17 / Chapter 2.2.3 --- Cross-Connected Topology --- p.19 / Chapter 2.2.4 --- Routing Scheme in Cross-Connected SAN --- p.21 / Chapter 3 --- Path Switching --- p.24 / Chapter 3.1 --- Cross-path Switching Principle --- p.24 / Chapter 3.2 --- Capacity Assignment --- p.28 / Chapter 3.3 --- Route Assignment --- p.31 / Chapter 4 --- Path Switching in Cross-Connected SAN --- p.34 / Chapter 4.1 --- Path Switching in SAN --- p.34 / Chapter 4.1.1 --- Connectionless Traffic --- p.36 / Chapter 4.1.2 --- Connection-Oriented Traffic --- p.39 / Chapter 4.1.3 --- Mixed Traffic --- p.47 / Chapter 4.2 --- Measurement Based Algorithm --- p.53 / Chapter 4.3 --- Repetition Rate --- p.59 / Chapter 5 --- Conclusion --- p.63

Lee Ka-lun. / "September 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.