Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 131-141). Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 174-187). Available also in a digital version from Dissertation Abstracts.

D.Phil. / This dissertation deals with the fabrication, characterisation, and applications of long-period gratings in optical fibre communications and sensing systems. The aim of this project is to assess long-period gratings as media for active or passive fibre devices, particularly as components for the telecommunications industry. A review of the properties and characteristics of fibre gratings associated with the photosensitivity of germanosilicate fibres is provided, which includes a theoretical analysis of the principles of operation for short-period gratings (fibre Bragg gratings) and long-period gratings. The simulations of the spectral response from these two types of gratings are also presented. A number of long-period grating fabrication methods and techniques, which were reported by some researchers, are reviewed. In this project, the normal long-period gratings and phase-shifted long-period gratings are fabricated by using a line-narrowed KrF excimer laser combined with the metal amplitude mask technique. The metal mask is made of a stainless steel sheet, and the slot width (periodicity) is processed by using high quality photographic tooling. Three normal long-period gratings with different periodicities and one phase-shifted long-period grating can be manufactured simultaneously because there are four metal masks imprinted in one inexpensive stainless steel sheet. The mass-production of long-period gratings becomes possible, and the number of gratings that can be written is limited only by the excimer laser beam or metal mask dimension orthogonal to the fibre axis. The fibres that are used in our experiments are photosensitive optical fibres (PS1500). Long-period gratings can be written directly into these fibres without hydrogenation. Two types of long-period grating devices are investigated and developed for applications in dense wavelength division multiplexing (DWDM)networks: erbium-doped fibre amplifier (EDFA) gain-flattening filters and wavelength-tuneable add/drop multiplexers. Firstly, the transmission characteristics of phase-shifted long-period gratings are simulated theoretically by a combination of the coupled-mode theory and the fundamental-matrix method. It is suggested that a phase-shifted long-period grating device cascaded with another normal long-period grating can be used to flatten the gain spectrum of an EDFA containing three gain peaks. The experimental results show that a broad amplifier with peak-to-peak variations of less than 0.7 dB over 36 nm from 1526 to 1562 nm, which covers the entire C-band of the EDFA, can be realized practically. Next, a wavelength-tuneable add/drop multiplexer is designed and configured. In this device, four identical long-period gratings are assembled on piezoelectric ceramic fibre stretchers. The modelling of the device predicts that 50 ITU DWDM-channel signals could be selected in the wavelength range from 1526.25 to 1563.75 nm with 0.75 nm channel spacing and the cross-talk is less than –39 dB while the total insertion loss is about 0.24 dB. There are some significant advantages of wavelength-tuneable add/drop multiplexing devices over conventional fibre Bragg grating-based devices. (1) There is back reflected light and almost no cross-talk power penalty because the long-period grating couples light into forward-propagating modes. (2) Signal channel isolation is very high due to three stages of coupling mechanisms used in this device, which includes core-cladding, cladding-cladding and cladding-core, efficiently filtering out non-resonant light. (3) The insertion loss of the device is limited only by the separation of two long-period gratings, because there are no losses on non-resonant wavelengths of long-period gratings. Several other applications of long-period gratings in optical sensing systems are also described, and some are experimented on including axial strain sensors, structural bend sensors, temperature sensors, refractive index sensors and chemical concentration sensors.

This thesis reports original work on suppression of transient gain excursions in an erbium-doped fibre amplifier (EDFA). The work presented in this thesis is a detailed investigation of four closed-loop systems that control the EDFA gain dynamically. The performance of the four closed-loop systems is evaluated by analytical work, supplemented by computer simulations and insystem measurements performed on a hardware EDFA. In addition, a stability analysis of the four closed-loop systems is presented. In the stability analysis presented in this thesis, nonlinear nature of the four closed-loop systems is taken into consideration. In the stability analysis, in addition to proving that the four closed-loop systems considered are stable, it is proven that for any practical values of the EDFA gain at the initial time of observation, the EDFA gain is restored to the desired value in steady state. These outcomes of the stability analysis are supported by simulation results and experimental results. Errors in system modelling, change in the operating point of the nonlinear closed-loop system, and measurement noise are important aspects of practical implementations of systems that control the EDFA gain dynamically. A detailed analysis of the effects these practical aspects have on the performance of the four closed-loop systems considered is presented. The analysis is validated using computer simulations and experimental measurements. In most of the work reported in the literature on controlling the EDFA gain, controllers that include feedforward and/or feedback components are employed. In the traditional approaches to combining the feedforward and the feedback components, large transient excursions of the EDFA gain can still occur due to errors in the control provided by the feedforward component. In this thesis, a novel approach to combining the feedforward and the feedback components of the controller is presented. Based on the analytical work, the computer simulations and the experimental work presented in this thesis, the novel approach provides a significant reduction in the excursions of the EDFA gain in the transient period.

Thesis (Ph.D.)--University of Western Australia, 2007.

Recent experiments with optical fibers have reached a remarkable development for optical communication spectroscopy as well as a medical technology. Hollow optical fibers are required for optical communications. The measurement of the transmission of light through fibers can provide information about the fiber quality and about the far-field energy which radiates from the fiber end. We used five flexible hollow fused quartz fibers to study laser beam propagation down the fiber axis. Five different refractive index fluids were prepared and inserted into the fiber core to measure the transmitted intensity as a function of core property. The plots of the normalized, relative transmitted intensity measured as a function of the beam insertion point show the dependence of the transmitted intensity as a function of fiber diameter and refractive index fluid.

A study is hereby presented on system embedded photonic interconnect technologies, which would address the communications bottleneck in modern exascale data centre systems driven by exponentially rising consumption of digital information and the associated complexity of intra-data centre network management along with dwindling data storage capacities. It is proposed that this bottleneck be addressed by adopting within the system electro-optical printed circuit boards (OPCBs), on which conventional electrical layers provide power distribution and static or low speed signaling, but high speed signals are conveyed by optical channels on separate embedded optical layers. One crucial prerequisite towards adopting OPCBs in modern data storage and switch systems is a reliable method of optically connecting peripheral cards and devices within the system to an OPCB backplane or motherboard in a pluggable manner. However the large mechanical misalignment tolerances between connecting cards and devices inherent to such systems are contrasted by the small sizes of optical waveguides required to support optical communication at the speeds defined by prevailing communication protocols. An innovative approach is therefore required to decouple the contrasting mechanical tolerances in the electrical and optical domains in the system in order to enable reliable pluggable optical connectivity. This thesis presents the design, development and characterisation of a suite of new optical waveguide connector interface solutions for electro-optical printed circuit boards (OPCBs) based on embedded planar polymer waveguides and planar glass waveguides. The technologies described include waveguide receptacles allowing parallel fibre connectors to be connected directly to OPCB embedded planar waveguides and board-to-board connectors with embedded parallel optical transceivers allowing daughtercards to be orthogonally connected to an OPCB backplane. For OPCBs based on embedded planar polymer waveguides and embedded planar glass waveguides, a complete demonstration platform was designed and developed to evaluate the connector interfaces and the associated embedded optical interconnect. Furthermore a large portfolio of intellectual property comprising 19 patents and patent applications was generated during the course of this study, spanning the field of OPCBs, optical waveguides, optical connectors, optical assembly and system embedded optical interconnects.

Shi Lei = 溶凝膠分佈反饋波導激光器之光學性質的研究 / 石蕾. / "September 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (p. 150-171) / 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. / Shi Lei = Rong ning jiao fen bu fan kui bo dao ji guang qi zhi guang xue xing zhi de yan jiu / Shi Lei.

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