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.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 110-123). Available also in a digital version from Dissertation Abstracts.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 56-58). Also available in electronic version.

Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2007. / Ali Adibi, Committee Member ; Rick Trebino, Committee Member ; John Barry, Committee Co-Chair ; William Rhodes, Committee Member ; Steve McLaughlin, Committee Member ; Gee-Kung Chang, Committee Chair.

Thesis (Ph.D.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves105-108)

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.

No description available.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The properties of photo-induced gratings in germania doped glass fibers were studied. Permanent phase gratings in a fiber core were fabricated by the mixing of two contra propagating waves. Experiments are described and results are presented which show that the strength of a photoinduced grating is strongly dependent on the writing power as well as the laser writing wavelength. A rigorous development of linear coupled mode theory for the contra propagation geometry is given and used to model the experimentally observed grating responses as a function of fine tuning frequency of probing light. Measurements have been done of the amplitude and phase response of the grating structure and compared with theoretical models of uniform and chirped gratings. The theoretically predicted negative group velocity dispersion in fiber grating was observed interferometrically and described in detail. The nonlinear coupled mode theory has been fully implemented in a computer program and some numerical results are given in the second part of this thesis. The dynamics of a pulse propagating in the fiber grating is simulated and the results show its dependence on pulse energy, frequency detuning, and the type of grating geometry. A limitation is found in the dispersion property of a constant amplitude fiber grating so that the pulse compression ratio and the width of a compressible pulse is strictly limited to ≅250 picoseconds.