M.Ing. / Bragg gratings written in polymer optical fibres are much more sensitive to temperature and strain measurements than silica fibre with a lower Young's modules and higher temperature coefficient. The good biocompatibility of polymer fibres makes them ideal medical sensors for in vivo strain and temperature measurements as well as excellent chemical sensors that can easily be doped with organic compounds. Most of the Bragg gratings in polymer optical fibres are inscribed around 1550 nm where the attenuation is as large as 1 dB/em. Grating fabrication was investigated at 980 nm where the attenuation was discovered to be optimal (less than 0.1 dB/em). The polymer optical fibre was spliced to silica optical fibre through butt-coupling and affixed with optical adhesive to produce transmission loss of between 7 and 25 dB (at 980 nm). Preliminary results show that it may be possible to create fibre Bragg gratings in polymer optical fibre at 980 nm. Gratings inscribed in fibre with an energy density of between 80 and 150 mJ/cm2 supplied by Paradigm Optics (MORFOP3) had a repeatability of 25%. With the fibres supplied by Prof. Peng (PBzMA- PEMA- PMMA co-polymer) a success rate of more than 90% was achieved when using energy densities around 70 mJ/cm2 • However, these gratings were weak and disappeared within 48 hours. The strength of these gratings varied from grating to grating. The reason of this instability is unknown and should be further investigated. The temperature sensitivity of polymer optical fibre at 976 nm was found to be -100 ±17 pm;oc corresponding with the reported value of -94 pm;oc at 976 nm.

No description available.

Thesis (Ph.D.)--Pennsylvania State University, 2007. / Mode of access: World Wide Web.

This thesis contributes to the realisation of plasmonic lasers based on plasmon polariton Bragg gratings. The scope of this thesis is twofold. In the first section, entitled Passive plasmonic Bragg grating characterization, the results of the testing and characterization of a new design of plasmonic Bragg gratings in the near-infrared are presented. The reflection and transmission responses expected from plasmon-polariton Bragg gratings (PPBGs) are treated theoretically using the transfer matrix method (TMM) and the numerical model is validated experimentally. The experimental setup and procedures are then described in detail. Results show that the near-infrared plasmon polariton Bragg gratings possess a Bragg reflection at a wavelength close to the Bragg wavelength predicted by TMM. In the second section, Gain optimisation and bleaching of IR-140 doped PMMA, an in-depth analysis of the gain medium (IR-140 dye doped poly(methyl methacrylate) better known as PMMA) is performed. This gain medium was selected as a gain layer for active plasmonic gratings and distributed feedback lasers designed by a colleague Ph.D. candidate. The optimized molecular weight of IR-140 in PMMA was found to be 0.9% to obtain a material gain of 81 cm-1.

M.Phil. (Electrical and Electronic Engineering) / A numerical model of an Erbium-Ytterbium co-doped distributed feedback (DFB) fiber laser is developed. The DFB fiber laser is a short length fiber laser whose feedback is distributed throughout the cavity. Its main advantage is its single longitudinal mode operation. The amplifying medium of a DFB fiber laser is a few centimetres long rare earth doped fiber. The feedback is obtained by a fibre Bragg grating printed in the core of the rare earth doped fiber. This type of laser emits naturally in two longitudinal modes. To obtain the single longitudinal mode operation, a π phase shift is introduced in the middle of the grating. Erbium doped DFB fiber lasers present the advantage of emitting single frequency light in the 1550 nm region where telecommunication fibers present the minimum loss. However due to the relatively short length of the gain medium, the number of available Erbium ions is small; as a result pump power absorption is low and the efficiency of the fiber laser is strongly reduced. The straightforward solution to this problem could be increasing the concentration of Erbium ions. This solution however has the disadvantage of increasing the Erbium ions interactions, thus leading to detrimental effect like cooperative upconversion and excited state absorption, which in term reduce considerably the laser efficiency. The best solution is to use Ytterbium ions as sensitizers along with Erbium ions to enhance the pump absorption, hence the efficiency of the laser. A model of the DFB fiber laser is an indispensable tool for its design, because it allows one to predict characteristic behaviour that would be both difficult and costly to deduce in laboratory conditions. The model developed in this project is based on rate equations of the Er3+-Yb3+ gain medium and coupled mode equations describing the laser field propagation in the fibre Bragg grating structure. The equations are solved using a quasi-analytical iterative method along with transfer matrix method with appropriate boundary conditions. The quasianalytical method used in this thesis is more robust than numerical solutions because it does not require providing an initial guess on the solution. Furthermore this method is hundreds time faster than the exact numerical solution while giving almost similar results.

Thesis (Ph. D.)--Drexel University, 2005. / Includes abstract and vita. Includes bibliographical references (leaves 127-132).

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 50-54). Also available on the World Wide Web.

M.Ing. / Fibre Bragg gratings (FBGs) have been manufactured for the first time in South Africa by means of the phase mask method. It is possible to manufacture not only uniform FBGs, but also chirped FBGs. The optical fibre that is used for imprinting the FBGs can also be hydrogen loaded locally. FBGs with a reflectivity of 99.7% and higher can be written by making use of the experimental setup presented in this thesis. It is possible to manufacture a FBG with a centre wavelength that has any value between the Bragg wavelength and approximately 6 nm lower than the Bragg wavelength. This is done by stretching the optical fibre prior to the writing process. FBGs have been simulated in MATLAB to get an idea of what one may expect during the manufacturing process. The program makes it possible to simulate the effects of changes in grating length, index modulation, pressure, temperature and strain on the centre wavelength of an FBG. Dispersion is explained in detail. Chromatic dispersion, which is part of dispersion as a whole, can be cancelled by making use of an FBG. The different techniques for the measurement of chromatic dispersion is explained. Some insight is given on dispersion (the pulse broadening in the time domain due to the different velocities of different wavelengths from the source's finite optical bandwidth) compensation. An FBG that was manufactured locally has been tested as a dispersion compensator. It was found that an FBG is effective in performing this function.

No description available.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 140-144).