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Long-Period Fiber Gratings Fabricated In B-Ge Codoped Fibers And Their Applications

Posted on:2013-05-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:Barerem-Melgueba MaoFull Text:PDF
GTID:1228330395992931Subject:Optical communication technology
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It is undeniable that the advent of optical fiber-based devices has revolutionized the telecommunications industry by providing high-quality, high performance, high-capacity and high speed telecommunications links. Optical fiber-based devices have also made enormous changes in the sensors industry. The discovery of photosensitivity in optical fibers and the possibility to change the core refractive index in single mode fibers lead to a special type of optical fiber-based devices called fiber gratings:fiber Bragg gratings and long-period fiber gratings. Optical fiber gratings are widely used in optical communication field as well as in fiber optic sensors field; they present numerous advantages such as immunity to electromagnetic interference, small size, high sensitivity, light weight.In this thesis, we have fabricated some long-period fiber gratings in B-Ge codoped photosensitive fibers and experimentally demonstrated some of their potential applications. High photosensitive B-Ge codoped fibers with mode field diameters allowing them to be spliced to standard telecommunications fibers are used instead of hydrogen-loaded fibers in order to avoid the time and energy consuming hydrogen-loading process and to avoid the gratings instability effects due to hydrogen out diffusion.Firstly, we present a start of the art in the field of fiber gratings. Then, a review of fiber gratings theory is presented. Two different formalisms used for theoretical analysis of fiber gratings are reviewed:the coupled-mode theory and the transfer matrix method.A review of photosensitization techniques and photosensitivity mechanisms is depicted followed by a review of fiber gratings fabrication techniques. The fiber gratings fabrication system developed in our laboratory is presented.Experimental investigations of thermal response of long-period fiber gratings fabricated in B-Ge codoped fibers are presented. The long-period fiber gratings show high temperature sensitivity and can be used as temperature sensors. The temperature sensitivities of these gratings have to be considered when they are designed for telecommunications applications.We have proposed and demonstrated a liquid level sensor based on the refractive index sensitivity of long-period fiber gratings by measuring the wavelength shifts of a particular attenuation band. We compare the performances of two long-period fiber gratings based liquid level sensors that are fabricated using two B-Ge co-doped fibers with different doping concentrations. The experimental results show that the fiber dopants concentrations have significant effects on the shift of long-period fiber gratings’ resonance wavelengths. Our investigations offer a route to improve the measurement sensitivity of liquid level sensors based on long-period fiber gratings and also to understand the mechanisms underlying these types of sensors.
Keywords/Search Tags:Fiber gratings, long-period fiber gratings, doping concentrations, temperaturesensitivity, refractive-index sensitivity, liquid level sensor
PDF Full Text Request
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