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Title: Development of polymer fibre bragg grating sensors for medical applications
Authors: Bonefacino, Julien
Advisors: Tam, Hwa-yaw (EE)
Keywords: Optical fibers
Polymers -- Optical properties
Optical fiber detectors
Optical fibers in medicine
Issue Date: 2017
Publisher: The Hong Kong Polytechnic University
Abstract: Polymer optical fibres (POF) have attracted increasing interest in recent years due to their intrinsic properties. Indeed, their low Young's modulus and high thermo-optic coefficient rendered them excellent sensors in some applications. However plastic fibres exhibit high attenuation that limits the sensing range. This is particularly true for Poly(methyl methacrylate)-based fibres (PMMA). Furthermore, the fabrication of fibre Bragg grating (FBG) in the PMMA core has demonstrated to be a very long process in POF. Last but not least, the coupling of the light source in the POF is also an issue that has to be tackled. In this thesis, the preform fabrication process has been investigated in an attempt to reduce the attenuation in fabricated PMMA based fibres. Preparation of preforms in a sealed glove box under Argon flushing has allowed significant increase of the purity of our preforms, which led to a decrease of the fibre attenuation. The coupling of the light source in the polymer fibre was tackled by the invention of fibre that embedded the light source element. Indeed, a novel fibre design composed of 2 core layers, one being doped with laser dye, and the outer core layer being the light guiding medium was investigated. The coupling of the photo-generated fluorescence of the inner core layer into the outer core layer was good enough to be detected 2 metres away from the pumping point, which is the commonly admitted length required for bio-sensing.
This thesis also details the fabrication of UV photosensitive step index POF and the implementation of a novel process, which we called "pull-through" method, permitting fabrication of good quality single mode POF (SM-POF). Besides, the investigation on photosensitive core dopants allowing rapid production of FBGs has led to fabrication of single mode fibres composed of a unique core dopant, permitting both increase of the core refractive index and photosensitivity, thus further decreasing the POF attenuation. Two chemical molecules, namely Diphenyl Sulphide (DPS) and Diphenyl Disulfide (DPDS) were investigated and allowed fabrication of FBGs in less than a second; with preference given to DPDS due to better UV sensitivity and lower attenuation. Indeed, fabrication of FBG in DPDS core doped single-mode polymer optical fibre in 7 ms (limited by equipment) was demonstrated, which is to date a word record, potentially allowing fabrication of gratings during the fibre drawing process. Last but not least, the fabricated FBGs demonstrated excellent stability and good sensing properties. Demonstration of heart beat and respiration detection using 7 ms FBG is clearly a breakthrough in sensing with wavelength shift larger than results reported in any kind of fibres. Finally, the chemical process being responsible for the excellent photosensitivity of our fibre was investigated and the conclusion was made that vulcanization was presumably the dominant effect, authorizing fabrication of ultra-fast FBGs exhibiting remarkable sensing properties and tremendous stability.
Description: xiii, 158 pages : color illustrations
PolyU Library Call No.: [THS] LG51 .H577P EE 2017 Bonefacino
Rights: All rights reserved.
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