Microstructured optical fibres: fabrication, properties, and devices

Lu, Ping (2012) Microstructured optical fibres: fabrication, properties, and devices. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (60MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

In this thesis, several novel microstructured fibre-optic devices are investigated on their designs, fabrication techniques, characteristics, and applications. Firstly the dependences of the sensitivity and time response on the coating thickness of polyimide-coated fibre Bragg gratings (FBG) as well as factors influencing these properties are revealed. Intelligent sensing of multiple environmental parameters (salinity, saccharinity, and strain) with a single-fibre sensor system is achieved through the use of multiplexed FBGs with coatings of different polymers (acrylate and polyimide) and specifications. Simultaneous measurement of magnitude and direction of deflection using a FBG cantilever sensor with possible temperature compensation is realized based on Optical low-coherence reflectometry, which reveals the internal structure of the sensing FBG in correlation with its optical properties. Secondly, simultaneous wavelength locking and spectral filtering by a FBG embedded polarization maintaining fibre Sagnac loop mirror through temperature, strain, and polarization tuning is accomplished. The system is also applied to perform simultaneous temperature and axial strain measurement. Thirdly, various fibre Mach-Zehnder interferometers (FMZI) are fabricated using different light steering elements (fibre taper and fibre lateral-shifted junction) to form either a double elements (symmetrical and asymmetrical) or triple elements structure. Simultaneous measurement of temperature and refractive index or strain with a fibre Mach-Zehnder interferometry of high sensitivity is realized based on these FMZIs. Fourthly femtosecond laser induced micro-spots are fabricated inside optical fibres and their optical characteristics are investigated. FMZIs consisting of the femtosecond laser induced spot and either a fibre taper or another spot are fabricated for measurement of temperature, strain, and refractive index. Lastly a femtosecond laser microfabrication approach is adopted to create several all-fibre devices such as long period fibre gratings, fibre core mode attenuators, fibre bandpass filter, and fibre mode converter. The method takes advantage of the flexibility of femtosecond laser micromachining and the specifications of these devices which can be arbitrarily modified by changing the femtosecond laser illumination parameters.

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