Dissertations / Theses on the topic 'Optical fibre'
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1
Baker, Stephen Ross. "Optical fibre lasers." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239585.
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Travis, Adrian Robert Leigh. "Optical fibre multiports." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254520.
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Papadopoulos, P. "Optical fibre holographic gratings." Thesis, University of Salford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381732.
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Pendock, Graeme John. "Optical fibre dye lasers." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308241.
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Xu, Fei. "Optical fibre nanowire devices." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/65527/.
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The Optical Fibre Nanowire (OFN) is a potential building block in future micro- and nano-photonic device since it offers a number of unique optical and mechanical properties. In this thesis, the background and fundamental features of nanowires are introduced; the theory, design and demonstration of novel nanowire devices are discussed. At first, a short adiabatic taper tip is manufactured, and it is used as optical tweezers for trapping 1μm microspheres. Then, the most important devices - the OFN resonators including the simple Optical Nanowire Loop Resonator (ONLR) and complicated 3D Optical Nanowire Microcoil Resonator (OMNR) - are investigated theoretically and experimentally. A one-turn loop resonator and two-, three-, and four-turn ONMR are demonstrated experimentally; several kinds of methods on optimizing the ONMR profile are presented to make the manufacture of high-Q ONMRs easier. In order to protect and stabilize the ONMR, embedding the device in Teflon is demonstrated. Finally, more applications in refractometric sensing are presented: schemes of sensors based on an embedded ONLR and ONMR are presented. The sensor sensitivities are calculated: 700 nm/RIU (RIU is the Refractive Index Unit) can be achieved at the wavelength of 970 nm for a diameter of 600 nm. Additionally, a refractometric sensor based on an embedded ONMR is demonstrated experimentally; its sensitivity is about 40 nm/RIU.
6
Galloway, Peter Colin McLaren. "Holographic optical elements for optical fibre application." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389195.
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Bristow, Julian Paul Gregory. "Integrated optical components for optical fibre sensors." Thesis, University of Glasgow, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329519.
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Mortimore, David Bryan. "Tapered fibre devices for optical fibre communication systems." Thesis, University of Essex, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296363.
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Brady, Geoffrey Phillip. "Fibre Bragg grating sensors : interrogation and multiplexing techniques." Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309781.
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Martinez, Pinon F. "Characterizing single-mode fibres and single-mode fibre lenses." Thesis, University of Southampton, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383403.
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Dobb, Helen L. "Fibre gratings in novel optical fibres for applications in sensing." Thesis, Aston University, 2007. http://publications.aston.ac.uk/8102/.
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This thesis presents the fabrication of fibre gratings in novel optical fibres for sensing applications. Long period gratings have been inscribed into photonic crystal fibre using the electric-arc technique. The resulting sensing characteristics were found to depend on the air-hole geometry of the particular fibre. This provides the potential of designing a fibre to have enhanced sensitivity to a particular measure and whilst removing unwanted cross sensitivities. Fibre Bragg gratings have been fabricated in a variety of polymer optical fibres, including microstructured polymer optical fibre, using a continuous wave helium cadmium laser. The thermal response of the gratings have been characterised and found to have enhanced sensitivity compared to fibre Bragg gratings in silica optical fibre. The increased sensitivity has been harnessed to achieve a grating based device in single mode step index polymer optical fibre by fabricating an electrically tunable fibre Bragg grating. This was accomplished by coating the grating region in a thin layer of copper, which upon application of a direct current, causes a temperature induced Bragg wavelength shift.
12
Horikis, Theodore. "Soliton radiation in optical fibre." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251957.
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Allsop, Thomas David Paul. "A fibre optical strain sensor." Thesis, University of Plymouth, 1999. http://hdl.handle.net/10026.1/2779.
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Strain-sensing elements, fabricated in standard communications-grade single mode optical fibre, are increasingly being considered for application in structural health monitoring. The reason for this is the numerous advantages demonstrated by these devices compared with traditional indicators. This thesis describes work carried out on optical sensors at the University of Plymouth. The aim of this work was to achieve an optical fibre strain sensing system capable of measuring absolute strain with good resolution and having wide dynamic range, without bulky optical equipment and not susceptible to misalignment due to handling. Earlier work was devoted to study on an intrinsic Fabry-Perot interferometric sensor and an optical phase-shift detection technique. The sensing element investigated relied on the end face of an optical fibre as one mirror and the second mirror being a layer of Titanium Dioxide (TO2). Although some results are included, it was soon realised that this sensor had a number of problems, particularly with fabrication. As no simple solution presented itself, consideration was given to a sensor that made use of the change in reflectance of an intra-core fibre Bragg grating when the grating was subjected to strain. The bulk of work described in this thesis is concerned with this type of sensing element. The grating structure is inherently flexible and a number of structural formats were studied and investigated. The first and simplest grating considered was two linearly chirped Bragg gratings used in a Fabry-Perot configuration (a grating resonator). The sensor was tested using the sensing detection system and although the fabrication problems were overcome absolute strain measurement was unattainable. To achieve this end, a theoretical study of a number of grating structures was carried out using the T-matrix Formalism. Confidence in using this approach was gained by comparing the spectral behaviour of a proposed grating with results, which were given by another theoretical model for the same proposed grating. The outcome of this study was that two structures in particular showed promise with regard to absolutism (the measure of true strain) and linearity. Discussions held with the department of Applied Physics at Aston University about fabrication resulted in one of the proposed designs being abandoned due to difficulties of fabrication. The second structure showed more promise and fabrication attempts were put in hand. This grating is linearly-chirped with a Top-hat function and a sinusoidal perturbation as a taper function of the refractive index modulation. Experiments were performed, data were acquired and system performance for this sensor is presented. The thesis concludes that using such a fibre Bragg grating as the sensing element of a strain sensing system enables it to measure absolute strain without using bulky optical equipment. At present, the resolution of strain is limited by the quality of the grating being fabricated (anomalies on profile), this should improve once the fabrication technique is refined.
14
West, Ian Philip. "Optical fibre based pulse oximetry." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262607.
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Mears, Robert Joseph. "Optical fibre lasers and amplifiers." Thesis, University of Southampton, 1987. https://eprints.soton.ac.uk/396453/.
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This thesis describes the development and characterisation of single-mode optical fibre lasers and amplifiers. Although the fibre laser configuration was first employed over twenty years ago, its application to conventional optical fibre technology has not been demonstrated previously. The new devices are based on single-mode fibres doped with rare-earth ions, notably neodymium and erbium. The combination of strong absorption bands, long fluorescence lifetimes; low fibre losses in the infra-red and small fibre cores have made possible very low threshold and efficient fibre lasers. Experiments on the tunability, output spectra and pulsed operation of these devices are described. A number of world firsts, including the Lowest, threshold and widest tuning range of a doped glass laser, and the efficient CW operation of an erbium-doped three level laser, have been achieved. High-gain amplification at 1.54µm, the preferred wavelength for optical communication, has also been demonstrated. The results have been modelled by adapting conventional laser theory to the single-mode fibre configuration, and some simple design criteria are considered.
16
Ludden, Brendan Patrick. "A distributed optical fibre sensor." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/272327.
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Petermann, Ingemar. "Fibre Bragg Gratings : Characterization, Realization and Simulation." Doctoral thesis, Stockholm : Department of microelectronics and applied physics, Royal institute of technology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4381.
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Altuncu, Ahmet. "Distributed erbium doped fibre amplifiers (DEDFAs) for use in long haul and high bit rate soliton transmission systems." Thesis, University of Essex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388156.
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Abobaker, Abdosllam M. "Analytical design of dispersion-managed optical fibre transmission systems." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2008. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=24668.
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Lyyttkäinen, Katja Johanna. "Control of complex structural geometry in optical fibre drawing /." Connect to full text, 2004. http://setis.library.usyd.edu.au/adt/public_html/adt-NU/public/adt-NU20041011.120247.
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Lyytikäinen, Katja Johanna. "Control of complex structural geometry in optical fibre drawing." Connect to full text, 2004. http://hdl.handle.net/2123/597.
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Thesis (Ph. D.)--University of Sydney, 2004.Title from title screen (viewed 14 May 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Physics, Faculty of Science. Includes bibliographical references. Also available in print form.
22
Trifanov, Irina. "Fibre optical sources and systems for optical coherence tomography." Thesis, University of Kent, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.593914.
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Optical Coherence Tomography (OCT) is a powerful imaging technology in biomedical research and medicine. It enables in situ. 3D visualization of tissue structure and pathology, without the need. to excise the tissue and resolution approaching that of histology. OCT has had the most clinical impact in ophthalmology, where it provides structural and quantit ative informat ion that cannot be obtained by any other modality. The objective of the work presented in this thesis was the development of new imaging methods and optical devices to progress the OCT technology in t erms of its versatility, as well as to improve on parameters such as resolution, wavelength availability, integration effort and reliability. One of the most desired features in high resolution imaging is the display of simultaneously generated confocal images. The implementation of a confocal channel at the core of an OCT with quasi-simultaneous display of both images is demonstrated by synchronous optical switching of the power in the reference arm of the interferometer with the scanner determining the line in the final raster. The 1.0-1.1 11m region of the optical spectrum emerged as an attractive option compared to the standard 700-900 nm region, due to increased penetration beyond the retina, into the choroid, and reduced scat tering. Therefore, in this thesis, two novel optical sources based on fiber optic technology at 1 micrometer have been researched, assembled and tested: (a) a broadband ASE source based on combination of Yb-doped and Nd-doped silica fibers . The source emits at a cent ral wavelength of 1060 nm with a full-width-halfmaximum exceeding 70 nrn and 20 m\V output power; and (b) a swept fiber laser source emitting at 1065 nm central wavelength, with :::::l 50 nm tuning range and 40 m Woutput average power. A simple solution to linearize the sweeping in wavenumber (optical frequency), as required for image rendering, is demonstrated. The two prototype sources have been packaged and their performances validated in fully func tional OCT systems.
23
Marra, Giuseppe. "Transfer of optical frequency combs over optical fibre links." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/350220/.
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In just over a decade the optical frequency comb technique has completely transformed the field of frequency metrology. These devices have made the measurement of the frequency of light a much easier and affordable task when compared to with earlier techniques. With both research and technology development on these devices becoming more mature, optical frequency combs have been affecting other science areas. Applications are already found in spectroscopy, attosecond physics and astrophysics and more science and engineering areas can be expected to be affected in the near future. The dissemination over optical fibre of optical frequency combs between research labs, or between research labs and industry, could facilitate and accelerate this process. In particular, with optical frequency standards currently exhibiting a fractional accuracy better than 10^-17 and optical frequency combs making this accuracy available across a wide spectrum, new experiments could be devised in a wide range of research fields if ultra accurate microwave and optical frequencies were to be made available beyond the walls of metrology laboratories. However, before the work presented in this thesis, limited research was undertaken to test how accurately an optical frequency comb could be transferred over optical fibre. Environmentally-induced noise in the fibre, dispersion issues and other processes taking place during the propagation and detection of the optical signal could all degrade its quality to a level incompatible with the desired applications. The experiments described here demonstrate that optical frequency combs can be disseminated over optical links, from several-km to many tens of km-long, whilst preserving the stability and accuracy of its mode frequency spacing and mode frequency to a level compatible with the majority of the most demanding frequency metrology applications.
24
Ferreira, Ricardo Xavier da Graça. "Acoustic optical modulation in optical fibre for sensing applications." Master's thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/11646.
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Mestrado em Engenharia FísicaO presente trabalho teve como objetivo desenvolver um sensor de fibra óptica intrínseco para viscosidade com base no efeito acústoótico aplicado em redes de Bragg. Foram utilizadas fibras de silica e poliméricas para medições com baseadas no espectro e no tempo de resposta da rede quanto sujeitas ao efeito acústo-ótico. O resultado é um viscosímetro multi-paramétrico com um distinto potencial futuro. Com base no conhecimento adquirido, é proposto um novo design e mecanismo de detecção.
The present work aimed to develop an intrinsic optical fibre sensor for viscosity based on the acousto-optic effect applied into fibre Bragg grating. Polymer and silica optical fibres were employed for measurements based on the spectra and the grating response times when subjected to the acousto-optic effect. The results is a multi-parameter viscometer with a distinctive future potential. Based on the knowledge acquired, a new design and sensing mechanism is advanced.
25
Xu, Ming Gang. "The measurement of physical fields using optical fibres and fibre gratings." Thesis, University of Southampton, 1995. https://eprints.soton.ac.uk/399097/.
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In this thesis a number of novel optical fibre and fibre Bragg grating sensors have been investigated for the purpose of measuring physical fields, particularly strain, temperature and pressure. These sensors are based on using short coherence length light source. Two laboratory prototypes of interferometric fibre pressure sensors have been demonstrated using a hollow-glass microsphere and optical fibres, respectively. These are intended for ultimate application as strain sensors for smart structures. A novel white-light polarimetric interrogator is demonstrated. The device consists of two equal lengths of highly-birefringent fibre, spliced with their polarization axes orthogonal. The dispersion effect on the responsivity of white-light interferometry is evaluated using a simplified transfer function. Using Jones matrix and Poincaré sphere analysis methods, the device performance has been discussed. Experimental results are presented by thermally-scanning the device for the interrogation of sensing interferometer. A fibre Bragg grating sensor for measuring pressure, strain and temperature is evaluated using measured data from over twenty different fibre gratings including Bragg gratings in highly-birefringent fibres. Intensive experimental results on thermally-induced decay of fibre gratings are presented for the evaluation of their potential in a wide variety of sensors and multiplexed systems. A first demonstration of a fibre grating interrogation system using an acousto-optic tunable filter is presented. The system involves frequency-shift-keying of the RF drive to the filter to track the measurand-induced wavelength shifts of multiplexed fibre gratings. An equivalent linear model has been developed to describe the operation of a wavelength tracking loop. Experimental results for both open-loop and close-loop operations are presented for strain and temperature measurements. Three novel techniques to resolve the thermal effect in strain measurement using fibre gratings are demonstrated. The first method involves using surface-mounted fibre grating pairs to compensate for thermal effects. The second technique uses two superimposed fibre gratings (single sensing element) to simultaneously measure strain and temperature. Last but not least by using a chirped Bragg grating in a tapered optical fibre as a strain sensing element, strain sensing can be made to be temperature-independent. Both theoretical analysis and experimental work are presented for these approaches.
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Muguro, Kennedy Mwaura. "Effects of polarization in a distributed raman fibre amplifier." Thesis, Nelson Mandela Metropolitan University, 2011. http://hdl.handle.net/10948/d1014621.
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The need to exploit the large fibre bandwidth and increase the reach has seen the application of the Raman fibre amplifier (RFA) become indispensable in modern light wave systems. The success and resilience of RFAs in optical communication is deeply rooted in their unique optical properties and new technologies which have allowed the amplifier to come of age. However, the full potential of RFAs in optical communication and other applications are yet to be realized. More so are its polarization properties which still remain largely unexploited and have not been fully understood. In this work, fundamental issues regarding distributed RFA have been investigated with the aim of acquiring a better understanding of the amplifier polarization characteristics which have potential applications. In particular the effects of polarization mode dispersion (PMD) and polarization dependent loss (PDL) have been demonstrated both by simulation and experiment. The possibility of Raman polarization pulling in single mode fibres (SMFs) has also been addressed. Polarization sensitivity of RFA has been known for a long time but the clear manifestation of it has become evident in the advent of modern low PMD fibre. Unlike EDFAs which make use of special doped fibre, RFAs require no special fibre for operation. Besides, RFA uses a very long length of fibre and as such the fibre polarization characteristics come into play during amplification. In the demonstrations presented in this thesis a fibre of PMD coefficient < 0.05 pskm-1/2 was regarded as low PMD fibre while one having coefficient ≥ 0.05 pskm-1/2 was categorized to have high PMD unless otherwise stated. Several experiments were performed to evaluate the RFA gain characteristics with respect to fibre PMD and the system performance in the presence of noise emanating from amplified spontaneous emission (ASE). Analysis of Raman gain statistics was done for fibres of low and high PMD coefficients. The statistics of PDG and on-off gain were eventually used to demonstrate the extraction of PMD coefficients of fibres between 0.01- 0.1 pskm-1/2 using a forward pumping configuration. It was found that, at increasing pump power a linear relationship exists between forward and backward signal gain on a dB scale. The interaction of PDL and Raman PDG in the presence of PMD were observed at very fundamental level. It was found the presence of PDL serves to reduce the available on-off gain. It was also established that the presence of PMD mediates the interaction between PDG/PDL. When PMD is high it reduces PDG but the presence of PDL introduces a wavelength dependent gain tilting for WDM channels. Further analysis revealed that signal polarization is influenced by the pump SOP due to the pulling effect which is present even at moderate pump power.
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Lefrançois, Marcel. "Aspects of tapered optical fibre polarizers." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26720.
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This thesis proves that it is possible in principle to make in line optical fibre polarizers from tapered optical fibres surrounded by a quartz cladding. The theory of light propagation and polarization in fibres was reviewed as background information and several fabrication processes were evaluated and tried experimentally. The best results are obtained by heating a quartz tube in an oxy-propane flame, so that it collapses onto the fibre. Unfortunately, due to residues remaining between fibre and quartz tube, and due to large differences in melting points the results are quite irreproducible, and routine fabrication of polarizers with predictable properties is not yet feasible by the methods described in this thesis.Science, Faculty of
Physics and Astronomy, Department of
Graduate
28
Baker, Sioned Mari. "Perturbed solitons in birefringent optical fibre." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298276.
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Inci, M. Naci. "Optical coatings for fibre optic sensors." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/1455.
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Merchant, David Frank. "Optical fibre fluorimeter for online measurement." Thesis, Liverpool John Moores University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313161.
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Smith, Richard. "Optical fibre sensors for radioactive environments." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318305.
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Tubb, Andrew John Colwill. "Optical fibre surface plasma wave sensors." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624855.
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Ford, Helen Diana. "Optical fibre wavelength filters and multiplexers." Thesis, Cranfield University, 1994. http://dspace.lib.cranfield.ac.uk/handle/1826/10410.
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Polarisation-based
wavelength-division multi-/demulti-plexers (WDMs) and
filters have been designed, constructed and evaluated. These are compact devices made
from single-mode optical fibre possessing high linear birefringence.
Ihe WDMs accept two input wavelengths in a common state of polarisation, and
produce orthogonally polarised outputs which are spatially separated using a
polarisation-selective element. The maximum separation demonstrated is 1.5 nm, and
the minimum 0.04 nm, which is two orders of magnitude better than that achieved b
most other in-line WDMs.
A few metres of fibre only are required. Instantaneous cross-
talk values below -15 dB have been measured experimentally, and theoretical analysis
of the devices predicts that values below -28 dB should be attainable. Temperature
sensitivity currently limits long-term cross-talk, but also offers the possibility of tuning
the centre wavelength. Methods of reducing environmental sensitivity include judicious
choice
of fibre type and appropriate packaging of the WDMs. These techniques are
investigated and discussed. Incorporation of the WDMs in optical fibre sensing networks
is demonstrated, as is separation of frequency-shifted stimulated Brillouin scattered
light, generated in a fibre, from the pump frequency.
Filters are constructed
using concatenated sections of birefringent fibre,
positioned between two polarisers. Rotation of the polarisation azimuth between sections
is achieved
by twistíng portions of the fibre to induce circular birefringence. Thus
devices are made from a single strand of linearly birefringent fibre, less than one metre
in
length. Passband widths and separations are selected b changing the number of
twisted sections in the filter, and altering lengths and twist angles of sections. A
minimum passband width ofI0 nm has been demonstrated, at a passband separation
of60 nm. Environmental stability is suíciently good for the devices to be operated as
passive components.
34
Geiger, Harald. "Quasi-distributed optical fibre strain sensors." Thesis, University of Southampton, 1995. https://eprints.soton.ac.uk/399104/.
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This thesis presents for the first time two complementary techniques to monitor the optical path length in optical fibre over both long and short sensing lengths. Both techniques may be used to measure the physical environment of the optical fibre, in particular strain and temperature, and are suitable for multiplexed operation. Signal-to-noise analysis shows that current optical time domain reflectometry (OTDR) systems do not fully exploit the spatial resolution theoretically available. A new OTDR technique exploits the theoretical findings to monitor the range of reflective markers in an optical fibre. Measuring strain in fibre sections of several metres is demonstrated. 100?m spatial resolution has been achieved with a pulse duration equivalent to 1 m fibre length and within one second measurement time. The first fibre Bragg grating interrogation system using an acousto-optic tunable filter (AOTF) is described. The interrogation system locks the AOTF wavelength to the wavelength of a selected grating. Measuring the frequency of the AOTF control signal provides an accurate measurement of the grating wavelength. A detailed system analysis is presented to enable the optimisation of system parameters. A wavelength resolution corresponding to 0.4 microstrain is achieved within 0.1sec measurement time, close to the resolution predicted by the system model. This technique allows the use of fibre gratings as sensors for the measurement of both quasi-static and dynamic strains. The combination of the two systems facilitate the utilisation of optical fibre to monitor a structure both over a few metres and at critical points. Both sensor types offer new measurement possibilities as embedded structure monitors, for example for in-service health and usage monitoring or as nerves for active control of smart structures.
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Pilling, Neil Anthony. "Optical fibre measurements in power systems." Thesis, University of Liverpool, 1992. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282738.
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Volanthen, Mark. "Multiplexed and distributed optical fibre sensors." Thesis, University of Southampton, 1997. https://eprints.soton.ac.uk/394567/.
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This thesis presents three novel optical fibre sensor systems which monitor optical path lengths. The systems have been used to measure strain in an optical fibre. All three systems make several measurements at different locations along a fibre, allowing the spatial distribution of a measurand to be obtained. For the first time, incoherent optical frequency domain reflectometry is used together with time division multiplexing to measure the optical path length of an array of fibre sections. Sensing sections are 5m long and are defined by broadband optical reflectors. A closed loop interrogation system is demonstrated to monitor the sensors in real time with an accuracy of 2.1µ(epsilon)/(root)Hz, in good agreement with the theoretically predicted value. Simultaneous monitoring of multiple fibre Bragg grating sensors, several millimetres in length, is also demonstrated by simultaneously generating multiple passbands in a single acousto-optic tunable filter. This is the only technique demonstrated to simultaneously monitor multiple gratings using a single wavelength-tunable device. The first distributed Bragg grating sensor to measure arbitrary strain profiles is also demonstrated. Low-coherence interferometry selects the interrogation position and a tunable filter measures the local wavelength. Two configurations of the technique are presented, which have achieved spatial resolutions of 300µm and real-time strain measurements with 5.4µ(epsilon)/(root)Hz accuracy, showing good agreement with theoretically predicted values. The only grating sensor network to be both distributed and multiplexed is presented together with the first results.
37
Johnson, Ian Paul. "Grating devices in polymer optical fibre." Thesis, Aston University, 2012. http://publications.aston.ac.uk/18094/.
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This thesis presents the fabrication of fibre Bragg gratings (FBGs) and long period gratings (LPGs) in polymer optical fibre (POF). Possible fabrication techniques were discussed to fabricate FBGs in polymer optical fibre including a detailed description of the phase mask inscription technique used to fabricate FBGs in both single and multi mode microstructured polymer optical fibre (mPOF). Complementing the fabrication of polymer optical fibre Bragg gratings (POFBGs), a technique has been developed to permanently splice POF to silica optical fibre with the use of an optical adhesive. This allowed for the fabricated POFBGs to be characterised away from the optical table, allowing for application specific characterisation. Furthermore Bragg gratings have been fabricated in polymer POF with a Bragg response within the 800nm spectral region. Within this spectral region, POF predominantly manufactured from PMMA experiences considerably smaller attenuation losses when compared to the attenuation losses within the 1550nm spectral region. The effect of thermally annealing fabricated POFBGs has been studied. This included demonstrating the ability to tune the Bragg wavelength of a POFBG sensor to a desired wavelength. Thermal annealing has also been used to manufacture wavelength division multiplexed sensors with the use of a single phase mask. Finally POFBGs have been fabricated in Topas Cyclic Olefin Copolymer. Fabrication of Bragg gratings within this copolymer allowed for the first demonstration of near immunity to relative humidity whilst monitoring changes in temperature of the environment the POFBG sensor was in. Bragg gratings fabricated in the Topas copolymer demonstrated sensitivity to relative humidity which was 65 times less than that of a PMMA based POFBG sensor. This decrease in sensitivity has the potential to significantly reduce the potential of cross sensitivity to relative humidity whilst being employed to monitor measurands such as temperature and axial strain.
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Simpson, Alexander George. "Optical fibre sensors and their interrogation." Thesis, Aston University, 2005. http://publications.aston.ac.uk/8006/.
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This thesis describes novel developments in the fabrication and understanding of type IA fibre Bragg gratings, the uses of said gratings as optical sensors and the interrogation of optical sensors using tilted fibre Bragg gratings. This thesis presents the most detailed study of type IA gratings performed to date and provides the basis of a dual grating optical sensor capable of independently measuring strain and temperature. Until this work it was not known how to reliably fabricate type IA gratings or how they would react to high ambient temperatures, nor was it known what effect external parameters such as fibre type, dopant levels, inscription laser intensity, or hydrogenation levels would have on the physical properties of the grating. This comprehensive study has yielded answers to all of these unknowns and produced several unexpected uses for type IA gratings, such as the use of the previously unreported strong loss band at 1400nm to locally heat fibres by optical absorption and thereby fabricate optically tuneable gratings which do not affect directly adjacent standard gratings. Blazed fibre Bragg gratings have been studied in detail and used to produce several high quality prototype sensor interrogation systems yielding stability an accuracy values unsurpassed by similar devices reported in literature. An accurate distribution map of light radiated by blazed gratings is shown for the first time and has been studied in respect of polarisation state showing that for certain easily achievable conditions a blazed grating spectrometer may be deemed to be polarisation insensitive. In a novel implementation of the system, it is shown that the dynamic wavelength range of a blazed grating spectrometer may be at least doubled by superimposing blazed gratings.
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Chen, Xianfeng F. "Advanced optical fibre gratings and applications." Thesis, Aston University, 2006. http://publications.aston.ac.uk/8103/.
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This thesis describes a detailed study of advanced optical fibre sensors based on fibre Bragg grating (FBG), tilted fibre Bragg grating (TFBG) and long-period grating (LPG) and their applications in optical communications and sensing. The major contributions presented in this thesis are summarised below. The most important contribution from the research work presented in this thesis is the implementation of in-fibre grating based refractive index (RI) sensors, which could be the good candidates for optical biochemical sensing. Several fibre grating based RI sensors have been proposed and demonstrated by exploring novel grating structures and different fibre types, and employing efficient hydrofluoric acid etching technique to enhance the RI sensitivity. All the RI devices discussed in this thesis have been used to measure the concentration of sugar solution to simulate the chemical sensing. Efforts have also been made to overcome the RI-temperature cross-sensitivity for practical application. The demonstrated in-fibre grating based RI sensors could be further implemented as potential optical biosensors by applying bioactive coatings to realise high bio-sensitivity and bio-selectivity. Another major contribution of this thesis is the application of TFBGs. A prototype interrogation system by the use of TFBG with CCD-array was implemented to perform wavelength division multiplexing (WDM) interrogation around 800nm wavelength region with the advantages of compact size, fast detection speed and low-cost. As a high light, a novel in-fibre twist sensors utilising strong polarisation dependant coupling behaviour of an 81°-TFBG was presented to demonstrate the high torsion sensitivity and capability of direction recognition.
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Blank, Lutz Christian. "High capacity optical fibre transmission systems." Thesis, Bangor University, 1992. https://research.bangor.ac.uk/portal/en/theses/high-capacity-optical-fibre-transmission-systems(39ab5e67-373b-4ff4-ab06-ebb362123c5f).html.
Full textAbstract:
In this thesis a number of system design options are studied for the generation and processing of ultra—high speed optical data, based on the technique of Optical Time Division Multiplexing. The limits are investigated with regard to maximum unregenerated transmission distances for linear propagation over single mode fibre with large chromatic dispersion. Overall, the aim is to minimise the bandwidth requirements of electronic and opto—electronic system components for a given optical line capacity whilst at the same time maximising the chromatic dispersion limited propagation distances, thus exploring the potential for future system and network operating speeds of several tens of Gbit/s. A summary of standard system designs and their performance in terms of maximum system speed and dispersive fibre propagation provides an introduction into the field of high performance fibre optic data communication systems. Particular examples are used to introduce the device models subsequently employed in the analysis of new system configurations. This includes a description of the system performance measurements which are the basis for the performance analyses of the proposed ultra—high speed systems. In the field of fibre transmission research a variety of electrical interface and optical line signal formats are being investigated, each being appropriate for particular application areas and offering varying compromises between performance, complexity and user friendliness. In the context of this thesis the investigations are limited to high capacity time division multiplexed configurations, which represent a medium to longer term alternative as well as a complementary approach to the currently widely pursued system capacity upgrades by means of optical wavelength or frequency division multiplexing. Moreover, ultra—high speed time division multiplexed transmission is fundamentally compatible with WDM system operation, providing a future upgrade path for multi—wavelength systems being developed at the present time. The vehicle for these investigations is a set of computer models. Optical signal generation, pulse propagation in single—mode fibre, optical time domain processing, amplification and optical receiver detection are all included in the models to allow end—to—end system performance studies. Experimental results are presented at various stages to validate the models employed.
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Leon-Saval, Sergio G. "Optical fibre transitions for device applications." Thesis, University of Bath, 2005. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425651.
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Zhang, Chi. "Fibre Bragg gratings in polymer optical fibre for applications in sensing." Thesis, Aston University, 2012. http://publications.aston.ac.uk/16428/.
Full textAbstract:
This thesis presents the potential sensing applications of fibre Bragg gratings in polymer optical fibres. Fibre Bragg gratings are fabricated in different kinds of polymer optical fibres, including Poly methyl methacrylate (PMMA) and TOPAS cyclic olefin copolymer based microstructured polymer optical fibres and PMMA based step-index photosensitive polymer optical fibre, using the 325nm continuous wave ultraviolet laser and phase mask technique. The thermal response of fabricated microstructured polymer optical fibre Bragg gratings has been characterized. The PMMA based single mode microstructured polymer optical fibre Bragg gratings exhibit negative non-linear Bragg wavelength shift with temperature, including a quasi-linear region. The thermal sensitivity of such Bragg gratings in the linear region is up to -97pm/°C. A permanent shift in the grating wavelength at room temperature is observed when such gratings are heated above a threshold temperature which can be extended by annealing the fibre before grating inscription. The largest positive Bragg wavelength shift with temperature in transmission is observed in TOPAS based few moded microstructured polymer optical fibre Bragg gratings and the measured temperature sensitivity is 250±0.5pm/°C. Gluing method is developed to maintain stable optical coupling between PMMA based single mode step index polymer optical fibre Bragg gratings and single mode step index silica optical fibre. Being benefit from this success, polymer optical fibre Bragg gratings are able to be characterised for their temperature, humidity and strain sensitivity, which are -48.2±1pm/°C, 38.3±0.5pm per %RH and 1.33±0.04 pm/µε respectively. These sensitivities have been utilised to achieve several applications. The strain sensitivity of step index polymer optical fibre Bragg grating devices has been exploited in the potential application of the strain condition monitoring of heavy textiles and when being attached to textile specimens with certain type of adhesives. These polymer fibre Bragg grating devices show better strain transfer and lower structure reinforcement than silica optical fibre Bragg grating devices. The humidity sensitivity of step index polymer optical fibre Bragg grating devices is applied to detecting water in jet fuel and is proved to be able to measure water content of less than 20 ppm in Jet fuel. A simultaneous temperature and humidity sensor is also made by attaching a polymer fibre Bragg grating to a silica optical fibre Bragg grating and it shows better humidity measurement accuracy than that of electronic competitors.
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Madden, W. Iain. "Analysis and development of all fibre wavelength selective fibre optic components." Thesis, University of Strathclyde, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248512.
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Laufer, Jan. "Photothermal determination of optical coefficients using an optical fibre sensor." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394370.
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Mustapha, Mazlyn Mona. "Non-coherent optical fibre-based CDMS using optical orthogonal codes." Thesis, Cranfield University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435041.
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Jauncey, Ian Michael. "Diode-pumped active fibre devices." Thesis, University of Southampton, 1989. https://eprints.soton.ac.uk/421958/.
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Xu, Wei. "Thermally poled fibre devices." Thesis, The University of Sydney, 1999. https://hdl.handle.net/2123/27574.
Full textAbstract:
Poling of silica glass, silica fibre and silica planar waveguides is an exciting research
field. The thermal poling technique has been demonstrated to produce large second
order nonlinearities and linear electro-optic coefficients in silica glass, silica fibre and
silica planar waveguides. In this thesis, efforts have been made both to obtain large,
stable and reliable linear electro—optic coefficients in silica fibre using thermal poling
and to understand the mechanisms for the thermal poling effects in silica fibre.
Firstly, the thermal poling conditions for boron co-doped germanosilicate fibre were
optimized and the dependence of the thermal poling induced linear electro-optic
coefficient on the poling voltage, poling temperature and poling time were analyzed.
To improve the efficiency of optimizing the poling conditions for different types of
silica fibre, an in situ poling technique was deployed to study aluminum co-doped
germanosilicate fibre. It is found that the thermal poling history has significant
influence on the induced linear electro-optic effect. Furthermore, the in situ technique
was also employed to measure and analyze the decay behavior of the induced linear
electro-optic coefficient in boron co-doped germanosilicate fibre.
Secondly, an innovative method was proposed to investigate the frozen—in fields
existing in the thermally poled fibres. The frozen-in fields are the cause for the
induced linear electro-optic effect in silica fibre. This method can be used to measure both the magnitude and the direction of the frozen—in fields. Furthermore, this method
is able to measure the third order nonlinearity of the fibre core. It is the first time that
it has been observed that the third order nonlinearity of the fibre core increases after
thermal poling.
Next, it was found that the time evolution of the linear electro-optic coefficient in
thermally poled silica fibre is very different for different polarity of the poling
voltage. There are two distinct processes in thermal poling: the faster linear process of
charge migration and the subsequent single exponential process of charge ionization.
It is the first time that it has been shown that there are two frozen-in fields in
thermally poled fibre: the shielding field and the ionization field. Both the fields are
able to produce a linear electro-optic effect in silica fibre. Furthermore, It was found
that the charge distributions in thermally poled fibre could move during thermal
poling. It is the first time that the competition between the shielding field and the
ionization field seen by the core has been analyzed and it is shown to be a linear
process. The third order nonlinearity of the poled fibre core is fairly constant during
this competition, but it is still larger than that of the unpoled fibre core.
Finally, the thermal poling technology and the Bragg grating technology were
integrated to demonstrate a single fibre (low frequency) intensity modulator.
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Lyytik�inen, Katja Johanna. "Control of complex structural geometry in optical fibre drawing." University of Sydney. School of Physics and the Optical Fibre Technology Centre, 2004. http://hdl.handle.net/2123/597.
Full textAbstract:
Drawing of standard telecommunication-type optical fibres has been optimised in terms of optical and physical properties. Specialty fibres, however, typically have more complex dopant profiles. Designs with high dopant concentrations and multidoping are common, making control of the fabrication process particularly important. In photonic crystal fibres (PCF) the inclusion of air-structures imposes a new challenge for the drawing process. The aim of this study is to gain profound insight into the behaviour of complex optical fibre structures during the final fabrication step, fibre drawing. Two types of optical fibre, namely conventional silica fibres and PCFs, were studied. Germanium and fluorine diffusion during drawing was studied experimentally and a numerical analysis was performed of the effects of drawing parameters on diffusion. An experimental study of geometry control of PCFs during drawing was conducted with emphasis given to the control of hole size. The effects of the various drawing parameters and their suitability for controlling the air-structure was studied. The effect of air-structures on heat transfer in PCFs was studied using computational fluid dynamics techniques. Both germanium and fluorine were found to diffuse at high temperature and low draw speed. A diffusion coefficent for germanium was determined and simulations showed that most diffusion occurred in the neck-down region. Draw temperature and preform feed rate had a comparable effect on diffusion. The hole size in PCFs was shown to depend on the draw temperature, preform feed rate and the preform internal pressure. Pressure was shown to be the most promising parameter for on-line control of the hole size. Heat transfer simulations showed that the air-structure had a significant effect on the temperature profile of the structure. It was also shown that the preform heating time was either increased or reduced compared to a solid structure and depended on the air-fraction.
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Lyytikäinen, Katja Johanna. "Control of complex structural geometry in optical fibre drawing." Thesis, The University of Sydney, 2004. http://hdl.handle.net/2123/597.
Full textAbstract:
Drawing of standard telecommunication-type optical fibres has been optimised in terms of optical and physical properties. Specialty fibres, however, typically have more complex dopant profiles. Designs with high dopant concentrations and multidoping are common, making control of the fabrication process particularly important. In photonic crystal fibres (PCF) the inclusion of air-structures imposes a new challenge for the drawing process. The aim of this study is to gain profound insight into the behaviour of complex optical fibre structures during the final fabrication step, fibre drawing. Two types of optical fibre, namely conventional silica fibres and PCFs, were studied. Germanium and fluorine diffusion during drawing was studied experimentally and a numerical analysis was performed of the effects of drawing parameters on diffusion. An experimental study of geometry control of PCFs during drawing was conducted with emphasis given to the control of hole size. The effects of the various drawing parameters and their suitability for controlling the air-structure was studied. The effect of air-structures on heat transfer in PCFs was studied using computational fluid dynamics techniques. Both germanium and fluorine were found to diffuse at high temperature and low draw speed. A diffusion coefficent for germanium was determined and simulations showed that most diffusion occurred in the neck-down region. Draw temperature and preform feed rate had a comparable effect on diffusion. The hole size in PCFs was shown to depend on the draw temperature, preform feed rate and the preform internal pressure. Pressure was shown to be the most promising parameter for on-line control of the hole size. Heat transfer simulations showed that the air-structure had a significant effect on the temperature profile of the structure. It was also shown that the preform heating time was either increased or reduced compared to a solid structure and depended on the air-fraction.
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Couny, Francois. "Photonic solutions towards optical waveform synthesis." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.478946.
Full textAbstract:
This thesis presents the development of photonic tools towards the realisation of an optical intensity waveform synthesiser and of an attosecond pulse synthesiser based on the generation and Fourier synthesis of a continuous-wave coherent spectral comb spanning more than 3 octaves (UV to mid-IR) by use of a gas-filled hollow core photonic crystal fibre (HC-PCF).