Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 94 for “"Bragg gratings"”.
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Microscopic characterisation of fibre Bragg gratings
… characterization of optical fibres and fibre Bragg gratings, by the use of a non-invasive microscopic technique, namely differential interference contrast microscopy. The thesis aims to provide detailed information on the structural and optical properties of optical fibres and fibre Bragg …
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Integrated chirped Bragg gratings for dispersion control
… device for this purpose. A monolithic chirped Bragg grating is presented with dispersion and bandwidth characteristics coinciding with the previously mentioned regimes. The device, based on a deeply etched tapered waveguide design, may be fabricated fully post-growth, lending it a significant …
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Fabrication and applications of fibre Bragg gratings
The consequences of fabricating Bragg gratings in various fibres, with or without hydrogen loading, and with varying laser power levels are explored. Three new techniques for fabricating chirped gratings are presented. Beams with dissimilar wavefront curvatures are interfered to give chirped …
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Intragrating sensing using chirped optical fibre Bragg gratings
… sensing systems employing chirped fibre Bragg gratings (CFBGs) are investigated. Intragrating sensing is the process of obtaining a continuous profile of a measurand over the grating length from either the amplitude or phase, or both the amplitude and phase of its measured reflection …
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Passive and active Bragg gratings for optical networks
This thesis investigates fibre Bragg grating (FBG) devices. Specifically, it consists of the developments and applications of two groups of devices: the optical phase en/decoders and the tunable fibre Bragg gratings based on an S-bending technique. The advantage of an S-bending tuning FBG is that …
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Fibre bragg gratings for microwave photonics and sensing
… of microwave transversal filters using fibre Bragg grating arrays and the building of fibre Bragg grating based magnetic-field sensors. Some theoretical background about fibre Bragg gratings, photosensitivity, fibre Bragg grating sensors and filters are presented. Fibre Bragg grating sensors …
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Fiber Bragg Gratings Strain Sensors for Railway Applications
… to their electrical counterparts. A fiber Bragg grating (FBG) strain sensor has been employed for this study to detect and distinguish normal and lateral loads on rail tracks. A theoretical analysis of the relationship between strain and displacement under vertical and horizontal strains on …
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Integrated optical filters using Bragg gratings and resonators
… study of optical filters made using integrated Bragg gratings and Bragg resonators. Various topologies for making add/drop filters using integrated gratings are outlined. Each class of devices is studied in detail and the theoretical tools needed for designing the add/drop are developed. …
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Microscopic and spectral characterisation of optical Fibre Bragg gratings
Fibre Bragg gratings (FBGs) have found extensive application in lasers, amplifiers, signal filtering in telecommunications and sensing. The underlying mechanisms and fundamental properties of FBGs are not completely understood, which stands in the way of full exploitation of FBG-based devices …
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Fully Distributed Multi-parameter Sensors Based on Acoustic Fiber Bragg Gratings
… applications. A novel concept of acoustic fiber Bragg grating (AFBG) is conceived with inspiration from optical fiber Bragg grating (FBG). This AFBG structure exploits periodic spatial perturbations on an elongated waveguide to sense variations in the spectrum of an acoustic wave. It achieves ten …
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Distributed fiber-optic strain and temperature sensors using photoinduced bragg gratings
… fiber-optic strain sensors using photo induced Bragg gratings is presented. The one dimensional wave equation is solved for a slowly varying sinusoidal modulation of the index of refraction. The solution is found to take the form of a fourier transform for low reflectivity «15%) gratings. As a …
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Fabrication and application of short and novel structure in-fibre Bragg gratings
… application of short and novel structure fibre Bragg gratings. The basic theoretical concepts of in-fibre Bragg gratings and photosensitive mechanisms are introduced together with an overview of fabrication methods and applications presented to date. The fabrication of fibre Bragg gratings using …
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Theoretical Study of Laser Beam Quality and Pulse Shaping by Volume Bragg Gratings
… of short light pulses by the chirped volume Bragg gratings (CBG) is reviewed based on spectral decomposition of short pulses and on the wavelength-dependent coupled wave equations. The analytic theory of diffraction efficiency of a CBG with constant chirp and approximate theory of time delay …
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Temperature and strain sensing using rare earth fluorescence and Bragg gratings in optical fibres
… strain effects on rare earth fluorescence and Bragg gratings in optical fibres. The development and performance of simultaneous temperature and strain measurement systems utilising a combined technique of the fluorescence intensity ratio and the Bragg wavelength shift are investigated.
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High-Speed Quasi-Distributed Optical Fiber Sensing Based on Ultra-Weak Fiber Bragg Gratings
… sensing by employing serial ultra-weak fiber Bragg gratings (UW-FBGs) and dispersive components. Various factors which have influence on the system performance, including wavelength resolution, spatial resolution and sensing rate, are analyzed. Different types of light sources and dispersive …
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Transverse mode selection and brightness enhancement in laser resonators by means of volume Bragg gratings
… explores the angular selectivity of volume Bragg gratings (VBGs) and their use as spatial transverse mode filters in a laser resonator. Selection of the fundamental mode of a resonator is explored using transmission Bragg gratings (TBGs) as the spatial filter. Simulations and experimental …
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The use of loop mirrors and chirped fibre Bragg gratings in actively-modelocked fibre lasers
… dispersion is obtained using a chirped in-fibre Bragg grating.Systems operating both at 76MHz and gigahertz frequencies are presented, the latter using a semiconductor laser amplifier to enhance nonlinear action in the loop mirror. A novel dual-wavelength system in which two linear cavities share …
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