Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Yüksel Aldoğan, KıvılcımSubject: search.filters.subject.Optical sensors

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  • Master Thesis
    Development of Simulation Tool for Fbg-Based Phase-Otdr Vibration Sensors
    (Izmir Institute of Technology, 2021) Yüksel Aldoğan, Kıvılcım; Yüksel Aldoğan, Kıvılcım; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Over the last twenty years, phase-sensitive optical time-domain reflectometer based distributed vibration sensors have attracted increasing attention as a research topic and commercial product. Due to their capability to detect external perturbations along fiber in real-time, they have found applications in several sectors such as oil\&gas pipeline monitoring, border security, transportation, and so on. Recently, the implementation of fiber Bragg gratings into these systems has become popular in order to improve sensing performance and several system configurations adopting a wide range of signal processing techniques have been presented. In this thesis, a simulation tool for distributed vibration sensing systems based on FBG-based phase-sensitive optical time-domain reflectometry is developed. In this context, firstly, the operation principle of optical time-domain reflectometry and system parameters affecting the performance are investigated. Secondly, fiber Bragg grating structures and their implementation into phase-sensitive optical time-domain reflectometer based vibration sensors are studied. By utilizing the one-dimensional impulse response model, fiber Bragg grating implementation-related problems, spectral shadowing crosstalk and multiple reflection crosstalk, and different sensor configurations are analyzed. Based on this model, the numerical simulation tool is developed by constructing fiber, fiber Bragg grating, and probe pulse structures. The operation of the developed simulation tool is verified by comparing obtained results with theory. Then, the capabilities of the developed tool are demonstrated by conducting several simulations with conventional Phase-OTDR and FBG-based Phase-OTDR configurations.
  • Master Thesis
    Analysis and Implementation of Long Period Fiber Grating and Fresnel Reflection-Based Sensors for Refractive Index Measurement of Liquids
    (Izmir Institute of Technology, 2017) İde, Cansu; Yüksel Aldoğan, Kıvılcım; Yüksel Aldoğan, Kıvılcım; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Refractive index (RI) is one of the physical properties of material, such as boiling/ melting point, density, and elasticity. As one of the distinctive features of the material, measurement of the RI is nowadays used in many areas including the food, oil and petro-leum industry, biomedical applications, and environmental analysis. In recent years, fiber optic based refractometers become highly popular thanks to the advantages they provide compared to other methods used in the above-mentioned fields. In this context, two intrinsic fiber optic refractive index sensors were investigated in this thesis: long-period fiber grating (LPFG) based- and Fresnel reflection based- re-fractometers. The former examines the changes in the resonant wavelength interrogated by an Optical Spectrum Analyzer (OSA) whereas the latter uses SMF tip as sensing point interrogated by an Optical Time-Domain Reflectometer (OTDR) from a distant location. In the framework of the thesis, we first of all, provided a detailed field-specific literature survey giving an overview of the fiber optic-based refractive index sensors. Then, the operation principles of LPFG were studied including the modelling aspects of this sensing element. For this purpose, transmission spectra of LPFGs to external refrac-tive index changes have been simulated employing the two-layer fiber geometry. Next, the principles of Fresnel reflection-based sensor were investigated. Finally, experimental work was realized on different concentrations of glucose-water, glycerol-water solutions, and various chemicals. Our experimental results show an excellent agreement with the theory which demonstrated the capability of measuring RI of liquids for both methods investigated in the scope of thesis.
  • Master Thesis
    Analysis and Modelling of a Novel Approach for the Interrogation Unit of Fiber Bragg Grating Sensors Using Optical Frequency Domain Reflectometry Techniques
    (Izmir Institute of Technology, 2014) Pala, Deniz; Yüksel Aldoğan, Kıvılcım; Yüksel Aldoğan, Kıvılcım; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    The main purpose of this thesis is to demonstrate the feasibility of using polarization properties of FBGs interrogated by OFDR for quasi-distributed sensing applications. A fiber Bragg grating (FBG) is a constant and periodic refractive index value modulation within the core along an optical fiber. This modification is generally obtained by exposing the fiber core of a photosensitive optical fiber to an intense ultraviolet (UV) interference pattern. At the fabrication process of Bragg gratings, only one side of the fiber expose to UV light. As a result, refractive index change is not constant at the cross section of fiber. This non-uniformity on the refractive index gives rise to photo-induced birefringence which combines with the birefringence resulting from the slightly elliptical shape of the optical fiber and creates a global birefringence value. In the presence of the birefringence, the reflection (transmission) spectrum of Bragg grating is degenerated into two reflection (transmission) spectra corresponding to a pair of orthogonal polarization modes (x and y modes). The ratio between maximum and minimum optical transmitted power of these modes are defined as Polarization Dependent Loss (PDL). We analyzed the reflection spectrum, transmission spectrum and the PDL of the cascaded FBGs interrogated by an OFDR by the way of simulations. Based on the simulation results, we demonstrated the feasibility of a novel FBG interrogation method which can be implemented in quasi-distributed strain sensors embedded into composite materials.