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, Kıvılcım

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Now showing 1 - 7 of 7
  • Master Thesis
    Design and Modelling of Ring Resonators: Feasibility Study for Temperature Sensors
    (01. Izmir Institute of Technology, 2023) Yüksel Aldoğan, Kıvılcım; Yüksel Aldoğan, Kıvılcım; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Ring resonator structures have garnered significant attention in the field of photonics due to their versatile nature. Temperature can influence the refractive index of the materials used in the resonator, which in turn affects the resonance wavelengths and transmission properties. The purpose of this study was to examine how temperature variations impact the performance of ring resonators. By measuring the resonator response at different temperatures and analyzing the data, it is aimed to understand the thermal behavior of the ring resonators, assess their suitability for practical applications and lays the foundation for further advancements in the design and optimization of ring resonator-based systems. Within the scope of this thesis, all-pass and add-drop type ring resonators have been produced, and measurements have been carried out at 25 and 35 degrees Celsius. In addition, numerical calculations and simulations of the ring resonators have been performed and compared with experimental data.
  • Master Thesis
    Fiber Optic Current Sensor Interrogated by Phase-Sensitive Optical Time-Domain Reflectometer
    (Izmir Institute of Technology, 2022) Yüksel Aldoğan, Kıvılcım; Yüksel Aldoğan, Kıvılcım; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In this thesis, a novel method for current sensing using an FBG-assisted Phase-Sensitive Optical Time Domain Reflectomter (Phase-OTDR) with Mach-Zehnder Inter-ferometer is proposed. The detrimental effect of the intrinsic linear birefringence of the sensing fiber is solved by calibration. An FBG pair is written at the two ends of the spun fiber coil to eliminate phase fading and increase the measurement accuracy. A simulation tool was developed to study the feasibility of the approach and the sensor performance by a well-established Phase-OTDR model with the Jones formalism. The effects of bending-and FBG-induced linear birefringence are investigated as well as the impact of the detector noise.
  • 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 Implementation of Optical Fiber Sensors for Process Monitoring of Composite Materials
    (Izmir Institute of Technology, 2016) Yılmaz, Anıl; Yüksel Aldoğan, Kıvılcım; Yüksel Aldoğan, Kıvılcım; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    The use of composite materials in many industrial applications and structures under high stress (airplane wings, unmanned air vehicles, wind turbines, etc.) has been exponentially growing thanks to their lightweight, superior strength, durability, and corrosion resistance. However, the unique mechanical properties of composite materials cannot be fully exploited without monitoring them when material is placed under constraints. It is essential to monitor their behavior not only in the field but also during manufacturing process to ensure the high quality of manufactured materials. For this purpose, the use of optical fiber sensing, particularly the embedding of fiber Bragg grating (FBG) sensors into composite materials has been gaining growing popularity thanks to various advantages of FBGs. In this context, the main purpose of this thesis is to demonstrate the feasibility of using optical fiber sensors for process monitoring (cure and resin flow) of fiber reinforced thermoset composite materials. The first sensor type studied in the thesis was based on Fresnel reflection. The capability of monitoring the curing profile of liquid matrix (mixture of resin and hardener) has been demonstrated by the way of Fresnel reflection sensor interrogated by Optical Time Domain Reflectometry (OTDR). Then, FBG sensors were embedded into composite plates to measure the temperature change during resin injection and cure cycle, as well as determining the residual strain inside the material. In spite of the popularity of using FBG sensors, most recent researches clearly prove that there is still a lack of technical maturity in real life applications in interrogating embedded FBGs for strain measurements. There is still room for new sensing approaches. In the last part of the thesis, we proposed a novel method to interrogate fiber cavity ring-down (CRD) loop by using OTDR which makes this sensing approach more practical and cheaper than the conventional techniques. Thanks to these advantages, our proposed interrogation method can be implemented for strain measurements inside the composite materials as an alternative to the FBG sensors.
  • Master Thesis
    Exploiting Second Harmonic Generation for Microelectronics Interface Characterization
    (Izmir Institute of Technology, 2016) Soylu, Gizem; Yüksel Aldoğan, Kıvılcım; Dinleyici, Mehmet Salih; Yüksel Aldoğan, Kıvılcım; Dinleyici, Mehmet Salih; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    This thesis aims to develop a technique to characterize microelectronic interfaces based on Second Harmonic Generation (SHG) method. In the experiment part of this study, silicon wafers with thermal and native oxide, silicon-on-insulator (SOI), pure glass and glass with TiO2 thin film samples were used to observe Second Harmonic (SH) signal. The experiments have been performed in IMEP-LAHC laboratory in Grenoble, France. In addition, the measurements were carried out with “Harmonic F1X” which is a femtosecond laser developed by the company FemtoMetrix based in California/USA (FemtoMetrix). Three contributions to SHG were investigated experimentally: the electric dipole approximation due to symmetry breaking at the surface/interface, a dc electric field because of the charge separation at the interface, and lastly bulk contributions. Then, the phenomenological model of surface SHG (Mizrahi & Sipe, 1988) was simulated in MATLAB, and the ratios of the elements of second order nonlinear susceptibility (χzzz/χzii and χizi/χzii) for the silicon wafers were identified with comparing the model with the experimental results. In addition, it was shown that surface and bulk contributions can be separated by using specific polarization states and azimuthal orientations. To show this separation, Fourier coefficients, which describes the crystal facial orientations of the total SHG, were determined for the silicon wafers. Furthermore, it was observed that there are some critical parameters which have an effect to SHG: the polarization states of the incident light and second harmonic light, the angle of incidence of the incoming light and the oxidation types of silicon. Finally, SOI has been used to check whether the effecting factors are same for silicon wafers. The findings demonstrate that SHG is a powerful technique to characterize the surface/interface and the bulk of the sample in microelectronic industry.
  • 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.