Thesis Type: Postgraduate
Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey
Approval Date: 2020
Thesis Language: Turkish
Student: SELİN ECE KİPRİKSİZ
Supervisor: MURAT YÜCELAbstract:
Fiber Bragg grating-based (FBG) sensors, a kind of optical sensors that are alternative to conventional sensors, are used in many applications due to their advantages. In this thesis study, FBG-based temperature sensors in uniform, apodized and chirped structures and a tilted FBG-based (TFBG) sensor capable of simultaneously measuring the temperature and strain were designed using the Optigrating 4.2.3 software. The effects of the optimized apodized and chirped structures on reflectivity and bandwidth were investigated. The temperatures of the FBGs designed were changed with 10 ºC periods, and the changes that occurred in the grating period and wavelengths were examined. In the sensors designed using a FBG since the Bragg wavelength is sensitive to both temperature and strain changes, simultaneous temperature and strain measurement is not performed because the cross-sensitivity cannot be distinguished from each other. Due to the tilted structure of TFBG fringes, the sensitivity of the core and cladding resonances, which are observed simultaneously in the transmission spectrum, to temperature and/or strain is different. A TFBG sensor with a tilt angle of 5°, which was capable of measuring temperature and strain simultaneously, was designed. While only the temperature changing with 10 ºC periods was applied to the TFBG in the first stage, the strain changing with 100 μƐ periods was applied to it in the second stage, and simultaneously changing temperature and strain were applied to it in the third stage, and the linear shifts occurring at the wavelengths were calculated through software. In the stage of designing a temperature sensor, different thermal expansion and thermo-optic coefficients were used, and the amounts of shifts caused by these coefficients at the wavelength were examined. It was observed that the wavelength change that occurred with the simultaneous application of temperature and strain was equal to the total wavelength change that occurred in the non-simultaneous application of temperature and strain. It was observed that the sensors designed showed different spectra from each other due to their different structural features.