Research On Mach-Zehnder Optical Fiber Temperature Sensor Based On Twin-core Fiber Grating

With the rapid economic and social development, engineering quality and environmental pollution have become the important issues that restrict the harmonious development of our society. To develop new sensors used for monitoring is a hot topic. Compared to the traditional electrical sensors, the optical fiber sensors have many advantages:small volume, compact structure, electromagnetic immunity, high sensitivity and so on. According to the lightwave parameters that is modulated, optical fiber sensors can be classified into five kinds:intensity modulation optical fiber sensors, frequency modulation optical fiber sensors, phase modulation optical fiber sensors, wavelength modulation optical fiber sensors, polarization modulation optical fiber sensors. Especially, the wavelength modulation optical fiber sensors have been widely used because of the advantages of high accuracy and stability. In this thesis, the paper proposes a new type of optical fiber sensors based on fiber Mach-Zehnder interferometers.This paper first sets up double waveguide model and analyses the coupling theory and the coupled-mode equations, according to the structure of twin-core fiber. The study shows that the two fiber cores have equal mutual coupling coefficient in the fully coupling case, and analyse the transmission characteristics of twin-core fiber. Under the condition of imperfect coupling,δ2/K12K21 can accurately reflect the strength of fiber coupling, and 8 is the phase mismatch, K12K21 is the product of mutual coupling coefficient.Secondly, the paper has analysed the coupling characteristics of Fiber Bragg Grating(FBG). When the optical wave transmisses in the fiber gratings, the transmission characteristics of the waveguide is different from the regular. The paper presents the detailed theoretical derivation of the coupling characteristics of FBGs and studys the influence of modulation depth for the FBGs’reflection spectrum bandwidth.At the end of this paper, the sensing characteristics of the fiber Mach-Zehnder interferometers are analysed, the paper designs a MZ optical fiber sensor based on twin-core fiber grating, and studys the temperature sensing properties and the transmission spectrum at different temperatures of the optical fiber sensor. The study shows that the transmission spectrum will have a wavelength drift as the temperature changes, when the temperature rises, the transmission spectrum drifts towards longer wavelength. According to the linear relationship between the temperature and the wavelength drifts, we can know the temperature sensitivity of the optical fiber sensor at the specific wavelength. At the wavelength of 1500nm, the temperature sensitivity of the optical fiber sensor is 0.01724nm/℃; at the wavelength of 1550nm, the temperature sensitivity is 0.01786nm/℃; at the wavelength of 1600nm, the temperature sensitivity is 0.01832nm/℃.