Study On Fiber-optic Wave Sensors Based On Mach-zehnder Interferometer

Inspection technique based acoustic emission and the other ultrasonic or guided waves theory is one of the important non-destructive testing methods. The essence of all above techniques is detection of stress waves. Traditional wave sensor employs generally the electronic sensitive components, while optical fiber sensor is smaller, lighter and immunity to electromagnetic interference. The contents of this thesis are as following:Firstly, the principle of Mach-Zehnder interferometer system is introduced. The effects of initial phase difference, amplitude of stress waves and polarization state to sensing properties of optical fiber sensor are analyzed. The optimal initial detection state is found for the optical fiber sensor based on Mach-Zehnder interferometer. Then, the contribution of longitudinal and transverse strain and the refractive index to the sensitivity of optical fiber sensor are investigated respectively, as well as the sensitivity without coating.Secondly, since the straight optical fiber sensing arm of the traditional Mach-Zehnder interferometer is insensitive to deformation. This work enwinds the optical fiber into helical annulus to sense the stress waves. In this case, the phase difference of this sensor is analyzed under simple stress condition. Then a series of experiments are carried out to find out its sensing properties.Finally, two kinds of reusable optical fiber sensors are proposed. Their sensing properties are investigated with finite element analysis and experiments. They are used to detect the Lamb wave and acoustic emission signals. Results show their feasibility of stress wave detection.