Helical Fiber MZI For Torsion Sensing Application

With the continuous progress of society and the rapid development of science and technology,the demand for engineering quality monitoring and environmental parameters testing continues to increase.The design and research and development of new sensors are becoming a hot topic in the academic and engineering circles.Compared with the traditional sensor,because of the advantages of smart,small body,anti-electromagnetic interference,corrosion resistance,anti-high temperature and pressure,remote monitoring,reusable,more and more are used in the monitoring of external parameters,in the construction of bridges,automobile ships,petrochemicals,marine navigation and so on civilian military field has a huge application prospects.Especially phase modulation fiber optic sensor,because it can be a wide range of external parameters for a wide range of fast and accurate dynamic measurement and become a hot spot for such research.In this type of fiber optic sensor,the optical fiber Mach-Zehnder interferometer(MZI)is one of the most widely used structural forms;its principle is to use the external parameters of the fiber signal arm to adjust the beam,change the signal arm And the reference arm between the phase difference,thus changing the interferometer output signal,and then use the demodulation technology to obtain real-time changes in the measured parameters.All-fiber MZI is the interference of the two interferometer arm and beam splitting device integrated in the same fiber,making the device more integrated,intelligent,and thus in recent years by the academic and engineering attention.In this thesis,in order to realize torsion,we propose two types of new all-fibers MZI.Theoretical model is set up,and experiments are carried out to confirm it.The experimental results are basically agree with theory.The main contents and research achievement are as follows:1.An interferometer using a single-mode fiber helix(SFH)was fabricated by the flame-heated treatment for torsion sensing application.For the first time to our knowledge,this kind of interferometer was designed and experimentally demonstrated.By launching a linear polarized beam into the SFH,interference was formed at the output of the structure because of the fiber bending-induced birefringence.Theoretical analysis shows that,when the sensor part is twisted,the geometrical change will bring a resonant dip wavelength shift,and the torsion sensitivity is related to the helix radius and pitch.From the experiment data,the torsion sensitivity reaches 1.691 nm·m /rad from-9.39 rad/m to 13.42 rad/m for the SFH with a radius of 0.30 mm and pitch of 1.23 mm.2.A miniature polarimetric interferometer was fabricated based on a microfiber helix(MFH)for torsion sensing application.For the first time to our knowledge,this kind of interferometer was designed and experimentally demonstrated.By launching a beam into the MFH,the interference was formed at the output of the structure because of the fiber bending-induced birefringence.Theoretical analysis shows that the resonant dip wavelength will shift regularly when torsion is applied to the sensor part.Additionally,the torsion sensitivity of the interferometer is related to the parameters of MFH.From the experiment data,the torsion sensitivity reaches 12.66nm·m/rad from 0rad/m~1.34rad/m and 8.04nm·m/rad from-2.35rad/m~0rad/m.