Investigation On Mach-Zenhder Optical Fiber Transverse Load Sensing Based On Polarization Characteristic

In this thesis,we mainly studied the transverse load sensor which based on the polarization character and designed three optical fiber transverse load sensor based on the polarization characters.The article ana lyzes the sensing principle,fabrication method and their application.The main contents are shown as follows:1.The development process of fiber sensor was introduced in detail,and the research status,development and applications of transverse load in the field of transverse load sensing were introduced briefly.In this work,the polarization character of single mode fiber and polarization-maintaining optical fiber(PMF)was clearly studied.Because of the refractive index difference between the orthogonal axis,the PMF can keep the polarization with no varies.When the trasverse load was applied on the PMF,the energy of the two orthogonal polarization modes will be coupled with each other,influencing the intensity propagating in the fiber cladding.2.A transverse load sensor based on the Mach-Zehnder interferometer(MZI)with PMF was presented.By using the core-offset fusion splicing method,the MZI was constructed with PMF between two single mode fibers.Along with the transverse load ranging from 0.196 N/mm to 0.588 N/mm,The experimental results showed that the sensor has the sensitivities of 12.85 d B/(N/mm)and 30.69 d B/(N/mm)for the fast and slow axis resonant wavelengths of 1485 nm and 1545 nm in the interference pattern,respectively.3.A transverse load sensor based on in-line Mach-Zehnder interferometer(MZI)was presented.The sensor head is formed by a long period fiber grating and Bowknot-type taper structure through fusion splicing.With the increasing of transverse load on the LPG,the couple efficiency between the core mode and the cladding mode of LPG changed,which further brings about a change of the interference fringe visibility.The experimental results show that the structure with a 3 cm-long LPG has the sensitivity of-10.476 d B/(N/mm)for the wavelengths of 1562 nm.4.A transverse load fiber sensor based on Mach-Zehnder interferometer constructed by a Bowknot-type taper between a single mode fiber and a polarization maintaining fiber(PMF)was proposed.Due to the polarization maintaining fiber's birefringence,the interference pattern of the Mach-Zehnder interferometer has two different wavelength peaks,whose intensities changed with the transverse load applied on the polarization maintaining fiber.The experimental results showed that the structure with a 2cm-long polarization maintaining fiber has the sensitivities of 104.52 d B/(N/mm)and-102.94 d B/(N/mm)for the fast and slow axis resonant wavelengths of 1485 nm and 1545 nm in the interference pattern,respectively.