The Research On Optical Fiber And Laser Sensor Based On Polarization Maintaining Fiber For Simultaneous Strain And Temperature Measurement

With the development of science and technology,owing to electromagnetic interference resistance,corrosion resistance,high sensitivity,large dynamic range,small size,optical fiber sensor is widely applied to structural health monitoring,environmental monitoring,oil temperature monitoring,border security,aerospace and other fields.As a special optical fiber sensor,the modal interferometer fiber sensor can realize different modes interference only in one fiber.When the external environment parameters change,the effective refractive index of the fiber will be varied with them,which can cause the interference spectra shift.Once the shift can be observed by the optical spectrum analyzer,the changes of the environment parameters will be measured.In this paper,a kind of optical fiber and laser sensor based on polarization maintaining fiber modal interferometer are studied,the main content of dissertation is summarized as follows:(1)A compact polarization maintaining fiber(PMF)sensor based on the modal interference principle for simultaneous strain and temperature measurement is designed.The cladding mode in the PMF will be excited by the core-offset at one splicing point,the cladding mode and the core mode will be recoupled and interfered at the other splicing point which forms a fiber bubble.Using the polarization beam splitter and an optical switch,the direction of the linearly polarized light can be easily switched between the fast axis and the slow axis in the PMF.Because the effective refractive indices of the fast and slow axis in the PMF are not the same,different interference spectra will be generated.In the experiment,the temperature and strain response characteristics of the fiber sensor is researched.The strain sensitivities are measured to be it can be-1.25 pm/?? for fast axis mode and 0.429 pm/?? for slow axis mode.The temperature sensitivities are 79 pm/? and 20 pm/?,respectively.Using the sensitive matrix,we can obtain that the variations of temperature and strain by measuring the interference spectrum shift.When the wavelength resolution is 0.01 nm,the temperature and strain resolution of the fiber sensor can be 0.285? and 10.0??.(2)An optical fiber laser sensor for simultaneous strain and temperature measurement is designed.Based on the structure mentioned above,a fiber modal filter is fabricated by the misalignment fusion.Then,the filter is introduced in the fiber ring cavity laser.By adjusting the optical switch in the experiment,it is found that two different oscillation wavelengths can be excited in the fiber laser.The response characteristics of the two different oscillation wavelengths are studied and analyzed.When the laser resolution is 0.01 nm,we can obtain that the temperature and strain resolution of the laser sensor are 0.53 ? and 49.6 ?? in 19-39?,the temperature and strain resolution of the laser sensor are 0.34 ? and 25.2 ?? in 39-69?.