Research On The Optical Fiber Sensor Based On Polarization-maintaining And D-shaped Fiber

Compared with traditional optical fiber sensor,the inter-modal interference optical sensor b ased on polarization-maintaining fiber and D-shaped fiber has the advantages of high sensitivity,compact structure,low cost and strong anti-disturbance capability.This kind of sensor shows an enormous application prospect and has been used in the measurements of refractive index,tempe rature,strain,displacement,vibration,pressure widely and so on.It has been a focus in the field of optical fiber sensing technology.In this thesis,we proposed and fabricated two kinds of optical fiber sensors by using polarization-maintaining and the D-shaped optical fiber.The two optical fiber structures sensors were constructed by single mode-polarization-maintaining-single mode fiber(SPS)and single mode-polarization-maintaining-D-shaped-single mode fiber(SPDS),respectively.The sensing principles of the two kinds of sensor are theoretically analyzed and the measurements of curvature,mass,pressure,temperature,liquid level,refractive index by using the sensors were implemented in experiment.Moreover,the influences of the length of polarization-maintaining fiber on the sensitivity of sensors were studied.The main contents of this thesis include the following aspects:1.An optical fiber sensor constructed by single mode-polarization maintaining-single mode fiber(SPS)structure is fabrication and experimentally demonstrated.The measurements of curvature,mass and pressure by using this SPS structure were implemented and the influence of the length of polarization-maintaining fiber(PMF)on the sensor sensitivity is also studied in experiment.The results of experiment show that:(1)The length of PMF has some influence on the curvature sensitivity of the sensor.The maximum curvature sensitivity achieves 59.849 nm/m~-11 when the length of PMF is 11cm.(2)The quality sensitivity of sensor is inversely proportional to the length of PMF.The quality sensitivity can reach up to 1.446nm/g when the length of the PMF is 7 cm.(3)Two types of pressure loading devices were designed for pressure measurement.The results show that the sensitivity of the sensor decreases slightly with the length of PMF increase.The sensor sensitivity obtained by the two means of pressure loading are 6.049 nm/kpa and 7.896nm/kpa,respectively.The sensitivity of the second loading device is higher than the first.And thus the installation method of the sensor in practical application is needed to consider.2.A SPDS fiber structure-based Sagnac loop sensor is fabrication and experimentally demonstrated for measuring temperature,liquid level and refractive index(RI).The SPDS structure is fabricated by fusion spliced a section of polarization-maintaining fiber(PMF)to a piece of D-shaped multimode optical fiber(DMMF).Then the P-D structure is built into a Sagnac loop by using a 3dB coupler.The temperature,liquid level and RI characteristics of the sensor are investigated experimentally.The influences of the length of PMF on the sensing sensitivity are also studied.The experimental results display that:(1)In temperature measurement experiment,it is found that the length of PMF and the tail fiber of multimode fiber at both ends of the D-shaped fiber have slightly impact on the sensitivity of the sensor and the maximum temperature sensitivity reach 1.611nm/~oC when the length of PMF is 11 cm.(2)In liquid level experiment,two resonant dips are selected for liquid level measurement.The results show that the two resonant dips have different spectral responses to RI,which indicate that the sensor may realize simultaneous multi-parameter measurement.The second resonant dip has a higher sensitivity,reaching 0.602nm/mm in the two selected resonant dips.(3)In refractive index measurement,two resonant dips are chosen for measurement.The experimental results show that the sensitivity of the first resonant dip is higher than the second one,up to 122.189nm/RIU.The sensor shows a good linearity,and the R~2 reaches up to 0.985.