Research On Interferometric Optical Fiber Sensor Based On Spherical-shape

With the development of technology of communication,people pay much more attention on optical fiber sensors.Due to the advantages of immunity to electromagnetic interference,high sensitivity,low cost and small size,optical fiber sensors are applied in many fields and get a rapidly development.In rencent years,optical fiber sensors are moving in minitruization,real-time,high precision and networked.Nowadays,people try to improve the sensors' performance through technology.Meanwhile experts also try to use different sensing elements to design new sensing structures.Following the development trend of optical fiber sensors,in this thesis,using the different sensing elements such as fiber Bragg grating(FBG)and multimode fiber,we design novel sensors which can realize dual parameter measurements simultaneously.The primary details are as follows:1.Summarising the optical fiber sensors' research background,significance,classification and development trends.Based on the principle of typical interferometer,introducing the develop status of core-offset structure,taper structure and core dismatch structure.2.Making a detailed description of sensing principle of fiber Bragg grating sensors and interferometric sensors.3.A compact optical fiber sensor based on a Mach-Zehnder interferometer(MZI)embedded in fiber Bragg grating is proposed and experimentally demonstrated for temperature,refractive index(RI)and liquid level measurement.The MZI is realized by concatenating two spherical-shape structures separated by a middle section.Besides,we discuss the effects of different structure parameters of MZI.As a result,the resonant wavelength of the FBG FBGDip and the interference dip of the MZI Dip1 have the different sensitivities of temperature,RI and liquid level.Experiment results show that sensitivities of 0.0724nm/?,87.65nm/RIU and-0.029714nm/mm of Dip1 and 0.00989nm/? of FBGDip.Meanwhile FBGDip is insensitive to RI and liquid level.The simultaneous measurement of dual parameters can be realized by sensitive matrix.This sensor's resolutions of temperature,RI and liquid level are 1.00?,0.095%RIU and 2.80 mm,respectively.4.An optical fiber sensor based on a Mach-Zehnder interferometer cascaded with FBG for simultaneous measurement of refractive index and temperature.Using the resonant wavelength of the FBG FBGDip and the interference dip of the MZI Dip1,the RI and temperature of the surrounding medium can be unambiguously determined.The experiments results show distinctive spectral sensitivities of 0.07175 nm/? and-91.76667nm/RIU of Dip1 and 0.00909 nm/? of FBGDip.This sensor's resolutions of temperature and RI are 0.99? and 0.097%RIU,respectively.5.An all fiber sensor based on down-taper cascading spherical-shape structure by multimode fiber is proposed and experientally demonstrated.Choosing the Dip1 and Dip2 to take the experiment.Through the experiments,we can find that Dip1 is generated by Mach-Zehnder Interferometer includes core-core mode interference.While Dip2 are brought by core-cladding mode interference.By monitoring wavelength shift or intensity change of the Dip2,magnetic field measurement is realized with sensitivity up to-0.169nm/mT or-0.367dB/mT for wavelength and intensity measurements,respectively.Besides,two kinds of interference dips are sensitive to temperature,the sensitivity are 0.0506nm/?(Dip1)and 0.0829nm/?(Dip2),respectively.This sensor's resolutions of temperature and magnetic field are 0.197? and 0.072 mT,respectively.