Study On The Characteristic Of MC-FBG And Applications In Optical Fiber Sensors

With the deeply research on the characteristics and advantages of Fiber Bragg Grating (FBG), FBG has been widely used in optical fiber sensors and communications. And FBG has catched domestic and foreign scholars’eyes widely. FBG sensor has many advantages such as wavelength-encoded, anti-electromagnetic interference, reusability, small size, and light weight, so that it can be applied in many sensor applications. In this thesis, the displacement sensor, hydrostatic leveling system (HLS) and accelerometer based on the bending sensitivity of Multi-Core Fiber Bragg Grating (MC-FBG) were investigated in experiment and theoretic analysis.In this paper the mode field and birefringence effect of MCF was simulated. Then the bending sensitivity of MC-FBG was analyzed. Since the core in MCF is offset located in the cross-section, the FBG written in this offset core is sensitive to the bending.The bending sensitivity of Two-Core Fiber Bragg Grating (TC-FBG)and Seven-Core Fiber Bragg Grating (SC-FBG) used in the experiment is3.37×10-3/cm-1and2.705×10-3/cm-1, respectively.A novel method is proposed for displacement sensor through bending the SC-FBG into the Ω-shape. The sensitivity of displacement sensor is0.395nm/mm in experiment. Based on this, HLS is designed and the relationship between center wavelength shift and water level is1.8017nm/mm in experiment. The accuracy is1μm which is10times as high as the HLS on the market whose accuracy is0.01mm.A novel accelerometer was designed based on the bending sensitivity of TC-FBG, which was analyzed theoretically and measured experimentally, respectively. The sensitivity of the sensor is0.2995nm/g, and the resonant frequency is10.2Hz in theoretical analysis. The sensitivity of the sensor is0.314nm/g and resonant frequency is9.7Hz in experiment.So it can measure the acceleration signal which is both low frequency and small acceleration. We used the TCF as the cantilever beam without any loads. The resonant frequency is157.31Hz in theory and164Hz in experiment, respectively. It is higher than the TCF accelerometer with load.