Study Of Magnetic Field Sensing Based On Composite Fiber Gratings Coated With Magnetic Fluid

With the development of internet of things, the performance of intelligent products and equipments are enhanced by employing relevant technology. The magnetic field sensors have attracted considerable research interests due to their significant applications in current detection and magnetic field surveillance. Various fiber grating sensors have been developed for magnetic field measurement due to their favorable features such as anti-interference, high sensitivity, flexible maneuverability, compactness and fast responses. In this paper, we combine the characteristics of the composite fiber grating and magnetic fluid(MF) to put forward a new design of magnetic field sensor. By using tunable refractive index( RI)property of MF under the the applied magnetic field, many kinds of magnetic field sensors based on the composite fiber gratings including the cladding diameter reduction of fiber bragg grating(FBG), tilted long-period fiber grating(TLPFG) and the long period grating(LPG)cascaded with multimode fiber have been realized. The transmission characteristics of the fiber grating sensors under different applied magnetic fields have been theoretically analyzed and experimentally investigated. The main contents are as follows:(1) A magnetic field sensor based on the cladding diameter reduction of FBG is fabricated and demonstrated. In order to improve the interaction of the core guided model and environment, the cladding of FBG diameter is reduced by the HF etching method. For the resonance peak of FBG and the coupling core guided model with the cladding modes, the transmission spectrum change due to the effect of the magnetization of MF.(2) An intensity-interrogated fiber magnetic field sensor based on TLPFG has been proposed.The spectral characteristics of TLPFG are investigated, the core guided mode not only couples with the synthetic cladding mode, but also coulpes with a series of asymmetrical cladding modes. The experimental results and theoretical analysis show that resonance wavelengths for LP0 m and LP1 m of TLPFG present different characteristics by tuning the applied magnetic field intensity. The variation of transmission losses has a good linear with the intensity of magnetic field.(3) By cascading the corrosion multimode optical fiber( 105/125) and LPG, a dual-parameter measurement device has been proposed and experimentally demonstrated for simultaneous measurement of magnetic field and temperature. By splicing the LPFG with the etched MMF, the coupling between the core mode and different cladding modes of LPFG as well as the interferences between higher-order modes in the MMF could occur. Resonant notches corresponding to the multimode interference(MMI) and the LPG have distinctly different sensitivity to temperature change and applied magnetic field because of different transmission mechanisms. Using the sensing matrix method, we can effectively solve the temperature cross problems of the magnetic field sensor. What’s more, the resonant notchesfor the cooperated MMI and the LPG can detect a wide range of magnetic field.