The Magnetic Field And Refractive Index Sensor Based On Magneticfluids And Fiber

Magnetic fluid(MF)is a kind of stable colloidal system consisting of surfactant-coated magnetic nanoparticles dispersed in a suitable liquid carrier.It possesses both the features of magnetic property of solid magnetic materials and fluidity of liquids.Thus,MF presents versatile magneto-optical properties,such as tunable refractive index(RI),magneto-dielectric anisotropy etc.On the other hand,optical fiber sensing techniques,as novel sensing technologies,are booming over the past decades.Duo to their particular characteristics,such as compactness,high-temperature resistance,anti-corrosion,immune to interference of electromagnetic and high sensitivity,they have been widely used in various physic parameters sensing.Considering these,the combination of fiber with MF may provide a prospective approach for novel photonic devices,such as switches and magnetic field sensors.First of all,a kind of magnetic field sensor based on the property of magnetic-fielddependent RI of MF is proposed.We present a new sensing structure based on singlemode-multimode-singlemode(SMS)structure and lateral-offset fusion splicing techniques.As the sensing structure is surrounded by magnetic fluids,a novel type of fiber magnetic field sensors is formed.Magnetic field sensing is achieved by monitoring wavelength shift or intensity variation of the interference valley.The magnetic field sensing sensitivities of 65.9 pm/Oe and 0.1185 dB/Oe are obtained for magnetic field strength ranging from 30 to 110 Oe.Besides,we also investigate the hysteresis and temperature cross-sensitivity of the magnetic field senor.Secondly,after the investigation of sensing charactors of the as-fabricated RTFC sensors,we propose a kind of high sensitivity magnetic field sensor taking advantage of the tapered fiber coupler and MF.The experimental results show that the sensitivity of the sensor is wavelength-dependent.The maximum sensitivity of 191.8pm/Oe is achieved at wavelength of around 1537 nm.In addition,a sensitivity of 0.037 dB/Oe is achieved by monitoring variation of the fringe visibility.Thirdly,a reflective all-fiber magnetic field sensor based on a MF-clad non-adiabatically tapered microfiber(NATMF)is proposed and experimentally demonstrated.The NATMF is fabrcate by two-step method(fusion splicer combining with the additional flame brushing method).Owing to the large evanescent field outside the NATMF surface,the transmission properties of the NATMF is extremely sensitive to the surrounding RI.Combine with tunable RI of MF,a high sensitivity magnetic field sensing could be achieved.To prove the previous analysis and deduction,we coat as-fabricated NATMF with MF,and then study the reflection spectrum of the NATMF vary with the magnetic field due.By monitoring the dip wavelength change in the reflection spectrum,the magnetic field strength can be interrogated.A relatively high magnetic field sensing sensitivity of 174.4 pm/Oe and-0.02 dB/Oe is obtained.Considering the compact size,low cost,large extinction ratio and high sensitivity of the proposed structure,it is promising for other tunable all-in-fiber photonic devices.Finally,a low-loss and highly sensitive RI sensor based on a reflective tapered fiber coupler(RTFC)is presented.The sensitivities of the as-fabricated RTFC sensors with different waist diameters are measured by immersing the RTFCs in glycerol-water solutions with different mass fractions,RI sensitivity can be achieved beyond 3617 nm/RIU.By comparing with other reflective RI sensors,we find the distinctive sensing prinple of our sensing structure.