Research On Optical Fiber Magnetic Field Sensor Based On S-cone And Magnetic Fluid

With the rapid development of optical communication and sensing technology,optical fiber sensor has been gradually used in bio-medicine,energy exploration,engineering monitoring and other fields which can contribute to its advantages of anti-electromagnetic interference,low cost and easy fabrication.As a novel type of colloidal material,magnetic fluids?MFs?has several unique optical properties,such as tunable refractive index and field-dependent transmission.In recent years,as an important category of optical fiber sensor,magnetic field sensor which fabricated by integrating magnetic fluids with optical fiber sensor has been widely researched.In this paper,three types of optical fiber interferometric magnetic field sensors were fabricated based on S-taper and magnetic fluids.And the interference spectral characteristics of the sensing structure have been analyzed and researched in detail.The main components of this paper are as follows:1.Intensity-interrogated magnetic field sensor based on down-fusion taper concatenated with S-taper has been proposed.The sensing structure is fabricated by a commercial fusion splicer,and the sensing head is made by encapsulated it with MFs into capillary.In this part,down-fusion taper serves as mode exciter,whereas the S-taper is employed to couple the cladding modes back into the fiber core.Owing to the fact that the refractive index of MFs generally increases with the increment of applied magnetic field intensity,the magnetic field sensing can be realized based on intensity interrogated.Experimental results indicate that the maximum magnetic field sensitivity reaches-0.02336 dB/Oe for a magnetic field ranging from 25 Oe to 200 Oe.And the temperature sensitivity reaches 0.07116 dB/?within a temperature range of 26?to 46?.2.Wavelength-interrogated magnetic field sensor based on S-taper and up-fusion taper has been proposed.The S-taper served as a higher mode exciter,whereas the up-taper is employed to couple the cladding modes back into the fiber core,so an interferometric spectrum could be acquired for sensing interrogation.The magnetic field and temperature can be sensed by monitoring the shift of the interference spectrum.At the same time,by exploiting the distinction between magnetic field intensity and temperature sensitivities of different dips that are selected for wavelength interrogation,temperature cross-sensitivity issue can be resolved.Experiment results show that the maximum magnetic field sensitivity reaches-0.03464 nm/Oe within a specific range of 40 Oe to 160Oe.The proposed sensor has a maximum temperature sensitivity of 0.04889 nm/?when the temperature increases from 27?to 45?.3.Intensity-interrogated magnetic field sensor based on S-taper embedded into long period grating?LPG?has been proposed.The LPG is fabricated by CO₂ laser,and then an S-taper is fabricated in the middle of LPG by using commercial fusion splicer.Using the principle of mode interference,the transmission characteristics of the sensing structure can be analyzed and demonstrated by packaging the MFs and the sensing structure.Select different interference dips/peaks as monitor samples,the maximum sensitivity can reach up to-0.036 dB/Oe within a specific range of 20 Oe to 140 Oe,and the temperature sensitivity reaches 0.06759 dB/?within a temperature range of 28? to 46?.