Research On The Interferometric Sensing Properties Of Macro-Bending Fiber And Its Application On Magnetic Field Measurement

For the past few years,all kinds of optical fiber sensors have been significantly developed due to their feasible integration with other fiber optics components,high sensitivity,small size,and capability for in-situ,real-time,remote,and distributed sensing,which has become the zealous research objects of scientists and facilitating devices in the engineering applications.As for the macro-bending fiber sensors,they have been widely applied in various areas on account of simple configuration and low cost.However,most of the measurements are realized by the change of light transmission loss induced by the external environment variables.Therefore,this kind of sensors is prone to be disturbed by environmental interruption and has a low measurement resolution.Hence,aiming at simplifying the fabrication technology and improving the performances of sensors,a novel optical fiber interferometer based on a macro-bending fiber is proposed in this thesis.This novel sensor is demodulated by wavelength.In the thesis,the interferometric sensing properties of the sensor are investigated both in theoretical and experimental manner.Further,combined with the functional material magnetic fluid,the measurement technology towards magnetic field based on the proposed sensor are researched,which enlarges the applied areas of the interferometric macro-bending fiber sensors.This thesis has completed the following main research work contents:(1)The influences of macro-bending towards the refractive index of fiber,transmission loss and numerical aperture and so on are stated and analyzed.According to that,a novel interferometric macro-bending optical fiber sensor is designed.Further,the working principles are analyzed and simulated.By exploring and researching the fabrication technology,the proposed sensor is well produced.With that,by changing the bending radii of the sensor,the output optical spectra are obtained and analyzed.(2)The measurement for the variations of RI is realized based on the proposed and prepared sensor.Further,the influences of temperature towards the sensing performances are analyzed and researched.Experimental results show that the relationships between temperature,refractive index and the resonant wavelength are linear,and the temperature and refractive index measurement sensitivities can reach to 0.418 nm/? and 224.39 nm/RIU,respectively.(3)The issues of cross-talk between temperature and refractive index of the proposed novel sensor are well addressed.Two different schemes are designed and realized to compensate the temperature or dual-parameter simultaneous measurement adopting the demodulation methods based on relative wavelength change,which well resolves the cross-talk sensitivity issue.(4)The applications of the proposed sensor into the measurement of magnetic field are realized based on the property of tunable refractive index of magnetic fluid.This new magnetic field macro-bending fiber sensor filled with magnetic fluid is designed and fabricated.By further constructing the measurement system,the magnetic field measurement properties are tested and analyzed.Experimental result shows that the sensitivity can reach to 83.3 pm/Gs.