| Evanescent wave transmission characteristics of microfiber that makes its transmission mode is very sensitive to changes of the external refractive index. If you combine narrow refractive passband of grating with high proportion of evanescent wave of micro- or nanoflber(MNF),we will get a new device which is micro- or nanofiber Bragg grating(MNFBG).It is not only able to get applied to the refractive index sensing but also get more applications to be developed at broader areas.This article is based on optical waveguide theory describing the optical transmission characteristics of MNF and establishing a theoretical model of MNF evanescent wave Bragg grating refractive index sensonand then we analyze and summarize the production methods,process refractive index sensing and measuring the current situation and development of the microfiber grating sensor.lt focuses on the method of hydrofluoric acid etched the single-mode fiber Bragg grating and made a microfiber Bragg grating refractive index sensor.and refractive index of liquid sensing characteristics.Designed an etching apparatus, which can be completed at a constant temperature corrosion, also prevent hydrofluoric acid to evaporating and use the three-liquid Stratification Method to control the portion of the fiber grating corrosion.Experimental results show that the study on etching the fiber,which temperature chooses generally 20 22°C,the etching solution etched about 30 minutes by 40%, about 90 minutes by 20% and about 80 minutes by 10%,which is stages etching method.Diameter approximately 8//w.6//m.4//w and 2fxm of MNFBG sensors was produced by this device after that use the MNFBG to measure the refractive index of different concentrations of sucrose solution at 22 C. Experiments show that the larger the refractive index.which corresponds to the resonant wavelength greater. When the temperature was 22 C the diameter of the MNFBG is about 8"w 6"w‘4"w and 2jum, corresponding to the refractive index sensitivity are 13 A 04rjm/RJU, 31.393nm/RIU, 74.6\2fim/RJU and 112.590??m/7?/6r?respectively. Research on the diameter of the fiber grating corresponds to refractive index sensitivity, analysis shows that:diameter of MNFBG is reduced that its sensitivity is not a linear function of the refractive index corresponds to the diameter of the fiber grating.This is from angle of the experiment to verify the MNFBG resonance wavelength change with the environment refractive index is not a linear relationship between the diameter of the fiber grating and the fiber grating refractive index sensitivity.Taking into account influence of temperature changes to the resonance wavelength, we use a three liquid Stratification Method for fiber gratings etched half, that is,half is ordinary FBG, the other half is MNFBG.Around 22℃ and the radius of micro- or nanofiber grating is 4.5μm,the MNFBG temperature sensitivity is 0.005nm/℃ and the refractive index sensitivity is 47.558 nm/RIU, after the temperature correction of the refractive index sensitivity is 47.553nm/RIU,which provide a reference for the refractive index measurement temperature experiments to solve the problem of the temperature cross sensitivity. Based on the MNFBG refractive index sensitive features, we research on a new functional materials magnetic fluid combination of micro- or nanofiber grating measures the magnetic field strength by experiments. For 15% of magnetic fluid solution when magnetic field is applied to it from 10~100m T, the refractive index of micro- or nanofiber Bragg grating sensor sensitivity is 61.6pm / m T.This provides some reference for more functional application of micro- and nanofiber gratings. |
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