| Sensing technology plays an important role in the development of modern information technology and brings great convenience to people's production and life.Among them,optical fiber sensing technology has attracted much attention of researchers due to their advantages,including immunity to electromagnetic interference,high safety,and remote measurement,etc.The fiber-optic Fabry-Perot(F-P)interference sensing structure owns the advantages like high reliability,good stability,and low cost.In this dissertation,the principle of the fiber-optic F-P sensing structure is analyzed in detail,besides two fiber-optic F-P sensors with different structures are designed and fabricated for the research of temperature monitoring and refractive index measurement,respectively.The findings in the F-P refractive index sensor research are extended to the fiber-optic sensors based on modal interference.The main contents of the dissertation are as follows:1.A novel fiber-optic F-P temperature sensor was fabricated by fixing a titanium wire and a standard SMF in two ends of a quartz capillary tube respectively.And then an air F-P cavity is formed between the end faces of the titanium wire and SMF.Its temperature sensing is performed by using the thermal expansion of titanium wire.The rationality of ignoring high-order reflected light was verified by the experiment.Its temperature sensing is performed by utilizing the thermal expansion of titanium wire fixed in the quartz capillary.The rationality of ignoring high-order reflected light was verified by the experiment.The spectra of heating and cooling processes were measured for three times in the temperature range of 1?50?,showing the high consistency and stability.Its sensitivity of the F-P cavity optical length changing with temperature is approximately-66.7 nm/?,and the accuracy can reach 0.1? by taking advantage of the binomial empirical formula instead of the commonly used linear one.2.At present,most studies on optical fiber refractive index sensors regard the refractive index of the test object as a constant,without considering the change in the refractive index of the medium with wavelength,and use a spectrum that does not include the 589.3 nm wavelength to measure the refractive index of the medium at this wavelength(nominal refractive index),thus a less rigorous conclusion may have been obtained in those studies.In this dissertation,theoretical analysis and experimental results prove that the traditional wavelength shift and double-peak optical path difference calculation method used in fiber-optic open-cavity F-P interferometers are not suitable for measuring the nominal refractive index of all media.It is speculated that other optical fiber refractive index sensors may also have the defect that they cannot be applied to refractive index measurement for all media.The most important thing is that a mutual calibration method of open-cavity F-P interferometers for refractive index measurement was proposed and verified,which is suitable for rapidly measuring the medium's dispersion curve at any wavelength band.It can supplement the deficiencies of Abbe refractometer in dispersion measurement,having broad application prospects in material analysis.3.Introduce the analysis of fiber-optic sensing structure based on modal interference from content 2.The relationship between the phase change produced by total reflection and the external refractive index was proposed,which can be used to explain the reason of the changes of the effective refractive index of the cladding with the test object,this theory completes the sensing mechanism.The theoretical analysis and experimental test prove that due to the dispersion curves of different media are different,the fiber-optic modal interference sensors are only suitable for liquid level monitoring or refractive index measurement of its calibration media,they also have the compatibility defects. |
PDF Full Text Request