| Recent years,optical fiber sensing technology(FST)has developed rapidly,and a variety of fiber sensors have been applied to various industries.Both sensitivity and reliability are the important evaluate criterion for the fiber sensors.Due to the light field in tapered fiber is released,and the transmission beam will be modulated easily,the sensitivity of fiber sensor will reach to a high value.In the other hand,the interferometric fiber sensor demodulated by wavelength,thus this kind of fiber is more reliable.Furthermore,the type of interfrometric sensors can be divided into transmission type and reflection type.For the processing technology,accompanied with the commercialization of femtosecond lasers,the femtosecond laser micromachining(FLM)technology is preponderant,and has become a research hotspot in this field.This dissertation research on the preparation and sensing application of interferometers based on tapered fiber fabricated by femtosecond laser which contain the transmittance Mach-Zehnder interferometer(MZI)and the transmittance/reflective Fabry-Perot interferometer(FPI)based on twin FBGs.The first chapter is the introduction.It summarize the development and processing technology of optical fiber;the principle and application of fiber sensor;the research value and the primary processing technique of tapered fiber;and the method of fabricating fiber interferometer.The second chapter summarize the theories and technology relate to femtosecond laser,such as the mode-locked theory,the laser amplification technique and the principle of femtosecond laser-matter interactions.At last,it introduces the FLM system whcih be used to process fiber in this research.The third chapter illuminates the research on the sensing characterization of MZIs.Then,the method of processing tapered fiber by arc discharge is described.Finally,a alcohol concentration sensor based on MZI and tapered fiber fabricated by femtosecond laser and arc discharge is presented.Furthermore,the relationshipbetween alcohol concentration and the spectrum has been studied,it conclude that this sensors are more sensitivity to refractive index than other kindred sensors.The fourth chapter illuminates the research on the sensing characterization of FBGs firstly by formula and simulation.Then,the processing technique of FBGs directly by femtosecond laser which contains Point-by-Point inscription and Line-by-Line inscription is introduced.In the end,an axial strain sensor based on tapered fiber and FPI which consist of twin FBGs fabricated by Line-by-Line inscription.Furthermore,it research on the strain distribution when axial strain applied on the tapered fiber by mechanical model through Solidworks,and presents the express of relationship between the taper fiber size and sensitivity by experimental data and geometric model.In the last chapter,it is a summarize and a outlook for this study.From the specific research content,this innovation of dissertation include:1)A potential alcohol concentration fiber sensor which based on MZI with a new structure,and the sensitivity of this device for refractive index as 1.5times as the highest sensitivity of kindred sensors has been reported.2)It study the Point-by-Point inscription Line-by-Line inscription technology with femtosecond.Then,the integrated FBGs and the titled FBGs have been fabricated successfully,and the FBG inscribed in the polarization maintaining optical fiber(PMF)too by using these methods.3)It demonstrates a potential axial strain fiber sensor which based on tapered fiber and FPI which consists of twin FBGs with high sensitivity.The highest sensitivity of the sensors fabricated during the experiment is as ~4.6 times as the sensors without taper.Finally,the method for enhancing the sensitivity of this sensor has been presented by theoretical analysis. |
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