| Fiber optic sensing technology originated in the 1970 s,and has been developing continuously and rapidly in the following decades.Compared with traditional photoelectric sensors,fiber optic sensing technology has many advantages,such as small size and can be embedded in a variety of structures.Light weight,will not affect the embedded structure;Strong anti-interference ability,especially in the harsh environment of strong tolerance,high temperature resistance,corrosion resistance,and sensitive to changes in the external environment,so it has been widely concerned by people,more and more become one of the hot spots of researchers.Fiber Bragg grating(FBG)sensor is a wavelength modulated optical fiber sensor technology.It has become one of the most popular technologies in optical fiber sensor because of its simple fabrication and strong reflected signal.In this thesis,we chose TFBG as the research object.TFBG is different from traditional Bragg grating(FBG),its grating area is not perpendicular to the fiber axis,but has a certain Angle,which leads to the different mode coupling in TFBG and FBG.Because of the different coupling modes,TFBG has advantages that traditional Bragg gratings do not have.It is sensitive not only to the change of temperature stress,but also to the change of refractive index of the light in the cladding,so it can be used to measure the external parameters such as humidity or concentration that cause the change of refractive index.The main contents of this thesis are as follows.1.Firstly,the spectral characteristics of TFBG were simulated using Optigrating software,and the changes of TFBG transmission spectrum were observed by changing the period,length,inclination Angle,radius of fiber core and cladding of grating.This has played a guiding role in the subsequent experimental measurement of TFBG.2.Second,based on the TFBG coupling mode theory,the single-parameter sensor performance of temperature,strain,refractive index and bending was measured experimentally,and their sensitivity was obtained respectively.Moreover,the TFBG and FBG are cascaded based on the Sagnack loop,and then the temperature and stress are measured.The change values of temperature and stress are calculated by using the dual-wavelength matrix method to achieve the dual-parameter measurement3.We deposited ITO film(tin-doped indium oxide)in the gate area of TFBG by pulsed laser deposition(PLD)technology,and then measured the sensing performance of coated-TFBG temperature,strain and refractive index.The result is that The temperature sensitivity of the TFBG is 6pm/℃ and the strain sensitivity is0.6nm/mε,which is twice the strain sensitivity of the bare grating.When the TFBG coated with ITO film measures the external refractive index,when the external refractive index is less than the cladding refractive index,the wavelength shifts with the refractive index to the intensity with the refractive index.When the external refractive index is greater than the cladding refractive index,it becomes that the envelope area of the cladding mode decreases with the increase of the refractive index.This phenomenon adds more measurable factors than bare grating sensing performance measurements.As the same time,we deposited graphene film in the gate area of TFBG by pulsed laser deposition(PLD)technology,and then measured the sensing performance of coated-TFBG temperature,strain and refractive index.The measured temperature sensitivity is almost the same as that of the bare grating,while the strain sensitivity has changed from 0.3nm/mε to 0.48nm/mε,and increased 60%.Finally,graphene oxide and zinc selenide were coated on TFBG,and their sensing characteristics were measured respectively to obtain their sensing sensitivity. |
