Study Of Fiber Optic Interferometer Based On Seven Core Fiber

With the continuous development of society and the progress of science and technology,sensor technology is playing an increasingly important role in all walks of life.The traditional electric sensor has been developed very mature and has been widely used.However,traditional electric sensors have many drawbacks in practical applications,such as being unable to measure in dangerous environments such as conductive,corrosive,flammable and explosive.Fiber optic sensors are sensors that use optical fibers as sensitive components.Due to the advantages of high sensitivity,anti-electromagnetic interference,simple structure,and convenient production,optical fiber sensors have been extensively studied by scholars.Among them,the multi-core optical fiber is a new type of special optical fiber.The sensor made of the multi-core optical fiber not only has a simple manufacturing process but also can meet the requirements of high sensitivity.In this thesis,several new Mach-Zehnder interferometers based on the seven-core optical fiber are designed and fabricated,and the temperature,strain and refractive index sensing characteristics of the sensor are investigated through experiments.The main work of this paper is as follows:1.The first part discusses the background and significance of multi-core fiber based sensor,and introduces the current research status of multi-core optical fibers,fiber Bragg gratings and Mach-Zehnder interferometer.The theory analyzes the mode interference theory in optical fiber,and elaborates the sensing mechanism of temperature,strain and refractive index in detail.It also introduces several typical interferometric sensors and their principles.2.Designed and manufactured a Mach-Zehnder sensor with convex cone structure.The sensor fusion splices a 30 mm weakly coupled seven-core optical fiber between the input single mode fiber and the output single mode fiber.By changing the welding parameters of the splitter,two convex cone structures are formed at the fusion points of the seven core fiber as beam splitter and coupler respectively.Experimental results show that the temperature sensitivity of the sensor at 1548 nm and 1567 nm is 60.59 pm/? and 100.46 pm/?,respectively.The strain sensitivity is 0 pm/??.The sensor is simple to manufacture,simple in structure,low in cost,and has good application prospects.3.A kind of optical fiber sensor with hydrogen-oxygen flame fusion taper is proposed and fabricated.The taper of the seven-core fiber is drawn by the hydrogen-oxygen flame fusion taper technology,and the waist diameter of the tapered of the seven core fiber is reduced from the original cladding 150 ?m to 46.99 ?m.After the tapering process,the distance between the cores of the seven core fiber decreases,the crosstalk between the cores increases,and the coupling efficiency between modes transmitted in the cores increases.The sensor has a good linear response to refractive index and temperature.The test results of temperature characteristics show that the temperature sensitivity of the resonance peak wavelengths around 1539 nm and1597 nm is 69.09 pm/? and 77.49 pm/?,respectively,and the linearity is 99.64% and 99.82%,respectively.The experimental results of the refractive index response characteristics show that the refractive index sensitivities of the valleys at 1557 nm,1571 nm and 1593 nm are 271.99pm/RIU,260.56 pm/RIU and 236.31 pm/RIU,respectively,and the linearity is 99.64%,99.51%and 99.56%,respectively.4.A temperature and strain dual-parameter measurement sensor based on seven-core optical fiber is realized.The sensor cascades the Mach-Zehnder interferometer and the fiber grating.The Mach-Zehnder interferometer is composed of fusion splicing a section of sevencore optical fiber between the input and output single mode fibers.The discharge parameters of the fusion splicer are adjusted to the two seven-core optical fibers.Two convex cone structures are formed at the two ends.A fiber grating with a center wavelength of 1547.98 nm is cascaded at the end of a fiber convex cone.The experimental results show that the Mach-Zehnder interferometer based on the seven-core fiber is only sensitive to temperature,with a temperature sensitivity of 93.11 pm/?C;while the fiber grating is sensitive to both temperature and strain,with temperature and strain sensitivity of 11.46 pm/? and 0.627 pm/??,respectively.The dualwavelength matrix method can be used to measure temperature and strain simultaneously.When the resolution of the spectrum analyzer is 0.02 nm,the temperature resolution and strain resolution of the sensor are 0.21 ? and 27.95 ??,respectively.In order to verify the feasibility of the coefficient matrix,the temperature and strain were changed at the same time and the wavelength drift was tracked.Using matrix formulas,the temperature and strain changes are calculated to be 9.22 ? and 1029.54 ??,respectively.The actual changes in temperature and strain are 9? and 1000??.The error of this matrix is 2.4% ? 3.0%.5.A coreless + seven core + coreless Mach-Zehnder interferometer cascade fiber grating sensor is proposed.The sensor solves the problem of cross sensitivity in temperature and strain measurement.A 3-mm coreless fiber is fused at both ends of a seven core fiber with a length of55 mm.The coreless fiber is used as the beam splitter and coupler respectively.The temperature sensitivity and strain sensitivity of MZI in the sensor are 74.1 pm/? and 0 pm /??,respectively.The temperature sensitivity and strain sensitivity of FBG are 9.83 pm/? and 0.625 pm/?,respectively.The sensor can measure temperature and strain simultaneously.