Research On The Sensing Properties Of Integrated Fiber Interferometers Based On Veriner Effect

With the development of optical fiber and optical devices,various special structures of optical fiber have been rapidly discovered and entered the field of vision of researchers.Because of its advantages of high integration,compact structure and low cost,optical fiber is widely used in optical devices such as optical switches,wavelength division multiplexers and optical filters,and also has important application value in the field of optical communication and optical fiber sensing.Among them,directional bending sensing,temperature sensing,stress sensing and refractive index sensing have very important practical significance in the field of structures health monitoring of architecture,transportation,aerospace,water conservancy,robot posture sensing,intelligent material internal deformation measurement,etc.Due to the advantages such as small size,anti-electromagnetic interference,low transmission loss,light weight,low cost,simple manufacture,easy reuse into network and embedability,the fiber optic sensors have paid attention to fiber optic sensors by many researchers.Therefore,the fiber optic interferometer is a kind of important sensor with broad application prospects.In some special cases,such as detecting the propagation trajectory of seismic waves,volcanic eruptions and so on,the sensitivity of traditional optical fiber interference sensing technology is not enough Therefore,it is of great significance to study the mechanism of optical fiber sensing sensitization.Vernier effect is an effective method to improve the sensitivity of measurement and is widely used in the field of sensing.Based on the theory of optical Vernier effect,several kinds of multi-parameter sensors based on eccentric-single-core and eccentric-multi-core fiber are proposed in this paper,which can be used to realize directional bending sensing,temperature sensing and stress sensing.The main content of the paper is as follows:1.A kind of Fabry-Perot(F-P)interferometer sensor based on ECF and DSHF is proposed with Vernier effect.Two kinds of sensors with large and small FSR difference between reference interferometer and sensing interferometer are produced.The sensing principle of the interferometer is analyzed theoretically,it is concluded that the Vernier effect will not occur when the FSR difference between the reference interferometer and the sensing interferometer is large,and when the FSR difference between the reference interferometer and the sensing interferometer is small,the Vernier effect will occur.The bending,temperature and stress sensing characteristics of two interferometers are also analyzed theoretically and experimentally.2.A sensor based on DCF-DSHF Michelson interferometers with Vernier effect by fiber tapered coupling is theoretically analyzed and tested.First,the manufacturing method and principle of the offset-core parallel Michelson interferometer with DCF-DSHF are introduced.The bending characteristics of the DCF-DSHF Michelson interferometer are analyzed theoretically and experimentally,and because of the asymmetry property of DCF,the interferometer can realize the direction recognition of the bending sensor.Then the theoretical research and the experiment test prove that the change of the ambient temperature can cause the drift of the output spectrum of the DCF-DSHF Michelson interferometer,and the interferometer is used to measure the change of temperature.The experimental results show that the interferometer can be used as directional sensor and temperature sensor.3.Based on the different refractive index of the three cores of TCF,two kinds of interferometers are proposed:TCF Michelson interferometer and TCF-DSHF Michelson interferometer.The fabrication method and interference principle of the TCF integrated Michelson interferometer are introduced,and then the bending,temperature and strain sensing characteristics of the interferometer are theoretically analyzed and experimentally studied;Based on the vernier effect,the fabrication method and interference principle of the TCF-DSHF Michelson interferometer made by fiber taper coupling method,and conducts theoretical analysis and experimental research on the bending,temperature and strain characteristics of the interferometer.The above two kinds of interferometers make use of the different refractive index of the three cores of TCF to realize the bending sensor with recognizable direction.Then it is proved by theoretical study and experimental test that the change of ambient temperature will cause the drift of the output spectrum of three kinds of interferometers,and the interferometer is used to measure the change of the temperature.The experimental results show that the interferometer can be used as a direction-recognizable bending sensor and a temperature sensor.Finally,the output spectra of three kinds of interferometers are used to measure the stress sensing characteristics by drift with the change of stress on the interferometers.