Sensing Technology Based On Dual-wavelength Fiber Laser And Four-wave Mixing Effect

In recent years,the rapid development of fiber sensing,fiber laser and communication technology has greatly promoted the informatization level of human society.The optical fiber devices have the advantages of small size,light weight,strong anti-electromagnetic interference capability,and excellent compatibility with the optical fiber system,such that they are widely used in the fields of optical fiber communication and fiber sensing.As the most widely used optical fiber passive device,fiber Bragg grating(FBG)has great application potential in many engineering fields,but the cross-sensitivity problem of FBG sensors severely limits its practical application.To meet this application requirement,we designed a dual-wavelength laser used for temperature-strain discriminated measurement,based on the fiber sensing and the fiber laser technology.The temperature-strain discrimination efficiency of this laser sensor is improved by the four-wave mixing(FWM)effect.The body and results of this thesis are listed as follows.(1)Firstly,the birefringence of polarization-maintaining fiber is studied in theory.The reflection spectrum of a polarization-maintaining fiber Bragg grating(PMFBG)is analyzed through the coupled mode theory.The temperature/strain sensing sensitivity of PMFBG is analyzed experimentally.(2)Secondly,a wide bandwidth is observed in reflection spectrum of the PMFBG,which reduces the detection resolution.To address this issue,the sensor realized with dual-wavelength laser and a PMFBG is proposed.The experimental results show that the optical signal-to-noise ratio of the dual-wavelength laser can reach 47 dB.At the same time,the temperature and axial strain sensing characteristics of the dual-wavelength laser are analyzed.(3)Finally,in order to improve the temperature-strain discrimination efficiency of the dual-wavelength fiber laser sensor,a laser sensing scheme based on FWM is studied.The FWM effect is used to generate idler and converted light,and the temperature/strain characteristics of the idler and converted light are used for temperature-strain measurement,which can effectively improve the discrimination efficiency.In the experiment,the difference in temperature sensitivity between the idler light and the converted light of the third order can reach to 4.32 pm/°C,while the sensitivity difference of the axial strain is 0.25 pm/N.Compared with conventional dual-wavelength laser based sensors,the temperature-strain discrimination efficiency of the laser sensing scheme based on FWM has been significantly improved.