Study On Fiber Bragg Grating Sensing And Demodulation Based On Wavelength Swept Source

With the wide application of FBG sensing technology,FBG sensing demodulation technology has become a research hotspot.In this paper,FBG sensing and demodulation technology based on wavelength swept source and all-optical wavelength conversion(AOWC)technique of sensing signals in sensing network are studied.RF signal controlled sweeping components is adopted to overcome the limitation of traditional mechanical sweeping methods,which improves the sweep rate and output linearity of the light source.Accordingly,the FBG sensing demodulation rate and precision are improved by the swept source.AOWC technology is used to transform all the sensing signals in one sensing link into time-multiplexed signals at a specific wavelength in order to improve the utilization rate of spectral resources in the sensing network.The main contents are as follows:1.Research on FBG dynamic stress sensing demodulation based on single wavelength swept source1)The FBG sensing demodulation experiments of piezoelectric ceramic vibration are studied when the fixed single-frequency light source is used as the sensing light source.The vibration frequency range of cylindrical piezoelectric ceramic and piezoelectric ceramic stack is measured respectively.2)The principle of single wavelength swept source is studied.A single sideband modulator is used to realize the optical signal sweeping.66.67 kHz sweep output within the range of 3 nm is obtained experimentally with ±1.5 dBm flatness,which has the linearity of 0.99997.3)The vibration frequency measurement experiments of FBG dynamic stress based on the swept source are studied.The real time measurement of FBG's high frequency vibration is achieved under the sweep rate of 40 kHz.The demodulation results of frequency range from 5Hz to 11 kHz are obtained.25 ?s transient frequency mutation is measured.2.Research on FBG static sensing demodulation based on parallel swept source1)The principle of parallel swept source based on single sideband modulator and the realization of sweeping loop are studied.Three DFB lasers coupled as a seed source are used to realize the parallel optical signal sweeping,and 200 kHz sweep output within the range of 3 nm is obtained experimentally with ±1.5 dBm flatness,which has the linearity of 0.99991.2)The experiments of FBG temperature and static strain sensing demodulation based on parallel swept source are studied.The parallel demodulation of multiple FBG sensing information is realized without affecting the demodulation precision and rate.The average temperature sensitivity of 10.055±0.005pm/?,linearity of 0.99789 and the average static strain sensitivity coefficient of 1.614±0.002pm/??,linearity of 0.9975 are obtained respectively when the sweep step is 0.04 nm and 0.02 nm.Meanwhile,parallel demodulation of temperature and static strain sensing is studied.3.Research on all-optical wavelength conversion of FBG sensing signals1)A multi-link sensing network model based on AOWC technology is studied.The principle of all-optical wavelength conversion using electro absorption modulator(EAM)is studied,and the parameters of AOWC are optimized experimentally.2)All-optical wavelength conversion experiments are carried out on FBG temperature and static strain sensing signals.The maximum temperature deviation and deflection deviation before and after the conversion are only 0.0169? and 1.6E-4pm respectively,which proves that the effect of wavelength conversion is very good,so each node in the sensing network can share the same spectral resource.