Studies On FBG Sensing Based On Wavelength Step-swept Laser Source And Wavelength Conversion Of Sensing Signals

In the demodulation system of FBG sensor,the demodulation speed,resolution and multiplexing numbers of FBG are three important indicators.In this paper,FBG sensing based on the wavelength step-swept laser and wavelength conversion technology is proposed.The wavelength step-swept laser using radio frequency signals controlling single sideband(SSB)modulator to realize wavelength sweeping,not only avoid wavelength non-linearity introduced by mechanical sweep unit,but also reduce the restrictions on FBG demodulation resolution due to the sweep method of the external laser cavity.The wavelength conversion technology converts the multi-wavelength sensing signal into the time division signals with a specific wavelength,releasing the spectrum resources occupied by each sensing node and improving the number of multiplexed sensors.The main contents are as follows:1.Research on FBG sensing based on single wavelength step-swept laser1).Using DFB laser with narrow linewidth as a seed source,stable output of the single wavelength step-swept laser is obtained.The wavelength linearity is 1 when the sweep step is 80 pm.2).The waveforms of FBG at different states of temperatures/strains based on the single wavelength step-swept laser are measured.A LabVIEW program is adopted to calculate the center wavelength of FBG.The sensitivity of strain is 1.566 pm/?? and the wavelength-strain linearity is over 0.994.The temperature sensitivity is 10.004pm/°C and the wavelength-temperature linearity is over 0.998.The demodulation results were compared with the results of spectrometer and the maximum deviation of the center wavelength is 5pm.2.Research on FBG sensing based on multi-wavelength parallel step-swept laser1).With four DFB lasers coupling as a seed source,four-wavelength parallel step-swept laser with a sweep step of 20 pm is abtained.The overall flatness of the output laser is ± 2.65 dBm and the sweep range is 1.6nm(1548.72 nm ~ 1550.32nm)with a scanning frequency of 133.3k Hz.2).Temperature sensed by FBG based on the multi-wavelength parallel step-swept laser is measured.The calculated temperature sensitivity is 10 pm/°C and wavelength-temperature linearity is 0.99487.The wavelength reproducibility is higher than 1.91 pm.The maximum deviation of the center wavelength demodulating results based on the multi-wavelength parallel step-swept laser and the results of the spectrometer is 6.32 pm,equal to the temperature of 0.6°C.3.Wavelength conversion of FBG sensing signals1).A conceptual model of the sensor network based on wavelength conversion which can realize the efficient utilization of spectrum resources is proposed.The wavelength conversion experiment based on electro-absorption modulator is designed and carried out on the wavelength conversion of FBG sensing signal.The demodulation results are consistent before and after the wavelength conversion.The temperature and static strain linearity are higher than 0.9929.2).The conversion efficiency and signal to noise ratio of the sensing signals are studied.The conversion efficiency and SNR under the conditions of various amplitudes of signal pulses and various powers of probe light are measured.The results showed that the onversion efficiency and SNR become smaller when the amplitude of signal pulse decreases and the conversion efficiency increases and SNR decreases as the power of probe light increasing.