Research On Fiber Bragg Gratings Sensing Based On Tunable Laser

Fiber Bragg Gratings(FBG)can be sensors with high sensitivity and long life due to the high reliability provided by the optical communication industry.FBG sensors make sensing network by multiplexing to fulfill a semi-distributed sensing,which make the setup of sensors easy.Firstly,the multiplexing of FBG sensors is analyzed according to the industrial application,which focuses on the time division multiplexing technique.The chirped sine signals are applied to realize a compact time division multiplexing,which is based on the characters of auto correlation function of signal.This method only requires a slow sampling rate of ADC to separate different multiplexed sensors.Accordingly,the interval of time can be shorten.Besides,a high precision FBG sensing network need a wavelength tunable laser with high performances,such as high wavelength precision,fast tuning speed and wide tuning range.Accordingly,Distributed Bragg Reflector(DBR)laser is a good candidate for FBG sensing but with small scanning range.Here,a new type DBR laser,Digital Supermode DBR laser(DS-DBR)is investigated,which contains a chirped Bragg gratings as one of the reflector.DS-DBR laser is designed for the long haul optical communication that required the wavelength is tuned among some specific value defined by ITU,which is separated by 0.4nm.According to the requirement of FBG sensing,the tuning principle of DS-DBR is researched for high speed tuning and continuous tuning.The rear grating and phase domain are investigated to evaluate their performance.It is found that the laser can be tuned continuously with precision 0.1pm by modifying the phase driver circuit of laser.A current driver is designed accordingly to drive DS-DBR laser to tune continuously with a span of 50 nm at the rate of 1MHz.Further,we demonstrate the FBG sensing based on the continuous DS-DBR laser and DSP technology.A single FBG sensing is firstly demonstrated,which gets a high precision with 0.1pm.Next,a time division multiplexed FBG sensing system,coded by the chirped sine wave,is demonstrated which gives a short time interval as 10 meters in distance.However,The sensing system is demonstrated on the static condition and on the sensing of temperature and strain,whose measurement precision is low as 4pm due the crosstalk between the FBGs.