Study On Temperature Tuning Technology Of Fiber Bragg Grating

Fiber bragg grating (FBG) is a important fiber passive component, it is widely usedin fiber sensing and communication system because of its excellent merit such as smallscale, low cost, wavelength modulation, easy to form sensor network. The developmentof temperature tuning technology of fiber bragg grating is reviewed in this paper. Thispaper is focused on temperature tuning technology of FBG.On theoretical aspect: transfer matrix method, as a numerical solution of thecoupled-mode theory, is expounded, the MATLAB simulation code is given for spectrumanalysis of FBG under non-uniform temperature field; detailed ways to design a I/Vtransimpedance amplifier is also presented.On simulation aspect: through the assistance of COMSOL, a excellent finite elementanalysis software, heat transfer property of single mode fiber(SMF) in radial and axialdirection is obtained, the time constant is approximately 1.3ms for both heating andcooling period, the heat diffusion depth of bare fiber is about 7mm; for copperized fiber,with a film thickness of 3μm, the maximal achievable temperature is 700 degreecentigrade at 200mW, it takes 4s to reach steady-state.A fiber heater based on graphite is designed, temperature distribution property offiber in axial direction is investigated and the reflection spectrum is analyzed throughtransfer matrix method, results show good performance on wavelength tuning, 6nmtuning range is obtained at 10W heating power for 60mm long graphite heater, spectrumchirp and bandwidth broadening is neglectable; A novel fiber heater model constructedby graphite and copper electrode is presented, The fiber heater has great prospect intailoring the spectrum of FBG as it can produce various non-uniform temperature field ongrating region through adjusting the positions or numbers of electrodes; An importantheat transfer property of fiber is obtained that fiber can sense non-uniform temperaturefield along fiber axial direction with no distortion, and heat transfer of fiber along axialdirection hardly has any influence on it.The experimental work includes: a dual I/V converter was designed and tested, 6.6MHz bandwidth is achieve with a magnification of 10000; two kinds of fiber heaterequipments, halogen lamp heater and graphite heater, are designed and tested to achievewavelength tuning of FBG; wavelength demodulation experiment based on temperaturetuned FBG was demonstrated; apodization of the reflection spectrum of FBG wasrealized through chirped temperature tuning; thermal decay feature of the index ofrefraction of FBG was tested at 524K and the coefficients of the thermal decay modelwas obtained for further prediction of the long term stability of FBG under othertemperature environment.