Research On Technology Of Ifber Bragg Grating Sensor And Its Application In Biochemistry Sensing

Thanks to the advantages of immunity to strong interference, wavelengthdemodulation, absolute measurement and multiplexed sensing capability, fiber Bragggrating (FBG) sensors have been widely applied in the monitoring of temperature, strain,and pressure in the fields of large building structure, electric power system,petrochemical industry, and so on. In these fields, the study on its cross-sensing problemof multi-parameters is an important subject. In the past decade, as the rapiddevelopment of the biochemistry, medical science and life science, the refractive index(RI) sensors based on the fiber gratings have been gradually become one of theresearching focuses in the crossing fields between the fiber sensors and these subjects.In this dissertation, some basic problems of the FBG RI sensors are researched anddiscussed in detail, and the cross-sensing characteristics of multi-parameters of the FBGsensor are researched as well, and then the FBG sensors are applied in the measurementof the thermo-physical parameters in the bio-film reactor. The main contents of thedissertation are given as follows:1. Various RI sensors based on fiber gratings developed in the past decade aresummarized and compared. Their current research status, current applications status andtrend of development in the biochemical fields are summarized and analyzed in detail aswell. Then, the current research status of the cross-sensing problem of multi-parametersof the FBG sensor is summarized.2. Based on the existing researches of the single-end etched FBG RI sensor, amore completely theoretical model of its simultaneous measurement for the RI andtemperature is proposed, and the impact of its structured parameters on its RI sensitivityand linearity is analyzed in detail. The simulated results show that the RI sensitivity of asingle-end etched FBG can be enhanced by decreasing the diameter of its etching regionor by selecting a FBG with a relatively bigger grating pitch for its fabrication, but thesemethods will lower the linearity of the sensor and increase the theoretical error of thesensor in the RI measurement. Based on these theoretical results, the correspondingmethodology of linear approximation and error analysis of the sensor for RI measurement at the low RI area (1.333~about1.360) are established. In addition, asingle-end etched FBG sensor is fabricated and used in the simultaneous monitoring forthe bio-film thickness (or bio-film RI) and temperature in a simple bio-film reactor.Experimental results show that the sensor has a good linearity and RI sensitivity of6.894nm/RIU, and its resolution for the bio-film thickness and temperature is15.36±0.85μm and0.12oC, respectively, in the condition of the spectrum analyzer withwavelength resolution of1pm being used.3. The responsive characteristics of the etched FBG under uneven liquid mediumwith the RI distribution being linear are analyzed. The simulated results show that theband-width, the number of the micro-resonant peaks and the asymmetric degreed of thereflection spectrum of the etched FBG will increase as the increase of the RI gradientalong its axis and the D-value of the RI at both of its ends. In particular, the D-value ofthe wavelength between the maximum and the minimum micro-resonant peaks isapproximately linear related to the RI gradient at the low RI area (1.330~1.360). Basedon these theoretical results, the theoretical model for the linear-approximationmeasurement of the RI gradient by the etched FBG is established. And then, an etchedFBG with residual diameter of5.73μm is fabricated. Through the experimentalresearch, the rationality of the theoretical simulation and analyses and the potentialapplication of the RI gradient sensor based on the etched FBG are verified.4. The responsive characteristics of the Bragg wavelength, resonant-peakamplitude and3dB bandwidth of the etched Gaussian-apodized FBG to the RI areresearched and compared to that of the etched uniform FBG RI sensor. Experimentalresults show that the changing regulations of Bragg wavelength and resonant-peakamplitude of the etched Gaussian-apodized FBG with the RI are in accord with that ofthe etched uniform FBG. However, the3dB bandwidth of the etched Gaussian-apodizedFBG will become more and more narrow as the RI increase to the cladding or coreindex, at the same time, its reflection spectrum will become more and more smooth aswell.5. The theoretical cross-sensing model of the normal FBG affected by"temperature-pressure" and "temperature-strain-pressure" are deduced and analyzedfrom the perspective of its physical mechanism. The simulated results show that thevalues of cross-sensing term of the "temperature-pressure" and "temperature-strain- pressure" will change in a certain regulation with the changes of external parameters,fiber parameters and Bragg wavelength. Based on these theoretical results, somevaluable suggestions about how to reduce the systematic error and improve themeasurement accuracy in the practical applications are put forward as well. In addition,a three-dimensional temperature sensing array based on FBG sensors is designed andfabricated to measure the temperature distribution field in an industrial bio-film reactor,and the impact induced by the cross-sensing effect of the "temperature-pressure" of itssensing unit on the error of temperature measurement is analyzed. Experimental resultsshow that the three-dimensional temperature sensing array based on FBG sensors usedto measure the temperature distribution field in the industrial bio-film reactor is feasibleand effective. Compared to the traditional methods of thermocouple array, thethree-dimensional temperature sensing array based on FBG sensors can gain moretemperature data, higher temperature sensitivity and resolution. The temperaturesensitivities of these sensing units are from12.11pm/oC to13.55pm/oC, and thetemperature resolution of the FBG sensing unit of the maximum temperature sensitivitycan reach0.074oC, by using the spectrum analyzer with wavelength resolution of1pm.