Research On Fiber Interference-based Sensor For Simultaneous Measurement Of Dual Parameters

Optical communication is appearing a booming prospect due to the advantages of broadfrequency band, low transmission loss and small distortion. The optical gratings inject newvitality and vigor to the optical communication development with many instinctiveadvantages, such as low cost, high stability, corrosion resisting, immune to electromagneticinterference, multiplexing capability, adapt to work under hostile environment, and so on.Optical communication is developing toward the aim of integration, all-fiber devices, andintelligence, which is valued and favored by people.Compared with the conventional sensors, the fiber-interference-based sensor has broadresponse range, much higher sensitivity and resolution, and is also stable under specialworking environment, which has been applied in many sensing areas, such as temperature,strain, liquid level, refractive index, humidity and hydrophone.Simultaneous measurement of dual parameters can offer more information and greateravailability, which promote the practical process of fiber gratings. This thesis mainly focuseson the simultaneous measurement of dual parameters by using the combination of a fibergrating and a fiber-interference-based sensor. The main content includes:1) Depict generally on the development and applications of fiber gratings in recent years, andintroduce the simultaneous measurement of dual parameters of the fiber gratings. Analyzethe sensing principle and research status of fiber-interference-based sensors, and list sometypical fiber-interference-based sensors.2) Introduce briefly the temperature and strain sensing principle of fiber Bragg grating(FBG),and analyze the interference modes of single-mode-multimode-single-mode(SMS)structure in detail, then the numerical simulation of optical field distribution is carried outby use of beam propagation method(BPM). A sensor for simultaneous measurement oftemperature and refractive index(RI) is presented. The excited high order guided modesinterfere in the MMF. Due to the different response sensitivity coefficients of SMS andFBG, the simultaneous measurement is achieved with the resolution of±0.22℃å'ŒÂ±0.0015, respectively.3) The temperature and axial strain sensing principle of long period grating(LPG) and thebirefrigent effect of polarization maintaining fiber(PMF) are studied. A sensor forsimultaneous measurement of temperature and strain is designed by cascading an LPGand a Lyot fiber filter(LFF), which has a linear configuration with stable interferencespectrum. By measuring the different wavelength shifts of LFF and LPG, thesimultaneous measurement is achieved by use of a well-conditioned sensitivity matrixequation, and a resolution of±1℃å'ŒÂ±25με is obtained.4) A sensor for simultaneous measurement of temperature and RI is proposed by using a combination of an MMF-SMF-MMF(MSM) structure and an FBG. Firstly the interferenceprinciple of MSM structure is investigated. Considering the cladding mode nature of theSMF is more vulnerable to other parameters, the temperature sensitivity coefficient ofMSM structure is five times higher than that of FBG. Meanwhile, the numericalsimulation of optical field distribution is carried out by means of BPM, and thesimultaneous measurement is demonstrated due to the different responses of MSM andFBG. The resolution of±0.32℃and±0.0023is achieved.