High Sensitivity Optical Fiber Micro-displacement Sensing Research

The research on sensors is the key issue in intelligent control area,wherein, micro-displacement measurements play an emportant role in industrialproduction and our life. Owing to the advantages of high sensitivity,corrosion-resistant, anti-electromagnetic interference and small, micro-displacementsensors based on optical fibers sensors have unparalleled advantages compared totraditional electric-based sensors and have been widely applied in some specificareas. In this work, two high-sensitivity interferometric fiber micro-displacementsensor structures with the intensity and wavelength demodulation method werepresented. One was Mach-Zehnder interferometer (MZI) structure and the other wasFabry-Perot interferometer (F-PI) structure. Both of the sensing mechanism andfabrication methods were introduced. The main contents are list as fellowing:1、 The development of the fiber-based micro-displacement sensing technology wasintroduced. They were classified in types according to their demodulation andsensing methods, respectively. The advantages and disadvantages for each typewere briefly introduced. The mechanism of in-fiber MZI and F-PI wereresearched based on the modes interference theory.2、 A high sensitive optical fiber MZI based micro-displacement sensor withintensity demodulation method was presented. The MZI was fabricated by acore offset connecting of two single mode fibers and a bowknot-type taper. Thehigh order cladding modes was excited uniformly through a bowknot-type taper(BTT) made by a fusion splicer through tapered fusion method. The micro-displacement measurements were studied.(1) The fringe visibility of the interference pattern was determined by the coreoffset degree on the vertical axis (x/y axis) direction. Experimental resultsshowed that for the micro-displacement ranging from0to13μm, the proposedsensor showed high sensitivity of-1.89dB/μm and-1.93dB/μm, respectively. (2) The longitudinal (z axis direction) micro-displacement of the coreoffset was responded to the MZI transmission spectrum and varied withthe interferometer arm length. For the arm length of12,18,24and30mm, the proposed sensors showed high sensitivity of-0.362dB/μm,-0.385dB/μm,-0.332dB/μm and-0.235dB/μm, respectively.The theoretical simulation of the energy distribution by RsoftCAD andthe temperature sensing character of the MZI were also given.3、 A compact micro-displacement sensor by wavelength demodulation methodbased on double tilted fiber Bragg grating (TFBG) with an air-cavity wasreported. The TFBG was cut into two equal parts and the Fabry-Perot (F-P)cavity was composed by the ends of two tilted fiber Bragg gratting. Thewavelength spacing between two interference minima (free spectral range,FSR) growed with the length of the air-cavity increasing. Experimental resultsshowed that the sensitivity of the sensor within the measurement range of0to115μm is about0.475nm/μm.