Research on Bragg and Long-Period Fiber Gratings and Their Sensing Properties

Abstract: There is universal attention on fiber gratings and its application in fiber sensors and fiber communications. Fiber grating sensors offer many important advantages such as electrically passive operation, big signal bandwidth, high sensitivity and multiplexing capabilities, low weight, small configuration and suitable to be used in the high temperature, corrosive and dangerous environment. The fiber grating sensors possess broad application foreground in the safety scrutiny of especially situation, for example, big architecture and oil well. Fiber Bragg gratings (FBG) and long period fiber gratings (LPG) are the mainly research object in the dissertation. The fabrication, basic properties and sensing application of theirs are studied experimentally and theoretically. The following is the main content:The basic theoretical methods and numerical simulation tools for analysis of fiber grating properties is introduced. The spectral properties of uniform Bragg grating is analyzed by using coupling-mode theory.The fabrication of FBG in four different type photosensitive fiber through phase mask is finished successfully and the photosensitivity of the four-type fiber is studied. We fabricate amplitude mask using film evaporation technique and mechanic rolling tungsten filament technique. The fabrication of LPG in three different type photosensitive fiber is finished and the special properties of LPG written in H_2-loading fiber is primarily studied. The fabrication of fiber grating Fabry-Perot cavity, chirp fiber grating, fiber grating cladding mode and phase-shift long period fiber grating is also studied.We manufacture erbium-doped superfluorescence broadband source only using the element made in China. The project of detecting the sensing signal of fiber grating by using tunable FBG filter is designed and investigated theoretically and experimentally. Due to the excellent performance of the photoelectric detection system, the wavelength resolution of sensing detection is 2pm and the strain resolution is 1.7 με . The wavelength divided multiplex sensing properties is demonstrated experimentally based on the sensing system. Compare with tunable filter detection technique, the wavelength measurement technique using tunable source is analyzed theoretically. We design a kind of all-fiber sensing interrogation system, by using long-period fiber grating as edge filter to interrogate the sensing signal of the FBG sensor. The wavelength resolution of the sensing measurement is 0.05nm.A novel FBG Bourdon tube sensor has been constructed, utilizing the pressure mechanic amplify function of Bourdon tube. The measured pressure sensitivity is two orders of magnitude higher than a simple monomode fiber with an in-fiber grating. Especially the pressure sensitivity of the sensor can be determined by changing the parameters of the cantilever beam. Adopting polymer package technique, we coat fiber Bragg grating by using polymer with different mechanic properties. Due to the driving effect of the polymer substrate, the enhanced pressure sensitivity is more than 20 times and 31.7 times than that of a bare fiber grating. The packaged grating exhibits n…
Key words: Fiber Bragg Grating; Long Period Fiber Grtaing; Tunable Filter; Resolution; Polymer Package; Pressure Enhancement; Simultaneous Measurement; Chirp; Temperature sensitivity; Refractive Index; Cladding Radius; Bending

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