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Research On Optical Fiber Refractive-Index Sensing And Signal Interrogation Technology

Posted on:2011-06-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y C WangFull Text:PDF
GTID:1118330332984251Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
With the rapid development of information technology, fiber-optic communications technology and optical fiber sensing techniques are widely employed in mankind life and many areas. Optical fiber sensors have attracted considerable interests due to their advantages such as small size, compactness, immunity to electromagnetic interference, high sensitivity. Among them, the wavelength modulated sensors have wavelength multiplexing capability for multi-point sensing; can avoid disadvantages induced by instability of light source or fiber propagation attenuation. The main topics of this thesis are refractive-index sensing applications of thin-core fiber modal interferometer sensor and long-period grating sensor, and fiber Bragg grating strain sensing interrogation technique based on a Fourier domain mode locking.Firstly, a brief introduction is given about a fiber modal interferometer sensor based on thin-core fiber. When splicing a segment thin-core fiber between standard mode fibers, it can excite the high-order cladding modes because of the core mismatch, and interfere with the core guided mode. In the text introduced the sensor's structure and principle, and observed the change of interference peak position by etching the cladding. The experimental results show that it has higher refractive sensing sensibility.Then, the properties of fiber grating were theoretically analyzed with the coupled mode theory and transfer matrix method, and the spectral properties of fiber Bragg grating (FBG) and long period grating (LPG) were numerically calculated. The photosensitivity mechanism of the fiber and several enhancing photosensitivity method also were introduced, and the fiber grating fabrication system which used in the text.The LPG sensing was theoretically analyzed, and the effect of the refractive index of surrounding medium on its resonance wavelength was also introduced. In the text we presented a LPG sensor working in reflection mode, it consists of an LPQ a core mode scatter, and a fiber end-face mirror. The light passing through the grating is eliminated by the scatter, while the light coupled by the grating is reflected by the mirror and coupled back to the core. The sensor structure is compactness and can be used for biosensor detection.Finally, the sensing principle of the FBG and several sensing signal demodulation schemes of fiber grating were introduced. After that, we proposed an interrogation method of FBG sensor system based on Fourier domain mode locking (FDML), employed the FDML fiber laser into the sensing interrogation of the FBG By converting wavelength measurement to time measurement, we demonstrated a quasi-distributed FBG sensor system which can use the same Bragg wavelength. The system was tested by strain sensing and showed good performance.
Keywords/Search Tags:optical fiber sensor, fiber modal interferometer, refractive index sensing, fiber grating, etching, Fourier domain mode locking, interrogation
PDF Full Text Request
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