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Study Of Optical Fiber Sensors Based On Mach-Zehnder Interference

Posted on:2015-03-15Degree:MasterType:Thesis
Country:ChinaCandidate:J P ChenFull Text:PDF
GTID:2298330422992982Subject:Optics
Abstract/Summary:PDF Full Text Request
Mach-Zehnder fiber sensors based on the interferences between the different modes in asingle mode fiber (SMF) have been intensively studied in this thesis. The main researchingworks are shown as the following.1. The development, principle, classification, advantages and applications of fiber opticsensor are generally described. And, the fundamental principle, advantages and development ofthe Mach-Zehnder fiber sensors are introduced, providing an important theoretical basis andresearch idea for the following studies of the fiber sensors.2. An all-fiber Mach-Zehnder interferometer formed by sandwiching a thinned fiber taperbetween two core-offset joints for refractive index sensing have been proposed anddemonstrated. The core-offset joints are fabricated by using the splicing method on a standardSMF. The fiber taper is made by the flame-heated drawing technology, and has a very thinwaist with only several microns in diameter. When the surrounding refractive index of thesensor is changed, the dip and peak wavelengths in the transmission spectra will shift. In reverse,by demodulating the peak or dip wavelength shifts of transmission spectra, the surroundingrefractive index changes can be obtained. This sensor has extremely high sensitivities of5339and10377nm/refractive index unit (RIU) at the surrounding RI of1.334and1.35, respectively.3. We propose and fabricate a high-sensitivity Mach-Zehnder interferometer (MZI)refractive index sensor formed by concatenating two core-offset joints in a cladding-etched fiber.The MZI is thinned by chemical etching with hydrofluoric acid. The RI sensitivities of1288.05and2118.26nm/RIU are obtained by the MZI in the refractive index ranges of1.333~1.3685and1.3685~1.386, respectively.4. A high-sensitivity displacement sensor based on a bent MZI constructed by twocascaded COJs was proposed and experimentally demonstrated. The bending radius of the bentMZI is small and estimated to be~17mm. In this situation, the interference pattern of the MZIdepends strongly on the bending radius. According to this character, we devised the bent MZIas a displacement sensor in two ways providing two different bending types of the bent MZI.The maximum sensitivity obtained was up to0.835nm/μm. The proposed displacement sensoralso reveals the outstanding advantages of simple fabrication, low cost, high sensitivity, andgood linearity.5. An in-line MZI formed by cascading two S-bend fibers on a SMF is proposed andfabricated only using a common fusion splicer. The effects of the displacement or force on theMZI by stretching, leading to a shift in the transmission dip wavelength. The proposed MZIexhibits high sensitivities for displacement and force measurements by demodulating the peak or dip wavelength shifts of transmission spectra. Experimental results show that thedisplacement and force sensitivities of1.533nm/μm and177.1nm/N, respectively.
Keywords/Search Tags:Optical fiber sensors, fiber Mach-Zehnder interferometer, single mode fiber, refractive index, displacement
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