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Studies On Sensing Characteristics And Applications Of Side-hole Fibers

Posted on:2015-07-07Degree:MasterType:Thesis
Country:ChinaCandidate:Y XinFull Text:PDF
GTID:2298330431489077Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Side-hole fiber (SHF), with two air holes running in the cladding and inparallel to the core, was first proposed in1986. It has higher pressure sensitivity thanpanda fiber. Sensing characteristics and applications of SHF have been attractedmore and more attention in the following30years. In this paper, interferometertemperature sensors based the alcohol-filled SHF and the sensing characteristics ofSHF gratings have been demonstrated experimentally. The main contents are shownas following:1. The birefringence characteristics of SHF were analyzed from geometry, whichwas based on that the theory of fiber birefringence from geometry and stress. Then aresearch on the temperature characteristics of SHF gratings is presented.2. Two temperature interferometer sensors based alcohol-filled SHF have beendemonstrated. One is alcohol-filled SHF Mach-Zehnder interferometer fortemperature measurement. A Mach-Zehnder interferometer was formed by splicingone section of alcohol-filled polarization-maintaining SHF between two single modefibers (SMFs). The input light pass through the first fusion point excited claddingmodes. The interference patterns corresponding to the excited cladding modes andthe core mode are obtained. The temperature variation on the Mach-Zehnderinterferometer can be realized by detecting the resonant wavelength shift of theinterference patterns. The SHF is8-cm and the sensitivity of temperature sensor is0.105nm/°C. Another is alcohol-filled SHF Sagnac interferometer for temperaturemeasurement. A15-cm alcohol-filled SHF as a sensing head was inserted in Sagnacinterferometer. By monitoring one resonant wavelength of the Sagnac interferometerwith temperature variation, the temperature sensitivity is as high as86.8pm/°C. Thetwo sensors, with simple structure and low cost, can be applied in temperaturemeasurement.3. Long-period gratings (LPGs) have been fabricated in a SHF by using a pulsedCO2laser. Sensing characteristics of this SHF-LPG to temperature, surrounding refractive index and bend have been investigated. Experimental results show thatresonant wavelength of the SHF-LPG has a blue shift with temperature withsensitivity of-0.11nm/°C, a blue shift with increasing sensitivity with surroundingrefractive index ranging from1.335to1.44(the maximum sensitivity is achievedwhen the surrounding refractive index reaches the effective index of the fibercladding), and a red shift with bend-direction-dependent sensitivity up to9.36nm/m-1.4. Simultaneous measurement of strain and temperature sensor with SHF fiberbragg grating (FBG) have been demonstrated. The FBG was inscribed on the fusionsplicing joint region between SHF and SMF. It has two Bragg resonant wavelengths,which respond differently to strain and temperature. Strain-temperaturediscrimination and simultaneous measurement are therefore realized. Experimentalresults show that the measurement errors were less than±10με、±1oC. At the sametime, FBG was inscribed on the polarization maintaining SHF. Sensingcharacteristics of strain and temperature have been investigated. Two Braggwavelengths have the same strain sensitivity0.5pm/με, and the temperaturesensitivities are9.3pm/oC and9.6pm/oC, respectively. The first method resolvesdiscrimination between strain-temperature and simultaneous measurement of them. Ithas simple structure and low cost, which make it a better design forstrain-temperature discrimination.
Keywords/Search Tags:fiber sensors, side-hole fiber, fiber gratings, birefringence fiber
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