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Study On Multi-Parameter Fiber-Optic Sensors Based On Fiber Interferometer And Fiber Bragg Grating

Posted on:2014-01-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:J ShiFull Text:PDF
GTID:1228330392460363Subject:Communication and Information System
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Fiber-optic sensing technology is the sensing antenna in an information age. It hasattracted considerable interests due to the advantages of essential safety, immunity ofelectromagnetic interferences, suitable for remote monitoring system. Fiber-optic sensingtechnology has become an important branch of sensing technology. The research of newoptical fiber sensing structure and new sensing theory is the core content of fiber-opticsensor. Fiber-optic sensor exhibits the new characteristics of miniaturization, multipleparameters measuring, high resolution, and network trend. Our thesis focuses on themulti-parameters optical fiber sensors which based on inline Mach-Zehnder interferometer(MZI), high-birefringent Sagnac loop (Hi-Bi Sagnac loop), and cladding mode couplingof fiber Bragg grating (FBG).We will briefly discuss our work in the following sub-topics:1. Thin-core diameter fiber based MZI multi-parameter sensorsThe inline-MZI is fabricated by combination of thin-core diameter fiber and normalsingle mode fiber. We propose a multi-parameter fiber-optic sensor for simultaneousmeasurement of strain and temperature:1)The multi-parameter optical fiber sensor is fabricated by cascading two types ofthin-core diameter fiber. The whole manufacturing process only involves fiber splicing,so it exhibits the merit of low cost and ease of fabrication. The sensing performance ofsimultaneous measurement of strain and temperature is also evaluated.2)The measuring resolution and sensing error of the proposed sensor are experimentallystudied. The major factors that affect sensing resolution are discussed in detail.2. Sensitivity-enhanced liquid refractive index sensor by using taperedinline MZIA sensitivity-enhanced fiber-optic refractive index (RI) sensor based on a taperedsingle-mode thin-core diameter fiber is proposed and experimentally demonstrated. Thedetailed content is as follows:1)The sensing principle is that the effective refractive index of the cladding mode is sensitive to RI change of the surrounding medium. The sensing performance isexperimentally evaluated. And the proposed sensor features the advantages of highsensitivity, easy fabrication, and high operability.2)We focus on improving sensing sensitivity. An abrupt taper (hundreds of micrometerslong) by electric-arc-heating method is utilized, plays an important role in improvingsensing sensitivity. The experimental result shows that although the fiber taper is short,it can significantly enhance the RI sensitivity.3. Hi-Bi fiber Sagnac loop based multi-parameter optical fiber sensorsThe Hi-Bi fiber Sagnac loop based fiber-optic sensors feature the merits of highsensitivity, easy manufacture, and independent on input polarization. We propose twodifferent multi-parameter sensors, which are suitable for simultaneous measurement oftemperature and strain.1)The multi-parameter fiber-optic sensor by concatenating an erbium-doped fiber and aHi-Bi Sagnac loop is investigated. The sensor can be used in discrimination of strainand temperature. The light source with the central wavelength of1480nm is utilizedas pumping laser, and the simultaneous measurement of strain and temperature can berealized by monitoring the intensity and wavelength variation of the resonant peak.The erbium-doped fiber plays roles in both gain medium and temperaturecompensation. Extra wide-band source is eliminated, which simplify the proposedsensing system.2)Two parallel connected Hi-Bi Saganc loops for simultaneous measurement oftemperature and strain is proposed. A liquid crystal wavelength selected switch (WSS)functions as connecting and dynamically assigning wavelength bands for the twoHi-Bi Sagnac loops.4. Temperature and strain-independent fiber-optic refractometer usingcladding modes coupling of FBGA temperature and strain-independent fiber-optic RI sensor based on the structure ofan abrupt taper followed by an FBG is experimentally demonstrated. The proposed sensorcan significantly eliminate temperature and strain cross-sensitivities. It also exhibits theadvantages of small size, simple fabrication, and low cost. The detailed content is as follow:1)The arc-discharging induced non-adiabatic fiber taper, which is manufactured by acommercial fiber fused splicer, plays an important role in exciting and recoupling thecladding modes. The surrounding RI change can be determined by measuring thewavelength shifts of the cladding modes.2)We focus on the temperature and strain compensation method. The experimentalresults show that the resonant wavelengths of core mode and cladding modes havenearly identical strain and temperature response. So the relative wavelength shift ismonitored to eliminate the temperature and strain cross sensitivity. The compensatingmethod is simple and effective, which greatly verifies the practicability of theproposed sensor.
Keywords/Search Tags:Fiber-optic technology, multi-parameter sensor, Mach-Zehnder interferometer, high-birefringent fiber Sagnac loop, fiber Bragg grating
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