Investigation Of Photonic Crystal Fiber Sensor

Photonic crystal fiber has attracted great interest in the scientific due to their uniquestructure and special wave-guiding mechanism over the conventional optical fiber. In recentyears, photonic crystal fiber has already become a hot spot in the field of optical fibersensor. In this thesis, three photonic crystal fiber sensors with different structures areproposed and experimentally demonstrated by using the special wave-guiding mechanismand mode coupling of the photonic crystal fiber. The applications of the three photoniccrystal fiber sensors have also been introduced. The main content of the research work inthis thesis includes:1. Investigation on basic characteristics of the photonic crystal fiber. Two kinds of thephotonic crystal fiber used in this thesis are introduced. The arc parameter and splicing lossbetween the photonic crystal fiber and single mode fiber is investigated. The all-solidphotonic band gap fiber is easy to splice with the single mode fiber, and the splicing loss is0.7dB. The endlessly single mode fiber can be spliced with the single mode fiber by usingthe manual operation of the fusion splicer, and the splicing loss is1.3dB.2. Investigation on distributed pressure sensor based on the photonic crystal fiber. Thedistributed fiber optic sensor is fabricated by splicing a single mode fiber with a section ofan all-solid photonic band gap fiber, and the free end face of the all-solid photonic band gapfiber was filmed with a reflectivity of99%. The operation principle of the sensor wasanalyzed with and without the pressure. the intensity and the corresponding position of thepressure along the photonic crystal fiber can be interrogated simultaneously. Experimentalresults show that this sensor was implemented to realize the distributed measuring of thepressure. The variation of±0.1cm was achieved between the experimental result and thereal distance for an8cm-long photonic crystal fiber, and the height of the resonancewavelength is proportional to the pressure.3. Investigation on a miniature high-temperature sensor based on the photonic crystalfiber. The sensor head was fabricated by splicing a small segment of photonic crystal fiberto the single mode fiber. The free end face of the photonic crystal fiber was cleaved andpolished to a certain length. The temperature effect on this sensor was analyzed. The resultsshow that the resonance wavelength would be shifted with the change of the temperature.The temperature can be measured by interrogating the resonance wavelength in the optical spectrum of this sensor. Two demodulation schemes were used to investigate thehigh-temperature sensor. One demodulation scheme can measure the temperature bydetecting the intensity of the two lasers with different wavelengths. A high temperature ofup to500°C can be measured using the demodulation schemes. This approach makes itpossible to realize high-speed signal process, because the measurement speed is onlyaffected by the electronic processing unit. The other demodulation scheme is based on acharge coupled device (CCD) linear array based micro spectrometer. The temperature canbe measured by analyzing the temperature response of the high-temperature sensor.Experimental results show that the temperature range of1200°C and the temperatureresolution of1°C are achieved. The measurement precision is improved by using Splineinterpolation arithmetic. This sensor can measure the high temperature in a small volumedue to its small size of tens of microns. The performance of the miniature high-temperaturesensor was tested by measuring the temperature of a heating oven, a resistance wire of hightemperature and an electric iron. Experimental results obtained by the miniaturehigh-temperature sensor are agreed with that of the other sensor, which prove that theminiature high-temperature sensor can exactly measure the temperature. The miniaturehigh-temperature sensor is used to measure the temperature of an igniter wire. Theexperimental results are available and recognized by the research organization.4. Investigation on a photonic crystal fiber-based Mach-Zehnder interferometer withthe temperature compensation. This interferometer was fabricated by splicing a section ofthe photonic crystal fiber between two single mode fibers. The theoretical analysis indicatesthat the spectrum of this interferometer shifts to opposite directions with the temperatureand strain variation. The temperature compensation of the Mach-Zehnder interferometercan be realized by using materials with proper thermal expansion coefficients. Firstly, thetemperature performance and the strain response of the Mach-Zehnder interferometer wereexperimentally demonstrated. Then, the Mach-Zehnder interferometer was bounded to threepackaging materials and the effect of the temperature compensation was tested.Experimental results show that the ceramic is the most suitable material for the temperaturecompensation. The temperature stability of1.0pm/℃has been experimentallydemonstrated with the packaging material of ceramic. Finally, the relationship between thetemperature stability and the length of the ceramic packaged interferometer wasinvestigated. Experimental results also show that the temperature stability of theMach-Zehnder interferometer with the ceramic package remains substantially unchanged with different length of the photonic crystal fiber.