Study On Photonic Crystal Fiber Hydrophone

As the interferometric fiber optic hydrophone(FOH) has high sensitivity, largedynamic range and is easily used to make arrays, it is the core of the new generationphotoelectric sonar system, and is taking the place of the traditional piezoelectrichydrophone gradually. Photonic crystal fiber(PCF)is a new kind of special fiber, it notonly has some unique properties such as endless single mode, big mode-filed area andhigh birefringence effect, but also has a higher pressure sensitivity than traditional fiber.At present, researches about PCF stress sensor mainly focus on polarization statesensing and transmission spectrum sensing, most of which is fiber sensing withoutsensitivity enhanced. As is most suitable for underwater acoustic pressure sensing,interferometric photonic crystal fiber optic hydrophone(PCFOH) has not been reported.Therefore, to carry out the PCFOH research is of great significance to improve thepressure sensitivity.The dissertation has carried on theory and experimental research about PCFOHwhose sensitivity is enhanced by the mandrel structure with air cavity. Analysis hasbeen made on the pressure sensing mechanism of PCF, which has proved that PCF ismore sensitive than common single mode fiber(SMF) theoretically. By establishing theelastic mechanics and finite element method models, a deep research on the influence ofthe material and structure parameters has been made. After that, some PCFOH sampleshas been developed to take comparison experiments with SMFOH, and the results areconsistent with theoretical analysis. The main results of the present dissertation are asfollows:1. After the PCF is equivalent to the step fiber by equivalent refractive indexmodel, the equivalent material coefficient of PCF are studied, on which theanalysis demonstrates that the PCF is more sensitive than SMF about pressure.2. Utilizing the method of elastic mechanics and finite element, theoreticalsimulation model are established respectively to study on the pressure phasesensitivity of the PCFOH of mandrel structure with air cavity, and the resultshas only1dB difference. Besides, the PCFOH has a higher sensitivity thanSMFOH.3. Five PCFOH samples have been developed and then tested with the ordinarySMFOH which have the same structure. Test results show that the PCFOH hasa good linear response in its dynamic range and a flat response between20Hzand1600Hz frequency range. Furthermore, the sensitivity of PCFOH is1dBhigher than that of SMFOH, which is same with theoretical analysis.