| Interferometric fiber-optic sensor is considered to be one of the most hopeful fiber-optic sensors for its high sensitivity. However, when the interferometric fiber-optic sensor works at the low frequency band or ultra-low frequency band, the system has been badly influenced by the low frequency system background noise and environment disturbance. In order to detect the low frequency signal effectively, the methods for low frequency background noise suppression and environment disturbance reduction have been studied in this dissertation.First, the background noise of the fiber-optic sensing system has been analyzed. The low frequency optical noise of the sensing system based on phase generated carrier technique has been discussed. Then the influence factors from environment such as temperature have also been analyzed. By noise analysis, the main low frequency system background noise and environment disturbances have been clarified.Two schemes for laser phase noise suppression have been introduced. In addition, the scheme based on reference interferometer has been primarily studied. The limitation of the scheme in low frequency signal detection has been specially discussed, and then some improving methods have been put forward.A fiber optic acceleration sensor has been designed and fabricated based on the improved noise reduction scheme. The test of the system noise indicates that the low frequency phase noise of the improved sensing system has been obviously reduced, and the phase noise of sensing system has been reduced about 8dB in the frequency range from 1Hz to 300Hz, and the noise peak has been reduced about 12dB. The low frequency signal detection experiment has been carried out in the frequency range from 2Hz to 5Hz. the experiment results show that the low frequency signals have been detected effectively. The curve of acceleration sensitivity varying with frequency is flat in the frequency range from 2Hz to 200Hz; its acceleration sensitivity is about 178rad/g. |
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