Study On Interferometric Fiber Optic Acoustic Sensor System And AGC Scheme

Acoustic survey on a sound field is one research hot spot in the using of an interferometric fiber optic sensor. A typical application is the fiber optic acoustic sensor. Fiber optic acoustic sensor is a kind of complicated sensors with optics, mechanics and electronics. It has characteristics of high sensitivity, wide dynamic range, wide detection bandwith, high capability of anti electromagnetic disturbance etc. With the development of science and technologics, fiber optic acoustic sensor becomes the most typical technique in the research of hydroacoustic. Scientific and technical personnel pay more attention to it. It plays a significant role in national defense and national economy.At present, fiber optic acoustic sensor is taking a step from laboratory to engineering application. The study of this thesis was devoted to the practicality of fiber optic acoustic sensor.In this thesis, the physical foundation of the transducing theory based on strain effect, and the theory of phase generated carrier (PGC) were expounded first. The relation and restriction of each technical criteria was analysed and explained. Besides, problems in the process of the fiber optic acoustic sensor system accomplish were expounded based on practical situation of the detector facture, optical path debugging and circuit debugging.In order to solve the distubance of the interferometric signal fluctuation, which results in optical path and environment, the automatic gain control (AGC) system was theoretically analyzed and emulated in detail in this thesis. An AGC system reduces the fluctuation of the restituted signal's amplitude by stabilifying the amplitude of the interferometric signals. Peak to peak value type AGC has ever worked in compensating the fluctuation of the restituted signal's amplitude, which was caused by the changing of the polarization. But dealing with the interference signals without distinguish the differences of them results in the fluctuation of the restituted signals on the contrary. The defect is principled. Positive-Negative type AGC has appreciable superiority comparing with peak to peak value type AGC. The maximum errors of Positive-Negative type AGC are less than or close to 10% when modulation degree C changes within the range of 2.20～2.70rad. And it's less than the maximum error of peak to peak value type AGC out and away, when C=2.4rad. Division type AGC requires a relatively rigorous C, so it's restricted in practicality. The factor of the restriction was analyzed. These consequences can be significant references for further research.