Study Of Fiber Optic Magnetic Field Sensing For Towed Array Shape Measurement

The array shape measurement is one of the key techniques of the towed array sonar research. In order to realize all-optical-fiber structure in the main part of the fiber-optic hydrophone towed array, and meet the non-sound-position request of passive towed sonar, a new idea is proposed, which is to apply the fiber-optic Earth magnetic field sensing technology on the shape measurement of the optical fiber array.Due to the request of the directional angle precision in the shape measurement of the towed array, and the Earth magnetic field distribution characteristic of the main sea areas, a series of theoretic research about the array direction have been performed, and the performance request for the fiber-optic magnetic field sensor is obtained in the shape measurement of the optical fiber towed array. Based on the acquired material and by-past technology foundation, the feasibility of the shape measurement of the all-optical-fiber towed array with the fiber-optic magnetic field sensor has been proved by means of theoretic and experimental research. Then, an array direction measurement scheme, that is the fiber-optic Earth magnetic field sensing scheme, is brought forward, which can meet the precision request of the direction measurement in the towed array, and also be compatible with the fiber-optic hydrophone in the signal-procession part. Finally, fiber-optic magnetic field sensors used for the fiber-optic towed array are designed and achieved, and the directional angle measurement is realized by the fiberoptic magnetic field sensors through measuring the Earth magnetic field.The main works and the creative achievements in the dissertation are as follows:1. All-polarization-maintaining-fiber (PMF) interferometric Earth magnetic field sensors are presented and developed, which can stably measure the Earth magnetic field.2. The remaining parasitic interfering effect in the polarization maintaining fiber interferometer is theoretically analyzed. Corresponding methods is put forward to restrain the effect, which prompting the detecting precision of the all-PMF Earth magnetic field sensor.3. A desensitizing effect is found in the designing process of the all-polarization-maintaining-fiber sensor head which consists of a piece of magntostrictive strip bonded on the optical fiber ribbon at the two end of the strip. Then, corresponding effective technical method is proposed to control the effect, so as to ensure the efficiently transformation from the magnetostrictive strain to the phase in the sensing fiber.4. A new scheme is proposed, which is the directional angle measurement of the fiber-optic hydrophone towed array realized with fiber optic Earth magnetic field sensor. Two directional detection systems based on double in-line fiber-optic magnetic field sensors and planar perpendicular fiber-optic magnetic field sensors are respectively built, and the verifying experiments are finished, which have established a foundation for the magnetic field sensing directional engineering of the towed array.