Sagnac interferometer for differential rotation rate measurement
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The development of a fiber optic sensor for measurement of the differential rotation rate between two parallell axis is reported. Different designs based on the Sagnac Interferometer are considered, and a design for use in hull monitoring systems are recomended and demonstrated with the use of two standard interrogation techniques for optical gyroscopes. The recomended design consists of two fiber coils connected in series in a way such that light waves propagating in one direction in one coil, will propagate in opposite direction in the other coil. Since the two coils are connected by optical fiber, the sensor system are designed to measure oscillations or vibrations. The rotation rate sensor is insensitive to rotations equal for the two coils. The application at hand is measurement of vibration modes(e.g torsion) for use in hull monitoring systems in large sized objects such as ships and airplanes, where the amplitude of torsion oscillations indicates the load of the object.