Highly compact fiber optic gyrocompass for applications at depths up to 3000 meters

Octans is a fiber-optic gyrocompass with an integral motion sensor developed by Photonetics for demanding marine applications. In contrast with conventional gyrocompasses relying on a spinning gyroscope, Octans has no moving parts and utilizes instead three fiber optic gyroscopes (FOG) and three quartz accelerometers. The FOG technology is based on the relativistic Sagnac effect: light travels in opposite directions into a fiber optic coil, and interferes at the output with a phase-shift proportional to the rotation rate. Moreover, three accelerometers measure, after Schuler filtering, the local gravity vector. As the FOGs are enough accurate (typically a bias stability of 0,05 /spl deg//h), the observation of the gravity slow drift in the inertial space allows one to determine the Earth axis, thus the North direction. In addition, the real three-axis architecture allows Octans to act as a marine motion sensor and compute the complete attitude of the vessel in terms of roll, pitch, heave, surge and sway. Because of a specific algorithm, Octans is able to find the true heading without any help in three minutes even at sea. This system is obviously ideal for ROVs and AUVs applications: low power consumption, compact, light box and very low settling time.