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iXBlue has developed a family of fibre- optic inertial navigation systems that can be integrated into autonomous underwater vehicles (writes Rory Jackson). The Phins series comes with optimised packaging and interfaces to reduce size and weight. As iXBlue’s Claire Andre explains, “The sensors are designed to be integrated inside the AUV’s chassis. This external housing protects against harsh environments, and now the design of these products can accept smaller and lighter housings with fewer pin connectors.” The smallest sensor, the Phins C3, weighs 1.6 kg and is the first INS based on the FOG50 gyroscope (iXblue’s entry-level inertial measurement unit) developed for SWaP-optimised underwater navigation, having been designed with man-portable or even disposable UUVs in mind. The FOG50’s 500 m of silica-based fibre are configured in a 50 mm diameter coil, and the C3’s sensor block and CPU are separated from each other to ease integration when space is limited. The Phins C3 gives an AUV’s heading to 0.15 º , roll and pitch to 0.05 º , and position to 0.3% travelled distance, while consuming 12 W of power. The larger C5 (4.7 kg) and C7 (3.6 kg) systems require more space and power (at 18 W) but provide more accurate readings, including roll and pitch to 0.01 º . “The C5 uses our IMU90, with the same length of fibre as the FOG50, but the coil is 90 mm diameter and thus gives better performance. The C7’s IMU120 uses about 1 km of fibre, in a coil of 120 mm diameter,” Andre said. “All three systems, and all our FOGs, use a closed-loop, all-digital interferometric fibre-optic gyroscope configuration. We also use a broadband light source based on an erbium-doped fibre amplified spontaneous emission source.” Navigation All the models in the Phins series are designed to be integrated inside an AUV’s chassis Heading undersea