Based on the experience acquired early from pioneering work at Stanford University and Thomson-CSF starting in the mid 70s, fiber optic gyro (FOG) R&D began at Photonetics in the late 80s to yield OCTANS, a FOG-based inertial strapdown system providing attitude and gyro compassing, at the end of the 90s. This FOG activity was spun out from Photonetics in October 2000 to create iXsea with only 16 people. The product line was rapidly expanded with PHINS, an inertial-grade INS (Inertial Navigation System) and later with MARINS, a strategic-grade INS, as well as with ASTRIX systems developed for satellites in cooperation with EADS-Astrium (today Airbus Defence & Space). In 2010, iXsea merged with several subsidiaries of its parent company, iXcore, to create iXblue. Among these subsidiaries were iXfiber, a maker of specialty fibers, and Photline, producing lithium-niobate integrated optics, hence allowing iXblue to fully master the key FOG components supply chain. Ten years later, the ‘adventure' is continuing and the former start-up is now quite a significant player in the inertial world, especially for high-grade applications. The cumulated number of high-performance 3-axis systems in service has grown to over 8,000, i.e. more than 25,000 FOG axes, with a bias stability ranging from 30 mdeg/h down to 15 μdeg/h, and an angular random walk (ARW) performance ranging from 8 mdeg/√h down to 40 μdeg/√h depending on the size of their sensing coils (3 m2 to 1000 m2) and on the application!
In the frame of the SWARM mission, an Absolute Scalar Magnetometer (ASM) was developed by CEA-LETI in partnership with CNES (Centre National d’études spatiales) for the dynamic measurement of the earth’s magnetic field. This magnetometer is based on the principle of pumping a He4 cell by a Laser emitting at 1083nm. IXSPACE was in charge of the integration of the Ytterbium optical fibre laser used in the SWARM magnetometer, the optical fibre components selection and procurement for the Laser system, as well as the qualification of these components. IXSPACE has manufactured the engineering model, the two qualification models as well as the seven Laser Flight Models.
The aim of this article is to present how the qualification of the Fiber Optic Gyroscope technology from IXSEA has been achieved through the qualification of a large range of optical devices and related manufacturing processes. These qualified optical devices and processes, that are now fully mastered by IXSEA through vertical integration of the technology, can be used for other space optical sensors. The example of the SWARM project will be discussed.
Bragg gratings were written in the cores of 7 percent mole germania doped preform plates through exposure to cw UV light. The diffraction efficiencies of the holograms were measured at a probe wavelength of 633 nm. The photoinduced refractive index modulations were calculated from these data. Microscopic inspections of the plate surfaces have shown that UV exposure induced corrugations at the grating places. A phase shift interferometric microscope was used to measure the depths of the corrugations. These measurements have shown that the corrugation depths do not depend on the nature of the gas surrounding the plate at the time of the UV exposure. Afterwards, both the refractive index modulations and the depths of the corrugations were measured in the course of 30 min isochronal step annealing experiments. The heating induced refractive index modulation changes were calculated from the changes in the corrugation depths by means of as train densification model and then compared to the experimental ones. Heating the gratings up to 600 degrees C has shown that the densification process is thermally reversible.
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