Fibre optic gyroscope

A fibre optic gyroscope (FOG) is a gyroscope that uses the interference of light to detect mechanical rotation. The sensor is a coil of as much as 5 km of optical fiber.Two light beams travel along the fiber in opposite directions. Due to the Sagnac effect, the beam traveling against the rotation experiences a slightly shorter path than the other beam. The resulting phase shift affects how the beams interfere with each other when they are combined. The intensity of the combined beam then depends on the rotation rate of the device.

The development of low loss single mode optical fibre in the early 1970s for the telecommunications industry enabled Sagnac effect fibre optic gyros to be developed. These use an external laser diode source together with beam splitting objects to launch the laser light so that it travels in cw and acw directions through a cylindrical coil comprising many turns of optical fibre. The effective area of the closed optical path is thus multiplied by the number of turns in the coil. Path lengths of hundreds of metres are achievable. The first FOG was demonstrated in the US by Vali and Shorthill in 1976. Development of both the passive interferometer type of FOG, or IFOG, and the passive ring resonator type of FOG, or RFOG, is proceeding in many companies and establishments world-wide.

A FOG provides extremely precise rotational rate information, in part because of its lack of cross-axis sensitivity to vibration, acceleration, and shock. Unlike the classic spinning-mass gyroscope, the FOG has virtually no moving parts and no inertial resistance to movement. The FOG typically shows a higher resolution than a ring laser gyroscope but also a higher drift and worse scale factor performance. It is used in surveying, stabilization and inertial navigation tasks.

FOGs are designed in both open-loop and closed-loop configurations.

ee also

* Inertial Measurement Unit
* Vibrating structure gyroscope
* Quantum gyroscope
* Ring laser gyroscope

Manufacturers:
* Fizoptika Co
* IAI TAMAM
* IXSEA
* KVH Industries

References

* Anthony Lawrence, "Modern Inertial Technology: Navigation, Guidance, and Control", Springer, Chapters 11 and 12 (pages 169-207), 1998. ISBN 0387985077.
* G.A. Pavlath, "Fiber-optic gyroscopes", IEEE Lasers and Electro-Optics Society (LEOS) Annual Meeting, 1994. LEOS '94 Conference Proceedings, Volume 2, pages 237-238. 31 Oct-3 Nov 1994.
* R.P.G. Collinson, "Introduction to Avionics Systems", 2003 Kluwer Academic Publishers, Boston. ISBN 1-4020-7278-3.