Gyroscope that uses fiber optics
A
fibre-optic gyroscope
(
FOG
) senses changes in orientation using the
Sagnac effect
, thus performing the function of a mechanical
gyroscope
. However its principle of operation is instead based on the
interference
of light which has passed through a coil of
optical fibre
, which can be as long as 5 kilometres (3 mi).
Operation
[
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]
Two beams from a laser are injected into the same fibre but in opposite directions. Due to the
Sagnac effect
, the beam travelling against the rotation experiences a slightly shorter path delay than the other beam. The resulting differential
phase shift
is measured through interferometry, thus translating one component of the
angular velocity
into a shift of the interference pattern which is measured
photometrically.
Beam splitting
optics split light from a laser diode (or other laser light source) into two waves propagating in both clockwise and anticlockwise directions through a coil consisting of many turns of optical fibre. The strength of the
Sagnac effect
is dependent on the
effective area
of the closed optical path: this is not simply the geometric area of the loop but is also increased by the number of turns in the coil. The FOG was first proposed by Vali and Shorthill
[1]
in 1976. Development of both the passive interferometer type of FOG, or IFOG, and a newer concept, the passive ring resonator FOG, or RFOG, is proceeding in many companies and establishments worldwide.
[2]
Advantages
[
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]
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
or resonant/mechanical gyroscopes, the FOG has no moving parts and doesn't rely on inertial resistance to movement. Hence, the FOG is an excellent alternative to a mechanical gyroscope. Because of their intrinsic reliability and long lifetime, FOGs are used for high performance space applications
[3]
and military inertial navigation systems.
The FOG typically shows a higher resolution than a
ring laser gyroscope
.
[
citation needed
]
FOGs are implemented in both
open-loop
and
closed-loop
configurations.
Disadvantages
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]
Like all other gyroscope technologies and depending on detailed FOG design, FOGs may require initial calibration (determining which indication corresponds to zero angular velocity).
Some FOG designs are somewhat sensitive to vibrations.
[4]
However, when coupled with multiple-axis FOG and accelerometers and hybridized with Global Navigational Satellite System (
GNSS
) data, the impact is mitigated, making FOG systems suitable for high shock environments, including gun pointing systems for 105mm and 155mm howitzers.
See also
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]
References
[
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]
Sources
[
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]
- Anthony Lawrence,
Modern Inertial Technology: Navigation, Guidance, and Control
, Springer, Chapters 11 and 12 (pages 169?207), 1998.
ISBN
0-387-98507-7
.
- Pavlath, G.A. (1994). "Fiber-optic gyroscopes".
Proceedings of LEOS'94
. Vol. 2. pp. 237?238.
doi
:
10.1109/LEOS.1994.586467
.
ISBN
0-7803-1470-0
.
S2CID
117215647
.
- R.P.G. Collinson,
Introduction to Avionics Systems
, 2003 Kluwer Academic Publishers, Boston.
ISBN
1-4020-7278-3
.
- Jose Miguel Lopez-Higuer,
Handbook of Fibre Optic Sensing Technology
, 2000, John Wiley & Sons Ltd.
- Herve Lefevre,
The Fiber-Optic Gyroscope
, 1993, Artech House.
ISBN
0-89006-537-3
.