A fibre-optic gyroscope (FOG) senses changes in orientation using the

Sagnac effect The Sagnac effect, also called Sagnac interference, named after French physicist Georges Sagnac, is a phenomenon encountered in interferometry that is elicited by rotation. The Sagnac effect manifests itself in a setup called a ring interferomete ...

, thus performing the function of a mechanical

gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rotat ...

. However its principle of operation is instead based on the

interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extr ...

of light which has passed through a coil of

optical fibre An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a mean ...

, which can be as long as .

Operation

Two beams from a laser are injected into the same fibre but in opposite directions. Due to the

, the beam travelling against the rotation experiences a slightly shorter path delay than the other beam. The resulting differential

phase shift In physics and mathematics, the phase of a periodic function F of some real variable t (such as time) is an angle-like quantity representing the fraction of the cycle covered up to t. It is denoted \phi(t) and expressed in such a scale that it ...

is measured through interferometry, thus translating one component of the

angular velocity In physics, angular velocity or rotational velocity ( or ), also known as angular frequency vector,(UP1) is a pseudovector representation of how fast the angular position or orientation of an object changes with time (i.e. how quickly an objec ...

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

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 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.

Advantages

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

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 and military inertial navigation systems. The FOG typically shows a higher resolution than a

ring laser gyroscope A ring laser gyroscope (RLG) consists of a ring laser having two independent counter-propagating resonant modes over the same path; the difference in phase is used to detect rotation. It operates on the principle of the Sagnac effect which shift ...

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

Disadvantages

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. However, when coupled with multiple-axis FOG and accelerometers and hybridized with Global Navigational Satellite System (

GNSS A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location (longitude, latitude, and altitude/elevation) to high p ...

) data, the impact is mitigated, making FOG systems suitable for high shock environments, including gun pointing systems for 105mm and 155mm howitzers.

References

Sources

* Anthony Lawrence, ''Modern Inertial Technology: Navigation, Guidance, and Control'', Springer, Chapters 11 and 12 (pages 169–207), 1998. . * * R.P.G. Collinson, ''Introduction to Avionics Systems'', 2003 Kluwer Academic Publishers, Boston. . * José Miguel López-Higuer, ''Handbook of Fibre Optic Sensing Technology'', 2000, John Wiley & Sons Ltd. * Hervé Lefèvre, ''The Fiber-Optic Gyroscope'', 1993, Artech House. {{ISBN, 0-89006-537-3. Gyroscopes

Gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rotat ...

Operation

Advantages

Disadvantages

See also

References

Sources