![fibre-optic-interferometer](https://upload.wikimedia.org/wikipedia/commons/0/0b/Fibre-optic-interferometer.svg)
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 interferometer ...
, 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 rota ...
. 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 extra ...
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 means to ...
, 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
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 interferometer ...
, 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 v ...
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
A beam splitter or ''beamsplitter'' is an optical device that splits a beam of light into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding wide ...
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
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 interferometer ...
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
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 rota ...
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 shifts ...
.
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 pre ...
) data, the impact is mitigated, making FOG systems suitable for high shock environments, including gun pointing systems for 105mm and 155mm howitzers.
See also
*
Attitude and Heading Reference System
An attitude and heading reference system (AHRS) consists of sensors on three axes that provide attitude information for aircraft, including roll, pitch, and yaw. These are sometimes referred to as MARG (Magnetic, Angular Rate, and Gravity) sens ...
*
Hemispherical resonator gyroscope
The Hemispherical Resonator Gyroscope (HRG), also called wine-glass gyroscope or mushroom gyro, is a compact, low-noise, high-performance angular rate or rotation sensor. An HRG is made using a thin solid-state hemispherical shell, anchored by a ...
*
Inertial measurement unit
An inertial measurement unit (IMU) is an electronic device that measures and reports a body's specific force, angular rate, and sometimes the orientation of the body, using a combination of accelerometers, gyroscopes, and sometimes magnetometer ...
*
Inertial navigation
An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dir ...
*
Vibrating structure gyroscope
A vibrating structure gyroscope, defined by the IEEE as a Coriolis vibratory gyroscope (CVG), is a gyroscope that uses a vibrating structure to determine the rate of rotation. A vibrating structure gyroscope functions much like the halteres of fl ...
*
Quantum gyroscope
A quantum gyroscope is a very sensitive device to measure angular rotation based on quantum mechanical principles. The first of these was built by Richard Packard and his colleagues at the University of California, Berkeley. The extreme sensit ...
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 rota ...