156:, either in a special thin Faraday rotator, or via a longitudinal magnetic field on the gain medium, then further splits each circular polarization by typically a few hundred kHz, thus causing each ring laser to have a static output beat frequency of hundreds of kHz. One frequency increases and one decreases, when inertial rotation is present; the two frequencies are measured and then digitally subtracted to finally yield the net Sagnac-effect frequency splitting and thus determine the rotation rate. The Faraday bias frequency is chosen to be higher than any anticipated rotation-induced frequency difference, so the two counterpropagating waves have no opportunity to lock-in.
38:
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with a peak dither velocity on the order of 1 degree per second. Dither does not fix the lock-in problem completely, as each time the direction of rotation is reversed, a short time interval exists in which the rotation rate is near zero and lock-in briefly can occur. If a pure frequency oscillation is maintained, these small lock-in intervals can accumulate. This was remedied by introducing noise to the 400 Hz vibration.
101:. This means there is no friction, which eliminates a significant source of drift. Additionally, the entire unit is compact, lightweight and highly durable, making it suitable for use in mobile systems such as aircraft, missiles, and satellites. Unlike a mechanical gyroscope, the device does not resist changes to its orientation.
147:
can largely overcome this problem. The ring laser cavity is rotated clockwise and anti-clockwise about its axis using a mechanical spring driven at its resonance frequency. This ensures that the angular velocity of the system is usually far from the lock-in threshold. Typical rates are 400 Hz,
172:
ring, where rotation causes a relative phase shift between those beams when interfered after their pass through the fiber ring. The phase shift is proportional to the rate of rotation. This is less sensitive in a single traverse of the ring than the RLG, in which the externally observed phase shift
135:
RLGs, while more accurate than mechanical gyroscopes, suffer from an effect known as "lock-in" at very slow rotation rates. When the ring laser is hardly rotating, the frequencies of the counter-propagating laser modes become almost identical. In this case, crosstalk between the counter-propagating
151:
A different approach to avoiding lock-in is embodied in the
Multioscillator Ring Laser Gyroscope, wherein what is effectively two independent ring lasers (each having two counterpropagating beams) of opposite circular polarization coexist in the same ring resonator. The resonator incorporates
152:
polarization rotation (via a nonplanar geometry) which splits the fourfold-degenerate cavity mode (two directions, two polarizations each) into right- and left-circular-polarized modes separated by many hundreds of MHz, each having two counterpropagating beams. Nonreciprocal bias via the
173:
is proportional to the accumulated rotation itself, not its derivative. However, the sensitivity of the fiber optic gyro is enhanced by having a long optical fiber, coiled for compactness, in which the Sagnac effect is multiplied according to the number of turns.
73:
The first experimental ring laser gyroscope was demonstrated in the US by Macek and Davis in 1963. Various organizations worldwide subsequently developed ring-laser technology further. Many tens of thousands of RLGs are operating in
127:, rotation induces a small difference between the time it takes light to traverse the ring in the two directions. This introduces a tiny separation between the frequencies of the counter-propagating beams, a motion of the
131:
pattern within the ring, and thus a beat pattern when those two beams interfere outside the ring. Therefore, the net shift of that interference pattern follows the rotation of the unit in the plane of the ring.
97:. The advantage of using an RLG is that there are no moving parts (apart from the dither motor assembly (see further description below), and laser-lock), compared to the conventional spinning
431:
Beverini, N; Di
Virgilio, A; Belfi, J; Ortolan, A; Schreiber, K U; Gebauer, A; Klügel, T (2016). "High-Accuracy Ring Laser Gyroscopes: Earth Rotation Rate and Relativistic Effects".
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which also operates on the basis of the Sagnac effect, but in which the ring is not a part of the laser. Rather, an external laser injects counter-propagating beams into an
140:, so that the standing wave "gets stuck" in a preferred phase, thus locking the frequency of each beam to that of the other, rather than responding to gradual rotation.
57:
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
112:
on military aircraft, commercial airliners, ships, and spacecraft. These hybrid INS/GPS units have replaced their mechanical counterparts in most applications.
553:
115:"Ring laser gyroscopes (RLG) have demonstrated to currently be the most sensitive device for testing rotational motion with respect to an inertial frame."
89:
Schematic representation of a ring laser setup. At the beam sampling location, a fraction of each of the counterpropagating beams exits the laser cavity.
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between the counter-propagating beams, observed externally, results in motion of the standing wave pattern, and thus indicates rotation.
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Ring laser gyroscopes can be used as the stable elements (for one degree of freedom each) in an
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Macek, W. M.; Davis, D. T. M. (1963). "Rotation rate sensing with traveling-wave ring lasers".
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which shifts the nulls of the internal standing wave pattern in response to angular rotation.
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and have established high accuracy, with better than 0.01°/hour bias uncertainty, and
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MK39 Ship's
Internal Navigation System used in NATO surface ships and submarines
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Contemporary applications of the ring laser gyroscope include an embedded
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Weapons and
Systems Engineering Department, United States Naval Academy
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Optical Gyros and their
Applications (NATO RTO-AG-339 AC/323(SCI)TP/9)
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Statz, Hermann; Dorschner, T. A.; Holz, M.; Smith, I. W. (1985).
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For a somewhat similar system that uses fibre optic cables, see
739:"Pakistan Aeronautical Complex Kamra – JF-17 Thunder Aircraft"
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534:
Multioscillator Ring Laser
Gyroscopes and their applications
606:. Economic Times India via Press Trust of India. 2014-01-20
625:"Agni-V missile to take India into elite nuclear club"
778:"Inertial Navigation – Forty Years of Evolution"
604:"India successfully test fires Agni-IV missile"
556:. Farnborough. 22–28 July 2002. Archived from
108:capability to further enhance accuracy of RLG
508:. Elsevier (North-Holland Pub. Co). pp.
502:"3. The multioscillator ring laser gyroscope"
8:
490:, Donald MacKenzie, The MIT Press, (1991).
460:
380:
579:"Agni-III missile ready for induction"
554:"Honeywell's ADIRU selected by Airbus"
27:Instrument to measure angular velocity
433:Journal of Physics: Conference Series
7:
766:Canterbury Ring Laser Research Group
690:"B-52 Maps Its Way Into New Century"
504:. In Stich, M.L.; Bass, M. (eds.).
25:
339:Hemispherical resonator gyroscope
468:
453:10.1088/1742-6596/723/1/012061
1:
540:, Loukianov, D et al. (eds.)
439:(1). IOP Publishing: 012061.
793:General Electric Company plc
396:(3). AIP Publishing: 67–68.
830:Spacecraft attitude control
312:International Space Station
308:, used for roller alignment
110:inertial navigation systems
82:in excess of 60,000 hours.
76:inertial navigation systems
846:
354:List of laser applications
80:mean time between failures
29:
715:"MK 39 MOD 3A Ring Laser"
543:Retrieved 23 October 2019
204:US Anti-satellite missile
95:inertial reference system
651:Digital Avionics Systems
164:A related device is the
390:Applied Physics Letters
364:Optical ring resonators
248:MC-130H Combat Talon II
244:MC-130E Combat Talon I
119:Principle of operation
90:
42:
369:Fibre optic gyroscope
166:fibre optic gyroscope
160:Fibre optic gyroscope
88:
40:
32:fibre optic gyroscope
583:Press Trust of India
532:Volk, C. H. et al.,
234:F-16 Fighting Falcon
220:with the AMI upgrade
177:Example applications
136:beams can allow for
47:ring laser gyroscope
41:Ring laser gyroscope
445:2016JPhCS.723a2061B
402:1963ApPhL...2...67M
359:List of laser types
334:Active laser medium
287:Seahawk helicopters
825:Missile technology
820:Laser applications
776:A.D. King (1998).
344:Laser construction
229:F-15E Strike Eagle
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410:10.1063/1.1753778
138:injection locking
123:According to the
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727:on 2009-02-05.
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63:Interference
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183:Airbus A320
69:Description
810:Gyroscopes
804:Categories
795:: 140–149.
785:GEC Review
748:2017-02-26
700:2009-02-24
675:2008-10-16
635:2015-10-14
610:2015-10-14
589:2008-05-08
564:2008-07-16
519:0444869271
375:References
300:Trident II
213:Boeing 777
55:ring laser
475:CC BY 3.0
418:0003-6951
296:Trident I
239:HAL Tejas
145:dithering
99:gyroscope
662:. 1995.
629:BBC News
477:license.
323:See also
306:PARALIGN
302:Missiles
269:missile.
261:P3 Orion
188:Agni III
694:fas.org
510:229-332
441:Bibcode
398:Bibcode
267:Shaurya
202:ASM-135
192:Agni-IV
143:Forced
666:
516:
416:
277:MH-60S
273:MH-60R
197:Agni-V
791:(3).
781:(PDF)
725:(PDF)
718:(PDF)
536:, in
285:SH60B
281:SH60F
218:B-52H
664:ISBN
660:AIAA
656:IEEE
514:ISBN
414:ISSN
298:and
283:and
246:and
190:and
457:hdl
449:doi
437:723
406:doi
106:GPS
51:RLG
806::
789:13
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
