145:, 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.
27:
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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.
90:. 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.
136:
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,
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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
124:
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
140:
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
141:
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
162:
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.
62:
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
116:, 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
120:
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.
86:. 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
75:
420:
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
129:, 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.
46:
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
101:
on military aircraft, commercial airliners, ships, and spacecraft. These hybrid INS/GPS units have replaced their mechanical counterparts in most applications.
542:
104:"Ring laser gyroscopes (RLG) have demonstrated to currently be the most sensitive device for testing rotational motion with respect to an inertial frame."
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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
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185:
728:"Pakistan Aeronautical Complex Kamra – JF-17 Thunder Aircraft"
727:
206:
523:
Multioscillator Ring Laser
Gyroscopes and their applications
648:
644:
595:. Economic Times India via Press Trust of India. 2014-01-20
614:"Agni-V missile to take India into elite nuclear club"
790:
767:"Inertial Navigation – Forty Years of Evolution"
593:"India successfully test fires Agni-IV missile"
545:. Farnborough. 22–28 July 2002. Archived from
97:capability to further enhance accuracy of RLG
497:. Elsevier (North-Holland Pub. Co). pp.
491:"3. The multioscillator ring laser gyroscope"
479:, Donald MacKenzie, The MIT Press, (1991).
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25:
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791:
568:"Agni-III missile ready for induction"
543:"Honeywell's ADIRU selected by Airbus"
16:Instrument to measure angular velocity
422:Journal of Physics: Conference Series
755:Canterbury Ring Laser Research Group
679:"B-52 Maps Its Way Into New Century"
493:. In Stich, M.L.; Bass, M. (eds.).
13:
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328:Hemispherical resonator gyroscope
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442:10.1088/1742-6596/723/1/012061
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529:, Loukianov, D et al. (eds.)
428:(1). IOP Publishing: 012061.
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782:General Electric Company plc
385:(3). AIP Publishing: 67–68.
7:
819:Spacecraft attitude control
311:
301:International Space Station
297:, used for roller alignment
99:inertial navigation systems
71:in excess of 60,000 hours.
65:inertial navigation systems
10:
835:
343:List of laser applications
69:mean time between failures
18:
704:"MK 39 MOD 3A Ring Laser"
532:Retrieved 23 October 2019
193:US Anti-satellite missile
84:inertial reference system
640:Digital Avionics Systems
153:A related device is the
379:Applied Physics Letters
353:Optical ring resonators
237:MC-130H Combat Talon II
233:MC-130E Combat Talon I
108:Principle of operation
79:
31:
358:Fibre optic gyroscope
155:fibre optic gyroscope
149:Fibre optic gyroscope
77:
29:
21:fibre optic gyroscope
572:Press Trust of India
521:Volk, C. H. et al.,
223:F-16 Fighting Falcon
209:with the AMI upgrade
166:Example applications
125:beams can allow for
36:ring laser gyroscope
30:Ring laser gyroscope
434:2016JPhCS.723a2061B
391:1963ApPhL...2...67M
348:List of laser types
323:Active laser medium
276:Seahawk helicopters
814:Missile technology
809:Laser applications
765:A.D. King (1998).
333:Laser construction
218:F-15E Strike Eagle
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399:10.1063/1.1753778
127:injection locking
112:According to the
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716:on 2009-02-05.
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620:. 2012-04-19
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52:Interference
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172:Airbus A320
58:Description
799:Gyroscopes
793:Categories
784:: 140–149.
774:GEC Review
737:2017-02-26
689:2009-02-24
664:2008-10-16
624:2015-10-14
599:2015-10-14
578:2008-05-08
553:2008-07-16
508:0444869271
364:References
289:Trident II
202:Boeing 777
44:ring laser
464:CC BY 3.0
407:0003-6951
285:Trident I
228:HAL Tejas
134:dithering
88:gyroscope
651:. 1995.
618:BBC News
466:license.
312:See also
295:PARALIGN
291:Missiles
258:missile.
250:P3 Orion
177:Agni III
683:fas.org
499:229-332
430:Bibcode
387:Bibcode
256:Shaurya
191:ASM-135
181:Agni-IV
132:Forced
655:
505:
405:
266:MH-60S
262:MH-60R
186:Agni-V
780:(3).
770:(PDF)
714:(PDF)
707:(PDF)
525:, in
274:SH60B
270:SH60F
207:B-52H
653:ISBN
649:AIAA
645:IEEE
503:ISBN
403:ISSN
287:and
272:and
235:and
179:and
446:hdl
438:doi
426:723
395:doi
95:GPS
40:RLG
795::
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
