Showing papers on "Ring laser gyroscope published in 1981"

Sagnac effect in fiber gyroscopes

Abstract: We review the kinematic explanation of the Sagnac effect in fiber gyroscopes and recall that the index of the dielectric medium does not have any influence. Furthermore, we present a novel electrodynamic approach that confirms in more detail that the Sagnac phase shift of a ring-waveguide interferometer is the same as for the original Sagnac experiment with plane waves in a vacuum.

All-single-mode fiber-optic gyroscope with long-term stability

Abstract: A new all-fiber gyroscope is described. All components are constructed directly on a single continuous optical fiber, removing localized sources of reflection. A laser-diode source is used to reduce coherent scattering effects. Proper choice of modulation frequency is shown to reduce instabilities further. Long-term stability at rest of better than 0.2 masculine/h is observed with 30-sec integration time.

All-single-mode fiber-optic gyroscope.

Abstract: We present an optical fiber gyroscope that, for the first time, is composed completely of single-mode fiber-optic components. This system has increased simplicity and stability over previous bulk-optic designs and has the potential for very high rotation sensitivity.

Mode discrimination apparatus

Abstract: In an optical system such as a ring laser gyroscope cavity, oscillations occur in many transverse modes. The desired modes are allowed to exist by suppressing undesired modes utilizing a light stop apparatus. One light stop is made by treating a dielectric mirror with an electron beam causing a phase change to occur to the undesired reflected waves. An alternative light stop is made by depositing an absorptive material on a dielectric mirror for absorbing some of the energy of the undesired modes. Both light stop embodiments are adjustable with respect to a laser wave in a resonant cavity.

Influence of wave-front-conjugated coupling on the operation of a laser gyro.

Abstract: We present a theoretical analysis of a ring laser incorporating a wave-front-conjugating coupling element between the counterpropagating waves Our results demonstrate the possibility both of using a homogeneously broadened laser, such as a solid-state or dye laser, and of a substantial reduction in lock-in frequency

Ring laser gyro system

Abstract: A laser gyro system is disclosed wherein the lock-in error associated with the sensor signal deriving phase information of the phase relationship between a pair of lasing beams therein is accounted for and utilized for correction and/or control.

Dual input gyroscope

Abstract: A fiber-optic gyroscope designed to operate at maximum sensitivity by suping two equal-intensity input beams with a specific phase difference to the gyroscope optical coupler. When the coupler outputs into the gyroscope optical fiber coil are of equal intensity, reciprocity requires the gyroscope to operate at quadrature. This device is realized by splitting a laser beam into two paths with a phase shifter in one of the paths to control the phase shift and thereby the intensity of the beams, and coupling the light from these paths into a fiber optic coil via a four-port 3dB coupler.

Ring laser gyroscope suspension

Abstract: A torsional hinge is axially mounted within a central bore of a ring laser gyroscope body. The hinge comprises a plurality of angularly spaced wing sections having generally radially extending slits therein for permitting torsional motion of the gyroscope about the hinge. A plurality of spaced arcuate segments bridge a gap between the wing sections and the confronting surface of the bore and are cemented to the surface for securement of the hinge. By properly dimensioning and positioning the subtending contact areas of the hinge within the bore, the effects of thermal expansion of the hinge are minimized thereby inhibiting distortion of the gyroscope body as well as path length changes with temperature.

Ring laser gyroscope utilizing phase detector for minimizing beam lock-in

Abstract: Two of the three reflecting mirrors in a ring laser gyroscope are provided with transducers permitting the mirrors to control the ring laser gyroscope laser path. The third mirror is partially reflecting to permit some cavity radiation to exit. The radiation includes winking signal components which are related to laser beam lock-in. By controlling the phase difference between the signal components, minimum lock-in may be achieved.

Optical rate sensor

Abstract: An optical rate sensor (200) is disclosed for use in inertial reference systems to measure rates of angular rotation with substantially high resolution and sensitivity. The sensor (200) comprises a passive ring Sagnac interferometer (201) with a multiturn fiber optic ring (232) through which counter-propagating optical waves are transmitted. A nonreciprocal time variant phase modulation is applied to the waves along with periodic effective transposition of ring ports. The waves are combined to produce a "zero order" fringe pattern having an intensity varying in accordance with the relative phase between the counter-propagating waves. An intensity signal is derived from the fringe pattern having a phase offset corresponding to the Sagnac induced phase shift which in turn is linearly proportional to the angular rotation rate of the passive ring. Sampling, averaging and estimation circuits detemine the offset by detecting zero-crossing locations of the signal.

Precision Spectroscopy and Laser Frequency Control Using FM Sideband Optical Heterodyne Techniques

Abstract: In fundamental physical experiments using laser servolocking techniques,1 in passive ring laser gyro experiments, and in precision atomic/molecular spectroscopic measurements as well, the two overriding experimental concerns are maximizing the signal-to-noise ratio and obtaining highly symmetrical resonance profiles to facilitate precise line splitting. In this paper we discuss the technique of FM sideband optical heterodyne spectroscopy,2,3 which appears to be the experimentally optimum method for obtaining such high precision resonance profiles of maximal signal/noise ratio. We discuss the process in simple physical terms relative to stabilization of a laser to a resonant optical cavity, before turning to sub-Doppler resonance spectroscopy obtained by applying the sideband techniques to cw dye lasers and color center lasers. The final topic concerns our study of optical transients resulting from laser phase changes, studied with the optical heterodyne technique.

Piezoelectric motor for dithering ring laser gyroscopes

Abstract: A transducer for driving a spoke of a ring laser gyroscope is fastened at a point of neutral radius on the spoke. The transducer may be a piezoelectric crystal provided with a pair of electrodes which are driven in push-pull by an AC voltage to dither the gyroscope.

Ring laser gyroscope with doppler mirrors and offset actuators

Abstract: An equilateral triangular ring laser gyroscope contains drivers to vibrate two of the mirrors synchronously and oppositely along paths displaced by about 427° from the bisector of the vertex angles at which those mirrors are located The magnitude of displacement is about 0761 λ, where λ is the wavelength of laser radiation The purpose of the vibration is to reduce the lock-in effect in the ring laser gyroscope

Self-compensating gas discharge path for laser gyro

Abstract: A ring laser gyroscope having a self-compensating discharge path between a single anode and cathode which comprises equal segments in the laser path in series with a channel that interconnects the laser path and allows a single current to flow within the equal segments in opposite directions with respect to the laser beam thereby cancelling the Fresnel-Fizeau drag effect. This design is applicable also to laser gyroscopes having two or more rings in a single gyro block structure.

Optical gyroscope with time dependent wavelength

Abstract: A Sagnac rotation sensing interferometer disposed on a rotating platform use as a gyroscope comprising a wound optical fiber light path, a beam splitter for splitting a light beam into two beams directed to traverse the optical path in opposite directions, a light source circuit for generating a light beam which is switched between two wavelengths at a switching or modulation frequency substantially higher than the speed of change of the phase due to rotation, and a detector for extracting a signal from the recombined beam interference pattern at the wavelength modulation frequency, this signal being proportional to the phase shift caused by rotation.

Ring laser gyroscope cluster for strapped down navigation

Abstract: An inertial measurement unit using body dithered ring laser gyroscopes in which the individual ring laser gyroscopes are firmly attached to a common dithered structure and provisions made to cancel the reaction moment from the dithered structure by a passive resonator. The stable element, to which both the dithered structure and the passive resonator are attached with torsion springs, also serves as a non-vibrating foundation for strapped down accelerometers. The resulting structure contains fewer parts, has lower fabricating cost and permits a smaller package size than a conventional inertial measurement unit with individually body dithered ring laser gyroscopes.

Ring laser gyroscope with compensation

Abstract: A ring laser gyroscope having a triangular block configuration is dithered about its center of gravity. An optical wedge attached to the output mirror allows the center of support to include the line of symmetry of the block, thereby reducing temperature gradients, which could cause output signals in the absence of an input angular rate across the instrument. The optical wedge, a mirror and a beamsplitter form an interferometer to compensate the output signal of the ring laser to produce an output free from influence of the dither motion. The mirror and beamsplitter are adjustable to allow for small corrections necessary to exactly compensate the dither-motion and to achieve 90° phase shift between the outputs from photodetectors.

Compact, integral, 6-mirror, triaxial, laser rate gyro

Abstract: A triaxial ring laser gyroscope with three square optical paths which are planar and orthogonal with respect to one another, this laser gyroscope comprising six optical mirrors interconnected two by two by means of twelve optical path segments (capillary channels), said segments forming an octahedron, with one mirror for each corner, each of the mirrors operating simultaneously in two orthogonal optical paths.

Magnetic resonance gyroscope with spectral control

Abstract: A magnetic resonance gyroscope wherein the pump lamp includes an isotopic mixture of Hg, which controls the optical spectra of the pump beam to eliminate 201 Hg alignment moments and to reduce light-induced frequency shifts. The inclusion of quarter-wavelength plates, reflection polarizers, and adjustable magnetic fields acting on the pump and readout lamps permit fine tuning control over the respective spectra to further enhance the rate bias stability of the gyroscope.

Dither pick-off transducer for ring laser gyroscope

Abstract: A piezoelectric pick-off transducer is used for sensing dither velocity in a ring laser gyroscope. The pick-off transducer is mounted on a spoke connecting the hub and rim of the gyroscope and it comprises two spaced electrodes equidistant about the point of inflection of the spoke. A differential amplifier is connected at its input to the electrodes for generating a signal proportional to dither velocity.

Laser gyro mode locking reduction scheme

Abstract: A ring laser gyroscope is described having two counterpropagating primary modes and one or more secondary laser modes having a component c cos ω t to produce a dithering effect which reduces or eliminates the lock-in range of the primary modes. The ratio of c to ω is controlled to minimize J o (c/ω) wherein J o is the Bessel Function of the first kind of zero order. In one embodiment, cavity length control circuitry is adjusted to detune the cavity length to allow two secondary opposing modes of angular frequency separation ω to be generated within laser gain medium in the cavity while two primary counterpropagating modes operate well above threshold. Another embodiment has an external laser beam source for generating two secondary waves, at two light frequencies separated by an angular frequency ω, which are introduced into the ring laser path through a partially transmitting mirror which forms one of the corners of the ring laser closed loop path. In still another embodiment, part of one of the primary waves leaves the ring laser path through a partially reflective mirror and is acted upon by a mirror oscillating at an angular frequency ω which doppler-shifts the frequency of the extracted wave. This doppler-shifted mode is reintroduced into the ring laser path to diminish the range of lock-in frequency of the primary modes. In all embodiments, the magnitude of the ratio of c/ω is controlled to minimize J o (c/ω) to reduce the range of lock-in of the primary modes.

Ring laser gyroscope with fiber optic beam combiner

Abstract: An electromechanically dithered ring laser gyroscope includes a beam combiner utilizing optical fibers instead of conventional optics. This permits a beam measuring photodetector and associated electronics to be positioned outside the gyroscope or its enclosure. The invention further includes a dither compensator using optical fibers thereby replacing sensitive electronic or optical dither compensating components.

Vehicle navigation gyroscope correction - is made when vehicle is at rest using north-seeking gyroscope and frame relative angle nulling

Abstract: A gyroscope unit for a vehicle has a vertically supported navigation gyroscope with a north-seeking gyroscope enabling correction of the navigation gyroscope indication when the vehicle is at rest. The navigation gyroscope is rotated about its vertical axis (7) by resetting devices engaging the horizontally mounted frame. The north reference is transferred to the navigation gyroscope without gimbal errors even when the vehicle has an inclined attitude. This is achieved economically and without addition time. Measurement instruments (10) determine the deviation from 90 degrees of the angle between the planes of both gyroscope frames (2,4). The reset devices are controlled to correct the navigation gyroscope indication using the north-seeking gyroscope and according to the measured angular deviation. The deviation is nulled and the new navigation gyroscope direction determined by the north-seeking gyroscope.

Phase locked gyroscope wheel supply for synchronous hysteresis motor

Abstract: Electrical and mechanical synchronization of two or more synchronously driven gyroscopes, mounted on the same platform, to minimize cross-talk induced drift, is achieved by bringing one gyroscope to a speed which is slightly higher than the other by driving it at a slightly higher frequency. At speed, coincidence of mechanical position is established by means of signals from pick-offs on each gyro and the drive for the faster gyroscope is shifted to the lower frequency. Electrical synchronism is established by restarting the lower frequency generator to instantaneously establish a predetermined relationship between a pick-off signal and the frequency generator. Phase-lock start-up of a single gyroscope by instantaneous shift of the phase of the driving voltage, relative to the gyroscope wheel position, is also provided.

Azimuth Determination Using a Low Noise Ring Laser Gyro Inertial Measurement Unit.

Abstract: : The performance requirements for a ring laser gyro inertial measurement system to achieve sub-arc second azimuth determination capability have been developed. Parallel theoretical studies link these requirements to identifiable laser gyro design parameters and indicate that a feasible design could be implemented within practical constraints. A feasibility system is being assembled which will consist of 3 Raytheon RB-25 multioscillator gyros and 3 Bell Aerospace Model XI accelerometers. The instrument cluster will be mounted on a single-degree-of-freedom rotary fixture. Rotation of the cluster will be used to washout long-term error contributors with a Kalman filter using a pseduo-velocity measurement technique.

Limiting accuracy of the laser gyro

Abstract: Analyses of spontaneous fluctuations in a ring laser were made in several papers as described in detail in [i, 2]. In the theory of limiting accuracy of the laser gyro there are two qualitatively different approaches leading to different dependence of the mean square error o on the averaging time T. The semi-classical theory of ring lasers was used in [3] to apply the phase diffusion model and obtain the expression