Showing papers on "Ring laser gyroscope published in 1991"

Laser gyro at quantum limit

Abstract: We show that a certain fundamental limit applies to the accuracy of all optical rotation sensors which use laser light as a probe. We derive this fundamental rotation-rate uncertainty from the Heisenberg uncertainty relations and Glauber's minimum uncertainty states. The same relationship is obtained from a spontaneous-emission noise formulation. We present experimental data on a (nondithered) four-frequency ring laser gyroscope for which this limit is attained.

Femtosecond ring dye laser: a potential new laser gyro.

Abstract: Measurements on a passively mode-locked dye laser demonstrate a sensitive gyro-type response, when Fresnel drag in air is used to simulate rotation. Such a response is unexpected for a homogeneously broadened ring laser.

Ring laser gyroscope enhanced resolution system

Abstract: Disclosed herein is a Ring Laser Gyroscope Enhanced Resolution System comprising, in a preferred embodiment, a sampling frequency modulation phase-locked loop (or "chirp") which is used in combination with the fast filter. Enhanced resolution is achieved by using the fast filter (preferably a moving average digital filter) to gather optically integrated rate data and accumulate this data. During the data gathering process, the accumulated data is sampled at a rate set by a frequency modulated ("chirper") phase-locked loop in order to remove undesirable data due to aliasing effects upon the digital filter. In this manner, an enhanced resolution of the gyroscope angular measurement is achieved.

Signal processing system for correcting ring laser gyroscope readout

Abstract: An RLG signal processing system in which RLG quadrature errors are corrected by adding to one signal a portion of the other signal whose magnitude is a function of the magnitude of the quadrature error. Output buffer amplifiers restore the output signal to equal amplitude.

Mode-locked active gyro solid state lasers

Abstract: A ring laser gyro that minimizes and avoids the effects of lock-in and backscatter. A ring laser is pumped in a lasing cavity with a mode-locked laser. Dual counterrotating pumped pulses are precisely positioned to avoid overlay in optical elements that contribute to lock-in and backscatter. The position of the stimulated counter rotating laser beams is controlled by two methods. In the first method the pumped pulses are synchronized with a wave propagation delay line. In the second method the pumped pulses are chopped by an acousto-optic modulator shutter to precisely time the location of the pumped pulses. Both methods are can be combined to achieve a hybrid synchronized and acousto-optic modulated approach.

Wavelength sensor for fiber optic gyroscope

Abstract: An error compensated Mach-Zehnder Interferometer wavelength sensor integrd fiber optic chip for scale factor correction of fiber optic gyroscopes. A 90° twisted optical fiber polarizer couples the light from a point in the gyroscope optical fiber circuit where light is found to have traversed the optical sensing coil of the gyroscope in both directions to the input of the fiber optic Mach-Zehnder Interferometer. The light output of the interferometer is converted to electrical signals which are used to servo lock the peak depth of phase modulation of the interferometer and provide a digital output corresponding to the wavelength change sensed by the gyroscope. Temperature and input power variations otherwise adversely affecting the gyroscope performance are thus compensated. Gyro resolution is maintained to within 1Å without temperature stabilization or output conditioning over the entire temperature range of operation.

Picosecond pulsed diode ring-laser gyroscope.

Abstract: We have demonstrated a novel solid-state ring-laser gyroscope, which utilizes as the gain media a pair of semiconductor diodes in an external ring cavity. The use of homogeneously broadened gain media is made possible by actively mode locking the laser. We observe no evidence of frequency locking between the counterpropagating optical pulse trains generated in the cavity to within the limit of our experimental resolution.

Pressure-equalized self-compensating discharge configuration for triangular ring laser gyroscopes

Abstract: A triangular ring laser gyroscope having a single anode, single cathode, and self-compensating discharge path which cancels gyro bias, bias drift, and noise. The discharge path extends from the anode through a cross channel in the center of the gyro block to the cathode. Counter-propagating laser beams traverse one segment of the discharge path in the direction of the Langmuir flow from anode to cathode, and another segment of the discharge path of equal length in a direction opposite to that flow. The Langmuir return flow from cathode to anode occurs along the walls of the gyro cavity, producing a more uniform gas flow velocity in the central region of the discharge path. Drag effects on the counter-propagating laser beams are equal but opposite, and the laser beams traverse a more uniform region of the Langmuir flow when thermally-induced changes in the gyro cause beam wandering. Gyro bias, bias drift, and noise are substantially cancelled.

Multioscillator ring laser gyroscope adaptive digitally controlled cavity length control system

Abstract: Disclosed herein is a Digitally Controlled Cavity Length Control System comprising, in a preferred embodiment, an adaptive servo-loop for cavity length, modulation depth and amplitude control, and of the multioscillator ring laser gyroscope; thereby, permitting the simultaneous control of these elements. The cavity length control of the multioscillator, by including a variable RF detector gain, allows the operation of the gyroscope in a slightly detuned fashion to minimize magnetic sensitivity. In this manner, the multioscillator gyroscope may be maintained at a stable operating point suitable for modeling.

An improved optical branching/coupling unit for an optical fiber gyroscope, and navigation system employing the same

Abstract: In an optical fiber gyroscope, the sensitivity thereof is optimized with a phase bias afforded by utilizing the phase characteristics of an optical branching/coupling unit. Further, the fluctuation of the intensity of a light source and the error and secular change of the phase characteristics of the optical branching/coupling unit are compensated by an electronic circuit. Moreover, an optical fiber loop is located in a heat insulation casing so as not to be affected by an ambient temperature change, thereby to prevent the drift of the optical fiber gyroscope attributed to an temperature change. Thus, the optical fiber gyroscope of high measurement accuracy is provided.

Pulsed diode ring laser gyroscope

Abstract: A pulsed diode ring laser gyroscope and method of modulation are provided to greatly reduce the occurrence of frequency locking in optical gyroscopes at low rotational rates. One or two optical diodes serve as optical amplifiers for a pair of counterpropagating optical pulses circulating in an optical ring resonator. The amplifiers are driven twice each round trip (once for each pulse) using pulses much shorter than the round trip time. The short optical pulses overlap in regions of the resonator generally isolated from light scattering elements. The pulses are produced by gain switching the optical amplifiers with an electrical current pulse train having a fundamental period synchronous with the optical round trip time in the resonator cavity. With this modulation scheme, the diodes can be thought of as gates that open twice each round trip-once for each of the counterpropagating pulses. During each on time, the diodes amplify only a clockwise or counterclockwise pulse. Backscattered light from any optical element, which is not coincident with either of the pulses, is absorbed by the amplifiers.

Sagnac effect in the colliding-pulse-mode-locked dye ring laser

Abstract: A colliding-pulse-mode-locked dye ring laser was mounted on a rotary stage and the beat frequency of the two output pulse trains was measured as a function of the rotation rate. The measurements are in good agreement with the Sagnac theory.

Triangular phase-modulation approach to an open-loop fiber-optic gyroscope.

Abstract: A new approach to an open-loop, all-fiber gyroscope with a wide dynamic range and a linear scale factor is described For signal processing, the Sagnac phase shift is converted into a phase shift in the low-frequency electrical signal by using a triangular phase-modulation waveform followed by gate switching The basic principle of this technique and experimental results are reported

In-flight scale factor calibration of ring laser gyro systems

Abstract: In-flight scale factor calibration of a ring laser gyro is encumbered by the dependence of scale factor on light beam intensity and by the susceptibility of the intensity monitor to decalibration. The monitor may be calibrated in flight by modulating the mirror alignment, the laser current, or both to modulate the intensity. The intensity modulation produces a modulation of the scale factor. The ratio of the amplitude of scale factor modulation to the amplitude of the measured intensity modulation should be the same in-flight as during factory calibration. If it is not, the intensity monitor is calibrated by multiplying its output by the change in the ratio, and the calibrated intensity measurement rather than the raw intensity measurement is used to determine the scale factor.

Ring laser gyro dither stripper

Abstract: A dither stripper for laser gyro dither including a digital microcomputer which controls the stripping of the dither signal from the inertial navigation signal of the laser gyro. The dither stripper schedules internal A/D conversions using an A/D conversion arbitration scheme as well as calculates the expected system sample clock. Accurate dither stripping is achieved using a phase locked loop feedback system which compensates for real time changes in dither pickoff components while incorporating an accurate gain control mechanism.

Computer generated cavity length control with automatic gain control for ring laser gyros

Abstract: A ring laser gyro having a ring laser that preferably has four legs and four corner mirrors. At least one of the corner mirror is partly transmissive, and the transmitted beam is sensed and converted into a digital signal. The digital signal is fed back in two computer loops to at least one digital-to-analog converter, and thence to a transducer which drives at least one corner mirror inward and outward. One of the computer loops includes a stepped demodulator having four steps per cycle. The steps have voltages at the operating voltage of the transducer, that voltage plus an increment, the operating voltage, and that voltage less a decrement. The first loop sends an operating voltage to the digital-to-analog converters. The second loop demodulates the beam signal at a second harmonic of the demodulation of the first loop to produce a voltage signal which controls the amplitude of dithering of the movable mirrors. A stepped modulator, in synchronism with the demodulator of the first loop, delivers a modulation signal to the digital-to-analog converters to step the movable mirrors. The operating voltage moves the mirrors into a position wherein the laser cavity operates at its intensity mode peaks.

Method and system for correcting random walk errors induced by rate reversals in a dithered ring laser gyroscope

Abstract: A correction to the output angle of the ring laser gyroscope is calculated as a function of the phase difference and the magnitude of coupling between the two counterpropagating beams when the dither oscillations change direction. A pair of heterodyne detectors produce heterodyne signals indicative of the interference pattern between the counterpropagating beams. A signal indicative of the sum of the separate beam intensities is demodulated with the heterodyne signals to determine the magnitude of coupling between the beams in the ring laser gyroscope.

Scale-factor-stabilized fiber-optic gyroscope based on a spectrum-broadened laser-diode source

Abstract: A spectrum-broadened laser-diode source that uses the optical feedback and current-modulation effects has been adopted as the light source of a fiber-optic gyroscope to reduce the inherent phase noise. The scale factor of the gyroscope has also been stabilized.

Deep phase-modulation approach to an open-loop fiber optic gyroscope

Abstract: A new approach to an open-loop, all-fiber gyroscope with a wide dynamic range and linear scale factor is described For signal processing, the Sagnac phase lift is converted into a phase shift in the low-frequency electrical signal by using a deep sinusoidal phase-modulation waveform followed by gate switching With the duty cycle of the gating signal selected to be in the range between 20 and 70%, the scale factor is stable with respect to change in the amplitude of the phase modulation signal by as much as 15% The basic principle of the technique and experimental results are reported >

Active current control apparatus

Abstract: An active current control apparatus for a ring laser gyro includes an apparatus for generating a control signal representative of a current value, such as, for example a microprocessor controller. Apparatus for supplying actively controlled current to the anode of the ring laser gyro in response to the control signal is coupled to the control signal so as to provide a constant current in the ring laser gyro beam path.

Ring laser gyro having two magnetic mirrors

Abstract: Method and apparatus for switchably controlling the bias of a ring laser angular rate sensor using two switchably controllable magnetic mirrors for rate sensor operation away from lock-in regions. For a sensor input rate that is less than a threshold value, a control means switchably energizes each of the magnetic mirrors in a manner such that their respective optical effect is additive, one with the other, for biasing the rate sensor at a first desired operating point. For a sensor input rate that is at least equal to the threshold value, the control means switchably energizes each of the magnetic mirrors in a manner such that their respective optical effect is subtractive, one from the other, for biasing the rate sensor at a second desired operating point.

Cavity length controller for ring laser gyroscope applications

Abstract: A mechanically self-stabilized cavity length controller for use within a ring laser gyroscope, including piezoelectric elements which are employed to move mirrors and effect a change of the laser path length. More particularly, a cavity length controller consisting of component parts fabricated from dissimilar materials, and configured so as to largely cancel any thermally-induced dimensional variations by virtue of the differential thermal expansion rates of the various component parts. The cavity length controller also includes two piezoelectric plates affixed to opposite sides of a deformable diaphragm which is coupled to a mirrored surface within the cavity. To correct for any nominal, thermally-induced cavity variations which might still be evident in a cavity employing the controller, an electrical potential is applied to the piezoelectric plates, causing the radial expansion of one plate and the simultaneous radial contraction of the other, thereby deforming the diaphragm. This deformation results in a corresponding shift in the displacement of the coupled mirrored surface. Such a shift would effectively vary the length of a laser path which included the mirrored surface.

Multioscillator ring laser gyroscope local oscillator-based output optics detection system

Abstract: A rotational sensing system for a Multioscillator ring laser gyroscope is disclosed herein that can operate with a simple upright symmetric optics mechanism, where the required signal separation is performed fully electronically, with the use of a local oscillator. The technique allows for rotational rate and direction detection, as well as cavity length control, with a minimum of cross-talk.

Use of Spectral Methods in Strapdown ISS Data Processing

Abstract: Characteristic frequencies and frequency bands are identified in the output of the inertial sensor block in a Ring Laser Gyro Strapdown Survey System by using Fast Fourier Transformation and are related to physical causes such as vehicle motion, environmental noise and sensor errors. A significant disturbance in the gyro and accelerometer outputs caused by the dither mechanism of the laser gyro is discussed. A frequency filtering approache to decrease the disturbing frequencies are studied. The effect of the filtering on the system performance is presented for field test results.

Gyroscopes: Current and Emerging Technologies

Abstract: Gyroscopes and accelerometers are unique devices, the critical input sensors for inertial navigation and surveying systems. Among the many types of gyroscopes only a few have proved adequate for precise inertial applications. These are the ring laser gyroscope (RLG), electrostatic suspended gyroscopes (ESG), air-bearing floated-gimbal spinning mass gyroscopes, and dynamically tuned rotor gyroscopes (DTG). All have been developed to a high art among precision instruments, with supremely low noise and bias errors. Extensive acceptance of inertial navigation systems in commercial flight service, particularly using RLGs, has also required and stimulated development of practical and competitve reliability, cost, and lifetime.

Ring laser gyroscope arranged for maintaining ionized gas discharge transverse to the optical axis of the gyroscope

Abstract: A ring laser gyro features an arrangement wherein the ionized gas atoms flowing in a sealed envelope in an optical cavity flow transverse to the optical axis of the gyro in the optical gain sections thereof, thereby eliminating gas flow bias errors. An arrangement of the type described has the added advantage of providing a larger gas reservoir in small ring laser gyros which increases the life of the gyro. The transverse discharge arrangement obviates the necessity of equal curents flowing through gas ionizing electrodes and minimizes the tendency for gas flow oscillations at high current values.

Fiber optic gyroscope with wide dynamic range analog phase tracker

Abstract: A simple analog phase tracking circuit used with an open-loop fiber gyrose is disclosed that imitates the operation of a true closed-loop gyroscope, by electronically generating a sinusoidal output which nulls the Sagnac phase shift. The nulling or tracking technique is based on the generation of sine and cosine dependent interferometric outputs from an open-loop gyroscope using dynamic phase modulation. Cross-multiplication of the outputs with electronically generated phase shift components and combining these signals obtained from the cross multiplication process produces a component which is dependent on the difference between the Sagnac phase shift and the electronically generated phase. By controlling the electronic phase shift, the output can be nulled. In this way, the phase tracking approach imitates the operation of a true closed-loop gyroscope and uses the simple structure of open-loop gyroscope. The scheme has a wide dynamic range, relatively low drift and short term noise. The analog phase tracker significantly increases dynamic range, as a large number of 2π phase excursions could be accommodated with digital tracking. The electronics are very simple and are low in cost.

Acceleration sensing ring laser gyroscope

Abstract: A ring laser gyroscope functions both as a standard gyroscope and as an accelerometer. As the ring laser gyroscope experiences acceleration along its input axis, the frame bends and position sensing photodiodes are utilized to detect the optic axis motion and laser beam intensity. By measuring optic axis shifts along the gyro input axis during acceleration, a signal proportional to acceleration is obtained.

Radio frequency excited ring laser gyro

Abstract: Apparatus for stabilizing the position of the exciting electric component of a radio frequency electromagnetic field within the excited plasma of a ring laser, using two adjacent quarterwave coils, and driving the coils from a radio frequency source to ensure that the adjacent open ends of the two coils have electric field components that produce a steep gradient of electric field within the gas plasma of the ring laser.