Showing papers on "Ring laser gyroscope published in 1988"

The ring laser gyro

Abstract: The authors recall the basic principles and advantages of the ring laser gyro (RLG) which is the most widely developed of all optical gyroscopes based on the Sagnac effect. The main error sources which can affect RLG performances are discussed, and among them gas flows in the active medium and frequency synchronisation of counterpropagating waves or 'lock-in'. Particular attention is given to locking phenomenon: the predominant influence of mirrors backscattering is emphasized and means devised to overcome this problem are explained. Some important design rules used in the RLG construction are defined. Two representative examples of RLG for different applications are described including the triaxial RLG in a single optical block.

Multi-mode fiber optic resonator gyroscope

Abstract: A fiber optic resonant gyroscope in which the laser beam is coupled to a frequency modulator which produces three spatially separated beams frequency shifted from one another by a predetermined amount equal to the difference between the N th and N th +1 traveling wire resonant modes of the fiber optic ring, a portion of the outputs from the laser frequency modulator being applied to travel in one direction around the fiber optic ring, a portion of the other two outputs being applied to travel in the opposite direction around the fiber optic ring. Detectors are employed to detect the N th and, N th -1 and N th +1 resonant modes and the signals from these detectors are fed back to the modulators to cause the respective output beams to track the respective modes. The signal values fed back are used to provide an output signal indicative of the Sagnac shift.

Fibre optic gyroscope with nulling feedback control loop

Abstract: A fibre optic gyroscope arrangement having a nulling feedback control loop, the gyroscope including means 40 for varying wavelength of the light source 41 for a predetermined period of time at switch-on of the gyroscope and means for subsequently operating the light source 41 at a fixed wavelength.

Ring laser gyro and magnetic mirror therefor

Abstract: A laser gyroscope is formed as a sealed, unitary assembly of mirrors optically contacted to a monolithic gyro block without any means, such as Brewster windows, for isolating the laser plasma from any of the mirrors. The mirrors are fabricated with hard multilayer dielectric films which can withstand plasma exposure. A magnetic mirror utilizing the transverse Kerr effect to separate the frequencies of counter-propagating beams, and to avoid lock-in, includes a Ni-Fe alloy layer over which is directly deposited a thin iron or iron alloy layer to form a rotationally switchable Kerr effect combination. The magnetic field for switching is generated by an electric current developed in two pairs of orthogonally disposed wires embedded in the substrate immediately below the iron and Ni-Fe alloy layers. A specially designed multilayer dielectric stack is disposed on one of the mirrors, for example over the iron and Ni-Fe alloy layers on the magnetic mirror, and is configured to suppress S mode oscillation in order to limit the gyro to P mode operation.

Ring laser gyroscope mirror orientation system and method

Abstract: A method and system of ring laser gyroscope mirror orientation is disclosed which provides minimal backscatter within the closed optical pathway as a result of analysis and manipulation of the speckle pattern associated with each of the mirrors defining the optical pathway.

Thermally neutral dither motor design

Abstract: A thermally neutralized ring laser gyro with a dither spring mounted into a central bore of a gyro block which permits dither of the block about an axis of the spring with thermal expansion effects being minimized. The dither spring has a central mounting member, a tubular outer ring member with outer surface segments secured to the block bore, radial members adjoined to and extending outward from the central member to the ring member, generally T-shaped junctions in the ring member and between adjacent ones of the outer surface segments with the radial members being adjoined to the inside of the junctions and an outer surface of each junction being spaced inwardly toward the axis from a major outer diameter defined by the segments and being in non-contact with the block bore. A method of obtaining improved thermal neutrality in a dither gyro includes the steps of leaving a void between each junction and the block bore, and then the further step of expanding the junctions into the voids when the gyro temperature changes.

Optically differentiating and adding passive ring laser gyroscope

Abstract: Disclosed herein is an improved passive ring laser gyroscope with two systems: common mode and differential mode error systems. The common mode error system modulates counter propagating coherent radiation. The modulated light from a common source is split at a beam splitter before the reasonator cavity and then optically recombined at the same beam splitter for further propagation to an electronic detecting and demodulation servo system. The resulting electronic error signal is used to adjust the ring resonator and the laser so that the frequency output of the coherent radiation of the laser is substantially equal to the resonance frequency of the ring resonator. The differential mode error system optically substracts counter propagating radiation signals emanating from the resonator cavity to form a differential error signal that is detectable by an electronic detector for further processing by demodulation. This output signal is used to servo and drive acousto-optic modulating frequency shifters, one for each counter propagating radiation of the ring resonator. The difference between the frequencies at which the acousto-optic modulators are driven is made equal to the difference between the frequencies of the counter propagating radiation of the ring resonator. In this manner a reading of the difference of the frequencies driving the two acousto-optical modulators provides a beat signal which is directly translatable to a reading indicating the rate of rotation of the gyroscope.

Open-loop fiber-optic gyroscope using intensity-modulated source and phase modulation.

Abstract: A simple open-loop approach to a standard fiber-optic gyroscope that uses an intensity-modulated source is described. Direct readout of the Sagnac effect in an open-loop form is obtained by applying a sinusoidal modulation to the source and the phase modulator at the proper frequency, with the modulation depth of the source adjusted appropriately. Experimental results show good linearity over a wide dynamic range.

Development and field testing of a RLG strapdown inertial survey system

Abstract: The authors describe the successful modification of a ring laser gyro (RLG) strapdown inertial reference unit into a strapdown inertial survey system (SISS) for geodetic positioning. The system, a Litton LTN-90-100, has been modified into a land-vehicle mode inertial survey system by developing specialized software and error control techniques. The software package integrates the raw body rate and acceleration data from the LTN-90-100 into velocity and coordinates of the system. The error states of the SISS are estimated by a Kalman filter-smoother using regular zero velocity measurements and occasional control coordinates as updates. The system was tested on an L-shaped baseline near Calgary and results show that a positioning accuracy of better than 1 m (1 sigma ) is achievable. >

Velocity control system using piezoelectric transducers

Abstract: A piezoelectric activated dither suspension system for a ring laser gyroscope has all of the transducer elements connected in parallel to simultaneously produce sustaining torque for dither motion and respond to a back component of current produced by the vibrational motion of the gyro block. The generated current, separated from drive currents from the torquer amplifier by a transformer or, in an alternative embodiment, by sensing resistors, produces the very signal used to control and sustain the oscillations. By utilizing all transducers both as torquer and pickoff elements, economies of drive efficiency, wiring simplification and circuit redundancies are achieved.

Laser power monitoring optics for a ring laser gyroscope

Abstract: Instead of using two power monitoring photodiodes and associated summing circuitries for adding the power of the laser beams circulating in the cavity of a ring laser gyro, the present invention eliminates one of the photodiodes and uses, in its stead, reflective means for directing both of the laser beams onto the remaining power monitoring photodiode, which automatically measures and sums the light intensities or power from the laser beams and provides as an output the thus added power directly to the necessary electronic circuitry to maintain constant the pathlength of the cavity.

Radio frequency excited ring laser gyroscope with common induction coil

Abstract: A split gain multi-mode ring laser gyroscope is disclosed having a radio frequency excitation induction coil which also serves the magnetic mode suppression system, suppressing undesirable modes of the gain curve to achieve the split gain effect. The induction coil serves as an important common component of both the gain medium excitation and mode suppression systems. The induction coil is suitably configured to carry both AC and DC signals.

Fiber-optic passive ring-resonator gyroscope using an external-cavity laser diode

Abstract: We report a fiber-optic passive ring-resonator gyroscope that uses an external-cavity laser diode. The external-cavity laser diode is useful as the light source for the gyroscope if an appropriate cavity length is chosen. A rotation detection sensitivity of 10−2 rad/sec was obtained with an integration time of 10 sec.

Multiple ring paths in one block

Abstract: A laser gyro system wherein a plurality of nonplanar ring laser gyros are nested within a common supporting block of material. The nonplanar ring laser gyros have a ring path whose circumscribing volume has a size of the order of the volume of the supporting block, each ring path utilizing a portion of the volume unused by the other. In one embodiment, a cubic block contains two orthogonal tetrahedral ring laser gyros. The two rings intersect and share a common gas envelope. In another embodiment, the supporting block contains two orthohedral ring laser paths.

Common mirror triaxial ring laser gyroscope having a single internal cathode

Abstract: A compact three axis ring laser gyroscope having six laser corner mirrors which are positioned on the faces of a parallelopiped laser block, and method for making. Preferably the laser block is a cube. The laser block has a plurality of conduits therein for defining a plurality of closed laser beam-paths for guiding counterpropagating laser waves. Each laser beam-path has a gain medium therein and is formed to define a sensing axis for detection of rotations of the laser block. A single cathode is positioned inside the laser block, preferably substantially at its geometric center, and a plurality of anodes are mounted to the laser block and spaced apart from the cathode. A ion flow path is formed between each anode and the cathode such that application of a suitable electrical potential difference between the anodes and the cathode produces counterpropagating laser beams in each laser beam-path. The anodes are arranged to eliminate undesired Fresnel-Fizeau phase shifts by ensuring that each of the three ring gyros has two opposing ion flows.

Multiple axis ring laser gyroscope with longitudinal excitation

Abstract: A ring laser gyroscope in which RF excitation is used to cause gas discharge as opposed to DC excitation which is used in conventional ring laser gyroscopes. External surfaces of the body of the ring laser gyroscope are metallized to form electrodes and an RF signal is capacitively coupled to gas reservoirs forming part of the lasing cavities.

Beam combiner assembly for ring laser gyroscope

Abstract: A beam combiner assembly for a ring laser gyroscope is fabricated by positioning two diffraction gratings, mounted onto respective light transmissive substrates, with respect to the output mirror of the gyro block at an offset angle such that an interference fringe pattern is projected onto the photodetector of the ring laser gyroscope. By tilting the diffraction gratings, with respect to the plane of the output mirror, a corrected number of lines per unit length for the diffraction gratings may be effected, thereby providing a beam combiner assembly which is compensated for manufacturing imperfections and other intolerances. Also, the high sensitivity of angular adjustments for the conventional prism beam combiner is overcome.

Scatter symmetrization in multi-mode ring laser gyros

Abstract: SCATTER SYMMETRIZATION IN MULTI-MODE RING LASER GYROS Abstract Disclosed herein is a method and apparatus for achieving scatter symmetrization in a multi-mode non-planar ring laser gyro The retro scatter effect which results in scatter coupling in each of the left and right circular polarized sets of beams is equalized, so that the scatter coupling may be common-mode rejected during the analysis phase of the ring laser gyro operation This equalization is achieved by unique orientation of the mirrors and the non-reciprocal polarization rotator The non-reciprocal rotator which may be a Faraday rotator, is rotated in such a manner that its angle of rotation relative to an angle fixed at the plane of incidence of one of the mirrors of the leg is proportional to the positioning of the rotator along the axis between the mirrors of this leg In this manner equal scatter coupling will occur in the left and right circularly polarized light and this scatter coupling may be common-mode rejected for purposes of deriving accurate rotational information Scatter symmetrization is also achieved by con-figuring the mirrors in legs of equal length so the amount of image rotation attributed to each leg is proportional to the leg length

Method of constructing a moment insensitive pathlength control mirror assembly for a ring laser gyroscope

Abstract: In a precision ring laser gyroscope, to eliminate the effect of an unwanted and unintentional moment generated as a result of a force being applied onto a pathlength controller, a pathlength control assembly is constructed to have optimal hub and diaphragm portions such that the mirror element mounted thereto does not tilt in response to the unintentional moment.

A ring laser gyro based navigator for space launch vehicle guidance

Abstract: The existing guidance and navigation system for the Centaur upper stage launch vehicle is being replaced with a single-package inertial navigation unit (INU) that includes updated electronics and inertial sensors in a strapped-down mechanization. The INU was adapted from an existing system based on a ring laser gyro (RLG) that was selected for its performance and adaptability to the space application. Adaptations were required to accommodate: space launch requirements, including qualification in accordance with MIL-STD-1540B; mission accuracies/performance requirements; and vehicle requirements. The adapted RLG INU features a proven electronic design, a single package (which includes inertial measurement and flight control subsystems), a large inertial sensor production base, and existing test facilities. >

Faraday magnet for the reduction of multi-oscillator bias thermal sensitivity

Abstract: Disclosed herein is a ring laser gyroscope having a non-reciprocal polarization rotation device such as a Faraday rotator configured to provide, through use of a Faraday magnet, a relatively uniform magnetic field across the profile of the Faraday rotator. By providing a uniform magnetic field across the diameter of the Faraday rotator, the magnetic lensing effects are reduced and the thermal sensitivity of the gyroscope's bias is substantially reduced.

Fibre optic gyro

Abstract: A fibre optic gyroscope arrangement having a nulling feedback control loop, the gyroscope including means 40 for varying wavelength of the light source 41 for a predetermined period of time at switch-on of the gyroscope and means for subsequently operating the light source 41 at a fixed wavelength.

Error correction apparatus at the dither turnaround point and method therefor

Abstract: A correction to the output angle of a ring laser gyroscope (10) 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 (50A, 508) 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 (92) with the heterodyne signals to determine the magnitude of coupling between the beams in the ring laser gyroscope (10).

Mode Interactions in Four-frequency Degeneracy-lifted Ring Lasers

Abstract: A non-planar ring cavity, with a non-reciprocal bias in the form of the longitudinal Zeeman effect on the gain medium, has been used to demonstrate four-mode bidirectional operation in a He-Ne ring laser at 632·8 nm. It has also been shown that this ring system is sensitive to rotation.

Development of a tightly integrated ring laser gyro based navigation system

Abstract: The development of a small, tightly integrated GPS/inertial navigation system (INS) is being pursued following the development of a miniaturized GPS receiver and a compact multiaxis ring laser gyro The tradeoffs involved in achieving the present system architecture, along with a system description and performance summary, are presented A description of both the inertial hardware and the GPS receiver hardware, as well as a detailed implementation of both Kalman filters (inertial and receiver), is discussed Finally, the test program is presented >

Partly transparent mirror for a ring laser gyro

Abstract: A ring laser gyro system having a special and improved partly transparent output corner mirror (20) which allows substantially undistorted circularly polarized coherent light beams to be extracted from a ring laser and delivered to a beam detector. The improved mirror sandwiches a non-quarterwave film-stack (34) between two quarterwave, film-stacks (30, 32), each having alternate high index of refraction and low index of refraction films. The film stacks are positioned on a dimensionally stable, thermally stable, transparent substrate (45). The improved mirror achieves nearly zero phase retardation and a Tp/Ts ratio equal to one.

Multipole magnetic geometry for a ring laser gyroscope

Abstract: Disclosed herein is a multi-pole magnetic geometry for a multi-oscillator ring laser gyroscope. Multi-pole magnetic geometry configurations are disclosed which are useful for providing Faraday rotation where the multi-oscillator uses a Faraday rotator and high magnetic field effect where the nature of the multi-oscillator ring laser gyroscope is of split gain configuration. The multi-post magnetic geometry includes a plurality of top or bottom loaded diametrically opposed north and south pole axially directed magnets which are positioned substantially transverse to the optical pathway but suitable for providing axially directed magnetic fields to portions of the optical pathway only where desired. The multi-pole magnetic geometry disclosed herein substantially produces a magnetic flux that is restricted in its position to localized portions of the optical pathway with low far field effects.

Ring laser gyro

Abstract: PURPOSE:To obtain a gyro which is able to detect an angle of rotation through a beam by transmitting a light introduced from a light emitting part to an annular interference part in the annular interference part clockwise as well as counterclockwise, thereby detecting its output beam at photodetector parts. CONSTITUTION:A light emitting part 7 is in the stand-by condition at a beam splitter part 4 in the transmission light introduction part of an interference part 2 and at the beam splitter part 5 as the transmission takeoff part of the above-mentioned interference part 2, two sets of photodetectors 8 and 9 which detect beams transmitted clockwise as well as counterclockwise in the interference part 2 are in the stand-by condition. Optical waveguides 3, 3, and 3 consisting of a single crystal fiber of the annular interference part 2 oscillate at 10 mW of threshold and oscillations are taken out of the photodetectors 8 and 9 through the beam splitter part 5 of the takeoff part. Once this ring laser gyro is mounted at a rotational motion system, the extent of its rotation speed, its direction and the like can be determined by deflections of both output beams.