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Showing papers on "Ring laser gyroscope published in 1987"


Journal ArticleDOI
TL;DR: In this article, a theory is presented which describes the lock-in threshold as a function of the beam path geometry, which is a helpful tool to minimize the lockin threshold by an optimization of the resonator geometry.
Abstract: Experiments on laser gyros with adjustable beam path geometry yield a strong dependency between the lock-in threshold and the distribution of the backscatter sources. Based on a simple vector formalism, a theory is presented which describes the lock-in threshold as a function of the beam path geometry. In accordance with the experimental results, the theory is a helpful tool to minimize the lock-in threshold by an optimization of the resonator geometry. The theory also offers an explanation of the fact that the quality of laser gyros often differs, even between gyros of the same production series, under the same operating conditions and with mirrors of comparable quality.

47 citations


Patent
01 Dec 1987
TL;DR: In this article, a nonstandard spherical resonator which produces laser radiation having spherical modes of oscillation is formed entirely within a sphere (12,24) of laser gain material, and the resonator is pumped to produce the spherical modes.
Abstract: A nonstandard spherical resonator which produces laser radiation having spherical modes of oscillation is formed entirely within a sphere (12,24) of laser gain material. The resonator is pumped to produce the spherical modes. By pumping an isotropically coated sphere (12) at normal incidence the entire sphere forms the resonator, and the laser radiates uniformly in all directions as from a point source (20). By pumping obliquely to totally internally reflect the laser radiation at the surface of the sphere (24), or by applying an equatorial coating (36) on the sphere to internally reflect the laser radiation, a toroidal region (30), within the sphere forms the resonator. The pumping volume can be controlled so that the laser radiation is single longitudinal mode and single frequency by limiting the active mode volume. Prisms (32,37) can be used for input and output coupling to the toroidal resonator; an optical fiber (34) can also be used for output coupling. A compact laser design uses a Nd:YAG sphere pumped by a laser diode. The spherical resonators can be used for tracking, holography, levelling and ring laser gyroscope applications. The toroidal resonator forms an ideal ring laser for use as a gyroscope; a sphere (50) with three orthogonal toroidal resonators (44,46,48) provides three degree of freedom measurement capability.

36 citations


Patent
23 Mar 1987
TL;DR: In this article, a phase locked passive ring resonator gyroscope comprising a fixed frequency reference signal generator (Fm), a single piece body having laser and passive resonator cavities, a laser means using the laser resonator cavity responsive to a laser control signal from a laser servo for providing a single frequency light source (F0) and having respective upper and lower side bands at frequencies F0+Fm and at F0-Fm.
Abstract: A phase locked passive ring resonator gyroscope comprising a fixed frequency reference signal generator (Fm); a single piece body having laser and passive resonator cavities; a laser means using the laser resonator cavity responsive to a laser control signal from a laser servo for providing a single frequency light source (F0) for frequency modulating the single frequency light source to form a light source (F0) and having respective upper and lower side bands at frequencies F0+Fm and at F0-Fm; first and second voltage controlled oscillator means responsive to respective first and second control signal for frequency shifting the first and second frequency modulated ray center frequencies by a first and second variable offset frequencies to form a propagating and counterpropagating light sources; the second resonator cavity being a passive high Q evacuated cavity; a detector means for detecting a first offset frequency error signal and for detecting a second offset frequency error signal; cavity servo means responsive to the first and second offset frequency error signals from the detector means for providing, a first control signal to the first voltage controlled oscillator means for frequency shifting the first frequency modulated ray by a first variable offset frequency to maintain the propagating light beam in the second resonator at peak resonance and to provide a second control signal to the second voltage controlled oscillator means for frequency shifting the second frequency modulated ray by a second variable offset frequency (F2) to control and maintain the counterpropagating light beam (FCCW) at peak resonance; means for constantly adjusting the passive cavity path length servo signal to keep the passive cavity at peak resonance at a frequency substantially mid-range between the propagating and the counterpropagating beams; output counter means for measuring and outputting the frequency difference between the first variable offset frequency (F1) and the second variable offset frequency (F2), the measured frequency difference representing the difference in frequency due to an input gyro body rate about the gyro sensitive axis.

28 citations


Journal ArticleDOI
TL;DR: It has been demonstrated that a 1.5-microm distributed feedback InGaAsP laser can be used as a coherent light source in a passive ring cavity-type fiber gyroscope and a formula for the detector shot noise-limited sensitivity of detection of rotation was derived.
Abstract: It has been demonstrated that a 1.5-μm distributed feedback InGaAsP laser can be used as a coherent light source in a passive ring cavity-type fiber gyroscope. A formula for the detector shot noise-limited sensitivity of detection of rotation was derived for this type of gyroscope. Its value in the present experimental setup was estimated as being 0.8 · τ1/2 degree/hour, where τ represents the integration time of measurements. Experiments showed that the uncertainty of the detection of rotation was 1.5°/h at τ = 100 s, which was governed by the slight reflection of light at the AR-coated fiber edges and residual frequency fluctuations of the laser.

24 citations


Journal ArticleDOI
TL;DR: The influence of noise color on the phase diffusion in a ring-laser gyroscope is studied by use of an (formally) exact solution of the time-independent Fokker-Planck equation.
Abstract: The influence of noise color on the phase diffusion in a ring-laser gyroscope is studied by use of a (formally) exact solution of the time-independent Fokker-Planck equation. Novel asymmetries in the distribution which develop with increasing noise correlation time are predicted and verified with an electronic model of the corresponding Langevin equation.

20 citations


Patent
30 Sep 1987
TL;DR: In this paper, an improved fiber optic gyroscope with a substantial improvement in dynamic range and scale factor stability over a basic fiber-optic gyroswope is disclosed.
Abstract: An improved fiber optic gyroscope with a substantial improvement in dynamic range and scale factor stability over a basic fiber optic gyroscope is disclosed. In a preferred embodiment of the invention the detected output of the gyroscope is demodulated to yield first and second voltage levels respectively proportional to preselected sine and cosine components of the detected output. These first and second voltage levels are respectively switched between a feedback network which stabilizes the drive level and a rate sensing circuit which senses the rotation rate. Such switching occurs when operational states are switched in order to stabilize the drive level from the feedback network and to provide the most sensitive one of the first and second voltage levels to the rate sensing network.

16 citations


Patent
06 Apr 1987
TL;DR: In this paper, a ring gyroscope for sensing rotations about three orthogonal axes is presented, where a pair of anodes and a cathode cooperate with the intersecting cavities and, in one embodiment, with bypass tubes.
Abstract: A ring loser gyroscope for sensing rotations about three orthogonal axes. A frame includes and internal arrangement of three intersecting cavities, each of which is arranged for measuring rotation about one of the orthogonal axes. Each cavity comprises a non-planar arrangement of four cavity legs. A pair of anodes and a cathode cooperate with the intersecting cavities and, in one embodiment, with bypass tubes, whereby undesired Fresnel-Frizeau phase shifts are eliminated by gas flow effect cancellations.

16 citations


Journal ArticleDOI

16 citations


Patent
29 Jun 1987
TL;DR: In this paper, a multioscillator ring laser gyroscope includes a frame that encloses a closed optical path in which four circularly polarized optical waves propagate, and a combining optics system combining the waves to produce an interference pattern.
Abstract: A multioscillator ring laser gyroscope includes a frame that encloses a closed optical path in which four circularly polarized optical waves propagate. A combining optics system combining the waves to produce an interference pattern. A pair of photodetectors are placed in the interference pattern in half quadrature with respect to the interference pattern so that the detectors produce oscillatory output signals that are in quadrature with respect to each other. Signals indicative of the beat signal in the interference pattern are processed to determine the rotation rate, the direction of rotation and to provide a cavity length control signal.

12 citations


Proceedings ArticleDOI
11 Mar 1987
TL;DR: In this article, an optical fiber gyroscope configuration which utilizes dual wavelength determination of the Sagnac shift is described, and it is shown that this provides a means of extending the unambiguous rotation sensing range, and thus the dynamic range.
Abstract: An optical fiber gyroscope configuration which utilizes dual wavelength determination of the Sagnac shift is described. It is shown that this provides a means of extending the unambiguous rotation sensing range, and thus the dynamic range, of the gyroscope. An increase in unambiguous sensing range ~ x 45 is demonstrated using an all-fiber gyroscope, giving an absolute dynamic range of ~ 10 6.© (1987) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

11 citations


Patent
19 Oct 1987
TL;DR: In this paper, phase errors that occur when a dithered ring laser gyroscope enters its deadband are measured, and a correction is applied to the output of the ring LM to compensate for these phase errors.
Abstract: Phase errors that occur when a dithered ring laser gyroscope enters its deadband are measured, and a correction is applied to the output of the ring laser gyroscope to compensate for these phase errors. The counterpropagating beams in a ring laser gyroscope are heterodyned to produce a pair of quadrature heterodyne signals that indicate the angular output of the laser ring laser gyroscope. The phase angle error between one of the heterodyne signals and either the sum or difference of the separate beam intensities is determined, The phase angle error signal is used to produce a control signal for adjusting the output of the ring laser gyroscope to correct for errors introduced at or near turnarounds in the dither cycle.

Patent
06 Apr 1987
TL;DR: In this paper, a polyhedron having three facets is used as the beam combiner for the gyroscope, and the beam power monitoring diodes are mounted on either side of the fringe detector facet.
Abstract: In a monolithic gyro assembly having three ring laser gyroscopes each measuring the inertial rotation of an axis, a polyhedron having three facets is used as the beam combiner for the gyroscope. On one of the facets is mounted a fringe detector for providing inertial rotation information for the gyroscope. On the remaining two facets, on either side of the fringe detector facet, are mounted beam power monitoring diodes for measuring the power of the light intensity of the respective beams. The directly measured power from the beams is then used to move a piezoelectric transducer to maintain constant pathlengths for the gyroscope.

Patent
20 Feb 1987
TL;DR: In this article, an apparatus and method for path length control for a laser gyro using two external gain cells and the shifted gain spectra of two neon isotopes is presented.
Abstract: An apparatus and method for path length control for a laser gyro using two external gain cells and the shifted gain spectra of two neon isotopes. The laser cavity is stabilized by detecting the difference in the amplification rate between the two gain cells that are traversed by two rays. Absorption cells may be used to replace the gain cells.

Patent
28 Oct 1987
TL;DR: In this paper, the scale factor errors due to retroscatter in a ring laser gyroscope are determined and used to correct the gyro scale factor by extracting a portion of both of the two counterpropagating light beams and measuring their respective intensities, creating intensity modulation indices representative of the sum and difference intensity.
Abstract: The intensity and frequency variation due to retroscatter in a ring laser gyroscope are determined and used to correct the gyro scale factor. The orthogonal types of scatter due to dielectric variation and due to height variation, which lead to common mode phase delays of 0 and π/2 respectively are taken into account in calculating the correction to the scale factor. The scale factor errors are determined in terms of observable quantities. Scale factor error control is accomplished by extracting a portion of both of the two counterpropagating light beams and measuring their respective intensities, creating intensity modulation indices representative of the sum and difference intensities, using closed loop control of the real-time difference between the intensities of the beam in the ring laser gyro to reduce scale factor variation using push-pull mirror control of at least two mirrors. The residual error after push-pull mirror control minimization is output for use by a navigation system computer.

Proceedings ArticleDOI
11 Mar 1987
TL;DR: The phase reading fiber optic gyroscope (FOG) has a scale factor which increases with the length of the optical fiber as mentioned in this paper, which makes it more sensitive to the Sagnac phase shift between two counterpropagating beams.
Abstract: The Sagnac phase shift between two counterpropagating beams is the basis for all optical gyroscopes [11, although it is detected in a variety of ways. In the ring laser gyro and various "closed loop" optical gyroscopes, the scale factor (e.g. counts per unit rotation rate) is fixed by the area of the optical medium whereas the phase reading fiber optic gyroscope (FOG) has a scale factor which increases with increasing length of optical fiber. Thus development of low-loss fibers holds the possibility of extremely sensitive gyroscope operation, and has made the FOG a competitive optical gyroscope. Although most of the first decade of FOG development has concentrated on improving sensitivity, attention is now turning to other aspects of performance.


Patent
22 Oct 1987
TL;DR: In this paper, the axial magnetic field was applied to the gain region of an out-of-plane ring laser gyroscope to shift the center of the gain profile for the clockwise right circularly polarized and anticlockwise left circularly polarizing beams.
Abstract: An out of plane ring laser gyroscope comprises a frame and a cavity formed in the frame to provide a non-planar closed optical pattern A gain medium produces two light beams propagating in opposite directions in the cavity A magnetic device applies an axial magnetic field to the gain medium to allow only light of opposite circular polarizations to lase in opposite directions The gain medium and resonant cavity alone will allow left and right circularly polarized modes to lase in both clockwise and anticlockwise directions simultaneously The application of the axial magnetic field to the gain region shifts the center of the gain profile for the clockwise right circularly polarized and anticlockwise left circularly polarized beams with respect to the gain profile center for the anticlockwise right circularly polarized and clockwise left circularly polarized beams The cavity length can then be adjusted so that lasing action in two of the four modes is suppressed leaving only modes of opposite polarization propagating in opposite directions The out of plane geometry of the cavity forces these modes to resonate at greatly different frequencies and hence prevents frequency locking over a very large range of input rotation rates

Patent
28 Aug 1987
TL;DR: In this paper, an asymmetric ring laser gyroscope includes a laser gain medium for generating a clockwise beam of coherent light and a counter-clockwise beam, such that the counter-light is parallel but oppositely directed with respect to the clock-light.
Abstract: An asymmetric ring laser gyroscope includes a laser gain medium for generating a clockwise beam of coherent light and a counterclockwise beam of coherent light, such that the counterclockwise beam is parallel but oppositely directed with respect to the clockwise beam. At least three reflectors constrain the clockwise and counterclockwise beams to propagate in a closed path. A means for detecting the frequency difference between the clockwise and counterclockwise beams is provided. An acentric photorefractive plate is positioned within the closed path such that the c-axis of the plate is parallel to the clockwise and counterclockwise beams in the plate.

Journal ArticleDOI
TL;DR: In this article, a nonplanar ring cavity was used to demonstrate polarization frequency splitting providing reciprocal bias for a multi-oscillator ring laser gyroscope, and a bias of 94 MHz was observed for a cavity with a longitudinal mode spacing of 260 MHz.
Abstract: A non-planar ring cavity has been used to demonstrate polarization frequency splitting providing reciprocal bias for a multi-oscillator ring laser gyroscope. A bias of 94 MHz has been observed for a cavity with a longitudinal mode spacing (c/L) of 260 MHz. The bias agrees well with the passive cavity splitting predicted by a Jones matrix analysis of the cavity. The application of a non-reciprocal bias, in the form of the Zeeman effect on the gain medium, has demonstrated four-mode operation in a He-Ne ring laser operating at 632·8 nm.

Journal ArticleDOI
TL;DR: In this article, the effect of noise color on the mean beat frequency of a ring-laser gyroscope was analyzed based on the matrix continued fraction technique and compared to measurements made on an electronic circuit model, and to digital simulations.
Abstract: We present a theoretical analysis of the effect of noise color on the mean beat frequency of a ring‐laser gyroscope based on the matrix continued‐fraction technique. The results are compared to measurements made on an electronic circuit model, and to digital simulations.

Patent
28 Oct 1987
TL;DR: A ring laser gyroscope uses a lasingmode suppression technique to circumvent frequency locking rather than more common frequency biasing methods as mentioned in this paper, which allows left and right circularly polarized, on-axis modes to lase when an included gaseous gain medium is electrically discharged.
Abstract: A ring laser gyroscope uses a lasing-mode suppression technique to circumvent frequency locking rather than more common frequency biasing methods. The device operates with a four-mirrored nonplanar optical path that allows left and right circularly polarized, on-axis modes to lase in each direction when an included gaseous gain medium is electrically discharged. A uniform axial magnetic field is applied to the gain region in order to produce a splitting of the gain curve into two parts separated in frequency by the cavity free spectral range. By small adjustments to the cavity length the two gain curves are centered about consecutive cavity longitudinal mode sets, each consisting of four modes. Consequently only two modes from each set can lase, thus creating a four-mode ring laser gyroscope with arbitrarily large lasing mode frequency spacings controlled primarily by the cavity geometry. The device may be configured to operate with a single isotope of neon in the gain medium. A simple magnetic field servo mechanism provides a high degree of immunity to external magnetic field charges.

Patent
01 May 1987
TL;DR: In this paper, a passive ring resonator gyroscope consisting of a single piece body having an integral first and second resonator cavity was used to measure the relative frequency difference between the CW and CCW beams by converting both servo error outputs into frequency.
Abstract: A passive ring resonator gyroscope comprising a single piece body having an integral first and second resonator cavity. The first resonator cavity contains a single frequency laser means to provide a sharply tuned single frequency light source to the second resonator cavity. The single frequency light source is sharply tuned and is split to form first and second sources. The second resonator cavity is a passive high Q cavity having a closed second optical path. The two light sources are fed to the second resonator and propagate as CW and CCW beams within the second resonator. A first servo channel tunes the frequency of the CW beam to a resonance peak. A second servo channel tunes the CCW beam to its resonance peak. By converting both servo error outputs into frequency, the relative frequency difference between the CW and CCW beams are recorded as the frequency shift in response to the body rate rotation about the sensitive axis. The first and second control signals are algebraicly added to provide a passive cavity path length difference servo signal which is integrated. A SECOND ADDER adds the integrated passive cavity difference signal to the reference signal (Fm) to provide the passive cavity path length servo signal to a passive cavity path length adjusting means for constantly adjusting the passive cavity path length servo signal to keep the passive cavity at peak resonance at a frequency substantially mid-range between the propagating (FCW) and the counterpropagating beams (FCCW).

Journal ArticleDOI
Daniel P. Johnson1
TL;DR: In this article, the effects of physical dither on a three-axis RLG system were analyzed using frequency domain analysis methods, and the authors determined the sources of these interactions and the magnitude of their contributions to system error.
Abstract: The performance of a dithered ring laser gyro on a laboratory test bench can vary significantly from its performance in a three-axis inertial navigation system. Dynamic interactions between the sensors can create unacceptable error drift rates, as well as physically influencing other instrumentation. Using frequency domain analysis methods the engineer can determine the sources of these interactions and the magnitude of their contributions to system error. In this paper we construct the frequency model and then use it to determine the effects of physical dither on a three axis RLG system.

Patent
21 Aug 1987
TL;DR: In this article, a ring laser gyroscope with a multi-layer dielectric stack and a layer having an optical thickness of a half wavelength was designed to enhance the absorption of s-polarised radiation relative to that of p-Polarized radiation.
Abstract: A mirror for a ring laser gyroscope comprising a multi-layer dielectric stack and a layer having an optical thickness of a half wavelength so as to enhance absorption of s-polarised radiation relative to that of p-polarised radiation.

Journal ArticleDOI
TL;DR: In this paper, the Saxon-Hutner result is used to suggest a method to circumvent all locking and trapping phenomena in a dithered ring-laser gyroscope.
Abstract: In this paper we discuss the possibilities to circumvent the lock-in nonlinearities in a dithered ring-laser gyroscope by random modulation. We review the Cayley matrix formulation of the theory of a dithered ring laser and show that it is particularly suitable to give both an intuitive understanding and a quantitative calculational tool for the effects of randomness on the gyroscope performance. The relationship of our problem to the related physical problems of an overdamped Josephson junction and a random atomic chain is pointed out. The Saxon–Hutner result is utilized to suggest a method to circumvent all locking and trapping phenomena in the laser gyroscope. The effects of amplitude or frequency noise are discussed, but it is found that the introduction of a randomly varying phase is most efficient in eliminating phase trapping. This can be used to provide an even distribution of the Cayley-mapping fixed points around the unit circle that provides the most even phase motion possible. The response of the gyroscope is then found to be optimally linear. All numerical calculations reported are based on the analytically solvable square-wave dither case, but, using the intuitive picture of the process provided by the Cayley transformation method, we argue that the results are qualitatively valid also in the case of a phase-modulated sinusoidal dither signal. The work is related to earlier work on ring lasers and Josephson junctions.

Patent
01 Oct 1987
TL;DR: In this article, a rectangular-parallel-piped prism is used to extract portions of the counterpropagating beams from a ring laser of a gyro, which is then transmitted to a sensor to control the length of the ring laser cavity.
Abstract: The apparatus of this invention uses a rectangular-parallelepiped prism to extract portions of the counterpropagating beams from a ring laser of a gyro. Such prism is easier to build than prisms having other than right angles. One beam bounces within the prism, but it is not perfectly reflected, and a portion of the beam is transmitted to a sensor to control the length of the ring laser cavity. The two beams are combined to produce a heterodyne signal by using two partly transmissive mirrors on two parallel surfaces of the prism, and by positioning a third side surface at a critical angle relative to one of the beams.

PatentDOI
21 Aug 1987
TL;DR: In this paper, a dither pulse eliminator for use in a ring laser gyroscope comprises a feedback circuit for demodulating a combined signal output signal and means for averaging the dither components so as to obtain residual dither error.
Abstract: A dither pulse eliminator for use in a ring laser gyroscope comprises a feedback circuit for demodulating a combined gyroscope output signal so as to obtain the dither components and means for averaging the dither components so as to obtain residual dither error. Signals dependent on residual dither error are supplied to magnitude and phase adjustment means which adjust an incoming dither signal to reduce or eliminate residual dither error.

Patent
04 Apr 1987
TL;DR: In this article, the authors proposed a waveguide for forming a ring resonator on the periphery of a substrate made of a heat resistant material, and disposing a polarizer, a phase modulator, a light source and a photodetector inside the waveguide.
Abstract: PURPOSE:To improve the environmental characteristic and to reduce the size by forming a waveguide for forming a ring resonator on the periphery of a substrate made of a heat resistant material, and disposing a polarizer, a phase modulator, a light source and a photodetector inside the waveguide. CONSTITUTION:A glass thick film 2 is formed of SiO2 on a substrate 1. Ge, Ti-doped SiO2 film 11 of approx. 5mum thick is formed on the film 2. Then, a mask 12 having 3, 6, 6 patterns is formed on the film 1. Subsequently, the film 11 except the mask 12 is etched by reactive ion etching, and waveguides 3, 6, 6 are formed on the film 2. Thereafter, recesses 13... for mounting a laser diode, a photodiode, a phase modulator are formed. Then, the laser diode 4, the photodiodes 5, 5 and the phase modulator 8 are mounted in the recesses 13, metal is deposited on the waveguides 6, 6 to become polarizers to form polarizers 7, 7, thereby obtaining a laser gyroscope.

Journal ArticleDOI
TL;DR: A new type of heterodyne fiber-optic gyroscope using orthogonally polarized light components with different frequencies is described, which allows a doubling of the Sagnac phase shift free from noise sources raised from differences in frequency and path.
Abstract: A new type of heterodyne fiber-optic gyroscope using orthogonally polarized light components with different frequencies is described. Each counterpropagating beam consists of the orthogonal components transmitted in the principal axes of a polarization-maintaining fiber coil. A pair of beat signals containing Sagnac phase shifts with opposite signs can be produced by selectively superimposing the counterpropagating components. Detection of the difference between the two beat signals allows a doubling of the Sagnac phase shift free from noise sources raised from differences in frequency and path. In a preliminary experiment, a long-term stability of 5°/h was attained.

Patent
17 Apr 1987
TL;DR: In this paper, a ring laser gyro is constructed by a cylindrical body with a ring resonator and a disk-shaped substrate with an optical element, such as a laser or the like.
Abstract: PURPOSE:To improve a temperature characteristic and increase a resolving power by constructing a ring resonator having a phase modulator around a cylindrical body composed of a material with a low coefficient of expansion and forming an optical element on a disk-shaped substrate provided on the end of the ring resonator. CONSTITUTION:A ring laser gyro 1 is constituted by a cylindrical body 2 provided with a ring resonator and a disk-shaped substrate 3 provided with an optical element, such as a laser or the like. Both the cylindrical body 2 and substrate 3 are made of a material with a low coefficient of thermal expansion, such as quartz, saphire, ceramics or the like, and united by adhesion. A thin film wave directing path 4 made of quartz glass or the like that constitutes the ring resonator is formed around the outer circumferential surface of the cylindrical body 2. In the approximately middle intermediate position, a phase modulator 5 is provided. Due to such structure, the ring resonator can have a sufficiently large optical path length, a resolving power is high, a temperature characteristic is stable and reliable and the size of the whole apparatus can be reduced.