Showing papers on "Ring laser gyroscope published in 1984"

Phase-reading, all-fiber-optic gyroscope.

Abstract: An open-loop, all-fiber-optic gyroscope with wide dynamic range and linear scale factor is described. This novel approach converts the Sagnac phase shift into a phase shift in a low-frequency electronic signal by using optical phase modulation followed by amplitude modulation of the electronic signal. Preliminary experimental results verify the theoretical predictions.

Pseudo-heterodyne detection scheme for the fibre gyroscope

Abstract: The results of a preliminary investigation of a phase-swept pseudo-heterodyne scheme suitable for use with all-fibre versions of the fibre gyroscope are presented. The output carrier, which is phase-modulated by the Sagnac shift, is generated by employing a sinusoidal phase modulation via a piezoelectric fibre stretcher in combination with selective detector gating

Gated phase-modulation approach to fiber-optic gyroscope with linearized scale factor.

Abstract: A phase-modulation approach to closed-loop fiber-optic gyroscopes is described that uses an all-fiber gyroscope, which can provide a linearized scale factor. Preliminary experimental results with manual closing of the feedback loop show good linearity in the scale factor. This approach has, in theory, an inherent suppression of source-wave- length dependence of the scale factor.

Fibre gyroscope with passive quadrature detection

Abstract: A novel configuration for the optical fibre gyroscope is described which utilises highly birefringent fibre and polarisation mode selection to achieve a stable π/2 bias. By operating the system using a combination of both the unbiased and π/2 biased Sagnac outputs, the possibility of wide dynamic range operation is realised.

All-fiber gyroscope with polarization-holding fiber

Abstract: An all-fiber gyroscope is reported that is constructed entirely of polarization-holding fiber. The random-drift coefficient was 5 x 10(-3) deg/ radicalh. Gyro bias drift is shown to be stable over periods of hundreds of hours. Device construction details and some thermal dependence of components are given.

Path length controller for ring laser gyroscope

Abstract: A ring laser gyro path length controller has a cup-like fixture which mounts a piezoelectric actuator and is bonded directly to the gyro block. A mirror assembly is concentrically located within the fixture and is independently mounted to the gyro block thereby enabling independent assembly and disassembly of the fixture and the assembly. Diaphragm sections of the assembly are coaxially positioned and connected to a diaphragm section of the fixture so that bidirectional displacement of the assembly may occur and the moment generated by the actuator results in an axial deflection force on the assembly. A strip of material having a high coefficient of expansion is mounted to the piezoelectric actuator to augment the deflection force as temperature increases thereby reducing the power demands of the actuator.

Fiber gyroscope with phase-modulated single-sideband detection.

Abstract: Phase-modulated single-sideband detection is applied to a fiber gyroscope. The Sagnac phase is linearly transposed into the phase of an electrical low-frequency signal by using an integrated-optic phase modulator, which is driven by a proper modulating waveform. This detection scheme can provide a high dynamic range. The principle and first experimental results are reported.

Fiber Optic Gyroscopes

Abstract: Inertial guidance and navigation systems are known to be very useful for aircrafts, missiles, land vehicles, robots… For the moment, they make use of mechanical gyroscopes or gas laser gyroscopes. Now the development of low-loss optical fibers and compact and reliable semi-conductor light sources for the telecommunication industry has made possible a new approach: the fiber-optic gyroscope [l, 2, 3]. This device is only composed of low-mass solid-state components-and does not require any mechanical movement (this is still the case with laser gyros which need dithering to solve their lock-in problem about zero rotation).

Method and apparatus for reducing quantization error in laser gyro test data through high speed filtering

Abstract: The use of a high speed moving average filter is shown to filter high speed errors, including white noise in angle and quantization errors, from the output data of a ring laser gyro while it is being tested. The filtered data permits investigation of the lower speed, random walk in angle error of the gyro being tested. For best results, several moving average filters are connected in series.

Thin film passive ring resonator laser gyro

Abstract: Passive ring resonator laser gyro in which the clockwise and counterclockwise beams do not coexist in the resonator. The laser gyro employs thin film technology. In particular, the preferred laser is a gallium aluminum arsenide laser. Light from the laser is phase-modulated by means of a thin film electro-optic modulator comprising a channel waveguide disposed on an electrically active material and flanked by electrodes for modulating the phase of light from the laser. An electro-optic switch is provided for switching light from the laser to inject alternatingly clockwise and counterclockwise beams into the resonator. The resulting gyro is extremely compact and simply implemented into an integrated, thin film package. Because the clockwise and counterclockwise beams do not coexist in the resonator, various beam interaction effects such as beats, backscatter and feedback into the laser are eliminated.

Laser Gyro Dither Random Noise

Abstract: The error angle created when an alternating bias is used to bias the laser gyre is given for different operating conditions. These conditions are defined by the time required to reverse the biase angle by one count. 1. Slow dither--where the time for reversal is long (i.e., greater than a "characteristic time" of the inverse of the lock-in frequency). 2. Fast dither--where the frequency and reversal rates of the gyro bias are very high (i.e., the time for reversal of a count is less than the "characteristic time"). 3. Very fast dither--where the reversal of the bias rate is virtually instantaneous (less than the time for one count, i.e., 1/F output). This is referred to as square wave dither.

Open loop thin film laser gyro

Abstract: The laser gyro includes a laser and a ring resonator. Apparatus is provided for coupling counter-propagating beams of light from the laser into the resonator. The frequency of the laser is scanned across the resonance frequency of the resonator in steps superimposed on a dc level. The intensity of light in one of the counter-propagating beams is detected during each of the steps and the difference in intensity of the detected light is determined. The difference in the intensity of the detected light is used to alter the dc level of the steps so as to drive the difference to zero. The intensity of light in the other of the counter propagating beams is detected during each of the steps and the difference in intensity is also detected. This difference is indicative of the rotation rate of the gyro.

History Of The Laser Gyro

Abstract: The ring laser gyro had its beginning with the observation that rotation removed the degeneracy between the clockwise and the counterclockwise traveling waves in a resonant cavity, and that the frequency difference was directly proportional to the angular rotation rate l. The measurement of rotation by the interference of electromagnetic waves in non-resonant or non-reentrant structures was recognized more than a half century earlier in 1897 by Oliver Lodge2. His research apparatus which is shown in Figure 1 consisted of mirrors at the corners of a 1 m x 6 m rectangle, light source, semi-transparent plate, and telescope, and was used in his study of the drag of the ether by rotating steel discs. In his negative comments concerning ether drag, he included the following comment. "Hence if, --, the whole apparatus, lantern, optical frame, telescope, observer and all were mounted on a turntable and caused to rotate, a reversible shift of the bands should be seen. ----The effect would be of an aberrational kind, the opposite light beams being accelerated and retarded by the motion appropriately.----My present optical apparatus mounted on a turntable revolving 4 times a minute should show something, viz.: 1/100th band shift each way. A certain amount of discomfort during the accelerative stages of any speed could hardly be avoided, and even

Lock-In Growth In A Ring Laser Gyro

Abstract: In a Ring Laser Gyro (RLG), because of coupling of the clockwise and counterclockwise rotating beams of light, at low input rotation rate, the frequencies of the two lock together causing the lock-in phenomenon. Both theory and experiments-have explained this lock-in phenomenon as due to mirror backscattering. Mirror backscattering comes mainly from mirror surface and coating imperfections. In RLG application, lock-in, characterized by SQL, the rotation rate below which the gyro output is locked, affects performance in several ways. First of all, it creates a dead band where the gyro does not operate, secondly, it affects scale factor linearity and stability; and thirdly, in a mechanically dithered RLG, it contributes directly to the increase in angular random walk noise in gyro output. The understanding and reduction of SQL is therefore very important in RLG technology.

Ring laser gyro

Abstract: PURPOSE:To obtain a ring laser gyro, which has no degradation in reliability due to the problem of coupling for taking out an output and is suitable for mass production, by forming specific ring lasers, an output waveguide, a light detector, and a nonreflecting terminal in the same substrate. CONSTITUTION:Y branches 11a and 12a having directivity are provided in ring lasers 11 and 12 so that they are oscillated only in the reverse direction each other. They are not oscillated to the other directions since propagation loss is large. The ring laser 11 is oscillated only in the clockwise direction, and the ring laser 12 is oscillated only in the counterclockwise direction. An output waveguide 13, which forms a directional coupler that is coupled to both ring lasers 11 and 12, is provided between the two ring lasers 11 and 12. The parts of the outputs of the ring lasers 11 and 12 are taken out and synthesized, and the result is guided to a light detector 15. At the other end of the output waveguide 13, a nonreflecting terminal 14, which absorbs the reflection from the light detector 15 and natural emitted light from the ring lasers 11 and 12, is provided.

Simplified readout optics for a ring laser apparatus

Abstract: An optical readout arrangement features a unitary optical element which serves both as a substrate for the corner mirror of the ring laser gyro and as a prismatic beam folding and combining arrangement for the readout elements.

Pathlength controller for ring laser gyroscope

Abstract: The present invention provides for initializing the particular intensity peak selected to operate about, based upon the initial temperature of the gyroscope in order to maintain a selected integer number of wavelengths as the initial cavity path length from start up to start up. In addition, the present invention provides an optimum available movement of the mirrors due to changing the voltage over the available voltage swing for the anticipated range and direction of temperature changes from the start up temperature, over which the gyroscope is expected to operate.

A 58 m 2 Passive Resonant Ring Laser Gyroscope

Abstract: A description of the elements of a 7.62 m x 7.62 m Passive Ring Resonator Laser Gyro (PRRLG) is given. Predicted performance of the device is shown to be in the 3 x 10 -8 to 4 x 10 -10 earth rate unit (ERU) range.

Ring laser gyro detector lens system

Abstract: A ring laser gyroscope detector lens system for mounting on a ring laser gyroscope body having a resonant cavity. The ring laser gyroscope body has CW and CCW counterpropagating light beams propagating in a plane normal to the rate input axis of the ring laser gyroscope. The ring laser gyroscope detector lens system comprises a means for extracting a component of each of the CW and a CCW light beams from the cavity and for providing extracted CW and CCW beams. A means for combining the extracted CW and CCW beams to form an interference light source receives the extracted light. A planar array of detector element receives light from an objective lens means responsive to the interference light source. The objective lens means is typically a cylindrical lens that forms an interference light source pattern on the planar array of detector elements. A bias and amplification means is provided for conditioning each of the detectors in the array to be independently responsive to incident light intensity. The amplification means is further characterized to provide a detector output signal for each respective detector in response to the incident light intensity penetrating a predetermined threshold. The phase relationship between the detector output signals and the repetition rate of the detector output signals characterize the rotational polarity and rotational rate of the ring laser gyroscope body on the input axis.

Out-Of-Plane Laser Gyro Configurations And Magnetic Biases

Abstract: Nonplanar active ring laser cavities and their uses for the gyro builder are discussed and it is shown how a slightly nonplanar configuration may create magnetic sensitivities and how they may be controlled. Another origin of magnetic biases in both square and triangular ring laser gyros, namely stress-induced linear birefringence in the gyro mirrors, is examined and possible experimental arrangements for measuring the size of birefringences produced by stress in mirrors suggested.

Analog fiber gyro with extended linear range

Abstract: A gyroscope system for obtaining an extended linear dynamic range for platform rotation rate measurements comprising a first fiber optic gyroscope with a first optical fiber coil described by a first quantity L 1 R 1 /λ 1 where L 1 is the length of the first optical fiber coil, R 1 is the radius of the first fiber coil, and λ 1 is the light source wavelength, this first quantity being chosen to provide a linear output for a first range of small rotation rates of the platform; a second fiber optic gyroscope with a second optical fiber coil described by a second quantity L 2 R 2 /λ 2 with this second quantity being chosen to provide a linear output for a second range of large rotation rates of the platform, with this second range partially overlapping the first range; voltage controlled oscillators for converting the gyroscope signals to pulse frequency signals; a circuit for determining whether a reference rotation rate within the overlap between the first and second ranges has been reached and generating a control signal in accordance therewith; a pulse counter; and a switch for switching one or the other of the pulse frequency signals to the pulse counter in accordance with the control signal so that a gyroscope which is operating within its linear range is utilized.

A discussion of coning errors exhibited by inertial navigation systems

Abstract: : The mechanisms by which so called 'coning errors' occur in a strapdown inertial navigation system are explained by reference to a single mathematical theorem. Typical values of coning errors are derived and ae shown to be significant for a 1 nm/h inertial navigator. Various methods of evaluating and reducing coning errors are discussed. Originator-supplied keywords include: Dither; Ring laser gyroscope; and Vibration.

Multiple axis ring laser gyroscopes

Abstract: In a multiple axis ring laser gyroscope in which one or more of the laser cavity corner mirrors is or are shared by different cavities and in which the laser beams in these different cavities operate at the same nominal frequency, scattering of the beam in one cavity into another cavity by the shared mirror(s) may produce disadvantageous lock-in effects. To at least lessen this possibility, the frequencies of the beams in the gyroscope disclosed herein are offset one from another, the offset being sufficient to affect lock in but not so great that the frequency of any beam is overly far from the lasing medium gain curve center. The frequency offsets may be produced by introducing offset bias signals into some channels of the gyroscope path length control servosystem.

Autofocus Motion Compensation for Synthetic Aperture Radar and Its Compatibility with Strapdown Inertial Navigation Sensors on Highly Maneuverable Aircraft

Abstract: : This thesis investigated the feasibility of using state-of-the-art strapdown inertial navigation systems to motion compensate synthetic aperture radar aboard highly maneuverable aircraft. The applicable equations were first derived to obtain a comparison between inertial navigation system capabilities and synthetic aperture radar motion compensation requirements. Both turned gyro and laser gyro systems were investigated to determine the applicability for the task. The autofocus motion compensation technique was studied to determine if its range and squint angle boundaries could be improved by the use of highly accurate strap-down inertial navigation system measurements. It was determined that state-of-the-art strapdown inertial systems have the capability to motion compensate synthetic aperture radars in maneuvering aircraft and can improve the range and squint angle boundaries using the autofocus motion compensation technique. The results illustrate the ability of tactical aircraft to obtain high resolution imagery, as well as navigation and target information, while maintaining the low life-cycle cost of strapdown technology.

Phase-Conjugate Ring Gyros And Photorefractive-Biased Ring Gyros

Abstract: We consider two types of ring gyro operation which are designed to reduce the lock-in threshold and to bias the gyro away from the dead band, respectively In the phase-conjugate ring gyro, the two lasing modes are coherently coupled and mutually phase-conjugated The coherent phase relationship between the two modes provides the basis for resisting the frequency pulling due to backscattering In the photorefractive-biased ring laser gyro, the nonreciprocal optical transmission leads to a split in both oscillation frequency and intensity This splitting provides the bias for operation away from the dead zone

Reduction Of Beam Coupling In A Ring Laser Gyro By Doppler Shifting Of Scattered Light

Abstract: We report here the successful reduction of the lock-in band of a triangular ring laser gyro by dithering two flat diaphragm mirrors 180 degrees out of phase along their normals. This causes a frequency shift of the backscattered light of each beam out of the capture band of the counterpropagating beam. After properly matching the phase and amplitudes of the mirror drives we obtained a residual lock-in roughly two orders of magnitude below the undithered value. A quantitative explanation of this result is given.

Laser gyro device

Abstract: A laser gyro for detecting rates of rotating the gyro having a primary dither means for eliminating lock-in at low rates of rotation and a secondary dither means for eliminating nonlinearities in the gyro output when the input rate is a harmonic of the primary dither frequency The gyro includes a body having a polygonal shaped cavity therein with a mirror disposed at each of the corners thereof to form a closed loop path for two counter-rotating beams The primary dither includes means for dithering two mirrors 180 DEG out of phase to maintain the cavity path length constant The secondary dither includes a current dither for differentially modulating the current in each leg of the gyro to randomly null nonlinearities in the gyro output