Showing papers on "Ring laser gyroscope published in 1985"

The ring laser gyro

Abstract: This paper presents a review of both active and passive ring laser devices. The operating principles of the ring laser are developed and discussed, with special emphasis given to the problems associated with the achievement of greater sensitivity and stability. First-principle treatments of the nature of quantum noise in the ring laser gyro and various methods designed to avoid low-rotation-rate lock-in are presented. Descriptions of state-of-the-art devices and current and proposed applications (including a proposed test of metric theories of gravity using a passive cavity ring laser) are given.

Closed-loop fiber-optic gyroscope with a sawtooth phase-modulated feedback.

Abstract: Theoretical and experimental investigations of a closed-loop fiber-optic gyroscope are reported. Phase nulling is accomplished by applying a sawtooth modulation to an integrated-optic phase modulator located at one side of the sensing loop. The frequency of the phase modulation is proportional to the rotation rate, thus permitting a digital readout. The influence of a finite flyback period on the scale factor is investigated.

Borehole inertial guidance system

Abstract: In order to improve the accuracy of borehole survey systems utilizing probes (18) with inertial components including inclinometers (32, 34, 36), two ring laser gyro units (42, 44) are included to provide rotation information to the system. When the probe (18) is moving in a borehole (12), inclinometer information is used to produce a synthetic rotation signal to take the place of a third gyro and the earth's rotation is used for a similar purpose in combination with signals from the two ring laser gyros (42, 44) when the probe (18) is stopped. Wire line velocity is used in combination with the inclinometer and gyro information to provide signals representing the probe velocity and position. Coordinate transformations are provided in the probe to transform the inertial signals and wire line velocity signals into earth reference coordinate system. Kalman filtering incorporates noninertial velocity data to reduce the effect of errors inherent in the generation of various input signals to the system.

Inertial reference system

Abstract: An inertial sensor assembly (ISA) includes a cluster of three ring laser gyros, each gyro producing an output signal having a pulse repetition rate representative of the rate of angular deviation of the ISA about one of three coordinate axes X, Y, and Z. The ring laser gyros are synchronously dithered at a relatively constant rate. The ISA also includes a triad of three accelerometers, with each accelerometer producing an output signal representative of the rate of velocity deviation of the ISA along one of the X, Y, and Z coordinate axes. A first processor, P1, accumulates the pulses produced by each ring laser gyro over its dither period. The resultant counts are stored in registers for subsequent sampling by the P1 processor at a periodic sampling rate which is greater than the dither rate. The P1 processor then synchronizes each sampled pulse count to a common sampling interval, thereby eliminating errors otherwise caused by using positional data values taken at different times. The P1 processor also compensates the ring laser gyro and accelerometer-produced signals at the sensor and the system level for effects such as temperature, bias offsets, scale factor and misalignment by the use of compensating coefficients stored in electrically erasable, programmable read-only memory. The processed data from the P1 processor are passed to a P2 processor which performs navigational computations to thereby produce computed positional information.

The Multioscillator Ring Laser Gyroscope

Abstract: The multioscillator (or four-frequency) ring laser gyroscope is discussed from both a theoretical and a practical point of view. Fundamentals of device operation are presented, important nonideal behaviors (error sources) are discussed and analyzed from first principles, typical multioscillator gyroscopes are described, and samples of representative data from developmental instruments in our laboratories are reviewed. A key to the development of practical multioscillator instruments has been the introduction of nonplanar ring resonators. The theoretical formalisms (geometric and wave optic) necessary for understanding the properties of nonplanar ring resonators, and nonplanar gyroscopes, are derived and discussed in detail. Much of the material presented is new.

Resonant waveguide laser gyro with a switched source

Abstract: Passive ring resonator laser gyro. The gyro eliminates the need for separate frequency control devices for the two counter propagating beams. A semiconductor laser diode, the source, is switched between two frequencies and its output is coupled into a branching waveguide. The light in the waveguide is coupled into a resonant ring waveguide and then sampled by detectors. The laser current is switched at a fixed rate between two values. The values are selected such as to cause the laser output to switch between the resonant frequencies of the two directions of propagation in the ring. These values are determined by a resonance tracking servo. The disclosed laser gyro eliminates the need for active frequency controlled devices in the waveguide structure resulting in less noise, better signal, and reduced cost.

Ring laser gyro readout assembly simplification with adjustment capability

Abstract: A readout apparatus responsive to clockwise and counter-clockwise counter-rotating light beams that have a frequency difference relatable to the rate of rotation of a ring laser gyroscope, the readout apparatus comprising means for removing a portion of the light beams from the ring of the ring laser gyroscope; means for displacing the removed counter rotating beams to overlap a portion of the light of the removed beams to form a first spot beam having fringe motion characterized by an array of co-parallel alternating stripe regions of high and low intensity light within the spot; a mask having an array of co-parallel, rotated, alternating transparent and opaque stripes; the mask being positioned to direct the fringe motion of the spot beam through the mask, the mask array of alternating and opaque stripes being aligned to form a second spot beam having a moire fringe motion characterized by an array of co-parallel alternating stripe regions of high and low intensity light within the spot moving transverse to the fringer motion of the spot beam; means for receiving the second spot beam and for detecting the moire fringe motion within the second spot beam characterized by an array of co-parallel alternating stripe regions of high and low intensity light within the spot moving transverse to the fringe motion of the first spot beam.

Ring laser gyro path-length-control mechanism

Abstract: Piezoelectric discs are mounted within conical members, one of which is contact with a mirror. Electrodes are applied across the piezoelectric discs. Voltage applied to the electrodes cause the diameter of the disc to contract deforming the conical members and moving the mirror. The conical members provide mechanical amplification resulting in mirror movements to control the path length in a ring laser gyroscope.

Electronic dither compensator for a ring laser gyro

Abstract: An electronic dither compensator for a ring laser gyroscope uses a velocity pickoff to eliminate the need for a differentiator following a displacement pick off in order to get a rate signal. The dither pickoff is converted, in a voltage to frequency converter, to a pulse train which is synchronized with the pulse train of the uncompensated input from the gyro detector. An automatic gain control with an amplitude control loop is provided. The pulses from the voltage-to-frequency converter and uncompensated inputs are synchronized and summed and differenced as selected by means of logic to produce gyro output pulses free from the effects of dither rate.

Laser angular rate sensor with dithered mirrors

Abstract: A laser angular rate sensor has four corner mirrors forming a substantially square ring laser to reflect two counterpropagating laser beams around a closed path. Dither vibrators are interconnected to two consecutive mirrors in the path to oscillate perpendicularly to their mirror surfaces with 180 degree phase opposition. In one embodiment the mirror displacement is controlled to an amplitude of substantially 0.541 times the wave length of the laser light. In a second embodiment the mirror displacement amplitude is controlled to minimize the alternating component beat amplitude between one of the two laser beams and light scattered by the mirrors from the other beam. A microprocessor responsive to the output beat frequency of the ring laser gyro disconnects the dither drives when the amplitude of the input angular velocity to be measured exceeds a predetermined value greater than the maximum limit of the lock-in range of the gyro.

Theory of a dithered-ring-laser gyroscope: A Floquet-theory treatment.

Abstract: This paper discusses the properties of a periodically dithered-ring-laser gyroscope in the approximation of a single phase-locking equation. We discuss both modulation of the input rotation, the phase of the backscattering, and its amplitude. The first two are found to be mathematically equivalent, and the last case is found to offer no advantages as compared with the undithered case. These conclusions are supported by a heuristic argument. The detailed mathematical treatment is based on Floquet theory, which allows us to obtain results by integrating over one dither period only. The locking condition can be determined from the Floquet exponent. For large input parameters the integration of the differential equation for the Floquet problem becomes numerically overwhelming, and the equivalent formulation in terms of an infinite matrix is utilized. This is evaluated using a method based on matrix continued fractions. In this way no restrictions on the parameters are necessary. The method is applied to the single-frequency dithering, and it is confirmed that the locking at zero rotation rate can be completely eliminated. The calculations also confirm the existence of higher-order lock-in zones, which are large just in those conditions which are optimal near zero rotation rate. Thus we conclude that with sinusoidal dither of one frequency it is not possible to avoid nonlinearities in the gyroscope response. In forthcoming publications we intend to discuss possible schemes to overcome this difficulty.

Pentagonal ring laser gyro design

Abstract: A ring laser gyroscope incorporates a resonant cavity generally shaped as an irregular pentagon having a portion thereof conformed as three legs of a rectangle closed by two symmetrical other legs to form an apex. As result the enclosed area is increased, increasing sensitivity and decreasing lock-in, while magnetic effects are reduced. Additionally, the irregular shape allows for the extension of the gain medium which therefore increases the effectiveness thereof.

Phase modulation fiber optic gyroscope

Abstract: A phase modulation type fiber optic gyroscope having a greatly improved output stability without a large increase in the number of basic components of the gyroscope system. In accordance with the invention, the d.c. component of the output of a light detecting element which provides the two circulating beams is sensed and employed to control the output of the light-emitting element so as to be constant.

Compensated dual cavity laser gyro

Abstract: A laser gyro has two adjacent laser cavities which are parallel and separated so that there are no common parts between the respective mode volumes. Each cavity supports a wave traveling in only one direction. Passive optical means external to the cavities are provided for establishing these directions of travel. Additionally, the passive means allows quick reversal of these directions of travel, which allows for the compensation of all frequency shifts which are not proportional to rotations. The passive reversal is accomplished with an optical element that is controlled to act alternately as a window and then as a mirror for light of only one wavelength. The gyro produces two output waves whose frequencies are shifted in opposite directions by rotation. The two frequencies are mixed and the resultant beat frequency is detected by optical heterodyning. The response is a linear output signal. Very low rotation rates may be sensed down to zero rotation and its accuracy is limited by quantum effects.

Apparatus for measuring differences in resonant frequencies of optical resonators.

Abstract: A laser gyroscope incorporates a toroidal resonator (36). Excitation waves are produced by a laser (10). The intensity of the laser beam (12) is modulated by a laser current modulator (14). The modulation frequency f1 is controlled in such a way that side bands f0-f1 and f0+f1 are forced to follow the resonance frequencies of the toroidal resonator (36) for left-handed and right-handed light if the resonance frequency f0 splits as a consequence of an inertial angle velocity due to the Sagnac effect. The modulation frequency then provides the measure of the angular velocity.

Ring laser gyro tilt mirror dither

Abstract: A tilt mirror dither for a ring laser gyro to eliminate lock-in at low rates of rotation. The tilt mirror dither includes means (36, 38) for vibrating two of the ring laser gyro mirrors (30, 28), each in a rotational mode about an axis to tilt the mirrors back and forth, the mirrors being vibrated at the same frequency but 180o out of phase to maintain the path length of the laser beams constant. In one embodiment (Fig. 2A) an up-down tilt mirror dither is provided and in another embodiment (Fig. 2B) a side-to-side tilt mirror dither is provided.

Two servo loop passive ring laser gyroscope

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 tunes the frequency of the linear laser to the resonance peak of the CW beam in the second resonator. A second servo means is provided to shift the frequency of 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 second resonator cavity is located and dimensioned in relation to the first resonator cavity to have similar path length changes in response to the induced body dimension changes.

Path length adjuster for ring laser gyro

Abstract: Apparatus for maintaining the length of a ring laser path and of its branches substantially constant during temperature and stress changes, using forcers directed outward toward the apexes of the ring laser and perpendicular to the laser path.

Optical fiber laser gyroscope

Abstract: PURPOSE:To simplify the constitution, by splitting light from a linearly polarized light source by a semitransparent mirror made of a thin metal film, which is arranged at a specified angle, inputting the light beams into both end surfaces of an optical fiber, making the reflected light beams interface through the semitransparent mirror, and giving the phase difference of 90 deg CONSTITUTION:Incident light (b) from a semiconductor laser 1 for linearly polarized light is split into a reflected light beam b1 and a transmitted light beam b2 by a semitransparent mirror 5 made of a thin metal film Both light beams b1 and b2 are inputted to both end surfaces of an optical fiber 6 having polarization-plane maintaining characteristic The output light beams b'1 and b'2 are inputted to the mirror 5 again The obtained interference light beam b3 is received by a light receiving element 4, and an angular velocity of rotation OMEGA is obtained At this time, the incident angle of the light (b) to the mirror 5 and the reflecting angle phi are made to be set at 75 deg The phase delay after the reflections of two times is made to be 90 deg The phase delay after the transmissions of two times is made to be 0 The phase difference of the light beam b3 is made to be 90 deg Thus the sensitivity when the angular velocity is 0 is made maximum, and conventional constituent elements to be added can be omitted

Theory of a dithered-ring-laser gyroscope. II. Cayley transformations and square-wave dithering.

Abstract: This paper reformulates the problem of a dithered-ring-laser gyroscope as a mapping of points on the unit circle onto other such points. These mappings are represented by Cayley matrices. The relationship to our earlier Floquet theory is established, and it is shown how the properties of the mapping determine the lock-in behavior and the dynamics of the system. With square-wave dithering the mapping can be calculated analytically, and the expression allows rapid numerical exploration of the behavior in various regimes of operation. The Cayley transformation method is found to offer a convenient and intuitively transparent way to handle the locking phenomenon in a dithered ring laser.

Circuit for increasing the resolution of a laser gyroscope with clock synchronization

Abstract: A laser gyroscope signal generator for increasing the resolution of the gyroscope, the signal generator being responsive to a sequence of pairs of phase shifted first and second laser gyroscope output pulses each being characterized to have a first and second laser gyroscope output pulses each being characterized to have a first and second logic state, said first and second output pulses in each pair having a leading or lagging phase relationship determined by the direction of rotation the laser gyroscope sourcing said pairs of phase shifted output pulses, the laser gyroscope output signal generator also being responsive to a system clock signal source for providing a clock signal having a pulse recurrent frequency greater than the pulse recurrent frequency of said phase shifted first and second laser gyroscope output pulses, the output signal generator comprising: a memory means responsive to said phase shifted first and second LGO (laser gyroscope output) pulses and said clock signal for transferring the logic state of each respective LGO pulse into a memory in synchronization with clock signal and for providing a clock cycle synchronized first and second LGO pulse and the complement of said second synchronized pulse LGO synchronized second LGO pulse; a first means responsive to said first and second clock synchronized LGO pulse for providing a first exclusive-OR signal characterized as the exclusive-OR of said first and second clock synchronized LGO impulse and for providing a complement second clock cycle delayed first exclusive-OR signal; and a second means responsive to said first synchronized LGO pulse and said clock signal for providing a second clock cycle signal delayed synchronized first LGO pulse.

Multiple ring laser gyro power supply

Abstract: Prior power supplies adapted to provide power to the lasers of multiple ring laser gyros were inefficient in that they were required to have power output capabilities far in excess of that required to sustain laser operations. Such inefficiency is greatly reduced by the present power supply comprising a DC power source (30) for producing a firing voltage at a first terminal (40) and a sustaining voltage at a second terminal (42), and interface means (50) associated with each laser (12, 13, 14) for coupling the laser to the first and second terminals. The firing voltage is capable of firing each laser, and the sustaining voltage is capable of sustaining current flow through each laser after firing. Each interface means comprises a resistor (52, 53, 54) connecting the laser to the first terminal and a diode (55, 56, 57) for connecting the laser to the second terminal such that the diode does not permit current flow between the first and second terminals.

External mirror type gas laser tube

Abstract: PURPOSE:To obtain the titled laser suitable for ring laser gyroscope by a method wherein a discharge outlet is provided in the neighborhood of the center of a laser fine tube, and anodes in the neighborhood of Brewster windows at both ends, respectively; then the discharge outlet is arranged at the center of the cylindrical cathode in a vacuum casing. CONSTITUTION:The anode 5' is buried also in the neighborhood of the Brewster window 3' of the laser fine tube 1, anodes thus being provided in a total of two, and the discharge outlet 2'' is arranged at the center of the anode 6, i.e., nearly at the center of the fine tube. The construction of other parts is almost the same as that of the conventional laser tube. This construction brings gas flows 12 and 12' due to DC discharge which direct to the cathode from the anodes 5 and 5' in symmetry, and therefore the variation in the frequency of a laser beam passing through the laser fine tube is cancelled. Accordingly, in the case of constructing the external mirror type ring laser gyro, a piece of laser tube is sufficient, and the structure and the adjustment of the device are simplified.

Ring laser gyro with randomized mirror dither

Abstract: A ring laser gyro employing a periodic primary dither to eliminate lock-in at low rates of rotation and a random secondary dither to eliminate residual lock-in. The primary dither is provided by a dither motor (36) coupled to the body (10) of the gyro and responsive to a sine wave drive signal to vibrate the gyro body in a rotational mode. The secondary dither is provided by randomly vibrating two of the laser gyro mirrors (28, 30) in a direction perpendicular to the face of the mirrors and in a complementary manner to maintain constant the length of the path traveled by the beams.