Litton Systems, Inc.

Virgil E Sanders

Thomas J Hutchings

Dana Z Anderson

A ring laser gyroscope is described having two counterpropagating primary modes and one or more secondary laser modes having a component c cos .omega. t to produce a dithering effect which reduces or eliminates the lock-in range of the primary modes. The ratio of c to .omega. is controlled to minimize J.sub.o (c/.omega.) wherein J.sub.o is the Bessel Function of the first kind of zero order. In one embodiment, cavity length control circuitry is adjusted to detune the cavity length to allow two secondary opposing modes of angular frequency separation .omega. to be generated within laser gain medium in the cavity while two primary counterpropagating modes operate well above threshold. Another embodiment has an external laser beam source for generating two secondary waves, at two light frequencies separated by an angular frequency .omega., which are introduced into the ring laser path through a partially transmitting mirror which forms one of the corners of the ring laser closed loop path. In still another embodiment, part of one of the primary waves leaves the ring laser path through a partially reflective mirror and is acted upon by a mirror oscillating at an angular frequency .omega. which doppler-shifts the frequency of the extracted wave. This doppler-shifted mode is reintroduced into the ring laser path to diminish the range of lock-in frequency of the primary modes. In all embodiments, the magnitude of the ratio of c/.omega. is controlled to minimize J.sub.o (c/.omega.) to reduce the range of lock-in of the primary modes.

Laser gyro mode locking reduction scheme

A Zeeman ring laser gyro is described which includes a laser medium of helium-neon consisting of dual isotopes of Ne.sup.20 and Ne.sup.22 in which 53.5% is Ne.sup.20 and 46.5% is Ne.sup.22 by volume. The laser also includes a reciprocal anisotropic dispersion element of quartz which optically splits right and left circularly polarized laser waves by 250 MHz. The portion of the laser cavity in which laser emission is stimulated is exposed to a colinear magnetic field of 30.sub.-20.sup.+10 gauss. The combined optimum parameters produce a laser gyro insensitive to changes in detuning frequencies and magnetic fields.

Zeeman multioscillator ring laser gyro insensitive to magnetic fields

A nonplanar ring laser for use as a laser gyro includes an even number of at least six reflecting surfaces which are preferably all made from the same coating batch or coating run so that they have substantially the same anisotropy characteristics. The mirrors are divided into pairs of mirrors, and the mirrors in at least each pair must match in their anisotropic characteristics. Note that the matched mirrors need only be in the laser path but not necessarily adjacent. The nonplanar geometric arrangement of the reflecting surfaces is such that the reflecting plane of incidence of each mirror is at substantially a right angle to the reflecting plane of incidence of at least one of the adjacent mirrors in the laser path. Note that the reflecting plane of incidence of each mirror may optionally be at right angles to the reflecting planes of incidence of both its adjacent mirrors in the laser path. The angles of incidence of the mirrors in each matched pair must be substantially the same. Using this geometry, and at least the mirrors in each matched pair being from a single coating batch having the same anisotropy characteristics, the phase and attenuation shifts which are introduced by imperfect coatings are cancelled in the ring laser cavity. Due to the substantial reduction in phase and attenuation anistropy this ring laser configuration reduces coupling between the two modes travelling in the same direction when used in a multioscillator laser gyro, and therefore improves gyro performance.

Isotropic nonplanar ring laser

A ring laser gyroscope system is provided in which four frequencies of oscillation are allowed to simultaneously propagate within the ring laser cavity, with two modes propagating in each direction. Separation of the resonant frequencies is accomplished through reciprocal, nonreciprocal, and anisotropic optical effects within the laser path, plus Zeeman effect produced by a magnetic field in a predetermined intensity range over the laser gain plasma. The magnetic field substantially parallel to the laser path over the gain medium reduces the effects of hole burning or source depletion when the amplitudes of the field is within a predetermined intensity range to allow frequencies of the four modes to be spaced closer together. The system employs cavity length control circuitry to optimize system output. Rotation of the system results in frequency changes which are detected and processed to yield inertial rotation information.

Four mode Zeeman laser gyroscope with minimum hole burning competition

A four mode ring laser gyro has its four modes at different frequencies combined and applied to a single photo diode. The output from the photo diode is applied to a non-linear device, and the resultant sum and difference frequencies are applied to (1) a laser cavity length control circuit, (2) a rotation rate detection circuit, and (3) a rotation direction determination circuit. The cavity length control circuit operates by the determination of 100% modulation of one of the beat frequencies by a second one. The direction determination circuit utilizes the phase of an AC dithering power supply which varies the anode to cathode plasma current of the laser gyro.

Multioscillator ring laser gyro output information processing system

A compact and reliable dithered laser gyro utilizes a rectangular laser path geometry to reduce scattering and thereby improve anti-locking capabilities of the laser gyro. In addition, the rectangular geometry serves to reduce the overall package size of the laser gyro and permits the mounting of the anti-lock mechanical dithering drive mechanism within the laser gyro unit. A counterbalance is also provided to reduce vibration from the unit.

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Newbury Park, CA, United States of America

Virgil E Sanders