# US 4,396,290 A · Two pump-frequency-stimulated Brillouin scattering ring laser gyroscope

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- Number: US 4,396,290 A
- Document ID: US4396290A
- Status: Granted
- Kind: A
- Application number: 06/078,258
- Filed: 1979-09-24
- Granted: 1983-08-02
- Earliest claimed: 1979-09-24
- Assignees: University of Utah Research Institute
- Inventors: Glen J. Morris
- Web page: https://patentgrep.com/patent/US4396290A

## CPC

- G01C 19/64: Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
- H01S 3/083: Ring lasers {(fibre ring lasers H01S3/06791)}
- H01S 3/302: {in an optical fibre}
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL

## Abstract

An improved ring laser gyroscope is disclosed that uses two counterrotating beams separated in frequency by an amount that is large compared to lock-in thresholds. The two beams are heterodyned together to obtain a beat frequency whose magnitude is proportional to rotation rate. In the preferred embodiment, the gyroscope utilizes an optical fiber waveguide as the laser cavity. The two countercirculating beams are generated via the mechanism of stimulated Brillouin scattering within the cavity. The two Brillouin ring lasers are pumped by two beams derived from an external pump laser. The derived beams are shifted in frequency by acousto-optic modulators. Lock-in is eliminated at all rotation rates. Other error sources common to ring laser gyroscopes are eliminated or greatly reduced.

## Claims

### Claim 1

A two-frequency ring laser gyroscope comprising:
a pump laser;
means for dividing the pump laser beam into two equal intensity beams;
means for modulating the two derived beams to shift their frequencies to a different frequency from the pump beam and from each other;
means for coupling the two-frequency-shifted beams into opposite ends of an optical fiber waveguide ring;
an optical fiber waveguide ring to be used as a laser cavity;
means for pumping the optical fiber waveguide cavity by the two derived beams in both the clockwise and counterclockwise directions simultaneously in order to excite stimulated Brillouin scattering in both directions around the ring;
means for optically closing the ring on itself so that the stimulated Brillouin scattering results in two oppositely circulating Brillouin ring lasers;
means for extracting a portion of each Brillouin ring laser beam and bringing the two extracted beams to a common point;
means for mixing the two extracted beams together in a photodiode to produce a beat frequency proportional to the ring rotation rate about an axis perpendicular to the plane of the ring;
means for measuring the magnitude of the beat frequency so derived;
means for generating the electrical signals required to drive the laser beam modulators; and
means for signal processing required to detect, amplify and filter the beat frequency signal.