Ring laser gyro with an injected third beam

Details Ring laser gyro with an injected third beam Ring laser gyro with an injected third beam

2000-02-08

2002-02-26

Turner, Samuel A. (Department: 2877)

Optics: measuring and testing

By light interference

Rotation rate

C356S461000

Reexamination Certificate

active

06351311

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a laser device. More particularly, it relates to a gyro that uses laser beams.
2. Related Background Art
Known gyros for detecting the angular velocity of a moving object include mechanical gyros comprising a rotor or an oscillator as well as optical gyros. Particularly, optical gyros are bringing forth technological innovations in the field of gyro technologies due to their remarkable advantages including that they can start to operate instantaneously and show a broad dynamic range. Various optical gyros are known to date including ring laser type gyros, optical fiber gyros and passive type ring oscillator gyros. Of these, the ring laser type gyro that utilizes a gas laser is the earliest comer and gyros of this type are popularly used in aeroplanes at present. In recent years, small and highly sophisticated ring laser type gyros that are formed on a semiconductor substrate have been proposed. See, inter alia, Japanese Patent Application Laid-Open No. 5-288556.
According to the above patent publication, a ring-shaped gain waveguide
1100
is formed on a semiconductor substrate
1000
having an pn-junction and carriers are injected into the gain waveguide
1100
from an electrode
2200
as shown in
FIG. 29
of the accompanying drawings in order to generate a laser oscillation. Then, the laser beams that are propagating through the gain waveguide
1100
clockwise and counterclockwise are partly taken out to interfere with each other in a photo-absorption region
1700
. Then, the intensity of the interfered beams is taken out through another electrode
2300
as a photoelectric current. In
FIG. 29
, reference numerals
1500
and
1501
denote the laser beams propagating clockwise and counterclockwise respectively and reference numeral
1505
denotes a mirror.
Japanese Patent Application Laid-Open No. 57-43486 (U.S. Pat. No. 4,431,308) describes a gyro that utilizes the change in the terminal voltage of the element produced by the rotation thereof without taking out the beams to the outside of the semiconductor laser element. Referring to
FIG. 30
of the accompanying drawings, a semiconductor laser element
5792
has upper and lower electrodes (
5790
,
5791
). In
FIG. 30
, reference numeral
5793
denotes a DC blocking capacitor and reference numeral
5794
denotes an output terminal, while reference numeral
5795
denotes a resistor. As seen from
FIG. 30
, the semiconductor laser element of the ring laser device is connected to a drive power source
5796
and the frequency difference (beat frequency) between the frequency of the beam propagating clockwise and that of the beam propagating counterclockwise that is produced when the device shows a certain angular velocity is detected as a change in the terminal voltage of the laser element.
Japanese Patent Application Laid-Open No. 4-174317 also describes a technology of detecting the change in the terminal voltage of a laser element caused by the rotation thereof.
However, any of the known technologies as described in the above patent documents cannot detect the sense of rotation of an object. This is because a common beat frequency is detected regardless of the sense of rotation so long as the object is rotating at the same angular velocity.
Thus, with known ring laser type gyros the sense of rotation of each of the beams has to be determined by applying a dither (micro-oscillation) and determining the correlation of the dither and the obtained signal.
Additionally, there are always a laser beam propagating clockwise (CW beam) and a laser beam propagating counterclockwise (CCW beam) in known ring laser type gyros. The oscillation frequencies of the two beams remain equal to each other as long as the gyro is held stationary but they come to show a difference once the gyro is driven to rotate. The difference of the oscillation frequencies of the two beams is small when the angular velocity of the gyro is low and then there arises a lock-in phenomenon where the oscillation frequencies are pulled and locked to either of the oscillation modes due to the nonlinearity of the medium. This lock-in phenomenon observable in known ring laser type gyros can be avoided by applying a dither in a predetermined direction in advance and thereby increasing the difference in the oscillation frequencies of the CW beam and the CCW beam.
SUMMARY OF THE INVENTION
Thus, it is an object of the present invention to provide a laser device that can detect the sense of rotation.
Another object of the present invention is to provide a gyro that can detect the sense of rotation.
According to the invention, the above object is achieved by providing a gyro comprising:
a laser device for generating a first and second laser beams to be propagated circuitally in opposite directions wherein an electric signal is taken out from said laser device,
wherein a third laser beam having an oscillation frequency different from that of the first laser beam is led to enter the laser device so as to be propagated circuitally in the same direction as the first laser beam.
Preferably, said third laser beam is made to enter the laser device from a corner mirror of a ring laser comprising said laser device or by way of an optical waveguide to be used for injection locking.
Preferably, said optical waveguide for injection locking is arranged in the proximity of said laser device so as to be optically coupled to the device.
Preferably, said optical waveguide for injection locking and said laser device are arranged within the penetrating depth of said third laser beam.
Preferably, said optical waveguide for injection locking is connected to the waveguide of the ring laser comprising said laser device.
Preferably, at least one of the end facets of said optical waveguide for injection locking is inclined against a plane perpendicular to the direction of propagation of said third laser beam propagating through said optical waveguide for injection locking.
According to the invention, there is also provided a gyro comprising:
a laser device for generating a first and second laser beams propagating circuitally in opposite directions; and
a photodetector for detecting the interfered beam caused by the interference of the first and second laser beams emitted from the laser device;
wherein a third laser beam having an oscillation frequency different from that of the first laser beam is led to enter the laser device so as to be propagated circuitally in the same direction as the first laser beam.


REFERENCES:
patent: 3323411 (1967-06-01), Killpatrick
patent: 3697181 (1972-10-01), Macek et al.
patent: 4431308 (1984-02-01), Mitsuhashi et al.
patent: 4807998 (1989-02-01), Weber
patent: 57-43486 (1982-03-01), None
patent: 4-174317 (1992-06-01), None
patent: 5-288556 (1993-11-01), None

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