Optics: measuring and testing – By light interference – Rotation rate
Reexamination Certificate
2001-07-10
2004-08-31
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Rotation rate
Reexamination Certificate
active
06785003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ring laser gyro for detecting rotation using a semiconductor ring laser.
2. Related Background Art
Conventionally, as gyros for detecting rotation, that is, angular velocity, of an object, mechanical gyros having a rotor and an oscillator, optical gyros, and the like are known. Since optical gyros can be instantaneously activated and have a wide dynamic range, they are making innovations in the field of gyros. Optical gyros can be categorized into ring laser gyros, optical fiber gyros, passive ring resonator gyros, and the like. Ring laser gyros using gas lasers have already been put into practical use in the field of airplanes. As small-sized ring laser gyros with high accuracy, gyros formed of semiconductor ring lasers have been proposed, which are disclosed in Japanese Patent Publication Nos. 62-39836, 6-38529 and Japanese Patent Application Laid-Open No. 4-174317.
A gyro formed of a semiconductor ring laser over a mechanical gyro having an oscillator are characterized by a smaller size, lower power consumption, and shortened activating time, which makes the gyro suitable for use as a gyro stabilizer in a still camera or a video camera for preventing blurred image due to movement of the camera.
In such a gyro, beat frequency has information on angular velocity. In order to detect the beat frequency, there is a method of converting the beat frequency to a voltage signal via a frequency-voltage conversion circuit, a method of directly detecting the beat frequency through a frequency counter, and the like.
SUMMARY OF THE INVENTION
However, a conventional gyro formed of a semiconductor ring laser can not detect the rotational direction from an output signal as it is. Therefore, minute rotational vibration (dithering) is added to detect the rotational direction from the correlation between the dithering and the signal. The Japanese Patent Publication No. 62-39836 and the Japanese Patent Application Laid-Open No. 4-174317 do not disclose the method of detecting the rotational direction.
A conventional ring laser gyro is required to improve the accuracy of detecting a beat signal.
In order to attain the above object, a ring laser gyro according to the present invention comprises at least one pair of semiconductor ring lasers, the semiconductor ring lasers being optically independent of each other and variation in a period of an impedance change in one of the pair being opposite to that in the other with respect to rotation in one direction. More specifically, a ring laser gyro comprising two or more semiconductor ring lasers, the semiconductor ring lasers being optically independent of each other, is characterized in that a change in beat frequency with respect to a change in angular velocity of a first ring laser is opposite to that of a second ring laser, and angular velocity of rotation of the gyro is detected by a signal representing a difference between a first beat frequency generated by the first ring laser and a second beat frequency generated by the second ring laser. In particular, the ring laser gyro is characterized in that the beat frequency generated by the first ring laser and the beat frequency generated by the second ring laser in a static state are equal to each other, and the rate of change in the beat frequency with respect to the change in the angular velocity of the first ring laser is equal to that of the second ring laser.
A ring laser gyro according to the present invention is provided with two semiconductor ring lasers, the semiconductor ring lasers being in planes nonperpendicular to each other, being optically independent of each other, and each being provided with an electric terminal for detecting an impedance change, a period of the impedance change between the terminals being varied according to applied angular velocity. When angular velocity in a direction is increased, frequency of the impedance change with respect to the first semiconductor ring laser is decreased, while frequency of the impedance change with respect to the second semiconductor ring laser is increased.
In the above structure, by carrying out signal processing with respect to a frequency change in the impedance change of the two semiconductor ring lasers, a signal which depends on the angular velocity can be separated from a change in the beat frequency in a static state and noises. The sign of variation in the signal which depends on the angular velocity of one semiconductor ring laser is opposite to that of the other semiconductor ring laser, while the sign of variation in the change in the beat frequency in a static state and the noises of one semiconductor ring laser is the same as that of the other semiconductor ring laser. In this way, the S/N ratio can be improved, and thus, the angular velocity and the rotational direction can be obtained with accuracy from a signal which depends on the angular velocity.
According to the present invention, in the ring laser gyro, each of the two semiconductor ring lasers has two laser beams, the two laser beams rotating in opposite directions in their respective optical resonators and having different frequencies of oscillation in a static state. The relationship in magnitude between the frequency of oscillation of the clockwise laser beam and the frequency of oscillation of the counterclockwise laser beam is reversed between the two semiconductor ring lasers.
In the above structure, the two laser beams of each of the two semiconductor ring lasers rotate in opposite directions in their respective optical resonators and have different frequencies of oscillation in the static state generate optical beat. Further, since the two semiconductor ring lasers are optically independent of each other, when the gyro provided with them is rotated, the frequencies of oscillation of the respective laser beams vary independently of each other. Since the relationship in magnitude between the frequency of oscillation of the clockwise laser beam and the frequency of oscillation of the counterclockwise laser beam is reversed between the two semiconductor ring lasers, when the gyro is rotated, the optical beat frequency in the optical resonator of one semiconductor ring laser is increased while that of the other is decreased. This variation in the optical beat frequencies is detected as a frequency change in the impedance change between the terminals of the semiconductor ring lasers.
By carrying out signal processing with respect to the obtained frequency change, a signal which depends on the angular velocity can be separated from a change in the beat frequency in a static state and noises. The sign of variation in the signal which depends on the angular velocity of one semiconductor ring laser is opposite to that of the other semiconductor ring laser, while the sign of variation in the change in the beat frequency in a static state and the noises of one semiconductor ring laser is the same as that of the other semiconductor ring laser. In this way, the S/N ratio can be improved, and thus, the angular velocity and the rotational direction can be obtained with accuracy from a signal which depends on the angular velocity.
Further, according to the present invention, in the ring laser gyro, the two semiconductor ring lasers have a tapered portion in a part of their respective optical waveguides. The tapered portion is formed of a first portion where the width of the optical waveguide becomes larger along a propagation direction of a clockwise laser beam and a second portion where the width of the optical waveguide becomes smaller. In the first semiconductor ring laser, the first portion is longer than the second portion, while, in the second semiconductor ring laser, the second portion is longer than the first portion.
Here, the tapered portions of the semiconductor ring lasers have structures introduced for the purpose of giving difference between the frequency of oscillation of the clockwise laser beam and the frequency of oscillation of the counterclockwise laser beam in
Mizutani Natsuhiko
Numai Takahiro
LandOfFree
Ring laser gyro with optically independent semiconductor... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ring laser gyro with optically independent semiconductor..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ring laser gyro with optically independent semiconductor... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3336147