Coherent light generators – Particular resonant cavity – Folded cavity
Reexamination Certificate
2001-07-10
2003-12-02
Leung, Quyen (Department: 2828)
Coherent light generators
Particular resonant cavity
Folded cavity
C356S459000, C356S461000
Reexamination Certificate
active
06658039
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser. In particular, the present invention relates to a ring laser and a ring laser type optical gyro for detecting rotation.
2. Related Background Art
A gyro is a sensor for detecting an angular velocity of a moving object. The gyro can be used for controlling the posture of an aircraft and a robot, detecting the position in car navigation, detecting sideways sliding of a car, preventing hand-shaking of a silver-salt camera, a digital camera, and a video camera, etc.
As a gyro, a mechanical gyro provided with a rotor and an oscillator, and an optical gyro are known. In particular, the optical gyro is capable of performing instantaneous start-up and has a large dynamic range, so that the optical gyro is bringing about innovation in the field of a gyro technique. Examples of the optical gyro include a ring laser type gyro, an optical fiber gyro, and a passive ring resonator gyro. Among them, the development of the ring laser type gyro using a gas laser was first launched, and it has already been put into practical use in an aircraft and the like. Recently, as a small ring laser type gyro with high precision, a semiconductor laser gyro integrated on a semiconductor substrate is also proposed. For example, Japanese Patent Application Laid-Open No. High 5-288556 describes this type of gyro. In this manner, a ring laser is important in terms of application to a gyro. In order to increase a signal
oise ratio as a gyro, it is desirable to minimize the number of oscillation modes.
However, in a conventional ring laser type gyro, restriction of the number of oscillation modes has not been studied well. In particular, a semiconductor laser has a large gain bandwidth (i.e., about 10 nm), so that a resonant mode in this bandwidth may oscillate. That is, a semiconductor ring laser is likely to oscillate in a multi-mode. In order to restrict the number of oscillation modes, the number of resonant modes present in the gain bandwidth may be decreased. However, a resonant optical filter such as a Fabry-perot resonator and a diffraction grating cannot be used for the following reason. If a resonant optical filter is used, a forward running wave and a backward running wave are coupled, and the coupling strength of counterpropagating laser lights becomes strong; as a result, the oscillation of one mode is suppressed. This phenomenon is known as lock-in, which causes a problem particularly in the case where the difference in oscillation frequency of counterpropagating laser lights is small (e.g., in the case where the rotation speed is small). Therefore, there is a demand for a ring laser capable of restricting the number of oscillation modes under the condition that a forward running wave and a backward running wave are not coupled.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a ring laser and a ring laser type gyro capable of restricting the number of oscillation modes so as not to cause lock-in.
In order to solve the above-mentioned problem, according to a first aspect of the present invention, a ring laser includes multiple paths with different optical path lengths, wherein at least part of the multiple paths is optically coupled, and a propagating direction of laser light propagating in an optical resonator is not reversed by the multiple paths.
In order to achieve the above-mentioned object, according to a second aspect of the present invention, in the first aspect of the invention, a ring laser has a structure such that counterpropagating laser lights having different oscillation frequencies are present in an optical resonator.
In order to achieve the above-mentioned object, according to a third aspect of the present invention, in the second aspect of the invention, a ring laser has a structure such that at least part of the multiple paths is provided with a mechanism for giving a loss difference or a net gain difference with respect to the laser lights counterpropagating in an optical resonator.
In order to achieve the above-mentioned object, according to a fourth aspect of the present invention, in the third aspect of the invention, a ring laser has a structure such that the mechanism for giving a loss difference or a net gain difference with respect to the laser lights counterpropagating in the optical resonator is a taper-shaped optical waveguide having an asymmetric shape.
In order to achieve the above-mentioned object, according to a fifth aspect of the present invention, in the third aspect of the invention, a ring laser has a structure such that the mechanism for giving a loss difference or a net gain difference with respect to the laser lights counterpropagating in the optical resonator is composed of an optical component including a polarizer.
In order to achieve the above-mentioned object, according to a sixth aspect of the present invention, in any one of the above aspects 1 to 5, a ring laser includes multiple electrodes capable of electrically and independently controlling at least part of the multiple paths.
In order to achieve the above-mentioned object, according to a seventh aspect of the present invention, in the first aspect of the invention, a ring laser has a structure such that only laser lights propagating in one propagating direction is present in the optical resonator.
In order to achieve the above-mentioned object, according to an eighth aspect of the present invention, in the seventh aspect of the invention, a ring laser has a structure such that at least part of the multiple paths is provided with a mechanism for giving a loss difference or a net gain difference with respect to laser lights counterpropagating in the optical resonator.
In order to achieve the above-mentioned object, according to a ninth aspect of the present invention, in the seventh aspect of the invention, a ring laser has a structure such that the mechanism for giving a loss difference or a net gain difference with respect to laser lights counterpropagating in the optical resonator is a taper-shaped optical waveguide.
In order to achieve the above-mentioned object, according to a tenth aspect of the present invention, in the seventh aspect of the invention, a ring laser has a structure such that the mechanism for giving a loss difference or a net gain difference with respect to laser lights counterpropagating in the optical resonator is composed of an optical component including a polarizer.
In order to achieve the above-mentioned object, according to an eleventh aspect of the present invention, in any one of the above aspects 7 to 10 of the present invention, a ring laser includes multiple electrodes capable of electrically and independently controlling at least part of the multiple paths.
In order to achieve the above-mentioned object, according to a twelfth aspect of the present invention, in a method for driving a ring laser, at least part of the multiple electrodes is electrically and independently controlled.
In order to achieve the above-mentioned object, according to a thirteenth aspect of the present invention, a gyro apparatus includes: a ring laser in any one of the aspects 1 to 6 of the invention; a power source of driving of the ring laser; an apparatus for measuring a difference in oscillation frequencies of laser lights; and an apparatus for controlling the power source of driving in accordance with the difference in oscillation frequency.
In order to achieve the above-mentioned object, according to a fourteenth aspect of the present invention, in the thirteenth aspect of the invention, a gyro apparatus includes an apparatus for measuring the difference in oscillation frequencies of laser lights counterpropagating in an optical resonator from a change in a current, a voltage, or impedance of the ring laser.
In order to achieve the above-mentioned object, according to a fifteenth aspect of the present invention, in the thirteenth aspect in the invention, a gyro apparatus includes: a photodetector for simultaneously rece
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Leung Quyen
Menefee James
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