Optics: measuring and testing – By light interference – Rotation rate
Reexamination Certificate
1999-10-18
2001-08-14
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Rotation rate
Reexamination Certificate
active
06275296
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a gyro and a method of operating such a gyro. More particularly, the present invention relates to an optical gyro adapted to reduce the coupling loss generated when laser beams are incident upon a photodetector and the noise generated by feedback laser beams reentering the laser from an external point of reflection as well as to a method of operating such an optical gyro.
2. Related Background Art
Mechanical gyros comprising a rotor and a vibrator as well as optical gyros adapted to detect the angular velocity of a moving object are known. Particularly, optical gyros are regarded as innovative because they can start to operate instantaneously and provide a wide dynamic range. Optical gyros including ring resonator type gyros, optical fiber gyros and passive type ring resonator gyros, of which ring resonator type gyros comprising a gas laser were developed most early and have been used in aeronautic applications and other applications. Recently, small, high precision, ring resonator type laser gyros have been proposed and Japanese Patent Application Laid-Open No. 5-288556 described such a gyro.
However, known ring resonator type laser gyros are so designed that a laser beam propagating clockwise and another laser beam propagating counterclockwise are once emitted therefrom to the outside and received by a photodetector, which transforms their optical beat into electric beat as signal. This means that a coupling loss arises when the laser beams are incident upon the photodetector. Additionally, known ring resonator type laser gyros need an optical isolator in order to avoid the noise generated by the laser beams returning from an external point of reflection to the laser.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a gyro that is totally or almost free from any coupling loss and optical feedback noise and a method of operating such gyro. Another object of the present invention is to provide a method of reducing the driving power necessary for driving a semiconductor ring laser. Still another object of the present invention is to provide a method of stabilizing the oscillation wavelength of a semiconductor ring laser.
According to the invention, there is provided a gyro comprising a ring resonator type semiconductor laser for emitting laser beams to be transmitted circularly in opposite senses relative to each other and a terminal for detecting the beat signal generated by the rotation of the ring resonator type semiconductor laser, said ring resonator type semiconductor laser having a central region for structurally obstructing the flow of any electric current.
According to an aspect of the invention, there is provided a gyro comprising a ring resonator type semiconductor laser for emitting laser beams to be transmitted circularly in opposite directions relative to each other and a terminal for detecting a beat signal, the active layer of the semiconductor laser being ring-shaped.
Preferably, the active layer is sandwiched by low refractive index layers showing a refractive index lower than that of the active layer and both the active layer and the low refractive index layers have a hollow pillar-like profile.
Preferably, said beat signal is detected as a change in the electric current flowing through, the voltage applied to or the impedance of the ring resonator type semiconductor laser.
According to another aspect of the invention, there is provided a gyro comprising a ring resonator type semiconductor laser for emitting laser beams to be transmitted circularly in opposite senses relative to each other and a means for detecting the beat signal generated by the rotation of the ring resonator type semiconductor laser, the active layer of said semiconductor laser being ring-shaped.
Preferably, said beat signal detection means includes at least a voltage detector, an electric current detector, an impedance detector, a frequency/voltage converter or a frequency counter.
According to still another aspect of the invention, there is provided a gyro comprising a ring resonator type semiconductor laser for emitting laser beams to be transmitted circularly in opposite senses relative to each other and a terminal for detecting a beat signal, said ring resonator type semiconductor laser having a central region at least partly showing a high resistivity.
According to still another aspect of the invention, there is provided a gyro comprising a ring resonator type semiconductor laser for emitting laser beams to be transmitted circularly in opposite senses relative to each other and a means for detecting the beat signal generated by the rotation of the ring resonator type semiconductor laser, said ring resonator type semiconductor laser having a central region at least partly showing a high resistivity.
According to still another aspect of the invention, there is provided a semiconductor device comprising a ring resonator type semiconductor laser having a ring-shaped active layer for emitting laser beams to be transmitted circularly in opposite senses relative to each other and a terminal for detecting a beat signal.
According to a further aspect of the invention, there is provided a semiconductor laser comprising an active layer and a low refractive index layer arranged above the active layer and showing a refractive index lower than that of the active layer, at least either the active layer or the low refractive index layer having a central region showing a high resistivity as a result of ion implantation.
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Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Turner Samuel A.
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