JP2001108448A - Gyro and its operation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gyro and its operation method capable of lowering a coupling loss generated when laser light is introduced into a light detector and a noise caused by returning light to a laser from external reflection points. SOLUTION: The gyro has a ring resonance type gas laser where lights circumferentially transmit mutually reversely to each other and detects beat signals as variation of current, voltage or impedance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas laser, and more particularly to a ring resonator gas laser. The present invention also relates to a gyro using a gas laser and a method for operating the gyro. More specifically, the present invention relates to a gyro capable of reducing coupling loss caused when laser light is incident on a photodetector and noise generated by returning light to a laser from an external reflection point, and a method of operating the gyro. .

[0002]

2. Description of the Related Art Conventionally, as a gyro used for detecting an angular velocity of a moving object, a mechanical gyro having a rotor and a vibrator and an optical gyro are known. In particular, the optical gyro is capable of instantaneous activation and has a wide dynamic range, and is thus innovating in the gyro technical field. The optical gyro includes a ring resonator laser gyro, an optical fiber gyro, a passive ring resonator gyro, and the like. Of these, the first to be developed is a ring resonator type laser gyro using a gas laser, which has already been put to practical use in aircraft applications and the like. Recently, a small and high-precision ring resonator type laser gyro has been proposed, and an example thereof is disclosed in Japanese Patent Application Laid-Open No. Hei 5-288556.

[0003]

However, the conventional ring resonator type laser gyro emits clockwise laser light and counterclockwise laser light from the laser to the outside of the laser once, and detects both laser lights. And received electrical beats as signals. For this reason, coupling loss has been present when the laser light is incident on the photodetector. In addition, since noise is generated by light returning to the laser from a reflection point outside the laser, it is necessary to use an optical isolator to avoid the noise.

In particular, since a gas laser is large, consumes large power, and is expensive, a gyro using the gas laser is required to have low power consumption and to be reduced in size and cost by reducing the number of parts. Was.

An object of the present invention is to provide a gyro having no or very few problems such as coupling loss and return light noise, and a method of operating the gyro.

[0006]

A gyro according to the present invention is characterized in that it has a ring resonator type gas laser in which light propagates in a counterclockwise direction, and has a terminal for detecting a beat signal. And

A gyro according to the present invention has a ring resonator type gas laser in which light propagates in a counter-rotating circular shape, and detects a beat signal.

According to the present invention, the beat signal is detected as a current flowing through the ring resonator type laser, a voltage applied to the ring resonator type laser, or a change in impedance of the ring resonator type laser. It is characterized by. More specifically, the beat signal is used to detect a current flowing through the ring resonator type laser, a voltage applied to the ring resonator type laser, or a frequency change of the impedance of the ring resonator type laser.

Further, the present invention is characterized in that the beat signal is extracted from at least one discharge electrode of the ring resonator type gas laser.

[0010] A gyro according to the present invention is characterized by having a ring resonator type gas laser in which light propagates in a counterclockwise direction and a beat signal detecting means.

The beat signal detecting means includes a voltage detecting circuit, a current detecting circuit, an impedance detecting circuit,
The gyro according to claim 7, further comprising a frequency-voltage conversion circuit.

Further, the present invention is characterized in that a current or a voltage for driving the ring resonator type gas laser is modulated at a frequency different from the frequency band of the beat signal.

Further, the present invention is characterized in that vibration is applied to the ring resonator type gas laser at a frequency different from the frequency band of the beat signal, and the beat signal is detected in synchronization with the vibration. .

A method of operating a gyro according to the present invention is a ring resonator type gas laser in which light propagates in a counterclockwise circular shape, and has a terminal for detecting a beat signal as a change in current, voltage or impedance. A method of operating the gyro, wherein a change in current, voltage or impedance detected from the terminal is used as a signal for determining the magnitude of the angular velocity applied to the ring resonator type gas laser.

First, the principle of detecting the rotational motion of an object using a ring resonator type laser will be described.

In the ring resonator type laser shown in FIG. 1, when laser oscillation occurs, light propagates in a circular manner.

Specifically, there are light (31) circling clockwise inside the laser and light circling counterclockwise (32).

When the ring resonator type laser is stationary, the clockwise laser light and the counterclockwise laser light have the same oscillation frequency.

However, when the laser is rotated, a difference occurs between the oscillation frequencies of the clockwise laser light and the counterclockwise laser light, which is known as the Sagnac effect. The difference Δf between the oscillation frequencies is given by the following equation.

Δf = (4S / λL) Ω (1) where S is a closed area surrounded by an optical path, λ is an oscillation wavelength of laser light, L is an optical path length, and Ω is an angular velocity of rotation.

In the case of a gas laser, there is a one-to-one correspondence between the population inversion and the impedance of the laser. If light interferes in the laser, the population inversion changes accordingly, and as a result, the impedance between the electrodes of the laser changes.

This change appears as a change in the current flowing through the laser when a constant voltage source is used as the driving power supply. In this case, a battery can be used as the constant voltage source, which leads to downsizing and weight reduction of the drive system.

When a constant current source is used, it appears as a change in terminal voltage. In either case, the state of light interference can be extracted as a signal.

Of course, it is also possible to directly measure a change in impedance with an impedance meter. In this case, unlike the case where the terminal voltage or the current flowing through the element is measured, the influence of the noise of the driving power supply is reduced.

As in the present invention, the laser is provided with a terminal for detecting a change in current, voltage, or impedance caused by a beat generated by interference of laser light traveling in opposite directions inside the laser. , A beat signal corresponding to the rotation can be extracted.

More specifically, the current flowing through the laser,
By detecting a voltage applied to the laser or a change in the frequency of the impedance of the laser itself, the rotational movement of the object is detected.

In the present invention, a change in one of the discharge electrodes (for example, anode potential) of the ring resonator type gas laser is taken out.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of a gyro according to the present invention and its operating method will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a schematic plan view showing an example of a gyro provided with a ring resonator type gas laser according to the present invention, in which light propagates in a circular manner.
This is the case where the orbital path of the laser light is rectangular. FIG.
In the figures, 1 is an electric terminal, 10 is a quartz tube made by hollowing out quartz, 11 is a mirror, 21 is an anode and 22
Is a discharge electrode, for example, 21 is an anode and 22 is a cathode. 31 is a clockwise laser beam, 32
Is a counterclockwise laser beam.

In the above configuration, when helium gas and neon gas are put into the quartz tube 10 and a voltage is applied between the anode 21 and the cathode 22, discharge starts and a current flows.

When the quartz tube 10 is stationary, the oscillation frequencies of the clockwise laser light and the counterclockwise laser light are exactly equal, 4.73 × 10 ¹⁴ Hz, and the oscillation wavelength λ is 63.
It is 2.8 nm. For example, if the quartz tube 10 functioning as a resonator receives a rotation of 180 degrees per second and the length of one side of the quartz tube 10 is 10 cm, the beat frequency is 496.5 kHz. At this time, if the power supply current is adjusted to be constant and the terminal voltage is monitored from the electric terminal 1, a signal having an amplitude of 100 mV and a frequency of 496.5 kHz is obtained.

In particular, as shown in FIG. 2, the anode of a ring resonator type gas laser 60 is connected to an operational amplifier 61 for a buffer.

Since the signal output from the amplifier 61 has a frequency corresponding to the angular velocity, the signal is converted into a voltage by a known frequency-voltage conversion circuit (FV conversion circuit). Detect rotation.

Of course, if desired characteristics can be obtained, the operational amplifier 61 ("voltage follower") can be omitted.

FIG. 3 shows an example of a circuit diagram in which the laser is driven at a constant current, the change in the anode potential of the laser 60 is read, and the rotation is detected.

The anode of the laser 60 has a protection resistor 63
Is connected to the output terminal of the operational amplifier 70, and the cathode of the laser 60 is connected to the inverting input terminal of the operational amplifier 70.

The resistor 71 is connected between the inverting input terminal of the operational amplifier 70 and the reference potential.

Here, when a constant potential (Vin) is applied to the non-inverting input terminal of the operational amplifier 70 from a microcomputer or the like, a constant current drive configuration in which the potential and the current determined by the resistor 71 flow through the laser 60 is adopted.

The anode of the laser 60 is connected to the operational amplifier 6
Connected to 1.

The operational amplifier 61 outputs a signal Vout. Since this signal has a beat frequency proportional to the angular velocity, the signal is converted into a voltage by a known frequency-voltage conversion circuit (FV conversion circuit) or the like, and rotation is detected.

Further, a frequency counter circuit can be used as the beat signal detecting means.

FIG. 4 shows an example of a frequency-voltage conversion circuit (FV conversion circuit). This circuit is composed of a transistor, a diode, a capacitor, and a resistor.
_C2 is represented by equation (2).

[0043]

[Outside 1] Here, E _i is the peak-to-peak value of the input voltage, and f is the beat frequency. C ₂ >> C ₁ , R ₀ C ₂ f <
By designing the circuit parameters to be 1, V _C2 = E _i C ₁ R ₀ f (3) as shown in equation (3), and a voltage output proportional to the beat frequency is obtained. Becomes possible.

Of course, in the case of constant voltage driving, a change in the current flowing through the terminal can be detected. Here, an example in which a change in terminal voltage is detected has been described, but a change in discharge impedance may be directly detected using an impedance meter.

In general, a gas laser has a small optical gain, so that the length of the resonator is long, and the gyro becomes large.

However, if the photodetector is not required as in the present invention, the size of the gyro itself can be reduced.

With such a configuration, the photodetector which has been essential for detecting the beat light in the related art becomes unnecessary, and as a result, there is no return light noise caused by the return light from the photodetector.

In the gyro having the above structure, an example using helium gas and neon gas has been described. However, the gyro may be any gas as long as it is a laser oscillating gas and a desired angular velocity can be detected. For example, there are an argon ion laser, a carbon dioxide laser, and an excimer laser.

Although the case where a quartz tube is used for producing a gas laser has been described, a polymer can also be used. In this case, it can be formed by a low-temperature process.
Note that as the polymer material, fluorinated polyimide, polysiloxane, PMMA (polymethyl methacrylate), epoxy, or polycarbonate can be used.

As the discharge electrode, aluminum, zirconium, tungsten or the like is used.

By the way, in the gyro having the above-described configuration, when the gyro is rotated, a difference appears between the oscillation frequencies of the clockwise clockwise laser beam and the counterclockwise clockwise laser beam, and the difference Δf is expressed by the above equation (1). Given. However, when the difference Δf between the oscillation frequencies is small, the oscillation frequency is pulled in due to the non-linearity of the laser medium, and a phenomenon called lock-in occurs, where Δf = 0.

Therefore, it is desirable to keep the oscillation frequency difference Δf fluctuating to avoid the lock-in phenomenon. Conventionally, a method of applying dither has been used as a method of avoiding the lock-in phenomenon.
Corresponds to the modulation of the angular velocity Ω.

In the case of a gas laser, the oscillation wavelength is modulated because the Q value of the resonator fluctuates by modulating the current or the voltage. This is because the oscillation wavelength of a gas laser is determined by the Q value of the resonance transition of an atom, a molecule, or an ion and the Q value of a resonator, and this phenomenon is known as attraction of the oscillation wavelength.

Therefore, λ in the equation (1) can be modulated, and as a result, a state where Δf always fluctuates can be created. Moreover, by modulating the signal with a frequency in a band different from the beat signal frequency, lock-in can be avoided without adversely affecting the signal.

Further, by applying a vibration to the gyro having the ring resonator type laser at a frequency different from the frequency band of the beat signal and detecting a signal from the terminal in synchronization with the vibration, the direction of the vibration and the terminal Correspondence of magnitude relation of voltage can be provided.

For example, when a vibration is applied in the clockwise rotation direction, the terminal voltage increases when the gyro receives clockwise rotation, and conversely, when the gyro receives counterclockwise rotation, the terminal voltage decreases. Become. Therefore, it is possible to identify whether the gyro is rotating clockwise or counterclockwise. Moreover, by modulating the signal at a frequency in a band different from the signal frequency, the direction of rotation can be detected without adversely affecting the signal.

More specifically, in order to provide dither, a piezoelectric element arranged close to the above-described gas laser and having a frequency of 20 k
By applying a voltage of Hz, the gas laser constituting the gyro can be given clockwise and counterclockwise rotation. By detecting a signal synchronized with the voltage applied to the piezoelectric element from the terminal 1, clockwise rotation and counterclockwise rotation can be distinguished. For example, when vibration is applied in the clockwise rotation direction, the terminal voltage increases when the gas laser is receiving clockwise rotation, and conversely, decreases when the gas laser is receiving counterclockwise rotation. Moreover, by modulating the signal at a frequency in a band different from the signal frequency, the direction of rotation can be detected without adversely affecting the signal.

Further, if necessary, the detection terminal of the ring resonator type gas laser 60 is provided with a protection circuit 61 to prevent the gas laser from being deteriorated or destroyed. FIG. 5 shows an example in which a voltage follower 61 is connected as a protection circuit. Here, 62 is a current source, 63 is an electric resistance, and 64 is a voltage detection circuit.

When a constant voltage source is used as the power supply, the angular velocity of rotation can be measured as a change in current flowing through the ring resonator type gas laser.

As shown in FIGS. 6 and 7, when the battery 65 is used as a constant voltage source, the driving system can be reduced in size and weight.

In FIG. 6, an electric resistor 63 is connected in series with the ring resonator gas laser, and the current flowing through the ring resonator gas laser is measured as a change in voltage across the electric resistor 63. On the other hand, in FIG. 7, an ammeter is connected in series with the ring resonator gas laser, and the current flowing through the ring resonator laser is measured directly. 6 and 7, reference numeral 66 denotes a voltmeter, and 67 denotes an ammeter. Even if the obtained signal is subjected to FV conversion, frequency-angular velocity conversion (FV
-Ω conversion).

FIG. 8 shows an example of a circuit diagram for driving the laser at a constant voltage, reading the change in the anode potential of the laser 60, and detecting the rotation.

The anode of the laser 60 is connected to the output terminal of the operational amplifier 72 via the resistor 63, and the cathode of the laser 60 is grounded to the reference potential.

When a constant potential (Vin) is applied to the inverting input terminal of the operational amplifier 72 from a microcomputer or the like, a constant voltage drive configuration is applied in which the potential is always applied to the resistor 63 and the laser 60.

The anode of the laser 60 is connected to the operational amplifier 6
Connected to 1.

The operational amplifier 61 outputs a signal Vout. Since this signal has a beat frequency proportional to the angular velocity, the signal is converted into a voltage by a known frequency-voltage conversion circuit (FV conversion circuit) or the like, and rotation is detected. Of course, the rotation detection may be performed by directly inputting the signal of the equipotential portion with the anode to the FV conversion circuit.

Next, FIG. 11 shows a case where the reference of the signal potential is set to the ground by using the subtraction circuit 75 in addition to the same constant voltage drive configuration as in FIG.

A constant potential V ₁ is applied to the inverting input terminal of the operational amplifier 72 from a microcomputer or the like. 60 is a ring resonator type laser, 61 is a voltage follower, 63 and 76-7
Reference numeral 9 denotes an electric resistance, which makes the resistance values of 76 and 77 and 78 and 79 equal.

The potentials V ₁ and V ₂ at both ends of the electric resistor 63 are connected to an inverting input terminal and a non-inverting input terminal of the amplifier 80 through a voltage follower and resistors 76 and 78 circuits. This makes it possible to detect a change in the voltage V ₂ −V ₁ (= V ₀ ) applied to the electric resistance 63 with the reference potential as the ground. That is, a change in the current flowing through the ring resonator laser 60 can be detected.

The rotation of the obtained signal is detected through an FV conversion circuit or the like.

Further, irrespective of the type of the constant current, a change in the impedance of the ring resonator type laser can be directly measured by an impedance meter. in this case,
Unlike measuring the terminal voltage or the current flowing through the element,
The influence of noise of the drive power supply is reduced. This example is shown in FIG. Reference numeral 68 denotes a power supply, and 69 denotes an impedance meter.

Further, if the gyro is provided with a total reflection surface for the laser light generated from the ring resonator type laser and the ring type resonator laser is constituted only by this total reflection surface, mirror loss is eliminated, so that the laser The oscillation threshold can be reduced.

It is also preferable that the total reflection surface is not provided within the range of the exudation distance of the evanescent light generated from the ring resonator type laser. If there is no reflector within the extruded distance of the laser evanescent light, the laser will be optically independent of other reflectors and not only will there be no loss due to external effects of the laser, but also no return light noise. Therefore, loss due to coupling and return light noise can be remarkably improved.

By mounting the gyro described in the present embodiment on an automobile or an airplane, the gyro can be used as an angular velocity detection or position detection device that can be made smaller than before.

(Second Embodiment) FIG. 10 is a schematic plan view showing another example of a gyro provided with a ring resonator type laser in which light propagates in a circular shape according to the present invention. The third embodiment differs from the first embodiment (FIG. 1) in that the circular path of the laser light is triangular. The other points are the same as in the first embodiment.

Also in this configuration, rotation can be detected based on the same principle as in the first embodiment. As long as the right-handed laser light and the left-handed laser light pass through the same path, the shape of the orbital path through which the light propagates is not limited to the above-described squares, triangles, and circles. The functions and effects described in the first embodiment can be obtained.

[0077]

As described above, according to the gyro according to the present invention, the ring resonator type gas laser in which the light propagates in a circular shape is generated by the interference of the laser light traveling in opposite directions inside the laser. By detecting a change in current, voltage or impedance caused by the generated beat, a beat signal corresponding to the rotation can be detected. A gyro that can omit an optical system can be provided.

Further, by providing a total reflection surface for the laser light generated from the ring resonator type gas laser, mirror loss is eliminated, so that the laser oscillation threshold can be reduced.

Further, within the exudation distance range of the evanescent light generated from the ring resonator type gas laser,
By adopting a configuration in which the total reflection surface is not provided, the laser becomes optically independent of other reflectors, so that not only loss due to the influence of the outside of the laser is eliminated but also return light noise does not exist.

In the gyro operating method according to the present invention, in the optical gyro having the above-described configuration, the change in the current, voltage, or impedance detected from the terminal is determined by the angular velocity applied to the ring resonator type gas laser. Since it is used as a signal to determine the magnitude of the optical gyro, a photodetector and an optical system for optical coupling, which are indispensable in the conventional optical gyro, are not required. A gyro operation method that can solve the problem can be provided.

In addition, by a method of modulating a voltage or a current for driving the ring resonator type gas laser at a frequency different from the frequency band of the signal, it is possible to avoid a lock-in phenomenon caused by nonlinearity of a laser medium. Modulation at a frequency in a band different from the signal frequency can also avoid adverse effects on the signal.

Further, by applying a vibration to a gyro provided with the ring resonator type gas laser at a frequency different from the frequency band of the signal, and detecting the signal from the terminal in synchronization with the vibration, the signal is adversely affected. , The direction of rotation can be easily detected.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an example of a gyro according to the present invention.

FIG. 2 is an example of a circuit diagram showing a method of detecting a beat signal accompanying rotation by a ring resonator type gas laser according to the present invention.

FIG. 3 is an example of a circuit diagram showing a method for detecting a beat signal accompanying rotation by a ring resonator type gas laser according to the present invention.

FIG. 4 is a circuit diagram illustrating an example of an FV conversion circuit.

FIG. 5 is a circuit diagram showing a method for detecting a beat signal accompanying rotation of a ring resonator gas laser according to the present invention.

FIG. 6 is a circuit diagram showing a method for detecting a beat signal accompanying rotation of a ring resonator gas laser according to the present invention.

FIG. 7 is a circuit diagram showing a method for detecting a beat signal accompanying rotation of a ring resonator gas laser according to the present invention.

FIG. 8 is a circuit diagram showing a method for detecting a beat signal accompanying rotation of a ring resonator gas laser according to the present invention.

FIG. 9 is a schematic plan view showing an example of a gyro according to the present invention.

FIG. 10 is a schematic plan view showing an example of a gyro according to the present invention.

FIG. 11 is an example of a circuit diagram showing a method for detecting a beat signal accompanying rotation of a ring resonator gas laser according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric terminal 10 Quartz tube 11 Mirror 21 Anode 22 Cathode 31 Clockwise laser beam 32 Counterclockwise laser beam 60 Ring resonator type gas laser 61 Protection circuit 62 Current source 63 Electric resistance 64 Voltage detection circuit 65 Battery 66 Voltmeter 67 Ammeter 68 Power supply 69 Impedance

Claims (18)

[Claims] 1. A gyro having a ring resonator type gas laser in which light propagates in a counter-rotating circular shape, and detects a beat signal. 2. The gyro according to claim 1, wherein the ring resonator type gas laser detects the beat signal as a change in current, voltage, or impedance. 3. The method according to claim 1, wherein the beat signal is detected as a current flowing through the ring resonator type laser, a voltage applied to the ring resonator type laser, or a change in impedance of the ring resonator type laser. gyro. 4. The method according to claim 1, wherein the beat signal is detected as a current flowing through the ring resonator type laser, a voltage applied to the ring resonator type laser, or a frequency change of an impedance of the ring resonator type laser. Gyro. 5. The gyro according to claim 1, further comprising a terminal for detecting the beat signal as a change in current, voltage or impedance. 6. The gyro according to claim 1, wherein the beat signal is extracted from a discharge electrode of the ring resonator type gas laser. 7. The gyro according to claim 1, further comprising: a ring resonator type gas laser in which light propagates in a counterclockwise direction, and a beat signal detecting means. 8. The gyro according to claim 7, wherein said beat signal detection means includes a voltage detection circuit, a current detection circuit, or an impedance detection circuit. 9. The gyro according to claim 7, wherein said beat signal detecting means includes a frequency-voltage conversion circuit. 10. The gyro according to claim 7, wherein said beat signal detecting means includes a frequency counter circuit. 11. The gyro according to claim 7, wherein said beat signal is taken out from a discharge electrode of said ring resonator type gas laser. 12. An aircraft or automobile equipped with the gyro according to claim 1. 13. The gyro according to claim 1, wherein a current or a voltage for driving the ring resonator type gas laser is modulated at a frequency different from a frequency band of the beat signal. 14. A vibration is applied to the ring resonator type gas laser at a frequency different from the frequency band of the beat signal, and the beat signal is detected in synchronization with the vibration.
A gyro according to any one of claims 1 to 11. 15. The gyro according to claim 1, wherein the ring resonator type gas laser is a helium / neon gas laser, an argon ion laser, or a carbon dioxide gas laser. 16. A gyro according to claim 1, wherein said ring resonator type gas laser has a triangular, quadrangular or circular ring shape. 17. The gyro according to claim 1, wherein the ring resonator type gas laser has a total reflection surface on a side surface. 18. A method of operating a gyro having a ring resonator type gas laser in which light propagates in a counter-rotating circular shape and a terminal for detecting a beat signal as a change in current, voltage or impedance. A method for operating a gyro, wherein a change in current, voltage or impedance detected from the terminal is used as a signal for determining the magnitude of the angular velocity applied to the ring resonator type gas laser.