JP2002310667A - Ring laser gyro - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ring laser type gyro with a satisfactory signal-noise ratio by suppressing noises due to spontaneous emission and limiting the number of oscillation modes by a method which will not a lock-in cause. SOLUTION: Noises generated by spontaneous emission light, that combines clockwise laser beam 11 with a counterclockwise laser beam 12, are suppressed by light 21 generated in a non-orbital course 1. Because of the existence of an asymmetrical taper 7, the oscillation threshold of the clockwise laser beam is smaller than the oscillation threshold of the counterclockwise laser beam. As a result, when both laser beams are oscillating, the light intensity of the clockwise laser beam is higher than the light intensity of the counterclockwise laser beam. The end face of the course 1 is inclined relative to the laser beam propagating direction, in order to avoid lock-in, in which progressive waves and regressive waves are together combined to cause oscillation only in one of the modes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical gyro for detecting rotation, and more particularly to a ring laser type optical gyro.

[0002]

2. Description of the Related Art A gyro is a sensor for detecting the angular velocity of a moving object. It can be used for attitude control of an aircraft or a robot, position detection in car navigation, side slip detection of a car, and prevention of camera shake of a silver halide camera, a digital camera, and a video camera.

As a gyro, a mechanical gyro having a rotor and a vibrator and an optical gyro are known. In particular, optical gyros are being revolutionized in the gyro technical field because they can be activated instantaneously and have a wide dynamic range. The optical gyro includes a ring laser gyro, an optical fiber gyro, a passive ring resonator gyro, and the like. Of these, the first to be developed is a ring laser type gyro using a gas laser, which has already been put to practical use in aircraft and the like. A gyro using a semiconductor laser has also been proposed as a small and highly accurate ring laser gyro. As this known document, for example, there is Japanese Patent Publication No. 62-039836, and an example is shown in FIG.

[0004]

In order to increase the signal-to-noise ratio in a ring laser gyro, it is necessary to reduce the noise. An essential part of the laser light noise is spontaneous emission light coupled to the oscillation mode. However, in the conventional ring laser gyro, much less attention has been given to controlling spontaneous emission light to reduce noise.

In the case of a semiconductor laser, since the gain band is as large as about 10 nm, a resonance mode in this band can oscillate. That is, the semiconductor ring laser type gyro easily oscillates in multiple modes. In order to further improve the signal-to-noise ratio, it is important to limit the number of oscillation modes, and this can be achieved by reducing the number of resonance modes present in the gain band. However, a resonant optical filter such as a Fabry-Perot resonator or a diffraction grating cannot be used. This is because the resonance type optical filter combines the traveling wave and the backward wave. If a resonance type optical filter is used, the laser beams circling in opposite directions to each other cause strong coupling, and the oscillation of one mode is suppressed. This phenomenon is known as a lock-in phenomenon, and is particularly problematic when the difference between the oscillation frequencies of the laser beams circulating in opposite directions is small, such as when the rotation speed is small. For this reason, a ring laser gyro that can limit the number of oscillation modes in a state where the traveling wave and the backward wave are not coupled has been desired.

On the other hand, it is common practice to dither a ring laser type gyro to release the lock-in phenomenon. Further, the conventional ring laser type gyro cannot detect the rotation direction by itself.
For this reason, the rotation direction is determined from the correlation between the dither direction and the signal.

Accordingly, the present invention is to provide a ring laser type gyro having a good signal-to-noise ratio by suppressing noise due to spontaneous emission and limiting the number of oscillation modes by a method that does not cause lock-in. It is an issue.

It is another object of the present invention to provide a ring laser type gyro which can detect a rotation direction and a rotation speed without a mechanical mechanism such as dither.

[0009]

A ring laser type gyro according to the present invention for solving the above-mentioned problems comprises a circular path having a first emission wavelength distribution, at least a part of the circular path, and an optical path. And at least a non-circular path having a second emission wavelength distribution different from the first emission wavelength distribution, and an end of the non-circular path has a reflection suppressing structure.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGS. 1 and 2, a description will be given of how noise caused by spontaneous emission of a semiconductor ring laser type gyro is suppressed. FIG.
FIG. 1 is a top view schematically showing a structure of a ring laser type gyro of the present invention, and shows an optical waveguide 1 which is a non-circular path.
Are optically coupled to the optical waveguide 2 which is a circular path. Further, in the figure, reference numeral 11 denotes clockwise laser light, 12 denotes counterclockwise laser light, and 21 denotes light generated in the non-circular path 1. FIG. 2 is a diagram showing an emission spectrum. A solid line indicates an emission wavelength distribution in the optical waveguide 2 which is a circular path, and a broken line indicates an emission wavelength distribution in the optical waveguide 1 which is a non-circular path. As can be seen from this figure, the peak wavelength of each light intensity is about 0.03 μm.
m different.

Now, a ring laser has a plurality of stable points, and the oscillation mode is defined by these stable points. In addition, a switching phenomenon between a plurality of modes determined by the stable point is observed. Further, random spontaneous emission light is coupled to the oscillation mode, and the oscillation mode fluctuates, resulting in noise. Thus, (1) there are a plurality of stable points,
In the case where three conditions are satisfied, that is, (2) switching between stable points occurs, and (3) a random generation term or a driving force exists, a stochastic resonance phenomenon (Stochastic) is satisfied.
Resonance) is known to exist. The stochastic resonance phenomenon is a phenomenon in which noise is most suppressed when a random term has a certain value, and the noise increases when the random term is larger or smaller than this value. This stochastic resonance phenomenon occurs as a result of nonlinear interaction, and is likely to occur in a system having a nonlinear gain, such as a laser. The emission spectrum of FIG. 2 shows the amplified spontaneous emission light (Amplified Spontaneous Em).
issue) and is affected by this non-linear gain.

Here, consider a case where light having an emission spectrum as shown by a broken line in FIG. 2 is generated in the optical waveguide 1 which is a non-circular path by current injection or optical excitation. Since the optical waveguide 1 which is a non-circular path is optically coupled to the optical waveguide 2 which is a circular path, this light enters the optical waveguide 2 which is a circular path. Then, due to the nonlinear interaction between the incident spontaneous emission light and the spontaneous emission light generated in the circular path, the spontaneous emission light coupled to the oscillation mode is suppressed. As a result, fluctuation of the oscillation mode is reduced, and a ring laser type gyro having a large signal-to-noise ratio is realized.

Here, it is the non-circular path that shifts the spectral distribution of light generated in the optical waveguide 1 which is a non-circular path and the optical waveguide 2 which is a circular path. This is to prevent light generated in the optical waveguide 1 from affecting the oscillation mode itself.

When two modes of laser light coexist, it is known that the following relationship exists between the oscillation frequency and the photon number density.

[0015]

(Equation 1) Here, Φi is a phase, Ωi is a resonance angular frequency, σ _i is a coefficient representing a mode pull-in, ρ _i is a coefficient representing a self-extrusion of a mode, and τ _ij is a coefficient representing a mutual extrusion of a mode. Here, i, j = 1, 2; i ≠ j. Now, when the light intensities of the two laser lights circulating in opposite directions are different, that is, when the photon number density S ₁ ≠ S ₂ , f ₁ ≠ f ₂ is obtained from the equation (1).

In the ring laser type gyro described above, if laser lights having different oscillating frequencies co-exist in the optical resonator in the circumferential directions opposite to each other,
A gyro capable of detecting the rotation direction can be realized. The principle will now be described.

The wavelength of the first laser light circulating clockwise is defined as the wavelength. Further, the wavelength of the second laser light that circulates counterclockwise is defined as the wavelength. When the ring laser type gyro is rotated clockwise, the oscillation frequency f ₁ of the first laser light in the clockwise direction is compared with the oscillation frequency f ₁₀ in the non-rotation.

[0018]

(Equation 2) Only decrease. Here, is the closed area surrounded by the optical path of the first laser light, is the optical path length of the first laser light, and Ω is the angular velocity of rotation. On the other hand, the oscillation frequency f ₂ of the second laser beam in the counterclockwise direction is larger than the oscillation frequency f ₂₀ when the laser beam is not rotating.

[0019]

(Equation 3) Only increase. Here, is the closed area surrounded by the optical path of the second laser light, and is the optical path length of the second laser light. At this time, the first laser light and the second laser light coexist in the ring laser type gyro. Therefore, the difference between the oscillation frequencies of the first laser light and the second laser light in the ring laser gyro, that is,

[0020]

(Equation 4) Is generated. On the other hand, when the ring laser gyro rotates counterclockwise, beat light having the following frequency is generated.

[0021]

(Equation 5) If there are two or more oscillation modes in the ring laser gyro, the population inversion shows a time variation corresponding to the difference between the oscillation frequencies of the modes. This phenomenon is known as population inversion pulsation. In the case of a current injection type laser such as a gas laser or a semiconductor laser, there is a one-to-one correspondence between the population inversion and the impedance of the laser. And
When light interferes in the laser, the population inversion changes accordingly, resulting in a change in the impedance between the electrodes of the laser. This change appears as a change in terminal current when a constant voltage source is used as the drive power supply. Also,
If a constant current source is used, the state of light interference can be extracted as a signal as a change in terminal voltage. of course,
The change in impedance can also be measured directly with an impedance meter. Therefore, a change in current, voltage or impedance of the ring laser gyro can be used as a beat signal according to rotation. Of course, the laser light propagating in the circular direction opposite to each other in the resonator of the ring laser type gyro is emitted to the outside,
If the light is simultaneously incident on the photodetector, a beat signal can be extracted from the photodetector. It is also preferable to perform statistical processing such as averaging and difference using both the change in the current, voltage or impedance of the ring laser gyro and the signal from the photodetector as the beat signal, in order to reduce noise.

Now, according to the present invention, equations (4) and (5)
As shown in (2), the beat frequency increases or decreases according to the rotation direction. Therefore, the rotation direction can be detected by observing the increase / decrease of the beat frequency from the non-rotation time. The rotation direction can be detected when the difference between the oscillation frequencies satisfies the condition (f ₂ −f ₁ ) ≧ 0.

If the oscillation wavelengths of the first laser light and the second laser light are equal, (f ₂₀ −f ₁₀ ) = 0, and the beat frequency (f ₂ −f ₁ ) takes a positive or negative value. If the absolute values of the beat frequencies are equal, only the same signal is detected, and in this case, the rotation direction cannot be detected. On the other hand, according to the present invention, if the sign of the beat frequency is always the same (however, the sign is positive in the description) and only the absolute value changes depending on the rotation direction,
The rotation direction can be detected.

Here, attention should be paid to: In a ring laser gyro, when backscattered light exists,
The so-called lock-in, in which the traveling wave and the backward wave are combined and only one mode oscillates, occurs. In order to avoid this, it is important to eliminate the reflection point in the ring laser type gyro. Therefore, in order to realize the reflection suppressing structure, in the example of FIG. 1, the end surface of the non-circular path 1 is inclined from the propagation direction of the laser light. In addition, as the reflection suppressing structure, a path 3 that becomes narrower as approaching the end as shown in FIG. 3 is employed, or an antireflection film 5 is formed on the end face of the non-circular path 4 as shown in FIG. Is also good.
It goes without saying that combining these reflection suppressing structures is more effective in reducing backscattered light.

Next, a configuration in which clockwise and counterclockwise laser beams are converted into single modes will be described with reference to FIG. The inner path (length d _{3 of} one round) and the outer path (length d ₄ > d _{3 of} one round) are connected at points A and B. In FIG. 5, the inner path and the outer path are optically coupled at two points so that the laser light propagates through a common path as much as possible in order to minimize the injection current to the element. I have. Assuming that the equivalent refractive index of the path is n _eff , the resonance wavelength λ ₃ for the inner path
And the resonance wavelength λ ₄ for the outer path are λ ₃
= N _eff d ₃ / m ₃ and λ ₄ = n _eff d ₄ / m ₄ . Here, m ₃ and m ₄ are each a positive integer. When the equivalent refractive index n _eff = 3.2, d ₃ = 600 μm and d ₄ = 66
FIGS. 6A and 6B show the resonance characteristics for 0 μm, respectively.
Shown in In the figure, the horizontal axis represents the wavelength, and the vertical axis represents the power transmittance of the ring resonator. From this figure, it can be seen that there are a plurality of resonance peaks having the same transmittance, and the intervals between the resonance modes are slightly shifted in FIGS. 6 (a) and 6 (b).

If the inner path (length d _{3 of} one circumference) and the outer path (length d _{4 of} one circumference) are optically coupled at at least one point, the ring resonator has: It becomes a composite resonator. The resonance mode of the composite resonator is shown in FIG.
In (a) and (b), it is determined when the resonance wavelengths match. The result is shown in FIG. As can be seen from this figure, the number of resonance modes is shown in FIGS.
It is significantly reduced compared to. In addition, a main mode having a large transmittance and a sub-mode having a small transmittance appear. In FIG. 5, the inner path and the outer path are optically coupled at two points. However, in order for the ring resonator to be a composite resonator, at least the inner path and the outer path must be It goes without saying that it is only necessary to optically couple at one point.

The oscillation mode is determined by the resonance mode existing in the gain band of the gain spectrum. FIG. 7 (a)
2 shows an oscillation spectrum when the ring resonator is constituted only by the inner path, and FIG. 2B shows an oscillation spectrum in the composite resonator. From this figure, it can be seen that a ring laser gyro having only a single path as in (a) easily oscillates in multiple modes, whereas in the composite resonator as in (b), the submode is sufficiently suppressed, It can be seen that the vertical mode is single. In this example, the composite resonator is configured using two paths having different optical lengths. However, it is needless to say that the number of paths configuring the composite resonator may be three or more.

Some care must be taken when forming a composite resonator. That is, while the laser light propagates through the composite resonator, its circling direction does not reverse. If the circling direction of the laser beam is reversed, the traveling wave and the backward wave are combined in a part of the path, and lock-in occurs.

As described above, the gyro of the present invention generates a beat signal at rest and during rotation. The beat frequency of this signal can be converted into a voltage level and output by inputting the beat signal to a frequency-voltage conversion circuit. Needless to say, a frequency counter may be used instead of the frequency-voltage conversion circuit. As described above, since the beat frequency includes a component proportional to the angular velocity of rotation, the relationship between the rotational speed and the output of the frequency-voltage conversion circuit or the frequency counter can be obtained in advance to obtain the output of the beat frequency. Can be converted to angular velocity. Thus, a ring laser type gyro capable of detecting the rotation direction can be realized by coexisting laser beams circling in opposite directions and having different oscillation frequencies in the optical resonator.

Finally, at least a part of the plurality of routes is
The reason for performing the electric control independently of the other paths will be described. If a current can be passed through the non-circular path independently, the emission intensity in the non-circular path can be controlled independently of the circular path. As a result, it is possible to always generate the emission intensity at which stochastic resonance occurs most efficiently. Also, the refractive index of the path can be modulated by changing the magnitude of the injection current or the applied voltage. Therefore, the optical length of the path can be changed by electric control. Due to the difference in optical length of multiple paths,
Since the number of resonance modes can be limited, if at least a part of the plurality of paths can be electrically controlled independently of the other paths, the difference in optical length can be controlled so that the most stable single longitudinal mode operation can be realized. Become like As a result, compared to a case where the refractive indices of a plurality of paths are controlled by a single electrode (the refractive indices of the respective paths change in the same manner), it is easier to control so that the difference in optical length is optimal.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a drawing which best illustrates the features of the present invention and shows a top view of an optical waveguide of a ring laser type gyro. In the figure, 1 is a non-circular path, 2 is a circular path, 7 is an asymmetric taper, 11 is a clockwise laser beam, 12 is a counterclockwise laser beam, and 21 is a non-circular path 1. It is the light generated by The non-circular path 1 is a circular path (optical waveguide)
2 optically coupled.

In the above configuration, the light 21 generated in the non-circular path 1 outside the optical resonator is transmitted to the circular path 2
Into the optical resonator composed of The light 21 suppresses noise generated by spontaneous emission light combined with the clockwise laser light 11 and the counterclockwise laser light 12. Further, because of the asymmetric taper 7, the oscillation threshold value of the clockwise laser light becomes smaller than the oscillation threshold value of the counterclockwise laser light. as a result,
When both of these laser lights are oscillating, the light intensity of the clockwise laser light becomes greater than the light intensity of the counterclockwise laser light. When the injection current is 6 mA, the light intensities of the clockwise and counterclockwise laser beams are 3.3 mW and 2.6 mW, respectively. When the semiconductor ring laser gyro is stationary, the laser light 11
And the oscillation wavelength of the laser beam 12 are substantially equal, and the oscillation wavelength λ
Is about 1.55 μm. However, since the light intensities of these laser lights are different, at a driving current of 6 mA,
The oscillation frequency of laser light 11 and laser light 12 is 20k
Hz. Then, the laser beams 11 and 12 interfere in the semiconductor ring laser type gyro. At this time, the power supply current was adjusted to be constant, and the voltage between the anode and the cathode was monitored.
A signal having a frequency of 20 kHz at V is obtained. That is, a beat signal can be detected even when the semiconductor ring laser gyro is stationary. In FIG. 1, the orbital path 2 is circular, and the length of one circumference is 600 μm.
At this time, 3 seconds per second, such as camera shake or automobile vibration
When the laser beam 12 is rotated clockwise at a speed of 0 degrees, the oscillation frequency of the counterclockwise laser light 12 increases by 103.225 Hz. On the other hand, the oscillation frequency of the clockwise laser light 11 decreases by 103.225 Hz. Therefore, the beat frequency Δf is 20 kHz + 206.45 Hz.

On the other hand, when the semiconductor ring laser type gyro is rotated counterclockwise at a speed of 30 degrees per second,
The beat frequency Δf is 20 kHz-206.45 Hz.

In this way, not only the rotation angular velocity but also the rotation direction can be detected by increasing or decreasing the beat frequency from the standstill. Conventionally, the beat frequency fluctuates by about 1% due to spontaneous emission noise, but the fluctuation is reduced to about 0.1% by reducing spontaneous emission noise by stochastic resonance. Here, there is something to note. In a ring laser gyro, when backscattered light is present, a traveling wave and a backward wave are combined, and so-called lock-in in which only one mode oscillates occurs. In order to avoid this, it is necessary to eliminate the reflection point in the ring laser type gyro. Therefore, in order to realize the reflection suppressing structure, in the example of FIG. 1, the end surface of the non-circular path 1 is inclined from the propagation direction of the laser light. In addition,
In the present embodiment, the shape of the ring resonator is circular. Needless to say.

(Second Embodiment) FIG. 3 is a drawing that best illustrates the features of the present invention and shows a top view of an optical waveguide of a ring laser type gyro. In FIG.
Is a non-circular path, and 23 is light generated in the non-circular path 3. The difference from the first embodiment is that the non-circular path 3
Is narrowed toward the end as shown in FIG. Such a reflection suppressing structure is also effective in reducing backscattered light.

(Third Embodiment) FIG. 4 is a drawing that best illustrates the features of the present invention, and shows a top view of an optical waveguide of a ring laser type gyro. In FIG.
Is the light generated in the non-circular path 4, and 24 is the light generated in the non-circular path 4. The difference from the first embodiment is that the non-circular path 4
Is that an anti-reflection film 5 is formed on the end face. Such a reflection suppressing structure is also effective in reducing backscattered light.

The end face of the non-circular path may be inclined from the direction of propagation of the laser beam, the non-circular path may become narrower as approaching the end, or an anti-reflection film may be formed on the end face. The combination of the above structures is also suitable for further reducing the backscattered light.

(Fourth Embodiment) FIG. 5 is a drawing that best illustrates the features of the present invention, and shows a top view of an optical waveguide. In the figure, the inner path (length d _{3 of} one round)
2 and an outer route (length d ₄ > d ₃ ) 6 are connected at points A and B. Assuming that the equivalent refractive index of the path is n _eff , the resonance wavelength λ ₃ for the inner path and the resonance wavelength λ ₄ for the outer path are respectively λ ₃ = n _eff d ₃ /
m ₃ , λ ₄ = n _eff d ₄ / m ₄ Where m ₃ , m
₄ is a positive integer. Equivalent refractive index n _eff = 3.
6A and 6B show resonance characteristics for d ₃ = 600 μm and d ₄ = 660 μm, respectively. In the figure, the horizontal axis represents the wavelength, and the vertical axis represents the power transmittance of the ring resonator. From this figure, it can be seen that there are a plurality of resonance peaks having the same transmittance, and the intervals between the resonance modes are slightly shifted in FIGS. 6 (a) and 6 (b).

In FIG. 5, the inner route (the length d of one round)
₃ ) Since the ring 2 and the outer path (length d ₄ d ₃ ) 6 are optically coupled at points A and B, this ring resonator becomes a composite resonator. The resonance mode of the composite resonator is determined when the resonance wavelengths overlap in FIGS. 6A and 6B. The result is shown in FIG. As can be seen from this figure, the number of resonance modes is significantly reduced as compared with FIGS. 6 (a) and 6 (b). Moreover,
A main mode having a large transmittance and a submode having a small transmittance appear. In FIG. 5, the inner path and the outer path are optically coupled at two points. However, in order for the ring resonator to be a composite resonator, at least the inner path and the outer path must be It goes without saying that it is only necessary to optically couple at one point.

The oscillation mode is determined by the resonance mode existing in the gain band of the gain spectrum. FIG. 7 (a)
2 shows an oscillation spectrum when a ring resonator is constituted only by the inner path 2, and (b) shows an oscillation spectrum in the composite resonator. From this figure, it can be seen that a ring laser gyro having only a single path as in (a) easily oscillates in multiple modes, whereas in the composite resonator as in (b), the submode is sufficiently suppressed, It can be seen that the vertical mode is single. In this example, two optical lengths different from each other are used.
Although the composite resonator is configured using one path, it goes without saying that the number of paths configuring the composite resonator may be three or more.

Further, since the inner path and the outer path are optically coupled as shown in FIG. 5, while the laser light propagates in the composite resonator, the circling direction does not reverse. As a result, the traveling wave and the backward wave do not combine due to the coupling of the paths. Therefore, a single longitudinal mode can be realized without lock-in.

A semiconductor ring laser gyro is constructed using the ring resonator shown in FIG. At a driving current of 6 mA, the oscillation wavelength λ when the semiconductor ring laser type gyro is stationary is about 1.55 μm. Since the light intensities of these laser lights are different, a driving current of 6 m
In A, the oscillation frequencies of the laser light 11 and the laser light 12 differ by 20 kHz. Then, the laser beams 11 and 12 interfere in the semiconductor ring laser type gyro. At this time, if the power supply current is adjusted to be constant and the voltage between the anode and cathode is monitored,
A signal having an amplitude of 100 mV and a frequency of 20 kHz is obtained.
That is, a beat signal can be detected even when the semiconductor ring laser gyro is stationary.

In FIG. 5, the orbital path 2 is circular, and the length of one circumference is 600 μm. At this time, if the laser beam 12 is rotated clockwise at a speed of 30 degrees per second, such as camera shake or vehicle vibration, the oscillation frequency of the counterclockwise laser light 12 increases by 103.225 Hz. on the other hand,
The oscillation frequency of the clockwise laser beam 11 is 103.22
Decreases by 5 Hz. Therefore, the beat frequency Δf is 20 kHz + 206.45 Hz. On the other hand, when the semiconductor ring laser type gyro is rotated counterclockwise at a speed of 30 degrees per second, the beat frequency Δf becomes 20 kHz.
-206.45 Hz.

In this way, not only the rotational angular velocity but also the rotational direction can be detected by increasing or decreasing the beat frequency from the standstill.

FIG. 8 shows a state when the beat signal at this time is measured by a spectrum analyzer. FIG.
(A) is a case where there is only one laser light path. On the other hand, FIG. 8B shows a case where the composite resonator is configured as shown in FIG. In both figures, the horizontal axis is the displacement from the center frequency, and the vertical axis is the spectrum intensity. When the longitudinal mode is multi-mode, the spectrum width is wide as shown in FIG. On the other hand, when the ring laser type gyro oscillates in a single longitudinal mode, as shown in FIG.
The spectrum width is reduced, and the signal-to-noise ratio for beat signal detection is improved. Note that the spectral line width in FIG.
This is 1/100 in FIG.

It is also preferable that at least a part of the plurality of paths be electrically controlled independently of the other paths.
Now, the reason will be described. If a current can be passed through the non-circular path independently, the emission intensity in the non-circular path can be controlled independently of the circular path. As a result, it is possible to always generate the emission intensity at which stochastic resonance occurs most efficiently. Also, the refractive index of the path can be modulated by changing the magnitude of the injection current or the applied voltage. Therefore, the optical length of the path can be changed by electric control. Since the number of resonance modes can be limited by the difference in the optical length of the plurality of paths, the most stable single longitudinal mode operation can be realized if at least a part of the plurality of paths can be electrically controlled independently of the other paths. Thus, the difference in optical length can be controlled. As a result, compared to a case where the refractive indices of a plurality of paths are controlled by a single electrode (the refractive indices of the respective paths change in the same manner), it is easier to control so that the difference in optical length is optimal.

(Fifth Embodiment) FIG. 9 is a diagram best representing the features of the fifth embodiment of the present invention. In the figure, 6 is a non-circular path, and 26 is light generated in the non-circular path 6. The difference from the first embodiment is that the non-circular path 6 and the circular path 2 are not connected. However, as shown in FIG. 9, if the non-circular path 6 and the circular path 2 are arranged close to each other, they are optically coupled, and as a result, the same effect as in the first embodiment is obtained. Obtainable.

[0048]

According to the present invention described above, a ring laser type gyro having a good signal-to-noise ratio can be achieved by suppressing noise due to spontaneous emission light and limiting the number of oscillation modes by a method that does not cause lock-in. Can be provided.
Further, the rotation direction and the rotation speed can be detected without a mechanical mechanism such as dither.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a ring laser type gyro according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an emission wavelength distribution spectrum for explaining the principle of the present invention.

FIG. 3 is a diagram illustrating a ring laser gyro according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a ring laser type gyro according to a third embodiment of the present invention.

FIG. 5 is a diagram illustrating a ring laser gyro according to a fourth embodiment of the present invention.

FIG. 6 is a diagram illustrating a resonance mode of a ring laser gyro according to a fourth embodiment of the present invention.

FIG. 7 is a diagram illustrating an oscillation spectrum of a ring laser gyro according to a fourth embodiment of the present invention.

FIG. 8 is a diagram illustrating the spectrum of a beat signal of a ring laser gyro according to a fourth embodiment of the present invention.

FIG. 9 is a diagram illustrating a ring laser gyro according to a fifth embodiment of the present invention.

FIG. 10 is a diagram illustrating a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-circular path 2 Non-circular path 3 Non-circular path 4 Non-circular path 5 Anti-reflection film 6 Non-circular path 7 Asymmetrical taper 11 Clockwise laser beam 12 Counterclockwise laser Light, 21, 23, 24, 26 Light generated in a non-circular path

Claims (11)

[Claims] 1. A circular path having a first emission wavelength distribution, and optically coupled to at least a part of the circular path;
And a non-circular path having a second emission wavelength distribution different from the first emission wavelength distribution, wherein an end of the non-circular path is a reflection suppressing structure. Laser type gyro. 2. The ring laser type gyro according to claim 1, wherein the reflection suppressing structure is constituted by an end face inclined from a propagation direction of the laser light. 3. A ring laser type gyro according to claim 1, wherein said reflection suppressing structure comprises a path which becomes narrower as approaching an end. 4. The ring laser type gyro according to claim 1, wherein the reflection suppressing structure is constituted by an end face on which an anti-reflection film is formed. 5. A combination of two or more of an end face inclined with respect to a propagation direction of a laser beam, a path narrowing as approaching the end, or an end face having an anti-reflection film formed thereon, wherein the reflection suppressing structure is inclined. The ring laser type gyro according to claim 1, wherein the gyro comprises: 6. The laser beam wherein the orbital path has a plurality of paths having different optical lengths, and at least a part of the plurality of paths is optically coupled and propagates in an optical resonator. 6. The ring laser type gyro according to claim 1, wherein the circling direction of the gyro is not reversed by the plurality of paths. 7. The circuit according to claim 1, wherein the orbital path includes at least an asymmetric taper portion, and laser lights having different light intensities propagate in opposite orbiting directions in the optical resonator. Item 7. A ring laser type gyro according to items 1 to 6. 8. A ring laser type gyro according to claim 1, wherein laser lights having different oscillation frequencies coexist in the optical resonator and propagate in opposite circular directions. 9. The ring laser gyro according to claim 1, further comprising a plurality of electrodes capable of electrically controlling at least a part of the path independently. 10. A method of driving a ring laser gyro, wherein at least a part of the plurality of electrodes is electrically controlled independently. 11. The peak of the first emission wavelength distribution,
2. The ring laser gyro according to claim 1, wherein the gyro is different from a peak of the second emission wavelength distribution.