JP2002310666A - Semiconductor ring laser gyro - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ring laser gyro which is less liable to be affected by irregularities of side surfaces of light guides, and resulting in having little back scattering, and resisting the occurrence of lock-in phenomena. SOLUTION: In each of the light guides constituting a ring resonator, a high resistance layers 40 are formed on both sides of an active layer 24. Regions, having no light gain, are thereby formed on both sides of the active layer 24 having a light gain. The resistance layers 40 are in contact with air (refractive index of 1). The refractive index of a semiconductor is about 3.5, and the difference in refractive indices actualizes an index light guide structure. Further more, a gain light guide structure is formed in the index light guide structure. Since the resistance layers (semiconductor) 40 have no optical gain, light intensity is small at their interfaces. Even if the side surfaces of the light guides have irregularities, the light intensity of back scattering light is made small relative to laser light and the lock-in phenomenon, due to non-linearity effects being less liable to occur. The resistance layers 40 without optical gains can be actualized by proton injection or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates 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. Among them, the earliest development started with a ring laser type gyro using a semiconductor laser,
It 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, there is, for example, Japanese Patent Publication No. Sho 62-039836, an example of which is shown in FIG.

[0004]

In a conventional ring laser gyro, when the rotation speed is low, a lock-in phenomenon occurs in which the oscillation frequency is pulled into one mode due to the nonlinearity of the medium. The cause of this lock-in phenomenon is backscattered light generated by minute irregularities on the side and end faces of the optical waveguide. The presence of the backscattered light makes the lock-in phenomenon more likely to occur because the backscattering increases the coupling between the laser lights circulating in the opposite direction. To release the lock-in phenomenon,
(1) Increasing the rotation speed increases the oscillation frequency difference between the laser beams circulating in the opposite direction to reduce the coupling coefficient between the laser beams. (2) Reduces the irregularities on the side and end surfaces of the optical waveguide. Proposals have been made to suppress backscattered light. As the former method, a high-speed dither of about 300 degrees / second is applied to a ring laser gyro in advance. On the other hand, as the latter method, it is effective to use a smooth mirror. Further, the conventional ring laser type gyro cannot detect the rotation direction by itself. Therefore, the rotation direction is determined from the correlation between the dither direction and the signal.

Accordingly, an object of the present invention is to provide a ring laser type gyro which is hardly affected by the unevenness of the side surface of the optical waveguide, as a result, the backscatter is small and the lock-in phenomenon does not easily occur.

Another object of the present invention is to provide a ring laser type gyro capable of detecting a rotation direction and a rotation speed without a mechanical mechanism such as dither.

[0007]

In order to solve the above problems, a ring laser type gyro of the present invention includes at least an optical waveguide having at least a gain waveguide structure inside a refractive index waveguide structure for a horizontal transverse mode. I have.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The light intensity of backscattered light from a semiconductor ring laser gyro will be described with reference to FIGS. 1, 2, and 14 to 17. FIG.

FIG. 1 is a top view schematically showing the structure of a ring laser type gyro according to the present invention.
Is a ring resonator. FIG. 2 is a sectional view schematically showing the structure of the ring laser type gyro of the present invention.
AA 'of FIG. As shown in FIG. 2, a high resistance layer 40 is formed on both sides of the active layer 24 in the cross section of the optical waveguide constituting the ring resonator. Thus, regions without optical gain are formed on both sides of the active layer 24 having optical gain. The high resistance layer 40 is in contact with air (refractive index 1). The refractive index of a semiconductor is about 3.5, and a refractive index waveguide structure is realized by this difference in refractive index. That is,
As shown in FIG. 14, a gain waveguide structure is formed in the refractive index waveguide structure. If there is a sufficient difference between the region having no optical gain formed on both sides of the active layer 24 and the region having optical gain, the optical gain of the regions formed on both sides of the active layer 24 as shown in FIG. It need not be zero.

Here, backscattering will be considered. In a semiconductor ring laser, the main cause of backscattering is unevenness or roughness on the side surface of the optical waveguide. Due to the unevenness on the side surface, the complex refractive index is spatially modulated, and as a result, the backscattered light and the laser light are combined. At this time, both the real part and the imaginary part of the complex refractive index are affected. FIG.
FIG. 15 shows a calculation result of the amplitude reflectance of the backscattering in the structure of FIG.

For comparison, FIG. 17 shows a calculation result of the amplitude reflectance of backscattering for another refractive index waveguide structure shown in FIG. The horizontal axis in each of FIGS. 15 and 17 is a step of unevenness. In these figures, the dashed line
The position where the amplitude reflectance of the backscattering is 0.01 is shown. Also,
The resonator length L is 300 μm, and the parameter is the oscillation wavelength. 15, the active layer width 4 [mu] m, the high-resistance layer width 2 [mu] m, the amplitude absorption coefficient a _c of the high-resistance layer 40 is a calculation result in the case of an optical waveguide of -25cm ^-1. The entire width of the optical waveguide is 8 μm
It is. The oscillation wavelength is 1.55 μm, 1.3 μm, 0.8
Although the amplitude reflectance curve with 5 μm as a parameter is shown, the curves for wavelengths of 1.3 μm and 0.85 μm overlap. The equivalent refractive index of the semiconductor layer is uniform and 3.2. From FIG. 15, it can be seen that the amplitude reflectance of the backscattering becomes 0.01 when the roughness of the interface, that is, the unevenness of the side wall where the high-resistance layer 40 contacts the air is 82 nm. On the other hand, FIG. 17 shows the calculation results in the case of an optical waveguide having an active layer (core) width of 4 μm, a cladding width of 2 μm, an equivalent refractive index of the core of 3.2, and an equivalent refractive index of the cladding n _c of 3.19. The width of the entire optical waveguide is 8 μm. An amplitude reflectance curve is shown in which the oscillation wavelength is 1.55 μm, 1.3 μm, and 0.85 μm as parameters.
The curves for m and 0.85 μm overlap. The amplitude reflectance of the back scattering is 0.01 when the interface roughness, that is, the unevenness of the cladding side wall is about 27 nm. When the results of FIGS. 15 and 17 are compared with each other for the unevenness when the amplitude reflectance of the backscattering becomes 0.01, it can be seen from FIG. The value of the unevenness is about three times. That is, the structure of FIG. 14 has smaller backscattering for the size of the unevenness. The reason for this is that in FIG. 14, since there is no optical gain at the interface between air and the high-resistance layer (semiconductor), the light intensity at the interface is small, and light does not feel much unevenness at the interface. Therefore, even if the side surface of the optical waveguide has irregularities, the light intensity of the backscattered light with respect to the laser light is reduced, and the lock-in phenomenon due to the nonlinear effect is less likely to occur. On the other hand, in FIG. 17, since the optical gain is uniform between the core and the clad, the light intensity at the interface between the air and the clad (semiconductor) is large, and the light feels strongly at the interface. Therefore, the amplitude reflectance of the backscatter is larger than that of FIG. In this case, if the side surface of the optical waveguide has irregularities, backscattered light having such a light intensity that the nonlinear effect cannot be ignored is generated. Then, a lock-in phenomenon occurs.

Although FIG. 1 shows a square ring resonator, the shape of the ring resonator is not limited to this and may be any shape. Further, the high resistance layer can be realized by proton implantation or the like.

Finally, a method of detecting the rotation direction will be described. FIG. 13 is a top view showing a structure in which an asymmetrical taper 2 is provided on the inner periphery. With this structure, a difference in laser light loss can be made depending on the circling direction. In the case of FIG. 13, the loss for the clockwise laser light is smaller than the loss for the counterclockwise laser light. Therefore, the light intensity of the clockwise laser light is greater than that of the counterclockwise laser light. When two modes of laser light coexist, the oscillation frequency f _i and the photon number density S _i (i =
It is known that there is the following relationship between (1) and (2).

[0014]

(Equation 1) Here, Φ _i is a phase, Ω _i is a resonance angular frequency, σ _i is a coefficient representing mode pull-in, ρ _i is a coefficient representing mode self-extrusion, and τ _ij is a coefficient representing mode mutual extrusion. 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 as described above, if laser lights having different oscillating frequencies co-exist in the optical resonator and propagate in opposite circular directions,
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 λ1. Further, the wavelength of the second laser light circulating counterclockwise is defined as λ ₂ (λ ₁ ). When rotating the ring laser type gyro clockwise, the clockwise first
The oscillation frequency f ₁ of the laser beam as compared with the oscillation frequency f ₁₀ during non-rotation

[0017]

(Equation 2) Only decrease. Here, S ₁ is a closed area surrounded by the optical path of the first laser light, L ₁ 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.

[0018]

(Equation 3) Only increase. Here, S2 is a closed area surrounded by the optical path of the second laser light, and L2 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,

[0019]

(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 semiconductor laser and a semiconductor 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 terminal current when a constant voltage source is used as the drive power supply. 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, a 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, if the laser light propagating in the opposite direction in the resonator of the ring laser gyro is emitted to the outside and 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 takes a positive or negative value. If the absolute values of the beat frequencies are equal, only the same signal is detected,
In this case, the rotation direction cannot be detected. On the contrary,
If the sign of the beat frequency is always the same (however, the sign is positive in the description) and only its absolute value changes depending on the rotation direction as in the present invention, the rotation direction can be detected. .

As described above, the gyro of the present invention generates a beat signal when stationary and when rotating. 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.

[0025]

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, reference numeral 1 denotes a ring resonator. FIG. 2 is a sectional view cut along the line AA ′ in FIG. In the figure, 11 is a cathode, 21
Is a semiconductor substrate, 22 is a buffer layer, 23 is a light guide layer, 24 is an active layer, 25 is a light guide layer, 26 is a cladding layer, 27 is a cap layer, and 28 is an anode. Also,
3 to 9 are cross-sectional views illustrating the steps of manufacturing the semiconductor laser gyro according to the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. In each figure, reference numeral 31 denotes a photoresist.

First, referring to FIGS. 3 to 9, FIG.
The manufacturing process of the semiconductor laser gyro of the present invention shown in FIG.

First, as shown in FIG. 3, an n-InP substrate 21 (thickness: 350 μm) is formed by using a metal organic chemical vapor deposition method.
On the InP buffer layer 22 (0.05 μm thickness),
An undoped InGaAsP optical guide layer 23 having a composition of 1.3 μm (thickness 0.15 μm), an undoped InGaAsP active layer 24 having a composition of 1.55 μm (thickness 0.1 μm),
Undoped InGaAsP optical guide layer 25 (thickness 0.15 μm) having a composition of 1.3 μm, p-InP clad layer 26
(Thickness: 2 μm) p-InGaAsP having a composition of 1.4 μm
A cap layer 27 (thickness 0.3 μm) is grown.

After the crystal growth, as shown in FIG.
On the AsP cap layer 27, Cr /
Au is formed by vapor deposition. Then, using a spin coater, AZ-1350 (manufactured by Hoechst) is applied as a photoresist 31 on the anode 28 to a thickness of 1 μm. After performing a heat treatment at 80 ° C. for 30 minutes as a pre-bake, the wafer is exposed with a mask.

The photoresist 31 after development and rinsing is
It has a slightly tapered shape as shown in FIG. Also,
The minimum width of the stripe is 5 μm, the maximum width is 20 μm, and the length of one circumference is 764 μm.

Thereafter, the wafer is introduced into a reactive ion etching apparatus, and as shown in FIG.
Dry etching of r / Au is performed. The gas used for the etching is Ar for Au and CF ₄ for Cr. Next, the height of the optical waveguide is set to 3.2 using chlorine gas.
The semiconductor layer is etched to a thickness of μm. This is shown in FIG.

Thereafter, proton implantation is performed using the photoresist 31 as a mask to form a high-resistance layer 40.

Then, as shown in FIG.
1 is peeled off. Thereafter, the anode 28 is annealed in a hydrogen atmosphere to realize ohmic contact.

Next, as shown in FIG.
Then, AuGe / Ni / Au is deposited as a cathode 11.

Finally, annealing is performed in a hydrogen atmosphere to make ohmic contact. In order to change the angle between the end face and the side wall, etching is performed separately for the end face and the side face. In this case, when the end face is etched, the side face area is protected by covering it with a photoresist or the like. Conversely, when the side surface is etched, the end surface region is protected by covering it with a photoresist or the like.

In the above configuration, when the injection current is 6 mA, the light intensities of the clockwise and counterclockwise laser beams are both 4 mW. When the semiconductor ring laser gyro is stationary, the oscillation wavelength of the clockwise laser light and the counterclockwise laser light are equal, and the oscillation wavelength λ
Is 1.55 μm. When it is rotated clockwise at a speed of 30 degrees per second, which is about camera shake or the vibration of a car,
The oscillation frequency of the counterclockwise laser light is 103.225
Hz. On the other hand, the oscillation frequency of the clockwise laser light decreases by 103.225 Hz. Therefore, the beat frequency Δf is 206.45 Hz. Thus, the measurement of the rotational angular velocity becomes possible. In the present embodiment, the shape of the ring resonator is a quadrangle, but it is needless to say that the shape is not limited to this, and may be any shape such as a circle, a hexagon, and a triangle.

In FIG. 2A, since the high resistance layers 40 are formed on both sides of the active layer 24, the current is efficiently injected only into the light emitting portion. As a result, a low oscillation threshold current and high slope efficiency are realized.

To simply realize the gain waveguide structure,
As shown in FIG. 2B, the width of the anode 28 may be smaller than the ridge width. However, in this case, since the carrier concentration in the region near the interface between the ridge and the air becomes small, this region has a small optical gain or gives a loss to laser light. Therefore, FIG.
The oscillation threshold current is higher and the slope efficiency is lower than in the structure of (1).

(Second Embodiment) FIG. 10 shows a second embodiment of the present invention.
3 is a drawing that best illustrates the features of the embodiment of the present invention, and shows a cross-sectional view of an optical waveguide of a ring laser type gyro.
In the figure, reference numeral 30 denotes an insulating film. The same components as those in FIG. 2 are denoted by the same reference numerals.

According to the above configuration, the insulating film 30 serves as a protective film on the side surface, which also contributes to improvement of the reliability of the device.

(Third Embodiment) FIG. 11 shows a third embodiment of the present invention.
3 is a drawing that best illustrates the features of the embodiment of the present invention, and shows a cross-sectional view of an optical waveguide of a ring laser type gyro.
In the figure, reference numeral 50 denotes a low refractive index layer. The same components as those in FIG. 2 are denoted by the same reference numerals.

According to the above configuration, current is efficiently injected only into the light emitting section. When the low-refractive-index layer 50 is formed of a semiconductor, the low-refractive-index layer 50 may have a Fe-doped resistance layer or a multilayer structure such as a pnpn structure. Further, as the low refractive index layer 50, polyimide or the like may be used. In order to efficiently confine light in the active layer, the refractive index of the low refractive index layer 50 is
It is necessary that the refractive index be smaller than the refractive index of the active layer 24.

(Fourth Embodiment) FIG. 12 shows a fourth embodiment of the present invention.
3 is a drawing that best illustrates the features of the embodiment of the present invention, and shows a cross-sectional view of an optical waveguide of a ring laser type gyro.
In the figure, 30 is an insulating film, and 40 is a high resistance layer.
The same components as those in FIG. 2 are denoted by the same reference numerals.

The difference from FIG. 10 is that the side surface of the active layer 24 is
Is not exposed to air at all during device fabrication,
This structure is suitable when an AlGaAs-based material or the like that is easily oxidized is used.

(Fifth Embodiment) FIG. 13 shows a fifth embodiment of the present invention.
FIG. 3 is a drawing that best illustrates the features of the embodiment of the present invention, and shows a top view of an optical waveguide of a ring laser type gyro.
In the figure, reference numeral 2 denotes an asymmetric taper.

In the above configuration, there is a difference in loss depending on the circling direction of the laser light. In the case of FIG. 13, the loss for the clockwise laser light is smaller than the loss for the counterclockwise laser light. For this reason, 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, clockwise,
The light intensity of the counterclockwise laser light is 3.3m each
W, 2.6 mW. When the semiconductor ring laser gyro is stationary, the oscillation wavelengths of both laser beams are almost equal, and the oscillation wavelength λ is about 1.55 μm. However, since the light intensities of these laser beams are different, the oscillation frequencies of the clockwise laser beam and the counterclockwise laser beam differ by 20 kHz at a driving current of 6 mA. These laser lights interfere with each other in the semiconductor ring laser gyro. At this time, if the power supply current is adjusted to be constant and the voltage between the anode and the cathode is monitored, a signal having an amplitude of 100 mV and a frequency of 20 kHz can be obtained. That is, a beat signal can be detected even when the semiconductor ring laser gyro is stationary.

At this time, if the camera is rotated clockwise at a speed of 30 degrees per second, such as camera shake or automobile vibration,
The oscillation frequency of the counterclockwise laser light is 103.225
Hz. On the other hand, the oscillation frequency of the clockwise laser light decreases by 103.225 Hz. Therefore, the beat frequency Δf is 20 kHz + 206.45 Hz.
Becomes 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.

[0047]

According to the present invention described above, it is possible to provide a ring laser type gyro which is less affected by backscattering and does not easily cause a lock-in phenomenon. Further, a ring laser gyro that can detect the rotation direction and the rotation speed without a mechanical mechanism such as dither is realized.

[Brief description of the drawings]

FIG. 1 is a top view showing a structure of a semiconductor laser gyro according to the present invention.

FIG. 2 is a sectional view showing a structure of a semiconductor laser gyro according to the present invention.

FIG. 3 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser gyro according to the present invention.

FIG. 4 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser gyro according to the present invention.

FIG. 5 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser gyro according to the present invention.

FIG. 6 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser gyro according to the present invention.

FIG. 7 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser gyro according to the present invention.

FIG. 8 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser gyro according to the present invention.

FIG. 9 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser gyro according to the present invention.

FIG. 10 is a sectional view showing a structure of a semiconductor laser gyro according to the present invention.

FIG. 11 is a sectional view showing a structure of a semiconductor laser gyro according to the present invention.

FIG. 12 is a sectional view showing a structure of a semiconductor laser gyro according to the present invention.

FIG. 13 is a top view showing the structure of the semiconductor laser gyro according to the present invention.

FIG. 14 is a sectional view showing a structure of an optical waveguide of a semiconductor laser gyro according to the present invention.

FIG. 15 is a diagram showing calculation results for the relationship between the amplitude reflectance of backscattering and the unevenness in the waveguide of FIG. 14;

FIG. 16 is a sectional view showing a structure of an optical waveguide of a refractive index guide type.

17 is a diagram illustrating a calculation result with respect to a relationship between an amplitude reflectance of backscattering and a step of unevenness in the waveguide of FIG. 16;

FIG. 18 is a diagram for explaining a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ring resonator 2 Asymmetric taper 11 Cathode 21 Semiconductor substrate 22 Buffer layer 23 Light guide layer 24 Active layer 25 Light guide layer 26 Cladding layer 27 Cap layer 28 Anode 30 Insulating film 31 Photo resist 40 High resistance layer 50 Low refractive index layer

Continued on front page F term (reference) 2F105 AA02 AA03 AA08 BB01 DD07 DD11 2H047 KA04 KA05 KA12 MA07 NA04 QA02 RA01 5F073 AA03 AA45 AA55 AA66 CA12 CB02 CB22 DA05 DA16 DA25 EA26 EA27

Claims (3)

[Claims] In the width direction of a refractive index waveguide for a horizontal transverse mode, a range from a center to a predetermined distance is such that the refractive index waveguide is an optical waveguide having a gain, and a range from the predetermined distance to a side wall is: A semiconductor ring laser gyro, wherein the refractive index waveguide is an optical waveguide having no gain waveguide. 2. The ring laser gyro according to claim 1, wherein the refractive index waveguide or the gain waveguide has an asymmetric shape. 3. The ring laser gyro according to claim 1, wherein the specific resistance of the optical waveguide having no gain is higher than the specific resistance of the optical waveguide having the gain.