JP2003042769A - Optical gyro and driving method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To switch measurement precision and power consumption according to the motion state of a body while keeping a measurement band narrow. SOLUTION: The optical gyro has a plurality of annular resonator type semiconductor lasers, each having asymmetrical tapered parts in one travel direction of laser light and the travel direction of laser light reverse to the mentioned travel direction, in part of an optical waveguide, and the plurality of annular resonator type semiconductor lasers have tapered parts 13 and 14 which tilt differently from each other. A driving method for the optical gyro has a plurality of annular resonator type semiconductor lasers having different oscillation threshold current differences between the laser light in one travelling direction and the laser light in the reverse direction and injects currents corresponding to the respective annular resonator type semiconductor lasers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical gyro for detecting rotation using a ring resonator type semiconductor laser and a method for driving the optical gyro.

[0002]

2. Description of the Related Art Conventionally, to detect a rotational angular velocity, a gyro using a rotor that uses the law of conservation of angular momentum, a mechanical gyro such as a vibration gyro that uses Coriolis force, and an optical gyro that uses the Sagnac effect are used. Has been used. The optical gyro includes a ring laser gyro, an optical fiber gyro, a passive ring resonator gyro, and the like. Since these optical gyros do not require a mechanically movable part, they have no mechanical wear and can have a long life. Furthermore, it has the advantage that it can be activated instantaneously and has a wide dynamic range, which was an epoch-making invention in the gyro field. However, the optical gyro has a problem in that it is larger than the vibration gyro. For example, even if it is installed in a camera shake correction device, the optical gyro requires a large space inside the camera, so its position becomes the vibration gyro. I had to give up. Recently, as a compact and highly accurate ring laser type gyro, an innovative gyro composed of a ring resonator type semiconductor laser on a semiconductor substrate has been proposed. As this publicly known document, Japanese Patent Publication No. 62-3983
No. 6, JP-A-4-174317, JP-B-6-
There is 38529 publication.

This conventional technique will be described with reference to FIG. FIG. 7 shows a ring resonator type semiconductor laser gyro disclosed in Japanese Patent Publication No. Sho 62-39836, and FIG.
Is a plan view of a gyro composed of a ring resonator type semiconductor laser on a semiconductor substrate, and FIG. 7B is a sectional view thereof.

In FIG. 7, a ring resonator type semiconductor laser 505 has electrodes 506 and 507 on the upper and lower sides, and an insulating layer 508, a p-type GaAs layer 509, and a p-type Al _X Ga ₁ are provided between the electrodes 506 and 507. _-X As layer 510, n-type Al _X G
a _1-X As layer [waveguide] 511, n-type Al _X Ga _1-X As
The layer 512 and the n-type GaAs layer 513 are interposed. However,
x is different in each layer. This ring resonator type semiconductor laser 5
Since the driving power source 502 is connected between both electrodes 506 and 507 of No. 05 via the resistor 501, the injection current is
The ring-shaped waveguide 511 flows in a ring shape from 06.
Is produced and ring laser oscillation is performed.

When the ring laser oscillation is performed, clockwise and counterclockwise laser lights exist independently in the ring resonator type semiconductor laser, and the ring resonator type is present at a certain angular velocity with respect to the axial direction of the ring. When the semiconductor laser rotates, a difference occurs between the oscillation frequencies of the clockwise and counterclockwise laser light due to the Sagnac effect, and a beat occurs. Due to this beat, the light intensity changes at the beat frequency, and as a result, the impedance between the terminals of the ring resonator type semiconductor laser 505 changes at the beat frequency. When the ring resonator type semiconductor laser 505 is driven by a constant current, the change in the impedance is detected from the output terminal 504 via the DC blocking capacitor 503 as a change in the terminal voltage of the ring resonator type semiconductor laser 505. can do. Thus, the angular velocity can be detected by measuring the beat frequency.

Due to such a system, the ring resonator type semiconductor laser gyro does not require a photodetector or an optical isolator as a countermeasure against backscattering. Therefore, it is smaller than the vibrating gyro, and has features that power consumption can be reduced and start-up time can be shortened. It is suitable for use as, for example, an image stabilization device for still cameras and video cameras, and a vehicle navigation system.

Now, let us consider a case where such a gyro is mounted on a vehicle and used for detecting the position of the vehicle, that is, for car navigation. In the position detector of the car navigation, the moving distance of the vehicle and the traveling direction of the vehicle are constantly measured, and if the initial position of the vehicle is known, the subsequent current position of the vehicle can be calculated. In this car navigation, a geomagnetic sensor and a gyro are used to detect the traveling direction of the vehicle.

It is known that when a gyro is used to detect the traveling direction of a vehicle in car navigation, the required accuracy of angular velocity detection differs when the vehicle is running and when it is stopped. That is, when the vehicle is running,
A high-speed response to the angular velocity fluctuation is required rather than the detection accuracy, but a high-speed response to the angular velocity fluctuation is not required when the vehicle is stopped, and high accuracy is required for the gyro angular velocity detection. That is, if only the measurement accuracy of the angular velocity is described, the accuracy required when the vehicle is stopped is higher than the accuracy when the vehicle is running. The reason for this is that the heading of the vehicle can be obtained by time-integrating the angular velocity detected by the gyro, but if noise is added to the detected signal, it will be accumulated as an integration error and the vehicle will stop in particular. This is because all the noises related to the angular velocity detection are accumulated as the azimuth detection error during the period in which the detection is performed.

[0009]

As described above, the angular velocity measurement accuracy required for the gyro may differ depending on the state of the moving object. The angular velocity accuracy detected by the ring resonator type semiconductor laser gyro is determined by the spectral line width of the laser light rotating clockwise and counterclockwise in the ring resonator type semiconductor laser. The narrower the spectral line width of each of the clockwise and counterclockwise laser beams, the narrower the spectral line width of the beat generated by these two laser beams. Since the ring resonator type semiconductor laser gyro converts an angular velocity into a beat frequency, the narrower the frequency spectrum line width of this beat, the higher the accuracy of angular velocity detection. In order to narrow the spectral line width of laser light,
Increase the injection current to the ring resonator type semiconductor laser,
The laser light intensity may be increased. However, increasing the injection current leads to higher power consumption and faster deterioration of the ring resonator type semiconductor laser.

Therefore, when the vehicle is used for navigation, the injected current is increased during the stop period of the vehicle where the accuracy of angular velocity detection is required, while the injected current is decreased during the traveling period of the vehicle so that the state of the vehicle is reduced. It is conceivable that the injection current is switched according to the above conditions to achieve both required accuracy and reduced power consumption.

However, considering the use of this method in a ring resonator type semiconductor laser gyro which gives a loss difference to clockwise and counterclockwise laser beams, another problem arises. That is, in the ring resonator type semiconductor laser gyro, the intensity difference between the clockwise and counterclockwise laser light changes due to the injection current, which changes the dependence of the beat frequency on the angular velocity. Therefore, the measurement band of the beat frequency must be widened to the range of movement of the beat frequency caused by the increase / decrease of the injection current. However, the fluctuation of the terminal voltage due to the beat is weak, and an amplifier for signal amplification must be arranged at the signal output stage of the gyro.However, widening the measurement band means widening the band of this amplifier. Lead to doing. Then, the shot noise of the semiconductor laser and the thermal noise of the series resistance of the semiconductor laser are amplified by the amplifier, and the noise on the signal obtained after the amplifier increases in proportion to the frequency bandwidth to be amplified, and the measurement accuracy is increased. Will be deteriorated. Further, widening the measurement band leads to high functionality so that the signal processing circuit can detect a high-frequency signal from the gyro, and inevitably follows the path of high cost.

The above-mentioned conventional example, Japanese Examined Patent Publication No. 62-3983.
No. 6, JP-A-4-174317, JP-B-6-
Japanese Patent No. 38529 does not mention the measurement accuracy of the gyro and the signal processing.

It is an object of the present invention to provide an optical gyro that can maintain a narrow measurement band, switch the angular velocity measurement accuracy as needed, and can be driven with low power consumption at low cost.

[0014]

The optical gyroscope of the present invention for achieving the above object is provided, in a part of an optical waveguide, with one traveling direction of laser light and a traveling direction of laser light opposite to the one traveling direction. A plurality of ring-shaped resonator type semiconductor lasers having tapered portions asymmetrical with respect to each other are provided, and the plurality of ring-shaped resonator type semiconductor lasers are optical gyros having the tapered portions having different inclinations.

Further, the optical gyro driving method of the present invention comprises a plurality of ring resonator type semiconductors having different oscillation threshold current differences between the laser light in one traveling direction and the laser light in the traveling direction opposite to the one traveling direction. A method for driving an optical gyro having a laser, which is a method for driving an optical gyro that injects a current corresponding to each ring resonator type semiconductor laser.

In the present invention, a part of the optical waveguide of the ring resonator type semiconductor laser is provided with an asymmetric taper, and one traveling direction (for example, counterclockwise) in the ring resonator type semiconductor laser and a direction opposite to the one traveling direction are provided. By providing a loss difference to the laser light in the traveling direction (clockwise, for example), there is a difference between the oscillation threshold currents of the clockwise and counterclockwise laser lights.

Then, one traveling direction (eg counterclockwise)
And two or more ring resonator type semiconductor lasers having different taper asymmetries so that the difference in the oscillation threshold current of the laser light in the traveling direction opposite to the one traveling direction (for example, clockwise) is different from each other. Prepare

When driving the two or more ring resonator type semiconductor lasers, the beat frequency range corresponding to the measurement angular velocity range is set within the measurement frequency band for each ring resonator type semiconductor laser. The drive system has a function of determining a drive current and driving each of the ring resonator type semiconductor lasers with the drive current.

When each of the two or more ring resonator type semiconductor lasers is driven by the driving current, the spectrum line widths of the respective ring resonator type semiconductor lasers are different from each other, which causes a movement condition of a moving object. Accordingly, a ring resonator type semiconductor laser to be driven is appropriately selected.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. 1, 2, 3, 4, 5, and 6.

(First Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 (a) is a plan view of a first embodiment of an optical gyro of the present invention, and FIG. 1 (b) is A- of FIG. 1 (a).
It is a sectional view of an A'line. 10 is an optical gyro, 11 and 12
Are ring resonator type semiconductor lasers, 13 and 14, respectively.
Is a portion of the optical waveguide where the waveguide width changes,
That is, it is a tapered portion. Inside the ring resonator type semiconductor laser, the counterclockwise orbiting mode 15 and the clockwise orbiting mode 16 coexist.

Two ring resonator type semiconductor lasers 11,
12 was produced as follows. First, the semiconductor multilayer structure shown in the element cross-sectional view of FIG. 1 was formed by a metal organic chemical vapor deposition method. That is, on the n-InP substrate 102,
An undoped InGaAsP optical guide layer 103 having a composition of 1.3 μm (thickness 0.15 μm) and an undoped InGaAsP active layer 104 having a composition of 1.55 μm (thickness 0.1 μm)
m), a 1.3 μm composition undoped InGaAsP optical guide layer 105 (thickness 0.15 μm), a p-InP clad layer 106 (thickness 1.5 μm), and a p-InGaAs cap layer 107 were crystal-grown. A photoresist was applied, and the mask pattern was exposed and developed to form a ring resonator-shaped resist pattern. A ring resonator type semiconductor laser having a height of 3 μm and made of a high-mesa ridge waveguide was formed by reactive ion etching using chlorine gas. Cr / Au was vapor-deposited on the ridge waveguide to form the p-electrode 108. AuGe on the underside of the wafer
/ Ni / Au was vapor-deposited to form the n-electrode 101. After being alloyed in a hydrogen atmosphere, the interface between the p and n electrodes and the semiconductor was brought into ohmic contact.

Each ring resonator type semiconductor laser 1
If 1 and 12 are not optically independent, the laser beam is reflected back to the other ring resonator type semiconductor laser, the oscillation frequency is affected, and the beat signal due to rotation cannot be obtained purely. Become. Therefore, the ring resonator type semiconductor lasers 11 and 12 are optically independent of each other.

Since the ring resonator type semiconductor lasers 11 and 12 are optically independent of each other, when the plurality of ring resonator type semiconductor lasers 11 and 12 formed on the same substrate are arranged, the laser light beams of the ring resonator type semiconductor lasers 11 and 12 are mutually separated. The lasers are spaced so that they do not combine. In order to avoid the influence of evanescent light, the interval is set to approximately 15 μm or more.

Each ring resonator type semiconductor laser 11,
The tapered portions 13 and 14 of 12 are counterclockwise laser light 15 inside the respective ring resonator type semiconductor lasers.
Is to add a loss difference to the clockwise laser light 16. This causes a difference between the oscillation threshold currents of the clockwise and counterclockwise laser light in the ring resonator type semiconductor laser. This difference is designed so that the ring resonator type semiconductor laser 12 is larger than the ring resonator type semiconductor laser 11.

FIG. 2 shows a signal processing system of the optical gyro according to the present invention. In FIG. 2, 10 is an optical gyro, 11,
Reference numerals 12 are the ring resonator type semiconductor lasers shown in FIG. 201 is a constant current source that outputs an injection current I _a ; 202 is a constant current source that outputs an injection current I _b ;
Is a switch, 204 is an amplifier, 205 is a comparator,
206 is a counter and 207 is a signal processing circuit.

The ring resonator type semiconductor laser 11 has a constant current.
Injection current I by source 201_aDriven by, ring resonance
The semiconductor laser 12 is injected by the constant current source 202.
Flow I _bSo that they are not driven at the same time
In addition, the switch 203 is designed.

When the rotational angular velocity is applied while the optical gyro 10 is driven, the voltage fluctuation frequency signal between the terminals output from the ring resonator type semiconductor laser 11 or 12 is first AC-coupled input depending on the angular velocity. Amplified in a specific frequency band by the amplifier 204 having a voltage fluctuation of a magnitude detectable by the comparator 205. The comparator 205 shapes the frequency signal into a rectangular wave. After that, the counter 206 counts the number of pulses. Then, by the signal processing circuit 207,
The angular velocity is calculated from the number of pulses.

Now, consider the case where the ring resonator type semiconductor laser 11 is driven by the constant current source 201.

At this time, the ring resonator type semiconductor laser 1
Inside 1, the counterclockwise laser beam 15 and the clockwise laser beam 16 are generated, and the oscillation frequencies of these two laser beams are different even at rest. This is due to the action of the asymmetric taper portion 13 of the ring resonator type semiconductor laser 11, as described below. The laser light propagates while repeating total reflection at the interface of the optical waveguide, but in the tapered portion 13, the incident angle to the interface of the optical waveguide changes, so that waveguide loss occurs. This taper part 1
Since 3 is an asymmetrical shape with respect to the orbiting direction, the incident angle at the taper portion 13 is different depending on the orbiting direction, resulting in a loss difference.

Due to the resonator loss difference due to the circulating direction of the laser light, a difference occurs in the photon number density between the counterclockwise laser light 15 and the clockwise laser light 16. A non-linear optical effect occurs when two laser beams coexist. There is the following relationship between the oscillating frequencies f _j of two coexisting laser beams and the photon number density S _j , and it can be seen that if the photon number densities are different, the oscillating frequencies of the two laser beams are different. .

2πf ₁ + dΦ ₁ / dt = ω + σ ₁ −ρ ₁ S ₁ −τ ₁₂ S ₂ (1) 2πf ₂ + dΦ ₂ / dt = ω + σ ₂ −ρ ₂ S ₂ −τ ₂₁ S ₁ (2) where Φ _j is the phase, ω is the resonance angular frequency, σ _i is the mode pull-in coefficient, ρ _i is the coefficient indicating the mode self-extrusion,
τ _ij is a coefficient indicating mutual extrusion of modes. However, i, j = 1, 2; i ≠ j.

From the above, since the oscillation frequencies f ₁₀ and f ₂₀ of the laser light are different when stationary, a beat occurs at a frequency Δf ₀ = f ₂₀ −f ₁₀ (3).

Thus, inside the ring resonator type semiconductor laser gyro, the photon number density S _j of the two laser beams is
If there is a difference in the
It can be seen that ₀ occurs, but this stationary beat frequency Δ
It will be understood from the following consideration that f ₀ depends on the injection current value of the ring resonator type semiconductor laser 11.

FIG. 3A shows injection current (I) -light intensity (L) characteristics of clockwise light and counterclockwise light in the ring resonator type semiconductor laser 11. Further, FIG. 3B shows a ring resonator type semiconductor laser 1
3 is a graph showing injection current (I) -light intensity (L) characteristics of clockwise light and counterclockwise light in FIG.
Attention is now directed to FIG. 3A, which is the IL characteristic of the ring resonator type semiconductor laser 11.

As described above, the asymmetric taper portion 13
Therefore, there is a difference in the intensity of the laser light that circulates in opposite directions.
Therefore, as shown in FIG.
The I-L characteristics of each laser beam are straight lines with different slopes.
Draw. Therefore, the intensity difference ΔL between the two laser beams
It can be seen that changes with respect to the injection current value I. sand
That is, in this embodiment, a ring resonator type semiconductor is used.
The injection current I is applied to the laser 11. _aCan only flow, but injection current
I_bIf you think now that you can also flow, you can see in Fig. 3 (a).
The injection current value is I_aThen the intensity difference is ΔL_aNext to
Injection current value is I_bThen the intensity difference is ΔL_bTo be
It

According to the equations (1) and (2) representing the nonlinear optical effect between the two laser lights, if the difference between the photon densities S ₁ and S ₂ of the two laser lights changes, Accordingly, the oscillation frequencies f ₁ and f of the two laser beams are
It can be seen that the difference of ₂ changes. Therefore, when the injection current is changed in the stationary state, the difference between the two laser light intensities changes accordingly, and the beat frequency in the stationary state changes.

When the optical gyro 10 is rotated clockwise at the angular velocity Ω while the constant current source 201 is driving the ring resonator type semiconductor laser 11 by the switch 203, the inside of the ring resonator type semiconductor laser 11 is rotated. The oscillation frequency f ₁ Ω of the clockwise first laser light 16 is f ₁ Ω = f ₁₀ −2SΩ / (λ ₁ L) (4) where S is the area surrounded by the ring resonator type semiconductor laser,
L is the optical path length, and λ ₁ is the wavelength of the clockwise clockwise laser light in the medium. At the same time, the oscillation frequency f ₂ Ω of the counterclockwise second laser light 15 is f ₂ Ω = f ₂₀ + 2SΩ / (λ ₂ L) (5) λ ₂ is the medium of the counterclockwise laser light at rest It is the inner wavelength.

Since the clockwise first laser light and the counterclockwise second laser light coexist in the ring resonator type semiconductor laser gyro, the first laser light and the second laser light are combined. Beat light having a frequency different from the oscillation frequency is generated. The beat frequency ΔfΩ during rotation is ΔfΩ = f ₂ Ω−f ₁ Ω = f ₂₀ + 2SΩ / (λ ₂ L) −f ₁₀ + 2SΩ / (λ ₁ L) = f ₂₀ −f ₁₀ + (2SΩ / L). (1 / λ ₂ + 1 / λ ₁ ) = Δf ₀ + (2SΩ / L) · (1 / λ ₂ + 1 / λ ₁ ) (6) The beat light causes the pulsation of the population inversion at the beat frequency ΔfΩ and changes the impedance between terminals. Therefore, when the constant current driving is performed, the voltage fluctuation is observed in the voltage between terminals at the frequency of ΔfΩ. However, since the observable frequency is always positive, | ΔfΩ | is obtained.

As described above, if the injection current value to the ring resonator type semiconductor laser 11 is changed, the intensities of the counterclockwise laser light 15 and the clockwise laser light 16 are correspondingly changed. The difference changes and the beat frequency at rest changes. In this embodiment, only the injection current I _a is applied to the ring resonator type semiconductor laser 11, but the injection current I _b is changed in order to clarify the change in the dependence of the beat frequency on the angular velocity due to the difference in the injection current. If the injection current value is I _a , the stationary beat frequency is Δf _0a , and if the injection current value is I _b , the stationary beat frequency is Δf _0b. Since it takes a beat frequency, this 2
At three different injection current values, the function of the beat frequency ΔfΩ with respect to the rotational angular velocity Ω also has its own form. The absolute value of the function is shown below.

| ΔfΩ _a | = | Δf _0a + (2SΩ / L) · (1 / λ _2a + 1 / λ _1a ) | (7) | ΔfΩ _b | = | Δf _0b + (2SΩ / L) · (1 / λ _2b + 1 / λ _1b ) | (8) where ΔfΩ _a is the beat frequency for the angular velocity Ω at the injection current value I _a , ΔfΩ _b is the beat frequency for the angular velocity Ω at the injection current value I _b , and λ _1a Is the in-medium wavelength of the clockwise laser light at rest with injection current I _a , λ _2a is the in-medium wavelength of the counterclockwise laser light at rest with injection current I _a , and λ _1b is the injection current I _b The in-medium wavelength of the clockwise laser light in the stationary state at λ _2b is the in-medium wavelength of the counterclockwise laser light in the stationary state at the injection current I _b .

In FIG. 4, solid lines a and b respectively indicate
The figure shows the function of the voltage variation frequency between terminals output from the ring resonator type semiconductor laser 11 with respect to the angular velocity Ω at the injection current values I _a and I _b .

Here, the functions represented by the equations (7) and (8) are represented by the straight line portions of the solid lines a and b and the wavy line extending them. In the wavy line portion, the clockwise and counterclockwise laser light 16 in the ring resonator type semiconductor laser gyro 10,
There is a case where 15 becomes a strong coupling state and two-mode independent laser oscillation cannot be performed. At this time, the beat of light and the voltage fluctuation between terminals cannot be observed. This phenomenon is called lock-in. Due to this lock-in phenomenon, the function of the actually observed terminal voltage fluctuation frequency with respect to the angular velocity Ω behaves as shown by solid lines a and b.

The shaded area in FIG. 4 indicates the band in which the voltage fluctuation signal between the terminals of the ring resonator type semiconductor laser gyro is amplified by the amplifier 204 shown in FIG.
This area is the measurable band. Since the voltage variation between the terminals of the ring resonator type semiconductor laser is weak, only the signal within the frequency band in the shaded region can be actually detected. However, when the width of the measurement band is widened, the shot noise of the semiconductor laser and the noise caused by the thermal noise of the series resistance of the semiconductor laser increase in proportion to the measurement bandwidth after the amplification. Therefore, expanding the measurement band to measure a wide angular velocity range sacrifices high precision measurement.

As shown in FIG. 4, when Ω = 0 at rest, the solid line a is within the measurement band. Therefore, when the ring resonator type semiconductor laser 11 is driven by the injection current I _a , _a beat at rest is obtained. It emits the frequency | Δf _0a | and can recognize that it is stationary. On the other hand, the injection current I
When driven with _b (<I _a ), the ring resonator type semiconductor laser 11 emits a beat frequency | Δf _0b | at rest.
Since this is outside the measurement band as shown in FIG. 4, the stationary time cannot be known.

Next, consider the case where the ring resonator type semiconductor laser 12 is driven. Ring resonator type semiconductor laser 1
2, the taper portion 14 is designed so that the oscillation threshold current difference between the clockwise and counterclockwise laser light is larger than that of the ring resonator type semiconductor laser 11. Therefore, if the injection current is the same as the injection current to the ring resonator type semiconductor laser 11, the ring resonator type semiconductor laser 1
When 2 is driven, the intensity difference between the clockwise and counterclockwise laser light becomes larger in the ring resonator type semiconductor laser 12. Therefore, in the ring resonator type semiconductor laser 12, a stationary beat having a frequency higher than that of the ring resonator type semiconductor laser 11 is generated. Therefore, at the injection currents I _a and I _b , the ring resonator type semiconductor laser 12 is obtained.
The function of the beat frequency with respect to the angular velocity is as shown in FIG. That is, at the injection current I _b (<I _a ), as shown by the solid line b in FIG. 5, the beat frequency behaves with respect to the angular velocity and the beat frequency falls within the measurement band, but at the injection current I _a , Since the intensity difference between the clockwise and counterclockwise laser light becomes too large, it goes out of the measurement band as shown by the solid line a in FIG.

From the above consideration, in order to keep the beat frequency generated from the ring resonator type semiconductor lasers 11 and 12 within the measurement band, the ring resonator type semiconductor laser 11 is used.
With the injection current I _a and the ring resonator type semiconductor laser 12 with the injection current I _b (<I _a ).

FIG. 3 shows a ring resonator type semiconductor laser 1.
I and L characteristics of the clockwise and counterclockwise laser light in 1
(Fig. 3 (a)) and ring resonator type semiconductor laser 12
IL characteristics of clockwise and counterclockwise laser light in
(FIG. 3B) shows a ring resonator type semiconductor
Laser 11 is injected current I_aClockwise when driven with
The counterclockwise light intensity is equivalent to that of the ring resonator type semiconductor laser 1.
2 is the injection current I_b(<I _a) Clockwise when driven by
It is greater than the light intensity counterclockwise. Therefore,
Of the beat signal generated in the ring resonator type semiconductor laser 11.
The spectrum line width is the same as that of the ring resonator type semiconductor laser 12.
Ring cavity type semiconductor laser narrower than the line width of a spectrum
When driving 11, the angular velocity measurement with higher resolution
It will be possible. On the other hand, the ring resonator type semiconductor laser 12
If it is driven, the ring resonator type semiconductor laser 11
The resolution is inferior because the spectral line width of the beat signal is wide.
However, since the injection current is low, it can be driven with low power consumption.
Noh.

Thus, by appropriately switching the injection current and the ring resonator type semiconductor laser to be driven by the method described above, the accuracy of angular velocity measurement and power consumption can be selected according to the situation, and Enables narrow band measurement.

The driving of the two ring resonator type semiconductor lasers described above may be manually switched, or may be shared by time division. That is, the switching of the switches may be set such that the time of the ON state of the ring resonator type semiconductor lasers 11 and 12 is, for example, 1: 1 or the ratio may be changed as necessary. May be. In this embodiment, InGaAsP is used as the semiconductor material.
/ InP system was used, but GaAs system, ZnSe system, In
A material system such as a GaN system that can cause laser oscillation by current injection may be used.

(Second Embodiment) A second embodiment of the optical gyro of the present invention will be described with reference to FIG. In FIG. 6, 400 is an optical gyro, and 401, 402,
Reference numerals 403 are ring resonator type semiconductor lasers having respectively different oscillation threshold current differences between clockwise and counterclockwise laser lights, and constant current sources for outputting current values I _a , I _b , and I _c , respectively. Driven by 404, 405, 406. Reference numeral 407 is a switch, 408 is an amplifier, 409 is a frequency (f) -voltage (V) conversion circuit, and 410 is a signal processing circuit.

The optical gyro 400 has the same structure as that of the first embodiment except that the number of ring resonator type semiconductor lasers is three. Ring resonator type semiconductor lasers 401, 4
The taper portion is designed so that the oscillation threshold current difference between the clockwise and counterclockwise laser light becomes larger in the order of 02 and 403.

The inter-terminal voltage fluctuation frequency signal output from the ring resonator type semiconductor laser 401 or 402, 403 is amplified by the amplifier 408 within a limited band,
The f-V conversion circuit 409 extracts a voltage corresponding to the frequency of the beat signal, and the signal processing circuit 410 calculates an angular velocity according to the input voltage.

The difference between the oscillation threshold currents of the clockwise and counterclockwise laser light given to the ring resonator type semiconductor laser is the ring resonator type semiconductor lasers 401, 402,
403 in order, and the injection current increases in order of I _a , I _b , and I _c , and as in the first embodiment, injection is performed so that the beat frequency range corresponding to the measurement angular velocity range is within the measurement band. The currents I _a , I _b and I _c are defined.

The spectral line width of the beat signal of each ring resonator type semiconductor laser is narrow in the order of the ring resonator type semiconductor lasers 401, 402 and 403, while the power consumption is large in the order of 401, 402 and 403. According to this embodiment, it is possible to switch the measurement accuracy in three stages according to the measurement situation.

[0057]

As described above, according to the present invention,
The measurement accuracy and power consumption can be appropriately switched according to the motion state of the object (particularly the vehicle) while keeping the measurement band in a narrow range.

Further, the effect of lock-in can be removed from the measurement by not including DC near the measurement band.

In this way, by suppressing the measurement band to be narrow, the influence of noise that increases in proportion to the measurement band width is reduced, and the high band of the detector is prevented, so that the cost is reduced. can do.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an optical gyro according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a drive system and a signal processing system of the optical gyro according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining IL characteristics of clockwise laser light and counterclockwise laser light in two ring resonator type semiconductor lasers constituting the optical gyro according to the first embodiment of the present invention. Is.

FIG. 4 is a diagram illustrating a function of a beat signal frequency with respect to an angular velocity of one of the ring resonator type semiconductor lasers constituting the optical gyro according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a function of a beat signal frequency with respect to an angular velocity of another ring resonator type semiconductor laser which constitutes the optical gyro according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating an optical gyro drive system and a signal processing system according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a conventional ring resonator type semiconductor laser gyro.

[Explanation of symbols]

10 Optical Gyro 11 Ring Resonator Type Semiconductor Laser 12 Ring Resonator Type Semiconductor Laser 13 Tapered Part 14 Tapered Part 15 Counterclockwise Laser Light 16 Clockwise Laser Light 101 n-Electrode 102 n-InP Substrate 103 InGaAsP Light Guide Layer 104 InGaAsP active layer 105 InGaAsP optical guide layer 106 p-InP clad layer 107 p-InGaAsP cap layer 108 p-electrode 201 Constant current source 202 that outputs the current I _a 203 Constant current source 203 that outputs the current I _b 203 Switch 204 Amplifier 205 comparator 206 counter 207 signal processing circuit 401 ring resonator type semiconductor laser 402 ring resonator type semiconductor laser 403 ring resonator type semiconductor laser 404 current outputs the I _a and outputs a constant current source 405 current I _b the constant current source 406 current I Constant current source 407 that outputs _c Switch 408 Amplifier 409 f-V conversion circuit 410 Signal processing circuit 501 Resistor 502 Power supply 503 Capacitor 504 Output terminal 505 Ring resonator type semiconductor laser 506 Electrode 507 Electrode 508 Insulating layer 509 p-type GaAs layer 510 p-type Al _X Ga _1-X As layer 511 n-type Al _X Ga _1-X As layer [waveguide] 512 n-type Al _X Ga _1-X As layer 513 n-type GaAs layer

Claims (5)

[Claims] 1. A plurality of ring resonator type semiconductor lasers, each of which has, in a part of an optical waveguide, a taper portion which is asymmetrical in one traveling direction of laser light and in a traveling direction of laser light opposite to the one traveling direction. An optical gyro having a plurality of ring resonator type semiconductor lasers, each of which has the taper portion having a different inclination. 2. A method of driving an optical gyro having a plurality of ring resonator type semiconductor lasers having different oscillation threshold current differences between a laser beam in one traveling direction and a laser beam in a traveling direction opposite to the one traveling direction. There is a method of driving an optical gyro that injects a current corresponding to each ring resonator type semiconductor laser. 3. The value of the current is set so that a beat signal output from each of the ring resonator type semiconductor lasers is within a measurement band. A method for driving the described optical gyro. 4. The method of driving an optical gyro according to claim 2, wherein the spectral line widths of beat signals output from the plurality of ring resonator type semiconductor lasers are different from each other. 5. The plurality of ring-shaped resonator type semiconductor lasers have a tapered portion in a part of an optical waveguide, which is asymmetrical in one traveling direction of laser light and in a traveling direction of laser light opposite to the one traveling direction. 3. The method for driving an optical gyro according to claim 2, wherein the plurality of ring resonator type semiconductor lasers have the tapered portions having different inclinations.