JP2000230831A - Optical gyro - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ring laser gyro capable of operation at a low threshold value by detecting a rotating direction without applying mechanical fine vibration (dither), suppressing generation of lock-in phenomenon by restraining backward scattering in a light leading-out part, and further restraining loss in the light leading-out part. SOLUTION: This optical gyro is provided with a semiconductor ring laser 11 having a carrier injection means, a ring-shaped resonator, and a light output means outputting a part of clockwise light and a part of counterclockwise light, an optical element 13 converting the propagation direction of at least one out of the clockwise light 18 and the couterclockwise light 19 outputted from a ring laser, and a plurality of photo detecting elements 14, 15 arranged at a position where the clockwise light and the couterclockwise light overlap with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical gyro device for detecting rotation using a semiconductor ring laser, and more particularly to a semiconductor optical gyro device capable of detecting a rotation direction.

[0002]

2. Description of the Related Art Conventionally, as a gyro for detecting the rotation of an object, that is, an angular velocity, a mechanical gyro having a rotor and a vibrator and an optical gyro are known. Since the optical gyro can be activated instantaneously and has a wide dynamic range,
It is bringing innovation in the gyro field.

The optical gyro includes a ring laser gyro, an optical fiber gyro, a passive ring resonator gyro, and the like. A ring laser type gyro using a gas laser has already been put to practical use in aircraft and the like. A semiconductor laser gyro integrated on a semiconductor substrate has been proposed as a small, high-precision ring laser gyro. As this known document, there is JP-A-5-288556.

According to the above publication, as shown in FIG.
A ring-shaped gain waveguide 1100 is formed on a semiconductor substrate 1000 having a pn junction.
A carrier is injected from the electrode 2200 into the inside to generate laser oscillation. Then, a part of each of the laser light propagating clockwise and counterclockwise in the gain waveguide 1100 is extracted and caused to interfere in the light absorption region 1700, and the interference light intensity is extracted from the electrode 2300 as a photocurrent. I have.

[0005]

However, the conventional ring laser type gyro cannot detect the rotation direction from the output signal as it is, and applies a minute rotation vibration (dither) to the gyro.
The direction of rotation was detected from the correlation between dither and signal.

Further, in a ring laser gyro that extracts light from a ring laser element and receives light with another element, backscattering at the light extraction section causes an optical difference between clockwise light and counterclockwise light. Due to the coupling, the lock-in phenomenon occurred in a region of small angular velocity. This is because the oscillation frequency is pulled into the frequency of one mode due to the coupling between the clockwise light and the counterclockwise light, and no signal is output.

Therefore, a first object of the present invention is to detect the direction of rotation without applying mechanical micro vibration (dither).

It is a second object of the present invention to suppress back-scattering at the light extraction portion, to prevent a lock-in phenomenon from occurring, and to detect a rotation direction.

A third object of the present invention is to suppress loss at the light extraction unit, enable operation at a low threshold value, and detect the rotation direction.

A fourth object of the present invention is to increase the strength of a detection signal and to detect the direction of rotation.

A fifth object of the present invention is to widen an allowable range of an assembly error of an element and to detect a rotation direction.

A sixth object of the present invention is to form all components monolithically on a substrate and detect the direction of rotation.

[0013]

A semiconductor laser gyro according to the present invention for achieving the above object comprises a carrier injection means, a ring-shaped resonator, and a light for outputting a part of clockwise and counterclockwise light. A semiconductor ring laser having an output means, an optical element for converting at least one propagation direction of clockwise and counterclockwise light output from the ring laser, and an overlapping position of the clockwise and counterclockwise light Having a plurality of light receiving elements.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of operation of a semiconductor laser gyro according to the present invention will be described below with reference to equations.

A semiconductor laser gyro according to the present invention comprises: a semiconductor ring laser having carrier injection means, a ring-shaped resonator, and light output means for outputting a part of clockwise and counterclockwise light; An optical element for converting at least one propagation direction of the outputted clockwise and counterclockwise light is provided, and a plurality of light receiving elements are disposed at positions where the clockwise and counterclockwise light overlap.

In the above configuration, a clockwise rotation mode and a counterclockwise rotation mode exist independently in a ring resonator in which a gain is generated by current injection. If the element has no angular velocity with respect to the inertial frame (is stationary),
There is no difference between the oscillation frequencies of the clockwise mode and the counterclockwise mode, and laser oscillation occurs at the gain peak wavelength of the active layer.

A part of the clockwise and counterclockwise light is output from the ring resonator by the output means, and the optical path is bent by an optical element for changing the propagation direction of at least one of the output light, so that the light is bent at a predetermined location. (Hereinafter, referred to as an observation surface) are made to reach the clockwise and counterclockwise light in an overlapping manner.

For the sake of simplicity, consider the case where the observation surface is separated from the light output means and can be handled as parallel beams, and the two beams are incident at an angle of ± ε / 2 with respect to the normal to the observation surface. Think about it. When the clockwise light enters from the positive direction of the x-axis, where the intersection of the incident slope and the observation surface is the x-axis, the light intensity distribution on the observation surface is expressed by the following equation.

I = Io [1 + cos {2πεx / λ + 2π (f1-f2) t}] (1) where λ is the wavelength of light when the semiconductor laser gyro is stationary, and f1 and f2 are clockwise lights, respectively. And the oscillation frequency of counterclockwise light. When the semiconductor laser gyro is stationary, the interference fringes do not change with time because f1 = f2. The pitch of the interference fringes is λ / ε
It can be seen that

Here, the semiconductor laser gyro has an angular velocity Ω
When rotated clockwise, the oscillation frequency of the clockwise first laser light decreases by Δf1 = 2SΩ / λL (2) as compared with the non-rotated state. Where S is the area surrounding the ring resonator, L
Is the optical path length of the laser. At the same time, the clockwise second
The oscillation frequency of the laser light increases by Δf2 = 2SΩ / λL (3) as compared with the non-rotational time.

At this time, the light intensity distribution represented by the equation (1) is equal to the frequency difference (f2) between the second laser light and the first laser light.
−f1) = Δf1 + Δf2 = 4SΩ / λL, and the interference fringes move in the negative direction of x.

When the laser gyro rotates counterclockwise, it vibrates at a frequency difference (f1-f2) = Δf1 + Δf2 = 4SΩ / λL between the first laser light and the second laser light,
The interference fringes move in the positive x direction.

Even when the two light beams are not parallel beams, the interference fringe pitch represented by the equation (1) is unequal, so that the movement of the interference fringes according to the beat remains unchanged.

By arranging a plurality of light receiving elements on the observation surface at intervals different from the pitch of the interference fringes, light intensity vibrations having different phases are detected, the absolute value of the angular velocity of rotation is known from the vibration frequency, and the phase difference is detected. Thus, it is possible to detect the moving direction of the interference fringes.

According to the first aspect of the present invention, the light output means for outputting a part of the light is provided on a mirror section connecting the first waveguide and the second waveguide. And the angle between the normal to the mirror surface and each waveguide is
Slightly larger than the critical angle of the mirror.

In the second invention, the light output means for outputting a part of the light is provided in a mirror portion connecting the first waveguide and the second waveguide, and each of the light output means and the normal line of the mirror surface are provided. Is slightly larger than the critical angle of the mirror. In the above configuration, in the light output means, most of the light emitted from the first waveguide is incident on the mirror under the condition of a critical angle or more, so that it is totally reflected and coupled to the second waveguide. Some light having a component that travels obliquely to the mirror is incident on the mirror at a critical angle or less, and a part of the light is extracted outside the ring resonator. The remaining light is reflected by this mirror and coupled to the second waveguide, and almost no light returns to the first waveguide. Therefore, the coupling of the clockwise light and the counterclockwise light at the light extraction portion (backward) Scattering) can be suppressed.

A third invention is characterized in that the mirror has an elliptical cylindrical surface. In the above configuration, the lateral confinement of the waveguide is weakened at the connection between the first and second waveguides, and the spread of the beam coming from one of the waveguides is efficiently converged at the curvature given to the mirror, and the first beam is efficiently converged. 2 is coupled to the second waveguide. It is intended to suppress the loss at the light extraction portion of the ring resonator and to operate at a low threshold.

In a fourth aspect, the optical element for changing the propagation direction of the output light is formed of an elliptic cylinder.
Alternatively, the optical element that changes the propagation direction of the output light is a slab waveguide with a diffraction grating. In the above configuration, since the optical element that changes the propagation direction of the output light is an elliptic cylindrical surface or a slab waveguide with a diffraction grating, the output light is collimated and the contrast of interference fringes is increased, so that the detection signal intensity is increased. Is what you do.

According to a fifth aspect of the present invention, the plurality of light receiving elements include light receiving elements formed in an array. Alternatively, as the plurality of light receiving elements,
It has a CCD array. In the above configuration, a plurality of arrayed light receiving elements or CCDs having more than two light receiving elements are provided.
By using an array, the moving direction of the interference fringes can be detected by signal processing even if the pitch of the interference fringes on the observation surface deviates from the design. That is, electrical correction can be performed even if the position of the light receiving element deviates from the designed observation surface, and the allowable range of element assembly errors can be widened.

A sixth invention is characterized in that the plurality of light receiving elements have the same layer structure as a ring laser. Alternatively, a laser element having the same layer configuration as the ring laser is used as the plurality of light receiving elements. According to the above configuration, the ring resonator laser, the optical element that changes the propagation direction of the output light, and the light receiving element have the same layer configuration, so that all the components can be formed monolithically on the substrate.

[0031]

[First Embodiment] A first embodiment of the optical gyro of the present invention will be described with reference to FIG.

11 is a ring resonator type semiconductor laser device,
12 is a laser beam extraction unit, 13 is a mirror, 14 and 15
Is a photodetector, and 16 and 17 are total reflection mirrors of a ring resonator. The ring resonator type semiconductor laser element 11, the mirror 13, and the light receiving elements 14, 15 having the same layer structure as the laser were manufactured as follows.

First, the semiconductor multilayer structure shown in FIG. 2 was formed by metal organic chemical vapor deposition. That is, n-I
Non-doped In of 1.3 μm composition is formed on nP substrate 102.
GaAsP light guide layer 103 (0.15 μm thickness),
Undoped InGaAsP active layer 1 of 1.55 μm composition
04 (0.1 μm in thickness), a non-doped InGaAsP light guide layer 105 having a composition of 1.3 μm (0.15 μm in thickness)
m), p-InP cladding layer 106 (1.5 μm thickness)
The p-InGaAs cap layer 107 was crystal-grown. A photoresist was applied, and the mask pattern was exposed and developed to form a resist pattern having a waveguide shape and a mirror shape.
A high mesa-shaped ridge waveguide having a height of 3 μm and a mirror were formed by reactive ion etching using chlorine gas. Plasma CV over SiN as insulating film
Formed by Method D. The contact window was obtained by removing SiN above the ridge waveguide. Cr / Au was vapor-deposited on the upper portion of the ridge waveguide and on the side surface of the mirror 13 to form a reflection film of the p-electrode 108 and the mirror. AuGe / Au under the wafer
Was deposited to form an n-electrode 101. Alloying was performed in a hydrogen atmosphere, and the p- and n-electrodes were brought into ohmic contact.

The photodetectors 14 and 15 are applied with a reverse bias, and a current corresponding to incident light is detected.

The laser oscillation of the device will be described. For example, if the refractive index of the semiconductor layer is 3.5, total reflection occurs when the angle between the laser beam and the normal to the interface between the semiconductor and air is 16.6 degrees or more. In the total reflection mirrors 16 and 17 of the ring resonator type laser, the angle between the waveguide and the normal to the semiconductor / air interface is 33.5 degrees, which is the condition of total reflection. On the other hand, in the laser light extraction unit 12,
The angle between the waveguide and the semiconductor / air interface is 23 degrees, and a part of the guided mode light does not satisfy the condition of total reflection and is radiated outside. However, the reflectivity of the laser beam extraction portion was 90% or more, and the mirror loss was suppressed to about 3.5 cm ^{-1 in} the case of a 300 μm waveguide element, and the laser oscillated at a threshold value of 20 mA, for example.

In the ring resonator, a clockwise rotation mode and a counterclockwise rotation mode exist independently. If the element has no angular velocity with respect to the inertial frame (is stationary),
There is no difference between the oscillation frequencies of the clockwise mode and the counterclockwise mode, and laser oscillation occurs at the gain peak wavelength of the active layer.

The reflection at the laser beam extraction unit and the extraction of a part of the light will be further described based on the analysis by ray tracing in FIG. The angle between the normal line of the end face and the light ray is different at each point on the end face AD, and the angles θ _A , θ _B , θ
_C, and theta _D is referred to as the angle of incidence on the end face. OB is a line obtained by extending the center line of the ridge waveguide. Ridge waveguide 131
Therefore, the guided mode light that has entered the slab waveguide portion 132 without confinement in the lateral direction spreads in a fan shape around the OB in the slab. In FIG. 3, when moving from the point A to the point D on the end face AD, the incident angle θ gradually decreases, and at the point C, θ _C matches the critical angle at this interface. Since the angle of incidence is less than the critical angle between point C and point D on the interface, some light is reflected and some light is extracted to the outside. (The optical path of the reflected light is not shown in FIG. 3.) On the interface AD, the intensity distribution of the fan-shaped spread incident beam is Gaussian as shown in the figure,
Since the area of total reflection (the range from point A to point C in the figure) covers 90% of this Gaussian distribution, the reflectance at this interface is 90% or more. Although the description here is for the right-handed mode light in the ring resonator in accordance with FIG. 3, a part of the light can be extracted in the same manner for the left-handed mode.

Next, the clockwise mode light extracted in this way is turned back by the mirror 13 and interferes with the counterclockwise light.

FIG. 4 shows this optical path. 18 is a part of the clockwise light extracted from the laser, and 19 is a part of the counterclockwise light extracted from the laser. Clockwise light 18
Is folded back by the mirror 13 and overlaps the counterclockwise light 19 on the observation surface to form an interference fringe.

On the observation surface, two photo detectors 1
4 and 15, the distance between the centers is the pitch of the interference fringe pattern.
= 1 / 2N + ε of λ / ε. With this arrangement, the cos (2π
(F1−f2) t) and a signal corresponding to cos (2π (f1−
f2) t) + 2p (ε / λ · Λ / 4) = cos (2π (f1
A signal corresponding to −f2) t + π / 2) = − sin (2π (f1−f2) t) is obtained, so that the moving direction of the interference fringe pattern, that is, the magnitude relationship between f1 and f2, can be determined by signal processing, and rotation Direction can be detected. The angular velocity of the rotation can be determined from the period of the vibration of the interference fringes. Alternatively, the angular velocity of rotation can be determined from the moving speed Λ · (f1−f2) of the interference fringe pattern.

When the optical gyro rotates clockwise at an angular velocity of 30 degrees per second due to camera shake or a change in the attitude of the automobile, the oscillation frequency f1 of the laser beam becomes 200.
Hz, and the oscillation frequency of f2 decreases by 200 Hz.
The photodetectors 14 and 15 detected a signal of 400 Hz, and obtained a rotation speed and a rotation direction from this. The photodetectors 14 and 15 may detect a change in impedance by applying a forward bias.

In this embodiment, InGa is used as a semiconductor material.
AsP / InP system was used, but GaAs system, ZnSe
Or a material system such as an InGaN system.

[Second Embodiment] Referring to FIG.
An example will be described. 21 is a ring resonator type semiconductor laser device, 22 is a laser beam extraction part, 23 is a mirror, 2
Reference numeral 4 denotes an array-shaped photodetector, and reference numerals 25 and 26 denote a total reflection mirror of a ring resonator.

The ring resonator type semiconductor laser device 21 and the mirror 23 are made of an InGaAsP-based semiconductor as in the first embodiment, and the fabrication steps are the same as in the first embodiment. In the present embodiment, the shape of the laser beam extracting portion is different from the planar shape of the first embodiment and is a curved surface.

FIG. 6 shows the reflection of light rays on an elliptical mirror.
Will be described with reference to a ray tracing diagram of FIG.

The curved surface has an elliptical shape, and the point where the upper and lower waveguides and the slab waveguide on the ellipse are in contact is the focal point of the ellipse. On AB on the curved surface, the incident light from the upper waveguide satisfies the condition of total reflection and is collected on the lower waveguide. On the curved surface BC, the incident angle becomes equal to or smaller than the critical angle, the light does not become totally reflected, and some light is extracted outside. Since 90% of the Gaussian-shaped light intensity distribution of the waveguide is reflected by the total reflection portion, this elliptical mirror functions as a corner mirror having a reflectance of 90% or more.

The light extracted from the ring laser turns the clockwise light back by the mirror 23 and interferes with the counterclockwise light. FIG. 5 shows this optical path. 28 is a part of the counterclockwise light extracted from the laser, 29 is a part of the clockwise light extracted from the laser, and is turned back by the mirror 23. And interference fringes are formed. In the present embodiment, an end face obtained by cleaving the substrate on which the semiconductor laser element and the mirror are formed is used as an observation surface, and the interference fringe pattern is monitored by an array-shaped photodetector 24 provided on the observation surface. .
The output from the photodetector array was subjected to signal processing to detect the moving direction and vibration period of the interference fringe pattern. From this, the rotation direction and rotation speed could be obtained.

In this case, the angular velocity and the rotation direction can be known even if the respective laser beams deviate from the conditions described in the first embodiment that can be handled as parallel light.

When the device is made of an AlGaAs-based material and the oscillation wavelength is a wavelength at which a silicon CCD has sensitivity, the interference fringe pattern may be observed by a CCD array device.

[Third Embodiment] A third embodiment will be described.
A description will be given based on FIG.

The difference from the first and second embodiments is the configuration of the mirror for forming interference fringes with the extracted light.
Reference numeral 30 denotes an optical gyro element according to the present invention. 31 is a ring resonator type semiconductor laser device, 32 is a laser beam extraction part, 33 and 34 are concave mirrors, 35 is a turning mirror, and 36 and 37 are photodetectors. The configuration of the ring resonator type semiconductor laser is similar to that of the first or second embodiment. In this embodiment, instead of the mirror which turned back light in one direction in the first and second embodiments,
Each of the left-handed and right-handed light is converted into a parallel beam by using a cylindrical concave mirror to suppress the beam spread in a plane horizontal to the substrate. On the observation surface provided on the cleavage plane of the element, interference fringes due to clockwise and counterclockwise light are formed,
As in the first and second embodiments, two photodetectors 3
6, 37, it was possible to detect the moving speed and the moving direction of the interference fringes to know the rotational speed and the direction of the element.

Compared with the previous embodiment, the beam is collimated by the cylindrical mirror, so that the contrast of the interference fringes is improved, and interference fringes having a uniform pitch are formed because the interference fringes are formed between substantially parallel beams. Therefore, the requirement for the positional accuracy for installing a detector having an interval of N + と し た times the interference fringe pitch L has been relaxed.

[Fourth Embodiment] Regarding the fourth embodiment,
A description will be given based on FIG. 41 is a ring resonator type semiconductor laser device, 42 is a laser beam extraction part, 43 and 44
Is a slab waveguide with a diffraction grating, and 45 and 46 are photodetectors. The configuration of the ring resonator type semiconductor laser is
This is the same as the first or second embodiment. In the present embodiment, a slab waveguide with a diffraction grating is used instead of the mirror that turned back light in one direction in the first and second embodiments. Reference numerals 43 and 44 denote slab waveguides on which concentric diffraction gratings are respectively formed. Each of right-handed and left-handed light extracted from the element is coupled to the slab waveguide, where the light is reflected by the diffraction grating. Emitted from the substrate in a direction substantially perpendicular to the substrate. At this time, the beam emitted due to the bending of the diffraction grating pattern is collimated parallel light.

In FIG. 8, in the direction perpendicular to the substrate surface (paper surface),
On the observation plane AA ^* placed parallel to the substrate surface, interference fringes of clockwise light and counterclockwise light are formed. As in the first and second embodiments, the moving speed and the moving direction of the interference fringes were detected by the two photodetectors 36 and 37, and the rotational speed and the direction of the element could be known.

According to the configuration of the present embodiment, the distance between the observation surface and the laser beam extracting portion can be increased without increasing the element size, and the angle ε between the clockwise light and the counterclockwise light can be increased. It is possible to increase the pitch of the interference fringes on the observation surface while keeping the pitch small, and the requirements for the positional accuracy of the photodetector can be relaxed.

[0056]

According to the first aspect of the present invention described above, an optical gyro element capable of detecting the angular velocity and the direction of rotation can be obtained.

Further, according to the second aspect of the present invention, an optical gyro element capable of detecting the angular velocity and the rotational direction of rotation, which can be detected from a small angular velocity without sacrificing the lock-in characteristic, is obtained.

According to the third aspect of the present invention, an optical gyro element which can be operated at a low threshold value, consumes small power, and can detect the angular velocity and direction of rotation can be obtained.

According to the fourth aspect of the present invention, an optical gyro element having a large detection signal strength and a good S / N ratio and capable of detecting the angular velocity and direction of rotation can be obtained.

According to the fifth aspect of the present invention, an optical gyro element having a wide allowable range of element assembly errors and capable of detecting the angular velocity and the rotation direction of the element is obtained.

According to the sixth aspect of the present invention, an optical gyro element having a small number of components and capable of detecting the angular velocity and the rotation direction of the rotation is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first embodiment according to the present invention.

FIG. 2 is a diagram showing a layer structure of a semiconductor laser of a device according to a first embodiment of the present invention;

FIG. 3 is a diagram illustrating an operation of a light extraction unit according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the formation of interference fringes according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a second embodiment according to the present invention.

FIG. 6 is a diagram illustrating the operation of a light extraction unit according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a third embodiment according to the present invention.

FIG. 8 is a diagram for explaining a fourth embodiment according to the present invention.

FIG. 9 is a conceptual diagram of a conventional semiconductor optical gyro.

[Explanation of symbols]

 11, 21, 31, 41 Ring resonator type semiconductor laser 104 InGaAsP active layer 12, 22, 32, 42 Optical output unit 13, 23, 33, 34, 35 Optical path conversion mirror 14, 15, 36, 37, 45, 46 Photodetector 18 Right-handed light 19 Left-handed light 24 Photodetector array 43, 44 Slab waveguide with diffraction grating

Claims (9)

[Claims] 1. A semiconductor ring laser having carrier injection means, a ring-shaped resonator, and light output means for outputting a part of clockwise and counterclockwise light, and a clockwise and a clock output from the ring laser. A semiconductor laser gyro comprising: an optical element for changing at least one propagation direction of counterclockwise light; and a plurality of light receiving elements disposed at positions where the clockwise and counterclockwise light overlap. 2. A light output means for outputting a part of the light,
2. A mirror provided in a mirror section connecting the first waveguide and the second waveguide, wherein an angle between a normal line of the mirror surface and each waveguide is larger than a critical angle of the mirror. Light gyro. 3. The optical gyro according to claim 2, wherein said mirror has an elliptical cylindrical surface. 4. The optical gyro according to claim 1, wherein the optical element that changes the propagation direction of the output light has an elliptical cylindrical surface. 5. The optical gyro according to claim 1, wherein the optical element that changes the propagation direction of the output light is a slab waveguide with a diffraction grating. 6. The light-receiving element according to claim 1, wherein the plurality of light-receiving elements include light-receiving elements formed in an array.
Light gyro. 7. The optical gyro according to claim 1, wherein the plurality of light receiving elements include a CCD array. 8. The optical gyro according to claim 1, wherein the plurality of light receiving elements have the same layer configuration as a ring laser. 9. The optical gyro according to claim 1, wherein a laser element having the same layer structure as a ring laser is used as said plurality of light receiving elements.