JP3751553B2 - Method of forming a circular optical path and optical gyro using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a method for forming a circulating path, in which relates to an optical gyro using the same.
[0002]
[Prior art]
Inertial sensors, that is, acceleration sensors and angular velocity sensors, have been used for inertial navigation of aircraft and rockets. Here, accuracy was more important than price and size.
[0003]
In recent years, inertial sensors have been applied to airbag operation, vehicle position / posture control and travel direction calculation, handheld camera shake correction, robot position / posture control, game control, and human body position / posture detection. ing.
[0004]
Development of devices using silicon micromachining is active in the production of this sensor. The main structure is that a weight is supported by a beam, and a change in weight due to acceleration is read by a change in capacitance or a resistance change due to deformation. Various gyros are applied to the angular velocity detection, and there are a vibration type gyro using a Coriolis force acting on a vibrating object and an optical gyro using a Sagnac effect.
[0005]
Examples of such technical documents include the following.
[0006]
(1) Maechu Journal of Welding Society Vol. 69, no. 6, pp511-513 (2000)
(2) Esashi Measurement and control Vol. 36, no. 11, pp808-817 (1997)
(3) The optical gyro has performance such as a quick reaction and a wide dynamic range. Regarding the optical fiber gyro, the Japanese Examined Patent Publication No. 62-39836, the Japanese Examined Patent Publication No. 2-60127, and the branch coupling are special. Kaihei 7-91964 is cited.
[0007]
(4) Examples of the optical gyro in which an optical fiber is developed into an optical waveguide include Japanese Patent Laid-Open Nos. 5-288556 and 7-198979.
[0008]
(5) On the other hand, Japanese Patent Application Laid-Open No. 10-93133 is cited as an example of using the anisotropic etching characteristics of a single crystal silicon substrate to provide a side wall with respect to the substrate and use it as a mirror.
[0009]
(6) Similarly, as a method of forming an inertial sensor by providing a vibrating body or a beam on a silicon substrate by anisotropic etching, JP-A-7-294260, JP-A-9-196682, and JP-A-11 -237247 gazette.
[0010]
[Problems to be solved by the invention]
As described above, fiber gyros and the like have been put into practical use, but there is a demand for downsizing of electronic components for in-vehicle use and robot mounting. Although there is a proposal of a waveguide type optical gyro, no optical gyro using a silicon substrate or the like and capable of batch production has been reported.
[0011]
The present inventors have conducted research and development of various sensors, particularly inertial sensors, using silicon micromachining technology. Thus, the present invention intends to realize a ring laser gyro using silicon micromachining technology.
[0012]
The present invention relates to measurement and control using light, and uses a silicon (111) surface or (111) surface coated material together as a mirror and a semi-transparent mirror, and in particular, forms a circular optical path. By doing so, it can be applied to ring laser gyros and various interferometers.
[0013]
In view of the above situation, the present invention reduces the number of steps of adjusting a mirror for generating an optical path as compared with a configuration using a conventional mechanical structure material, and is capable of mass production and low production in combination with the capability of batch production. a method for forming a round optical path can be made cost, and an object thereof is to provide an optical gyro using the same.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[1] In the method of forming a circular optical path, a coherent laser light source and a single crystal silicon substrate having a (110) plane as a surface are etched by anisotropic wet etching, and the surface is formed on the (110) plane. A single crystal having a (110) plane exposed by the etching of a (111) plane reflecting mirror depending on two types of orientations of an angle of about +54.7 degrees and about −54.7 degrees from the <110> direction A plurality of laser beams from the light source circulate perpendicularly to the silicon substrate, and the two types of orientations are used to form clockwise and counterclockwise circular optical paths. An optical ring circuit is formed by the circular optical paths. It is characterized by forming.
[0015]
[2] The method for forming a circulating optical path according to [1], wherein a part of the circulating optical path is taken out of the circulating optical path by using a part of the circulating optical path as a semi-transparent mirror.
[0016]
[3] In the method of forming a circular optical path according to [1] above, a part of the (111) plane mirror is made movable to generate interference with respect to light that passes through or reflects outside the circular optical path. The interference width is controlled as it is.
[0017]
[4] The method for forming a circulating optical path according to [3], wherein the movable mirror is used for feedback control.
[0018]
[5] An optical gyro, which derives the two-way light obtained by the method of forming a circulating optical path according to [1] above to the outside of the circulating optical path, and detects a change in interference light of the derived light. It is characterized by.
[0019]
[6] An optical gyro characterized in that a mirror of the optical circulation optical path obtained by the method for forming a circulation optical path described in [1] is made movable and used for feedback control.
[0020]
[7] An optical gyro, wherein the circular optical path obtained by the method for forming a circular optical path according to [1] has a ring laser gyro function.
[0021]
With such a configuration, it is possible to form a surface having a relative angle and a mirror surface with extremely high accuracy by anisotropic wet etching in a single crystal of silicon. For example, a single crystal silicon substrate having the (110) plane as a surface is formed with a plurality of (111) planes perpendicular to the surface by anisotropic wet etching. Using this surface as a mirror, coherent laser light is introduced to form an optical circulation path of clockwise light and counterclockwise light. A laser resonance circuit is formed by selecting the wavelength and the distance between the mirrors. Here, by making a part of the mirror a semi-transparent mirror, the interference light can be measured by taking out the light of both directions to the outside of the circulating optical path.
[0022]
In addition, by making a part of the mirror movable, the angle at which the optical paths around the two intersect can be made variable, and the interference width can be controlled. If a mirror having a (110) plane is made of a cantilever and is displaceable by acceleration, the optical path length changes due to the displacement, and the interference fringes change. In addition, using a semi-transparent mirror or the like, a beat due to the difference in oscillation frequency between the two lights is observed and the angular velocity can be measured. A laser medium is installed in the optical path of the laser light and is oscillated by resonating in the circulating optical path, or laser light oscillated from the outside is introduced.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0024]
FIG. 1 is a configuration diagram of a circulating optical path showing the basic configuration of the present invention.
[0025]
In this figure, the silicon substrate 1 having the (110) plane as a surface is etched by anisotropic wet etching to form (111) plane mirrors 2 to 5 on the surface. The (111) plane mirrors 2 to 5 depend on two types of orientations on the (110) plane, with angles of about +54.7 degrees and about −54.7 degrees from the <110> orientation. Circulating optical paths 6 and 7 are formed using these two kinds of directions. In addition, a semi-transparent (half) mirror and an angle adjustable mirror are used in combination to generate observable interference.
[0026]
That is, the mirrors 2 to 5 are (111) planes formed by anisotropic wet etching, and have very accurate angles determined by crystal orientations. The substrate 1 that holds the mirror may be formed by bonding a single crystal silicon wafer having a (110) surface to a substrate such as glass and etching it to the thickness of the silicon wafer. It may be formed by etching (half etching).
[0027]
FIG. 2 is a configuration diagram of a circulating optical path showing the first embodiment of the present invention.
[0028]
As shown in this figure, by appropriately setting the positions of the mirrors 8 to 11, the area surrounded by the clockwise and counterclockwise light of the circulating optical path can be determined independently. This is important for applications using the Sagnac effect, such as ring laser gyros.
[0029]
If clockwise or counterclockwise light is introduced into such an optical path, interference can be observed with these lights. The interference may be observed on the mirror surface, or may be observed externally with a semi-transparent mirror. When light is introduced from outside and circulated, if the angle of one or a plurality of mirrors 8 to 11 can be adjusted, the generated interference fringe interval becomes wide and observation becomes easy. For example, when the angle of the mirror 10 can be slightly changed and is displaced in the direction such as the position 12, the counterclockwise light is displaced like the path 13, and interference fringes with the clockwise light generated in the mirror 11. Can be widened.
[0030]
FIG. 3 is a configuration diagram of a circulating optical path showing a second embodiment of the present invention, which is an example in which a part of light circulating around a mirror is taken out to measure interference.
[0031]
In this case, the circular optical path formed by the mirrors 14 to 17 can form an optical path that takes the completely same path, so that an optical resonance circuit can be formed. Here, among the light circulated by the mirrors 14 to 17, the clockwise light passes through the semi-transmissive mirror 14, and the counter-clockwise light passes through the semi-transmissive mirror 15 and interferes with the external mirrors 18 and 19. Give birth. Here, if one or both of the external mirrors 18 and 19 are formed so that the angle can be displaced, the interference fringes can be widened and observation can be facilitated as in the example of FIG.
[0032]
Thus, for example, by separating the optical path for observation (formed by the mirrors 18 and 19) and the optical path for resonance (formed by the mirrors 14 to 17), the observation is performed to widen the interference fringe interval. Even if the angle of the mirror for adjustment is adjusted, there is an advantage that it does not affect the optical path for resonance.
[0033]
If high reflectivity is required for the mirror, the (111) surface is coated with a highly reflective material such as metal or a dielectric layer. This can be realized by lengthening the wavelength.
[0034]
FIG. 4 is a configuration diagram of a circulating optical path showing a third embodiment of the present invention, which is another example of taking out a part of the circulating light to the outside and measuring interference.
[0035]
As shown in this figure, the mirrors 20 to 23 are for forming a circulating optical path, of which the mirrors 20 and 21 are semi-transmissive mirrors. The mirrors 24 to 27 are circular optical paths for interference observation.
[0036]
1 to 4 can form an optical resonance circuit, and therefore, the optical path shape is determined by a method such as inserting a laser diode in the optical path, enclosing a laser medium such as HeNe, and exciting it. Laser oscillation can be performed.
[0037]
FIG. 5 shows an example of an acceleration sensor using the present invention, and FIG. 6 shows an example of an angular velocity sensor (gyroscope).
[0038]
In FIG. 5, a part 28 of the mirror in the circulating optical path is formed so as to be displaced by acceleration. The optical path is displaced by the displacement, and the interference fringes generated in the part of the mirror 28, 29, 30 or 31 change. This is used for acceleration detection. In this case, a part of the mirror that makes the interference fringe constant (illustrated by the mirror 29 in FIG. 5) can be moved to perform feedback control so that the interference fringe is constant.
[0039]
The introduction of light into the circulating optical path can be performed by, for example, the laser diode 32 that emits light at both end points placed in the circulating optical path. Light may be introduced from the light source outside the circular optical path into the circular optical path.
[0040]
In FIG. 6, the area difference [area (40) −area (41)] surrounded by the clockwise and counterclockwise directions of the circulating optical path is increased, and the angular velocity is detected using the Sagnac effect. Sensitivity is proportional to this area difference [area (40) −area (41)]. In order to perform laser oscillation in the resonance circuit formed by the mirrors 33 to 36, a laser diode 39 that is not coated with a reflective film (or coated with an antireflection film) is provided in the circulating optical path.
[0041]
The optical path including the laser diode 39 (circular optical path by the mirrors 33 to 36) is used exclusively for resonance circuit formation, and the beat due to the difference in oscillation frequency between the clockwise light and the counterclockwise light generated by the Sagnac effect is detected by an external interference observation unit ( Observed by the mirrors 37 and 38).
[0042]
The angle of a part of the mirrors 33 to 36 constituting the resonance circuit for adjusting the resonance and a part of the mirrors 37 and 38 of the interference observation unit for adjusting the interference fringe interval may be made variable. .
[0043]
FIG. 7 is a cross-sectional view of a mirror manufacturing process showing the first embodiment of the present invention. Here, a case where electrical insulation is required between mirrors will be described.
[0044]
(1) First, as shown in FIG. 7A, a substrate 101 such as glass and a (110) silicon oxide film 103, 104 formed on both sides of a silicon base 102 are prepared and bonded together. .
[0045]
(2) Next, as shown in FIG. 7B, the silicon oxide film 104 on the surface of the joined body is patterned.
[0046]
(3) Next, as shown in FIG. 7C, (110) the silicon substrate 102 is through-etched by anisotropic wet etching using the patterned silicon oxide film 104 'as a mask. Reference numeral 105 denotes a (111) plane mirror after through etching, and the reflection state of the (111) plane mirror 105 is shown in FIG.
[0047]
(4) Next, as shown in FIG. 7C, in the step (3), the (111) plane mirror 105 is slightly tapered or its surface is rough. As shown in FIG. 7D, the mirror surface and semi-transparent mirror surface adjustment etching is performed. Reference numeral 106 denotes the finished mirror surface and the mirror surface after semi-transparent mirror surface adjustment etching, and the reflection state of the mirror is shown in FIG. In addition, since the semi-transparent mirror surface needs to be formed thin, the film thickness can be adjusted in this step.
[0048]
As is apparent from FIG. 9, it is possible to form a mirror that is comparable to a commercially available reflection mirror.
[0049]
FIG. 10 is a cross-sectional view of a mirror manufacturing process showing a second embodiment of the present invention. Here, the case where all the structures may be electrically connected will be described.
[0050]
(1) First, as shown in FIG. 10A, (110) a silicon substrate 201 having silicon oxide films 202 and 203 formed on both sides is prepared.
[0051]
(2) Next, as shown in FIG. 10B, (110) the silicon oxide film 203 on the upper surface of the silicon substrate 201 is patterned.
[0052]
(3) Next, as shown in FIG. 10C, (110) the silicon substrate 201 is half-etched by anisotropic wet etching using the patterned silicon oxide film 203 'as a mask, and the half-etching is performed. A protective film 204 is formed on the bottom surface 201A of the recessed portion of the silicon substrate 201 ′. Reference numeral 205 denotes a (111) plane mirror after half-etching.
[0053]
(4) Next, as shown in FIG. 10D, mirror surface and semi-transparent mirror surface adjustment etching is performed. Reference numeral 206 denotes a mirror surface after the mirror surface and semi-transparent mirror surface adjustment etching.
[0054]
In addition, after each mirror surface and semi-transparent mirror surface adjustment etching described above, a mirror comparable to a normal mirror was obtained. That is, the thickness of the semi-transparent mirror is controlled while holding the mirror while selecting the etchant. TMAH [tetramethylammonium hydroxide (tetramethylammonium hydroxide): silicon etchant] is used in combination with KOH.
[0055]
Also in this embodiment, a substrate (glass or the like) may be provided on the bottom side of the (110) silicon substrate 201.
[0056]
FIG. 11 is a sectional view of a mirror manufacturing process showing the third embodiment of the present invention. Here, the case where a cantilever movable part is required is demonstrated.
[0057]
(1) First, as shown in FIG. 11A, a substrate 301 such as glass having an etching portion 302 obtained by etching a part of the surface, and (110) silicon oxide films 304 and 305 on both sides of a silicon base 303. Prepare what was formed, and join them together.
[0058]
(2) Next, as shown in FIG. 11B, (110) the silicon oxide film 305 on the upper surface of the silicon substrate 303 is patterned.
[0059]
(3) Next, as shown in FIG. 11C, using the patterned silicon oxide film 305 ′ as a mask, (110) through etching of the silicon substrate 303 is performed by anisotropic wet etching to form glass or the like. It penetrates through the etching part 302 of the substrate 301. Here, the cantilever movable part 306 is formed. Reference numeral 307 denotes a (111) plane mirror after through etching. Reference numeral 304 'denotes a patterned silicon oxide film.
[0060]
(4) Next, as shown in FIG. 11D, mirror surface and semi-transparent mirror surface adjustment etching is performed. Reference numeral 308 denotes the mirror surface and the mirror surface after semi-transparent mirror surface adjustment etching.
[0061]
As described above, the present invention
[1] A coherent laser light source, perpendicular to the substrate, the reflective surface for reflecting light (reflection mirror) is arranged, with a reflective surface, forming a clockwise and counter-clockwise circulating light path, this An optical ring circuit is formed by the circulating optical path. Both directions of light are derived to the outside of the circulating optical path, and changes in the interference fringes of the derived light are detected. An optical gyro using this is provided.
[0062]
[2] A silicon substrate having the (110) plane as a surface is etched by anisotropic wet etching, and a (111) plane perpendicular to the surface is used as a light reflecting mirror. When a high reflectance is required, a metal or dielectric is coated on the (111) plane.
[0063]
By combining the above two techniques, for example, a circular optical path is formed by anisotropic wet etching. In that case, a (111) plane of single crystal silicon is used.
[0064]
In addition, a laser medium is disposed in the laser optical path, and a laser resonance circuit is formed by the circulating optical path by the emitted light. In this case, it is necessary to adjust the distance between the mirrors to the wavelength. Alternatively, a laser beam oscillated from the outside is introduced into the circulating optical path to form a resonance circuit.
[0065]
Furthermore, by using a partially translucent mirror as the reflecting surface, a part of the circulating light is extracted outside the circulating optical path, and a signal is extracted by the photodetector. Interference is detected by superimposing light in both directions. You may make it observe an interference fringe on the surface of a mirror.
[0066]
Further, a part of the mirror is made movable to control the interference fringes.
[0067]
A part of the mirror is, for example, a cantilever and is formed so as to be displaced by acceleration, and the optical path is displaced by the displacement, and the interference fringe changes. This is detected to constitute an acceleration sensor.
[0068]
An optical gyro serving as an angular velocity sensor using interference fringe detection by the Sagnac effect is configured by making a difference in the area surrounded by light around both sides.
[0069]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0070]
【The invention's effect】
As described above in detail, according to the present invention, the adjustment process of the mirror for generating the optical path is reduced as compared with the configuration using the conventional mechanical structural material, and batch production is possible. Combined with this, mass production and cost reduction can be achieved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a circulating optical path showing a basic configuration of the present invention.
FIG. 2 is a configuration diagram of a circulating optical path showing a first embodiment of the present invention.
FIG. 3 is a configuration diagram of a circulating optical path showing a second embodiment of the present invention.
FIG. 4 is a configuration diagram of a circulating optical path showing a third embodiment of the present invention.
FIG. 5 is a diagram showing an example of an acceleration sensor using the present invention.
FIG. 6 is a diagram showing an example of an angular velocity sensor (gyroscope) using the present invention.
FIG. 7 is a cross-sectional view of a mirror manufacturing process showing a first embodiment of the present invention.
FIG. 8 is a diagram showing a reflection state of a (111) plane mirror after through etching according to the present invention.
FIG. 9 is a diagram showing a reflection state of a mirror surface and a mirror surface after semi-transparent mirror adjustment etching according to the present invention.
FIG. 10 is a sectional view of a mirror fabrication process showing a second embodiment of the present invention.
FIG. 11 is a sectional view of a mirror fabrication process showing a third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Silicon substrate 2-5, 8-11, 14-17, 18, 19, 20-23, 24-27, 28-31, 33-36, 37, 38 (111) plane mirror 6,7 Circular optical path 12 Position 13 path 32, 39 laser diode 40, 41 area 101, 301 glass substrate 102, 201, 303 (110) silicon substrate 102 ', 303' etched silicon substrate 103, 104, 202, 203, 304, 305 silicon Oxide film 104 ', 203', 304 ', 305' Patterned silicon oxide film 105, 307 (111) plane mirror 106, 206, 308 after through-etching mirror surface, mirror surface after semi-transparent mirror surface adjustment etching 201 ′ Half-etched silicon substrate 201A Bottom surface of recess 204 Protective film 2 05 (111) mirror after half etching 302 Etching part 306 Cantilever movable part

Claims (7)

A coherent laser light source and a single crystal silicon substrate having a (110) plane as a surface are etched by anisotropic wet etching, and about +54.7 degrees from the <110> orientation on the (110) plane is etched on the surface. And a laser from the light source perpendicular to the single crystal silicon substrate having the (110) plane exposed by the etching of the (111) plane reflecting mirror depending on two kinds of orientations at an angle of about -54.7 degrees A circular optical path characterized by forming a plurality of light so as to circulate, forming a clockwise optical path and a counterclockwise optical path using the two kinds of orientations, and forming an optical ring circuit by the circular optical path Forming method.   2. The method of forming a circulating optical path according to claim 1, wherein a part of the circulating light is taken out of the circulating optical path by using a part of the circulating optical path as a semi-transparent mirror. .   2. The method of forming an orbiting optical path according to claim 1, wherein a part of the (111) plane mirror is movable with respect to light that passes through or reflects inside the orbiting optical path, and the interference width is maintained while causing interference. A method for forming a circulating optical path, characterized in that   4. The method for forming a circulating optical path according to claim 3, wherein the movable mirror is used for feedback control.   An optical gyro characterized in that the light of both directions obtained by the method for forming a circulating optical path according to claim 1 is derived outside the circulating optical path, and a change in interference light of the derived light is detected.   An optical gyro characterized in that a mirror of the optical circulating optical path obtained by the method for forming a circulating optical path according to claim 1 is made movable and used for feedback control.   An optical gyro characterized in that the circular optical path obtained by the method for forming a circular optical path according to claim 1 has a ring laser gyro function.

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