JP3728589B2 - Two-divided transflective concave mirror and ring laser gyro provided with the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a two-divided transflective readout concave mirror and a ring laser gyro including the same, and more particularly to a two-divided transflective readout concave mirror that is easy to downsize and manufacture and can be easily incorporated into a ring laser gyro. It relates to a ring laser gyro.
[0002]
[Prior art]
The operation principle of the ring laser gyro RLG will be described with reference to FIG.
By forming a closed annular resonator 10 in the glass block 1 and applying a voltage between the first anode 21 and the second anode 22 and the cathode 2, a plasma discharge is generated, and a clockwise CW laser is generated. The light and the counterclockwise CCW laser light propagate and circulate independently along the annular optical path 11 while being reflected by the semi-transmissive concave mirror 31, the second plane mirror 32, and the third plane mirror 33. Reference numeral 13 denotes a counterbore hole, which is formed in a part of the annular optical path 11 from the viewpoint of securing a gas capacity as a laser resonator. A part of the CW laser light is transmitted through the semi-transmissive concave mirror 31 and retroreflected at the corner cube 34, reflected by the external semi-transmissive mirror 35 and incident on the photodetector 36. The CCW laser light passes through the semi-transmissive concave mirror 31 and the external semi-transmissive mirror 35 and is directly incident on the photodetector 36. By the way, the CW laser beam and the CCW laser beam interfere with each other immediately before entering the photodetector 36 to generate interference fringes. The photodetector 36 detects this interference fringe.
[0003]
When the angular velocity ω is input with the center of the annular optical path 11 as an axis, the starting point of the light moves during one round of the laser light, so the time for the laser light to make one round of the annular optical path 11 is apparent. It is different. That is, the time apparently increases for laser light circulating in the same direction as the input angular velocity ω, and the time is apparently reduced for laser light circulating in the opposite direction to the input angular velocity ω. The time difference required for one round between the CW laser light and the CCW laser light appears as a frequency difference between the two laser lights. The previous interference fringes are generated due to the frequency difference between the two laser beams. The input angular velocity ω can be measured by analyzing the interference fringes.
[0004]
In the semi-transparent concave mirror 31 described above, a concave reflecting surface 311 that is a laser light reflecting surface and a flat surface 312 that is a portion in optical contact with the glass block 1 are integrally formed. In order to align the laser beam circulating to the appropriate light reflection / transmission point of the semi-transmissive concave mirror 31, the flat surface 312 of the semi-transmissive concave mirror 31 is a flat surface that is a fixed surface for fixing the semi-transmissive concave mirror 31 of the glass block 1. The translucent concave mirror 31 is positioned and fixed on the flat surface 12 while being translated along the surface 12.
[0005]
[Problems to be solved by the invention]
In the conventional example described above, the semi-transparent concave mirror 31 has the concave reflecting surface 311 and the flat surface 312 which are integrally structured, causing the following problems.
(1) The concave surface portion of the concave mirror is generally formed into a spherical surface. Therefore, there is only one point at the apex of the concave reflecting surface 311 where the laser beam should be aligned on the concave reflecting surface 311 of the semi-transmissive concave mirror 31. If this one point is scratched, rough, or otherwise damaged, laser light scattering will increase and the performance of the RLG will be impaired.
[0006]
(2) Scattering on the concave reflecting surface 311 of the transflective concave mirror 31 has a distribution depending on the position, but it cannot move freely for the convenience of laser beam alignment, so use the position where scattering is best. I can't. This also impairs the performance of the RLG.
(3) To reduce the size of the RLG, it is necessary to reduce the size of the semi-transmissive concave mirror 31 as well. When the semi-transmissive concave mirror 31 is downsized, the diameter of the concave reflecting surface 311 is reduced, and the amount of recess of the flat surface 312 becomes shallow correspondingly. Due to the shallow depth of the flat surface 312, there is a greater risk of scratching the surface during polishing of the semi-transmissive concave mirror 31, which makes processing difficult. This will be described in more detail. In the polishing process of the semi-transmissive concave mirror 31, first, the entire surface is concave-polished to form the concave reflecting surface 311, and then the planar polishing is performed. Since the radius of curvature of the concave reflecting surface 311 is about several thousand mm, even if the diameter of the concave reflecting surface 311 is 15 mm, the depth of the recess of the concave reflecting surface 311 is only about several μm. If the semitransparent concave mirror 31 is to be miniaturized, the diameter of the concave reflecting surface 311 is inevitably reduced, and the depth of the recess is also reduced. By the way, since the abrasive grains used at the time of planar polishing are usually free abrasive grains having a particle diameter of several μm, when the depth of the concave of the concave reflective surface 311 becomes shallow, the concave reflective surface that has already been polished with high accuracy. The surface of 311 will be roughened. Further, it is difficult to obtain flatness within a limited machining allowance. If the polishing process is continued without satisfying the flatness, the diameter of the concave reflecting surface 311 rapidly decreases, and the concave surface is further roughened. Become. Further, a defective product that does not satisfy the diameter standard of the concave reflecting surface 311 is formed, and the previously formed concave polishing becomes useless. Although a method of performing concave polishing after surface polishing is also conceivable, it is more difficult to polish with high accuracy within a limited machining allowance.
[0007]
{Circle over (4)} Although the semi-transparent concave mirror 31 may need to be removed, a delicate laser beam alignment operation is required again when the semi-transparent concave mirror 31 is attached.
The present invention provides a transflective readout concave mirror that solves the above-described problems and a ring laser gyro provided with the same.
[0008]
[Means for Solving the Problems]
Claim 1: One surface is a flat surface 412 and the other surface is a convex surface 413. The concave substrate is provided with a plano-convex ring 41 in which a central hole 411 is formed at the center, and a concave reflecting surface 421 is formed. 42, the curvature radius of the concave reflection surface 421 and the curvature radius of the convex surface 413 are designed to be equal, and the plano-convex ring 41 and the concave substrate 42 are combined with the convex reflection surface 413 and the concave reflection surface 421 in contact with each other. A readout concave mirror was constructed.
[0009]
In a second aspect of the present invention, there is provided a two-part semi-transmission readout concave mirror in which the convex surface 413 of the plano-convex ring 41 is a spherical surface and the concave reflecting surface 421 of the concave substrate 42 is a spherical surface. A readout concave mirror was constructed.
Further, in the second aspect of the present invention, in the two-part semi-transmission readout concave mirror described in any one of the first and second aspects, the two-part semi-transmission is obtained by mirror-finishing both the flat surface 412 and the convex surface 413 of the plano-convex ring 41. A readout concave mirror was constructed.
[0010]
In this case, the annular resonator 10 is closed in the glass block 1, and the clockwise laser beam and the counterclockwise laser beam are independently propagated and circulated along the annular optical path 11, thereby the both-way laser. In the ring laser gyro for extracting and detecting a part of light through the semi-transmissive readout concave mirror 4, the semi-transmissive readout concave mirror 4 has one surface as a flat surface 412 and the other surface as a convex surface 413, and a central hole 411 at the center. And a concave substrate 42 on which a concave reflecting surface 421 is formed. The curvature radius of the concave reflecting surface 421 and the curvature radius of the convex surface 413 are designed to be equal to each other. A ring laser gyro which is a two-part semi-transmissive readout concave mirror in which the concave substrate 42 is combined with the convex surface 413 in contact with the concave reflecting surface 421 is configured.
[0011]
In the ring laser gyro described in claim 5, the ring laser gyro is configured such that the convex surface 413 of the plano-convex ring 41 is a spherical surface and the concave reflecting surface 421 of the concave substrate 42 is a spherical surface.
In addition, in the ring laser gyro according to any one of claims 4 and 5, a ring laser gyro in which both the flat surface 412 and the convex surface 413 of the plano-convex ring 41 are mirror-finished is configured.
[0012]
Further, in the ring laser gyro according to claim 7 of the present invention, a ring laser gyro in which a flat surface 12 which is a fixed surface for fixing the two-part semi-transmissive readout concave mirror 4 of the glass block 1 is mirror-finished is configured.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the example of FIG. FIG. 1 is a sectional view of the embodiment. In the embodiment, the same reference numerals are given to the members common to the conventional example.
In FIG. 1, reference numeral 4 denotes a two-divided transflective concave mirror, which is composed of a two-divided plano-convex ring 41 and a concave substrate 42.
[0014]
The plano-convex ring 41 is formed with a center hole 411 through which a laser beam passes at the center. One surface 412 is formed as a flat surface, and the other surface 413 is formed as a convex surface. Both the flat surface 412 and the convex surface 413 are mirror-finished. The concave substrate 42 has a concave reflecting surface 421 formed thereon. The radius of curvature of the concave reflecting surface 421 is designed to be equal to the radius of curvature of the convex surface 413 of the plano-convex ring 41. In particular, the concave reflecting surface 421 and the convex surface 413 are formed into spherical surfaces.
[0015]
Here, the assembly order of RLG will be described.
In order to configure the resonator 10, it is necessary to align the laser beam with the concave reflecting surface 421 of the concave substrate 42 of the two-divided transflective reading concave mirror 4. As a procedure for implementing this, first, the concave surface of the concave substrate 42 is used. The reflective surface 421 and the convex surface 413 of the plano-convex ring 41 are temporarily optically contacted to integrate the concave substrate 42 and the plano-convex ring 41 to constitute the two-divided transflective readout concave mirror 4. Since the convex surface 413 of the plano-convex ring 41 is also mirror-finished as described above, the concave reflecting surface 421 and the convex surface 413 can be in optical contact.
[0016]
Next, the plane 412 of the plano-convex ring 41 in the two-part semi-transmission readout concave mirror 4 that has been temporarily optically contacted is fixed to the flat surface 12 that is a fixing surface for fixing the two-part semi-transmission readout concave mirror 4 of the glass block 1. Slide to align for alignment. The flat surface 12 is also mirror-finished. When the alignment is achieved, the plano-convex ring 41 is fixed to the glass block 1 by optically contacting the flat surface 412 with respect to the flat surface 12, and eventually, the two-part transflective readout concave mirror 4 which is temporarily optically contacted is provided with the glass block. 1 is fixed to one flat surface 12. Here, the concave substrate 42 is released from the temporary optical contact with the plano-convex ring 41. The concave substrate 42 released from the temporary optical contact with the plano-convex ring 41 is free from scratches, roughness and other damage while sliding the concave reflecting surface 421 along the surface of the convex surface 413 of the plano-convex ring 41 1. Search for a point and select this point as the best position for scattering. The concave reflecting surface 421 and the convex surface 413 in the state of holding the best point with respect to this scattering are optically contacted to form an aligned two-part transflective readout concave mirror 4.
[0017]
【The invention's effect】
As described above, according to the present invention, even if scratches, roughness, and other damages are scattered on the concave reflecting surface 421, if a good point with respect to scattering can be searched at one place, the laser beam can be searched here. Can be used without discarding the concave substrate 42. In the end, the production yield can be improved by dividing the transflective concave mirror into two parts.
[0018]
Then, the temporary optical contact between the concave substrate 42 and the plano-convex ring 41 is removed, and the point searched by sliding the concave reflecting surface 421 along the surface of the convex surface 413 is selected as the best position with respect to scattering. With respect to this point, the angle deviation of the reflecting surface of the laser beam does not occur between the point at the time of provisional optical contact and the alignment of the laser beam does not change. This is because, as described above, the radius of curvature of the concave reflecting surface 421 and the radius of curvature of the convex surface 413 are designed to be equal, and the curved surface is formed into a spherical surface. In some cases, it may be necessary to remove and reassemble the two-divided transflective readout concave mirror 4 from the glass block 1 of the RLG. In this case as well, the plano-convex ring 41 is left coupled to the flat surface 12 of the glass block 1 to form a concave surface. Simply removing the substrate 42 is sufficient. When the concave substrate 42 is optically contacted again, there is no need to perform troublesome and delicate alignment adjustment work of the laser beam.
[0019]
In the conventional example, when the semi-transparent concave mirror 31 is to be downsized, the diameter of the concave reflecting surface 311 is reduced, and the amount of the recess in the flat surface 312 is correspondingly reduced. Although there is a greater risk of scratches on the surface during processing, according to the present invention, since the cylindrical raw material having a constant diameter is polished to form the concave reflecting surface 421 of the concave substrate 42, the conventional example is concerned. There is no need, and polishing can be repeated until the flatness and other standards are satisfied without changing the diameter of the concave reflecting surface 421.
[0020]
Further, according to the present invention, the concave mirror is a two-part semi-transmissive readout concave mirror 4 comprising a concave substrate 42 and a plano-convex ring 41 to which the concave substrate 42 is joined. Laser light circulating along the annular optical path is formed on the glass block 1. The laser light that has passed through the counterbore hole 13 and the center hole 411 formed in the plano-convex ring 41 is received by the concave reflecting surface 421 formed on the concave substrate 42. Here, the center hole 411 of the plano-convex ring 41 can be configured to be small within a range that does not block the laser beam, and the diameter of the concave substrate 42 can be designed and manufactured correspondingly. That is, no matter how small the diameter of the concave substrate 42 is designed and manufactured corresponding to the center hole 411 of the plano-convex ring 41, the concave substrate 42 is bonded and fixed to the glass block 1 via the plano-convex ring 41. By designing and producing the diameter of the plano-convex ring 41 larger than the diameter of the opening of the counterbore hole 13, the concave substrate 42 can be bonded and fixed to the place where the counterbore hole 13 of the glass block 1 is formed. By the way, conventionally, the semi-transmissive readout concave mirror is configured only by the concave substrate 42 on which the concave reflecting surface 421 is formed, and adopts a configuration in which the translucent readout concave mirror is directly bonded and fixed to the glass block 1 without the plano-convex ring 41 to which the concave substrate 42 is bonded. Therefore, the opening of the spot facing hole 13 where the concave substrate 42 is bonded and fixed to the glass block 1 is formed to have a small diameter so as not to interfere with the bonding and fixing of the concave substrate 42. It was necessary to guarantee the bonding and fixing. The counterbore hole 13 having a small opening may have a stepped hole having a small inner diameter but a large inner volume. This is because the internal volume of the spot facing hole 13 formed in a part of the annular optical path 11 of the laser resonator cannot be made extremely small in order to secure the gas capacity of the annular optical path 11 beyond a certain required amount. is there. In order to process the counterbore hole 13 into a stepped hole, a special grindstone tool having a thick tip portion, a thin shaft portion and low rigidity is required, and the processing itself is not easy. However, in the present invention, as described above, by designing and manufacturing the plano-convex ring 41 so that the diameter of the plano-convex ring 41 is larger than the diameter of the counterbore hole 13, the small-diameter concave substrate 42 can be formed regardless of the shape structure of the spotlight hole 13. The glass block 1 can be bonded and fixed where the counterbore hole 13 is formed. The counterbore hole 13 can be a simple cylindrical counterbore hole 13 formed by a grindstone tool made of a simple shape material.
[0021]
In addition, since the concave substrate polishing jig and the film-attached jig are finite in size, the concave substrate having a smaller diameter should be placed on the polishing jig and the film-attached jig more naturally than the concave substrate having a larger diameter. The number of concave substrates that can be increased. Since the processing time per lot is the same regardless of the number of concave substrates placed on the polishing jig and the film-coated jig, the polishing cost per film and the film-coated cost can be reduced. This leads to a lower cost of manufacturing the concave substrate.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment.
FIG. 2 is a diagram illustrating a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Glass block 10 Resonator 11 Annular optical path 12 Flat surface 2 Cathode 21 First anode 22 Second anode 31 Semi-transmission concave mirror 32 Second plane mirror 33 Third plane mirror 34 Corner cube 35 External semi-transmission mirror 36 Photodetector 4 Divided transflective concave mirror 41 Plano-convex ring 411 Center hole 412 Plane 413 Convex surface 42 Concave substrate 421 Concave reflective surface

Claims (7)

One surface is a flat surface and the other surface is a convex surface, comprising a plano-convex ring in which a central hole is formed through the center,
Comprising a concave substrate on which a concave reflective surface is formed;
The radius of curvature of the concave reflecting surface and the radius of curvature of the convex surface are designed to be equal,
A two-divided transflective concave mirror characterized by combining a plano-convex ring and a concave substrate with a concave reflecting surface in contact with a convex surface. The two-divided transflective readout concave mirror according to claim 1,
A two-divided transflective concave mirror characterized in that the convex surface of the plano-convex ring is a spherical surface and the concave reflecting surface of the concave substrate is a spherical surface. In the two-divided transflective readout concave mirror according to any one of claims 1 and 2,
A two-part transflective readout concave mirror characterized in that both the plane and convex surface of the plano-convex ring are mirror-finished. An annular resonator closed inside the glass block is constructed to circulate clockwise and counterclockwise laser beams independently along the annular optical path, and a part of both laser beams pass through a semi-transmissive readout concave mirror. In the ring laser gyro
The transflective concave mirror has a plano-convex ring in which one surface is a flat surface and the other surface is a convex surface, and a central hole is formed through the central portion, and a concave substrate on which a concave reflecting surface is formed, A ring laser characterized in that it is a two-part semi-transmission readout concave mirror in which the radius of curvature of the concave reflecting surface and the radius of curvature of the convex surface are designed to be equal, and the plano-convex ring and concave substrate are combined in contact with the concave reflecting surface. gyro. The ring laser gyro according to claim 4, wherein
A ring laser gyro characterized in that the convex surface of the plano-convex ring is a spherical surface and the concave reflecting surface of the concave substrate is a spherical surface. In the ring laser gyro according to any one of claims 4 and 5,
A ring laser gyro characterized in that both the plane and the convex surface of a plano-convex ring are mirror-finished. In the ring laser gyro described in claim 6,
A ring laser gyro characterized in that a flat surface, which is a fixed surface for fixing a half-transmission readout concave mirror of a glass block, is mirror-finished.

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