JPH08290925A - Production of optical element and production of rotation asymmetric mold for molding optical element - Google Patents

Abstract

PURPOSE: To easily obtain an optical element having an optical function surface of non-rotation symmetric shape by pressing an optical element raw material with a mold having an optical function surface of non-rotation symmetric shape formed by unevenly etching the rotation-symmetric surface of the mold base material. CONSTITUTION: In a method for producing an optical element having a rotation non- asymmetric non-spherical surface on the optical function surface by heating and pressing a pair of molds wherein either one of the molds has a rotation non-asymmetric surface and an optical raw material disposed between the molds, an intermediate assembly 100 having a mask 4 disposed above the surface 1a of a mold base material 1 or the surface 3 of a protecting film disposed thereon through a mask jig 7 and the mold base material 1 having the surface 1a on which a rotation symmetric non- spherical surface is preliminarily formed is disposed in an etching device. Argon ion beams 6 are downward irradiated from places above the mask 4 in order to etch the surface 1a of the mold base material 1 or the surface 3 of the protecting film 2. The mold base material 1 is thus processed into a mold having a rotation non- asymmetric spherical surface and can transfer the surface shape of the mold to the surface of a pressed optical element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical element such as an aspherical lens used in an optical device and a method of manufacturing a rotationally asymmetric type suitable for the method.

[0002]

2. Description of the Related Art Generally, an optical head for an optical disk or a magneto-optical disk is always driven in the radial direction of the disk in order to track the recording surface of the disk. Therefore, in most cases, the off-axis region of the objective lens is used to read data from or write data on the recording surface of the disc. However, the optical performance of the lens in the off-axis region is inferior to the optical performance in the paraxial region because the astigmatism increases in the off-axis region. Further, the light from the semiconductor laser used as the light source has an astigmatic difference. Further, the second lens for collecting the light reflected by the recording surface of the disc on the photodetector also has astigmatism. Therefore, the recording / reproducing performance of the optical head is further deteriorated.

Therefore, various methods have been proposed to improve the performance of the optical head. As a first conventional example, for example, Japanese Patent Laid-Open No. 5-107467 proposes an objective lens having at least a rotationally asymmetric optical function surface. By forming the optically functional surface of the objective lens in a rotationally asymmetric manner, it is possible to generate an astigmatism component in the aberration on the optical axis. The direction of the objective lens is adjusted so that the astigmatism generated by the rotationally asymmetric surface cancels the aberration caused by the semiconductor laser or the second lens. As a second conventional example, a method of directly polishing an optical material to process it is known.

As a third conventional example, for example, US Pat. No. 5,015,280 proposes a technique for manufacturing an optical element by press molding. The press molding method is a method of transferring a mold shape to an optical material. Therefore, if the mold can be processed with high precision, a desired optical element can be easily manufactured. If the optical element to be manufactured is rotationally symmetric, such as a rotationally symmetric aspherical lens, the mold can be formed using an ultra-precision CNC controlled machine tool. The mold is rotated about the optical axis, and the grinding or cutting tool is fed and moved along a non-arcuate locus which is the cross-sectional shape of the lens. Thereby, the mold can be relatively easily manufactured with a shape accuracy of about 0.1 μm.

As a fourth conventional example, for example, Japanese Patent Laid-Open No. 5-1
Japanese Patent Laid-Open No. 07467 proposes a method of generating astigmatism by controlling molding conditions using a rotationally symmetrical mold.

[0006]

However, as a practical problem, it is very difficult to manufacture a rotationally asymmetric optical element as in the first conventional example. Further, in the second conventional example, the direct polishing method, the optical material such as glass and the grindstone are oscillated with each other and rubbed against each other for polishing, so that only a flat or spherical shape can be inevitably processed. Therefore, the conventional direct polishing method has a problem in that an optical element having a rotationally asymmetrical shape cannot be manufactured.

In the third conventional example, when the optical element to be manufactured has a rotationally asymmetric optical function surface, the processing machine for making the mold is very complicated, highly accurate and expensive. That is, for example, an encoder is attached to the spindle of a processing machine to detect the rotation angle of a die, while measuring the rotation angle of the die, while controlling the forward and backward movements of the tool with high accuracy during one revolution of the die or the spindle. , Must be repeated. Furthermore, it is difficult to ensure the shape accuracy of the mold formed by this processing. Further, in order to make the position of the tool follow the rotation of the die or the spindle, the spindle must be rotated very slowly, which causes a problem that the machining time of the die becomes long.

In the fourth conventional example, the molding temperature, temperature gradient,
It is necessary to control and manage the molding pressure and the shape of the molding material with high precision. Further, it is difficult to secure the yield in mass production of optical elements, and there is a problem that the direction of astigmatism of the lens is not fixed.

As described above, it has been difficult to manufacture an optical element having a rotationally asymmetrical shape by the conventional manufacturing method.
It is an object of the present invention to provide a method for easily manufacturing an optical element having a non-rotationally symmetric optical functional surface and a method for manufacturing a mold suitable for the method.

[0010]

In order to achieve the above object, a method of manufacturing an optical element according to the present invention comprises placing an optical material between a pair of molds and heating the optical material and the mold to a predetermined temperature. Then, a method of manufacturing an optical element for transferring the shape of the optical functional surface of the mold to the surface of the optical material by pressing the mold, wherein at least one optical functional surface of the mold is rotationally asymmetric, The rotationally asymmetric shape is formed by unevenly etching the rotationally symmetric surface of the die base material.

In the above structure, the rotationally asymmetric shape of the mold is formed by a dry etching method, and the dry etching method is performed at a position where the mask is in contact with the rotationally symmetrical surface of the mold base material or a position separated upward from the surface to be rotated. It is preferable to irradiate the rotationally symmetric surface of the die base material with an ion beam or a radical beam in the arranged state.

Alternatively, in the above structure, the rotationally asymmetrical shape of the mold is formed by a wet etching method, and the wet etching method removes a resist on at least the rotationally symmetric surface of the mold base material except a portion having a predetermined shape to be etched. It is preferable to form a film and immerse at least the rotationally symmetrical surface of the die base material in an etching solution.

In each of the above constructions, it is preferable that the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. Further, in each of the above configurations, it is preferable that the rotationally asymmetric shape is a shape that produces an astigmatism component of the axial wavefront aberration when transferred to an optical element. Also,
In each of the above configurations, it is preferable that the protective film is uniformly formed on the rotationally asymmetric surface of the mold.

On the other hand, according to another method of manufacturing an optical element of the present invention, an optical material is arranged between a pair of molds, the optical material and the mold are heated to a predetermined temperature, and the mold is pressed. A method of manufacturing an optical element, wherein the shape of an optical functional surface of the mold is transferred to the surface of the optical material, wherein at least one optical functional surface of the mold is rotationally asymmetrical, and the rotationally asymmetrical shape is on a mold base material. It is formed by nonuniformly etching the rotationally symmetric surface of the protective film formed on.

In the above structure, the rotationally asymmetrical shape of the mold is formed by a dry etching method, and in the dry etching method, the mask is in contact with the rotationally symmetrical surface of the protective film on the mold base material or upward from the surface to be rotated. It is preferable to irradiate the rotationally symmetrical surface of the protective film with an ion beam or a radical beam in a state where the protective film is arranged at a distant position.

Alternatively, in the above structure, the rotationally asymmetric shape of the mold is formed by a wet etching method, and the wet etching method is formed on at least the surface of the mold base material except for a portion having a predetermined shape to be etched. It is preferable that a resist film is formed on the rotationally symmetric surface of the protective film, and at least the rotationally symmetric surface of the die base material is immersed in an etching solution.

In each of the above structures, it is preferable that the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. Further, in each of the above configurations, it is preferable that the rotationally asymmetric shape is a shape that produces an astigmatism component of the axial wavefront aberration when transferred to an optical element.

In still another method of manufacturing an optical element of the present invention, an optical material is arranged between a pair of molds, the optical material and the mold are heated to a predetermined temperature, and the mold is pressed. A method of manufacturing an optical element, wherein the shape of the optical functional surface of the mold is transferred to the surface of the optical material by the method, wherein at least one optical functional surface of the mold is rotationally asymmetrical, and the rotationally asymmetrical shape is a mold base material. It is formed by forming a film nonuniformly on the rotationally symmetric surface of.

In the above structure, the rotationally asymmetric shape of the mold is formed by a sputtering method, a PVD (physical vapor depo
sition) method or a CVD (chemical vapor deposition) method, and the method is used for forming the mask at a position in contact with the rotational symmetry plane of the die base material or at a position separated upward from the rotational symmetry plane. It is preferable to irradiate the particles on the rotationally symmetrical surface of the die base material in the arranged state.

Further, in each of the above constitutions, it is preferable that the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. Further, in each of the above configurations, it is preferable that the rotationally asymmetric shape is a shape that produces an astigmatism component of the axial wavefront aberration when transferred to an optical element.

On the other hand, in the method for producing a rotationally asymmetric mold for molding an optical element of the present invention, the mask is arranged at a position in contact with the rotationally symmetrical surface of the mold base material or at a position separated upward from the surface to be rotated, and the mold base material is used. The rotationally symmetric surface of the mold base material is nonuniformly etched by irradiating the rotationally symmetric surface of 1. with an ion beam or a radical beam.

Another method for manufacturing a rotationally asymmetric mold for optical element molding of the present invention is to form a resist film on at least a rotationally symmetric surface of a mold base material except a portion having a predetermined shape to be etched, The rotationally symmetric surface of the die base material is non-uniformly etched by immersing the rotationally symmetric surface of the die base material in an etching solution.

According to still another method for producing a rotationally asymmetric mold for optical element molding of the present invention, the mask is in contact with the rotationally symmetrical surface of the protective film formed on the mold base material or at a position separated upward from the surface to be rotated. And irradiating the rotationally symmetric surface of the protective film with an ion beam or a radical beam, the rotationally symmetric surface of the protective film is unevenly etched.

According to another method of manufacturing a rotationally asymmetric mold for optical element molding of the present invention, a resist is formed on at least a rotationally symmetric surface of a protective film formed on a mold base material, except for a portion having a predetermined shape to be etched. A film is formed and at least the rotationally symmetric surface of the protective film is immersed in an etching solution to non-uniformly etch the rotationally symmetric surface of the protective film.

In each of the above constructions, it is preferable that the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. Further, in each of the above configurations, it is preferable that the rotationally asymmetric shape is a shape that produces an astigmatism component of the axial wavefront aberration when transferred to an optical element.

In still another method for manufacturing a rotationally asymmetric mold for molding an optical element of the present invention, a film is nonuniformly formed on the rotationally symmetric surface of a mold base material. In the above structure, the rotationally asymmetric shape of the mold is formed by sputtering, PVD (physical vapor depletion).
position) method or CVD (chemical vapor deposition) method, and the method is to place the mask at a position in contact with the rotational symmetry plane of the die base material or at a position separated upward from the rotational symmetry plane. It is preferable to irradiate the particles on the rotationally symmetrical surface of the die base material in the arranged state. Further, in each of the above configurations, it is preferable that the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. Further, in each of the above configurations, it is preferable that the rotationally asymmetric shape is a shape that produces an astigmatism component of the axial wavefront aberration when transferred to an optical element.

Further, when the die base material is directly etched, it is preferable to uniformly form a protective film on the rotationally asymmetric surface of the die.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) A first embodiment of a method for manufacturing an optical element and a method for manufacturing a mold suitable for the same according to the present invention will be described with reference to FIGS. 1 to 5, 12 and 13. Optical element 50 to be manufactured by the method of the present invention
Is an aspherical lens, for example, and is shown in FIG. The optical function surface 51 of the optical element 50 is a rotationally asymmetric aspherical surface, and has a vertical ridge line 52 and a horizontal ridge line 53. The radius of curvature in the vertical direction is different from the radius of curvature in the horizontal direction. therefore,
The ridgelines 52 and 53 each focus on two different points. The optical element 50 has astigmatism on its axis. The optical element 50 is manufactured by press molding an optical material arranged between a pair of molds. At least one of the molds has a rotationally asymmetric aspherical surface, which is transferred to the surface of the optical material. Therefore, the optical function surface 51 of the optical element 50 is formed.

Next, a method of manufacturing a mold having a rotationally asymmetric aspherical surface will be described. As shown in FIG. 1, the intermediate assembly 100 includes a mold base material 1, a mask 4, and a mask jig 7. The mold base material 1 is made of a cemented carbide containing tungsten (W) and carbon (C) as main components. A protective film 2 may be formed on the surface 1a of the mold base material 1 in order to prevent scratches on the mold surface and fusion of the optical material during molding. Mask 4
Is arranged at a position above the surface 1a of the die base material 1 or the surface 3 of the protective film 2 via the mask jig 7 and separated by a predetermined distance. The argon (Ar) ion beam 6 is irradiated downward from above the mask 4 in order to etch the surface 1a of the mold base material 1 or the surface 3 of the protective film 2. The mold base material 1 becomes a mold having a rotationally asymmetric aspherical surface when the mold manufacturing process is completed.

A rotationally symmetric aspherical surface is previously formed on the surface 1a of the mold base material 1 by the conventional method for forming a rotationally symmetric aspherical surface. The mold base material 1 is rotated around an axis corresponding to the optical axis of the optical element to be manufactured. Then, the grindstone is fed and moved so that the processing point where the grindstone and the die base material are in contact with each other draws a non-arcuate cross-sectional shape along a predetermined direction of the optical element 50, for example, a ridgeline 52 in FIG.
The shape accuracy of the mold base material 1 processed by this processing method is ±
It was about 0.1 μm. When the protective film 2 is formed on the surface 1a of the mold base material 1, platinum-iridium (Pt-I
r) A protective film made of an alloy or the like is formed with a thickness of 3 μm by a sputtering method.

As is apparent from FIG. 2, the shaded portion is the portion shielded by the mask 4 of the die base material 1. For example, the diameter of the molding surface of the mold base material 1 including the edge part is 5 mm.
And the diameter of the surface 1a or 3 is 4 mm. The size of the rectangular opening 5 is 5 mm × 2 mm, and each opening 5 is 1 m.
They are arranged in parallel at an interval of m.

Next, the intermediate assembly 10 shown in FIG.
0 is placed in the etching apparatus shown in FIG. In the first embodiment, an ECR (electron cyclotron resonance) ion beam etching apparatus is used. The etching apparatus includes an etching chamber 9, a stage 10 on which the intermediate assembly 100 is mounted, an ion beam acceleration electrode 11 provided on the upper end of the etching chamber 9, and an ion gun 13 provided on the etching chamber 9. It is equipped with.

When the intermediate assembly 100 is mounted on the stage 10, air is removed so that the inside of the etching chamber 9 becomes a vacuum. Then, argon (Ar) gas
It is introduced into the ion gun 13 through the gas introduction valve 14,
Plasma 12 is generated. The ion acceleration electrode 11 extracts Ar ions from the plasma 12 and irradiates the intermediate assembly 100 with the ion beam 6. Surface 1a of mold base material 1
Alternatively, atoms or molecules on the surface 3 of the protective film 2 are repelled by the collision of incoming ions. Thereby, the surface 1a of the die base material 1 or the surface 3 of the protective film 2 is etched.

In the first embodiment, the maximum diameter of the intermediate assembly 100 was 15 mm. Etching room 9
Seven intermediate assemblies 100 were mounted on the inner stage 10. The diameter of the ion beam flux from the ion gun 13 is 6
It was 0 mm. The mask 4 was separated from the surface 1a of the mold base material 1 or the surface 3 of the protective film 2 by 10 mm. The etching conditions are as follows. Pressure of introduced Ar gas 0.09P
a, the acceleration voltage of the ion beam 6 was 800 V, the current density of the ion beam 6 was 1.0 mA / cm ² , and the irradiation time of the ion beam 6 was 3 minutes.

The time required for machining one die is the time required for assembling the intermediate assembly 100 and the intermediate assembly 10.
It was about 90 minutes (one and a half hours) including the time for setting 0 in the etching chamber 9 and the time for drawing air to make the inside of the etching chamber 9 a vacuum. If the diameter of the ion beam bundle can be further increased, a large number of molds can be efficiently manufactured.

The cross-sectional shape of the mold thus formed was measured in the X-axis and Y-axis directions shown in FIGS.
FIG. 5 shows the measurement results. In FIG. 5, the horizontal axis represents the distance from the center of the mold to the measurement point, and the vertical axis represents the amount of deviation between the rotationally symmetric shape before etching and the rotationally asymmetric shape after etching at the measurement point as 0 Is expressed as. As is apparent from FIG. 5, the surface 1a of the mold base material 1
Alternatively, since the region of the surface 3 of the protective film 2 along the Y axis is covered with the mask 4 and uniformly etched by the ion beam 6, the cross-sectional shape of the mold in the Y axis direction changes from the rotationally symmetric shape before etching. I haven't. On the other hand, the region apart from the center of the mold in the X-axis direction has more ion beam 6
Therefore, the cross-sectional shape of the mold in the X-axis direction is gently inclined from the center toward the peripheral portion. as a result,
The surface shape of the surface 1a of the die base material 1 or the surface 3 of the protective film 2 after etching is rotationally asymmetric, such as a toric surface. The overall radius of curvature of the mold in the X-axis direction is larger than the radius of curvature of the mold in the Y-axis direction.

Further, another mold having a rotationally symmetrical surface is prepared in advance by a conventional method. FIG.
As shown in, an optical material 60 such as glass or resin is placed between the molds 61 and 62. One of the molds 61 and 62 has a rotationally asymmetric surface formed by the above etching method, and the other has a rotationally symmetrical surface formed by a conventional method. The molds 61 and 62 and the optical material 60 are heated to a predetermined temperature at which at least the surface of the optical material 60 is softened. The molds 61 and 62 are pressed with a predetermined pressure so that the surface shapes of the molds 61 and 62 are transferred to the surface of the optical material 60. Then, the molds 61 and 62 and the optical material 60 are cooled, and the optical element 50 which is an aspherical lens having the rotationally asymmetric optical function surface 51 is obtained.

In the first embodiment, the maximum deviation of the cross-sectional shape of the die in the X-axis direction in the outer peripheral portion is set to 0.15 μm. Repeat the above etching process 5 times for a total of 35
I made individual molds. The shape error of the mold is 0.1
It was ± 0.02 μm with respect to 5 μm.

The press molding process was repeated to obtain 10
00 lenses were molded. Optical glass SF8 was used as an optical material. Optical element 50 molded using the above mold
Is a rotationally asymmetric optical function surface 5 such as a toric surface.
Since it has 1, the optical element 50 produces astigmatism.
When the optical performances of the optical elements 50 were measured, each optical element 50 produced substantially the same amount of astigmatism in substantially the same direction. The average value of the astigmatism was 30 mλ (mλ: 1/1000 of the wavelength of the light source used), which was an appropriate value as an objective lens of an optical head for an optical disk device. Moreover,
The wavefront aberration of the entire optical element 50 was also good. An optical head was assembled using this optical element 50. Optical element 50
Is mounted so that off-axis astigmatism in the radial direction of the optical disk is canceled by on-axis astigmatism due to the rotationally asymmetric aspherical surface. The reproduction characteristic of the optical disc by the optical head using the optical element 50 of the first embodiment was superior to the reproduction characteristic using the conventional optical head using the conventional rotationally symmetric lens.

By controlling the shape of the opening 5 of the mask 4, the distance between the mask 4 and the surface 1a of the mold base material 1 or the surface 3 of the protective film 2, the etching conditions and the etching amount, a desired rotationally asymmetrical shape can be obtained. Can be formed. This makes it possible to obtain an optical element that produces a desired astigmatism.

In the first embodiment, argon ions were irradiated to etch the mold base material or the protective film on the surface of the mold base material. However, the same shape can be obtained by a dry etching method using other ions or radicals. Can be obtained. Further, when forming the protective film 2, the protective film 2 was formed on the surface 1a of the mold base material 1 and the surface 3 of the protective film 2 was etched before the etching treatment. The surface 1a of the base material 1 may be rotationally asymmetrically etched, and then the protective film 2 may be uniformly formed. Further, the surface 1a of the mold base material 1 or the surface 3 of the protective film 2 may be etched by scanning with an ion beam without using a mask.

(Second Embodiment) A second embodiment of the method for producing an optical element and the method for producing a mold suitable therefor according to the present invention will be described with reference to FIGS. 6 to 8. In the second embodiment, the manufacturing process of the optical element using the shape and the mold of the optical element to be manufactured is substantially the same as that of the first embodiment. However, the method of manufacturing a mold having a rotationally asymmetric aspherical surface is different.

As shown in FIG. 6, the entire surface of the mold base material 20 is covered with the resist film 22 except for the openings 23 and 24. The opening 23 is formed so as to face the surface 21 of the die base material 20. Openings 24 for forming marks
Are formed so as to face the edge portion 21 a of the surface 21. The mold base material 20 having the resist film 22 is immersed in the etching solution 25. Therefore, the surface 21 of the mold base material 20 is etched into a rotationally asymmetric shape. The mold base material 20 is made of chromium alloy stainless tool steel.

The surface 21 of the die base material 20 is roughly formed into a rotationally symmetric aspherical shape by a conventional method. At least the surface 21 of the die base material 20 is coated with an electroless nickel plating film (not shown). Furthermore, the mold base material 20
The nickel-plated film on the surface 21 is cut with a diamond tool using an ultra-precision lathe. Therefore, the nickel-plated film on the surface 21 on the mold base material 20 is, for example, as shown in FIG.
A rotationally symmetric aspherical surface is formed so as to exactly match the cross-sectional shape of the optical element 50 along the ridgeline 52 shown in FIG. As the etching solution 25, a 5-fold diluted solution of sulfuric acid was used.

For example, the radius of the surface 21 of the mold base material 20 is 2
The width of the flat edge portion 21a was 1 mm. Therefore, the total radius of the molding surface of the mold base material 20 including the edge portion was 3 mm. Mold base material 2 excluding openings 23 and 24
The entire surface of 0 is covered with the resist film 22 so as not to be etched by the etching solution 25.
The opening 23 is arranged along the axis Y shown in FIG. 7. The opening 23 had a width of 1 mm and a length of about 4 mm.
The opening 24 is provided on the axis X orthogonal to the axis Y. The diameter of the opening 24 was 0.6 mm.

The etching solution 25 has a diameter of about 200 mm.
It is filled with the glass container and kept at 40 ° C. The mold base material 20 covered with a resist film having a maximum diameter of 16 mm is 4
It was placed in a basket made of 0 resin and immersed in the etching solution 25 for 5 minutes. After that, the basket was taken out of the etching solution 25 and washed with pure water. As a result, the surface 21 of the mold base material 20
The upper nickel-plated film was rotationally asymmetrically etched.

The cross-sectional shape of the mold formed by the above method was measured in the X-axis and Y-axis directions shown in FIG. The measurement result is shown in FIG. In FIG. 8, the horizontal axis represents the distance from the center of the mold to the measurement point, and the vertical axis represents the amount of deviation between the rotationally symmetric shape before etching and the rotationally asymmetrical shape after etching at the measuring point, with the center of the mold being 0. It is a representation. As is clear from FIG. 8, the central portion of the nickel plating film on the surface 21 of the mold base material 20 in the Y-axis direction is not covered with the resist film 22 and is uniformly etched by the etching solution 25. The cross-sectional shape of the mold in the Y-axis direction has not changed from the rotationally symmetric shape before etching. On the other hand, the peripheral portion of the nickel-plated film on the surface 21 in the X-axis direction is covered with the resist film 22, and the central portion of the mold is etched more by the etching solution than the peripheral portion. In the sectional shape, the peripheral portion is relatively higher than the central portion by about 0.1 μm. Furthermore, FIG.
At a distance (radius) from -2 to -3 of
A recess is formed at a position opposed to. As a result, the shape of the mold surface becomes rotationally asymmetric, such as a toric surface. The radius of curvature of the mold in the X-axis direction is relatively smaller than the radius of curvature of the mold in the Y-axis direction.

When the shapes of 40 molds formed by the above method were measured, the shape error of the cross-sectional shape of the mold in the X-axis direction was -0.02 μm to +0.03 μm with respect to the average deviation amount of 0.1 μm. Within the range, and the variation was small.

In order to prevent scratches on the surface of the mold and fusion of the optical material during molding of the optical element, a protective film of platinum-tantalum (Pt-Ta) alloy is formed on the rotationally asymmetric surface of the mold by sputtering. A protective film having a thickness of 2 μm was formed.

Further, another mold having a rotationally symmetric aspherical surface is prepared. Similar to the first embodiment shown in FIG. 13,
Optical material 60 made of polycarbonate resin is used as molds 61 and 62.
Place between. One of the molds 61 and 62 has a rotationally asymmetric surface formed by the above etching method, and the other has a rotationally symmetrical surface formed by a conventional method. After heating the optical material 60 and the molds 61 and 62 to a predetermined temperature, the molds 61 and 62 were pressed at a predetermined pressure. afterwards,
The optical material 60 and the molds 61 and 62 were cooled. In this way, the optical element 50 was obtained.

By repeating such a press molding process, 1000 lenses were molded with the same mold. FIG.
As shown in FIG. 3, the optical element 50 manufactured by press molding using the above mold has the rotationally asymmetric optical function surface 51 such as a toric surface, so that the optical element 50 produces astigmatism. When the optical performances of the optical elements 50 were measured, each optical element 50 produced substantially the same amount of astigmatism in substantially the same direction. The average value of astigmatism was 25 mλ (mλ: 1/1000 of the wavelength of the light source used), which was an appropriate value for the objective lens of the optical head for the optical disk device. In addition, the wavefront aberration of the entire optical element 50 was good. An optical head was assembled using this optical element 50. As shown in FIGS. 7 and 8, the optical element was positioned by detecting a mark indicating a rotationally asymmetric direction. In the second embodiment, since it is not necessary to actually measure the astigmatism, when the optical element 50 is attached to the optical head, the optical element 50 can be easily attached in the direction having the optimum optical performance. it can. The reproduction characteristic of the optical disc by the optical head using the optical element 50 of the second embodiment was superior to the reproduction characteristic using the conventional optical head using the lens molded by the conventional rotationally symmetrical shape mold.

By controlling the shape of the opening 23 of the resist film 22, the etching conditions and the etching amount, a desired rotationally asymmetrical shape can be formed in the mold. This makes it possible to obtain an optical element that produces a desired astigmatism. Furthermore, the etching process is not limited to the example shown in FIG. Only a portion of the mold base material 20 including the surface 21 may be immersed in the etching solution. In this case, the resist film 22 may be provided only near the surface 21 of the die base material 20. The component of the etching solution 25 may be any as long as it can etch the material of the mold base material 20. In the second embodiment, sulfuric acid was used to etch the nickel plating film on the surface 21 of the mold base material 20, but any other material can be used as long as it can etch the mold base material or the protective film on the surface thereof. May be used. Further, in the second embodiment, the nickel plating film on the surface 21 of the mold base material 20 is etched, but the surface 21 of the mold base material 20 may be directly etched.

(Third Embodiment) A third embodiment of the method for manufacturing an optical element and the method for manufacturing a mold suitable for the same according to the present invention will be described with reference to FIGS. 9 to 11. In the third embodiment, the manufacturing process of the optical element using the optical element and the mold to be manufactured is substantially the same as that of the first embodiment. However, the manufacturing method of the mold having the rotationally asymmetric aspherical surface is different from that of the first embodiment. In the third embodiment, a sputtering method is used as a method of forming a rotationally asymmetric mold.

As shown in FIG. 9, the intermediate assembly 200
Includes a mold base material 30, a mask 33, and a mask jig 35. The mask 33 is arranged above the die base material 30 via a mask jig 35. The sputtered particles 36 are generated by the mask 3
The film 31 flies downward from above to form a film 31 on the surface of the mold base material 30. The mold base material 30 is made of cermet containing alumina as a main component.

Prior to the sputtering step, a rotationally symmetric aspherical surface is formed on the surface 30a of the die base material 30 by a conventional method. The mold base material 30 is rotated about an axis corresponding to the optical axis of an optical element such as a rotationally asymmetric aspherical lens to be molded. In the grinding wheel, the processing point where the wheel comes into contact with the die base material is in a predetermined direction of the optical element 50, for example, the ridge line 52 in FIG.
It is moved so as to draw a non-circular cross-sectional shape along.

As shown in FIG. 10, the shaded area is the mask 33.
This is a portion that shields the mold base material 30 by. For example,
The diameter of the surface 30a of the mold base material 30 was 6 mm, and the size of the rectangular opening 34 was 6 mm × 4 mm. Mask 33
The distance between and the surface 30a of the mold base material 30 was 5 mm.

Next, 14 intermediate assemblies 200 were arranged on a holder having a diameter of about 100 mm of the sputtering apparatus, and air inside the sputtering apparatus was evacuated to make a vacuum. Then, argon (Ar) gas was introduced into the sputtering device. The pressure of the argon gas was 0.13 Pa, and the discharge was generated with the RF power of 100 W. Pt-R
Sputtering was performed for 60 minutes with the target e. As a result, the film 31 having a non-uniform thickness was formed on the surface 30a of the die base material 30 so as to be rotationally asymmetric. In the third embodiment, the material of the film 31 is platinum-rhenium (Pt-R) formed by a sputtering method.
e) Alloy. The film 31 also functions as a protective film for preventing scratches and fusion of optical materials during molding. The thickness of the film 31 in the central part of the mold was 2 μm. Also,
The thickness of the film 31 at a position 2.5 mm away from the center of the mold in the X-axis direction was 1.87 μm. The displacement of the cross-sectional shape of the mold in the X-axis direction from the initial rotationally symmetrical shape was 0.13 μm. The shape error of the mold is 0.
It was ± 0.02 μm with respect to 13 μm.

The cross-sectional shape of the mold in the X-axis and Y-axis directions shown in FIG. 10 was measured. The measurement result is shown in FIG. 11, the horizontal axis represents the distance from the mold center to the measurement point, and the vertical axis represents the original rotationally symmetric shape formed on the surface 30a of the mold base material 30 at the measurement point and the surface 32 of the film 31. The amount of deviation is expressed with the center of the mold being 0. Figure 11
As is apparent from the above, since the central portion of the surface 30a of the die base material 30 in the Y-axis direction is not covered by the mask 33 and the film 31 is uniformly formed thereon, the cross section of the die in the Y-axis direction is formed. The shape has not changed from the initial shape of the surface 30a of the mold base material 30. On the other hand, the mold base material 3 in the X-axis direction
0 is covered by the mask 33 in the vicinity of the outer peripheral portion thereof, and the amount of particles adhering to the vicinity of the central portion of the surface 30a of the die base material 30 is larger than the amount of particles adhering to the peripheral portion thereof. The cross-sectional shape of is a shape that gently inclines outward from the center. As a result, the film 3 on the mold base material 30
The surface shape of the mold corresponding to the surface 32 of 1 is rotationally asymmetric such as a toric surface. The additional radius of curvature in the X-axis direction is larger than the radius of curvature in the Y-axis direction as a whole.

Further, another mold having a rotationally symmetric aspherical surface is prepared, and the mold 61 is formed as in the first embodiment shown in FIG.
Optical material 60 made of optical glass VC79 between 62 and 62
Was placed. One of the molds 61 and 62 has a rotationally asymmetric aspherical surface formed by the sputtering method, and the other has a rotationally symmetric aspherical surface formed by a conventional method.
The optical material 60 and the molds 61 and 62 were heated to a predetermined temperature, and the molds 61 and 62 were pressed at a predetermined pressure. Then, the optical material 60 and the molds 61 and 62 were cooled. In this way, the optical element 50 was obtained.

By repeating the press molding process as described above, 1000 optical elements were manufactured with the same mold. The optical element 50 molded by the above mold has the rotationally asymmetric optical function surface 51 such as a toric surface, so that the optical element 50 produces astigmatism. When the optical performance of the optical element 50 was measured, each optical element 50 produced substantially the same amount of astigmatism in substantially the same direction. The average value of astigmatism is 25 mλ (m
[lambda]: 1/1000 of the wavelength of the light source used, which was an appropriate value as an objective lens of an optical head for an optical disk device. In addition, the wavefront aberration of the entire optical element 50 was good. An optical head was assembled using this optical element 50. The optical element 50 is mounted so that the rotationally asymmetric aspherical surface cancels off-axis astigmatism in the radial direction of the magneto-optical disk. Optical element 50 of the third embodiment
The reproduction characteristics of the magneto-optical disk by the optical head using
It was superior to the reproduction characteristics of the conventional optical head using the conventional rotationally symmetric lens.

The shape of the opening 34 of the mask 33, the mask 33
A desired rotationally asymmetric shape can be formed in the mold by controlling the distance between the surface of the mold base material 30 and the surface 30a of the mold base material 30, the sputtering conditions, the amount of particles adhering to the surface 30a of the mold base material 30, and the like. This makes it possible to obtain an optical element that produces a desired astigmatism.

In the third embodiment, the sputtering method is used as the method for forming the film 31, but PVD (physica) is used.
l vapor deposition) method and CVD (chemical vapor depos
ition) method may be used. Further, the film 31 also serving as a protective film
However, the intermediate layer may be rotationally asymmetrical and the protective film may be uniformly formed on the intermediate layer.

In each of the first, second, and third embodiments, as shown in the plan views of FIGS. 2, 7, and 10,
The mold base materials 1, 20 and 30 are rotationally symmetric with respect to the entire mold, but the shape of the mold base material is not necessarily limited to the rotationally symmetric shape. For example, if the surface on which the optically functional surface is formed is rotationally symmetric, then the shape of other parts of the mold base material, such as the outer peripheral part of the molding surface, the neck of the mold, the collar, etc. May have a rotationally asymmetric shape such as a rectangular cross section.

Further, in each of the above embodiments, the shapes of the surfaces 1a, 3, 21 and 30a of the mold or the protective film are symmetrical with respect to the Y axis, but the present invention forms an axially asymmetric optical functional surface. Can be applied for. The configurations of the masks 4 and 33 and the mask jigs 7 and 35 are not limited to the above-described embodiments, and may be any as long as they can shield etching particles or film-forming particles.

[0065]

As described above, the method of manufacturing an optical element of the present invention comprises the steps of disposing the optical material between a pair of molds, the step of heating the optical material and the mold to a predetermined temperature, and the optical material. Pressing the mold to transfer the shape of the mold to the surface of the mold, wherein at least one surface of the mold is rotationally asymmetric. According to this method, since the rotationally asymmetric shape of the mold is transferred to the surface of the optical element, it becomes possible to mass-produce optical elements having the same optical performance.

The rotationally asymmetric shape of the mold is obtained by unevenly etching the rotationally symmetric surface of the mold base material or the protective film provided on the surface thereof, or on the rotationally symmetric surface of the mold base material. The non-uniform deposition of the film facilitates the manufacture of the mold without the use of special and expensive processing machines. Further, the mold base material having a rotationally symmetrical shape on the surface can be easily formed by a conventional cutting or grinding method. Further, since the etching rate or the film forming rate is stable in the etching process or the film forming process, the processing amount can be easily controlled. Therefore, the rotationally asymmetrical shape of the mold can be accurately formed without damaging the initial rotationally symmetric shape of the mold base material.

Further, a step of disposing the mask on the rotationally asymmetric shape of the mold on a rotationally symmetric surface of the mold base material or at a position apart from the surface of the rotationally symmetric surface upward, and rotational symmetry of the mold base material through the mask. Formed by dry etching treatment having a step of irradiating various surfaces with ions or radicals, or a step of forming a resist film on at least a rotationally symmetric surface of a mold base material etc. excluding a portion having a predetermined shape to be etched. By forming at least the rotationally symmetric surface of the die base material or the like by the wet etching process including the step of immersing it in the etching solution, the etching process technology conventionally used can be applied. As a result, a rotationally asymmetric mold can be relatively easily obtained without newly using a special device or technique.

Further, in the method of non-uniformly depositing a film on the rotationally symmetric surface of the die base material, the rotationally asymmetric shape of the die is separated from or above the rotationally symmetric surface of the die. A sputtering method, a PVD (physical vapor deposition) method, and C
It can be formed by any method selected from the VD (chemical vapor deposition) method, and the film forming technique which has been conventionally performed can be applied. In particular, it becomes possible to form a toric surface or a cylindrical surface on the surface of the mold, which was difficult to manufacture by the conventional method. Further, a large number of molds can be formed at the same time by etching treatment or film formation treatment. Therefore, the time required for forming one die can be shortened, and the cost per die can be reduced.

In the method of etching the surface of the die base material through a mask or forming a film on the surface of the die base material, the optically functional surface of the die base material may have a shape of the opening of the mask and / or the die base material. A desired shape can be formed by adjusting the position of the optical function surface with respect to the optical function surface. Furthermore, the film-forming method can be applied to the conventional process of forming a protective film or a release film on the optical function surface of a mold, and a rotationally asymmetric structure can be achieved without increasing the number of mold manufacturing processes. A mold can be formed.

Furthermore, since the rotationally asymmetric shape of the mold is configured to generate an astigmatic component in the axial wavefront aberration when the rotationally asymmetric shape is transferred to the optical element, the above method An optical element such as an aspherical lens having at least one rotationally asymmetrical optical functional surface manufactured by can produce an astigmatism component in the axial wavefront aberration. Therefore, it is possible to mass-produce optical elements that generate almost the same amount of astigmatism in substantially the same direction.

Further, by detecting the direction of astigmatism generated by the rotationally asymmetric optical function surface of the optical element and marking the (mounting) direction of the optical element, the mark is positioned at a predetermined position of the optical device. By doing so, the optical element can be easily mounted. Therefore, it is possible to omit adjusting the direction of the optical element with respect to the optical axis while monitoring astigmatism. Furthermore, if an uneven shape corresponding to the mark is formed on the edge part of the mold,
The mark can be formed on the edge portion of the optical element at the same time when the optical element is manufactured. Therefore, it is possible to omit the detection of the direction of the astigmatism generated by the rotationally asymmetric optical function surface.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method for forming a mold and an intermediate assembly used in a first embodiment of a method for manufacturing an optical element and a method for manufacturing a mold suitable for the optical element of the present invention.

FIG. 2 is a plan view of the intermediate assembly shown in FIG. 1 showing the shapes and relative positions of the mold base material and the mask in the first embodiment.

FIG. 3 is a perspective view showing the shape of the mold formed in the first embodiment.

FIG. 4 is a side sectional view showing an etching apparatus used in the first embodiment to form a mold.

FIG. 5 is a graph showing data corresponding to the cross-sectional shape of the mold after etching in the X and Y directions of the axes in FIGS. 2 and 3 in the first embodiment.

FIG. 6 is a side sectional view showing a method for forming a mold used in the second embodiment of the method for manufacturing an optical element and the method for manufacturing a mold suitable for the optical element of the present invention.

FIG. 7 is a plan view of an intermediate stage of the mold base material showing the shapes and relative positions of the mold base material and the mask in the second embodiment.

8 is a graph showing data corresponding to the cross-sectional shape of the mold after etching in the X and Y directions in FIG. 7 in the second embodiment.

FIG. 9 is a side sectional view showing a method for forming a mold and an intermediate assembly used in a third embodiment of the method for manufacturing an optical element of the present invention and the method for manufacturing a mold suitable for the same.

10 is a plan view of the intermediate assembly shown in FIG. 9 showing the shapes and relative positions of the mold base material and the mask in the third embodiment.

FIG. 11 shows axes X and Y of FIG. 10 in the third embodiment.
Showing the data corresponding to the cross-sectional shape of the mold after film deposition in the horizontal direction

FIG. 12 is a perspective view showing an optical element manufactured by the method of the present invention.

FIG. 13 is a side sectional view showing a press molding step of the method for manufacturing an optical element of the present invention.

[Explanation of symbols]

 1: Mold base material 1a: Mold base material surface 2: Protective film 3: Protective film surface 4: Mask 5: Rectangular opening 6: Ion beam 7: Mask jig 9: Etching chamber 10: Stage 11: Ion beam accelerating electrode 12 : Plasma 13: Ion gun 14: Introducing valve 20: Mold base material 21: Mold base material surface 22: Resist film 23: Opening 24: Opening 25: Etching solution 30: Mold base material 30a: Mold base material surface 31: Film 32 : Film surface 33: mask 34: rectangular opening 35: mask jig 36: sputtered particle 50: optical element 51: optical function surface 52: ridge line 53: ridge line 60: optical material 61: mold 62: mold 100: intermediate assembly Body 200: Intermediate assembly

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Shimizu 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (26)

[Claims] 1. An optical material is disposed between a pair of molds, the optical material and the mold are heated to a predetermined temperature, and the mold is pressed to change the shape of the optical functional surface of the mold to the optical material. A method for manufacturing an optical element that is transferred to the surface of
At least one optically functional surface of the mold is rotationally asymmetric, and the rotationally asymmetric shape is formed by unevenly etching a rotationally symmetric surface of a mold base material. 2. The rotationally asymmetric shape of the mold is formed by a dry etching method, and the dry etching method arranges a mask at a position in contact with a rotationally symmetric surface of the mold base material or at a position separated upward from a surface to be rotated. The method for manufacturing an optical element according to claim 1, wherein the rotationally symmetric surface of the die base material is irradiated with an ion beam or a radical beam in this state. 3. The rotationally asymmetric shape of the mold is formed by a wet etching method, and the wet etching method forms a resist film on at least the rotationally symmetric surface of the mold base material except for a portion having a predetermined shape to be etched. 2. The method for manufacturing an optical element according to claim 1, wherein at least the rotationally symmetrical surface of the die base material is immersed in an etching solution. 4. The method of manufacturing an optical element according to claim 1, wherein the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. 5. The method for manufacturing an optical element according to claim 1, wherein the rotationally asymmetrical shape is a shape that produces an astigmatism component of axial wavefront aberration when transferred to an optical element. . 6. The method of manufacturing an optical element according to claim 1, wherein a protective film is uniformly formed on the rotationally asymmetric surface of the mold. 7. An optical material is disposed between a pair of molds, the optical material and the mold are heated to a predetermined temperature, and the mold is pressed to change the shape of the optically functional surface of the mold to the optical material. A method for manufacturing an optical element that is transferred to the surface of
At least one optically functional surface of the mold is rotationally asymmetric, and the rotationally asymmetric shape is manufactured by nonuniformly etching a rotationally symmetric surface of a protective film formed on a mold base material. Method. 8. The rotationally asymmetric shape of the mold is formed by a dry etching method, and the dry etching method separates a mask from a position in contact with a rotationally symmetric surface of a protective film on the mold base material or upward from a surface to be rotated. The method of manufacturing an optical element according to claim 7, wherein the rotationally symmetric surface of the protective film is irradiated with an ion beam or a radical beam in a state where the optical film is arranged at a position. 9. The rotationally asymmetric shape of the mold is formed by a wet etching method, and the wet etching method removes a protective film formed on at least the surface of the mold base material except for a portion having a predetermined shape to be etched. The method for manufacturing an optical element according to claim 7, wherein a resist film is formed on the rotationally symmetric surface, and at least the rotationally symmetric surface of the die base material is immersed in an etching solution. 10. The method of manufacturing an optical element according to claim 7, wherein the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. 11. The method of manufacturing an optical element according to claim 7, wherein the rotationally asymmetrical shape is a shape that produces an astigmatism component of the axial wavefront aberration when transferred to the optical element. . 12. An optical material is disposed between a pair of molds, the optical material and the mold are heated to a predetermined temperature, and the mold is pressed to change the shape of the optically functional surface of the mold to the optical material. A method of manufacturing an optical element for transferring onto a surface of a mold, wherein at least one optically functional surface of the mold is rotationally asymmetric, and the rotationally asymmetric shape forms a film unevenly on a rotationally symmetrical surface of a mold base material. The manufacturing method of the optical element formed by this. 13. The rotationally asymmetric shape of the mold is formed by any method selected from a sputtering method, a PVD (physical vapor deposition) method and a CVD (chemical vapor deposition) method, and the method uses a mask as the mold. The optical element according to claim 12, wherein the optical element is manufactured by irradiating the rotational symmetry plane of the die base material with particles in a state of being arranged in a position in contact with the rotational symmetry plane of the base material or at a position separated upward from the rotational symmetry plane. Method. 14. The method of manufacturing an optical element according to claim 12, wherein the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. 15. The method for manufacturing an optical element according to claim 12, wherein the rotationally asymmetrical shape is a shape that produces an astigmatism component of axial wavefront aberration when transferred to an optical element. . 16. A mask is arranged at a position in contact with the rotationally symmetric surface of the die base material or at a position apart from the surface to be rotated upward, and the rotationally symmetric surface of the die base material is irradiated with an ion beam or a radical beam. A method for manufacturing a rotationally asymmetric mold for optical element molding, wherein a rotationally symmetric surface of a mold base material is nonuniformly etched. 17. A mold is formed by forming a resist film on at least a rotationally symmetric surface of a mold base material except a portion having a predetermined shape to be etched, and immersing at least the rotationally symmetric surface of the mold base material in an etching solution. A method for manufacturing a rotationally asymmetric mold for optical element molding, wherein a rotationally symmetric surface of a base material is nonuniformly etched. 18. A mask is disposed at a position in contact with the rotationally symmetric surface of the protective film formed on the mold base material or at a position separated upward from the surface to be rotated, and an ion beam or a radical is provided on the rotationally symmetric surface of the protective film. A method of manufacturing a rotationally asymmetric mold for optical element molding, wherein the rotationally symmetric surface of the protective film is nonuniformly etched by irradiating a beam. 19. A resist film is formed on at least a rotationally symmetric surface of a protective film formed on a mold base material except for a portion having a predetermined shape to be etched, and at least a rotationally symmetric surface of the protective film is etched. A method for producing a rotationally asymmetric mold for optical element molding, wherein the rotationally symmetric surface of the protective film is non-uniformly etched by immersing the protective film in a non-uniform manner. 20. The method for producing a rotationally asymmetric mold for optical element molding according to claim 16, wherein the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. 21. The optical element molding rotation according to claim 16, wherein the rotationally asymmetrical shape is a shape that produces an astigmatic component of axial wavefront aberration when transferred to an optical element. Asymmetrical manufacturing method. 22. A method for producing a rotationally asymmetric mold for optical element molding, wherein a film is formed nonuniformly on the rotationally symmetric surface of a mold base material. 23. The rotationally asymmetric shape of the mold is formed by any method selected from a sputtering method, a PVD (physical vapor deposition) method and a CVD (chemical vapor deposition) method, and the method uses a mask as the mold. 23. The optical element molding according to claim 22, which is performed by irradiating particles on the rotationally symmetric surface of the die base material in a state of being arranged in a position in contact with the rotationally symmetric surface of the base material or at a position separated upward from the rotational symmetric surface. A rotationally asymmetric manufacturing method. 24. The method for producing a rotationally asymmetric mold for optical element molding according to claim 22, wherein the rotationally asymmetric shape of the mold is a toric surface or a cylindrical surface. 25. The optical element molding rotation according to claim 22, wherein the rotationally asymmetrical shape is a shape that produces an astigmatic component of axial wavefront aberration when transferred to an optical element. Asymmetrical manufacturing method. 26. The method for producing a rotationally asymmetric mold for optical element molding according to claim 16 or 17, wherein a protective film is uniformly formed on the rotationally asymmetric surface of the mold.