JP2003177213A - Microlens, method for manufacturing the same and optical pickup device using microlens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized and lightweight microlens which can decrease the color aberration at a low cost suitable for mass production. <P>SOLUTION: When the microlens 1 is constituted by combining first to third microlens parts L1, L2, L3 all in a convex lens form so as to increase the NA, the third microlens part L3 is formed by using a material having the Abbe number different from that of the material for the first and second microlens parts L1, L2. Thereby, the color aberration can be decreased by selecting the Abbe numbers without varying the constitution of the microlens 1 or adding a new element. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a microlens,
The present invention relates to a manufacturing method thereof and an optical pickup device using a microlens.

[0002]

2. Description of the Related Art FIG. 6 shows an example of the structure of a conventional optical pickup for an optical disk device. In general, it is composed of a semiconductor laser (LD) 100 that emits linearly polarized laser light, a collimator lens 101, a polarization beam splitter 102, a quarter wave plate 103, an objective lens 104, a detection lens 105, and a photodiode 106. ing. Laser light emitted from the semiconductor laser 100 and having a polarization parallel to the paper surface is collimated by a collimator lens 101. Next, this collimated light is transmitted to the polarization beam splitter 102 and 1 /
The linearly polarized light is changed to circularly polarized light through an optical isolator constituted by the four-wave plate 103. When reflected on the recording surface of the optical recording medium 107, the turning direction of the circularly polarized light changes,
When it passes through the four-wave plate 103 again, it becomes polarized light perpendicular to the paper surface. Further, the polarization beam splitter 102
Is reflected by and travels toward the photodiode 106,
The photodiode 106 is focused by the detection lens 105.
Incident on. Actually, there are optical components and mechanisms such as focus error detection, track error detection, and servo control system based on the detection result, but they are omitted here. Further, in this illustrated example, in order to simplify the optical pickup device,
This is shown as a reproducing method when the optical recording medium 107 records information by the difference in reflectance.

In such a configuration, the spot size can be obtained only up to the wavelength of light due to the diffraction limit of light. The spot size w can be expressed as follows.

W ∝λ / sin θ ′ (1) where θ ′ is the exit angle of the objective lens 104 and NA (numerical aperture) of the objective lens 104 is NA. = Sin θ ′ λ is the wavelength of the laser light emitted from the LD 100.

Therefore, if the NA of the objective lens 104 is increased, the spot size becomes smaller, and by extension the optical recording medium 1
It is possible to increase the capacity of 07.

There is a limit to increasing NA with only a single lens, and a plurality of lenses are used. For example, a method of increasing the NA by using a two-group two-lens lens is known.

Further, in order to reduce the spot size,
The light source wavelength may be shortened, and specifically, a short wavelength LD of 440 nm or less is used. On the other hand, it is known that chromatic aberration becomes a problem due to such a shortened wavelength. "Chromatic aberration" is an aberration that occurs when a lens or optical system has to deal with multiple wavelengths or continuous wavelengths. Since the refractive index of the optical material varies depending on the wavelength, the focal length of the lens also varies. That is, the refractive index of the optical material has wavelength dispersion, and the refractive index for blue light is larger than that for red light. The wavelength of the laser light emitted from the LD has a wavelength width of approximately several nm. Also, the so-called "mode hopping" in which the laser light emitted from the LD suddenly fluctuates with a center wavelength of several nm due to temperature changes in the LD itself.
May cause.

Therefore, a short wavelength LD having a wavelength of 440 nm or less
When using, the chromatic aberration generated in the objective lens due to the wavelength shift becomes an unacceptable important problem. There are two possible causes for the large chromatic aberration at short wavelengths. The first reason is that when a general objective lens handles a short wavelength, the change in the refractive index becomes large with respect to a minute wavelength variation, and the defocus amount, which is the amount of movement of the focus, becomes large. The second cause is the higher density of the optical recording medium.
It is necessary to make the spot diameter focused by the objective lens as small as possible as the capacity increases, but the focal depth d of the objective lens
As is expressed by d = λ / (NA) ² , the shorter the wavelength handled, the smaller the depth of focus d, and even a slight defocus is not allowed.

In order to reduce the chromatic aberration of the objective lens, it is possible to manufacture the lens using an optical material having a small dispersion (the Abbe number indicating the degree of the chromatic aberration is large). Further, the objective lens can be an achromat lens composed of a plurality of lenses. When this is written as a formula, it becomes as follows. If the focal length of the _first lens is f ₁ , the Abbe number is ν ₁ , the focal length of the _second lens is f ₂ and the Abbe number is ν ₂ , and the two lenses are in contact with each other, then 1 / f = 1 / f ₁ + 1 / f ₂ …………………… (2) 0 = 1 / f ₁ ν ₁ + 1 / f ₂ ν ₂ ……………… (3) it can. When the equations (2) and (3) are solved, the focal lengths f ₁ and f ₂ are respectively f ₁ = (ν ₁ −ν ₂ ) / ν ₁ * f (4) f ₂ = (Ν ₁ −ν ₂ ) / ν ₂ * f ……………… (5). Therefore, as shown in FIG. 7, one of the two lenses is a convex lens 110 and the other is a concave lens 11.
It is 1. In this way, it is possible to achromatize with two lenses. However, there is a problem that an achromatic lens (achromatic lens) composed of a plurality of lenses is heavy.

There is also a method of separately adding an aberration correction optical system to correct chromatic aberration (see Japanese Patent Laid-Open No. 2000-19388). Although this uses a combination of a convex lens and a concave lens, a hologram, or the like, it is necessary to add new parts, and there is a problem in securing and adjusting the space.

On the other hand, a lens having a lens size smaller than several 100 μm is called a microlens, and in recent years, it has been CCD.
It is also used in LCD projectors. There is a movement to use such a microlens in an optical disk device. By using the microlens, the optical system can be downsized, and in addition, the microlens having a large NA has a small distance working distance between the bottom surface of the lens and the optical recording medium, thereby reducing the size of the optical pickup device. Because you can do it.

[0012]

However, the conventional achromatic lens as described above uses glass materials having different dispersions (different Abbe numbers) and is composed of a convex lens and a concave lens. Is required
There is a problem that the weight of the movable part of the optical pickup device increases because the two pieces are simply bonded.

In addition, in the structure in which the aberration correction optical system proposed by Japanese Patent Laid-Open No. 2000-19388 is separately added, it is necessary to add new parts, which complicates the adjustment process and increases the cost. There is.

Further, in the method using a hybrid lens having a diffracting action and a refracting action proposed in Japanese Patent Laid-Open No. 9-311271 and Japanese Patent Laid-Open No. 2000-285500, the diffraction grating requires a fine pitch, and the lens There is a problem that it is not easy to process.

There is also a proposal example of a single lens having a refractive index distribution as disclosed in Japanese Patent Laid-Open No. 2001-126296, but there is a problem that it is not easy to manufacture.

An object of the present invention is to provide a small and lightweight microlens capable of reducing chromatic aberration at low cost suitable for mass production, and a manufacturing method thereof.

An object of the present invention is to provide a microlens which can broaden the range of material selection and can relax manufacturing conditions, and a manufacturing method thereof.

It is an object of the present invention to provide a microlens capable of further reducing chromatic aberration and a manufacturing method thereof.

An object of the present invention is to provide a microlens capable of achieving a higher NA and a manufacturing method thereof.

It is an object of the present invention to provide a microlens which can be manufactured more easily and a manufacturing method thereof.

[0021]

According to another aspect of the present invention, there is provided a microlens having a first lens substrate having a first microlens portion formed in a convex lens shape, and a second microlens portion having a convex lens shape. A second lens substrate formed and attached to the first lens substrate so that the second microlens portion faces the first microlens portion, and these first and second lenses. A convex lens shape is formed on a side surface of the second lens substrate opposite to the second microlens portion side by a material having a different Abbe number from that of the substrate so as to be convex toward the second microlens portion side. And a third microlens portion.

Therefore, in constructing a microlens in which first to third microlens parts each having a convex lens shape are combined, the first and second microlens parts are made of materials having different Abbe numbers from each other. By forming the microlens part 3 in FIG. 3, a compact and lightweight microlens capable of reducing chromatic aberration by selecting the Abbe number without changing the structure of the microlens itself or adding a new element.

According to a second aspect of the present invention, in the microlens according to the first aspect, the first and second lens substrates and the third microlens portion are formed of a material having a different Abbe number from that of the material of the third microlens portion. The thin plate 4 is provided on the outer surface side of the third microlens portion.

Therefore, by providing the fourth thin plate having a different Abbe number, the range of material selection for the third microlens portion is widened, and the microlens is manufactured in which the manufacturing conditions are relaxed. Further, the fourth thin plate can also have a function as a protective layer against scratches and dust.

According to a third aspect of the present invention, in the microlens according to the first or second aspect, the refractive index of the material of the third microlens portion is larger than the refractive index of the second lens substrate.

Therefore, since the third microlens portion also acts as a convex lens, the microlens has a higher NA.

The invention according to claim 4 is the invention according to claims 1 to 3.
In the microlens according to any one of items 1 to 5, the material of the first lens substrate and the material of the second lens substrate are the same.

Therefore, since the materials of the first and second lens substrates are the same, these can be manufactured under the same manufacturing conditions, and the manufacturing can be facilitated and the cost can be reduced.

The invention according to claim 5 is the invention according to claims 1 to 4.
In the microlens according to any one of items 1 to 5, the Abbe number of the material of the third microlens portion is larger than the Abbe number of the materials of the first and second lens substrates.

Therefore, by increasing the Abbe number of the material of the third microlens portion having a particularly short focal length, the chromatic aberration can be suppressed more effectively.

According to a sixth aspect of the present invention, there is provided a method of manufacturing a microlens, wherein the first lens substrate and the second lens substrate are each formed at a position deeper than the substrate surface by using a photolithography process and an etching process. A step of forming the first microlens portion and the second microlens portion in the form of convex lenses, and a photolithography process and etching on the side of the second lens substrate opposite to the side of the second microlens portion. Process is used to form a concave portion so as to be convex toward the second microlens portion side, and a material having an Abbe number different from that of the material of the first and second lens substrates is embedded in the concave portion to form a convex lens shape. A step of forming a third microlens portion,
The second lens substrate on which the third microlens portion is formed has the second microlens portion formed on the first lens substrate.
Adhering to the first lens substrate so as to face the microlens portion.

Therefore, since the microlenses can be manufactured by using a so-called semiconductor process, minute microlenses can be manufactured easily and with high precision, mass production is possible, and cost reduction can be achieved.

According to a seventh aspect of the present invention, in the method of manufacturing a microlens according to the sixth aspect, after forming the third microlens portion, the first and second lens substrates and the third microlens substrate are formed. The method includes a step of bonding a fourth thin plate formed of a material having a different Abbe number from the material of the lens portion to the outer surface side of the third microlens portion.

Therefore, also with respect to the microlens having the fourth thin plate, the microlens can be manufactured by using a so-called semiconductor process. Therefore, minute microlenses can be manufactured easily and highly accurately, and mass production is also possible. The cost can be reduced.

The invention described in claim 8 is the method for manufacturing a microlens according to claim 6 or 7, wherein the third microlens portion is made of a material having a refractive index higher than that of the second lens substrate. Is formed by.

Therefore, since the third microlens portion also functions as a convex lens, a microlens having a higher NA can be manufactured.

The invention according to claim 9 is the invention according to claims 6 to 8.
In the method for manufacturing a microlens according to any one of
The material of the first lens substrate and the material of the second lens substrate are the same.

Therefore, since the materials of the first and second lens substrates are the same, these can be manufactured under the same manufacturing conditions, and the microlenses can be manufactured easily and at low cost.

According to a tenth aspect of the invention, in the method of manufacturing a microlens according to any one of the sixth to ninth aspects, the third microlens portion is made of a material of the first and second lens substrates. It is formed of a material having an Abbe number larger than the Abbe number.

Therefore, by increasing the Abbe's number of the material of the third microlens portion, it is possible to manufacture a microlens capable of suppressing chromatic aberration more effectively.

An optical pickup device according to an eleventh aspect of the present invention is an objective lens including the microlens according to any one of the first to fifth aspects, wherein the light emitted from the light source is focused on the recording surface of the optical recording medium. To prepare for.

Therefore, since the microlens according to any one of claims 1 to 5 is provided as an objective lens, it is possible to provide a compact and thin optical pickup device capable of reducing chromatic aberration.

According to a twelfth aspect of the present invention, in the optical pickup device according to the eleventh aspect, the light source has a wavelength of 400.
It is a laser light source that emits laser light of 410 nm.

Therefore, especially when a short wavelength laser light source for emitting a laser beam having a wavelength of 400 to 410 nm is used, the chromatic aberration caused in the objective lens due to the wavelength shift, which is an important problem, can be suppressed to a small value, and the influence of the chromatic aberration can be suppressed. It is possible to exert a laser light condensing irradiation function with less radiation.

According to a thirteenth aspect of the present invention, in the optical pickup device according to the eleventh or twelfth aspect, the third microlens portion formed in a hemispherical shape or a superhemispherical shape is provided on the optical recording medium. It is arranged so as to face each other.

Therefore, by using the objective lens having a higher NA, it is possible to form a smaller light spot on the optical recording medium and to improve the recording density.

[0047]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the present invention.
It will be described based on. Microlens 1 of this embodiment
Is a convex lens-shaped first, second, and third microlens portions L1, L2, L
It is a three-sided lens in which 3 is arranged on the same optical axis, and the outer shape is configured as a flat plate device. Such a lens structure itself is disclosed in, for example, Japanese Patent Laid-Open No. 2000-280366.
It has already been proposed in the publication.

More specifically, first, the first microlens portion L1 is formed on the one surface of the first lens substrate S1 at a position deeper than the substrate surface into an aspherical convex lens shape. The second microlens portion L2 is formed in a convex lens shape by an aspherical surface at a position deeper than the substrate surface on one side of the second lens substrate S2. Further, the third microlens portion L3
Is formed with a concave portion 2 on the side surface of the second lens substrate S2 opposite to the second microlens portion L2 side so as to be convex toward the second microlens portion L2 side. By embedding, it is formed into a convex lens shape. The third microlens portion L3 is formed including the third lens substrate S3 portion that covers the surface of the second lens substrate S2. In addition, the third microlens portion L
3 is a spherical surface in the illustrated example, but may be an aspherical surface. Further, the second lens substrate S2 on which the third microlens portion L3 is formed is attached to the first lens substrate S1 so that the second microlens portion L2 faces the first microlens portion L1. Is completed as a microlens 1. Reference numeral 3 is an aperture member that forms an aperture that restricts the incident width of light that is incident from the first microlens portion L1 side. An air layer 4 is formed between the first and second microlens portions L1 and L2.
It is said that.

By the way, in the example of Japanese Patent Laid-Open No. 2000-280366, no consideration is given to the reduction of chromatic aberration.
Therefore, if a material that takes into consideration chromatic aberration due to refractive index dispersion, which is a problem when using a blue light source with a short wavelength, is selected, the aberration becomes large, and there is a problem that the signal deteriorates when used for an optical disc. is there.

With this basic structure, in the present embodiment, the Abbe numbers of the materials of the first and second lens substrates S1 and S2 are made different from the Abbe numbers of the material of the third microlens portion L3, And the third microlens portion L3
The Abbe number of the material of the first and second lens substrates S1,
It is configured to be larger than the Abbe number of the material of S2. Thereby, chromatic aberration can be reduced.

Consider this point. Since the microlens 1 of this embodiment is composed of three lens surfaces, the expressions (2) and (3) described above are respectively expressed by (6).
It can be rewritten as in equation (7).

1 / f = 1 / f ₁ + 1 / f ₂ + 1 / f ₃ (6) 0 = 1 / f ₁ ν ₁ + 1 / f ₂ ν ₂ + 1 / f ₃ ν ₃ ……………… (7) Focusing on equation (7), since the Abbe number ν is positive in order for this equation to hold, each microlens portion L1,
It is required that _one of the focal lengths f ₁ , f ₂ , and f ₃ of L2 and L3 be negative. However, in the configuration of the present embodiment, since a high NA is achieved with all convex lens configurations, a concave lens cannot be used. Therefore,
For the expression (7) to hold, each term on the right side should be 0. That is, the product of the focal length f and the Abbe number ν should be large. However, since it is a microlens, the focal length f
Is small and it is difficult to approximate the reciprocal of the product with the Abbe number ν to 0. However, for example, when the wavelength range of chromatic aberration is set to an extremely small range, the effective Abbe number ν shows a large value. For example, the wavelength range 400 of the material BK7
The effective Abbe number ν of 410 nm is a value exceeding 400. Therefore, even if the focal length f is in the order of sub-mm, the reciprocal of the product of the focal length f and the effective Abbe number ν can be sufficiently approximated to zero. In other words, it can be said that the larger the Abbe number ν, the greater the effect. In this way, chromatic aberration can be reduced.

Further, it will be verified by a concrete configuration example.

[Specific Example 1] The glass materials used in Specific Example 1 are as follows. Lens part L1 (substrate S1): BK7 (1.5168, 64.17) Lens part L2 (substrate S2): Synthetic quartz (1.45847, 67.
7) Lens part L3 (substrate S3): SK16 (1.62041, 60.3)
3) The numbers in parentheses after the material name indicate the refractive index nd and the Abbe number νd of the glass material (the same applies hereafter).

The rms wavefront aberration on the optical axis of the microlens 1 made of such a material is 0.0003λ.
(400 nm), 0.0001λ (407 nm), 0.
It was 0002λ (414 nm). It is preferable that the wavefront aberration is small, but it is generally said that the wavefront aberration of 0.07λ or less is sufficient (the same applies to the following).

[Specific Example 2] The glass materials used in Specific Example 2 are as follows. Lens part L1 (substrate S1): LF7 (1.57501, 41.49) Lens part L2 (substrate S2): K10 (1.50137, 56.41) Lens part L3 (substrate S3): SK16 (1.62041, 60.3)
3)

The rms wavefront aberration on the optical axis of the microlens 1 made of such a material is 0.0013λ.
(400 nm), 0.0003λ (407 nm), 0.
It was 0013λ (414 nm).

[Specific Example 3] The glass materials used in Specific Example 3 are as follows. Lens portion L1 (substrate S1): synthetic quartz (1.45847, 67.
7) Lens part L2 (substrate S2): synthetic quartz (1.45847, 67.
7) Lens part L3 (substrate S3): SK16 (1.62041, 60.3)
3)

The rms wavefront aberration on the optical axis of the microlens 1 made of such a material is 0.0012λ.
(400 nm), 0.0002λ (407 nm), 0.
It was 0012λ (414 nm).

Therefore, according to the present embodiment, the first to third microlens portions L1 each having a convex lens shape.
In forming the microlens 1 in which L2 and L3 are combined, the third microlens portion L3 is formed by using a material having an Abbe number different from those of the first and second microlens portions L1 and L2. A compact and lightweight microlens capable of reducing chromatic aberration without changing the configuration of the microlens 1 itself or adding a new element. In particular, regarding the specific example, although the specific example 1 has the best performance, the specific example 3 is preferable because it is preferable to process the same material in manufacturing in terms of cost.

A second embodiment of the present invention will be described with reference to FIG. The same parts as those shown in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted (the same applies to the following embodiments). The microlens 11 of the present embodiment is configured by providing the fourth thin plate S4 on the outer surface side of the third microlens portion L3 (third lens substrate S3) in the configuration of the microlens 1 described above. .

Here, the fourth thin plate S4 is formed in a planar shape from the material of the first and second lens substrates S1 and S2 and the third microlens portion L3 and the material of which Abbe number ν is different. .

The effect of the present embodiment will be demonstrated by a concrete configuration example.

[Specific Example 4] The glass materials used in Specific Example 4 are as follows. Lens part L1 (substrate S1): BK7 (1.5168, 64.17) Lens part L2 (substrate S2): Synthetic quartz (1.45847, 67.
7) Lens part L3 (substrate S3): SK16 (1.62041, 60.3)
3) Fourth thin plate S4: SF55 (1.76180,26.9
Five)

The rms wavefront aberration on the optical axis of the microlens 11 made of such a material is 0.0006λ.
(400 nm), 0.0001λ (407 nm), 0.
It was 0006λ (414 nm).

[Specific Example 5] The glass materials used in Specific Example 5 are as follows. Lens part L1 (substrate S1): LF7 (1.57501, 41.49) Lens part L2 (substrate S2): K10 (1.50137, 56.41) Lens part L3 (substrate S3): SK16 (1.62041, 60.3)
3) Fourth thin plate S4: SF55 (1.76180,26.9
Five)

The rms wavefront aberration on the optical axis of the microlens 11 made of such a material is 0.0008λ.
(400 nm), 0.0003λ (407 nm), 0.
It was 0006λ (414 nm).

[Specific Example 6] The glass materials used in Specific Example 6 are as follows. Lens portion L1 (substrate S1): synthetic quartz (1.45847, 67.
7) Lens part L2 (substrate S2): synthetic quartz (1.45847, 67.
7) Lens part L3 (substrate S3): SK16 (1.62041, 60.3)
3) Fourth thin plate S4: SF55 (1.76180,26.9
Five)

The rms wavefront aberration on the optical axis of the microlens 11 made of such a material is 0.0008λ.
(400 nm), 0.0003λ (407 nm), 0.
It was 0009λ (414 nm).

Therefore, according to the present embodiment, by forming the microlens 11 by providing the fourth thin plate S4 having a different Abbe number, the material selection range of the third microlens portion L3 is widened. The microlens 11 has the manufacturing conditions relaxed. Further, the fourth thin plate S4 can also have a function as a protective layer against scratches and dust.

A third embodiment of the present invention will be described with reference to FIGS.
It will be described based on. The present embodiment relates to a method for manufacturing the microlens 11, for example.

First, the first microlens portion L1 and the second microlens portion L2 are formed on each of the first lens substrate S1 and the second lens substrate S2. Therefore, as shown in FIG. 3A, the substrate 21 (S1, S2)
A photosensitive material 22 (resist) is applied on top. The film thickness of the photosensitive material 22 to be applied is about several μm to several tens μm depending on the height (sag) of the lens portion to be formed. In practice, the thickness of the photosensitive material 22 to be applied is set by the height of the lens formed on the substrate 21 and the ratio (selection ratio) between the etching rate of the material of the substrate 21 and the etching rate of the photosensitive material 22. For example, when the etching rates of the two are equal (selection ratio 1), the height of the photosensitive material 22 is made substantially equal to the height of the lens to be formed. In addition, the etching rate of the material of the substrate 21 is 2 times faster than that of the photosensitive material 22.
When the size is twice as large (selection ratio 2), the height of the photosensitive material 22 may be 1/2 of the lens height. Here, it is assumed that the etching rates of the two are equal. Further, as the photosensitive material 22 applied on the substrate 21, a photoresist or a photosensitive dry film used in usual semiconductor manufacturing can be used. The shape of the photomask used in the step of transferring the shape to the resist (photolithography step) is changed by selecting the positive type or the negative type, but the basic forming procedure is not changed. In this embodiment mode, a case of using a positive resist is described.

Next, as shown in FIG. 3B, patterning is performed by a photolithography process so that the photosensitive material 22 has the same shape as the lens. The patterning is performed by irradiating light through a mask having a transmittance distribution set to expose the photosensitive material 22 to light. When developed after irradiation with light, a resin having the same shape as the lens (since the selection ratio is 1) remains on the substrate 21. As the mask at this time, a mask having a transmittance distribution matched to the lens shape is prepared. As this mask, a mask having a density distribution may be used, or a mask having a layout in which fine dots have a desired transmittance distribution may be used. Further, in the illustrated example, the bonding structure 24 when the substrate S1 and the substrate S2 are butted and bonded to each other later is also patterned in advance.

Using the photosensitive material 22 having the lens shape 23 thus formed as a mask, the substrate 21 is etched (anisotropic etching) in a direction perpendicular to the substrate surface as shown in FIG. 3C. As the etching means, dry etching which is usually used in a semiconductor process can be used. Specifically, reactive ion etching (RIE),
The electron cyclotron resonance etching method (ECR) and the like. The gas used for dry etching can be selected depending on the substrate material. For example, when the substrate material is glass, CF ₄ , CH
F ₃ or the like can be used. Also, the etching rate,
N ₂ , O ₂ , and A are used as etching gas for adjusting selectivity.
A gas such as r can also be mixed.

In this way, the lens shape 2 is formed on the substrate 21.
5 (microlens portions L1 and L2) and a joint structure 26 used when abutting and adhering are formed. After that, the unnecessary photosensitive material (resist) 22 is removed (ashing) (see FIG. 3D). This results in the substrate 21
The lens shape 25 (microlens portions L1 and L2) is formed at a position deeper than the surface (surface of the bonding structure 26).

The first microlens portion L1 and the second microlens portion L2 are manufactured by exactly the same process. However, when the materials of the substrates S1 and S2 are different,
Since the etching rates are fundamentally different, it is necessary to find a manufacturing condition in which the same selection ratio can be selected by changing the etching conditions such as the etching gas so as to have a shape that matches the selection ratio during patterning.

Next, the third microlens portion L3 is formed. The third microlens portion L3 is formed on the opposite surface side of the second lens substrate S2 on which the second microlens portion L2 is formed. For this reason, first, as shown in FIG. 4A, the photosensitive material 31 is applied to the opposite surface of the substrate S2. The film thickness of the photosensitive material 31 to be applied is about several μm to several tens of μm depending on the height (sag) of the lens. The film thickness of the photosensitive material 31 is the same as that when the lens portions L1 and L2 are formed, and actually, the ratio of the lens height to be formed, the etching rate of the substrate material and the etching rate of the photosensitive material (selection Ratio). The photosensitive material 31 applied on the substrate L2 is the same as in the above case.

Then, as shown in FIG. 4B, patterning is performed by a photolithography process so that the shape of the photosensitive material 31 is the same as the lens shape. In patterning, light is irradiated through a mask having a transmittance distribution set to expose the photosensitive material 31. When the development is performed after the light irradiation, the resin having the same shape as the lens (since the selection ratio is 1) remains on the substrate S2. As the mask at this time, a mask having a transmittance distribution matched to the lens shape is prepared. As this mask, a mask having a density distribution may be used, or a mask having a layout in which fine dots have a desired transmittance distribution may be used.

The photosensitive material 31 having the lens shape 32 formed in this manner is etched (anisotropic etching) in the direction perpendicular to the substrate S2 as in the case of manufacturing the lens portions L1 and L2 (see FIG. 4 ( c)), and thereafter, unnecessary photosensitive material (resist) is removed (ashing) (FIG. 4).
(D)).

Next, as shown in FIG. 4E, a high refractive index material 33 is embedded in the concave portion 32 that is etched to form the third microlens portion L3. As the high refractive index material 33, the first and second lens substrates S1,
A material having an Abbe number different from that of S2 is used. At this time, the flat plate 34 (fourth thin plate S4) is attached after the high refractive index material 33 is embedded. When glass is used as the high-refractive index material 33, it is embedded by a sputtering method, and then flattened as a substrate S3, and a flat plate 34 is attached. When a resin material is used as the high-refractive index material 33, the flat plate 34 is made flat on the upper side before the resin is applied and the hardening treatment is performed, and then the hardening treatment is performed. When a resin is used as the high refractive index material 33, the fourth thin plate S4 can act as a protective layer for the resin material of the third microlens portion L3. Further, the resin material has a function as an adhesive. Both materials may be polished to obtain the exact thickness of the substrate. Thus
The second having the second and third microlens portions L2 and L3
The lens substrate S2 can be formed.

Finally, as shown in FIG. 4F, the first substrate S1 on which the first microlens portion L1 is formed and the first substrate S1 on which the second and third microlens portions L2 and L3 are formed. The second lens substrate S2 is affixed to the first and second microlens portions L1 and L2 so that the bonding structure 26 is butted. The bonding is performed using an adhesive. Adhesives include those that are cured by ultraviolet rays, those that are cured by heat, those that are cured by mixing two liquids, water glass bonding, etc., and the optimum adhesive is selected. At the time of bonding, alignment marks can be formed in advance on each of the substrates S1 and S2, and the alignment marks can be aligned to perform highly accurate alignment.

In this way, the microlens 11 is manufactured. At this time, it is possible to manufacture many microlenses 11 at one time by a wafer process, instead of manufacturing each one individually. At this time, the two substrates S1 and S2 are bonded to each other with high accuracy by using an alignment mark. If two wafer substrates are aligned, each optical element is aligned with the same accuracy, and the productivity is greatly improved. The individual microlenses 11 are cut out by dicing.

In the case of manufacturing the microlens 1, the step relating to the flat plate 34 (fourth thin plate S4) may be omitted.

According to this embodiment, since the microlens 11 can be manufactured by using a so-called semiconductor process,
The microlenses 11 can be easily and highly accurately manufactured, mass production is possible, and cost reduction can be achieved.

A fourth embodiment of the present invention will be described with reference to FIG. The present embodiment shows an application example to the optical pickup device 42 using the microlens 1 or 11 as the objective lens 41 as described above.

First, a configuration example of the optical pickup device 42 of the present embodiment will be described. In this optical pickup device 42, a semiconductor laser (LD) 44 as a light source and a photodiode (P) for detecting light reception are provided on a support base 43.
D) 45 and are mounted. Support base 43 is LD4
It is made of a material having good thermal conductivity so as to absorb the heat generated by Although not particularly shown, the support base 43 has a structure that does not twist during access to the optical recording medium 46. Furthermore, LD44
Is not provided on the submount in the example shown,
It may be placed on the submount depending on the thermal conductivity and arrangement. As the LD 44, for example, a laser diode having a short wavelength of emitted laser light of about 400 to 410 nm (for example, blue LD) is used.

The LD 44 is mounted so as to emit laser light in a direction parallel to the support base 43.
The reflection mirror 47 deflects (bends) the laser light toward the optical recording medium 46 side by 90 ° at a position facing 4
And a collimator 48 for converting the deflected and reflected laser light into parallel light. The reflection mirror 47 is 45 °
It is formed by performing Al reflection coating on the inclined surface of the LD 44 side having an angle of, and the collimator 48 is a microlens having an effective diameter of the exit side lens of 200 μm. Both the reflection mirror 47 and the collimator 48 are made of the same material (glass) and are integrally formed, and are attached so as to be embedded in the support base 43 by utilizing the collimator 48 portion. The term "integral" as used herein means an item that is produced separately and then integrated into a unit by bonding or the like. In the present embodiment, glass materials are used for all of them, but different materials may be used, for example, Si material is used for the reflection mirror 47 and glass is used for the collimator 48. At this time, the collimator 48 is configured to reduce chromatic aberration if chromatic aberration is a problem.

Further, an optical path separating means 49 is provided on the optical path on the emission side of the collimator 48 (on the side of the optical recording medium 46). The optical path separating means 49 has a function of transmitting the laser light as it is when it goes to the optical recording medium 46, and dividing the reflected light (signal light) from the optical recording medium 46 so as to go to the position where the PD 45 is located. is there. In this embodiment, polarized light is used, and the optical path separating means 49 is composed of a polarization hologram and a λ / 4 plate. A polarization hologram is one in which a material having birefringence is embedded in a grating groove and an optical path is separated according to the relationship between the direction of the grating groove and the polarization direction of light. At the same time, it is possible to give a light-collecting function by optimizing the grating pattern at the same time. In this embodiment, the polarization hologram has a light-collecting function. By using the hologram for the condensing lens unit, even if the condensing position changes due to the influence of the wavelength shift of the LD 44, the signal detection is not greatly affected. Further, the λ / 4 plate is a thin film or a sheet type in order to make the optical system small and thin.

Further, the optical path separating means 49 and the optical recording medium 4
An objective lens 41 is provided on the optical path between the objective lens 4 and 6. The objective lens 41 uses the microlens 1 or 11 having a flat outer shape as described above.
The microlens portion L3 of is set to be on the optical recording medium 46 side. In addition, the third microlens portion L3
With regard to (1), it is desirable to form a so-called solid immersion lens in the shape of a hemisphere or a super hemisphere.

The objective lens 41 is integrated with the optical path separating means 49 and is attached to the support base 43 via the focus / tracking control means 50 adhered to the optical path separating means 49. The focus / tracking control means 50 is a means for moving along the optical axis, a means for moving in a direction perpendicular to a track groove previously formed on the optical recording medium 46, and a signal from the PD 45 (focus error signal, track error signal). Is processed to calculate the amount of movement of each moving means. There are various methods for this signal processing. Here, the double beam size method is used for focus detection and the push-pull method is used for tracking detection. The movement amount is calculated by an electronic circuit. The moving means may be a piezoelectric element such as a laminated piezo, an electromagnetic induction type actuator, or an ultrasonic actuator. Further, the electrostatic actuator manufactured by using the semiconductor process is suitable for small size and thin shape, and can be manufactured by a process similar to the microlens manufacturing process as in the above-described embodiment. Although an actuator using a piezoelectric element is used in this embodiment, it may be appropriately selected in consideration of the movement amount, frequency response, size, and the like.

The operation of such an optical pickup device 42 will be described. First, the laser light emitted from the LD 44 is bent by the reflection mirror 47 and advances toward the optical recording medium 46. Next, the collimator 48 converts the divergent light into collimated light. At this time, since the profile of the laser light from the LD 44 is an ellipse due to the astigmatic difference, in the present embodiment, the light is collimated according to the minor axis of the ellipse and the light in the major axis direction is cut. The collimated light enters the optical path separation means 49, passes through the polarization hologram, and then the linearly polarized light is changed to circularly polarized light by the λ / 4 plate. After that, the light enters the objective lens 41 and converges to become light, and the optical recording medium 4
6 is irradiated. Here, in the case of recording, an appropriate modulation according to the signal is given to the LD 44 and irradiated onto the optical recording medium 46, and in the case of reproduction, the LD 44 is irradiated without being modulated. In the case of reproduction, the signal light from the optical recording medium 46 becomes divergent light as opposed to the time of irradiation and travels toward the upper side of the drawing. The light is collimated by the objective lens 41 and passes through the λ / 4 plate. Here, the circularly polarized light becomes linearly polarized light, but since the polarization direction is changed by 90 ° from the forward direction, when this light enters the polarization hologram, it becomes diffracted and condensed light and enters the PD 45. Here, the information is read by being converted into an electric signal and subjected to signal processing.

Therefore, according to the present embodiment, since the microlens 1 or 11 as described above is basically provided as the objective lens 41, a compact and thin optical pickup device 42 capable of reducing chromatic aberration is provided. be able to. Particularly, when the short-wavelength LD 44 that emits a laser beam having a wavelength of 400 to 410 nm is used, the chromatic aberration generated in the objective lens 41 due to the wavelength shift, which is an important problem, can be suppressed to a small level, and the laser beam is less affected by the chromatic aberration. The concentrated irradiation function can be exerted. Further, the third microlens portion L3 is formed into a hemispherical shape or a super hemispherical shape as a so-called solid immersion lens, and is opposed to the optical recording medium 46, so that the objective having a higher NA can be achieved. Since it becomes the lens 41, a smaller light spot can be formed on the optical recording medium 46, and the recording density can be improved.

[0093]

According to the first aspect of the present invention, in constructing a microlens including a combination of first to third microlens portions each having a convex lens shape, the first and second microlens portions are combined. Is a compact and lightweight micro-lens that can reduce chromatic aberration by forming the third microlens part using materials with different Abbe numbers without changing the structure of the microlens itself or adding new elements. A lens can be provided.

According to the invention described in claim 2, in the microlens according to claim 1, by providing a fourth thin plate having a different Abbe number, the range of material selection for the third microlens portion is widened, It becomes a microlens with ease of manufacturing conditions. Further, the fourth thin plate can also have a function as a protective layer against scratches and dust.

According to the third aspect of the invention, in the microlens according to the first or second aspect, the third microlens portion also functions as a convex lens, so that a higher NA is obtained.
It is possible to provide a microlens having

According to the fourth aspect of the invention, in the microlens according to any one of the first to third aspects, the materials of the first and second lens substrates are the same, so that these manufacturing conditions are the same. Therefore, it is possible to facilitate manufacturing and reduce cost.

According to the invention of claim 5, in the microlens according to any one of claims 1 to 4, by increasing the Abbe number of the material of the third microlens portion having a particularly short focal length, Chromatic aberration can be suppressed more effectively.

According to the method of manufacturing a microlens of the sixth aspect of the present invention, since the microlens can be manufactured by using a so-called semiconductor process, minute microlenses can be manufactured easily and highly accurately, and mass production is also possible. Therefore, the cost can be reduced.

According to the invention of claim 7, in the method of manufacturing a microlens according to claim 6, since the microlens having the fourth thin plate can be manufactured by using a so-called semiconductor process, Microlenses can be easily and highly accurately manufactured, mass production is possible, and cost reduction can be achieved.

According to the eighth aspect of the present invention, in the method for producing a microlens according to the sixth or seventh aspect, the third microlens portion also acts as a convex lens, so that a microlens having a higher NA is produced. be able to.

According to the ninth aspect of the invention, in the method of manufacturing a microlens according to any one of the sixth to eighth aspects, the materials of the first and second lens substrates are the same. The conditions can be the same, and the microlens manufacturing can be facilitated and the cost can be reduced.

According to the invention of claim 10, claim 6 is provided.
In the method for manufacturing a microlens according to any one of 1 to 9, by increasing the Abbe number of the material of the third microlens portion, it is possible to manufacture a microlens capable of suppressing chromatic aberration more effectively. it can.

According to the optical pickup device of the eleventh aspect of the present invention, since the microlens of any one of the first to fifth aspects is provided as an objective lens, a compact and thin optical pickup device capable of reducing chromatic aberration. Can be provided.

According to the invention of claim 12, claim 1
In the optical pickup device described in 1, the wavelength of 400
When a short wavelength laser light source that emits laser light of up to 410 nm is used, the chromatic aberration caused by the objective lens due to the wavelength shift, which is an important problem, can be suppressed to a small level, and the laser light focusing irradiation function is less affected by the chromatic aberration. Can be demonstrated.

According to the invention of claim 13, claim 1
In the optical pickup device described in 1 or 12, by using an objective lens with a higher NA, a smaller light spot can be formed on the optical recording medium, and the recording density is improved. You can also

[Brief description of drawings]

FIG. 1 is a sectional structural view showing a microlens according to a first embodiment of the present invention.

FIG. 2 is a sectional structural view showing a microlens according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional structure diagram showing, in the order of processes, steps of forming first and second microlens portions according to a third embodiment of the present invention.

FIG. 4 is a cross-sectional structural view showing a step of forming a third microlens portion and a bonding step in the order of processes.

FIG. 5 is a sectional structural view showing an optical pickup device of a fourth embodiment of the present invention.

FIG. 6 is a principle structural diagram showing a configuration example of a conventional general optical pickup device.

FIG. 7 is a cross-sectional structural view showing a structural example of an achromatic lens.

[Explanation of symbols]

1,11 micro lens 41 Objective lens 42 Optical pickup device 44 light source, semiconductor laser 46 optical recording medium L1 First microlens part L2 Second microlens part L3 Third microlens part S1 First lens substrate S2 Second lens substrate S4 Fourth thin plate

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) G11B 7/135 G11B 7/135 A 5D789 (72) Inventor Yoshiyuki Kiyozawa 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Company (72) Inventor Yasuhiro Sato 1-3-6 Nakamagome, Ota-ku, Tokyo F-Term Within Ricoh Company (Reference) 2H025 AB14 FA39 2H087 KA13 LA01 PA02 PA18 PB03 QA01 QA05 QA13 QA21 QA25 QA33 QA41 QA45 UA03 2H096 AA28 HA17 HA23 HA30 4G059 AA11 AB09 AC01 BB01 BB13 5D119 AA01 AA11 AA22 AA38 AA40 BA01 BB01 DA05 EC03 JA44 JB01 JB03 JB04 NA05 5D789 AA01 AA11 AA22 AA38 AA40 BA01 BB01 CA21 CA21 CA21 CA02 CA02 CA02 CA02 CA01 CA22 CA01 CA22 CA02 CA02 CA02 CA02 CA02 CA02 CA23

Claims (13)

[Claims] 1. A first lens substrate in which a first microlens portion is formed into a convex lens shape, and a second microlens portion is formed into a convex lens shape, and the second microlens portion is formed into the first lens substrate. A second lens substrate bonded to the first lens substrate so as to face the microlens portion, and the second lens made of a material having a different Abbe number from those of the first and second lens substrates. A microlens comprising: a third microlens portion formed in a convex lens shape on the side surface of the substrate opposite to the second microlens portion side so as to be convex toward the second microlens portion side. 2. A fourth thin plate formed of a material having a different Abbe number from the materials of the first and second lens substrates and the third microlens portion is provided on the outer surface side of the third microlens portion. The microlens according to claim 1. 3. The microlens according to claim 1, wherein the refractive index of the material of the third microlens portion is higher than the refractive index of the second lens substrate. 4. The material of the first lens substrate and the second lens substrate
The microlens according to any one of claims 1 to 3, wherein the lens substrate is made of the same material. 5. The microlens according to claim 1, wherein the Abbe number of the material of the third microlens portion is larger than the Abbe number of the materials of the first and second lens substrates. 6. A first microlens portion and a second microlens portion at a position deeper than the substrate surface by using a photolithography process and an etching process for each of the first lens substrate and the second lens substrate. Respectively in the form of a convex lens, and using a photolithography process and an etching process on the side of the second lens substrate opposite to the side of the second microlens portion, the second microlens portion Forming a concave portion so as to be convex toward the side and burying a material having a different Abbe number from the material of the first and second lens substrates in the concave portion to form a convex lens-like third microlens portion; The second lens substrate on which the third microlens portion is formed has the second microlens portion formed on the first lens substrate.
A step of adhering to the first lens substrate so as to face the microlens portion of the above. 7. A fourth thin plate formed of a material having a different Abbe number from the materials of the first and second lens substrates and the third microlens portion after forming the third microlens portion. 7. The method for manufacturing a microlens according to claim 6, further comprising a step of adhering the above to the outer surface side of the third microlens portion. 8. The method of manufacturing a microlens according to claim 6, wherein the third microlens portion is formed of a material having a refractive index higher than that of the second lens substrate. 9. The material of the first lens substrate and the second lens substrate
9. The method of manufacturing a microlens according to claim 6, wherein the lens substrate is made of the same material. 10. The third microlens portion is formed of a material having an Abbe number that is larger than the Abbe numbers of the materials of the first and second lens substrates.
7. The method for manufacturing a microlens according to any one of 1. 11. An optical pickup device comprising the microlens according to claim 1 as an objective lens for condensing light emitted from a light source onto a recording surface of an optical recording medium. 12. The optical pickup device according to claim 11, wherein the light source is a laser light source that emits laser light having a wavelength of 400 to 410 nm. 13. The microlens is arranged such that a third microlens portion formed in a hemispherical shape or a super hemispherical shape faces the optical recording medium.
2. The optical pickup device described in 2.