JP2002269794A - Objective lens for optical pickup, and optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic-molded objective lens for an optical pickup, that is high in precision, high in performance and easily manufacturability at low cost, and also to provide an optical pickup using the objective lens. SOLUTION: The objective lens for the optical pickup is composed of at least two or more plastic-molded lenses. A first abutment part 11 is provided on the periphery from the optical function part of a first lens, while a second abutment part 21 is provided on the periphery from the optical function part of a second lens that is placed opposite from the first lens 1. The first abutment part 11 of the first lens 1 and the second abutment part 21 of the second lens 2 are abutted on each other to form the objective lens 10 in the manufacturing and assembling. This objective lens is then assembled into an optical pickup.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup objective lens used for an optical pickup for recording or reproducing information on or from an optical information recording medium such as an optical disk, and an optical pickup objective lens using the objective lens. Related to optical pickup.

[0002]

2. Description of the Related Art Conventionally, a plastic molded single lens has been mainly used as an objective lens for an optical pickup. It is widely used in optical pickups for recording or reproducing CDs, MOs, and DVDs. Plastic mold objectives for DVDs or for both CDs and DVDs are required to have higher numerical apertures and higher precision than CDs, and are used to record or reproduce information at a higher density than DVDs. It is considered that the plastic molded single lens for the next generation optical information recording medium is required to have a higher numerical aperture, higher precision and higher performance than DVDs, and proposals therefor are beginning to be made.

Conventionally, glass molded single lenses have been used in some cases. However, compared to such glass lenses, plastic lenses have a lower specific gravity and can reduce the load on an actuator for driving the objective lens. Since the tracking of the objective lens can be performed at high speed, the plastic lens is overwhelmingly more advantageous than the glass lens. So far, the focus has been on the development and research of plastic molded single lens objective lenses that satisfy the desired performance. I have. Even today, there is no end to the research and development, and there is no shortage of technological development for improving the precision and performance of a very small diameter, small, and thin plastic molded single lens objective lens.

[0004]

SUMMARY OF THE INVENTION A plastic molded lens manufactured using a plastic material and a mold,
Since it is possible to easily produce a large number of lenses by accurately manufacturing a mold having a desired shape, it is generally preferable to contribute to high performance and low cost of the lens. However, achieving a high numerical aperture of an objective lens for an optical pickup with a plastic molded single lens increases sensitivity to lens performance due to shift of both optical surfaces, and the like.
Further, in the case of shortening the wavelength of the light source, such as using a blue-violet laser of about 400 nm as the light source of the optical pickup, the sensitivity becomes much larger, so that the technical difficulty in mold manufacturing and molding becomes higher. There is a problem that its realization is extremely difficult. Further, there is a problem that a plastic molded single lens finally obtained by making full use of a technique having a high degree of difficulty is necessarily expensive.

Therefore, the present invention can easily realize a high numerical aperture while using a plastic molded lens.
It is a primary object of the present invention to provide an objective lens for an optical pickup which can be manufactured with high precision and high performance, can be easily manufactured, and can be manufactured at low cost, and an optical pickup using the objective lens for the optical pickup.

[0006]

The above object is achieved by any one of the following constitutions. The invention according to claim 1 is an objective lens for an optical pickup including at least two or more plastic molded lenses,
A first contact portion is provided on a portion closer to the optical function portion of the first lens, and a second contact portion is provided on a portion closer to the optical function portion of the second lens disposed opposite to the first lens. An objective lens for an optical pickup, wherein a contact portion is provided so as to contact the first contact portion of the first lens and the second contact portion of the second lens. .

According to a second aspect of the present invention, there is provided an objective lens for an optical pickup comprising at least two or more plastic molded lenses, wherein a portion of the first lens which is closer to the optical function section than the second lens is formed of the second lens. An objective lens for an optical pickup, wherein the objective lens is configured to hold a portion on the peripheral side of the optical function part of the lens.

According to a third aspect of the present invention, a first contact portion is provided on a portion of the first lens closer to the periphery than the optical function portion,
The second lens is located on the peripheral side of the optical function part of the second lens.
3. A structure according to claim 2, wherein a contact portion is provided so that said first contact portion and said second contact portion come into contact with each other.
2. The objective lens for an optical pickup according to 1.,

According to a fourth aspect of the present invention, there is provided an objective lens for an optical pickup comprising two plastic molded lenses, wherein a first lens and a second lens are arranged in order from an object side (a light source side in the optical pickup). When the optical surface is a first surface, a second surface, a third surface, and a fourth surface in this order from the object side, the first surface and the third surface are configured as convex surfaces, and the first surface is formed. A first contact portion protruding toward the image side in the optical axis direction from the second surface is provided on a portion closer to the image side than the optical function portion of the lens. A second contact portion protruding toward the object side in the optical axis direction and having a cutout shape, wherein the first contact portion and the second contact portion are provided.
An objective lens for an optical pickup, wherein the objective lens is configured to be brought into contact with a contact portion to hold the second lens with the first lens.

The invention according to claim 5 is the objective lens for an optical pickup according to claim 4, wherein the outer diameter of the second lens is smaller than the outer diameter of the first lens.

According to a sixth aspect of the present invention, in the objective lens for an optical pickup according to the fourth or fifth aspect, the fourth surface is a flat surface. The invention according to claim 7, wherein the concave portion in the portion of the second lens on the fourth surface side closer to the outer peripheral side than the optical function portion is recessed toward the object side from the most image side position of the fourth surface. The objective lens for an optical pickup according to any one of claims 4 to 6, further comprising:

In the invention described in claim 8, the relative positioning between the first lens and the second lens in the optical axis direction is established by the contact between the first contact portion and the second contact portion. The objective lens for an optical pickup according to any one of claims 1, 3 to 7, wherein the objective lens is made.

According to a ninth aspect of the present invention, the first contact portion has a first vertical surface perpendicular to the optical axis, and the second contact portion has a second vertical surface perpendicular to the optical axis. 9. A relative position between the first lens and the second lens in the optical axis direction by contact between the first vertical surface and the second vertical surface. 2. The objective lens for an optical pickup according to 1.,

According to a tenth aspect of the present invention, the first lens and the second lens are brought into contact with each other in a direction perpendicular to an optical axis by the contact between the first contact portion and the second contact portion. The objective lens for an optical pickup according to any one of claims 1 to 3, wherein the objective lens is positioned.

According to an eleventh aspect of the present invention, the first contact portion has a first parallel surface in the optical axis direction, and the second contact portion has a second parallel surface in the optical axis direction. 1 parallel plane and the second
The objective lens for an optical pickup according to claim 10, wherein relative positioning between the first lens and the second lens in a direction perpendicular to an optical axis is performed by contact with a parallel surface. .

According to a twelfth aspect of the present invention, the first contact portion and the second contact portion abut on each other so that the first lens and the second lens are perpendicular to the optical axis and the optical axis. 8. The objective lens for an optical pickup according to claim 1, wherein relative positioning is performed in various directions.

According to a thirteenth aspect of the present invention, the first contact portion has a first vertical surface perpendicular to the optical axis and a first parallel surface in the optical axis direction, and the second contact portion has A second vertical surface perpendicular to the optical axis and a second parallel surface in the optical axis direction, wherein the first lens and the second lens are brought into contact by the first vertical surface and the second vertical surface. The relative positioning in the direction of the optical axis between the first lens and the second lens is performed by the contact between the first parallel surface and the second parallel surface. 13. The objective lens for an optical pickup according to claim 12, wherein the objective lens is positioned.

According to a fourteenth aspect of the present invention, the first lens and the second lens are tightly fitted by the contact between the first contact portion and the second contact portion. The objective lens for an optical pickup according to any one of claims 1 to 13, characterized in that:

According to a fifteenth aspect of the present invention, the first lens and the second lens are fitted with a clearance fit by the contact between the first contact portion and the second contact portion. The objective lens for an optical pickup according to any one of claims 1 to 13, characterized in that:

According to a sixteenth aspect of the present invention, the first lens and the second lens are fixed after the first lens and the second lens are fitted by the contact between the first contact and the second contact. An objective lens for an optical pickup according to any one of claims 1 to 15, characterized in that:

According to a seventeenth aspect of the present invention, the optical function part of the first lens and the optical function part of the second lens facing each other are separated from each other without being in contact with each other. An objective lens for an optical pickup according to any one of claims 1 to 16.

The invention according to claim 18 is that the diameter of the optical surface on the image side relative to the outer diameter of the plastic mold lens disposed closest to the image side (the side opposite to the light source in the optical pickup) is 40% or less. An objective lens for an optical pickup according to any one of claims 1 to 17, characterized in that:

According to a nineteenth aspect of the present invention, the first contact portion and the second contact portion are annularly formed around the optical function portion on the peripheral side of the optical function portion of each lens. The objective lens for an optical pickup according to any one of claims 1 to 18, wherein the objective lens is provided for:

According to a twentieth aspect of the present invention, a first image side plane perpendicular to an optical axis is provided on an image side on an outer peripheral side of the first contact portion, and the optical system of the second lens is provided. The optical pickup according to any one of claims 1 to 19, wherein a second image-side plane perpendicular to the optical axis is provided on the image side on the outer peripheral side of the functional unit. It is an objective lens.

The invention according to claim 21 is the optical pickup objective lens according to claim 20, wherein the first image-side plane and the second image-side plane are mirror surfaces. An invention according to a twenty-second aspect is an optical pickup using the objective lens for an optical pickup according to any one of the first to twenty-first aspects.

The invention according to claim 23 is the optical pickup according to claim 22, characterized in that the optical pickup is designed to be less than the Marechal limit. According to a twenty-fourth aspect of the present invention, in the objective lens for an optical pickup according to any one of the first to seventh aspects, the first abutting portion and the second abutting portion abut on each other. With the relative positioning between the first lens and the second lens in the optical axis direction being performed, the second lens is moved in a direction perpendicular to the optical axis in a clearance between the first lens and the second lens. An optical pickup characterized in that, when the lens is moved with respect to the first lens, a fluctuation amount of a wavefront aberration at an imaging position is equal to or less than a diffraction limit performance.

According to a twenty-fifth aspect of the present invention, there is provided the optical pickup objective lens according to any one of the first to twenty-first aspects, wherein the first lens is held by a lens frame driven by an actuator. An optical pickup characterized in that:

According to a twenty-sixth aspect of the present invention, in the optical pickup according to any one of the twenty-second to twenty-fourth aspects, the first lens is held by a lens frame driven by an actuator. It is.

[0029]

According to the above construction, the curvature of the optical surface becomes very large, as in the case of using a plastic molded single lens, in response to a demand for a high numerical aperture of an objective lens for an optical pickup, etc. Sensitivity to lens performance due to shifts between them also increases, mold processing and assembling accuracy for molding become very strict, and maintenance and management of product quality does not become extremely difficult. Then, a plurality of plastic molded lenses having a small numerical aperture are separately molded, and a plastic molded lens capable of coping with a high numerical aperture is obtained by combining them. Therefore, the moldability is good, the production is very easy, and the lens performance can be improved with good transferability to the mold.
In addition, since the objective lens for the optical pickup is configured such that at least two plastic molded lenses are in contact with each other or held by one of the lenses, each lens is positioned and fixed to the lens frame. Compared with such a case, higher precision and higher performance can be easily realized, and it is possible to easily cope with further higher numerical aperture and smaller size of the objective lens for an optical pickup. In addition, since a plurality of plastic mold lenses are used, it is easy to correct aberrations and errors of each lens such as astigmatism.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an objective lens for an optical pickup according to the present invention and an optical pickup using the same will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a sectional view of an objective lens for an optical pickup, and FIG. 2 is a schematic configuration diagram of an optical pickup incorporating the objective lens for an optical pickup of FIG. In the present embodiment, an example in which an objective lens is formed by two plastic mold lenses will be described.

In FIG. 1, an objective lens 10 for an optical pickup has an object-side lens 1 disposed on the light source side of the optical pickup, and is disposed on the side opposite to the light source of the optical pickup, and is connected to an optical information recording medium such as an optical disk. When recording or reproducing information, the optical system includes an image-side lens 2 facing the optical information recording medium. Although not shown, these lenses 1 and 2 both have a substantially circular outer peripheral shape when viewed from the optical axis direction, and have a substantially circular optical function portion centered on the optical axis. Each of the lenses 1 and 2 is a plastic mold lens in which plastic (resin) is used as a lens material and each is molded using a mold formed in a predetermined shape.
In the present embodiment, it is manufactured by injection molding in which a resin is injected into each mold and the shape of the mold is transferred.

In FIG. 1, the dashed line indicates the optical axis of the objective lens 10 for an optical pickup, and the dotted line limits the aperture such as a mirror frame (bobbin) supporting the objective lens and a stop provided separately in the optical pickup. This means that the light beam farthest from the optical axis in the light flux from the light source of the optical pickup that passes through the objective lens 10 for the optical pickup is shown by the means. Therefore, on the drawing, a portion inside (on the optical axis side) from the dotted line in each of the lenses 1 and 2 is an optical function unit actually used. However, in manufacturing a lens, it is general to provide a margin by making the optical function part larger than the part actually used, and the area that can be used as an optical surface in this embodiment is also indicated by a dotted line. It is slightly up to the outside.

In the lenses 1 and 2 of the present embodiment, the portion on the peripheral side of the optical function portion has a flange shape as shown in FIG. In the lens 1, a protruding portion protruding toward the lens 2 is provided on a flange portion which is a portion on the peripheral side of the optical function portion, and a contact portion 11 is provided on the optical axis side of the protruding portion. The contact portion 11 has a vertical surface 11a perpendicular to the optical axis of the lens 1 and a parallel surface 11b intersecting with the vertical surface 11a and parallel to the optical axis. The parallel surface 11b forms a part of the inner peripheral surface of the projection. Further, an image-side plane 12 in a direction perpendicular to the optical axis is provided on a side of the protruding portion opposite to the optical axis side. In the present embodiment, the image side plane 12 is a mirror plane of the same plane that is continuous with the vertical plane 11a.

On the other hand, in the lens 2, a flange portion, which is a portion on the peripheral side of the optical function portion, has a cut-out shape on the opposite side to the optical axis side and protrudes toward the lens 1. Is provided, and the contact portion 21 is
Was provided. The contact portion 21 includes a vertical surface 21a perpendicular to the optical axis of the lens 2 and a parallel surface 21b intersecting with the vertical surface 21a and parallel to the optical axis. The parallel surface 21b forms a part of the outer peripheral surface of the projection. The object-side optical surface of the lens 2 has a shape protruding toward the object side in the optical axis direction from the projection.

Also, a portion of the optical surface closer to the object side than the most image-side position of the optical surface, preferably in the optical axis direction of the lens 2, is located on the image side of the lens 2 and on the peripheral side of the optical function portion. A concave portion 23 which is recessed on the object side from the position closest to the image is provided.
In the present embodiment, the concave portion 23 is provided from the outer peripheral side to the outer peripheral portion of the portion on the outer peripheral side of the optical function portion. If the mold shape is designed such that burrs generated in the plastic mold lens are located in the concave portions 23,
It is possible to prevent burrs from being brought into contact with the surface of the optical disk which is disposed in the vicinity and damaging the optical disk. Specifically, for example,
Separating the mold of the portion including the optical surface where high precision is required from the mold around the portion is preferable in terms of the production of the mold of the optical surface portion and the cost, and in that case, these molds are used. It is preferable that the divided surface of the mold is located at the position of the concave portion 23 because the burr can be prevented from protruding toward the image side from the position of the lens 2 closest to the image side. Further, contact between the lens 2 and the optical information recording medium due to warpage of the optical information recording medium such as an optical disk can be reduced.

Further, in the present embodiment, the image side plane 22 in a direction perpendicular to the optical axis is provided in a part of the concave portion 23, specifically, on the outer peripheral side of the concave portion 23. The image side plane 22 was made a mirror surface like the image side plane 12. These image-side planes 12, 22
Are mirror surfaces in the direction perpendicular to the optical axes of the corresponding lenses 1 and 2, respectively.
The lens 1, 2 is formed by using a light source and a sensor 22 as a reflection surface.
It is possible to prevent tilted mounting between the optical pickup objective lens 10 and the lens frame of the optical pickup, thereby performing more accurate positioning and fixing.

In FIG. 1, R1, R2, R3, and R4 are optical surfaces corresponding to the optical function unit. Assuming a first surface, a second surface, a third surface, and a fourth surface in order from the optical surface disposed on the object side, the first surface R1 and the third surface R3 are convex surfaces that are convex on the object side. This convex surface was made aspheric. 2nd surface R2
Is a concave surface slightly concave on the object side, and the fourth surface R4
Is a plane perpendicular to the optical axis of the lens 2. When R4, which is the fourth optical surface, is a plane perpendicular to the optical axis, a portion on the peripheral side of the optical surface should be formed as a plane continuous with the optical surface. By using at least a part of the plane thus formed in the direction perpendicular to the optical axis as a mirror surface, the above-described image-side plane 22 can be used instead of the image-side plane 22 without special provision. be able to.

Since the objective lens 10 for the optical pickup is composed of two plastic molded lenses having four optical surfaces, the sensitivity of each optical surface accuracy to the optical performance can be suppressed small, and the design freedom of the optical surface can be reduced. Have been able to improve. In addition, the first surface and the third surface are formed as convex surfaces convex toward the object side, and the convex refracting surface is distributed, thereby realizing a high-performance objective lens for an optical pickup capable of coping with a high numerical aperture. Furthermore, by making the second surface concave, the air gap on the axis between the lenses can be reduced, and both lenses can be arranged close to each other. The thickness of the lens can be reduced. In the present embodiment, the on-axis thickness is about 4 to 5 mm. Further, when the fourth surface is a plane perpendicular to the optical axis as in the present embodiment, mold processing is facilitated, and shape accuracy and surface roughness are easily improved. Further, it is preferable because it is possible to prevent the optical performance from deteriorating due to the shift of both optical surfaces.

The plastic molded lenses 1 and 2 obtained by injection molding into the above-described shapes are then integrated to form an objective lens for an optical pickup. The integration of the lenses 1 and 2 may be performed when the lens is incorporated into the optical pickup, or one of the lenses may be integrated into a lens frame (such as a bobbin) and then the other lens may be integrated.
In the present embodiment, an example will be mainly described in which the lenses 1 and 2 are integrated and then incorporated into an optical pickup. In the case of assembling in this manner, since the assembly to the lens frame only needs to be performed once, the productivity in assembling the optical pickup is good, and the assembling accuracy can be improved.

In the present embodiment, the lens 1 and the lens 2 are integrated by the contact portion 11 of the lens 1 and the contact portion 2 of the lens 2.
This is performed by abutting with No. 1. By this contact, relative positioning between the lenses 1 and 2 is performed. Vertical surface 11
The relative positioning in the optical axis direction is performed by the contact between the lenses a and 21a, and the air gap between the lenses 1 and 2 can be set to a desired axial distance. The relative positioning in the direction perpendicular to the optical axis is performed by the abutment of the horizontal surfaces 11b and 21b, and the optical axis of the lens 1 and the optical axis of the lens 2 can be matched or the amount of deviation can be within a desired range. As described above, the relative positioning in the optical axis direction or the direction perpendicular to the optical axis can be performed by the contact, so that the high precision of the objective lens for the optical pickup using a plurality of plastic mold lenses can be achieved. It is easy to assemble and suitable for mass production.

When viewed from the optical axis direction, the horizontal surfaces 11b and 21b have a circular shape with the optical axis substantially at the center, and the diameter of the horizontal surface 11b with the optical axis at the center is only slightly smaller than the diameter of the horizontal surface 21b. It is formed small. Accordingly, the lens 1 and the lens 2 are fitted and held by the close fit, so that the lens 1 and the lens 2 are integrated. It is more preferable to adhere to the contact portions 11 and 21 using an ultraviolet-curable adhesive or the like from the viewpoint of obtaining strength. In the case of bonding with an adhesive or the like interposed therebetween, in order to obtain the accuracy of the axial lens spacing between the lenses 1 and 2 and sufficiently achieve the lens performance of the objective lens for an optical pickup, the vertical surface 11 is particularly required.
It is preferable to apply an adhesive to the a and 21a and to prevent the adhesive from flowing around.

The diameter y of the optical surface R4 on the image side of the lens 2
Is set to 40% or less of the outer diameter x2 of the lens 2. Conversely, the outer diameter x2 is 2.5 times or more the diameter y of the optical surface R4. Thereby, the minute optical surface of the lens 2 (R3 diameter around 0.2 mm, R4 diameter around 0.1 mm)
Has good molding accuracy. In addition, since the optical surface R4 is far from the contact surface, fluctuations in optical performance due to environmental changes can be suppressed. Furthermore, the outer diameter x of the lens 2
The outer diameter x1 of the lens 1 is larger than that of the lens 2. Thereby, the handleability of the objective lens 10 for the optical pickup when the lens 1 is fixed to the lens frame of the optical pickup holding the objective lens with an adhesive or the like is good, for example, by grasping the outer periphery of the lens 2, By rotating about the optical axis, mounting at a desired rotational position can be easily performed. The same applies to the case where the lens 1 is first attached to the lens barrel, and then the lens 2 is abutted on the lens 1 and fixed.

FIG. 2 shows an optical pickup to which the objective lens 10 for an optical pickup shown in FIG. 1 is applied.
The beam from the beam splitter 1 is a beam splitter 1
02, is converted into a parallel light beam through a collimating lens 103, passes through a quarter-wave plate 104, is stopped down to a predetermined numerical aperture by a stop 107, and is passed through an objective lens 10 to be an optical disk as an optical information recording medium. 120 transparent substrates 121
A spot is formed on the information recording surface 122 via the.

The reflected light beam modulated by the information pits on the information recording surface 122 becomes a parallel light beam again through the objective lens 10, and further becomes a convergent light through the stop 107, the 波長 wavelength plate 104, and the collimating lens 103. The light is reflected by the beam splitter 102 and is
Are converted into astigmatism and magnification by the photodetector 109.
Converge on the light receiving surface of Reference numeral 105 in the figure denotes an actuator as a distance adjusting means for focus control and tracking control, and a lens frame (bobbin) (not shown) holding the lens 1 of the objective lens 10 in which the lenses 1 and 2 are integrated. Is driven by the actuator 105.

In order to further improve the performance of the above-exemplified embodiment of the optical pickup in response to a higher numerical aperture and a shorter wavelength of the light source, instead of the collimating lens 103,
It is preferable that the optical pickup is provided with a means for correcting spherical aberration fluctuation and chromatic aberration. As means for correcting the spherical aberration fluctuation and chromatic aberration, for example, an optical system including a movable lens capable of changing the divergence angle of the output light beam with respect to the incident light beam can be used. The optical pickup objective lens of the present invention can be applied to such an embodiment of the optical pickup.

Of course, in each case, the optical pickup
The optical pickup is designed to be less than the Marechal limit performance, which is the minimum performance as an optical pickup, and satisfies the performance.

(Second Embodiment) FIG. 3 is a sectional view showing another embodiment of an objective lens for an optical pickup, and FIG.
The description of the same configuration as that described above is omitted. In FIG. 3, the objective lens 20 for an optical pickup is an example in which an objective lens is constituted by two plastic mold lenses, a lens 3 on the object side and a lens 4 on the image side. Each of the lenses 3 and 4 is manufactured by injection molding, has a substantially circular outer peripheral shape when viewed from the optical axis direction, and has a substantially circular optical function portion centered on the optical axis.

In the lens 3, a protrusion which is notched on the optical axis side and protrudes toward the lens 4 is provided on a flange portion on the peripheral side of the optical function portion. On the axial side, there is provided a contact portion 31 having a vertical surface 31a perpendicular to the optical axis of the lens 3 and a parallel surface 31b crossing the vertical surface 31a and parallel to the optical axis. On the other hand, in the lens 4, a protruding portion protruding toward the lens 3 is provided on a flange portion that is a portion on the peripheral side of the optical function portion, and the lens 4 is provided on the opposite side of the protruding portion from the optical axis side. And a contact portion 41 having a vertical surface 41a perpendicular to the optical axis and a parallel surface 41b crossing the vertical surface 41a and parallel to the optical axis. The first surface R1 and the third surface R3 are convex surfaces that are convex toward the object side, the second surface R2 is a concave surface that is slightly concave toward the object side, and the fourth surface R4 is an optical axis of the lens 4. Is a plane in a direction perpendicular to.

In this embodiment, similarly to the first embodiment, the contact portion 31 of the lens 3 and the contact portion 41 of the lens 4
The relative positioning between the lenses 3 and 4 is performed by abutting. However, unlike the first embodiment, the diameter of the horizontal plane 31b centered on the optical axis when viewed from the optical axis direction is only slightly smaller (3 μm) than the diameter of the horizontal plane 41b.
m to 10 μm), lens 3 and lens 4
Are fitted with a clearance fit.

Therefore, in a state where the vertical surfaces 31a and 41a are brought into contact with each other to perform relative positioning in the optical axis direction, that is, in a state where the air gap between the lenses 3 and 4 is a desired axial distance, It is preferable that the lens 4 and the lens 4 can be relatively easily rotated about the optical axis, and the amount of birefringence and astigmatism can be adjusted by adjusting the rotation. The lenses 3 and 4 were fixed between the horizontal surfaces 31b and 41b using an ultraviolet-curable adhesive to obtain a strongly integrated objective lens 20 for an optical pickup. At this time, in order to prevent the adhesive from leaking to the outside from the joint portion, it is preferable to provide a recess for storing the adhesive on the image side of the horizontal surface 41b or near the horizontal surface 41b on the outer periphery of the lens 4.

In such a clearance fit, when the lenses 3 and 4 are relatively moved in a direction perpendicular to the optical axis in the clearance, the fluctuation amount of the wavefront aberration at the image forming position in the optical pickup. Is below the diffraction-limited performance,
Preferably, the clearance is limited. Further, it is more preferable that the clearance amount is limited within an allowable range of the optical axis shift between the two plastic molded lenses that is allowed to satisfy the performance of the optical pickup.

(Other Embodiments) The objective lens for an optical pickup of the present invention and the optical pickup using the same are not limited to the above embodiments, but may be variously modified within the scope of the invention. Can be done.

In the above embodiment of the present invention, an example was described in which the contact portion was constituted by a vertical surface and a horizontal surface intersecting the vertical surface. However, the present invention is not limited to this shape, and various shapes can be adopted. it can. For example, the contact portion may be formed by a trapezoidal surface having one inclined surface, or the contact portion may be formed by an arc-shaped surface such as a part of a spherical surface. In any case, it is preferable that relative positioning between the lenses in the optical axis direction and the direction perpendicular to the optical axis is performed by the contact of the contact portion.

Although the contact portions are formed in a ring shape with each other, it is not necessary to provide the contact portions over the entire ring in order to position the lenses in the optical axis direction and / or the direction perpendicular to the optical axis. For example, a configuration may be adopted in which at least three portions are contact portions at substantially equal intervals.

In the above embodiment, an example is shown in which the diameter of the lens on the object side is larger than the diameter of the lens on the image side. In the objective lens for the optical pickup, the optical function portion required for the image-side lens may be relatively small, so making the diameter of the image-side lens larger than necessary is a waste of plastic molded lens material. Since the weight of the objective lens becomes unnecessarily heavy, it is preferable to reduce the diameter of the lens on the image side.

Furthermore, the present invention is not limited to the case where the objective lens for an optical pickup is composed of only two plastic molded lenses, but is applicable to the case where it is composed of two or more plastic molded lenses. it can. In that case, it is needless to say that it is preferable that the adjacent opposed lenses satisfy the relationship described in detail in the above embodiment. In the present embodiment,
Although an example in which a plastic mold lens is manufactured by injection molding has been described, various molding methods such as injection compression molding can be applied. Injection molding or injection compression molding is more preferred because it provides excellent transferability of the resin to the mold and provides a high-precision and high-performance plastic mold lens closer to the design.

[0058]

As described above, the present invention does not involve the difficulties of a single-piece molded objective lens, has good moldability, is very easy to manufacture, and has excellent lens performance. It is possible to obtain a plastic molded lens that can be transferred with good performance and that it can be easily assembled into an optical pickup, and that it can easily cope with even higher numerical aperture and miniaturization. An optical pickup can be obtained.

Furthermore, according to the first aspect of the present invention, high-precision positioning of the lenses can be easily achieved by contact. In addition, high-precision assembly of the objective lens for the optical pickup can be easily performed, and mass productivity can be improved.

According to the second aspect of the present invention, since the lenses are directly integrated with each other, high-accuracy alignment can be performed without increasing the number of parts and the number of mounting steps.

According to the third aspect of the present invention, high-precision positioning of the lenses can be easily achieved by contact. According to the fourth aspect of the present invention, since the lenses are directly integrated with each other, high-accuracy positioning can be performed without increasing the number of parts and the number of mounting steps, and the lens on the image side is held. Therefore, it is possible to increase the radial thickness of the flange, for example, in the vicinity of the contact portion of the lens on the object side, to secure the strength, and to maintain high performance with high accuracy even in environmental changes.

According to the fifth aspect of the present invention, the handleability is excellent and high-precision assembly can be easily performed. Further, even when the optical information recording medium such as an optical disk is warped, contact between the lens and the optical information recording medium can be reduced.

According to the sixth aspect of the present invention, mold processing is facilitated, and shape accuracy and surface roughness are easily improved. Further, it is possible to prevent the optical performance from deteriorating due to the shift of both optical surfaces.

According to the seventh aspect of the present invention, it is possible to prevent burrs generated by the divided surface of the mold from contacting the optical information recording medium. Further, even when the optical information recording medium such as an optical disk is warped, contact between the lens and the optical information recording medium can be reduced.

According to the eighth aspect of the present invention, positioning between the lenses in the optical axis direction can be easily achieved by contact. In addition, high-precision assembly of the objective lens for the optical pickup can be easily performed, and mass productivity can be improved.

According to the ninth aspect of the present invention, high-precision positioning of the lenses in the optical axis direction can be easily achieved by contact between the surfaces perpendicular to the optical axis. According to the tenth aspect, positioning in the direction perpendicular to the optical axis between the lenses can be easily achieved by the contact. In addition, high-precision assembly of the objective lens for the optical pickup can be easily performed, and mass productivity can be improved.

According to the eleventh aspect of the present invention, high-precision positioning of the lenses in a direction perpendicular to the optical axis can be easily achieved by contact between surfaces parallel to the optical axis. According to the twelfth aspect of the invention, the positioning of the lenses in the optical axis direction and the direction perpendicular to the optical axis can be easily achieved by the contact. In addition, high-precision assembly of the objective lens for the optical pickup can be easily performed, and mass productivity can be improved.

According to the thirteenth aspect of the present invention, high-precision positioning of the lenses in the optical axis direction and in the direction perpendicular to the optical axis is achieved by contact between the surfaces perpendicular to the optical axis and between the surfaces parallel to the optical axis. Easy to achieve.

According to the fourteenth aspect, it is possible to easily hold the lenses with each other with a simple configuration.
In the invention according to claim 15, relative rotation between lenses and adjustment of optical axis deviation can be easily performed, and the optical performance of the entire objective lens can be improved.

According to the sixteenth aspect of the present invention, since the fixing is performed after the fitting, the high-precision positioning of the lenses can be maintained, and the mutual holding of the lenses can be ensured. Claim 17
In the invention described in (1), the opposing optical surfaces between the lenses do not come into contact due to the contact of the contact portion, so that the optical surfaces are not damaged and an effective optical surface having an air gap can be utilized. In addition, the lens spacing can be easily controlled, and by appropriately controlling the height in the optical axis direction of the contact portion on the peripheral side of the optical function unit, the lens aberration can be easily controlled to control spherical aberration. Is also possible.

According to the eighteenth aspect of the present invention, it is possible to improve the forming accuracy of the minute optical surface. Further, it is possible to suppress the occurrence of distortion on the optical surface when assembling the objective lens for an optical pickup, and it is possible to suppress the fluctuation of the optical performance with respect to the environmental change.

According to the nineteenth aspect of the present invention, since the contact portion is provided annularly around the optical function portion, the stable shape accuracy of the contact portion can be obtained without impairing the fluidity of the resin even by injection molding. Can be achieved.

According to the twentieth aspect, it is possible to easily detect the inclination between the optical axes between the lenses and other optical systems, and to easily perform the adjustment. According to the twenty-first aspect, it is possible to more easily detect the inclination between the optical axes between the lenses and other optical systems, and to easily perform high-precision adjustment.

According to the twenty-second aspect of the present invention, it is possible to easily provide a high numerical aperture and high performance optical pickup using the objective lens for the optical pickup. Claim 2
The invention described in Item 3 is suitable as an optical pickup.

According to the twenty-fourth aspect of the present invention, an optical pickup having a minimum necessary objective lens performance can be easily obtained without requiring high-precision positioning.
According to the twenty-fifth or twenty-sixth aspect of the present invention, the objective lens can be easily mounted on the optical pickup by assembling one lens of the objective lens for the optical pickup composed of two or more lenses into the lens barrel. be able to.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of an objective lens for an optical pickup according to the present invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of an optical pickup according to the present invention to which the objective lens for an optical pickup shown in FIG. 1 is applied.

FIG. 3 is a sectional view showing a second embodiment of the objective lens for an optical pickup according to the present invention.

[Explanation of symbols]

 1, 2, 3, 4 Lens 10, 20 Objective Lens for Optical Pickup 11, 21, 31, 41 Contact Part 12, 22 Image Side Plane 23 Depression R1, R2, R3, R4 Optical Surface 110 Optical Pickup 120 Optical Information Recording Medium

Claims (26)

[Claims] 1. An objective lens for an optical pickup comprising at least two or more plastic molded lenses, wherein a first contact portion is provided on a portion of the first lens closer to an optical function portion than the first lens. A second contact portion is provided at a portion on the peripheral side of the optical function portion of the second lens disposed to face the one lens, and the first contact portion of the first lens and the second contact portion of the second lens are provided. An objective lens for an optical pickup, wherein the objective lens is configured to abut the two abutting portions. 2. An objective lens for an optical pickup comprising at least two plastic molded lenses, wherein a portion closer to an optical function portion of the first lens than an optical function portion of the second lens. An objective lens for an optical pickup, wherein the objective lens is configured to hold a peripheral portion. 3. A first contact portion is provided at a portion on the peripheral side of the optical function portion of the first lens, and a second contact portion is provided at a portion on the peripheral side of the optical function portion of the second lens. The objective lens for an optical pickup according to claim 2, wherein the first contact portion and the second contact portion are configured to contact each other. 4. An objective lens for an optical pickup comprising two plastic molded lenses, wherein a first lens and a second lens are arranged in order from an object side (a light source side in the optical pickup), and an optical surface is an object side. The first surface in order from
When the second surface, the third surface, and the fourth surface are set, the first surface and the third surface are configured as convex surfaces, and a portion closer to an optical function portion of the first lens than the optical function portion includes: A first contact portion protruding toward the image side in the optical axis direction from the second surface; and a notch shape protruding toward the object side in the optical axis direction in a portion on the peripheral side of the optical function portion of the second lens. A second contact portion is provided, and the first contact portion and the second contact portion are brought into contact with each other to hold the second lens with the first lens. Objective lens for optical pickup. 5. The objective lens for an optical pickup according to claim 4, wherein the outer diameter of the second lens is smaller than the outer diameter of the first lens. 6. The objective lens for an optical pickup according to claim 4, wherein the fourth surface is a flat surface. 7. A concave portion which is recessed on an object side of a position of the fourth surface closest to the object side on a portion of the second lens closer to the fourth surface than the optical function portion. The objective lens for an optical pickup according to any one of claims 4 to 6, wherein: 8. A relative positioning between the first lens and the second lens in the optical axis direction by the contact between the first contact portion and the second contact portion. The objective lens for an optical pickup according to any one of claims 1, 3 to 7. 9. The first contact portion is provided in a first direction perpendicular to an optical axis.
A vertical surface, the second contact portion includes a second vertical surface perpendicular to an optical axis, and the first lens and the second lens are contacted by the first vertical surface and the second vertical surface. 9. The objective lens for an optical pickup according to claim 8, wherein relative positioning in an optical axis direction between the two lenses is performed. 10. A relative positioning between the first lens and the second lens in a direction perpendicular to an optical axis by contact between the first contact portion and the second contact portion. The objective lens for an optical pickup according to claim 1, wherein the objective lens is an optical pickup. 11. The first contact portion has a first parallel surface in the direction of the optical axis, the second contact portion has a second parallel surface in the direction of the optical axis, and the first parallel surface and the second parallel surface. The objective lens for an optical pickup according to claim 10, wherein relative contact between the first lens and the second lens in a direction perpendicular to an optical axis is performed by contact with a parallel surface. 12. The relative positioning between the first lens and the second lens in the optical axis direction and in the direction perpendicular to the optical axis by the contact between the first contact portion and the second contact portion. The objective lens for an optical pickup according to any one of claims 1 to 3, wherein the objective lens is made. 13. The first contact portion has a first vertical surface perpendicular to the optical axis and a first parallel surface in the optical axis direction, and the second contact portion has a first perpendicular surface in a direction perpendicular to the optical axis. The second vertical plane and the second in the optical axis direction
A parallel surface, and the first vertical surface and the second vertical surface are brought into contact with each other to perform relative positioning in the optical axis direction between the first lens and the second lens, and to perform the first parallel operation. 13. The optical pickup according to claim 12, wherein relative contact between the first lens and the second lens in a direction perpendicular to an optical axis is performed by abutment between a surface and the second parallel surface. Objective lens. 14. The first lens and the second lens,
14. The optical pickup according to claim 1, wherein the first contact portion and the second contact portion are fitted to each other by tight fitting. Objective lens. 15. The first lens and the second lens,
14. The optical pickup according to claim 1, wherein the first contact portion and the second contact portion are fitted to each other by a clearance fit. Objective lens. 16. The first lens and the second lens,
The objective for an optical pickup according to any one of claims 1 to 15, wherein the first contact portion and the second contact portion are fixed after being fitted by contact with each other. lens. 17. The optical system according to claim 1, wherein the optical function part of the first lens and the optical function part of the second lens facing each other are separated from each other without being in contact with each other. The objective lens for an optical pickup according to claim 1. 18. The method according to claim 1, wherein the diameter of the optical surface on the image side relative to the outer diameter of the plastic mold lens disposed closest to the image side (the side opposite to the light source in the optical pickup) is 40% or less. Any one of claims 17
Item 7. The objective lens for an optical pickup according to item 1. 19. The first contact portion and the second contact portion,
19. The lens according to claim 1, wherein each of the lenses is provided in a ring shape around the optical function part on a peripheral side of the optical function part.
Item 7. The objective lens for an optical pickup according to item 1. 20. An image side closer to the outer periphery than the first contact portion,
A first image side plane perpendicular to the optical axis is provided, and an image side of the second lens on the outer peripheral side of the optical function unit,
The objective lens for an optical pickup according to any one of claims 1 to 19, further comprising a second image-side plane perpendicular to the optical axis. 21. The objective lens for an optical pickup according to claim 20, wherein said first image-side plane and said second image-side plane are mirror surfaces. 22. Any one of claims 1 to 21.
An optical pickup characterized by using the objective lens for an optical pickup described in the above item. 23. The optical pickup according to claim 22, wherein the optical pickup is designed to be less than the Marechal limit. 24. The first lens in the objective lens for an optical pickup according to claim 1, wherein:
When the relative position between the first lens and the second lens in the optical axis direction is determined by the contact between the contact portion and the second contact portion, the first lens and the second lens are When the second lens is moved with respect to the first lens in a direction perpendicular to the optical axis within the fitting clearance of (a), the fluctuation amount of the wavefront aberration at the imaging position is equal to or less than the diffraction limit performance. Optical pickup featuring 25. One of claims 1 to 21.
An optical pickup, wherein the first lens is held by a lens frame driven by an actuator, using the objective lens for an optical pickup according to any one of the preceding claims. 26. The apparatus according to claim 2, wherein said first lens is held by a lens frame driven by an actuator.
The optical pickup according to any one of claims 2 to 24.