JP3204031B2 - Mold for objective lens and objective lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding die for an objective lens of an optical pickup for optically reading information by projecting a light spot on an optical disk having information tracks on which high-density signals are recorded, and a molding die therefor. It relates to a molded objective lens.

[0002]

2. Description of the Related Art In general, a method of manufacturing a lens using a molding apparatus includes a method of putting a molding material (hereinafter referred to as a lens glass material) obtained by primary processing into a molding die and performing secondary molding (compression). Molding) and a method in which a molten molding material is charged into a mold and molded (injection molding).
Objective lenses molded by these manufacturing methods are generally corrected for aberrations so that the performance on the optical axis is the best in lens design, but the lens obtained as a finished product is actually There is some aberration depending on surface accuracy, molding method, temperature condition at the time of molding, and the like.

FIG. 5 shows an example of a conventional objective lens.
In FIG. 5, reference numeral 21 denotes an objective lens, which has a predetermined spherical portion 22 constituting an effective diameter of the lens and a peripheral flat portion (so-called edge portion) 23 outside the effective diameter, and 24 is marked on the flat portion 23. As mark. The asmark 24 is marked with oil-based ink or the like on the peripheral flat portion 23 outside the effective diameter of the objective lens 21 so that the astigmatism direction of the objective lens 21 can be determined.

FIG. 6 shows the configuration of an optical system of an optical pickup. Reference numeral 11 denotes a hologram laser unit, 12 denotes a rising mirror, 13 denotes a disk, 14 denotes an information track direction, and 21 denotes the objective lens described above. is there. Here, the tracking servo is applied to the objective lens 21 for the optical disk so as to follow the information track, and the objective lens 21 always operates in a direction perpendicular to the information track direction 14. In other words, the lens is used in a state where off-axis astigmatism is increased.

FIG. 7 shows a wavefront aberration generated when a finite objective lens of a general optical pickup moves in a direction perpendicular to the optical axis, and astigmatism, coma and spherical aberration, which are aberration components thereof. , And higher order aberrations. As a result, the wavefront aberration worsens as the displacement is made off-axis, and it can be seen that most of the components are astigmatism. Therefore, in the optical pickup, in order to suppress astigmatism caused by displacement of the objective lens in the tracking direction, the rotation direction around the optical axis is adjusted, and the astigmatism of the lens and the astigmatism generated off-axis are adjusted. The objective lens is incorporated into the head so as to cancel out.

Specifically, conventionally, a mark for determining the direction of astigmatism is marked outside the effective diameter of the objective lens, and the objective lens is set so that the direction of the astigmatism is perpendicular to the information track direction. It had to be placed on the head. Here, the astigmatism direction refers to the major axis direction of the light spot near the focal point closer to the lens among the two focal points on the image point side of the objective lens having astigmatism.

[0007]

However, in order to specify the direction of astigmatism of the objective lens, the astigmatism of the lens is inspected for all the finished lenses, and the direction of the astigmatism is determined using oil-based ink or the like. In this case, a marking step is required (an as-marking step), which hinders the efficiency of the work process and the reduction of the process cost.

The present invention has been made in view of the above circumstances, and has been proposed by the applicant of the present invention in Japanese Patent Application No. Hei 6-317911. An object of the present invention is to provide a molding die for an objective lens and an objective lens for obtaining an inexpensive lens by omitting an asmarking step in molding an objective lens having a mold shape to which aberration is added.

[0009]

Means for Solving the Problems In order to solve the above problems, a molding die for an objective lens of the present invention is formed by molding a glass material or a resin material using a molding die apparatus .
For recording and reproducing information on information tracks formed on a disc
A molding die for an objective lens used in obtaining an objective lens to be used for a head , wherein the molding die has a predetermined non-uniformity with respect to the information track direction on an axis of a lens obtained as a finished product. It has a shape that adds astigmatism,
Further, a marking shape is added to the mold so that a mark for indicating the direction of astigmatism provided on the axis of the lens is transferred outside the effective diameter of the objective lens.

In the objective lens of the present invention, a predetermined astigmatism is added to the information track direction on the axis of the lens obtained as a finished product by molding using the molding die. In addition , a mark indicating the direction of astigmatism provided on the axis of the lens is formed outside the effective diameter of the lens .

[0011]

According to the present invention, the objective lens mold has a shape such that a predetermined astigmatism is added on the axis of a lens obtained as a finished product, and indicates a direction of the astigmatism. Since a mold that is processed so that the as-marked shape is transferred outside the effective diameter of the objective lens to be molded is used, the astigmatism direction is marked outside the effective diameter of the objective lens at the same time as molding, and the astigmatism direction is marked. By omitting the marking step, an inexpensive molded lens can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the molding die for an objective lens according to the present invention will be described in detail with reference to the drawings. FIG.
(A) and (b) are a sectional view and a perspective view of an upper mold of a lens mold according to an embodiment of the present invention, and FIG. 2 is a perspective view of an objective lens molded by the mold of FIG.

In FIG. 1, reference numeral 1 denotes a molding die;
, A lower mold 3 and a side body mold 4, and a lens is formed in a central portion 5 of the lower mold 3. The molded lens is the objective lens 6 shown in FIG. 2. The upper mold 2 and the lower mold 3 are respectively provided with a mirror surface portion 2a and a mirror surface portion 3a for forming a spherical portion 6a which is an effective diameter portion of the objective lens 6 to be molded, and the objective lens 6 The flat portions 2b and 3b forming the edge portion 6b are formed respectively. As shown in FIG. 1B, a mark shape (asmarking shape) for indicating the astigmatism direction of the objective lens 6 formed by the molding die 1 is formed on the flat portion 2b of the upper die 2. 7 are formed. FIG.
In the figure, reference numeral 8 denotes an asmark formed by the asmarking shape 7 of the molding die 1.

Here, the mirror surfaces 2a and 3a of the mold 1 are
The objective lens 6 has such a shape that predetermined astigmatism is added on the optical axis thereof, and the asmarking shape 7 is formed in the astigmatism direction A. Therefore, the astigmatism direction A of the objective lens 6 formed by the molding die 1 can be determined by the asmark 8 formed on the edge 6b at the time of molding.

The asmarking shape 7 is formed on the peripheral flat portion 2b of the upper mold 2, which is one of the molds 1,
For example, it can be obtained by processing into a rough surface by irradiating an electron beam. As a result, the rough surface portion of the asmarking shape 7 is transferred to the formed edge portion 6b of the objective lens 6, and the asmark 8 is formed.

According to this embodiment, by using the molding die 1 as described above, the asmark 8 is transferred simultaneously with the molding of the objective lens 6, so that the Can be molded. 3 and 4 show another embodiment. As shown in FIG. 3, in the peripheral flat portion 2b of the upper die 2 of the molding die 1, the astigmatism direction A of the mirror surface portion 2a of the upper die 2 is shown. Is formed as an asmarking shape 9 having a shape in which the portion of the mark is concavely removed. By molding with the mold 1 having such a shape, an asmark 10 having a convex shape can be formed as shown in FIG. The astigmatism direction of the objective lens 6 can be determined from the convex asmark 10, and the same effect as in the above-described embodiment can be obtained.

[0017]

As described above, the present invention provides a method for manufacturing a glass material or a glass material.
By molding the resin material using a molding machine,
For recording and reproducing information on information tracks formed on a disc
Used to obtain the objective lens for the head
A mold for a lens, wherein the mold has a shape such that predetermined astigmatism is added to the information track direction on an axis of a lens obtained as a finished product. And
And a molding die for the objective lens in which a marking shape is added to the molding die so that a mark for indicating the direction of astigmatism provided on the axis of the lens is transferred outside the effective diameter of the objective lens. As a result, a predetermined astigmatism is added on the axis of the lens obtained as a finished product, and a mark indicating the direction of the astigmatism is formed outside the effective diameter of the lens. An asmark for discriminating the direction of astigmatism can be transferred to the objective lens at the time of molding, so that a conventionally required asmarking step can be omitted, and a more inexpensive objective lens can be provided.

[Brief description of the drawings]

1A is a cross-sectional view of a molding die for an objective lens according to an embodiment of the present invention, and FIG.

FIG. 2 is a perspective view of an objective lens molded by the molding die.

FIG. 3 is a perspective view of an upper mold of an objective lens molding die according to another embodiment of the present invention.

FIG. 4 is a perspective view of an objective lens formed by the same mold.

FIG. 5 is a perspective view of a conventional objective lens for an optical disc.

FIG. 6 is a configuration diagram of an optical system of the optical pickup.

FIG. 7 is a characteristic diagram of off-axis performance of the objective lens for the optical disc.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Upper mold 2a Mirror surface part 2b Peripheral flat part 3 Lower die 3a Mirror surface part 3b Peripheral flat part 6 Objective lens 6a Spherical part 6b Edge 7 Asmarking shape 8 Asmark

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Claims (2)

(57) [Claims] An information formed on a disk is formed by molding a glass material or a resin material using a molding apparatus.
A molding die for an objective lens used for obtaining an objective lens used for a head for recording and reproducing information on an information track , wherein the molding die is mounted on an axis of a lens obtained as a finished product.
It has a shape such that a predetermined astigmatism is added to the information track direction , and is on the axis of the lens.
2. A molding die for an objective lens, wherein a marking shape is added to the molding die so that a mark for indicating a direction of astigmatism provided in the above is transferred outside an effective diameter of the objective lens. By wherein it is molded using a mold according to claim 1, wherein on the axis of the resulting lens as a finished product
With a predetermined astigmatism is added to the information track direction, the objective of the mark indicating the direction of astigmatism with on the axis of the lens is characterized in that it is formed in the effective diameter of the lens lens.