JPH08281819A - Mold for objective lens, and the lens - Google Patents

Abstract

PURPOSE: To obtain a low-cost molded lens by omitting the marking step of designating the disposing direction of an objective lens in the step of manufacturing an optical pickup. CONSTITUTION: The mold comprises molds 2 and 3 of the shapes for adding a predetermined astigmatism on the axis of a lens obtained as a complete product in the mold 1 for molding glass or resin material, a marking shape 7 so added to the mold 1 as to transfer the mark for indicating the astigmatism direction A out of the effective aperture of the lens, and a mark 8 transferred to identify the direction at the side 6b of a board out of the effective diameter of the lens 6 after molding.

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 projecting a light spot on an optical disc having an information track recorded with high density signals to optically read information, and a molding die thereof. The present invention relates to a molded objective lens.

[0002]

2. Description of the Related Art Generally, as a method of manufacturing a lens using a molding die apparatus, a molding material (hereinafter referred to as a lens glass material) obtained by primary processing is put into a molding die to carry out secondary molding (compression). Molding) and a method of injecting a molten molding material into a molding die and molding (injection molding).
In the objective lens molded by these manufacturing methods, the aberration is generally corrected by the lens design so that the performance on the optical axis is the best, but in reality, the lens obtained as a finished product is There is some aberration depending on the surface accuracy, the molding method, the temperature condition during 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 surface portion 22 forming the lens effective diameter and a peripheral flat portion (so-called edge portion) 23 outside the effective diameter, and 24 is marked on the flat portion 23. It is Asmark. 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 discriminated.

FIG. 6 shows a configuration diagram of an optical system of an optical pickup. 11 is a hologram laser unit, 12 is a raising mirror, 13 is a disk, 14 is an information track direction, and 21 is the above-mentioned objective lens. is there. Here, the objective lens 21 for the optical disk is subjected to tracking servo so as to follow the information track, and always operates in the direction perpendicular to the information track direction 14. That is, the lens is used in a state where the astigmatism off-axis 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 its aberration components, astigmatism, coma and spherical aberration. , And higher-order aberrations. As a result, it can be seen that the wavefront aberration becomes worse as it is displaced off-axis, and most of its 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 astigmatism of the lens and the astigmatism generated off-axis are adjusted by adjusting the rotation direction around the optical axis. The objective lens is incorporated in the head so that and cancel each other.

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

[0007]

However, in order to specify the astigmatism direction of the objective lens, the astigmatism of the lens is inspected with respect to all the finished lenses, and the astigmatism direction is determined by the oil-based ink or the like. This requires a step of marking in (as marking step), which hinders the efficiency of work steps and the reduction of process cost.

The present invention has been made in view of the above situation, and a predetermined astigmatism on the axis of the objective lens, which was previously proposed by the applicant of the present application in the patent application of Japanese Patent Application No. 6-317911, was proposed. Provided are an objective lens molding die and an objective lens thereof, which are used for molding an objective lens having a mold shape to which aberration is added and which can obtain a lens at a low cost by omitting an asmarking step.

[0009]

In order to solve the above problems, the objective lens molding die of the present invention is used for obtaining a lens by molding a glass material or a resin material using a molding die device. A molding die for an objective lens, wherein the molding die has a mold shape such that a predetermined astigmatism is added on the axis of a lens obtained as a finished product, and the astigmatism direction is A marking shape is added to the molding die so that the mark for indicating is transferred outside the effective diameter of the objective lens.

Further, the objective lens of the present invention is molded by using the above-mentioned molding die, whereby a predetermined astigmatism is added on the axis of the lens obtained as a finished product, and the astigmatism direction thereof is added. Is a mark formed outside the effective diameter of the lens.

[0011]

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

[0012]

EXAMPLES Examples of the objective lens forming die of the present invention will be described in detail below with reference to the drawings. FIG.
2A and 2B are a cross-sectional view of a lens molding die and a perspective view of an upper die in one embodiment of the present invention, and FIG. 2 is a perspective view of an objective lens molded by the molding die of FIG.

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

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

The asmarking shape 7 is formed on the peripheral flat portion 2b of the upper die 2 which is one of the molding dies 1,
For example, it can be obtained by irradiating an electron beam to form a rough surface. As a result, the rough surface portion of the asmarking shape 7 is transferred to the edge portion 6b of the formed 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 at the same time as the molding of the objective lens 6, so that the objective lens 6 is not required to perform the asmarking step. 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 changed. The asmarking shape 9 is formed by removing the portion of the concave shape into a concave shape. By molding with the molding die 1 having such a shape, the convex shape of the asmark 10 can be formed as shown in FIG. The astigmatism direction of the objective lens 6 can be discriminated by the convex asmark 10, and the same effect as that of the above-described embodiment can be obtained.

[0017]

As described above, the present invention has a mold shape in which a predetermined astigmatism is added on the axis of the lens obtained as a finished product, and the astigmatism is obtained. A lens obtained as a finished product by molding using a molding die for an objective lens in which a marking shape is added to the molding die so that the mark for indicating the direction is transferred to the outside of the effective diameter of the objective lens. Since a predetermined astigmatism is added on the axis of and the mark indicating the astigmatism direction is formed outside the effective diameter of the lens, the astigmatism direction is discriminated in the objective lens when molding the lens. It is possible to transfer the asmark for the purpose, omit the asmarking step which has been conventionally required, and provide a cheaper objective lens.

[Brief description of 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. 1B is a perspective view of the same die.

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

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

FIG. 4 is a perspective view of an objective lens molded by the molding die.

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 disk.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. A molding die for an objective lens, which is used when a lens is obtained by molding a glass material or a resin material by using a molding die apparatus, wherein the molding die is an on-axis of a lens obtained as a finished product. Has a mold shape to which a predetermined astigmatism is added, and the marking shape is formed on the molding mold so that the mark for indicating the astigmatism direction is transferred to the outside of the effective diameter of the objective lens. A molding die for an objective lens, in which is added. 2. A mark that indicates a direction of the astigmatism while a predetermined astigmatism is added on the axis of the lens obtained as a finished product by molding using the molding die according to claim 1. The objective lens is formed outside the effective diameter of the lens.