JPS60234243A - Optical pickup - Google Patents

Abstract

PURPOSE:To use just a piece of a detection lens and to omit a lens barrel for reduction of cost by using a lens containing the spherical and cylindrical surfaces or the cylindrical surfaces having power meridians orthogonal to each other on both sides together with a positioning projection to a detecting optical system. CONSTITUTION:A detection lens 9 of a detecting optical system is made of glass or resin and contains the cylindrical and spherical surfaces or cylindrical surfaces having power meridians orthogonal to each other on both sides 9a and 9b. Furthermore a projection 9c for positioning of the revolving direction is provided at a part of the lens 9. Thus the function so far secured with two lenses can be attained with just a single lens. Thus the high reliability is obtained without producing an angle error of the power meridians nor a distance error between lenses. This can omit a lens barrel and reduces the cost of an optical pickup.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical pickup that optically reads information by projecting a light spot' onto an information track on which a high-density digital signal is recorded on a disk.

Conventional configuration and its problems The astigmatism method has conventionally been most commonly used as a method for detecting a focus error that occurs when light emitted from a laser is focused onto a disk by an objective lens.

As shown in FIG. 1, a convex lens 3 and a cylindrical lens 4 are arranged on the optical path 2 that guides recorded information from the disk 1 to the light receiving element 5, and the relative positions of the disk 1 and the objective 1/lens 2 are This method generates astigmatism in the light-receiving element 5-1- depending on the relationship. Specifically, as shown in Fig. 2, if the disk 1 and the objective lens are too close, or if the objective lens is at the a1 focal position, When b1 is far away, the spot shape of the light receiving element 6''- for each of C becomes as shown in the figure, and the focus error can be detected by calculating (6a+5b)-(5cm1-6d). When the detection optical system is placed in a parallel light beam, the detection optical system may be a combination of a convex lens 3 and a cylindrical lens 4 as shown in FIG. 1, or a combination of cylindrical lenses 4a, 4b (as shown in FIG. 3). A combination of two sheets arranged so that the z generating lines are orthogonal to each other is 1. When placed in a convergent beam, the fourth
As shown in the figure, a combination of a concave lens 7 and a cylindrical lens 4 has been conventionally used.

In FIG. 3, the concave lens Y is used because the one-focus error detection sensitivity is determined by the combined focal length of the collimating lens 8, concave lens 7, and cylindrical lens 4, and the vertical magnification of the focal length of the focus lens. This is to increase the vertical magnification by increasing the combined focal length, and to increase the distance between the respective beams on the light receiving element 5 when the three-beam method is used as the tracking error detection method.

However, in these examples, two lenses are used in the detection optical system, which increases the cost. In addition, the outer shape of the convex or concave lens is usually circular, and the outer shape of the cylindrical lens is square. , circular and rectangular, straddle,
Square and Square ffi The lens barrels that are assembled at regular intervals also have a very complicated shape, requiring a large number of assembly man-hours. Since the cylindrical lens is not rotationally symmetrical with respect to the optical axis, it is necessary to provide a protrusion on the lens barrel for positioning in the rotational direction or to process a groove.

Purpose of the Invention The present invention solves the above-mentioned problems and provides a low cost I
- Provides high performance optical pickup.

Structure of the Invention The present invention has a spherical surface and a cylindrical surface, or a cylindrical surface whose generatrix directions are perpendicular to each other, on both sides, and a convex portion or a concave portion k11111 for positioning in the rotational direction around the optical axis.
By using a lens made of a single material on the surface for the detection optical system, it is possible to reduce the cost of parts and the number of assembly steps, while also improving assembly accuracy.

Description of examples FIG. 5 shows an embodiment of the present invention.

The detection lens 9 is made of glass or resin, and includes 9a,
9b is cylindrical and spherical, or both are cylindrical.

If the detection lens 9id is made of glass, it can be made without a hub, and if it is made of resin, it can be made by molding.

In the astigmatism method, the two lenses of the detection optical system are
.

Distance accuracy and angular accuracy of each generatrix are very important when using two cylindrical lenses, and with conventional combination lenses, there are problems due to errors in the thickness of the individual lenses and errors in the processing accuracy of the lens barrel. This has caused errors in the distance between the lenses and misalignment of the generatrix lines during assembly, but in this example, the functions of two lenses are achieved with one lens, so there is no angular error in the generatrix lines or misalignment between the generatrix lines. There is no distance error and high reliability can be obtained.

By providing the protrusion 9Ci on a part of the detection lens, positioning in the rotational direction around the optical axis can be performed at the same time.

Furthermore, in the case of resin molding, in addition to the groove 10a for positioning in the rotational direction, grooves 10b for adjusting the detection lens 10 along the optical axis direction may also be molded at the same time, as shown in FIG. As described above, in this embodiment, the two lenses are integrated, and the grooves for positioning and adjustment in the rotational direction are also created at the same time, which greatly reduces the cost of the lens. There is no need for a lens barrel, and assembly accuracy can be greatly improved.

Effects of the Invention As described above, the present invention reduces the number of lenses in the detection optical system, which conventionally used two lenses, to one and also has the function of a lens barrel. (1) The cost of the lens can be reduced.

■ Eliminates the need for a lens barrel.

■ It is possible to improve assembly accuracy.

This effect can be obtained.

[Brief explanation of drawings]

Fig. 1 is a side view of a conventional example, Fig. 2 is a diagram of the principle of the astigmatism method, Figs. 3 and 4 are side views of a conventional example, and Figs. 6 and 6 are an embodiment of the present invention. FIG. 1. Disk, 2. Objective lens, 3. Convex lens, 4. Cylindrical lens, 6.. Light receiving element, 6..
Half mirror 17...Concave lens, 8-Collimating lens, 9...Mountain detection lens. Name of agent: Patent attorney Toshio Nakao To one person
(Figure 3, Figure 4, Figure 5, C)

Claims (1)

[Claims] On the optical path that guides recorded information from the disk to the light receiving element, one side has a cylindrical shape and the other side has a spherical shape or a cylindrical shape with a generatrix direction perpendicular to the generatrix of the cylindrical shape,
1. An optical pink amplifier characterized in that a single-use lens having a convex portion or four portions for positioning in a rotational direction around an optical axis is disposed on the side surface.