JP3092317B2 - Optical pickup - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for reading information stored in an optical disk.

[0002]

2. Description of the Related Art In recent years, optical disk devices have been widely used as external memory devices for computers or digital audio devices as large-capacity memory devices. The most important part in this optical disk device is a part for reading a signal from an optical disk, which is performed by an optical pickup. By the way, various systems are adopted for the optical pickup, and FIG. 3 shows an embodiment having the simplest configuration.

FIG. 3 shows a schematic configuration of a conventional optical pickup. In FIG. 3, reference numeral 1 denotes a lens for forming an image of a light beam 6 on a disk 5, and 2 denotes a semiconductor laser for irradiating the light beam 6. 3 is the reflected light 7 from the disk 5
Is a half mirror for guiding the light beam 6 of the semiconductor laser 2 onto the disk 5 and for guiding the reflected light 7 from the disk 5 to the photodetector 3.

At this time, the optical pickup needs to detect an error signal for focusing and tracking, but the photodetector 3 is divided into eight PD1 to PD8 as shown in FIG. Photodetector 3 for tracking
Above, the light beam 6 loses its tracking,
PD + PD2 + PD3 + PD to shift right or left
4 and the sum signal of PD5 + PD6 + PD7 + PD8, a signal dependent on tracking deviation is obtained, and a tracking error signal is obtained by a so-called push-pull method. For the focus, the sum signal of PD1 + PD5 + PD3 + PD7 and PD2 + P
By detecting the phase difference of the sum signal of D6 + PD4 + PD8, a focus error signal depending on the focus shift can be obtained by a so-called phase difference method.

[0005]

The problem of the optical pickup is to reduce the size and cost as much as possible, and a simple structure with a reduced number of parts is desired. In FIG. 3, it is technically possible to integrate the semiconductor laser 2 and the photodetector 3, and by placing them at the position of the original semiconductor laser 2, it can be expected that the half mirror 4 can be omitted. In this case, since the position of the photodetector 3 is the emission position of the light source, the return light from the disk 5 forms an image at the position of the photodetector 3, and a light beam having an appropriate diameter for obtaining an error signal is formed. In other words, an error signal cannot be obtained, that is, it is technically possible to integrate the semiconductor laser 2 and the photodetector 3 in order to reduce the size of the optical pickup. There is.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a compact optical pickup which can obtain an appropriate light beam on a light receiving surface even if a semiconductor laser and a photodetector are integrated. Aim.

[0007]

In order to achieve this object, the present invention provides an optical pickup comprising a lens having a plurality of spherical surfaces having different focal points, a photodetector, and a semiconductor laser.

[0008]

According to the optical pickup of the present invention, even if an optical pickup is constructed by integrating a semiconductor laser and a photodetector, the objective lens has two focal planes. Although an image is formed on the disk by the first focal plane, the reflected light from the disk irradiates a light beam to the photodetector by the second focal plane, so that a light beam diameter suitable for signal detection can be obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical pickup according to an embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic configuration of an optical pickup according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of a semiconductor laser and a photodetector integrated. 8 is FIG.
Is an objective lens having two focal planes for imaging a light beam, and 9 is an integrated module of a semiconductor laser chip 10 and a photodetector 11. Light beam 12 emitted from semiconductor laser chip 10 of integrated module 9
Is formed on the disk 13 by the center of the objective lens 8. The light beam 12 incident on the peripheral portion of the objective lens 8 does not form an image on the disk 13 and is scattered as light and does not participate in signal detection.

Next, the reflected light 14 from the disk 13 passes through the center of the objective lens 8 and forms an image on the center of the photodetector 11 and does not participate in error signal detection. Light passing through the peripheral portion hits a light beam on the photodetector 11 with an appropriate diameter, and focuses and focuses in the same manner as described in the conventional method in FIG.
The tracking error signal can be detected. As shown in FIG. 2, the integrated module 9 of the semiconductor laser chip 10 and the photodetector 11 is divided into eight parts as shown in FIG. Use space to attach. At this portion, the semiconductor laser chip 10 is attached vertically so that the light beam 12 is emitted perpendicularly to the detection surface of the photodetector 11, or the semiconductor laser chip 10 is attached laterally to the photodetector 11
Since the element is made of Si, a part of the element is cut into a mirror shape by etching, so that the light beam 12 is emitted vertically.

In the above description, the structure for changing the focal point between the central portion and the peripheral portion of the objective lens 8 has been described. Although various shapes are conceivable, such as having a lens surface, the effects are all the same.

[0013]

As is apparent from the above embodiment, the present invention can use a module in which a semiconductor laser chip and a photodetector are integrated by using an objective lens having two focal points in an optical pickup. This eliminates the need for a half mirror that was required in the conventional configuration, so that a very small optical pickup can be configured. In addition, cost reduction is possible because the number of parts is reduced at the same time as the size reduction.

Since the present invention does not use a part of the light beam due to its configuration, the utilization efficiency of the emitted light is considerably deteriorated. This is a major drawback in a writable optical disk device that requires a large amount of power, but a read-only optical disk does not require a large amount of power, so light utilization efficiency does not matter. Also cost is important,
Very useful in practice.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing main components of an optical pickup according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a photodetector section of the optical pickup according to the embodiment of the present invention.

FIG. 3 is a schematic side view showing main components of a conventional optical pickup.

FIG. 4 is an explanatory diagram of a conventional photodetector.

[Explanation of symbols]

 Reference Signs List 8 Objective lens 9 Integrated module 10 Semiconductor laser 11 Photodetector

Claims (1)

(57) [Claims] 1. An objective lens, a photodetector, and a semiconductor laser.
To read an optical disk on which information is stored
An optical pickup, wherein the objective lens has a different focus.
A plurality of spherical surfaces, and the spherical surface is
Make the focus different between the center of the lens and the
Is different in the horizontal direction of the objective lens, or
In the four diagonal directions of the laser,
The light beam emitted from the laser
Focus on the recording surface of the optical disk
The reflected light from the optical disk
Let it enter the other spherical surface of the object lens and guide it to the photo detector
So that the photodetector and the semiconductor laser are integrated
An optical pickup characterized by forming an integrated module .