JPH01130331A - Focus detection device for optical pickup - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Technical field The present invention relates to a focus detection device for an optical pickup.

BACKGROUND OF THE INVENTION Generally, in an optical pickup for recording and reproducing information on an optical disk, etc., a minute spot is irradiated onto the optical disk through an objective lens, and information is reproduced based on the reflected light. At this time, it is necessary to be in focus for good recording and playback, so it is necessary to detect the focus position to see if it is in focus and apply servo control so that the focus error signal is always 0. Common.

Here, the focus error signal is generally detected by receiving the light beam reflected from the optical disk by a light receiving element such as a 2-split 74-split light beam via a focus error detection optical system.

For example, there is a focus detection method using a knife edge method as shown in FIGS. 7 and 8. First, light is emitted from a laser light source, for example, a semiconductor laser 1. The laser beam is made into a parallel beam by a coupling lens 2, passes through a beam splitter 3 and a λ/4 plate 4, and is focused into a minute spot and irradiated onto an optical disk (optical information recording medium) 6 by an objective lens 5. . After the reflected light from the optical disk 6 passes through the objective lens 5 and the λ/4 plate 4 again, it is separated from the incident light by the beam splitter 3 and heads toward the detection system.

First, a condensing lens 7 is provided, and a two-split light receiving element 8 for focus detection is provided on the optical axis of the condensing lens 7. A knife 9 having a prism structure is provided between the condensing lens 7 and the light receiving element 8, extending half way into the convergent optical path and blocking a part of the light beam. Note that a light receiving element for detecting a track signal is provided on the side reflected by the knife 9.

Here, when the objective lens 5 is in focus, Fig. 14 (
As shown in a), the convergence position of the detection light reflected from the optical disk 6 and converged by the condenser lens 7 is at the center between the light receiving elements 8a and 8b of the two-split light receiving element 8, and the light receiving elements 8a,
A is the detection output of 8b.

When B is set, the setting is such that A=B.

Therefore, when the objective lens 5 and the optical disk 6 are out of focus, for example, when the optical disk 6 moves away, the convergence position by the condenser lens 7 moves to a position closer to the front than the light receiving element 8, as shown in FIG. 14(b). To do so, Naifetsuji 9
Detection outputs A and B of the light receiving elements 8a and 8b become A
>B, it is detected that a focus error has occurred. Then, the objective lens 5 is driven by the actuator so that A=B. Conversely, when the optical disk 6 approaches, the convergence position by the condenser lens 7 moves to a position behind the light receiving element 8 as shown in FIG. Detection output A.

B has a relationship of A<B, and it is detected that a focus error has occurred.

However, in the case of the conventional knife focus error detection method, if the optical components move due to changes in the atmosphere such as temperature or humidity, or due to changes over time,
Accurate focus error detection becomes impossible. for example,
If the °C beam splitter 3 is displaced in the direction of arrow α in FIG.
is not 0 and is considered to be out of focus.

This also applies when the light receiving element 8 itself is displaced in the direction of the arrow β.

In other words, if the optical component moves or is displaced due to a change in the atmosphere or the like, the initial setting value regarding focus error detection will be shifted as an error, making it impossible to perform accurate focus control.

Purpose The present invention was made in view of the above points.
It is an object of the present invention to provide a focus detection device for an optical pickup that can accurately detect a focus error without being affected by changes in optical components due to changes in humidity or changes over time.

Structure In order to achieve the above object, the present invention converges and irradiates a light beam from a laser light source as a minute spot onto an optical information recording medium through an objective lens, and detects a focus error signal based on the reflected light from the optical information recording medium. In a focus detection device for an optical pickup that performs One condensing lens is provided, and a light receiving element that receives the convergent light from the condensing lens, which is divided into multiple parts in the direction of division of the two light beams, is positioned on the optical axis away from the focal point of the condensing lens. It is characterized in that it is arranged and provided.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5. The same parts (basic structure of the optical pickup) as those shown in FIG. 7 are indicated using the same reference numerals. In this embodiment, first, two beam splitters 13 and 14 are used as light splitting elements to split a parallel light beam 12 reflected from an optical disk 6 and separated from the incident light by a beam splitter 3 into two mutually parallel light beams 12a and 12b. is provided. These beam splitters 13 and 14 are integrated. Also, two light beams 12a are generated by these beam splitters 13 and 14.

One collection lens 15- is provided in the traveling direction of the light beam 12b to allow both of these two light beams 12a and 12b to enter. Here, the optical axis 16 of the condenser lens 15 is set at the center between the beam splitters 13 and 14. One light receiving element 17 for detecting a focus error is provided at the converging side position of such a condensing lens 15. This light receiving element 1
7 is arranged so that its center is located on the optical axis of the condensing lens 15, but it is arranged at a position on the near side away from the focal point of this condensing lens 15, and the convergent light based on the two light beams 12a and 12b is 18a and 18 are configured to be able to receive light. The light-receiving element 17 is multi-divided, for example, into four, in the direction in which the two light beams 12a and 12b are divided, and has four light-receiving areas A to D. Then, the focus error signal is based on the outputs of these light receiving areas A-D, and is calculated as (A+D)-(
B+C).

Here, the light receiving state in the focused state is shown in FIGS. 2 and 3(a). That is, in the focused state, the condenser lens 1
The two light beams 12a and 12b for 5 are parallel light beams, and are converged by the condenser lens 15 to become each convergent beam 18a.
, 18b is a light receiving area A.

The light is received in the middle of B, and in the middle of light receiving areas C and D, respectively. Therefore, the focus error signal becomes (A+D)-(B+C)=O.

On the other hand, consider a case where the image deviates from the in-focus state. For example, when the optical disk 6 moves away, the beam splitters 3, 13 .
Two light beams 12a and 1 enter the condensing lens 15 through 14.
As shown in FIG. 4(a), the light beam 2b is not a parallel light beam but a convergent light beam. On the other hand, when the Y6 disk 6 approaches, the two beams 12a, 2b entering the condenser lens 15 through the beam splitters 3, 13, 14 become divergent as shown in FIG. 47(b). Two such convergent or divergent forms
The light beams 12a and 12b pass through the condenser lens 15 and reach the light receiving element 1.
When the light is converged and received on 7, the spot diameter and position are different from those when the beam is parallel due to the difference in optical path length, and each is shown in Fig. 5 (a).
) The light receiving state is as shown in (b).

That is, when the optical disk 6 moves away, (A+D)-(B+C)<O, as can be seen from FIG. 5(a). On the other hand, when the optical disk 6 approaches, as can be seen from FIG. 5(b), (A+D)-(B+C)>0.

In this way, a focus error signal is detected.

Now, let us consider the focus error detection operation when the optical components change due to changes in the atmosphere, changes over time, etc. in the focused state. For example, suppose that the beam splitter 3 or beam splitter 13, 14 is rotationally displaced in the direction of the arrow α in FIG. 1 in the focused state. Due to such displacement, the convergent lights 18a and 18b converged on the light receiving element 17 are shifted to the left as a whole, for example, as shown in FIG. 3(b).

However, in this case, the two light beams 1.2a and 12b, which are parallel light beams that have passed through the beam splitter 3 or 13.14, have the same amount of deviation, and the amount of deviation of the convergent beams 18a and 1.8b on the light receiving element 17 is the same. are also equal. Therefore, in the case of the arithmetic processing of (A+D)-(B+C), the amount of deviation is canceled out, and it is detected that (A+D)-(B10)=O1, that is, the in-focus state. this is,
The same applies when the light receiving element 17 itself is displaced in the direction of the arrow β perpendicular to the optical axis.

Note that in this example, a four-divided light receiving element 17 was used; however,
For example, as shown in FIG. 6, a light receiving element 19 consisting of three light receiving areas A, B, and C may be used. In this case, the focus error signal is detected by (A10)-B.

Effects As described above, the present invention splits the parallel light beam reflected from the optical information recording medium into two mutually parallel light beams using a light splitting element.
After splitting, the two beams are made to enter one condensing lens symmetrically with respect to the optical axis, and the two converged beams are received by a light receiving element that is multi-divided in the direction in which the two beams are divided. - Even if fluctuations or displacements occur in optical components due to changes in humidity or changes over time, it is possible to accurately detect a focus error signal in a state where the displacements are canceled out and removed.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an optical system showing an embodiment of the present invention, Fig. 2 is a side view showing the state of light flux when in focus, Fig. 3 is a plan view showing the state of light reception when in focus, and Fig. 4 is a side view showing the state of the light flux when it is out of focus, FIG. 5 is a plan view showing the light receiving state, FIG. 6 is a plan view showing a modified example, and FIG. 7 is an optical system configuration showing a conventional example. 8 are side views showing the detection operation. DESCRIPTION OF SYMBOLS 1... Semiconductor laser (laser light source), 5... Objective lens, 6... Optical disk (optical information recording medium), 12...
・・Parallel luminous flux, l 2 a, l 2 b-2 luminous flux,
13, 14... Beam splitter (light splitting element), 1
5... Condensing lens, 16... Optical axis, 17... Light receiving element, ¥5.1 Figure 3 Z country] 33 Figure r5a, l0b 14 Figure 37, l Figure procedure amendment export) 1988 March 1st, 2004 "04゛1"111' Suit 1, Indication of the case, Patent Application No. 62-288981 2, Name of the invention: Focus detection device for optical pickup Address: 1-3-6-4 Nakamagome, Ota-ku, Tokyo , representative
There are 107 people. Amendment to Japanese Patent Application No. 62-288981 Regarding this application, the description in the specification is amended as follows. 1, page 3, line 18 to page 4, line 1, “14th
2. Correct "Fig. 14" in the 8th line of page 4 to "Fig. 8". 2. Correct “Figure 14” on page 4, line 15 to “819<.

Claims (1)

[Claims] In a focus detection device for an optical pickup, the light beam from a laser light source is focused on an optical information recording medium as a minute spot through an objective lens, and a focus error signal is detected based on the reflected light from the optical information recording medium. A light splitting element is provided that splits the parallel light beam reflected from the information recording medium into two mutually parallel light beams, and one condenser lens is provided through which the two light beams from these light splitting elements are incident symmetrically on the optical axis. A light-receiving element that receives convergent light from the condensing lens that is divided into multiple parts in the direction of dividing the two light beams is provided at a position on the optical axis that is out of the focal position of the condensing lens. Focus detection device for optical pickup.