JPS63183631A - Focusing error detector - Google Patents

Abstract

PURPOSE:To execute a stable focusing control by providing a collimator lens on a position where the symmetry property to an axis orthogonal to a guide track is not influenced by a lens aberration, of a circuit pattern in a beam spot projected to a photodetector. CONSTITUTION:In a beam spot 52 projected to a 4-split photodetector 27, a part 53 which becomes a shadow is generated due to a diffraction by a guide track 23c. Even if this diffracted pattern 53 is in a focused state, a position relation to an information track 23b of an optical disk 23 is shifted. However, when the position is set so that an aberration of a collimator lens 22a and an objective lens 24a is negated, by turning a collimator lens unit 22, the pattern 53 becomes symmetrical to a boundary line Y-Y, namely, a state that no crosstalk is generated, even if the position relation of a beam spot 51 and the information track 23 is in any state. That is to say, by specifying the position relation of the guide track 23c, the collimator lens 22a and the objective lens 24a, a focusing control can be executed stably.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to recording information using an information recording disk, such as an optical disk or a magneto-optical disk, which is provided with concentric or spiral information tracks and guide tracks. The present invention relates to a focusing error detection device used in an optical information detection device for reproduction, etc.

[Conventional technology]

For example, as shown in FIG. 5, a conventional focusing error detection device includes a semiconductor laser 1 as a light source, a collimator lens 2 that converts the light beam emitted from the semiconductor laser 1 into a parallel light beam, and an information recording disk 3 that converts the parallel light beam into a parallel light beam. an objective lens 4 that collects the light to form a beam spot and takes in the reflected light flux reflected by the information recording disk 3; and a beam splitter 5 that changes the direction of the reflected light flux taken in by the objective lens 4; An optical system 6 consisting of a converging lens 6a and a cylindrical lens 6b, which images a beam spot using the reflected light flux as an astigmatic ray flux, and a distance of 45'' from the generatrix of the cylindrical lens 6b.
It has light-receiving sections 7a, 7b, 7C, and 7d divided into four parts in a square shape by two boundary lines in the direction, and receives the beam spot imaged by the optical system 6 and records information depending on the image formation state. It consists of a four-division photodetector 7 that detects focusing errors in the beam spot formed on the disc 3.

The information recording disk 3 has an information track 3b and a guide track 3c formed in concentric or spiral grooves on a substrate 3a made of a light-transmitting material such as glass, and further includes an amorphous alloy of rare earth and transition metal. An information recording medium 3d made of a thin film or the like is coated by vapor deposition, sputtering, or the like to enable high-density recording and reproduction.

Next, the principle for detecting a focusing error of the beam spot formed on the information recording disc 3 will be explained below.

First, the four light receiving parts 7a, 7b, 7 of the 4-split photodetector 7
The amount of light received at c and 7d is 5a-8b-3c-3d, respectively.
shall be. Also, the focusing degree f of the beam spot formed on the information recording disk 3 is (Sa+Sc) (Sb+Sd
).

Then, at the time of focusing, the beam spot 12 projected onto the four-split photodetector 7 becomes circular, as shown in FIGS. 6(a) and 6(b), so that the amount of light received by the four light receiving sections 5a
-3b-3c-5d are equal to each other. Therefore, the focusing degree f=(Sa+5c)−(Sb+sd) becomes O.

Furthermore, as shown in FIG. 6(c), when the distance between the information recording disk 3 and the objective lens 4 is short, the beam spot 12 projected onto the four-split photodetector 7 is as shown in FIG. 6(d). As shown, it is an ellipse whose long axis is in a direction parallel to the generatrix of the cylindrical lens 9. Therefore, the degree of focus f = (Sa
+Sc) (Sb+Sd) becomes negative.

On the other hand, as shown in FIG. 6(e), when the distance between the information recording disk 3 and the objective lens 4 is long, the beam spot 12 projected onto the four-split photodetector 7 is ), the direction a perpendicular to the generatrix of the cylindrical lens 9
It becomes an ellipse with 0 as the major axis. Therefore, the degree of focus f = (
Sa+Sc)-(Sb+3d) becomes positive.

Therefore, the above focus degree f= (Sa+5c)-(3b
+Sd) as a focusing error signal, it can be determined whether the distance between the information recording disk 3 and the objective lens 4 is appropriate, or whether it is long or short, depending on the sign or negative of the value.

Incidentally, in the beam spot 12 projected onto the four-split photodetector 7, a shadow portion (hereinafter referred to as a diffraction pattern) 13 is generated due to diffraction by the guide track 3c. Even when the diffraction pattern 13 is in focus as shown in FIGS. 6(a) and (b), the diffraction pattern 13 is
) (e) Due to the misalignment of the positional relationship between the beam spot 11 formed on the information recording disc 3 and the information trunk 3b of the information recording disc 3, as shown in (b) and (d) of FIG. 7, respectively.
As shown in (f), it changes.

When the collimator lens 2 and the objective lens 4 have no aberrations, the change in the diffraction pattern 13 is caused by the change in the information recording disk 3.
The shape is symmetrical with respect to an axis corresponding to a direction orthogonal to the guide track 3c. Therefore, the boundary line Y-Y between the light receiving parts 7a and 7b and 7C and 7d of the 4-split photodetector 7
However, if the four-split photodetector 7 is arranged so as to be aligned with the axis corresponding to the direction perpendicular to the guide track 3C, the diffraction pattern 13 will be any of the shapes shown in FIGS. Even if the focusing degree f= (Sa+Sc) (Sb+
Sd) becomes O, and it can be determined that the image is in focus.

[Problem that the invention seeks to solve]

However, in the conventional system described above, if the collimator lens 2 and the objective lens 4 have aberrations, the information recording disk 3
The positional relationship between the information track 3b and the beam spot 11 formed on the information recording disk 3 is shown in FIGS.
When shifted as shown in e), Fig. 8(b) (
d) As shown in (f), the symmetry of the diffraction pattern 13 with respect to the axis corresponding to the direction perpendicular to the guide track 3C of the information recording disc 3 may be impaired (hereinafter referred to as crosstalk). Focusing degree f=(Sa+Sc
) (Sb+Sd) even when in focus,
For example, the value in FIG. 8(b) is positive, the value in FIG. 8(d) is 0, and the value in FIG. 8(f) is negative.

Therefore, as shown in FIG. 9, even though the distance between the information recording disk 3 and the objective lens 4 is close to the in-focus state,
There is a problem in that the focusing error signal fluctuates greatly due to minute changes in distance, and focusing control may become unstable.

Therefore, by rotating the objective lens 4, the aberrations of the objective lens 4, the collimator lens 2, etc. can cancel each other out, and the crosstalk can be reduced.However, in general, the objective lens 4 and the information recording Since the distance from the medium 3 is only a few inches, it is very difficult to adjust the rotational position of the objective lens 4 and to fix it after adjustment while monitoring the focusing error i. Further, since the objective lens 4 is provided with many parts such as driving devices for focusing and tracking, it is difficult to adjust the rotation without affecting the accuracy of these parts.

[Means for solving problems]

In order to solve the above problems, the focusing error detection device according to the present invention includes a light source, a collimator lens that converts the light beam emitted from the light source into a parallel light beam, and an information track and a guide trunk that converts the parallel light beam into a parallel light beam. an objective lens that condenses the light onto the information recording disk to form a beam spot, and captures the reflected light flux reflected by the information recording disk; and an optical system that forms an image of the beam spot from the reflected light flux captured by the objective lens. and a photodetector that receives the imaged beam spot with a plurality of divided light receiving parts and detects a focusing error of the beam spot formed on the information recording disk based on the image formation state. In the apparatus, the symmetry of the diffraction pattern generated in the beam spot projected on the photodetector with respect to an axis corresponding to a direction orthogonal to the guide track is reduced to the extent that it is affected by aberrations of the collimator lens and the objective lens. It is characterized by a collimator lens installed at the moving position.

[For production]

Due to the above configuration, a diffraction pattern may occur in the beam spot projected on the photodetector due to diffraction by the guide track, or a deviation in the positional relationship between the beam spot formed on the information recording disk and the guide track may occur. By,
Even if the above-mentioned diffraction pattern changes, the symmetry of this diffraction pattern with respect to the axis corresponding to the direction orthogonal to the guide trunk is not impaired by the effects of aberrations of the collimator lens and the objective lens, so that the focusing error signal is Do not cause a decline in quality (,
Focusing errors can be detected stably.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

As shown in FIG. 1, the focusing error detection device includes a semiconductor laser 21 that is a light source, and a collimator lens 2 that converts the light beam emitted from the semiconductor laser 21 into a parallel light beam.
2a, and an objective lens 24a that focuses a parallel light beam onto an optical disk 23, which is an information recording disk, to form a beam spot, and captures a reflected light beam reflected by the optical disk 23. unit 24, a beam splitter 25 that changes the direction of the reflected light beam taken in by the objective lens 24a, and a converging lens 26a that focuses the reflected light beam whose direction has been changed into an astigmatism beam spot.
and an optical system 26 consisting of a cylindrical lens 26b.
and a four-division photodetector 27 which receives the beam spot imaged by the optical system 26 and detects a focusing error of the beam spot formed on the optical disk 23 based on the image formation state.

The collimator lens unit 22 includes a housing 28
It is rotatably provided in a recess 28a provided in the recess 28a, and is held by a presser spring 29.

The optical disk 23, which is an information recording disk, is formed on a substrate 23a made of a light-transmitting material such as glass, and has a substrate 23a made of a light-transmitting material such as glass.
Information tiger in a groove of 8 depth.

A guide track 23b and a guide track 23c are formed, and an information recording medium 23d made of an amorphous alloy thin film of rare earth and transition metal is coated by vapor deposition, sputtering, etc. to enable high-density recording and reproduction. .

Furthermore, the 4-split photodetector 27 includes a cylindrical lens 2
6b, and the optical disc 2
It has light receiving parts 27a, 27b, 27c, and 27d divided into four in a square shape by boundary lines x-x-y-y corresponding to directions parallel and perpendicular to the guide track 23c of No. 3.

On the other hand, as shown in FIG. 2, the objective lens unit 24 operates in the radial direction of the optical disc 23 as indicated by arrow A (hereinafter referred to as the tracking direction) and in the direction perpendicular to the optical disc 23 as indicated by arrow B (hereinafter referred to as the focus direction). )
It is designed to be driven by That is, a focus magnetic circuit consisting of a focus magnet 32, a focus yoke 33, and a focus magnetic gap 34 for driving in the focus direction is formed inside one end of the cylindrical fixed support 31. ing. Further, near the other end of the fixed support body 31, a tracking magnetic circuit is formed by a pair of tracking magnets 35 facing each other.

Inside the fixed support body 31, a rubber-like elastic body 36...
・Focus direction movable parallel spring 37 backed by...
An intermediate support body 38 is provided which is swingably supported. A focusing coil 39 is provided at the end of the intermediate support 38 to be inserted into the focusing magnetic gap 34 with a predetermined gap maintained therebetween.

Furthermore, inside the intermediate support body 38, an objective lens barrel 4 is swingably supported by tracking direction movable parallel springs 41, 41 backed by rubber-like elastic bodies 40, 40.
2 is provided. This objective lens barrel 42 has tracking coils 43, 43, which are close to the tracking magnetic magnets 35, 35 attached to its side wall, and a lens holder 44, which holds the objective lens 24a, at one end. On the other hand, a counterbalance weight 45 is provided on the other end side.

゛In the above configuration, as shown in FIGS. 3(b), 3(d), and 3(f), there is a shadow in the beam spot 52 projected on the 4-split photodetector 27 due to diffraction by the guide track 23C. (hereinafter referred to as a diffraction pattern) 53
occurs. Even when the diffraction pattern 53 is in focus, the beam spot 51 formed on the optical disc 23 and the information track 23b of the optical disc 23 are different from each other, as shown in FIGS. 3(a), (c), and (e). It changes depending on the positional relationship. However, collimator lens unit 2
By rotating the lens 2 and adjusting and setting so that the aberrations of the collimator lens 22a, objective lens 24a, etc. Beam spot 51 and information track 23b
Even in the case of the positional relationship with the boundary line Y, the diffraction pattern 53
-It becomes a symmetrical shape with respect to Y. In other words, no crosstalk occurs.

Therefore, the four light receiving sections 27a and 2 of the 4-split photodetector 27
The amount of light received at 7b, 27c, and 27d is 5a-3b, respectively.
−Sc−3d, and the focusing degree f of the beam spot 51 formed on the optical disc 23 is (Sa+5c)−(sb+
3a), this focusing degree f is always 0 when in focus, regardless of the positional relationship between the beam spot 51 and the information track 23b.

Therefore, as shown in FIG. 4, if the distance between the optical disc 23 and the objective lens 24a is close to the in-focus state, the in-focus state can be reliably detected by the positive or negative of the focus degree f, and stable focusing control can be performed. It can be carried out.

In general, the collimator lens unit 22 is not close to the optical disk 23 that rotates at high speed, and unlike the objective lens unit 24, it is not provided with many parts such as a driving device, so the above adjustment is easy. It can be carried out.

Note that once the rotational position of the collimator lens unit 22 is adjusted, there is no need to change it, so after the adjustment, it may be fixed to the housing 28 together with the collimator lens holder 22 using an adhesive or the like.

〔Effect of the invention〕

As described above, the focusing error detection device according to the present invention includes a light source, a collimator lens that converts the light beam emitted from the light source into a parallel light beam, and an information recording disk provided with an information track and a guide track to convert the parallel light beam into a parallel light beam. an objective lens that focuses the light to form a beam spot and captures the reflected light flux reflected by the information recording disk; an optical system that forms a beam spot from the reflected light flux captured by this objective lens; A focusing error detection device comprising a photodetector that receives a beam spot with a light receiving section divided into a plurality of parts and detects a focusing error of a beam spot formed on an information recording disk based on the imaging state of the beam spot. The collimator is placed in a rotational position such that the symmetry of the diffraction pattern produced in the beam spot projected onto the detector with respect to the axis corresponding to the direction orthogonal to the guide track is affected by the aberrations of the collimator lens and the objective lens. This is a configuration with a lens installed.

This ensures that the symmetry of the diffraction pattern generated in the beam spot projected onto the photodetector with respect to the axis corresponding to the direction orthogonal to the guide track is impaired due to the influence of aberrations of the collimator lens and the objective lens. Therefore, the quality of the focusing error signal does not deteriorate, and it is possible to perform stable focusing control.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of a focusing error detection device according to the present invention, FIG. 2 is a vertical cross-sectional view showing the structure of an objective lens unit, and FIGS. 3(a) to 3(f) are beam spots and information, respectively. An explanatory diagram showing the positional relationship with the track and the diffraction pattern, Fig. 4 is a graph showing the relationship between the distance between the optical disk and the objective lens and the focusing error signal, and Fig. 5 shows the configuration of a conventional focusing error detection device. 6(a) to 6(f) are explanatory diagrams showing the principle of focus detection of a conventional focusing error detection device, and FIGS. 7(a) to 7(f) are explanatory diagrams showing the principle of focus detection of a conventional focusing error detection device, respectively. 8(a) to 8(f) are explanatory diagrams showing the positional relationship between the beam spot and the information trunk and the diffraction pattern in FIG. An explanatory diagram showing the positional relationship between the spot and the information track and the diffraction pattern. FIG. 9 is a graph showing the relationship between the distance between the optical disk and the objective lens and the focusing error signal in a conventional focusing error detection device. 21 is a semiconductor laser. (light 1ffl), 22a is a collimator lens, 23 is an optical disc (information recording disc), 23b
23c is an information track, 23c is a guide track, 24a is an objective lens, 26 is an optical system, 27 is a 4-split photodetector (photodetector), 27a, 27b, 27C, and 27d are light receiving sections, 5
1.52 is a beam spot, and 53 is a diffraction pattern. Figure 4 Focus sync error number

Claims (1)

[Claims] 1. A light source, a collimator lens that converts the light beam emitted from the light source into a parallel light beam, and a collimator lens that focuses the parallel light beam onto an information recording disk provided with an information track and a guide track to form a beam spot. an objective lens that captures the reflected light beam reflected by the recording disk;
An optical system forms a beam spot from the reflected light flux taken in by this objective lens, and the formed beam spot is received by a light receiving section divided into a plurality of parts, and is formed on an information recording disk depending on the image formation state. A focusing error detection device comprising a photodetector for detecting a focusing error of a beam spot, wherein a diffraction pattern generated in the beam spot projected on the photodetector has symmetry with respect to an axis perpendicular to the guide track. A focusing error detection device characterized in that a collimator lens is installed at a rotational position where the degree of influence by aberrations of the collimator lens and objective lens is reduced.