JPH03268232A - Optical pickup - Google Patents

Abstract

PURPOSE:To allow the exact detection of a focusing error by dividing a photodetector with a blind zone having a prescribed width as a boundary along the direction corresponding to a direction where the track image of an information recording medium extend. CONSTITUTION:The information is recorded and reproduced by using the information recording medium 8 of an optical disk 5 concentrically or spirally provided with the tracks 6 and a focus is detected by introducing the luminous flux reflected by the optical disk 5 to the photodetector 15. The photodetector 15 is formed with four photodetecting parts 15a to 15d divided along the direction X-X corresponding to the direction where the information tracks 6 of the optical disk 5 extends and the direction Y-Y orthogonal therewith. Since the dividing line of the direction X-X is the blind zone 16 of a measurably wide width l, the exceeding part of the track image is formed within the blind zone even if the image tends to exceed to the other side of the boundary in the direction corresponding to the track direction by the rotation of the track image generated by the aberration of the optical system and, therefore, the detection of the focusing error is exactly executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup, and particularly to an optical pickup that performs recording and reproduction using an information recording medium provided with concentric or spiral tracks. [Technology] Conventionally, as an optical pickup for recording on or reproducing from an optical disk, for example, the one shown in FIG. 7 is known. In the figure, a beam emitted from a semiconductor laser 1 is made into parallel light by a collimator lens 2, passes through a beam splitter 3, enters an objective lens 4, is converged by the objective lens 4, and is guided to an optical disk 5.

The optical disc 5 has concentric or spiral information tracks 6.
An information recording medium 8 such as an amorphous alloy thin film of a rare earth transition metal is formed by vapor deposition, sputtering, etc. on a substrate 7 made of a light-transmitting material such as glass, on which guide tracks 6' are provided on both sides. The convergent light from the objective lens 4 forms a beam spot on the information recording medium 8.

The reflected light from the information recording medium 8 passes through the objective lens 4 again, is reflected at a right angle by the beam splitter 3, and then passes through the converging lens 10 and the cylindrical lens 11 to become a light beam having astigmatism. The light is incident on a four-divided photodetector 12 arranged at an angle of 45 degrees with respect to the generatrix direction of the photodetector 11.

Next, the principle of focus detection in the optical pickup will be explained.

In FIGS. 8(a) and 8(b), the photodetector 12 is divided into four parts.
5a-
Let it be 3d. At the time of focusing, the beam spot A on the photodetector 12 becomes circular as shown in FIG.
d are equal. Therefore, the focusing error signal (Sa+Sc) - (Sb+5) used as a signal for correcting the relative distance between the information recording medium 8 and the objective lens 4
d)=O.

Next, when the objective lens 4 approaches relatively to the information recording medium 8, the beam spot A on the photodetector 12 is shifted to the cylindrical lens 11, as shown in FIGS. 9(a) and 9(b).
parallel to the generatrix of It becomes an ellipse with the major axis being , and the focusing error signal (Sa+5c)-(Sb+Sd) becomes negative.

On the other hand, when the objective lens 4 moves relatively away from the information recording medium 8, the beam spot A on the photodetector 12 changes to the cylindrical lens 1 as shown in FIGS.
It becomes an ellipse whose major axis is the direction a0 perpendicular to the generatrix direction of 1, and the focusing error signal (Sa+5c) - (Sb
10Sd) is positive.

Next, during the focusing shown in FIGS. 8(a) and 8(b), a change in the diffraction pattern occurs in the beam spot A projected onto the photodetector 12 due to the diffraction by the guide track 6' due to the track deviation. Therefore, we will consider the influence of crosstalk that occurs on the focusing error signal.

First, consider an ideal case in which the optical system from the semiconductor laser 1, which is a light source, to the information recording medium 8 has no aberration. 11th
As shown in Figures (a) and (b), the photodetector 12 is arranged so that the X-X direction shown in the figure is parallel to the information track 6, and the Y-Y direction is perpendicular to the information track 6. , beam sub-B is irradiated onto the information track 6, and the reflected light is received by the photodetector 12. 11(a) and 11(b) show a state in which the beam spot B is shifted downward from the information track 6, FIGS. 12(a) and (b) show a state in which there is no vertical shift of the beam spot B, and FIG. 13. (a) and (g)) respectively show a state in which the beam spot B is shifted upward from the information track 6. In other words, Figure 11 (a
) (b) and FIGS. 13(a) and (b) are states where a tracking error exists, and FIGS. 12(a) and (b) are states where no tracking error exists, that is, tracking error signal (Sa+Sb) - (Sc+5d )=O state. In addition, Fig. 11(a)(b) to Fig. 13(a)
) (b) are all assumed to be in focus.

As is clear from FIGS. 11(a)(b) to 13(a)(b), the diffraction pattern on the photodetector 12 depends on the vertical position of the beam spot B, that is, the beam spot A pattern changes. However, Fig. 11(a)
Since the diffraction patterns in FIGS. 13(b) to 13(a) and 13(b) are all symmetrical about the Y-Y axis, no crosstalk occurs in the above focusing error signal.

Next, consider a case where the optical system from the semiconductor laser 1, which is the light source, to the information recording medium 8 has aberrations. When the optical system has an aberration (particularly astigmatism) and the direction of this aberration deviates from a direction parallel to (or perpendicular to) the information track 6, crosstalk occurs.

14(a) to 14(b) to FIG. 16(a) are diagrams showing the situation, and the arrangement direction of the photodetector 12 and the positional relationship between the information track 6 and the beam spot B are shown in FIG. 11
When the settings are the same as in FIGS. 13(a) and 13(a) and (b), and the beam spot B is shifted downward from the information track 6 in FIGS. 14(a) and 14(b), Figure 15 (a
)(b) is the 16th beam spot B if there is no shift.
Figures (a) and (b) show the case where the beam spot B is shifted upward.

In this case, unlike the cases shown in FIGS. 11 to 13, the diffraction pattern projected onto the photodetector 12 is disturbed due to aberrations of the optical system, and crosstalk occurs. For this reason, the focusing error signal (
Sa+5c)-(Sb+Sd) is shown in Fig. 14(a)(b)
is correct, O" in Figures 15(a) and (b), and O" in Figures 16(a) (
b) takes a negative value and generates an erroneous signal, making focusing control unstable.

Therefore, in general, in the above-mentioned optical pickup, by strictly controlling the surface precision of the optical components used,
This suppresses the occurrence of crosstalk.

Alternatively, as described above, since the direction of aberration affects the amount of crosstalk generated, the following method may be used to reduce crosstalk.

That is, as shown in FIG. 5, a parallel flat plate 13 made of glass is arranged between a semiconductor laser 1 as a light source and a collimator lens 2, and this parallel flat plate 13 is rotatable around an optical axis C. There is.

By the way, a parallel plate 13 with a thickness t and a refractive index n is spread at an angle α
If the lens is placed at an angle β in the light beam, an astigmatism W will occur. The direction of this astigmatism W can be adjusted by rotating the parallel plate 13 around the optical axis C, and the amount of astigmatism can be adjusted by changing the inclination angle β of the parallel plate 13, or changing the refractive index n or the plate. It can be controlled by changing the thickness t. Therefore, by using the parallel plate 13 described above, it is possible to solve the problem of deterioration of the focusing error signal due to astigmatism of the optical system.

FIG. 17(a) shows a focusing error signal obtained by an optical pickup that does not have the parallel plate 13. In this case, information track 6 is placed at beam spot B.
A large amount of crosstalk occurs when the crosstalk crosses, and malfunctions occur due to crosstalk especially near the in-focus point (point IIO11 on the horizontal axis).

FIG. 17(b) shows a focusing error signal when the parallel plate 13 is provided. In this case, almost no crosstalk occurs near the in-focus point, making stable focusing control possible.

By the way, optical pickups are used in optical information recording and reproducing devices (compact disc players, magneto-optical disc drives, etc.).
When incorporating the optical pickup into the optical information recording/reproducing apparatus, it is necessary to accurately attach the optical pickup adjusted so that crosstalk does not occur using the parallel plate 13 as described above.In other words, the optical pickup adjustment process The positional relationship between the optical pickup and the information recording medium 8 must be accurately reproduced even when attached to an optical information recording/reproducing device. It is difficult to install.

However, if the optical pickup is installed in an optical information recording/reproducing device in a different orientation than when adjusting the crosstalk, even if the installation has been adjusted beforehand, this installation will result in errors as described below. Crosstalk will occur.

That is, it is assumed that the crosstalk adjustment of the optical pickup 14 by the parallel plate 13 is performed in the state shown in FIG. 6(a). At this time, since the aberration is compensated by the parallel plate 13, the positional change of the beam spot B and the information track 6 and the accompanying change in the state of the detected light at the photodetector 12 are as shown in FIGS. 11(a) and 11(b). - It becomes as shown in FIGS. 13(a) and (b).

Next, as shown in FIG. 6 Φ), the optical pickup 14
When installed in the optical information recording/reproducing apparatus with a difference of ΔL from the adjustment shown in FIG. 18(a), the positional relationship of the detected light due to the positional change of the beam spot B and the information track 6 is as shown in FIG. 18(a). As shown in FIG. 19(a) and FIG. 20(a), it is tilted by Δθ with respect to the adjustment using the parallel plate 13.

As a result, changes in the state of the detected light at the photodetector 12 due to changes in the positions of the beam spot B and the information track 6 are as shown in FIGS.
Crosstalk occurs.

[Problem to be solved by the invention]

By the way, as is clear from FIG. 21, there is a relationship of Δθ-5in −' (ΔL/r) between Δθ, the radius r of the information track 6, and the above-mentioned deviation amount ΔL. That is, since the inclination angle Δθ of the information track 6 also depends on the radius r of the information track 6, the amount of crosstalk is not constant between the inner circumference and the outer circumference of the information recording medium 8. Therefore, if the optical big abutment is attached to the optical information recording/reproducing device with a positional deviation of ΔL, even if the crosstalk is readjusted on the optical information recording/reproducing device, the amount of crosstalk will vary depending on the radial position. There was a problem that crosstalk could not be completely suppressed because of the change in crosstalk.

[Means to solve the problem]

In order to solve the above-mentioned problems, an optical pickup according to the present invention performs recording and reproduction using an information recording medium in which tracks are provided concentrically or spirally, and at least the direction in which the image of the track extends and In an optical pickup including a light receiving element for focusing error detection that is divided along orthogonal directions, the light receiving element is divided along a direction in which the image of the track extends, with a dead zone having a predetermined width as a boundary. It is characterized by the presence of

[For production]

According to the above configuration, when a tracking error occurs and the track image should be formed on only one side of the boundary in the direction corresponding to the track direction on the light receiving element, the track image caused by the aberration of the optical system is Even if the image is about to protrude to the other side of the boundary in the direction corresponding to the track direction due to rotation, the boundary in the direction corresponding to the track direction is a dead zone of a predetermined width, so that the protruding part of the track image can be prevented. is formed within the dead zone and is not formed on the other side of the dead zone, so that focusing errors can be detected accurately.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 to 6.

As shown in FIG. 5, the optical pickup 14 includes a semiconductor laser 1, a collimator lens 2 that converts the light beam emitted from the semiconductor laser 1 into parallel light, and a light beam directed to the optical disk 5 side and the photodetector 2 side. a beam splitter 3 that splits the beam, an objective lens 4 that converges the light beam emitted from the semiconductor laser 1 and transmitted through the beam splitter 3 onto an information recording medium 8 of an optical disk 5, and a beam that is reflected by the optical disk 5 and passes through the objective lens 14. a converging lens 10 that converges the light beam reflected at right angles by the beam splitter 3, and a cylindrical lens 11 that guides the light beam from the convergence lens 10 as a light beam having astigmatism to a photodetector 15 in order to obtain a focusing error signal. It is equipped with

The optical disc 5 has concentric or spiral information tracks 6.
An information recording medium 8 such as an amorphous alloy thin film of a rare earth transition metal is deposited on a substrate 7 made of a light-transmissive material such as glass, on which a (track) and guide tracks 6' on both sides are provided, by vapor deposition, sputtering, etc. It is formed by.

Further, a parallel plate 13 made of glass is arranged between the semiconductor laser 1 and the collimator lens 2, and the parallel plate 13 is rotated about the optical axis C, or the thickness of the parallel plate 13 is adjusted to the refractive index n. By adjusting , the aberrations of the optical system are compensated.

As shown in FIG. 1, the photodetector 15 as a light receiving element is
The optical disk 5 is divided along the x-x direction corresponding to the direction in which the information track 6 extends and the Y-Y direction perpendicular thereto, forming four light receiving sections 15a to 15d. Here, in the X-X direction, there is a dead zone 16 with a width of 2, which is considerably wider than the normal dividing line.
It is divided along the normal dividing line 17 in the Y-Y direction.

In Figures 2(a)(b) to 4(a)(b), due to installation errors (see Figure 6) when attaching the optical pickup to the optical information recording/reproducing device, the information track 6 (not shown with hatching for convenience) A case is shown in which a tilt of an angle Δθ occurs between the beam spot B and the beam spot B, and the image of the information track 6 on the photodetector 15 rotates accordingly. However, in Figure 2 (a
) shows a state where the beam spot B on the optical disk 5 is shifted below the information track 6 and a tracking error occurs, FIG. 3(a) shows a state where there is no tracking error, and FIG. 4(a) shows a state where the beam spot B indicates a state in which a tracking error occurs as the information track 6 is shifted upward from the information track 6. In addition, FIGS. 2(a)(b) to 4(a)(b) are as follows:
All of the images show a state in which no focusing error has occurred.

As shown in FIG. 2(a), when the beam spot B deviates downward from the information track 4 and a tracking error occurs, as shown in FIG.
The image on the photodetector 15, that is, the beam spot A, which should be formed only on the light receiving parts 15c and 15d, protrudes from the light receiving part 15c,
Since a dead zone 16 of a predetermined width 2 is formed between
Since the beam sub-A protruding from the light receiving section 15c is formed within the fuwa zone 16 and is not formed on the light receiving section 15b, the focusing error signal (Sa+5c) - (Sb
+5d)=O.

Similarly, as shown in FIG. 4(a), when the beam spot B shifts upward from the information track 6 and a tracking error occurs, as shown in FIG. The beam spot A that should be formed only in the light receiving part 15a protrudes from the light receiving part 15a, but the beam spot A that should be formed in the light receiving part 15a is formed in the dead zone 16 and the beam spot A is not formed in the light receiving part 15d. Error signal (Sa+5c) - (S
b+5d)=O. Note that the width l of the dead zone 16 is determined by the inclination angle Δθ between the beam spot B on the optical disk 5 and the information track 6, and the beam spot A on the photodetector 15.
If the diameter of is φ, then ! It is sufficient that ≧φsinΔθ.

〔Effect of the invention〕

As described above, the optical pickup according to the present invention has a configuration in which the light-receiving element is divided along a direction corresponding to the direction in which a track image on an information recording medium extends, with a dead zone having a predetermined width as a boundary.

As a result, when a tracking error occurs and the track image should be formed on only one side of the boundary in the direction corresponding to the track direction on the light receiving element, the track image caused by the aberration of the optical system is rotated. Even if the track image is about to protrude to the other side of the boundary in the direction corresponding to the track direction, the boundary in the direction corresponding to the track direction forms a dead zone of a predetermined width, so that the protruding portion 5 of the track image is within the dead zone. Since the dead zone is not formed on the other side of the dead zone, focusing errors can be detected accurately.

[Brief explanation of drawings]

1 to 6 show one embodiment of the present invention. FIG. 1 is a schematic front view showing a photodetector. Figures 2(a)(b) to 4(a)(b) are explanations showing each beam spot on the information recording medium and the photodetector when the beam spot position on the information recording medium changes, respectively. It is a diagram. FIG. 5 is a schematic diagram of the optical pickup. FIG. 6 is an explanatory diagram showing that an error occurs when attaching an optical pickup to an optical information recording/reproducing apparatus. 7 to 21 show conventional examples. FIG. 7 is a schematic diagram of the optical pickup. FIG. 8(a) @ to FIG. 10(a) Φ) are explanatory views showing the light flux in the optical pickup and the beam spot on the photodetector when the focal position changes, respectively. Figures 11(a)(b) to 13(a)(b) show each beam on the information recording medium and the photodetector when the beam spot position on the information recording medium changes in the focused state, respectively. It is an explanatory view showing spots. Figures 14 (a) (b) to 16 (a) and (b) are information obtained when the beam spot position on the information recording medium changes in the focused state and when there is aberration in the optical system. FIG. 2 is an explanatory diagram showing each beam spot on a recording medium and a photodetector. FIG. 17(a) is a graph showing the relationship between the focal point position and the focusing error signal when no aberration compensation is performed. FIG. 5B is a graph showing the relationship between the focal point position and the focusing error signal when aberrations are compensated for. Figures 18(a)(b) to 20(a)(b) respectively show that the beam spot position on the information recording medium may change if an error occurs when installing the optical pickup to the optical information recording/reproducing device. FIG. 7 is an explanatory diagram showing each beam spot on the information recording medium epithelium 7 8 and the photodetector when the information storage medium changes. FIG. 21 is an explanatory diagram showing the relationship between the radial position of the information track and the inclination angle between the information track and the beam spot. 6 is an information track (track), 8 is an information recording medium, 1
5 is a photodetector (light receiving element), and 16 is a fuwa belt.

Claims (1)

[Claims] 1. Recording and reproducing is performed using an information recording medium having concentric or spiral tracks, and the image of the track is divided at least along the direction in which the image of the track extends and the direction orthogonal thereto. An optical pickup equipped with a light-receiving element for focusing error detection, characterized in that the light-receiving element is divided along a direction in which the image of the track extends, with a dead zone having a predetermined width as a boundary.