JPH052762A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain an exact sensor signal even for a direct-read-after write type disk or the change of phase type disk by arranging a spot for a tracking sensor along a track in the same direction with a spot for recording and reproduction by using two blazed diffraction grating, in the tracking sensor of a three beam method. CONSTITUTION:As for an optical system which condenses a light flux from a semiconductor laser 1 on a disk 6, a diffraction grating 30 is arranged between the semiconductor laser 1 and a beam splitter 4 and the state of the grating is used as the two blazed areas. Then, spots SP4 and SP5 for the tracking sensor are arranged in the same direction with a first spot SP1 for recording, reproduction and erasure on the disk 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing device, and more particularly to a tracking sensor in an optical disc device for optically recording / reproducing information.

[0002]

2. Description of the Related Art In an optical recording / reproducing apparatus, an optical head applies a minute spot to a predetermined track of a rotating optical information recording medium (hereinafter referred to as a disk) to record / reproduce data. I do. The given spot must then always be on the track. At this time, the track may be displaced due to the eccentricity of the disk, and the spot irradiation position needs to follow the displacement. As a means for following the position, there is a method of detecting that the spot irradiation position is displaced and mechanically moving the position of the objective lens with respect to the laser light. This deviation of the irradiation position is called a tracking error signal, and a "3 beam method" has been proposed as a sensor method.

FIG. 6 is a diagram showing a conventional three-beam method optical system. In the figure, 1 is a semiconductor laser which is a light source, 2
Is a diffraction grating, 3 is a collimator lens for obtaining a parallel light beam, 4 is a beam splitter, 5 is an objective lens, 6 is a disc, 7 is a focusing lens, and 8 is an optical detector. Semiconductor Ray
The light beam emitted from the laser 1 is made into a parallel light beam by the collimator lens 2, passes through the beam splitter 4, and the objective lens 5
Then, the light is focused on the disk 6. At this time, the semiconductor laser 1
Due to the action of the diffraction grating 2 disposed between the collimator lens 3 and the collimator lens 3, the light beam is diffracted to the ± 1st order, so that the disc 6
Second and third spots SP2 and SP3 are formed on both sides of the first spot SP1. The reflected light beam from the disk 6 is reflected by the beam splitter 4 and is incident on the photodetector 8 via the focusing lens 7. The optical detector 8 is the disk 6
8a corresponding to the upper spots SP1, SP2, SP3,
It is composed of three parts 8b and 8c. And
The tracking error signal TE is obtained by generating the difference signal of the photo detectors 8b and 8c by the differential amplifier 9.

In the tracking sensor system based on the 3-beam method, it is necessary that the second and third spots for tracking error detection, that is, SP1 and SP2 have the same reflectance on the disk. Therefore, this method was sufficient for a read-only or magneto-optical disk, but in a write-once optical disk or a phase change optical disk, tracking error can be correctly detected while recording information by the first spot. There wasn't. Therefore, a method has been proposed in which an accurate tracking error signal can be obtained for all optical disks while having the characteristics of the 3-beam method.

FIG. 7 is a block diagram showing a tracking error detecting method disclosed in Japanese Patent Laid-Open No. 82202/1990, which has the same structure as the conventional 3-beam method. However, the action of the diffraction grating 2 used is different.
That is, the cross-sectional shape of the diffraction grating 2 is rectangular but has a sawtooth shape, and the intensities of the + 1st order light and the −1st order light are different. This will be described with reference to FIG. 8A and 8B are diagrams showing the state of the diffraction grating and the intensity of transmitted light thereof. FIG. 8A shows a rectangular grating and FIG. 8B shows a sawtooth grating. In the case of a rectangular grating, the light beam which is vertically incident on the diffraction grating 2 is divided into 0-th order diffracted light that is not diffracted and ± 1st order diffracted light, diffracted light that is diffracted, and so on. The direction in which the light beam is diffracted depends on the lattice spacing d. As shown in FIG. 8A, the intensity of the divided light flux has a symmetrical intensity distribution with the 0th-order diffracted light having the maximum intensity as the center. On the other hand, in the case of a sawtooth grid (blaze grid) as shown in FIG.
The lattice has an inclination of θb (blaze angle). The direction in which the light beam is diffracted depends on the lattice spacing d and is not affected by θb. However, since the incident light flux is incident at an incident angle of θb with respect to the normal D of the lattice plane C, the maximum intensity distribution exists between the 0th-order diffracted light and the 1st-order diffracted light due to the influence of refraction.
The intensity of the -1st order diffracted light becomes extremely small. Japanese Patent Laid-Open No. 2-8
In JP-A 2202, the blazed diffraction grating is used to arrange the second and third beams in the same direction with respect to the 0th-order diffracted light.

FIG. 9 shows a diffraction grating disclosed in Japanese Patent Application Laid-Open No. 2-82202. Grating 1 having normals in the directions of θ1 and θ2 with respect to the track direction (x) of the disk 6
1 and 12 are formed. The lattice spacings are d1 and d2, respectively
And its cross-sectional shape is a sawtooth shape as shown in FIGS.

Next, the operation will be described. The light beam emitted from the semiconductor laser 1 is condensed on the disk 6, and the reflected light is received by the photo detector 8.
It is the same as the Mu method. However, since the diffraction grating 20 is a blazed diffraction grating as described above, the second and third spots SP4 and SP5 are formed on the same side of the first spot SP1 on the disc. That disk 6
Also on the photodetector 8 corresponding to the upper spot, the photodetectors 8d and 8e on the same side as 8a corresponding to the first spot.
Are arranged. In this way, the recording spot SP
Since the spots SP4 and SP5 for tracking error detection are arranged on the same side with respect to 1, the reflectances of SP4 and SP5 are the same even for a write-once type or a phase change type disc, and an accurate tracking error signal is obtained. Is obtained.

[0008]

By the way, in the conventional method, as described above, it is necessary to make two kinds of gratings on the same plane of one diffraction grating by overlapping.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to maintain the feature that the tracking sensor system by the 3-beam method can be used as a write-once type or a phase change type. The diffraction grating for realizing this effect is intended to obtain an optical recording / reproducing apparatus which does not need to form two kinds of gratings by overlapping.

[0010]

An optical recording / reproducing apparatus according to the present invention includes a diffraction grating for a 3 beam method tracking sensor in a light beam in a direction perpendicular to a track on a disk.
The laser diffraction grating is formed in each region so that the 1st-order diffracted light can be obtained in the same direction as the 0th-order diffracted light on the disc.

[0011]

The diffraction grating of the present invention produces first-order diffracted light in the same direction as the 0th-order diffracted light for recording and reproduction.

The spot shape is such that the 0th-order diffracted light is an elliptical spot whose major axis is perpendicular to the track, and the 1st-order diffracted light is an elliptical spot whose major axis is parallel to the track. The state can be obtained.

[0013]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an optical system, which has the same configuration as the conventional example, but the action of the diffraction grating 30 is different. This will be described with reference to FIG. FIG. 2 shows the state of the grating of the diffraction grating 30, which is divided into two regions in the x-axis direction (direction orthogonal to the track on the disk), and the normal direction of the grating is the y-axis in each region. For θ1 and θ2 respectively
Just leaning. The lattice spacings are d1 and d2, respectively.
Is.

Next, the state of the spot on the disk obtained by passing through the diffraction grating 30 will be described with reference to FIG. In the figure, 10 is a track on the disk 6, and SP4 and SP5 are second and third spots for the tracking sensor.
Since the spot as shown in FIG. 4 is obtained by the structure of the diffraction grating 30 shown in FIG. 2, the second and third spots in the track direction are obtained.
The direction of the spot is the same as the normal direction of the diffraction grating 30. In the 3-beam method, the interval between the second and third spots in the direction perpendicular to the track is the track pitch (P).
Since the largest sensor signal can be obtained at a distance of 1/4, the distance from the first beam is h as shown in the figure.
1 and h2, θ1 and θ2 are obtained by TAN (θ1) = (P / 4) / h1 TAN (θ2) = (P / 4) / h2.

Next, the shape of the spot will be described.
In the case of the present invention, the light beam diffracted by the diffraction grating is a semicircular light beam, and thus the focused spot is an elliptical spot having the minor axis in the dividing direction (x direction in FIG. 2) of the semicircle.
Therefore, when the diffraction grating is formed as shown in FIG. 2, the spot shape becomes as shown in FIG. 4, and the amplitude of the track crossing signal, that is, the tracking error signal can be increased. The diffraction grating of the present invention may be divided as shown in FIG. 3, but in this case, since the spot of the diffracted light is an elliptical spot having a short axis in the y direction, a spot as shown in FIG. The amplitude of the tracking error signal cannot be made large.

[0016]

As described above, according to the present invention, the diffraction grating is divided into two semi-circles, and each of the gratings is bladed.
Since the grating is a zigzag grating, the 3-beam method can be used as a tracking sensor even in the case of recording on a write-once or phase-change type disc, and the reproduced signal and the tracking error
There is an effect that the modulation rate of the signal can be increased.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical system of an optical recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a grating shape 1 of the diffraction grating according to the present invention.

FIG. 3 is a diagram showing a grating shape 2 of the diffraction grating according to the present invention.

FIG. 4 is a diagram showing a focused spot obtained in an embodiment of the present invention.

5 is a diagram showing a focused spot obtained by the diffraction grating shown in FIG.

FIG. 6 is a diagram showing an optical system of a conventional 3-beam method.

FIG. 7 is a diagram showing another conventional optical system.

FIG. 8 is a diagram illustrating the relationship between the shape of a diffraction grating and the intensity of diffracted light.

FIG. 9 is a diagram showing a state of another conventional diffraction grating.

10 is a diagram showing a cross section of the diffraction grating shown in FIG.

[Explanation of symbols]

1 light source 4 beam splitter 5 Objective lens 8 photo detectors 30 diffraction grating SP1 first spot SP4 second spot SP5 third spot

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[Procedure amendment]

[Submission date] March 26, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010]

An optical recording / reproducing apparatus according to the present invention includes a diffraction grating for a 3 beam method tracking sensor in a light beam in a direction perpendicular to a track on a disk.
Min, and in each region, blanking les as 1-order diffracted light in the same direction are obtained for the zero-order diffracted light on the disc - is obtained by forming a's of the diffraction grating.

Claims (2)

[Claims] 1. An objective lens which collects a light beam from a light source and emits the light beam to an information recording medium and enters a reflected light beam from the information recording medium, and a beam splitter which separates the light beam emitted from the light source and the reflected light beam. In an optical recording / reproducing apparatus having a beam splitter and a photodetector for detecting a tracking servo sensor signal for receiving the light beam separated by the beam splitter, there are two regions between the light source and the objective lens. Split,
Also, by arranging the diffraction grating in which the gratings of the respective regions are blazed, the second spot and the third spot are arranged in the same direction along the track from the first spot for recording / reproducing / erasing. Then, the optical recording / reproducing apparatus is characterized in that the position of the first spot is controlled based on the difference in light amount between the second and third spots. 2. The optical recording / reproducing apparatus according to claim 1, wherein the division direction of the diffraction grating is a direction orthogonal to the track direction.