JPH05225643A - Signal reproducing method for optical recording medium - Google Patents

Abstract

PURPOSE:To make density high and capacity large by shortening the track pitch of a magneto-optical disk, thereby increasing the track density. CONSTITUTION:The desired tack 21 of the magneto-optical disk 6 is reproduced by a main beam spot a. The adjacent tracks 22, 23 are heated up to the Curie temp. of the reproducing layer or above by beam spots b, c on both sides to temporarily erase the data of the reproducing layer of the adjacent tracks 22, 23, by which crosstalks are eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal reproducing method for an optical recording medium which scans an optical recording medium using a three-beam spot system to reduce crosstalk and reproduce a signal of a target track.

[0002]

2. Description of the Related Art Optical recording media are desired to have a higher recording density. This means that when considering a digital video signal as a signal to be recorded, it requires a data amount which is several to several tens of times larger than that of a digital audio signal, and even when recording a digital audio signal, it is necessary to use a disc or the like. This is because there is a demand to make the size of the medium smaller and further downsize products such as players.

The recording density of the optical recording medium is determined by the linear density along the scanning direction of the recording track and the track density according to the adjacent track interval (track pitch) in the direction orthogonal to the scanning direction.

Therefore, conventionally, the high recording density of the optical recording medium,
To increase the capacity, the track pitch has been reduced to increase the track density.

[0005]

However, when trying to increase the track density by narrowing the track pitch in order to increase the recording density and capacity of the optical recording medium, crosstalk (leakage of adjacent track signal leakage) occurs during reproduction. ) Increased and it became impossible to reproduce, so it was not possible to reduce the track pitch.

It is an object of the present invention to provide a signal reproducing method for an optical recording medium, which can reduce the track pitch of the optical recording medium and increase the density and capacity of the optical recording medium.

[0007]

A signal reproducing method for an optical recording medium according to the present invention uses a three-beam spot method and has a multilayer recording layer including at least a storage layer and a reproducing layer formed on the storage layer. In a signal reproducing method of an optical recording medium for scanning a signal on an optical recording medium to reproduce a signal, when reproducing a signal of a target track with a main beam spot, a beam spot on both sides simultaneously reproduces a curl of a reproducing layer on an adjacent track. It is characterized in that the temperature is higher than the temperature to reduce the crosstalk.

[0008]

In the signal reproducing method for the optical recording medium having the above-mentioned structure, when the signal of the target track is reproduced by the main beam spot, at the same time, the temperature of the adjacent track becomes higher than the Curie temperature of the reproducing layer by the beam spots on both sides. By raising the temperature to reduce the Kerr rotation, the data in the reproducing layer in the portions where the beam spots on both sides hit is temporarily erased to reduce crosstalk.

As a result, the track pitch can be narrowed as compared with the conventional one, and therefore the track density can be increased, which enables the optical recording medium to have a high density and a large capacity.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 2 is a device configuration diagram showing an embodiment of a signal reproducing method for an optical recording medium of the present invention. FIG. 2 shows a reproducing apparatus for a magneto-optical disk, and this magneto-optical disk reproducing apparatus uses a 3-spot system. Reference numeral 1 is a semiconductor laser element as a light source driven by a drive circuit (not shown), 2 is a collimator lens for collimating the laser light from the semiconductor laser element 1, 3 is a grating (diffraction grating), and the grating 3 is a collimator. Lens 2
The collimated beam from is diffracted and three beams are emitted. That is, the grating 3 divides the light source into three. The three beams from the grating 3 enter the objective lens 5 through the beam splitter (BS) 4, and are converged on the surface of the magneto-optical disk 6 by the objective lens 5.

The three beam spots a to c illuminated on the surface of the magneto-optical disk 6 by the objective lens 5 are as shown in FIG. Here, the main beam spot a is applied to the target track 21 to be reproduced, and the beam spots b and c on both sides are applied to the tracks (adjacent tracks) 22 and 23 adjacent to the target track 21. ing.

Incidentally, the track portions of the magneto-optical disk 6 (for example, the portions of the tracks 21 to 23 shown) are formed on a transparent substrate (not shown) as shown in FIG.
Have three. As shown in FIG. 3, the recording layer 33 is composed of a multilayer film including at least a storage layer 31 and a reproducing layer 32 formed on the storage layer 31 on a transparent substrate (not shown). Here, as each material of the storage layer 31 and the reproduction layer 32, a material having a Curie temperature of the storage layer 31 of Tc ₁ and a Curie temperature of the reproduction layer 32 of Tc ₂ (<Tc ₁ ) is used. There is.

Data is recorded on the recording layer 33 of each track of the magneto-optical disk 6. Here, for example, by applying a beam to the track to be recorded and raising the temperature above the Curie temperature Tc ₁ of the storage layer 31 to eliminate the coercive force of that portion and magnetize in the direction of the recording magnetic field applied from the outside. By recording information (so-called thermomagnetic recording), the same data is recorded in the storage layer 31 and the reproduction layer 32.

When the temperature of the portion where the beam spots a to c are applied is viewed in the disk radial direction, it becomes as shown in FIG.
That is, the temperature of the track portion to which the beam spot a is applied is lower than the Curie temperature Tc ₂ of the reproducing layer 32, and the temperature of the track portion to which the beam spots b and c are applied is higher than the Curie temperature Tc ₂ of the reproducing layer 32. And storage layer 3
It is lower than the Curie temperature Tc _{1 of 1} . The temperature distribution as shown in FIG. 4 is obtained by the design of the grating 3.

The laser beam reflected by the surface of the magneto-optical disk 6 enters the beam splitter 4 through the objective lens 5, is reflected there, and is polarized by the polarization beam splitter (PB).
S) 7 and enters the reproducing photodetector (PD) 8. On the light detecting surface of the reproducing photodetector 8, as shown in FIG. 6, the target track 2 is provided in the central area.
A reflected beam spot 61 corresponding to a beam spot (reading beam spot) a applied to one portion is applied, and regions on both sides thereof correspond to the beam spots b and c applied to adjacent track portions 22 and 23. The reflected beam spots 62 and 63 (hatched portions) are applied. Here, it is sufficient to detect the reflected beam spot 61 corresponding to the target track 21 portion and extract the reproduction signal.

Although not shown, a magnetic head for applying a reproducing magnetic field is arranged on the back surface (lower surface in the figure) of the magneto-optical disk 6 at the laser light irradiation position.

Before explaining the operation of the main part of the present invention, the magneto-optical disk 6 according to the present invention is an MSR (Magn).
Since the system uses an electronic super resolution (also called an iristor) system, the principle of this MSR system will be described first.

Now, the accumulation layer 31 of the recording layer 33 of the track
The same data as above and below is magnetically recorded on the reproducing layer 32. In the case of reproduction, if the beam is applied to the track and the part where the beam hits is a temperature lower than the Curie temperature Tc ₂ of the reproduction layer 32, not only the data of the storage layer 31 but also the data of the reproduction layer 32 is not destroyed. (Not erased). Furthermore,
When the portion of the track where the beam hits is near the Curie temperature Tc ₂ of the reproducing layer 32, Kerr rotation cannot be obtained (Kerr effect rotation angle θ _k becomes extremely small) and the reproducing layer 3
The 2nd pit (data) is erased and thus the data becomes unreadable. In this case, the Curie temperature Tc ₁ of the storage layer 31
Is set to a temperature higher than the Curie temperature Tc ₂ of the reproducing layer 32, the data in the storage layer 31 is not erased. Therefore, after that, when the temperature of the reproducing layer 32, which has been hit by the beam, becomes lower than the Curie temperature Tc ₂ of the reproducing layer 32, the data of the storage layer 31 thereunder is transferred to the reproducing layer 32 on the front surface side.
Is transferred to and returns to its original state.

The present invention utilizes the above-described principle of MSR, and the operation of the main part in reproducing the magneto-optical disk 6 will be described below.

During reproduction, the driving of the semiconductor laser device 1 is controlled by a driving circuit (not shown). Semiconductor laser device 1
The laser light emitted from is converted into a parallel beam by the collimator lens 2 and divided into three beams by the grating 3. These three beams are focused on the surface of the magneto-optical disk 6 through the beam splitter 4 and the objective lens 5 as shown in FIG. In this case, the temperature distribution as shown in FIG. 4 is formed in the radial direction of the magneto-optical disk 6 by hitting the three beam spots a to c on the surface of the magneto-optical disk 6.

When the main beam spot a is applied to the target track 21 to be reproduced and the laser beam scanning is performed for reproduction, the temperature of the portions of the adjacent tracks 22 and 23 where the beam spots b and c on both sides are reproduced is reproduced. Layer 32
Becomes higher than the Curie temperature Tc _{2 of the}
Since it is lower than the Curie temperature Tc _{1 of the same} ), the rotation angle θ _k of the Kerr effect becomes 0 as can be seen from FIG. 5, and the pits (data) in the reproduction layer 32 of the adjacent tracks 22 and 23 are temporarily erased and crosstalk is caused. Does not occur. On the other hand, since the temperature of the portion of the target track 21 where the main beam spot a hits is lower than the Curie temperature Tc ₂ of the reproducing layer 32 as shown in FIG. 4, the pit (data) of the reproducing layer 32 is not erased, It is converted into an optical signal by the Kerr effect and read.

As the beam spots a to c move in the scanning direction by the laser beam scanning, the temperature of the portions of the adjacent tracks 22 and 23 where the beam spots b and c hit first is the Curie of the reproducing layer 32. When the temperature drops below the temperature Tc _2, the data in the lower storage layer 31 is transferred to the upper reproduction layer 32 and returns to the original state.

As described above, since crosstalk does not occur when the signal of the target track 21 is reproduced, the track pitch p shown in FIG. 1 can be narrowed as compared with the conventional case, and therefore the track density can be increased. It enables high density and large capacity of the magneto-optical disk 6.

In the present embodiment (FIG. 2), the laser beam from one light source (semiconductor laser element 1) is divided into three light beams by using the grating 3, but the present invention is not limited to this. 3 without using 3 light sources
Two light beams may be generated, in which case the grating 3 can be dispensed with.

Further, in the present embodiment, the reproduction in the case where the magneto-optical disk 6 is used as the optical recording medium has been described, but the present invention is not limited to this, and the phase change type disk is used as the optical recording medium. It goes without saying that the same applies to reproduction when used.

The present invention is not limited to this embodiment, and various applications and modifications are conceivable without departing from the gist of the present invention.

[0027]

As described above, according to the signal reproducing method for the optical recording medium of the present invention, when the target track on the optical recording medium such as the magneto-optical disk is reproduced by the main spot, the beam spots on both sides are adjacent to each other. By increasing the temperature of the track to a temperature above the Curie temperature of the playback layer and reducing the Kerr rotation, data is temporarily erased (the signal (data) cannot be read) and crosstalk is reduced. The track pitch can be narrowed as compared with the above, and therefore, the track density can be increased, and accordingly, an effect such as high density and large capacity of the optical recording medium can be achieved.

[Brief description of drawings]

FIG. 1 is a plan view of an essential part of a magneto-optical disk 6 shown in FIG.

FIG. 2 is a device configuration diagram showing an embodiment of a signal reproducing method for an optical recording medium of the present invention.

FIG. 3 is a structural diagram showing an example of a recording layer of a track portion of FIG.

FIG. 4 is a temperature distribution diagram in the radial direction of the disk of FIG.

FIG. 5 is a characteristic diagram showing the relationship between temperature and the Kerr effect rotation angle θ _k .

FIG. 6 is an explanatory diagram of a light detection surface of the reproduction photodetector 8 of FIG.

[Explanation of symbols]

 1 Semiconductor Laser Element 2 Collimator Lens 3 Grating 4 Beam Splitter 5 Objective Lens 6 Magneto-optical Disk 7 Polarizing Beam Splitter 8 Playback Photodetector 21 Target Tracks 22, 23 Adjacent Track 31 Storage Layer 32 Playback Layer 33 Recording Layer

Claims (2)

[Claims] 1. A signal reproducing method for an optical recording medium which scans an optical recording medium to reproduce a signal by using a three-beam spot method, wherein a signal of a target track is reproduced by a main beam spot, and beams on both sides are simultaneously reproduced. A signal reproducing method for an optical recording medium, characterized in that the temperature of an adjacent track is made higher at a spot to reduce crosstalk. 2. The optical recording medium comprises a multilayer recording layer having at least an accumulation layer and a reproduction layer formed on the accumulation layer, and the Curie temperature of the reproduction layer is higher than the Curie temperature of the accumulation layer. 2. The signal reproducing method for an optical recording medium according to claim 1, wherein the signal reproducing method for the optical recording medium is configured so that the temperature of the adjacent tracks is raised to a temperature equal to or higher than the Curie temperature of the reproducing layer by the beam spots on both sides.