JP3301645B2 - Reproduction method of magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reproducing a magneto-optical recording medium.

[0002]

2. Description of the Related Art A magnetic field modulation method is known as a method of magneto-optical recording. In the magnetic field modulation system, a laser beam is radiated from an optical pickup to a magnetic layer of a magneto-optical recording disk in a DC manner to raise the temperature, and at the same time, a magnetic layer arranged on the opposite side of the optical pickup with the disk interposed therebetween. The overwrite recording is performed by applying a modulation magnetic field to the magnetic layer from the head.

In such magneto-optical recording, in order to utilize the beam from the semiconductor laser as efficiently as possible and to increase the recording density by increasing the resolution at the time of reading as much as possible, a laser beam must be applied to the magneto-optical recording disk. Since it is necessary to form an image as a small circular spot on the top, a laser beam from a semiconductor laser having an elliptical cross-section is usually shaped by a cylindrical lens placed in a collimator so that the cross-section becomes almost circular. You.

[0004]

However, when magneto-optical recording is performed with a laser beam having a circular cross section, the recording mark has an arrow shape. And (a) of FIG.
As shown in (b), (c), and (d), as the recording power increases, the width of the recording mark measured in the radial direction of the disk increases, and eventually extends to the adjacent track. The recorded signal is erased. This is usually called cross write, but in an area recorded with overpower, this cross write increases jitter. The recording marks shown in FIG. 1 were obtained by a heat conduction analysis simulation.

FIG. 2 shows the result of recording an EFM signal at a linear velocity of 1.4 m / s and changing the laser power, and measuring the jitter value of the 3T signal, which is the densest pattern. As shown in the figure, in recording only one track, the jitter value is low even when the recording power is increased, but when recording is continuously performed on all tracks, the range of low jitter value becomes extremely narrow. This is considered to be the effect of the cross light. While jitter value referred to as a fixed value or less recording power margin range of recording power that will fit (40 ns or less in the illustrated example) (P _W M), the recording power margin is narrowed in the case of continuous recording to the adjacent tracks, i.e. It can be seen that the allowable range of the recording power becomes narrow.

The dimensions of the arrow-shaped recording mark and its fine shape depend on various factors such as the above-described recording power, the linear velocity during recording, the thermal properties of the disk, the recording laser spot diameter, and the environmental temperature. In particular, in consumer products that can be used in various environments, for example, mini discs (MD), the recording marks are not always written in an optimal state. There is a demand for a reproduction method that is not easily affected by differences in the environment.

[0007] Even in the case of the light modulation method, when overwrite recording is performed, the same cross-write problem as described above occurs. The light modulation method is a method of recording by irradiating modulated light to a magnetic layer while applying a magnetic field from a magnetic head in a DC manner.

The present invention has been made in view of such circumstances, and when reproducing a magneto-optical recording medium on which overwrite recording has been performed, the size and shape of a recording mark due to recording power and recording conditions are reduced. The aim is to reduce the effects of differences.

[0009]

This and other objects are achieved by the present invention which is defined below as (1) to (3). (1) A method for reproducing a magneto-optical recording medium on which overwrite recording has been performed, wherein a reproduction laser beam is irradiated from a center of a recording track so as to be offset from a center of a recording track in a direction avoiding a region overwritten by a recording mark of an adjacent track. A method of monitoring an error flag and / or a jitter component of a read signal at the time of reproduction, and feeding back information on the error to a tracking servo system to adjust an offset amount of a reproduction laser beam. (2) The distance between the centers of adjacent recording tracks is 0.8 to 0.8
(1) The method for reproducing a magneto-optical recording medium according to the above (1), wherein the reproducing laser beam has an offset amount of 0.15 to 0.4 μm. (3) The method for reproducing a magneto-optical recording medium according to the above (1) or (2), wherein the magneto-optical recording medium is recorded by a magnetic field modulation method.

[0010]

As described above, when recording is continuously performed on adjacent tracks on a magneto-optical recording disk of the magnetic field modulation type, if the recording power is large, the recording marks are adjacent as shown in FIG. A cross light spreading to the track occurs. In the conventional magneto-optical recording disk drive, tracking is performed so that the reproduction laser beam traces the center of the recording track. Therefore, jitter increases due to the influence of crosstalk from an adjacent track, and errors frequently occur.

On the other hand, according to the present invention, as shown in FIG. 1D, at the time of reproduction in a recording state in which cross writing occurs, an offset voltage is applied to the tracking servo system so that the reproduction laser beam is The offset is made in the direction, that is, in the direction to avoid the area overwritten by the recording mark of the adjacent track, and the crosstalk from the adjacent track is reduced. For this reason, apparently, the recording power margin is expanded, and even when the recording power is too large, reproduction with less jitter and error can be performed.

Also, the size and shape of the recording mark change due to changes in the recording apparatus and the environment during recording, so that the state of the cross write also changes. Also, since the record mark may not exist on an adjacent track, the cross write It is preferable to change the offset amount of the reproduction laser beam in accordance with the state. Therefore, in the present invention, an error flag and / or a jitter component of a read signal is monitored at the time of reproduction, and information on these is fed back to a tracking servo system to adjust the offset amount of the reproduction laser beam.

As described above, in the present invention, the influence of the cross write can be reduced without superimposing a special control signal on the original recording signal, so that the present invention has a very wide range of application.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the reproducing method for a magneto-optical recording medium according to the present invention will be described below in detail.

In the present invention, the shift amount of the reproduction laser beam with respect to the center of the recording track, that is, the tracking offset amount is not particularly limited, and may be appropriately determined according to the track pitch, the size of the recording mark, and the like. When the thickness is about 8 to 1.6 μm, the tracking offset amount is 0.15 to 0.4 μm, and particularly, the tracking offset amount is 0.1 to 0.4 μm.
It is preferably 15 to 0.3 μm. If the tracking offset amount is too large, tracking servo becomes difficult. More specifically, the tracking offset amount may be determined so that the jitter amount and the error amount are equal to or less than values conforming to various standards.

FIG. 3 shows that the width of the recording mark is 0.5 μm,
The relationship between the tracking offset amount and the reproduction signal output at 1.0 μm and 2.0 μm is shown. As shown in the figure, when the width of the recording mark is 2.0 μm, even if the reproducing laser beam is offset from the center of the recording track by 0.5 μm, the output when the offset is not offset is -2.
Sufficient output of more than dB is secured. The results shown in the figure are obtained by simulation.

FIG. 4 shows that the offset amount of the reproduction laser beam from the center of the recording track is 0 μm, 0.1 μm, 0.
Recording power and EFM 3T for 2 μm
6 shows a relationship with a signal jitter value. In this case, 3
The tracking signal output by the beam method was approximated to a sine wave, and the offset amount was set by converting the offset voltage value from the recording track pitch. The tracking offset amount during recording was set to 0 μm. As shown in the figure, by offsetting the reproduction laser beam from the center of the recording track, the range where the jitter is low is widened, and the range of the recording power margin where the jitter amount is 40 ns or less is widened.

FIGS. 3 and 4 show the results for a magneto-optical recording disk in which the track pitch, that is, the distance between the centers of adjacent recording tracks is 1.6 μm.

When the tracking control is performed by the three-beam method or the push-pull method, usually, the optical axis shift of the objective lens of the optical pickup, the inclination of the disk in the radial direction, the asymmetry of the groove shape of the disk, and the like cause a problem. A DC offset appears in the stocking error signal. For this reason, even if the tracking error signal is zero, the laser beam may be deviated from the track center. Therefore, when the offset voltage is applied to the tracking servo system in the present invention, the offset voltage of the tracking servo system is adjusted such that the actual offset amount of the laser beam is optimized in consideration of the DC offset amount. It is preferable to determine.

The means for offsetting the reproduction laser beam is not particularly limited. Normally, tracking control is performed by driving an optical pickup or its objective lens based on a tracking signal, but by applying an offset voltage to a driving means of a tracking servo system,
When tracking is performed so that the tracking signal becomes zero, the reproduction laser beam can be offset from the center of the recording track. Then, as described above, the error flag and / or the jitter component of the read signal is monitored during reproduction, and information on these is fed back to the tracking servo system to adjust the offset amount of the reproduction laser beam, thereby achieving stable reproduction. It becomes possible.

For example, when the EFM signal is demodulated, if there are many errors, a pulse-like C ₁ flag, which is an error flag of the read signal, frequently occurs. This is monitored, and the generation amount of the C ₁ flag is minimized. What is necessary is just to adjust the offset voltage so as to decrease it.

Specifically, it is preferable to control the offset voltage in the procedure as shown in FIG. The output of C ₁ flag, as shown in FIG. 5 for, integrating as shown in. The reference voltage is determined as described above, and feedback is applied only when the reference voltage is exceeded. The signal output from the comparator when the voltage exceeds the reference voltage is integrated and added as an offset voltage. FIG. 6 shows a block diagram of an example of a circuit utilizing such a procedure.

The reference voltage may be set to a level at which error correction can be reliably performed. If the output integral value of C ₁ flag is less than the reference voltage, because all errors that occurred correctable, as shown on the right side of FIG. 5, there is no need to perform the offset.

[0024] may be Hatarakasere only the circuit in the case where C ₁ flag has been frequently on average, and the like to turn on the indicator light in this, warning that not be the optimum recording, such as Can be used. Also,
If the integration constant is set to a relatively large value, it is possible to prevent a problem that oscillation occurs in response to a sudden burst error.

The reproducing method of the present invention is applied to a magneto-optical recording medium in which cross writing occurs, usually a magneto-optical recording disk having a recording layer using an alloy of a rare earth element and a transition element. This is particularly effective when images are continuous, such as when crosslights occur in one direction. Further, the present invention is applicable not only to the magneto-optical recording medium of the magnetic field modulation system but also to the magneto-optical recording medium of the optical modulation system, but is particularly effective in the magneto-optical recording medium of the magnetic field modulation system.

[Brief description of the drawings]

FIGS. 1A, 1B, 1C, and 1D are diagrams showing an increase in the width of a recording mark with an increase in recording power.

FIG. 2 is a graph showing a relationship between a recording power and a jitter value of an EFM 3T signal.

FIG. 3 shows recording marks having widths of 0.5 μm, 1.0 μm,
9 is a graph showing a relationship between a tracking offset amount and a reproduction signal output at 2.0 μm.

FIG. 4 is a graph showing the relationship between the recording power and the jitter value of an EFM 3T signal when the offset amount of the reproduction laser beam from the recording track center is set to 0 μm, 0.1 μm, and 0.2 μm.

FIG. 5 is an explanatory diagram of offset voltage control.

FIG. 6 is a block diagram illustrating an example of a tracking control circuit to which the present invention is applied.

────────────────────────────────────────────────── (5) References JP-A-58-205936 (JP, A) JP-A-63-255881 (JP, A) JP-A-4-45315 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) G11B 11/105 586 G11B 7/005

Claims (3)

(57) [Claims] 1. A method for reproducing a magneto-optical recording medium on which overwrite recording has been performed, wherein a reproducing laser beam is offset from a center of a recording track in a direction to avoid an area overwritten by a recording mark of an adjacent track. Irradiate and read the error flag and / or
Alternatively, a reproducing method for a magneto-optical recording medium in which a jitter component is monitored and information on the jitter component is fed back to a tracking servo system to adjust an offset amount of a reproducing laser beam. 2. The reproduction of a magneto-optical recording medium according to claim 1, wherein the distance between the centers of adjacent recording tracks is 0.8 to 1.6 μm, and the offset amount of the reproduction laser beam is 0.15 to 0.4 μm. Method. 3. The reproducing method for a magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is recorded by a magnetic field modulation method.