JPH0714234A - Erasing of magneto-optical recording and recording/ reproducing apparatus - Google Patents

Abstract

PURPOSE:To eliminate drop of C/N and maintain high quality by controlling focus of laser beam at the erasing time to increase diameter of spot, and moreover, intensifying a magnetic field to be applied. CONSTITUTION:The magneto-optical recording apparatus is provided with a focus control means 13 in such a manner as being added to a light source drive circuit 1. A medium on which information is recorded, is irradiated with non- modulating laser beam of 8mW as in the case of the recording time under the condition that the focal depth is kept shallower than that in the recording time. Moreover, the magnetic field of 400Oe is impressed in the direction opposed to that of the recording time to the medium for the erasing purpose. In this case, a noise level of the reproduced signal of 1.5MHz is -72dB and a signal by carrier is not detected. Therefore, erasing can be performed without any incomplete erasing of the recording marks, while the irradiation intensity of laser beam is not increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of erasing a magneto-optical recording medium and a magneto-optical recording / reproducing apparatus capable of executing the method.

[0002]

2. Description of the Related Art Recently, an optical recording / reproducing system having characteristics such as high density, large capacity, high access speed and high recording / reproducing speed has been put into practical use, and research and development have been actively conducted for further improvement. The optical information recording medium has a disc shape and is called an optical disc. This is roughly classified into a read-only type and a recordable type.

In the read-only type, protrusions or depressions called bits (or pits or recording marks) are formed in the recording layer at the time of manufacturing the disc, and the presence or absence thereof or the length thereof represents information. The recordable type is roughly classified into a write-once type (also called a write-once or a DRAW) that can be recorded only once and a rewritable type that can repeatedly record and erase.

The former has a recording layer made of Te-C, Te-Se-Pb, a resin containing a dye, or the like, and when a laser beam is irradiated on this, a hole (bit) is opened.
Information is represented by the presence or absence of this bit or its length. The latter is currently in practical use as a phase change type (crystalline-amorphous) and a magneto-optical type. The phase-change type has a crystalline phase recording layer made of TeO ₂ -Tb-Ge or InSe, which is irradiated with a strong laser beam to heat the crystalline phase to a temperature above its melting point, and then to be cooled to an amorphous state. Form a bit. Information is represented by the presence or absence of this bit or its length.

The erasing laser beam crystallizes (erases) by heating an amorphous bit above the crystallization temperature and cooling it. Immediately after this erasing laser beam, a recording laser beam is irradiated to perform recording according to information. With this, recording and erasing are repeated. The magneto-optical type has a recording layer made of a magnetic thin film that can be perpendicularly magnetized. Once the direction of magnetization is aligned upward or downward (called initialization), this is irradiated with a laser beam and simultaneously recorded. By applying a magnetic field, a minute region (bit) whose magnetization direction is reversed is formed. Information is represented by the presence or absence of this bit or its length. When the bit is irradiated with linearly polarized light (weak laser beam), the plane of polarization of reflected light or transmitted light is rotated by + θ _k . This is called the Kerr effect or the Faraday effect. On the other hand, "ground" other than a bit
Part rotates -θ _k . Therefore, when the reflected light or the transmitted light is passed through a polarizer (detector), the bit can be captured as a change in the light amount. The change in the amount of light can be captured by the photoelectric conversion element as a change in the strength of the electric signal.

A typical magneto-optical recording layer is a rare earth-transition metal amorphous alloy such as TbFe, GdFe, Gd.
Single layer films such as Co, DyFe, GdTbFe, GdFeCo, GdFe / TbFe,
There are two-layer films such as GdFeCo / TbFeCo. In particular, a magneto-optical type magneto-optical recording medium is a high-density recording medium that has recently attracted attention because it can be recorded and reproduced many times by erasing recorded information.

When performing recording by magneto-optical recording, it is necessary to make the magnetization directions of the recording medium uniform before recording. This is called initialization. The writing (recording) of information to a recording medium that is magnetized in one direction (initialization) uses irradiation of a laser beam in which the irradiation intensity of the laser beam is modulated and application of a magnetic field. At this time, the laser beam is controlled so as to focus on the surface of the recording medium, and the temperature of the irradiated portion (laser beam spot) rises. The coercive force of the recording medium decreases as the temperature rises due to the laser beam irradiation. Eventually, the coercive force becomes zero at the Curie temperature of the material used for the recording medium. When the temperature of the recording medium reaches near the Curie temperature, the magnetization of the recording medium is reversed and information is recorded by applying a magnetic field from the outside in the direction opposite to the direction of initialization magnetization.

Erasure of recorded information is generally performed by irradiating an unmodulated laser beam and simultaneously applying a magnetic field. The laser beam is controlled so as to be focused on the surface of the recording medium as in the recording. At the portion where the coercive force is weakened due to the temperature rise due to the irradiation of the laser beam, it is possible to erase the information once recorded by applying a magnetic field from the outside in the opposite direction to that at the time of recording.

[0009]

The present inventor has repeatedly performed recording / reproducing by the conventional recording / reproducing method and erasing method. As a result, there is a problem that the C / N ratio of the reproduced signal is lowered each time recording / reproducing is repeated. Further, along with this, there has been a problem that the usage period of the recording medium is shortened. The present invention is to solve these problems.

[0010]

The inventor of the present invention has verified the cause of the decrease in the C / N ratio of the reproduced signal in each of the recording medium manufacturing method, recording / reproducing method and erasing method. As a result of verification, it was found that there is a problem in the irradiation method of the laser beam at the time of erasing. Conventionally, the laser beam spot diameter during erasure is the bit (hereinafter referred to as recording mark) diameter (width)
Since it has the same diameter as that of, it is theoretically possible to completely erase the recording mark. However, in reality, it is difficult for the laser beam spot to completely follow the recording mark during erasing. That is, a tracking error occurs. Therefore, the laser beam spot at the time of erasure and the recording mark are displaced from each other, and the old recording mark previously formed can be left unerased. As a result of research, it was found that when a new recording mark is formed in the state where there is an unerased portion, the unerased portion becomes noise and the C / N ratio decreases.

In order to solve this, the inventor of the present invention sets the irradiation intensity of the laser beam at the time of erasing higher than the irradiation intensity at the time of conventional erasing, and raises the temperature of the recording medium surface in a wider range (recording medium material). The Curie temperature) was used to invert the magnetization to erase it. However, when the irradiation intensity of the laser beam is increased, the area of high temperature becomes wider, but the temperature near the center of the laser beam spot becomes much higher than that of the conventional spot center. In magneto-optical recording, it has been found that when the magnetic film is heated to a high temperature and the magnetization reversal is repeated, the deterioration speed of the magnetic film increases.

Therefore, as a result of earnest research, the present inventor has developed a method of erasing magneto-optical recording which does not cause a decrease in C / N ratio even if recording / reproduction is repeated without increasing the irradiation intensity of a laser beam during erasing. I found it. Therefore, the present invention firstly provides: "First step: a step of rotating a magneto-optical recording medium on which recording marks are formed; second step: irradiating the recording medium with a laser beam which is not modulated to form a part of the recording medium. Locally heating the glass to near its Curie temperature; Third step: applying a magnetic field to the recording medium during the second step,
Reversing the direction of magnetization of the recording mark to the direction of magnetization of the recording mark; in the step of erasing the recording mark of the magneto-optical recording medium, the laser beam is controlled to a defocused state, and The method for erasing magneto-optical recording is characterized in that the magnetic field is controlled so as to be larger than that during recording (claim 1).

Second, according to "rotating means for rotating a magneto-optical recording medium, a laser beam light source, and binary information for recording the intensity of a laser beam, modulation is performed between a high level and a low level, or a constant level. In a magneto-optical recording / reproducing apparatus comprising a light source drive circuit for irradiating light without being modulated with intensity and a recording magnetic field applying means, a focus control means for controlling a spot of a laser beam to a defocused state and the external magnetic field are recorded. There is provided a magneto-optical recording / reproducing device (claim 2) characterized in that a magnetic field strength control means for increasing the magnetic field intensity is provided.

[0014]

FIG. 1 shows the temperature distribution on the surface of the recording medium due to the difference in the focus depth when the recording medium is irradiated with the beam with a constant laser beam irradiation intensity. Since the temperature distribution of the laser beam spot has a Gaussian distribution, the temperature distribution of the surface of the recording medium irradiated with the laser beam is highest at the center of the spot, and the temperature decreases as the distance from the center increases.

FIG. 1A shows the temperature distribution on the surface of the recording medium when the surface of the recording medium is focused, which is the conventional method, and FIG. 1B shows the focus distribution which is the invention of the present application. It is the temperature distribution on the surface of the recording medium when a laser beam is irradiated in this state. Then, at the time of erasing the recording mark, a portion (a, b in FIG. 1) where the surface temperature of the recording medium is heated to near the Curie temperature indicated by Tc is
The magnetization direction is reversed by the application of a magnetic field from the outside, and the recording marks are erased by aligning in one direction.

In the present invention, as shown in FIG. 1B, the focus of the laser beam at the time of erasing is controlled in the defocus state so that the spot diameter becomes larger than the recorded mark diameter. At this time, it is necessary that the temperature of the irradiated recording medium surface reaches the Curie temperature (T _c ) required for magnetization reversal. As a result, the area where the temperature is raised to the Curie temperature (T _C ) (temperature required for magnetization reversal) without increasing the laser beam power from that at the time of recording mark formation (a) in FIG. ) Can be enlarged as

Simultaneously with the control of the focus of the laser beam, the magnetic field applied at the time of erasing is controlled to make the intensity higher than that at the time of recording. This enables erasing with a lower laser beam irradiation intensity. As shown in FIG. 2, the coercive force of the magneto-optical recording medium decreases as the temperature of the recording medium rises. For example, set the strength of the magnetic field applied during erase to 0.
When 4 kOe is used, it is necessary to raise the temperature of the medium to T _B , but when the magnetic field strength is raised to 0.8 kOe, T _A
The magnetization can be reversed by raising the temperature to. That is, the region heated to T _A in FIG. 1 can be erased, and even when a laser beam with the same irradiation intensity is used, the intensity of the applied magnetic field can be increased to erase a wider region. .

[0018]

Example 1 A magneto-optical recording medium was rotated at a rotation speed of 1500 rpm, and a signal of 1.5 MHz was recorded at a location with a radius of 90 mm. The power of the laser beam applied during recording was 8 mW and the strength of the applied magnetic field was 300 Oe. When the recorded information was reproduced, the carrier level at 1.5MHz was -12dB and the noise level was -70dB.

A laser beam, which is not modulated in a state where the depth of focus is shallower than that at the time of recording, is applied to the medium on which the above information is recorded at 8 mW as in the case of recording, and the laser beam is irradiated in a direction opposite to that at the time of recording
Erase was performed by applying a magnetic field of 00 Oe. Playback signal 1.5MH
The noise level at z was -72 dB, and no signal due to the carrier was detected. FIG. 3 shows a schematic view of the magneto-optical recording / reproducing apparatus used in this example. In FIG. 3, the focus control means is installed in a state of being added to the light source drive circuit, but a circuit for controlling focus may be formed in the light source drive circuit.

The same applies to the magnetic field strength control means,
It may be incorporated in the recording magnetic field applying means.

[0021]

[Example 2] A laser beam which is not modulated in a state where the depth of focus is shallower than that at the time of recording is radiated on the medium on which the same information as that in Example 1 is recorded at 8 mW as in the case of recording, and 1000 Oe in the direction opposite to the direction of recording The magnetic field was applied to erase the data. The noise level of the reproduced signal at 1.5MHz was -72dB, and the signal due to the carrier was not detected.

[Comparative Example 1] A laser beam focused on the medium surface was applied in the same manner as during recording while applying a magnetic field of 300 Oe to the medium in which the same information as in Example 1 was recorded in the direction opposite to that during recording. It was erased by irradiation with a power of 8 mW.
The carrier level of the reproduced signal at 1.5 MHz was -55 dB and the noise level was -70 dB, and the information once recorded was not completely erased.

[Comparative Example 2] A laser beam focused on the medium surface was applied in the same manner as during recording while applying a magnetic field of 400 Oe to the medium in which the same information as in Example 1 was recorded in the opposite direction to that during recording. It was erased by irradiation with a power of 8 mW.
The carrier level of the reproduced signal at 1.5 MHz was -50 dB, and the noise level was -70 dB, and the information once recorded was not completely erased.

[Comparative Example 3] A laser was applied to a medium on which the same information as in Example 1 was recorded in the same direction as that during recording while applying a magnetic field of 300 Oe in the same direction as in Example 1 and with a shallow depth of focus. Erasing was performed by irradiating the beam with a power of 8 mW. The carrier level of the reproduced signal at 1.5MHz is -60d
B, the noise level was -70 dB, and the information once recorded was not completely erased.

[0025]

According to the present invention, the spot diameter is increased by controlling the focus of the laser beam during erasing, and the strength of the applied magnetic field is increased. As a result, the recording marks can be erased without being erased without increasing the irradiation intensity of the laser beam, so that the C / N ratio does not decrease and the quality of the magneto-optical recording medium can be maintained at a high level. Further, since the magnetic film is not deteriorated, the medium is used for a long period of time, which is economical.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a relationship between a focus depth and a temperature distribution on a surface of a recording medium.

FIG. 2 is an explanatory diagram showing the temperature of the recording medium and the coercive force of the recording medium.

FIG. 3 is a schematic diagram showing a magneto-optical recording / reproducing apparatus according to the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source driving circuit 2 ... Light source 3, 5, 7 ... Collimator lens 4 ... Beam splitter 6 ... Recording medium rotating means 9 ... Detector 10 ... Pulse waveform shaping circuit 12 ... Magnet 13 ... Focus control means 14 ... Magnetic field strength control means

Claims (2)

[Claims] 1. A first step: a step of rotating a magneto-optical recording medium having recording marks formed thereon; a second step: irradiating the recording medium with a laser beam which is not modulated so that a part of the recording medium has a Curie temperature. A step of locally heating close to the third step; a third step: applying a magnetic field to the recording medium during the second step,
In the step of erasing the recording mark of the magneto-optical recording medium, which comprises the step of reversing the direction of magnetization of the recording mark to the direction of magnetization of the recording mark; The method for erasing magneto-optical recording is characterized by controlling so that the value becomes larger than that during recording. 2. A rotating means for rotating a magneto-optical recording medium, a laser beam light source, and modulation between a high level and a low level or a constant intensity according to binary information to record the intensity of the laser beam. In a magneto-optical recording / reproducing apparatus including a light source drive circuit for irradiating light without writing and a recording magnetic field applying means, a focus control means for controlling a spot of a laser beam to a defocus state and the external magnetic field are made larger than during recording. A magneto-optical recording / reproducing apparatus comprising magnetic field strength control means.