JPH0676401A - Magneto-optical recording method for magneto-optical disk of large heat time constant, recording device and magnet0-optical disk - Google Patents

Abstract

PURPOSE:To exactly record in a disk of large heat time constant by a mark length recording system by adjusting a timing emitting and quenching laser beam by depending on the pattern of a data signal. CONSTITUTION:In the case of a light emitting timing, the shorter/the longer the previous quenching light time is, the light emitting timing is delayed/ quickened. In the case of a light quenching timing, the longer/shorter the previous quenching time, the light quenching timing is quickened/delayed. Thus, in a magneto-optical disk which has large data pattern dependency for forming a mark and more than 30nsec of heat time constant, the timing emitting/ quenching laser beam is adjusted by depending on the signal pattern of data. Thus, the edge shift amount of the mark becomes constant regardless of patterns, a recording can be exactly performed in the disk of large heat time constant by the mark length recording system and the window margin at the time of reproduction becomes wide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording method for recording on a magneto-optical disk having a large thermal time constant, a recording device and a magneto-optical disk.

[0002]

2. Description of the Related Art Currently, optical information recording / reproducing is currently performed on a read-only type such as a compact disc, a laser disc
Write-once type (perforated type) that can record only once
For example, an optical disc having a thin metal film or a cermet film as a recording layer, a type capable of repeating recording, reproduction, and erasing repeatedly, such as a magneto-optical recording type and a phase change type, have been put to practical use or tried.

Among them, the magneto-optical recording has received the most attention, and is being actively put into practical use at present. The recording medium used here is called a magneto-optical disk, and thousands of tracks on which information is recorded or from which information is to be recorded are formed in a spiral or concentric shape. Two types of information units corresponding to 0 and 1 are formed on this track and information is recorded. Actually, the track itself (that is, the ground portion) indicates the first information unit corresponding to one of 0 and 1, and the second information corresponding to the other of 0 or 1 in dots or islands on the track. A unit (recently called a mark) is formed. In this case, the presence or absence of the mark, the interval, and / or the length represent the information. Particularly, a method in which the edge position of the mark represents information is called mark length recording.

In this case, the magneto-optical recording apparatus mainly
Rotating means for rotating the magneto-optical disk, laser beam light source, irradiation optical system for irradiating the disk with a laser beam emitted from the light source, modulation means for emitting and extinguishing the laser beam according to a data (binarization information) signal to be recorded. , And magnetic means for applying a bias magnetic field to the irradiation position.

In this apparatus, while rotating the magneto-optical disk, a laser beam is irradiated onto the magneto-optical disk. At this time, the laser beam is caused to emit and extinguish according to a data signal to be recorded, and a bias magnetic field is applied to the irradiation position. By doing so, a mark whose magnetization direction is reversed is formed on the disk, and the data is recorded at the mark edge position.

[0006]

DISCLOSURE OF THE INVENTION In magneto-optical recording,
Recently, there has been a growing demand for improved storage capacity, and the present inventor
We prototyped a new magneto-optical disk and worked on high-density recording research. However, it has been found that, when attempting to perform high-density recording, this disc has a problem that the conventional technique cannot perform accurate recording and the wind margin is zero or extremely narrow. An object of the present invention is to solve such a problem.

[0007]

Means for Solving the Problems The present inventor first began earnest research to find out the cause of a problem. In the prior art, as shown in (2) in FIG. 2, the power input to simply laser light source is corresponding to the data signal to be recorded (1) high level (P _H), the low level (P _L) It was changing. In response to this, the laser beam emits light (P _H ),
Extinguish (P _L ) Strictly speaking, as shown in FIG. 3, in the case of light emission, complete light emission (high desired light emission intensity) is delayed (Δt) from the data signal. This Δt
Is called rise time. On the other hand, in the case of extinction, the complete extinction (low desired emission intensity or zero intensity) is slightly delayed (Δt) from the data signal. A low desired emission intensity may be desired for tracking and focusing purposes. The latter Δt is called the fall time.

When the laser beam is emitted to irradiate the disc, the temperature of the disc naturally rises.
Then, when the temperature of the disk reaches the critical temperature Tth near the Curie point, the magnetization is reversed by the bias magnetic field and the mark starts to be formed. There is naturally a deviation (Sf shown in FIG. 2) from the time when the data rises from 0 to 1 to start the light emission to the time when Tth is reached and the mark formation is started.
This shift amount Sf is called a mark edge shift amount. This is the amount of deviation on the front side of the mark, but there is also deviation on the rear side of the mark. This time, even if the data falls from 1 to 0 and the extinction is started, the temperature of the disk does not immediately drop below Tth and the mark formation continues. After a while, the temperature of the disk falls below Tth and the mark formation is completed. The amount of deviation (Sb shown in FIG. 2) from the time when the data falls from 1 to 0 and the light is extinguished until the formation of the mark is also called the edge shift amount of the mark.

In addition, light emission is started and the temperature rises and continues to rise even after reaching Tth. As a result, the temperature of the disk diffuses in the width direction of the track and the mark becomes thicker as it goes back. The mark has a teardrop shape, which is also inconvenient. The teardrop-shaped mark lowers the C / N ratio or produces an erase residue. As a result of further research,
It has been found that when high density recording is performed on a magneto-optical disk having a “thermal time constant t ₆₃ ” which will be described later, of 30 nsec or more, the amount of edge shift changes depending on the pattern of the data signal to be recorded. For example, the length of the mark is extended to become another mark, or the two marks are connected to each other to become another long mark. Due to this, it seems that recording could not be done accurately. This can be qualitatively understood. For example, if the next mark is formed immediately after a long mark, the disc will already be preheated and the next mark formation will start earlier.
On the contrary, when the mark is formed after the mark is not formed for a while, the disk is completely cooled and the next mark formation does not start at all. In this way, the change of the edge shift amount depending on the pattern of the data signal to be recorded is expressed as “pattern dependency”.

The present inventor has studied the thermal characteristics and "pattern dependence" of magneto-optical disks. In the process,
The present inventor first measured the later-described “thermal time constant t ₆₃ ” of the magneto-optical disk. The "thermal time constant t _63" is to eliminate the "pattern dependent" having the above magneto-optical disk 30 nsec, it invented a recording method and a recording apparatus for performing recording exactly. This is the present invention.

That is, the first aspect of the present invention is to "irradiate a laser beam onto the magneto-optical disk while rotating the magneto-optical disk. At this time, the laser beam is caused to emit and extinguish according to a data signal to be recorded, and is irradiated. By applying a bias magnetic field to the position, a mark whose magnetization direction is reversed is formed on the disk, and the data is recorded at the mark edge position. In the magneto-optical recording method, the disk has a "thermal time constant t _63". Is 30 nsec or more, and emits light and / or depending on the pattern of the data signal.
Alternatively, a recording method (claim 1) is provided in which the timing of extinction is adjusted so that the edge shift amount of the mark is constant regardless of the pattern.

A second aspect of the present invention is to "irradiate a laser beam onto the magneto-optical disk while rotating it.
The laser beam is caused to emit and extinguish in accordance with a data signal to be recorded, and a bias magnetic field is applied to the irradiation position to form a mark with the magnetization direction reversed on the disc, and the mark edge position is used to write the data. In the magneto-optical recording method for recording, the disk is
A recording method characterized in that the "thermal time constant t ₆₃ " is 30 nsec or more and one mark is formed by repeating emission and extinction of the laser beam in a short time (claim 2). "I will provide a.

Thirdly, the present invention relates to "rotating means for rotating a magneto-optical disk, a laser beam light source, an irradiation optical system for irradiating the disk with a laser beam emitted from the light source, and light emission according to a data signal for recording the laser beam. A magneto-optical recording device comprising a modulation means for extinguishing light, and a magnetic means for applying a bias magnetic field to an irradiation position, forming a mark with the magnetization direction reversed on the disk and recording the data at the mark edge position. ,
The disk has a “thermal time constant t ₆₃ ” of 30 nsec or more, and the timing of emitting and / or extinguishing is adjusted depending on the pattern of the data signal, and thereby the edge shift amount of the mark is patterned. A recording device (claim 3) characterized in that a compensating means for making it constant regardless of the above is added.

A fourth aspect of the present invention is "rotating means for rotating a magneto-optical disk, a laser beam light source, an irradiation optical system for irradiating the disk with a laser beam emitted from the light source, and a laser beam for emitting light according to a data signal to be recorded. A magneto-optical recording device comprising a modulation means for extinguishing light, and a magnetic means for applying a bias magnetic field to an irradiation position, forming a mark with the magnetization direction reversed on the disk and recording the data at the mark edge position. ,
The disk has a “thermal time constant t ₆₃ ” of 30 nsec or more, and repeats light emission and extinction for a short time during the time for which the laser beam is emitted to form one mark. A recording device (claim 4) characterized in that a compensation means is added.

Fifth, in the present invention, the "thermal time constant t ₆₃ " is 30.
A magneto-optical disk of nsec or more (claim 5) is provided.
Sixth, the present invention provides a magneto-optical disk having a “thermal time constant t ₆₃ ” of 40 nsec or more (claim 6). Finally, the present invention provides a magneto-optical disk having a “thermal time constant t ₆₃ ” of 50 nsec or more (claim 7). (

[0016]

[Operation] The thermal time constant will be described. When magneto-optical recording is performed on a magneto-optical disk by using a recording laser beam (pulse), when viewed from the standpoint of thermal diffusion, the magneto-optical disk has two types: an adiabatic magneto-optical disk and a heat-diffusive magneto-optical disk. Exists. It is assumed that the laser beam rises stepwise (like a rectangular wave) from extinction to emission as shown in (2) of FIG. 2 according to the data signal. At this time, the adiabatic disk has a temperature rise per unit intensity of the laser beam [° C./m, as compared with the thermal diffusion disk.
W] is large. That is, in the case of irradiation with the same intensity, the adiabatic disk takes a shorter time to reach the target temperature. On the other hand, an adiabatic disc is used for an instantaneous (elevated) tempera
Time required until saturation (ture profile) reaches (t
_sat ) is longer than the heat diffusion disk. See FIG. This is easy to understand if you think that clay pots are harder to heat and harder to cool than iron pots. The thermal time constant is t _sat
Corresponds to.

As a result of earnest research, the inventor of the present invention has invented a method of measuring the thermal time constant of a disk by first measuring the magneto-optical disk itself. Next, this measuring method will be described. <Measurement Method of Thermal Time Constant> A magneto-optical disk which is an object to be measured and a magneto-optical recording / reproducing apparatus (hereinafter also referred to as an evaluation drive) for evaluating a magneto-optical disk which is a measurement tool (measuring means) are prepared. . The laser beam has NA = 0.55,
The wavelength is 830 nm, and the rise time and fall time are both about 10 nsec. The magneto-optical disk is set in the evaluation drive, and the disk is rotated so that the track of the disk has a measurement linear velocity (V = 11.3 m / sec). Next, the spot of the laser beam of the evaluation drive is turned on on the track. That is, the focusing and tracking servo devices are activated.

Then, the laser beam is pulse-modulated. Although the temperature of the disk rises due to the irradiation of the laser beam, the pulse modulation has a duty cycle duty cycle in which a sufficient time interval is opened to consider that the heat generated by heating each pulse does not interfere with each other. Then, the disc is irradiated with pulses having various pulse durations (hereinafter, abbreviated as PDT; see FIG. 5), and
Calculate the "minimum power (Pth) that can be recorded on the disc" for each PDT. As shown in Figure 6, 1 / Pth
Plot the data on the vertical axis and the PDT on the horizontal axis. 1 / Pt
The saturation level of h is 100. As a typical value of the thermal time constant, select PDT with 1 / Pth of 63. This value is referred to herein, "thermal time constant t _63."

The magneto-optical disk having a large "thermal time constant t ₆₃ " is an adiabatic disk and has a large data pattern dependency of mark formation during recording. As a result of earnest research, the present inventor has found that, in a magneto-optical disk having a “thermal time constant t ₆₃ ” of 30 nsec or more, the mark formation has a large data pattern dependency, so that in the prior art, the information to be recorded is accurate. Found not to be recorded in.

In the prior art, as shown in FIG. 2, the intensity level (mW) of the laser beam is simply high (P _H , P _H ).
_L) a binary light emission (P _H) and extinction (P _L) timing is identical to the timing of the rise and fall of the input data signal (data to be recorded). However,
Strictly speaking, there is a delay Δt shown in FIG. 3, but this point is ignored for now. It has been found that such a simple recording method does not record the information accurately and therefore cannot be reproduced correctly.

According to one aspect of the present invention, the timing of emitting and / or extinguishing the laser beam is adjusted depending on the pattern of the data signal. Depending on the pattern
The timing of light emission can be advanced or delayed, and the timing of extinction can be advanced or delayed depending on the pattern. For example, in the case of light emission timing, when the extinction time before that is short (the disc is preheated),
The shorter the light emission timing is, the earlier the light emission timing is, and the longer the extinction time is, the earlier the light emission timing is advanced. In the case of the extinction timing, if the light emission time before that is long (heat accumulation occurs in the disk), the longer the extinction timing, the earlier the extinction timing.

The other one is to form one mark by not simply continuing to emit a laser beam when forming one mark, but repeating light emission and extinction for a short period during that time. The former is “thermal time constant t ₆₃ ”.
Directly offsets the "pattern dependence" due to the large thermal time constants in adiabatic disks of> 30 nsec. The latter treats heating by the laser beam as adiabatically as possible to form marks at precise edge positions with less laser energy, thereby reducing "pattern dependence".

Hereinafter, the present invention will be described more specifically with reference to Examples.

[0024]

EXAMPLE 1 "thermal time constant t _63" was prepared novel overwritable magneto-optical disk 36Nsec. Structure is resin layer / SiN (700Å) / magnetic film (1300Å) / SiN (700Å) /
It is a resin layer. This disc has the characteristics shown in FIG. After the initialization of the entire surface, this magneto-optical disk was rotated at a measurement linear velocity: V = 11.3 m / sec. The laser beam has NA = 0.55 and wavelength = 830 nm. Emission (P _H ) intensity is 11 mW and extinction (P _L ) intensity is 4.5 m
W. The rise time and fall time of this laser beam were both about 10 nsec.

The beam is pulse-modulated according to the data signal to be recorded. The data signal is 1/2 (2,7) RL
L., 0.54 μm / bit, NR of clock period = 24 nsec
A random signal for ZI mark length recording was used. Here, as shown in (Example) of FIG. 1, and adjusted depending emitting the laser beam (P _H) and quench (P _L) timing pattern of the data signal, and always constant edge shift amount .

The data thus recorded was reproduced with a laser beam intensity P _R = 1 mW and the wind margin at the level of BER = 10 ^-5 was measured. The wind margin was 35% of 12 nsec.

[0027]

2. Description of the Related Art Here, the timing of emitting and extinguishing a laser beam was not adjusted depending on the pattern of a data signal. This is the same as (conventional example) in FIG. Then, in the same manner as in Example 1, a random signal for recording the NRZI mark length was recorded and reproduced. As a result, there was no wind margin. In other words, no accurate data was recorded.

[0028]

Example 2 The same disk as in Example 1 was prepared. After initializing the entire surface, measure the magneto-optical disk linear velocity: V = 1
It was rotated at 1.3 m / sec. Example 1 laser beam
Is the same as. However, the emission intensity has an initial value P _H = 11
mW, and later P _HB = 10mW, quenching intensity P _L = 4.
It was set to 5 mW.

The beam is pulse-modulated according to the data signal to be recorded. The data signal is also the same as in the first embodiment. Here, as shown in (2) of FIG. 8, a device is used in which a second compensating means for repeating light emission and extinction for a short period of time during which a laser beam is emitted to form one mark is added. I was there.

The recorded data was reproduced with a laser beam intensity P _R = 1 mW, and the wind margin at the level of BER = 10 ⁻⁵ was measured. The wind margin was 40% of 12 nsec.

[0031]

As described above, according to the present invention, even if high density recording is performed on a magneto-optical disk having a “thermal time constant t ₆₃ ” of 30 nsec or more, accurate recording can be performed and a window at the time of reproduction can be obtained. Wide margin. The present invention also provides a magneto-optical disk having a “thermal time constant t ₆₃ ” of 30 nsec or more. This can be combined with the recording method of the present invention to form a mark having an accurate length with a small amount of laser energy.

[Brief description of drawings]

FIG. 1 is a chart (waveform diagram) showing emission and extinction of a laser beam modulated according to a data signal to be recorded. Strictly speaking, it is a chart (waveform diagram) of electric power input to the light source of the laser beam.

FIG. 2 is an example of a pattern (waveform) of a data signal to be recorded in the prior art, a chart showing emission and extinction of a laser beam at that time (chart of power input to a light source), and a disk at that time. It is explanatory drawing which shows the relationship of a temperature profile (temperature rising profile) and the mark formed.

FIG. 3 is a chart for explaining the relationship between the “power input to the light source of the laser beam” modulated according to the data signal to be recorded and the intensity of the laser beam that actually emits light.

FIG. 4 is a graph of a temperature profile showing the time required to reach saturation (t _sat ).

FIG. 5 is a waveform diagram illustrating a pulse time length (PDT).

FIG. 6 is a graph in which data is plotted with 1 / Pth as the vertical axis and PDT as the horizontal axis. PDT that 1 / Pth becomes 63
When is selected, this value becomes the “thermal time constant t ₆₃ ” number.

FIG. 7 is a “graph in which data is plotted with 1 / Pth as the vertical axis and PDT as the horizontal axis” of the disk used in the examples.

FIG. 8 is a waveform diagram showing the emission of a laser beam that forms one mark. (1) is a conventional example.
(2) are examples, to form the same one mark, the emission of the laser beam (P _H, P _HB) and extinction (P
_L ) is repeated. Emission, when repeating the quenching is characterized in that the lowering from the initial value P _H to P _HB light emission level.

Claims (7)

[Claims] 1. A magneto-optical disk is irradiated with a laser beam while rotating the magneto-optical disk, and the laser beam is caused to emit and to extinguish according to a data signal to be recorded,
And by applying a bias magnetic field to the irradiation position, a mark whose magnetization direction is reversed is formed on the disk,
In the magneto-optical recording method of recording the data at the mark edge position, the disc has a "thermal time constant t ₆₃ " of 30 nsec or more, and the disc emits and / or extinguishes light depending on the pattern of the data signal. The recording method is characterized in that the timing of the edge shift is adjusted so that the edge shift amount of the mark is constant regardless of the pattern. 2. A magneto-optical disk is rotated while being irradiated with a laser beam, wherein the laser beam emits and extinguishes in accordance with a data signal to be recorded,
And by applying a bias magnetic field to the irradiation position, a mark whose magnetization direction is reversed is formed on the disk,
In the magneto-optical recording method of recording the data by the mark edge position, the disk has a “thermal time constant t ₆₃ ” of 30 nsec or more, and the laser beam is repeatedly emitted and extinguished in a short time. A recording method characterized by forming one mark. 3. Rotating means for rotating a magneto-optical disk, a laser beam light source, an irradiation optical system for irradiating the disk with a laser beam emitted from a light source, a modulating means for emitting and extinguishing the laser beam according to a data signal to be recorded, And a magneto-optical recording device comprising magnetic means for applying a bias magnetic field to an irradiation position, wherein a mark having a magnetization direction reversed is formed on the disk, and the data is recorded at a mark edge position. The thermal time constant t ₆₃ ”is 30 nsec or more, and the timing of light emission and / or extinction is adjusted depending on the pattern of the data signal, whereby the edge shift amount of the mark is constant regardless of the pattern. A recording apparatus, characterized in that a compensation means is added. 4. A rotating means for rotating a magneto-optical disk, a laser beam light source, an irradiation optical system for irradiating the disk with a laser beam emitted from a light source, a modulating means for emitting and extinguishing the laser beam according to a data signal to be recorded, And a magneto-optical recording device comprising magnetic means for applying a bias magnetic field to an irradiation position, wherein a mark having a magnetization direction reversed is formed on the disk, and the data is recorded at a mark edge position. A thermal time constant t ₆₃ ”is 30 nsec or more, and a second compensating means for repeating light emission and extinction for a short period of time during which the laser beam is emitted to form one mark is added. A recording device characterized by the above. 5. A "thermal time constant t _63" is more 30nsec magneto-optical disk. 6. "thermal time constant t _63" is more 40nsec magneto-optical disk. 7. "thermal time constant t _63" is more 50nsec magneto-optical disk.