JP3547627B2 - Method and apparatus for reproducing information recorded on magnetically induced super-resolution magneto-optical recording medium - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for reproducing information recorded on a magneto-optical recording medium.
Magneto-optical disks are known as high-density recording media, but are required to have higher densities as the amount of information increases. Higher density can be achieved by reducing the interval between recording marks, but its recording and reproduction are limited by the size (beam spot) of the light beam on the medium.
[0002]
If the setting is such that only one recording mark exists in the beam spot, an output waveform corresponding to "1" or "0" can be observed as a reproduction signal depending on whether or not there is a recording mark.
[0003]
However, if the interval between recording marks is reduced so that a plurality of beam spots are present in the beam spot, the reproduced output does not change even if the beam spot on the medium moves, so that the output waveform becomes a straight line and the The presence or absence cannot be identified.
[0004]
In order to reproduce such a small recording mark having a period equal to or smaller than the size of the beam spot, the beam spot may be narrowed down. However, the size of the beam spot depends on the wavelength λ of the light source and the numerical aperture NA of the objective lens. And cannot be narrowed down sufficiently.
[0005]
[Prior art]
Recently, a reproduction method using a magnetically induced super-resolution medium (hereinafter, referred to as an MSR medium) for reproducing a recording mark having a size equal to or smaller than a beam spot using the current optical system as it is has been proposed. . This is a reproducing method in which when one mark in a beam spot is reproduced, another mark is masked to increase the reproducing resolution.
[0006]
For this reason, the MSR medium requires at least a mask layer or a reproduction layer for hiding another mark so that only one mark is reproduced at the time of signal reproduction, in addition to the recording layer for recording the mark.
[0007]
Hereinafter, this MSR medium and its recording / reproducing method will be briefly described. FIG. J. Appl. Phys. Vol. 31 (1992) pp. 568-575 Part 1. No. FIG. 2B is a diagram showing a configuration of an MSR medium disclosed in February 1992 and a positional relationship between a recording mark and a beam spot on a recording track.
[0008]
A magnetic reproducing layer 2, a magnetic switch layer 3, and a magnetic recording layer 4 are sequentially stacked on a transparent substrate (not shown). Data is recorded on the recording layer 4 in the direction of magnetization, and recording marks 6 are formed on the recording track 5 at a pitch smaller than the spot diameter of the laser beam to be irradiated.
[0009]
The reproducing layer 2 is made of GdFeCo, and has a Curie temperature of 300 ° C. or higher. The switch layer 3 is made of GdFeCoAl and has a Curie temperature of about 140 ° C. The recording layer 4 is made of GdFeCo, and has a Curie temperature of about 250 ° C.
[0010]
In the case of a magneto-optical recording medium, by controlling the power of the laser beam at the time of recording, the area where the Curie temperature is equal to or higher than Tc can be made smaller than the beam spot diameter, so that it is not so difficult to form a small recording mark.
[0011]
Next, a method of reproducing information recorded on a medium will be described. At room temperature, the direction of magnetization of the reproducing layer 2 matches the direction of magnetization of the recording layer 4 due to exchange coupling via the switch layer 3.
[0012]
However, in a portion (high-temperature region) where the temperature rises due to the irradiation of the reproducing laser beam 7 and exceeds the Curie temperature Tc of the switch layer 3, exchange coupling between the recording layer 4 and the reproducing layer 2 is broken. The magnetization direction of the portion of the reproducing layer 2 is aligned with the direction of the reproducing magnetic field Hr applied from the outside.
[0013]
As a result, the high-temperature area serves as a mask that covers the recording marks, and data recorded on the recording layer 4 can be read from the low-temperature area in the beam spot 8. In this way, the recording mark can be read from an area smaller than the beam spot diameter of the reproducing laser beam, and the resolution is substantially the same as when reproducing with a beam spot smaller than the beam spot diameter of the reproducing laser beam. Is obtained.
[0014]
FIG. 2 is a graph showing reproduction signal characteristics when the above-described MSR medium is used and when a conventional ordinary magneto-optical recording medium is used. When the MSR medium is used, good reproduction characteristics are obtained even when the recording linear density increases and the recording marks become smaller.
[0015]
The method of reading a recording mark from a low-temperature area by masking a high-temperature area in a beam spot as described above is called an FAD (Front Aperture Detection) method.
[0016]
Contrary to this example, a method of reading a recording mark from a high-temperature area by masking a low-temperature area in a beam spot is called a RAD (Rear Aperture Detection) method, and enables high-resolution reproduction similarly to the FAD method. .
[0017]
This RAD method can be realized with a magneto-optical disk having a two-layer film structure of a magnetic reproducing layer and a magnetic recording layer. An initializing magnetic field is applied just before the irradiation of the reproducing laser beam, so that only the reproducing layer is aligned with the magnetization direction of the initializing magnetic field when the recording mark passes through the initializing magnetic field.
[0018]
At this time, the recording layer holds the recording mark. Immediately after the application of the initialization magnetic field, the reproducing layer functions as a mask in a state where the data in the recording layer is covered by the reproducing layer. When the reproducing laser beam is irradiated, the temperature of the reproducing layer, which is a mask, rises.
[0019]
When the exchange coupling force between the recording layer and the reproducing layer becomes larger than the coercive force of the reproducing layer, the magnetization direction of the recording layer is transferred to the reproducing layer. That is, the mask of the reproducing layer is removed in the high temperature region, and the recording mark can be read from the high temperature region.
[0020]
[Problems to be solved by the invention]
As described above, when reproducing the FAD type MSR medium, it is necessary to apply the reproducing magnetic field Hr. However, since a normal magneto-optical disk reproducing apparatus has a configuration in which a magnetic field is not applied during reproduction, there is a problem that information recorded on an MSR medium cannot be reproduced with a normal reproducing apparatus as it is.
[0021]
FIG. 3 shows the relationship between the peripheral speed of the medium and the power of the reproducing laser beam in the MSR medium. This graph is a graph showing the minimum reproduction laser power when a C / N of 43 dB or more is obtained by changing the peripheral speed by setting the mark length to 0.4 μm.
[0022]
The reproduction laser power of an ordinary magneto-optical disk is about 1.0 to 1.5 mW and does not depend on the peripheral speed. On the other hand, the reproduction laser power itself is large in the MSR medium and the required minimum power value. Changes depending on the peripheral speed.
[0023]
Therefore, in a normal magneto-optical disk, it is not a problem if the laser diode continuously emits light while maintaining the above power, but it is necessary to always maintain a high laser power during reproduction in the MSR medium. There is a problem that the life of the diode is reduced.
[0024]
Accordingly, an object of the present invention is to provide a method and an apparatus for reproducing information recorded on a magneto-optical recording medium which can prevent the life of a light source from being shortened by increasing the power of a reproducing laser beam only when reproducing recorded information. It is to provide.
[0025]
[Means for Solving the Problems]
According to the present invention, a magneto-optical recording unit capable of reproducing information with a higher resolution than an optical resolution determined by the size of a beam spot formed on a magneto-optical recording medium by irradiation of a reproducing laser beam, and a preformat unit are provided. In the method for reproducing information recorded on a magneto-induction super-resolution magneto-optical recording medium, the method comprises the steps of: A method for reproducing information recorded on a magnetically induced super-resolution magneto-optical recording medium, characterized in that the power is larger than the power of a reproducing laser beam at the time of performing.
[0026]
Preferably, the switching of the power of the reproduction laser beam is performed according to a magneto-optical data read gate signal based on the ID detection signal of the preformat unit. Preferably, the circuit for switching the reproduction laser beam power is also used as the circuit for generating the laser beam power for recording.
[0027]
According to another aspect of the present invention, there is provided an optical system having a laser light source for irradiating a reproducing laser beam to a magneto-optical recording medium, the optical source being determined by the size of a beam spot formed on the magneto-optical recording medium by the irradiation of the reproducing laser beam. A magneto-optical recording unit capable of reproducing information at a resolution higher than the resolution, and a reproducing apparatus for information recorded on a magnetic induction super-resolution magneto-optical recording medium having a preformat unit, wherein the information recorded on the magneto-optical recording unit is recorded. magnetic induction super the reproducing laser beam power when reproducing information, characterized by comprising a switching means for switching to a larger laser beam power than the reproduction laser beam power when reproducing information of the preformat portion has An apparatus for reproducing information recorded on an image magneto-optical recording medium is provided.
[0028]
Preferably, the switching of the reproduction laser beam power by the switching means is performed according to a magneto-optical data read gate signal based on an ID detection signal of the preformat section.
[0029]
Preferably, the reproducing laser beam power is set according to the reproducing position of the magneto-optical recording medium. More preferably, the switching means comprises a switching circuit, and the switching circuit is also used as a circuit for generating a laser beam power for recording.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, with reference to the drawings, a description will be given of a reproducing method and apparatus according to the present invention, which is characterized by performing switching of a reproducing laser beam power when reproducing information recorded on an MSR medium.
[0031]
FIG. 4A shows the format of a recording sector of the MSR medium, and FIG. 4B shows the timing of the reproducing method of the present invention in accordance with the recording format shown in FIG.
[0032]
In the magneto-optical disk, a sector mark area where a sector mark is recorded by a preformat signal, a track number and a sector number are also recorded by a preformat signal at the head of each sector as shown in FIG. ID areas are provided in this order. Following these preformat areas, a data area in which user data is recorded is provided.
[0033]
In the case of reproduction, first, a sector mark is detected, and based on this, an ID read gate is opened and data in an ID area is read. When the reproduced ID number (track number, sector number) matches that of the sector to be reproduced, an ID detection signal is output.
[0034]
Based on the ID detection signal, a data read gate for reproducing data in the data area where the magneto-optical recording is performed is opened. Since the number of bytes in the data area per sector is determined in advance, when the reproduction of the data of a predetermined length is completed, the data read gate closes and the reproduction operation ends.
[0035]
In the reproducing method of the present invention, when reproducing magneto-optically recorded data, the reproducing laser power is made higher than when reproducing preformatted data or when in a standby state.
[0036]
As the switching timing of the reproduction laser power, a data read gate signal for opening the data read gate is used. While the data read gate is open, that is, when the data read gate signal is high, the reproducing laser power is increased to an intensity that is optimal for reproducing the data magneto-optically recorded on the MSR medium.
[0037]
By performing such control, the reproducing laser power can be reliably increased only during reproducing the magneto-optically recorded data, and in other cases, the reproducing laser power can be suppressed to a low level.
[0038]
By the way, in the MSR medium, the super-resolution effect cannot be obtained unless the temperature exceeds a predetermined temperature. Therefore, as shown in FIG. 3, when the peripheral speed changes, the minimum reproduction laser power at which the super-resolution effect can be obtained also differs. .
[0039]
Therefore, it is not necessary to maintain a constant high level of the reproducing laser power during reproducing the magneto-optically recorded data, and it is more effective to change the reproducing laser power according to the peripheral speed.
[0040]
The peripheral speed of the MSR medium can be easily calculated from the standardized radial position of the MSR medium. Further, the radial position can be easily known by reading the track number in the ID area.
[0041]
Therefore, based on the signal indicating the track number corresponding to the radial position, the current value to be applied to the laser diode to achieve the minimum necessary reproduction laser power that can be reproduced may be set.
[0042]
FIG. 5 is a schematic diagram showing a configuration of a reproduction laser power switching circuit used in the reproduction method and the reproduction apparatus of the present invention, which is configured in consideration of such points. In FIG. 5, reference numeral 50 denotes a laser diode as a light source, and 52 denotes a photodiode for monitoring a laser beam from the laser diode 50.
[0043]
An auto power control circuit (APC circuit) 54 controls a current flowing to the laser diode 50 based on the monitoring result of the photodiode 52 so that a laser beam having a predetermined power is emitted from the laser diode 50.
[0044]
A constant current circuit 58 is connected to the laser diode 50 via a switch 56 whose opening and closing are controlled based on the data read gate signal described above. Similarly, a constant current circuit 62 is connected to the photodiode 52 via a switch 60 whose opening and closing are controlled based on a data read gate signal.
[0045]
Each of the constant current circuits 58 and 62 is connected to a current value setting circuit 64 for setting an appropriate current value based on a signal indicating a radial position (track number). Output to the constant current circuits 58 and 62.
[0046]
In operation, when the data in the preformat recording section is reproduced during standby or when the data in the preformat recording section is reproduced, the switches 56 and 60 are opened without inputting the data read gate signal.
[0047]
Under the control of the APC circuit 54, the laser diode 50 emits light at a predetermined low laser power. When the signal indicating the track number of the ID area is read, the current value for outputting the lowest reproducible laser power corresponding to the peripheral speed at the track number in the current value setting circuit 64 is determined based on the track number. It is set and output to each of the constant current circuits 58 and 62.
[0048]
When the reading of the ID area is completed, a data read gate signal is output and input to each of the switches 56 and 60, and the reproduction of data in the magneto-optical recording section is started. At this time, the laser diode 50 emits light at the data reproduction power level of the magneto-optical recording section.
[0049]
Since the switch 56 is closed by the input of the data read gate signal, a current corresponding to the power increase flows from the laser diode 50 to the constant current circuit 58. At this time, the switch 60 is also closed at the same time, and the same amount of current flows from the photodiode 52 to the constant current circuit 62.
[0050]
Therefore, while the data read gate signal is being input, the magneto-optically recorded data is reproduced while maintaining a high reproduction laser power. That is, by absorbing the output current of the photodiode 52 corresponding to the increase in the power of the output beam of the laser diode 50 by the constant current circuit 62, the APC circuit 54 controls the laser power as if it did not change. Continue working.
[0051]
Then, when the data read gate signal is not input, that is, when the reproduction of the magneto-optically recorded data is completed, a low power laser beam is output from the laser diode 50.
[0052]
The circuit configuration shown in FIG. 5 is equivalent to the configuration of a circuit that generates a recording laser power for recording, and therefore these circuits can be used also.
[0053]
【The invention's effect】
As described above in detail, according to the present invention, the reproducing laser power is increased only when reproducing magneto-optically recorded information. Data can be reproduced with an appropriate reproduction laser power.
[Brief description of the drawings]
1A and 1B are diagrams illustrating the principle of reproduction of a conventional MSR medium, wherein FIG. 1A is a plan view of the medium, and FIG. 1B is a cross-sectional view of the medium.
FIG. 2 is a graph showing reproduction signal characteristics of an MSR medium and a normal magneto-optical recording medium.
FIG. 3 is a graph showing a relationship between a peripheral speed of an MSR medium and a reproduction laser power required for reproduction.
FIG. 4 is a format diagram of a recording sector and a timing chart of a reproducing method according to the present invention.
FIG. 5 is a configuration diagram of a circuit for implementing a reproduction method of the present invention.
[Explanation of symbols]
Reference Signs List 50 laser diode 52 photodiode 54 APC circuit 58, 62 constant current circuit

Claims (8)

A magneto-optical recording unit capable of reproducing information with a higher resolution than the optical resolution determined by the size of the beam spot formed on the magneto-optical recording medium by the irradiation of the reproducing laser beam, and a magnetic induction super-solution having a pre-format unit In a method for reproducing information recorded on an image magneto-optical recording medium,
Magnetic induction greater, wherein a reproducing laser beam power when reproducing information recorded on the magneto-optical recording unit, larger than the power of the reproducing laser beam in reproducing information of the preformat portion A method for reproducing information recorded on a resolution magneto-optical recording medium. A magneto-optical recording unit capable of reproducing information with a higher resolution than the optical resolution determined by the size of the beam spot formed on the magneto-optical recording medium by the irradiation of the reproducing laser beam, and a magnetic induction super-solution having a pre-format unit In a method for reproducing information recorded on an image magneto-optical recording medium,
The power of the reproducing laser beam when reproducing the information recorded in the magneto-optical recording unit is made larger than the power of the reproducing laser beam or the power of the standby laser beam when reproducing the information of the preformat unit. With
A method for reproducing information recorded on a magnetic induction super-resolution magneto-optical recording medium , wherein switching of the power of the reproduction laser beam is performed in response to a magneto-optical data read gate signal based on an ID detection signal of the preformat section. 3. The reproducing method according to claim 1, wherein the reproducing laser beam power is set according to a reproducing position of the magneto-optical recording medium. 4. The reproducing method according to claim 1, wherein a circuit for switching the reproducing laser beam power is also used as a circuit for generating a laser beam power for recording. A laser light source for irradiating the magneto-optical recording medium with a reproducing laser beam; reproducing information at a resolution higher than the optical resolution determined by the size of the beam spot formed on the magneto-optical recording medium by the irradiation of the reproducing laser beam; A magneto-optical recording unit capable of, and a reproducing apparatus for information recorded on a magnetic induction super-resolution magneto-optical recording medium having a pre-format unit,
Switching means for switching a reproduction laser beam power when reproducing information recorded in the magneto-optical recording section to a laser beam power larger than a reproduction laser beam power when reproducing information from the preformat section is provided. An apparatus for reproducing information recorded on a magnetic induction super-resolution magneto-optical recording medium, comprising: A laser light source for irradiating the magneto-optical recording medium with a reproducing laser beam; reproducing information at a resolution higher than the optical resolution determined by the size of the beam spot formed on the magneto-optical recording medium by the irradiation of the reproducing laser beam; A magneto-optical recording unit capable of, and a reproducing apparatus for information recorded on a magnetic induction super-resolution magneto-optical recording medium having a pre-format unit,
The reproducing laser beam power when reproducing the information recorded in the magneto-optical recording unit is larger than the reproducing laser beam power or the standby laser beam power when reproducing the information in the preformat unit. Switching means for switching to
The switching of the reproduction laser beam power by the switching means is performed in accordance with a magneto-optical data read gate signal based on an ID detection signal of the pre-format section, and recorded on a magnetic induction super-resolution magneto-optical recording medium. Information playback device. 7. The reproducing apparatus according to claim 5, wherein the reproducing laser beam power is set according to a reproducing position of the magneto-optical recording medium. 8. The reproducing apparatus according to claim 5, wherein said switching means comprises a switching circuit, said switching circuit also serving as a circuit for generating laser beam power for recording.

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