Magneto-optical recording and reproducing device using the modulation of intensities of the magnetic field and light beam

A magneto-optical recording and reproducing device for recording and reproducing data determined by negative magnetized areas in a magneto-optical recording medium. The device including a laser beam output level control means for controlling the intensity of a laser beam when recording data on the medium. The device prevents the causes of false signals and incorrect detection influenced by residual negative magnetized domains by increasing laser beam intensity when rewriting positive magnetized areas to erase residual negative magnetized areas.

FIELD OF THE INVENTION 
This invention relates to a magneto-optical recording and reproducing 
device which records, reproduces and erases data by laser beam spot 
emission to a magneto-optical recording medium. 
BACKGROUND OF THE INVENTION 
With reference to FIG. 5, conventional magneto-optical recording and 
reproducing devices (31) use a magneto-optical recording medium (21) 
composed of a laminated magnetic substance film (21b) having perpendicular 
magnetic anisotropy, and a protective film (21c) on the rear side of a 
substrate (21a). To record data to this magneto-optical recording medium 
(21), the magneto-optical recording and reproducing device (31) comprises 
the following components: a data generator (29), which outputs data to be 
recorded, a magnetic coil driver (28), which outputs a modulated control 
signal based on data from the data generator (29), a magnetic coil (27), 
which is driven by the control signal from the magnetic coil driver (28) 
and generates an alternating magnetic field, and a optical head (30), 
which emits a laser beam spot to the above mentioned magneto-optical 
recording medium (21). 
The optical head (30) is equipped with a laser beam source (22) that emits 
a laser beam, a condensing lens (24), which projects the laser beam spot 
on the magnetic substance film (21b) of the magneto-optical recording 
medium (21) by condensing the laser beam, a beam splitter (23) which 
changes the advancing direction of reflected-light from the 
magneto-optical recording medium (21) and leads the light to a 
photodetector (25), and a photodetector (25), that detects the 
reflected-light strength and other data. The laser beam source (22) of the 
optical head (30) is steady DC driven by the laser driver (26). 
When data is recorded to the magneto-optical recording medium (21) by such 
a magneto-optical recording and reproducing device (31), the laser beam 
emitted from the laser beam source (22) is condensed on the magnetic 
substance film (21b) of the magneto-optical recording medium (21) by way 
of the beam splitter (23), condensing lens (24), and the substrate (21a) 
of the magneto-optical recording medium (21). The laser beam spot is 
focused onto this magnetic substance film (21b). 
Thereafter at the local area of the magnetic substance film (21b) of the 
magneto-optical recording medium (21) onto which the laser beam has been 
focused, the coercive force is reduced as the local area temperature 
rises, and the magnetizing direction becomes easy to change. 
Therefore, if the alternating magnetic field, based on coded data output 
from the data generator (29) is generated by magnetic coil (27), the 
positive magnetized area (61-63), composed of a positively magnetized 
part, previously magnetized in a fixed direction at width d.sub.0, and the 
negative magnetized area (64-65), composed of a negatively magnetized part 
magnetized in the opposite direction to the positive magnetized area 
(61-63) onto the laser beam spot area, are formed on the magnetic 
substance film (21b) of the magneto-optical recording medium (21). This is 
shown in FIG. 6. Data recording and reproducing is done in accordance with 
the existence or absence of this negative magnetized part, that is, in 
accordance with the existence or absence, length, and location of the 
negative magnetized area (64-65). 
However, the width of the positive magnetized area (61-63) and the negative 
magnetized area (64-65) formed on the magnetic substance film (21b) of the 
magneto-optical recording medium (21), changes. This change is due to 
changes of the laser beam output level emitted from the laser beam source 
(22) and changes in the magneto-optical recording medium's (21) 
sensitivity, or the like. Consequently, the width is not always the same. 
For example as shown in FIG. 7, when recording new data, called 
"rewriting", to a data area recorded as having a width d.sub.0 for the 
positive magnetized area (61-63) and the negative magnetized area (64-65), 
the width d.sub.1 of the positive magnetized area (71-72) and the negative 
magnetized area (73-74), formed by new data, may become smaller than the 
width d.sub.0 of the previously written data in the positive magnetized 
area (61-63) and the negative magnetized area (64-65). 
In this example, the residual positive magnetized area (61a-63a) and the 
residual negative magnetized area (64a-65a) exist on the magnetic 
substance film (21b) of the magneto-optical recording medium (21), mixed 
with the positive magnetized area (71-72) and the negative magnetized area 
(73-74) formed by recording new data. The residual area is larger in width 
than d.sub.1 of the positive magnetized area (71-72) and the negative 
magnetized area (73-74), located in the already written positive 
magnetized area (61-63) and the negative magnetized area (64-65). 
The magneto-optical recording and reproducing device (31) reads and 
reproduces data in accordance with the existence or absence of the 
negative magnetized part, that is, or the existence or absence, length, 
and location, of the negative magnetized area. Considering the above 
example, when written data is reproduced by the magneto-optical recording 
and reproducing device (31), the residual negative magnetized area 
(64a-65a) which is a part of the negative magnetized area (64-65) formed 
based on old data, can possibly be reproduced as a negative magnetized 
area that exists a negative magnetized parts, together with the negative 
magnetized area (73-74) formed based on new data. 
In particular, in a means where the signal data is recorded in accordance 
with the length of the negative magnetized area, a pulse width modulation 
(PWM) for example, since the negative magnetized area edge position is 
important, if such residual negative magnetized areas (64a-65a) exist, as 
above mentioned, this may result in the false signal generation or the 
incorrect detection. 
Therefore conventional magneto-optical recording and reproducing devices 
have the problem reduced data recordation and reproduction reliability. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to present a 
magneto-optical recording and reproducing device that does not leave a 
part of the already written negative magnetized area on both sides of the 
newly written positive magnetized area, even though the width of the 
positive and the negative magnetized areas formed on the magnetic 
substance film (21b) of the magneto-optical recording medium (21) change, 
due to changes in laser beam emission output levels from a laser beam 
source and changes in the magneto-optical recording medium sensitivity. 
Another object of the invention is to present a magneto-optical recording 
and reproducing device structured such that the false signal and error 
detection are not influenced by a residual negative magnetized areas, 
which are part of the negative magnetized area formed based on old data, 
when the recorded data is reproduced, based on the existence or absence of 
negative magnetized parts, that is, the existence or absence, length, and 
position, of the negative magnetic area. 
Still another object of the invention is to present a magneto-optical 
recording and reproducing device with greatly improved data reading and 
writing reliability. 
In order to accomplish these objects the magneto-optical recording and 
reproducing device related to this invention is equipped with a laser beam 
source, an optical head that focuses a laser beam onto a magneto-optical 
recording medium having a magnetic substance film with perpendicular 
magnetic anisotropy, and a magnetic coil that generates an alternating 
magnetic field based on the data to be recorded. The device forms a 
positive magnetized part which is magnetized in a fixed direction on the 
magnetic substance film of the magneto-optical recording medium, and a 
negative magnetized part which is magnetized in the direction opposite to 
that of the positive magnetized parts. The magneto-optical recording and 
reproducing device reads and reproduces data based on the existence or 
absence of this negative magnetized part. 
Also, the magneto-optical recording and reproducing device is equipped with 
a laser beam output level control means. The laser beam output level 
control means controls the laser beam source output level for forming the 
positive magnetized part higher than the laser than when forming the 
negative magnetized parts so that the width of the positive magnetized 
parts becomes wider than that of the negative magnetized parts when the 
data is recorded. 
The above mentioned laser beam output level control, as part of the laser 
driver, drives the laser beam source. The laser beam output level control, 
drives the laser beam source for inputting and controlling of data 
recordation to the magneto-optical recording medium from the data 
generator into the laser driver, so that, when the data is recorded, the 
width of the positive magnetizing parts becomes wider than that of the 
negative magnetizing parts. The magneto-optical recording medium used with 
the magneto-optical recording and reproducing device, for example, 
comprises a substrate, perpendicular anisotropic magnetic film formed on 
the rear side of the substrate, and a protective film covering the 
magnetic substance film. The optical head, for example, comprises a laser 
beam source which emits the laser beam, a condensing lens which focuses 
the laser beam on the magnetic substance film of the magneto-optical 
recording medium by condensing the laser beam, a beam splitter which 
changes the advancing direction of the light reflected from the 
magneto-optical recording medium, and a photodetector which detects the 
strength (i.e., intensity) of the light reflected delivered through the 
beam splitter. 
The magneto-optical recording and reproducing device related to this 
invention is also equipped with a data generator for outputting data to be 
recorded to the magneto-optical recording medium, a magnetic coil driver 
for outputting a modulated control signals based on data output from the 
data generator, a magnetic coil for generating an alternating magnetic 
field driven by the control signal output from the magnetic coil driver, 
an optical head which for emitting a laser beam onto the magneto-optical 
recording medium, and a laser driver for driving the laser beam source of 
the optical head. Also, the laser driver in which the data output from the 
data generator is input, is equipped with the laser beam source output 
level control means for controlling the laser beam source output level 
when forming the positive magnetizing parts higher than that when forming 
the negative magnetized parts, so that, when the data is recorded to the 
magneto-optical recording medium, the width of the positive magnetized 
area, formed by the magnetic substance film of the magneto-optical 
recording medium being magnetized in a fixed direction, becomes wider than 
the width of the negative magnetized parts, formed by being magnetized in 
a direction opposite to that of the positive magnetized parts. 
Given this structure, the laser beam output level is controlled so that the 
laser source output level when forming the positive magnetized parts is 
higher than the output level when forming the negative magnetized parts. 
Hence, when new data recording is to be done in an area where the positive 
or negative magnetized areas have already been recorded to, the width of 
the newly recorded positive magnetized area always becomes wider than the 
width of the already recorded negative magnetized area.

DESCRIPTION OF THE EMBODIMENTS 
A preferred embodiment of the present invention is described below with 
reference being made to FIG. 1 and FIG. 4. As shown in FIG. 1, a 
magneto-optical recording and reproducing device (12) includes a 
magneto-optical recording medium (1) comprising a laminated substrate 
(1a), a magnetic substance film (1b) with perpendicular magnetic 
anisotropy, on the rear side of the substrate (1a), and a protective film 
(1c) covering the magnetic substance film (1b). To record data to this 
magneto-optical recording medium (1), the magneto-optical recording and 
reproducing device (12) comprises a data generator (9) which outputs data 
to be recorded, a magnetic coil driver (8) which outputs a modulated 
control signal based on the data output from the data generator (9), a 
magnetic coil (7), driven by a control signal output from the magnetic 
coil driver (8), which and generates an alternating magnetic field, an 
optical head (10) which focuses a laser beam onto the magneto-optical 
recording medium (1) and a laser driver (11). 
The optical head (10) is equipped with a laser beam source (2) which emits 
a laser beam, a condensing lens (4) which focuses the laser beam by 
condensing the laser beam on the magnetic substance film (1b) of the 
magneto-optical recording medium (1), a beam splitter (3) which changes 
the advancing direction of the light reflected from the magneto-optical 
recording medium (1) and directs the light to a photodetector (5), and a 
photodetector (5) which detects the strength (i.e., intensity) of the 
reflected light. 
The laser beam source (2) of the optical head (10) is set to be driven by 
the laser driver (11). In laser driver (11), the data output from the data 
generator (9) is input. When data is recorded on the magneto-optical 
recording medium (1), the laser driver (11) functions with means to 
control the laser beam output level. That is, in order to make the width 
of the positive magnetized parts formed by magnetizing the magnetic film 
(1b) in the fixed direction larger than the width of the negative 
magnetized parts formed by magnetizing it in an opposite direction to that 
of the positive magnetized parts, the laser driver (11) makes the laser 
beam output level when forming the positive magnetized parts higher than 
the laser beam output level at forming the negative magnetized parts. 
In this structure, when the data is recorded on the magneto-optical 
recording medium (1), the laser beam emitted from the laser beam source 
(2) is directed through the beam splitter (3), the condensing lens (4) and 
the substrate (1a) of the magneto-optical medium (1), and focuses onto the 
magnetic substance film (1b) of the magneto-optical recording medium (1). 
Then the local area of the magnetic substance film (1b) of the 
magneto-optical recording medium (1) onto which the laser beam is focused 
rises in temperature, the coercive force is decreased, and the magnetized 
direction can be easily changed. 
As shown in FIG. 2, if the magnetic field which is alternated based on the 
coded data output from the data generator (9) as generated from the 
magnetic coil (7), the positive magnetized area (41-43) which is made of 
the previous positive magnetized parts magnetized in a fixed direction, 
and the negative magnetized area (44-45) which is made of the negative 
magnetized parts magnetized in the opposite direction on the laser beam 
spot area, will be formed on the magnetic substance film (1b) of the 
magneto-optical recording medium (1). Data is recorded and reproduced 
based on the existence or absence of negative magnetized parts. In other 
words, data is recorded and reproduced based on the existence or absence, 
length, and location, of the negative magnetized areas (44-45). 
With reference to FIG. 4, the laser driver (11) increases the output level 
of the laser beam source (2), as the direction of the magnetic field, 
generated by the magnetic coil (7) based on the data output from the data 
generator (9), is in the direction for forming the positive magnetized 
parts on the magnetic substance film (1b) of the magneto-optical recording 
medium (1), as compared to the output levels for forming the negative 
magnetized parts. Because of this output level increase, the width of the 
positive magnetized area (41-43) becomes somewhat larger than the width 
d.sub.0. 
On the other hand, the width of the negative magnetized area (44-45), 
formed on the magnetic substance film (1b) of the magneto-optical 
recording medium (1) does not always become fixed, because of the changes 
in the laser beam output levels emitted from the laser beam source (2), 
and changes in the sensitivity of the magneto-optical recording medium 
(1). Therefore, when recording is new data is, called "rewriting", on an 
area where the data had been previously recorded with a width of more than 
d.sub.0 in a positive magnetized area (41-43) or a width d.sub.0 in the 
negative magnetized area (44-45) on the magnetic substance film (1b) of 
the magneto-optical recording medium (1) as shown in FIG. 3, the width 
d.sub.1 of the negative magnetized area (53-54), formed based on new data, 
may become smaller than the width d.sub.0 previously formed in the 
negative magnetized area (44-45). 
Even in such a case, however, when the positive magnetized area (51-52) is 
formed based on new data, the laser driver (11) controls the laser beam 
source (2) to output at a higher level, based on the data output from the 
data generator (9), as mentioned above. Therefore, the width of the new 
positive magnetized area (51-52) also becomes larger than the width 
d.sub.0. Hence, the front end side area (44a) of the negative magnetized 
area (44) in width d.sub.0 and the negative magnetized area (45), already 
formed in the area where the positive magnetized area (51-52) is newly 
formed, turn to become the positive magnetized area (51-52) without fail, 
with no residual part left. 
Also, in both areas of the newly formed negative magnetized area (53), 
residual negative magnetized area (44b--44b) occurs. This part is bigger 
than the width d.sub.1 of the negative magnetized area (53) in the already 
formed negative magnetized area (44). However, residual negative 
magnetized area (44b--44b) does not remain, unless in the range where the 
negative magnetized area (53) is to be formed. Therefore, in the 
magneto-optical recording and reproducing device (12), in which recording 
and reproducing the data is done according to the existence or absence of 
a negative magnetized part, that is, according to the existence or 
absence, length, and location, of the negative magnetized area (53-54), it 
is impossible for the residual negative magnetized area, which is a part 
of the negative magnetized area formed based on old data, to become the 
cause for the false signal or the error detection. 
Consequently, the influence of already recorded data can be prevented 
without fail when the rewrite is done and the reliability of recording and 
reproducing data can be improved. 
As mentioned thus far, the magneto-optical recording and reproducing device 
related to this invention is arranged so that the laser beam source, is 
equipped with an optical head, which focuses the laser beam onto the 
magnetic substance film of the magneto-optical recording medium with 
perpendicular magnetic anisotropy, and a magnetic coil which generates an 
alternating magnetic field based on data to be recorded. The 
magneto-optical recording and reproducing device forms on the magnetic 
substance film of the magneto-optical recording medium the positive 
magnetized parts which is being magnetized in a fixed direction, and the 
negative magnetized parts which is being magnetized in the direction 
opposite to that of the positive magnetized parts. The device records and 
reproduces data according to the existence or absence of the negative 
magnetized part. The device also includes, a means for laser beam source 
output control equipped to increases the laser beam source output level 
when forming the positive magnetized parts higher than when forming the 
negative magnetized parts when data is recorded, so that the width of the 
positive magnetized part becomes wider than the width of the negative 
magnetized parts. 
The magneto-optical recording and reproducing device of the present 
invention also comprises a data generator which outputs data to be 
recorded on the magneto-optical recording medium, the magnetic coil driver 
which outputs the modulated control signals based on data output from the 
data generator, a magnetic coil, which is driven by the control signal 
output from the magnetic coil driver and generates an alternating magnetic 
field, the optical head which focuses a laser beam onto the 
magneto-optical recording medium, and the laser driver which drives the 
laser beam source of the optical head and enters the data from the data 
generator. The device further comprises a control means for the laser beam 
output level, which makes the laser beam source output level when forming 
the positive magnetizing parts higher than that when forming the negative 
magnetizing parts, when data is recorded to the magneto-optical recording 
medium. Therefore, the width of the positive magnetized part, formed by 
magnetizing in a fixed direction on the magnetic substance film of the 
magneto-optical recording medium, becomes wider than the width of the 
negative magnetized parts, formed by magnetizing in the opposite direction 
to that of the positive magnetized parts. This is the special feature of 
this device. 
By using such a magneto-optical recording and reproducing device, even if 
the width of the positive magnetized area or the negative magnetized area 
to be formed changes, due to changes of the laser beam output level 
emitted from the laser beam source, or due to changes of the sensitivity 
of the magneto-optical recording medium, it will be impossible to leave a 
part of the already formed negative magnetized area on both sides of the 
newly formed positive magnetized area. 
Therefore, when the data is reproduced, that was recorded based on the 
existence or absence of the negative magnetized parts, that is, based on 
the existence or absence, length, and position, of a negative magnetized 
area made of a negative magnetized parts, this device can prevent the 
false signals and the incorrect detection caused by the influence of the 
residual reversed magnetized areas, which is a part of the reversed 
magnetized area formed based on the old data. Consequently, the effect is 
that the reliability of recording and reproducing data will be 
unquestionably improved.