Magneto-optical recording and reproducing device

Abstract: A magneto-optical recording and reproducing device (12) comprising an optical head (10) provided with a laser beam source (2), focusing a laser beam onto a magneto-optical recording medium (1) with a magnetic substance film (1b) of perpendicular magnetic anisotropy, a magnetic coil (7) generating an alternating magnetic field according to data to be recorded, and forming positive magnetized parts being magnetized in a predetermined direction, and negative magnetized parts being magnetized in the opposite direction of said positive magnetized parts on said magnetic substance film of said recording medium, recording and reproducing data by existence or absence of said negative magnetized parts, characterized in that there is provided a laser beam output level control means (11) controlling intensity of said laser beam at forming said positive magnetized parts more strongly than forming said negative magnetized parts, so that the width of said positive magnetized parts becomes wider than said negative magnetized parts. Hence, this device can prevent the causes of false signals and incorrect detection influenced by a residual negative magnetized domain which is a part of the negative magnetized domain formed according to old data, when record­ ed data according to the existence or absence of the nega­ tive magnetized parts, that is, according to the existence or absence, length, position et cetera of the negative mag­ netized domain comprising of the negative magnetized parts, is reproduced, consequently the reliability on recording and reproducing data can be improved.

Description: This invention is related 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. 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), as shown in Fig. 5. 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 an 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 photo detector (25), and a photodetector (25), that detects the reflected-light strength et cetera. 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). Onto this magnetic substance film (21b) the laser beam spot is focused. 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 because of a rise in the local area temperature, 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 positive magnetized part, previously magnetized in a fixed direction at width d₀, and the negative magnetized area (64-65), composed of a negative 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, location et cetera 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 of the magneto-optical recording medium (21) sensitivity, or the like. Consequently, the width is not always the same. For example, when recording new data, called "rewriting", to a data area recorded as the width d₀ of the positive magnetized area (61-63) and the negative magnetized area (64-65), the width d₁ of the positive magnetized area (71-72) and the negative magnetized area (73-74), formed by new data, may become smaller than the width d₀ of previously written data in the positive magnetized area (61-63) and the negative magnetized area (64-65). This is shown in Fig. 7. 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 d₁ 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, the existence or absence, length, location, et cetera 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 as 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 to 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 false signal generation or incorrect detection. Therefore, this conventional magneto-optical recording and reproducing device 31 has a problem in that the reliability of the data recorded and reproduced tends to decline. One magneto-optical recording and reproducing device of the type described above, and which uses PWM encoding for data recording, is known from EP-A-0,243,656. 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 an already written negative magnetized area on both sides of a 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) changes, due to changes in the laser beam emission output levels from the laser beam source and changes in the magneto-optical recording medium sensitivity or the like. Another object of the invention is to present a magneto-optical recording and reproducing device structured such that the false signal and the error detection does not occur influenced by a residual negative magnetized area, which is a part of the negative magnetized area formed based on the old data, when the recorded data is reproduced, based on the existence or absence of a negative magnetized part, that is, the existence of absence, length, position, et cetera of the negative magnetized area. Still another object of the invention is to present a magneto-optical recording and reproducing device of greatly improved read and reproduce data reliability. In one aspect, the invention provides a magneto-optical a magneto-optical recording and reproducing device for recording data by means of a track on a magneto-optical recording medium which exhibits perpendicular magnetic anisotropy, by controlling the direction of perpendicular magnetization along the track so as to create so-called positive and negative magnetized track portions, having opposite magnetization directions, according to the data to be recorded, and for reproducing the recorded data by the detection of said negative magnetized track portions, the device comprising a laser beam source and a magnetic field source for applying a laser beam spot and a localised magnetic field, respectively, to said recording medium in the recording process, characterised by laser beam control means for controlling the intensity of said laser beam during recording to be stronger when creating said positive magnetized track portions than when creating said negative magnetized track portions so that said positive magnetized track portions have greater width than said negative magnetized track portions. In another aspect, the invention provides a method for a method for recording data on a magneto-optical recording medium by means of a laser beam, in which data is recorded in a track which comprises magnetic domains created in the recording process, said magnetic domains having magnetization directions which alternate in the track direction in accordance with the recorded data, characterised in that the width of each domain is made dependent on its magnetization direction by varying the intensity of said laser beam in accordance with the magnetisation direction of the created magnetic domains during the recording process. The magneto-optical recording and reproducing device may be equipped with a laser beam source, an optical head that focuses a laser beam onto the magneto-optical recording medium with the magnetic substance film having perpendicular magnetic anisotropy, and a magnetic coil that generates an alternating magnetic field based on the data to be recorded. This device forms the positive magnetized part which is magnetized in a fixed direction on the magnetic substance film of the magneto-optical recording medium, and the 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, which controls the laser beam source output level at forming the positive magnetized part higher than the laser beam source output level at forming the negative magnetized parts, so that the width of the positive magnetized parts becomes greater than that of the negative magnetized parts when the data is recorded. The above mentioned laser beam output level control, for instance, is equipped in the laser driver for driving the laser beam source. Also, this laser beam output level control, for instance, is equipped in the laser driver for driving the laser beam source for input and control of data to be recorded 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 greater than that of the negative magnetizing parts. The magneto-optical recording medium used for the magneto-optical recording and reproducing device, for example, comprises a substrate, perpendicular magnetic anisotropic magnetic substance film formed on the rear side of this 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 reflected-light from the magneto-optical recording medium, and a photodetector which detects the strength et cetera of the reflected-light through the beam splitter. The magneto-optical recording and reproducing device of this invention may also be equipped with a data generator, which outputs data to be recorded to the magneto-optical recording medium, a magnetic coil driver which outputs a modulated control signal based on data output from the data generator, a magnetic coil which generates an alternating magnetic field driven by the control signal output from the magnetic coil driver, an optical head which emits a laser beam onto the magneto-optical recording medium, and a laser driver which drives 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 which controls the laser beam source output level at forming the positive magnetizing parts higher than that at 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 greater 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 in order that the laser source output level at forming the positive magnetized parts is higher than the output level at 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 greater than the width of the already recorded negative magnetized area. Fig. 1 is an illustrative view showing the construction of a magneto-optical recording and reproducing device of an embodiment of the present invention. Fig. 2 is an illustrative view showing the condition of a positive magnetized area and a negative magnetized area formed on a magnetic substance film of the magneto-optical recording medium used with the magneto-optical recording and reproducing device of the present invention. Fig. 3 is an illustrative view showing the condition of a positive magnetized area and a negative magnetized area, based on new data formed on the area where a positive magnetized area and a negative magnetized area have already been formed on a magnetic substance film of the magneto-optical recording medium used with a magneto-optical recording and reproducing device of the present invention. Fig. 4 is a time chart showing the relationship between a magnetic field direction generated by a magnetic coil and a laser beam source output level of a magneto-optical recording and reproducing device of the present invention. Fig. 5 is an illustrative view showing the construction of a conventional magneto-optical recording and reproducing device. Fig. 6 is an illustrative view showing the condition of a positive magnetized area and a negative magnetized area formed on a magnetic substance film of a magneto-optical recording medium by a conventional magneto-optical recording and reproducing device. Fig. 7 is an illustrative view showing the condition of a positive magnetized area and a negative magnetized area, based on new data formed on the area where a positive magnetized area and a negative magnetized area have already been formed on a magnetic substance film of a magneto-optical recording medium used with a conventional magneto-optical recording and reproducing device. An embodiment of the present invention is described below with reference being made to Figs. 1 to 4. As shown in Fig. 1, a magneto-optical recording and reproducing device (12) uses, for example, 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) which is driven by a control signal output from the magnetic coil driver (8) 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 reflected-light from the magneto-optical recording medium (1) and leads the light to a photodetector (5), and a photodetector (5) which detects the strength et cetera 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 this 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 as a 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 greater 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 at 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 condensed through the beam splitter (3), the condensing lens (4) and the substrate (1a) of the magneto-optical medium (1), and it then focuses a laser beam 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. Hence, if the magnetic field which is alternated based on the coded data output from the data generator (9) is 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). This is shown in Fig. 2. Data is recorded and reproduced based on the existence or absence of the negative magnetized parts. In other words, data is recorded and reproduced based on the existence or absence, length, location, et cetera of the negative magnetized area (44-45). By the way, the laser driver (11) controls the output level of the laser beam source (2) to be higher, 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 forming the positive magnetized parts on the magnetic substance film (1b) of the magneto-optical recording medium (1), than that in the direction forming the negative magnetized parts. This is shown in Fig. 4. Because of this, concerning the width d₀ of the negative magnetized area (44-45), shown in Fig. 2, the width of the positive magnetized area (41-43) becomes somewhat greater than the width d₀. 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), or the changes in the sensitivity of the magneto-optical recording medium (1). Therefore, when recording based on new data is done, called "rewriting", on an area where the data had been previously recorded with a width of more than d₀ in the positive magnetized area (41-43) or a width d₀ 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 d₁ of the negative magnetized area (53-54), formed based on new data, may become smaller than the width d₀ 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 was mentioned above. Therefore, the width of the new positive magnetized area (51-52) also becomes at least greater than the width d₀. Hence, the front end side area (44a) of the negative magnetized area (44) in width d₀ 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 d₁ of the negative magnetized area (53) in the already formed negative magnetized area (44). However, residual negative magnetized area (44b-44b) does not remain, except 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, location, et cetera 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 of a false signal or 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 of the present embodiment includes a laser beam source, and 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 are magnetized in a fixed direction, and the negative magnetized parts which are magnetized in the direction opposite to that of the positive magnetized parts. The device records and reproduces according to the existence or absence of the negative magnetized part. In this device structure, a means for laser beam source output control is provided, which makes the laser beam source output level at forming the positive magnetized parts higher than that at forming the negative magnetized parts, when data is recorded, so that the width of the positive magnetized parts become wider than the width of the negative magnetized parts. The magneto-optical recording and reproducing device of the present embodiment also comprises a data generator which outputs data to be recorded on the magneto-optical recording medium, the magnetic coil driver which outputs 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. In this laser driver, the data output from the data generator is input to control the laser beam output level, which makes the laser beam source output level at forming the positive magnetizing parts higher than that at forming the negative magnetizing parts, when data is recorded to the magneto-optical recording medium. Therefore, the width of the positive magnetized parts, formed by magnetizing in a fixed direction on the magnetic substance film of the magneto-optical recording medium, becomes greater 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, position, et cetera of a negative magnetized area made of 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.

Claims: A magneto-optical recording and reproducing device for recording data by means of a track on a magneto-optical recording medium which exhibits perpendicular magnetic anisotropy, by controlling the direction of perpendicular magnetization along the track so as to create so-called positive (41, 42, 43) and negative (44, 45) magnetized track portions, having opposite magnetization directions, according to the data to be recorded, and for reproducing the recorded data by the detection of said negative magnetized track portions (44, 45), the device comprising a laser beam source (2) and a magnetic field source (7) for applying a laser beam spot and a localised magnetic field, respectively, to said recording medium in the recording process, characterised by laser beam control means (11) for controlling the intensity of said laser beam during recording to be stronger when creating said positive magnetized track portions (51, 52) than when creating said negative magnetized track portions (53, 54), so that said positive magnetized track portions have greater width than said negative magnetized track portions. A magneto-optical recording and reproducing device according to claim 1, wherein said laser beam control means is provided in a laser beam driver (11) which drives said laser beam source (2) to control the output level of the laser beam. A magneto-optical recording and reproducing device according to claim 2, further comprising a data generator (9) which supplies data to be recorded to said laser beam driver (11), and wherein said magnetic field source comprises a magnetic coil (7) and a magnetic coil driver (8) which energises said magnetic coil to generate an alternating magnetic field in dependence upon data to be recorded supplied by said data generator (9). A magneto-optical recording and reproducing device according to any one of the preceding claims, including an optical head (10) which comprises said laser beam source (2), a condensing lens (4) which focuses the laser beam from said source onto a magneto-optical recording medium received in the device, a photodetector (5) which detects reflected light from said recording medium when data recorded thereon is reproduced, and a beam splitter (3) which directs said reflected light toward the photodetector. A method for recording data on a magneto-optical recording medium by means of a laser beam, in which data is recorded in a track which comprises magnetic domains created in the recording process, said magnetic domains having magnetization directions which alternate in the track direction in accordance with the recorded data, characterised in that the width of each domain is made dependent on its magnetization direction by varying the intensity of said laser beam in accordance with the magnetisation direction of the created magnetic domains during the recording process.

Inventors: KATAYAMA HIROYUKI, MIYAKE TOMOYUKI, NAKAYAMA JUNICHIRO, OHTA KENJI, TAKAHASHI AKIRA, KATAYAMA, HIROYUKI, MIYAKE, TOMOYUKI, NAKAYAMA, JUNICHIRO, OHTA, KENJI, TAKAHASHI, AKIRA
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1989
Main classification: G11B11
IPC codes: G11B11