JP2002074775A - Magneto-optical recording medium, magneto-optical reproducing method, and magneto-optical recording / reproducing apparatus - Google Patents

Abstract

(57) [Summary] [PROBLEMS] When a magnetic super-resolution medium whose recording / reproducing characteristics are unknown is applied to a drive, it takes a complicated operation and much time to determine the optimum recording / reproducing laser power. Also, even if the recording / reproducing conditions are required after a complicated operation or the like, generally, excessive laser power is applied to the medium to ensure recording regardless of the characteristics of the medium. When the routine for obtaining the condition is repeated, there is a concern that the medium may deteriorate. SOLUTION: The present invention provides a method for obtaining an optimum reproducing condition of a magnetic super-resolution medium whose recording / reproducing characteristics are unknown in a short time. Specifically, only the external reproduction magnetic field is applied before performing the recording operation, and the optimum reproduction power is determined using the reproduction signal in that state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recording / reproducing a magneto-optical recording medium, and more particularly, to a method for setting an optimum reproducing power in a magnetic super-resolution medium.

[0002]

2. Description of the Related Art Optical recording media have conventionally occupied an important position as a portable computer memory.
Due to the development of mobile information communication devices, simplicity and large storage capacity are expected more than ever.

Usually, a groove (track) is provided in advance in a spiral or concentric manner on an optical recording medium substrate, and information is recorded and reproduced by scanning the groove with a laser beam. In the case of a magneto-optical recording medium, the recording layer is made of an amorphous rare earth-transition metal alloy having perpendicular magnetic anisotropy, and information “0” and “1” corresponds to the direction of magnetization of a recording mark (magnetic domain). Depending on the orientation of the magnetic domain, it can function as two types of marks having different properties in terms of magneto-optical properties.

The most important factor in the performance of a recording medium is how much information can be recorded. This means that the track interval (track pitch) and the interval between recording marks are reduced. I do. However, in an optical recording medium, when the track interval or the interval between information recording marks is smaller than the laser beam spot diameter (λ / NA λ: laser wavelength, numerical aperture of an NA focusing lens), a plurality of recordings are made in the optical spot. There is a problem that the recording mark cannot be discriminated because the mark is inserted.

[0005] One solution to this problem is a magneto-optical super-resolution medium. This medium has two or more magnetic layers such as a reproducing layer or a magnetic layer for assisting the recording layer in addition to the recording layer. By combining the temperature distribution in the laser spot and the characteristics of the magnetic layer itself of the medium, the medium is effectively used. It is possible to reproduce information beyond the resolution of the laser. Also, by making the groove shape of the substrate uneven (Land / Groov)
It is known that a medium having a smaller track pitch can be manufactured by reducing the optical interference effect and the thermal interference effect.

[0006]

The use of magneto-optical super-resolution or the like as described above makes it possible to discriminate recording marks having a small track pitch and a short recording length beyond the resolution of the laser. However, these reproduction methods generally have a narrower reproduction power range in which correct signal reproduction can be performed, as compared with the conventional magneto-optical recording medium. On the other hand, when optimizing the recording / reproducing power for this magneto-optical super-resolution medium, the recording and reproduction conditions inevitably have a large correlation with each other due to the properties of the magnetic super-resolution medium. At the same time, it is difficult to optimize these two conditions. Because
For example, when recording is performed under the optimal condition (recording power at that time is Pw
0), the recording power (Pwh) is larger than the optimum reproduction power at that time.
The value is shifted to a value higher than the optimum reproduction power value (referred to as Pr0) when performed at 0. Conversely, when the recording is performed with a recording power lower than Pw0 (Pwl), the optimum reproducing power at that time is lower than Pr0. Also Land / Groove
In the case where a substrate is used, the above situation is further complicated because it is necessary to optimize the recording / reproducing power independently of each other due to the difference in the thermal state between the land portion and the groove portion.

For this reason, when a magnetic super-resolution medium whose recording / reproducing characteristics are unknown is driven, a complicated operation and a lot of time are required to determine the optimum recording / reproducing laser power. Also, even if the recording / reproducing conditions are required after a complicated operation or the like, generally, excessive laser power is applied to the medium to ensure recording regardless of the characteristics of the medium. When the routine for obtaining the condition is repeated, there is a concern that the medium may deteriorate.

[0008] When considering an optical disc from the viewpoint that a user can easily carry it in all weather conditions and record and reproduce information without stress, it is very difficult to obtain an optimum set value of laser power in recording and reproduction in a short time. is important.

[0009]

SUMMARY OF THE INVENTION According to the present invention, when a magneto-optical super-resolution medium of a type in which an information recording magnetic domain is transferred to a reproducing layer is used, an optimum reproducing laser power value is obtained in a short time, The aim is to save time.

Generally, in order to obtain the optimum reproducing power and recording power, one of the parameters is fixed, the other optimum value is obtained, and the other optimum value based on this optimum value is obtained. Need to be repeated several times. However, due to the nature of the magnetic super-resolution medium, the reproduction conditions and the recording conditions inevitably have a large correlation with each other, so that the required number of times of this routine increases. at the worst case,
In some cases, the optimum reproduction / recording power condition may not be found.
Further, depending on which power is set as the initial value, there is a difference in the number of times of the above-mentioned routine and the degree of convergence of the conditions.

The present invention provides a method for obtaining the optimum reproducing conditions of a magnetic super-resolution medium whose recording / reproducing characteristics are unknown in a short time.
Specifically, only the external reproduction magnetic field is applied before performing the recording operation, and the optimum reproduction power is determined using the reproduction signal in that state.

The magnetic super-resolution medium can be broadly divided according to the shape of the opening formed in the reproducing layer by the reproducing laser beam.
AD, FAD, and RAD are classified into three types. In the following, in particular, when a type magnetic super-resolution medium in which a recording layer and a reproducing layer are magnetically coupled by magnetostatic coupling is used. The method for obtaining the optimum reproduction power will be described.

Normally, the reproducing layer of a CAD type magnetic super-resolution medium is an in-plane magnetic film up to a certain temperature (Tcr), but its composition is adjusted so as to become a perpendicular magnetic film at a temperature above that temperature. is there. Therefore, the opening is opened at a laser power (Pcr) corresponding to Tcr or more, and the information recording magnetic domain of the recording layer can be seen. That is, the information recording magnetic domain existing in the recording layer is transferred to the reproducing layer. FIG. 1 schematically illustrates this. Tc inside the opening shown in FIG.
The temperature has reached r or higher, indicating that the readout layer changes to a perpendicular magnetization film and the information in the recording layer is transferred to the readout layer.

Here, let us consider a state in which an external reproducing magnetic field is always applied regardless of whether or not any recording is performed on the recording layer. When the laser power is small and the reproducing layer has not reached Tcr, the reproduced signal has a magnitude proportional to the external reproducing magnetic field intensity due to the Kerr rotation angle proportional to the external reproducing magnetic field intensity. On the other hand, when the laser power increases to some extent, the reproducing layer reaches Tcr and changes from an in-plane magnetic film to a perpendicular magnetic film, so that the reproducing signal sharply increases. If the laser power is further increased, Tc on the medium
However, the temperature in the vicinity of the center of the opening becomes too high and the Kerr rotation angle is reduced, so that the above-mentioned rapid increase in the signal amplitude can be suppressed. That is, it is understood that at least the reproduction power at which the signal amplitude sharply increases is a guideline of the optimum reproduction power.

The routine is repeated to determine the normal recording / reproducing power. To determine the initial value, a test recording area is created in one or more places in the magneto-optical recording medium in advance and the test recording is performed. There is also a method of using this when calculating the optimum reproduction laser power. As a result, it is possible to prevent the laser power from being applied more than necessary, and it is possible to suppress the degree of deterioration of the medium.

By using the above means, an appropriate value of the reproducing laser power can be easily and accurately obtained. As a result, the drive start-up operation time can be saved.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a sectional structure of a CAD type magneto-optical super-resolution medium used in the present invention. In the present embodiment, the information recording layer 2 is made of TbFeCo having perpendicular magnetization and having a compensating composition at room temperature as an information recording layer 2 on an L / G polycarbonate substrate 1 having a track pitch of 0.6 μm and a plate thickness of 0.6 mm. GdFe, which is a transition metal dominant composition in the in-plane magnetization film, is used as the auxiliary magnetic layer 3 for controlling the transfer magnetic field from the magnetic field 2, and the information reproducing layer 4 has a perpendicularization temperature (Tcr) of 150 ° C. GdFeCo with dominant composition
Was used. The magneto-optical recording medium 10 was manufactured by sandwiching the SiN film 5 between the information recording layer, the auxiliary magnetic layer, and the information reproducing layer, whereby the information recording layer and the reproducing layer were magnetostatically coupled.

FIG. 2 shows a reproduction signal amplitude of the magneto-optical recording medium 10 with respect to an alternating reproduction magnetic field intensity when a certain constant reproduction laser power is applied. When the reproducing power was 1.5 mW, the signal amplitude increased in a substantially proportional relation to the reproducing magnetic field. It is considered that this is because the laser power was small and the reproducing layer was 150 ° or less, and was in an in-plane magnetization state.

When the reproducing laser power is increased, 2 mW
As described above, when the reproducing magnetic field is 100 Oe or more, a sharp increase in the amplitude of the reproduced signal is observed. This is considered to be because the temperature of the reproducing layer exceeded Tcr and became a perpendicular magnetization film because the laser power became sufficiently large.

FIG. 2 shows a measurement that was performed after the recording layer was initialized, and a rapid change in the reproduced signal could be seen without initialization. FIG. 3 is a diagram showing a change in the reproduction signal amplitude with respect to the reproduction power when paying particular attention to the case where the reproduction alternating magnetic field is 200 Oe in the graph of FIG. The medium # 1 shows a large change in the reproduced signal from around 1.9 mW, and its change rate decreases around 2.2 mW. In the medium of # 2, a large change is observed in the reproduced signal from around 2.0 mW, and the change rate becomes small around 2.4 mW. Here, the mediums # 1 and # 2 have Tcr adjusted to 150 ° C. and 160 ° C., respectively.

FIG. 4 shows a measurement result of an error rate (BER) with respect to the reproduction power of the media # 1 and # 2 shown in FIG. Here, BER is an evaluation of a PR (1,1) signal recorded at an optimum recording power in a recording magnetic field of 200 Oe. As is apparent from FIG.
The BER is 2.1 mW and 2.4 m for 1 and 2, respectively.
These are the optimum reproducing powers because they are minimized at W.
That is, in FIG. 3, the position where the signal amplitude sharply changes when the reproduction alternating magnetic field is applied coincides with the optimum reproduction power.

FIGS. 5 and 6 are schematic views of an apparatus for performing magneto-optical reproduction according to the fifth and seventh aspects. However, the optical system and the periphery of the optical head are omitted. First, the operation of the device shown in FIG. 5 will be described.

When it is necessary to determine the recording / reproducing power,
First, a seek operation is performed on a predetermined test area on the disk. At this time, the controller outputs a digital High signal to one end of the AND circuit (103). Next, the pickup (101) detects a synchronizing signal which is previously formed as a pit on the disk. A special synchronization pattern is embedded in an area for obtaining the optimum recording / reproduction power, and this is compared with the synchronization circuit (102). When the detection signal and the synchronization signal match, the synchronization circuit outputs a digital High signal to the other end of the AND circuit. When the above two conditions are met, Hig is applied to the control signal generation circuit (104) through the AND circuit.
The h signal is transmitted, and the operation according to claims 6 and 8 starts.

The operation will be described below. There are the following three types of control signals output from the control signal generation circuit. That is, (1) a control signal for generating a certain magnetic field Hconst by the magnetic head drive circuit (105);
Set the reproduction laser power to a lower value (Prdev) for each constant power (Prdev).
min) to a high value (Prmax), a control signal output to the laser drive circuit (106), and (3) a sample hold (107) to hold the signal detected from the pickup for a certain time (Δt). Control signal output to In this embodiment, Hconst is 200 Oe, Prdev, Prmin,
0.1, 1.5, and 3.0 mW were used as Prmax, respectively. If the value of Prdev is reduced, the operation takes time, but the target operation can be executed more accurately. Δt corresponds to the time during which the reproduction power is kept constant. At this time, the linear velocity of the disk was set to 5 m / s.
It is desirable that min and Prmax be changed according to the linear velocity. The sample hold (107) holds the signal amplitude for each reproduction power (for each Δt). The delay circuits I (108) and II (109) are both set so as to delay the signal by Δt, so that at a certain time t, the delay circuit I (108) outputs t
The signal amplitude of −Δt is t from the delay circuit II (109).
The signal amplitude of −2 × Δt is the output signal. Therefore, assuming that the signal at the time t is W (t), the output signals from the differential circuits (110) and (111) are respectively W (t) −W (t
−Δt) and W (t−Δt) −W (t−2Δt). The comparator (112) compares these two signal levels, and outputs a digital signal High if the former signal is smaller than the latter signal. This corresponds to a case where the signal amplitude change rate at a certain reproduction power is smaller than the signal amplitude change rate at a lower reproduction power. At this time, the diode (110) provides the control signal generation circuit with the optimum reproduction power.
A control signal for ending a series of operations for obtaining Pr0 is transmitted.

The above is the method for obtaining the optimum reproduction power when using FIG. 5, but this can be changed as shown in FIG. Here, in FIG. 6, (100)-(10
5) has the same function as described in the description of FIG. A signal detected by the pickup (101) is differentiated with respect to a reproduction power sweep time by a differentiating circuit (200) and digitized by an AD converter (201). Then, the signal level at t0 and the signal level at t0−dt time by the delay circuit (203) are compared (204).
Are compared through Where dt is the reference clock circuit (2
02). The diode (204) extracts a case where the signal level during the time t0-dt is greater than the signal level during the time t0, and counts this by the counter (205). Number of counters obtained (N)
From the reference clock cycle (dt), the reproduction power (that is, the optimum reproduction power) when the differential signal amplitude at a certain reproduction power becomes smaller than the differential signal amplitude at a lower reproduction power. In the above case, the optimal reproduction power is Pr1 = P
rmin + N x dt x (dPr / dt).

FIG. 7 schematically shows the format of the medium used in this embodiment. Test zone-I, I in the figure
I and III are areas for determining the optimum recording / reproducing power provided for each disk, each zone (each band), and each frame. Mainly, test zone-I is used for adjustment when discs are replaced, test zone-II is used for adjustment especially when recording and reproducing across zones when using CAV, and test zone III is used for adjustment to environmental temperature Used for Performing the operations described in claims 6 and 8 in at least one of these area units has proved effective.

FIG. 8 shows the amplitude change rate, amplitude differential and the bit error rate (BER) measured by a normal error rate analyzer when the medium # 1 is measured by the apparatus shown in FIGS. Things. The amplitude change rate and the amplitude derivative had the maximum values at 2.3 mW and 2.2 mW, respectively. On the other hand, the reproduction power having the minimum BER was 2.1 mW. That is, it has been shown that the reproduction power to be used at the time of reproducing information can be accurately obtained by the circuits of FIGS.

FIG. 9 shows the optimum reproducing power, that is, the reproducing power at which the BER is reduced most, from 1.8 mW to 2.8 mW, and is derived using the values and the circuits shown in FIGS. It shows a comparison with the reproduction power. Regarding the results for any medium, the reproduction power at which the amplitude change rate and the amplitude derivative are maximized is 90% of the optimum reproduction power.
−110%, indicating that the reproduction power derived using the circuits shown in FIGS. 5 and 6 can be used as the information reproduction power.

FIG. 10 shows a flowchart for determining the optimum recording / reproducing power according to a conventionally used method, and a flowchart for determining the optimum recording / reproducing power using the present embodiment. In the latter case, the operation above the dotted line in FIG. 10 is not required, so that the time for obtaining the optimum recording / reproducing power can be reduced by about 50%. Claim 4
As described above, when the reference recording mark is recorded in a predetermined position (test zone) in advance, the operation above the dotted line in FIG. Was completed.

FIG. 11 shows the change in the optimum reproduction power that occurs when the operation for obtaining the optimum recording / reproduction power is repeated.
This shows the case of the conventional method and the case of performing the method according to claims 5-8. Since the medium used in the present embodiment has a reproducing layer on the light incident side, characteristic deterioration due to repetition of rewriting occurs on the reproducing layer side before the recording layer. At this time, since the vertical temperature of the reproducing layer rises due to the relaxation of the structure of the reproducing layer, the optimum reproducing power increases with the number of rewrites. As shown in the flow chart of FIG. 8, in the conventional method, an unnecessarily high recording power is applied when determining the provisional reproduction power. Therefore, according to repeated operation for obtaining the optimum recording power, after the 10 ⁵ times 0.1 mW, the post 10 ⁶ times shifted to 0.2mW high reproduction power side. Therefore, the characteristics in the test area used for obtaining the optimum recording / reproducing power and the characteristics in the user area gradually shift. That is, the error between the obtained reproduction power value and the reproduction power value that should be used originally increases. On the other hand, by using the method using the circuit of FIG.
The shift amount (error amount) could be suppressed to about 0.05 mW even in the operation after ^six times. Therefore, the difference in characteristics between the test area and the user area was reduced, and as a result, a recording / reproducing power with a small error could be obtained. Further, as described in claim 4, a certain predetermined position (te
Similarly, in the case where the reference recording mark has been recorded in advance in the (st zone), the above-described shift amount can be suppressed to 0.05 mW or less because a recording operation with a high recording power is not required.

[0032]

According to the present invention, an appropriate value of the reproducing laser power can be easily and accurately obtained. Thus, for example, when a medium (optical disk) is inserted into a drive, it can be set to be usable by the user in a short time. In addition, since it is not necessary to perform writing and reading by applying an excessive laser power to the medium as in normal test recording and test reproduction, thermal deterioration of the medium can be prevented.

[Brief description of the drawings]

FIG. 1 schematically illustrates a signal reproducing operation of a CAD magnetic super-resolution medium. (The direction of the arrow in the figure indicates the direction of magnetization. The shaded region indicates the transition region between the perpendicular magnetization film and the in-plane magnetization film.)

FIG. 2 shows a case where a reproducing alternating magnetic field strength is used as a parameter.
FIG. 4 is a diagram showing a reproduction signal amplitude with respect to a reproduction laser power.

FIG. 3 is a diagram showing a reproduction signal amplitude with respect to a reproduction laser power when a reproduction alternating magnetic field is 200 Oe.

FIG. 4 is a diagram showing BER reproduction power characteristics in the two types of media shown in FIG. 3;

FIG. 5 is a schematic circuit diagram for determining an optimum reproducing power according to the present embodiment.

FIG. 6 is a schematic circuit diagram for determining an optimum reproducing power according to the present embodiment.

FIG. 7 schematically illustrates a format of a medium used in the present embodiment.

FIG. 8 is an example of an output signal when the circuits of FIGS. 5 and 6 are used.

FIG. 9 shows the results obtained by examining media having different optimum reproduction powers using the circuits shown in FIGS. 5 and 6;

FIG. 10 is a flowchart comparing a flow chart of determining an optimum recording / reproducing power according to the present embodiment with a flow chart of a conventional method.

FIG. 11 is a diagram illustrating a change in the optimum recording / reproducing power that occurs when the operation for obtaining the optimum recording / reproducing power is repeated, in the case of the optimum recording / reproducing power determining method of the present embodiment and the determining method that is usually performed. .

[Explanation of symbols]

 Reference Signs List 1 polycarbonate substrate 2 information recording layer 3 auxiliary magnetic layer 4 information reproducing layer 5 SiN film 10 magneto-optical recording medium 100 controller 101 pickup 102 synchronization circuit 104 control signal generation circuit 105 magnetic head drive circuit 106 laser drive circuit 107 sample hold 108, 109 Delay circuit 112 Comparator 200 Differentiating circuit 201 A / D converter 202 Reference clock circuit 203 Delay circuit 204 Comparator 206 Counter

 ──────────────────────────────────────────────────の Continued on the front page (72) Noboru Isoe, 1-88 Ushitora, Ibaraki-shi, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Katsusuke Shimazaki 1-188, Ushitora, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd. (72) Inventor Masafumi Yoshihiro 1-88 Ushitora, Ibaraki-shi, Osaka F-term within Hitachi Maxell Co., Ltd. 5D075 AA03 CC11 CD11 EE03 FF13

Claims (8)

[Claims] 1. A magneto-optical recording medium comprising at least a magneto-optical recording layer and a reproducing layer for transferring information of the magneto-optical recording layer, and reproducing by irradiation with a reproducing laser beam. A reproduction signal is detected while changing the irradiation power of the laser beam, and a trial area for setting the optimal reproduction laser beam irradiation power is set at a predetermined position, and the trial area is initialized. A magneto-optical recording medium on which a predetermined pattern by recording is recorded. 2. A magneto-optical reproducing method of irradiating a reproducing laser beam to a magneto-optical recording medium having at least a magneto-optical recording layer and a reproducing layer for transferring information of the magneto-optical recording layer, comprising: Before performing recording / reproduction, a reproduction signal output is detected while changing a reproduction laser power while applying a magnetic field to the magneto-optical recording medium, and a reproduction laser power is set based on the detection result. A method for reproducing information by irradiating a laser beam to the magneto-optical recording medium to reproduce information. 3. The magneto-optical reproducing method according to claim 2, wherein the applied magnetic field is a DC magnetic field. 4. The magneto-optical reproducing method according to claim 2, wherein the applied magnetic field is an AC magnetic field. 5. A means for detecting a magneto-optical reproducing signal when the reproducing laser power is changed, wherein the reproducing laser power is changed at regular intervals, and a rate of change of the amplitude of the magneto-optical reproducing signal with respect to each reproducing power. 3. The magneto-optical reproducing method according to claim 2, wherein the reproducing laser power at which the rate of change is maximized is set as the reproducing laser power. 6. The reproducing laser power is swept based on a reference clock, a differential value of the magneto-optical reproducing signal amplitude value with respect to the reproducing power value is detected, and the reproducing laser power at which the differential value becomes maximum is determined by the reproducing laser. 3. The magneto-optical reproducing method according to claim 2, wherein the power is set as power. 7. A magneto-optical recording / reproducing apparatus comprising at least an optical head, a laser driving circuit, a magnetic head, a magnetic head driving circuit, and a control circuit for controlling the laser driving circuit and the magnetic head driving circuit. A magneto-optical recording / reproducing apparatus, comprising: a sample-and-hold circuit for detecting a rate of change of a magneto-optical reproducing signal amplitude with respect to a reproducing power; and a comparator for detecting a maximum value of the rate of change. . 8. The magneto-optical recording / reproducing apparatus according to claim 7, further comprising a differentiating circuit for detecting a differential value of a magneto-optical reproducing signal amplitude value with respect to a reproducing power value.