JP3104913B2 - Optical recording method and apparatus for disk-shaped recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for optically recording a disk-shaped recording medium, and more particularly, to a method for recording binary data for each data recording unit of a recording layer of a disk-shaped recording medium. The present invention relates to an optical recording method and apparatus for recording data by controlling the intensity of a laser pulse applied in accordance with the method.

[Summary of the Invention]

The present invention relates to a recording method for a magneto-optical disk which performs recording by magnetizing in a direction corresponding to a binary value of recording data for each data recording unit (magnetic domain, recording pit) of a recording medium layer of the magneto-optical disk. By performing recording so that the dimension of the data recording unit magnetized in the same direction as the initialization direction is made larger than the dimension of the data recording unit magnetized in the direction opposite to the initialization direction of the magnetization of the layer, The purpose of the present invention is to suppress the influence of the recording magnetization on the overwritten recording magnetization and to reduce noise during data reproduction. [Prior Art] In a magneto-optical disk, data in a recording medium layer is recorded according to binary values of recording data. Recording is performed by magnetizing the recording unit (magnetic domain or recording pit) so that the direction of magnetization is different. During reproduction, the polarization of the linearly polarized beam applied to the recording medium layer Using the magneto-optical effect (magnetic Kerr effect or Faraday effect) in which the light rotates, the binary value of the recording data is detected by utilizing the fact that the rotation direction of the polarization plane differs depending on the direction of the recording magnetization. I have.

Here, at the time of recording the data, for example, using a change in coercive force and magnetization when heating the recording medium by irradiating a laser beam, the data is written to the recording medium,
Depending on the material of the medium and the recording method, so-called overwriting (overwriting) in which a new magnetization pattern is written on the already recorded magnetization pattern is also possible.

Such magneto-optical disks are expected to be widely used in the future as computer peripherals and general memory media.

[Problems to be solved by the invention]

FIG. 8 shows a magnetization pattern on a medium (magneto-optical disk) and a reproduction signal thereof when the above-described overwriting is performed. In FIG. 8, A shows a plan view of the magnetization pattern when data writing is performed from the initial state. Here, the direction of magnetization in each data recording unit (magnetic domain or recording pit) in FIG. 8A (and FIG. 8C) is actually upward or downward perpendicular to the medium plane (paper surface). However, for convenience of illustration, it is indicated by an upward or downward arrow in the figure.
The magnetization pattern shown in FIG. 8A shows an example in which data is written with a relatively large laser power, and the reproduced output signal is obtained as shown in FIG. 8B. When writing new recording data (overwriting or overwriting) on the magnetization pattern of FIG. 8A, if the laser power is relatively small, a magnetization pattern as shown in FIG. 8C is formed. Sometimes. In FIG. 8C, since the laser power is small, a new magnetization pattern is written with a width smaller than the recording width of the previously recorded magnetization pattern of FIG. 8A. Some remain. If such unerased data is generated, the unerased magnetization is also reproduced during reproduction, and as shown in FIG. 8D, this is superimposed as noise on the original reproduced data signal. As a result, S / N is deteriorated as a result.

In order to reduce such adverse effects, it is conceivable to improve the accuracy of laser power control. However, it is necessary to consider the effects of disturbances such as temperature characteristics of the light receiving element for monitoring the laser light intensity. There is a limit to the accuracy of stabilizing the laser power, and when a magneto-optical disk is used between different devices, it is necessary to maintain the accuracy of the laser power between the devices. This is the situation at present.

Further, as shown in FIG. 9, a groove 2 having a depth of about λ / 8 to λ / 4 is formed in advance between adjacent recording tracks 1 on a recording medium layer of a magneto-optical disk (so-called pre-groove). There is also known a device which utilizes the fact that the information in the groove 2 does not affect the information recorded on the recording track 1 so as to avoid the adverse effect due to the size of the data recording unit. However, such pregroove formation not only causes an increase in cost due to the complexity of the disk manufacturing process, but also causes the groove 2 to hinder the track pitch when trying to narrow the track pitch in order to increase the recording density. Therefore, there is a problem that it becomes an obstacle to narrow track pitch.

The present invention has been made in view of such a point,
Without forming an extra structure such as a groove on the disk, it is possible to avoid the adverse effect due to the remaining erasure of the recorded information before overwriting (overwriting), and to reduce the noise at the time of reproduction. It is intended to provide a recording method and apparatus.

[Means for Solving the Problems] An optical recording method for a disk-shaped recording medium according to the present invention comprises:
In an optical recording method for recording data by controlling the intensity of a laser pulse applied according to the binary value of recording data for each data recording unit of a recording layer of a disk-shaped recording medium, the recording layer is initialized. The intensity of the laser pulse applied at the time of recording of the data recording unit is smaller than the intensity of the laser pulse applied at the time of recording of the data recording unit which is in a state different from the initial state, and the recording layer is in the initial state. By performing the recording by making the pulse width of the laser pulse applied at the time of recording of the data recording unit wider than the pulse width of the laser pulse applied at the time of recording the data recording unit which is in a state different from the initial state, The above-mentioned problem is solved.

Further, the optical recording apparatus for a disk-shaped recording medium according to the present invention controls data intensity by controlling the intensity of a laser pulse applied according to the binary value of the recording data for each data recording unit of the recording layer of the disk-shaped recording medium. In the optical recording device that performs, a laser diode that irradiates the laser on the disk-shaped recording medium, and a driving unit that generates a laser pulse that drives the laser diode to emit light according to a recording data signal, the driving unit includes: The intensity of a laser pulse applied during recording of a data recording unit in which the recording layer is in an initial state is smaller than the intensity of a laser pulse applied in recording of a data recording unit in a state different from the initial state, And the width of the laser pulse applied at the time of recording of the data recording unit in which the recording layer is the initial state, the state different from the initial state And wider than the pulse width of the applied laser pulse at the recording of the data recording unit to drive the laser diode, by performing the recording of data, to solve the problems described above.

[Operation] When a magneto-optical disk is assumed as the disk-shaped recording medium, a data recording unit magnetized in the same direction as the magnetization initialization direction of the medium has the same magnetization direction as the periphery of the recording area. There is no influence on the reproduction signal due to the size of the dimension, and by increasing the dimension of the data recording unit in the same direction, the data recording unit of the small dimension magnetized in the opposite direction can be rewritten without erasure. Further, even if the data recording unit magnetized in the opposite direction is formed with a small size, the remaining unerased portion of the large-sized data recording unit magnetized in the same direction as the initialization direction has the same direction as the surrounding magnetization. Therefore, it does not affect the reproduction signal.

〔Example〕

FIG. 1 and FIG. 2 are for explaining an example of a recording method of a magneto-optical disk capable of overwriting (overwriting) by a magnetic field modulation method prior to description of an embodiment of the present invention. In the figure, A indicates a laser pulse applied to the magneto-optical disk, B indicates a recording magnetic field applied to the magneto-optical disk, and C indicates a recorded magnetization pattern on the magneto-optical disk. Here, the direction of magnetization for each data recording unit C in each figure is actually upward or downward perpendicular to the medium plane (paper surface), but for convenience of illustration, it is upward or downward in the figures. This is indicated by a downward arrow.

In the examples shown in FIGS. 1 and 2, the size (width or area) of the data recording unit (magnetic domain, recording pit) corresponding to “1” of the recording data and magnetized upward in the drawing is larger than that of FIG. Recording is performed such that the size of the data recording unit magnetized downward in the figure corresponding to “0” of the recording data is increased. The direction of magnetization of the recording medium layer of the magneto-optical disk when the disk is initialized is downward in the figure, and the direction of magnetization around the recording area after the formation of the magnetization pattern is defined as this initial magnetization direction (down in the figure). Will remain. Note that the initialization is assumed to be a process of aligning the magnetization direction of the entire surface of the disk in one direction to be in an erased state at the time of factory shipment or before data recording.

FIG. 1 can be considered as, for example, the case where a magnetization pattern is first recorded and formed on an initialized magneto-optical disk. In the applied laser pulse for medium heating shown in FIG. 1A, the pulse intensity corresponding to “0” is larger than the pulse intensity (amplitude) corresponding to the recording data “1”,
When the recording data is "1" and when it is "0", the applied magnetic fields have opposite polarities as shown in FIG. 1B. The magnetization pattern on the medium recorded by the magnetic field modulation with the heating laser pulse of FIG. 1A and the modulation magnetic field of FIG.
As shown in FIG. That is, in FIG. 1C, the direction of the magnetization at the time of the initialization is indicated by a downward arrow in the figure, and the hatched portion in the figure indicates the recording unit (pit) of data “1”.
Thus, a magnetic domain magnetized in a direction opposite to the initial magnetization (upward in the figure) is formed. A recording unit (pit) of data “0” is formed with a size larger than that of the recording unit (pit) of data “1”. The direction of magnetization is downward in FIG. Are the same. Therefore, at the time of reproduction, no distinction is made between the recording unit of data "0" and the periphery of the recording section.

By applying a laser pulse as shown in FIG. 2A and a modulation magnetic field as shown in FIG. 2B to the medium on which such recording has been performed, that is, the pulse intensity corresponding to the recording data "1" By increasing the pulse intensity corresponding to "0", the recording pit of data "0" is formed with a larger dimension than the recording pit of data "1", and the magnetization pattern as shown in FIG. obtain. The broken line in FIG. 2C indicates the shape of the preceding recording pit (shown in FIG. 1C), and the hatched portion indicates the recording pit of data "1" in the opposite direction to the initial magnetization, as in FIG. 1C. Is shown. As apparent from FIG. 2C, when the pit of data "0" is recorded and formed over the portion where the pit of data "1" was previously formed, the size of the pit of data "0" is determined. Is large, there is no erasure of the pit of data “1”. On the other hand, when a pit of data “1” is recorded and formed over a portion where a pit of data “0” was previously formed, the surrounding magnetization direction (downward in FIG. ) Is the same as
During reproduction, there is no adverse effect due to the unerased part.

As described above, no erase residue that substantially adversely affects the reproduced signal does not occur, and it is possible to prevent S / N degradation of the reproduced signal due to the residual erase.

For simplicity of explanation, FIG. 1 has been described as the operation at the time of the first data recording on the initialized magneto-optical disk, but from the above description, FIG. It is clear that you can think about it.

Next, an example of the configuration of an apparatus for realizing the above-described recording method will be described with reference to FIG.

In FIG. 3, the magneto-optical disk 10 has a recording medium layer of a material capable of performing the above-described magnetic field modulation overwriting, and is rotated at a constant angular velocity or a constant linear velocity by a spindle motor 21. I have. For example, an NRZ modulation signal of recording data is input to the input terminal 11, and the recording data signal is supplied to a magnetic head driving circuit.
It is sent to the magnetic head 13 via 12. Further, the recording data signal is sent to the data discriminating circuit 14 to determine a binary value (“0” or “1”), and the value is sent to the laser diode driving circuit 15. The laser diode drive circuit 15
For example, by outputting a pulse having a large amplitude when "0" and a small amplitude when "1" to drive the laser diode 22 to emit light, the laser pulse as shown in FIG. 1A or FIG. It has gained. The laser light from the laser diode 22 is
After being converted into a parallel light beam by the collimator lens 23, the light is irradiated onto the magneto-optical disk 10 through the beam splitter 24 and the objective lens 25 constituting a so-called two-axis device for focusing and tracking, thereby heating the recording medium layer. I do. The recording unit (pit) corresponds to the direction of the applied magnetic field at this time.
Is magnetized, magnetic field modulation recording is performed.
A magnetization pattern as shown in FIG. C or FIG. 2C is recorded and formed.

At the time of reproduction, the laser diode 22 is constantly driven to emit light with a lower power than at the time of recording, and the laser light beam is applied to the magneto-optical disk 10 via the collimator lens 23, the beam splitter 24 and the objective lens 25. Magneto-optical disk 10
Is reflected by the beam splitter 24 through the objective lens 25, and is reflected by the half-wave plate, the focusing lens,
The light enters the polarization beam splitter 24 via an optical system 26 such as a cylindrical lens. The polarization beam splitter 24 separates the incident light into a P-polarized component (P-wave) and an S-polarized component (S-wave), and separates them into photodetectors (light receiving elements) 28 and 29, respectively.
Sent to. The difference component (push-pull output) between the signals from the photodetectors 28 and 29 becomes an information signal (a so-called MO signal) recorded magneto-optically.

As described above, it is only necessary to change the pulse amplitude (intensity) in accordance with the binary value of the recording data, so that the number of added parts on the apparatus configuration is small, or only a part of them is changed, which is economical.

The above is an example in which the present invention is applied to a magneto-optical disk that can be overwritten by a magnetic field modulation method. In addition, the present invention can also be applied to a magneto-optical disk that can be overwritten by a light intensity modulation method. it can.

That is, FIG. 4 is a diagram for explaining the operation of one embodiment of the present invention, FIG. 4A shows an applied laser pulse in the case of a magneto-optical disk of a light intensity modulation system, and FIG. Each shows a magnetization pattern (recording pit shape) on the medium. In FIG. 4B, for convenience of illustration, similarly to FIGS. 1C and 2C, the direction of magnetization originally perpendicular to the plane of the paper is indicated by vertical arrows on the plane of the paper.

In the light intensity modulation recording, as will be described later, the magnetization direction is recorded differently when the light is strong (the heating temperature is high) and when the light is weak (the heating temperature is low). The amplitude (intensity) of the laser pulse is small (weak) when the data is “0” and large (strong) when the data is “1”. Further, in this embodiment, the magnetization direction of the recording unit (pit) corresponding to the data “0” is the same as the magnetization direction at initialization (the magnetization direction around the recording area, downward in the figure). From the recording unit (pit) of this data “0”
It is important to make the size of the data “1” larger than the same size of the data “1”.
Is wider than the pulse width. By the application of the laser pulse having such a waveform, as shown in FIG.
Is recorded so that the size of the pit corresponding to the data "1" becomes larger than the size of the pit corresponding to the data "1" (the hatched portion in the figure).

FIG. 5 shows an example of the configuration of an apparatus for realizing the recording method of this embodiment. The same reference numerals are given to portions corresponding to those in FIG. 3 and the description is omitted.

In the Figure 5, with respect to the optical intensity modulation overwritable magnetooptical disk 40, the opposite across the disc position where the laser beam is irradiated position, a magnet 38 for the recording magnetic field H _R applied is arranged and, the magnet 39 of the initialization (initialization) field H _I for application is disposed in another position where the recording along the track is performed. In FIG. 5, upward in the figure the recording magnetic field H _R, has an initializing magnetic field H _I downward in FIG.

Also, recording data is supplied to the input terminal 31 in FIG. 5, and the recording data is sent to the data discriminating circuit 32, so that a binary value (“0” or “1”) is discriminated. The output signal from the data discriminating circuit 32 is sent to the changeover switch 33 as a changeover control signal.
When the data value is “1”, the data value is “0” at the selected terminal a.
At this time, the switching is controlled by the selected terminal b. The clock signal from the clock input terminal 34 is
2. The data is sent to the pulse generator 35 for data "1" and the pulse generator 36 for data "0". A pulse corresponding to data "1" from the pulse generation circuit 35, that is, a pulse having a high level and a narrow time width, is supplied to the selected terminal a of the changeover switch 33 and the data "0" from the pulse generation circuit 36.
The corresponding pulse, that is, a pulse having a low level and a wide time width, is sent to the selected terminal b of the changeover switch 33. Therefore, the changeover switch 33 outputs a pulse signal having a waveform shown in FIG. 4A composed of a pulse train having a level (amplitude) and a pulse width corresponding to the binary value of the recording data. 4A by driving the laser diode 22 to emit light.
The laser pulse shown in FIG.

Next, the recording operation principle of the light intensity modulation overwrite will be described with reference to FIGS. First, the recording medium layer of the magneto-optical disk used for this light intensity modulation overwriting has a first layer 41 called a holding or storage layer and a first layer 41 called a recording or writing layer. It has a multilayer structure having two layers 42. At the time of reproduction, the first layer 41 is irradiated with a laser light beam, and by detecting the difference in the rotation angle of the polarization plane of the reflected light, the binary of the recording data is determined.
In the recording data, a binary value is determined only by the magnetization direction of the first layer (recording unit, pit) 41 without depending on the magnetization direction of the second layer 42. For example, the state a in FIG. Since the magnetization direction of the layer 41 is downward, it represents “0”, and the state b is the first layer
Since the magnetization direction of 41 is upward, it represents “1”. Further, the coercivity of the first layer 41 represents the temperature characteristic such as curve H _c1 of FIG. 7, the coercive force of the second layer 42 shows the temperature characteristic as the curve H _c2 of FIG. 7.

State a and state b in FIG. 6 show the standard recording state of data “0” and “1” at medium temperature Ta in _a normal use state such as room temperature, respectively, for a unit recording pit (magnetic domain). There is shown a recording state after the magnetic field H _I according to the magnet 39 is applied, the magnetization direction of the second layer 42 is downward none.

When a recording laser beam (laser pulse) is applied from the states a and b, which are the standard recording states of these data “0” and “1”, first of all, the first layer 41 via the state c.
Curie temperature T reached _C1, further the Curie temperature T _C2 of the second layer 42 via the state d when the laser beam intensity is high
To reach. That is, when a low-level (small power) laser pulse corresponding to data “0” is applied, the coercive force H _C1 of the first layer 41 rapidly decreases as the medium temperature increases, and the medium temperature decreases. In the state c which has reached _TL , the coercive force H _C1 becomes very small, and when the temperature reaches the Curie temperature T _C1 , the coercive force H _C1 becomes zero. At this time, since the coercive force H _C2 of the second layer 42 is still relatively large, when the laser pulse application ends and the medium temperature decreases, the magnetization of the first layer 41 is changed by the so-called exchange force. In the medium temperature T _a at normal time (substantially equivalent to room temperature), the state a in FIG. 6, that is, the standard recording state of data “0” is obtained.

On the other hand, when a high-level (large power) laser pulse corresponding to data "1" is applied, the medium temperature exceeds the _TL state c and the Curie temperature T _C1 ,
The Curie temperature T _C2 of the second layer 42 is reached. State d in FIG. 6 is representative of the state before the temperature T _H to reach the Curie temperature T _C2, the magnetization of the first layer 41 is disappeared, so smaller magnetization of the second layer 42 I have. Upon reaching the Curie temperature T _C2, eliminates also the magnetization of the second layer 42, the reduction process of medium temperature after the laser pulse application end, the in the direction (upward in the drawing) of the recording magnetic field H _R that is applied at this time 2 Layer 42 is magnetized. This is shown in state e (temperature _TH ) and state f (temperature _TL ) in FIG. In state f, and also it appears magnetization in the first layer 41, first layer 41 to the recording magnetic field H _R the same direction as the second layer 42 by the exchange force be remote from the application region of (upward in the drawing) It is magnetized. Furthermore the temperature is lowered, approximately room temperature of the medium temperature T _a in the first six view state g, and the first layer
Reference numeral 41 indicates a recording state of data "1". Thereafter, when the above-described initialization magnetic field H _I (downward in the figure) is applied, the temperature becomes lower.
Only a small second layer 42 of the coercive force T _a are magnetized in the same direction (downward in the figure), because the coercive force of the first layer 41 is large enough to have a magnetic field H _I in magnetization orientation does not change, Fig. 6 The state becomes the standard recording state of data "1" shown in state b.

As described above, the recording state of the medium is the state a or b
Whether the recorded data is “0”
Regardless of whether it is "1" or not, the desired data recording state can be achieved by the magnitude of the amplitude (light intensity) of the applied laser pulse, and overwriting (overwriting) can be realized.

Even for such a magneto-optical disk capable of light intensity modulation overwriting, the pit size in the same magnetization direction as the magnetization direction in the periphery of the recording area is recorded and formed larger than the pit size in the opposite direction. The erasure of the recorded data is substantially eliminated, and the noise of the reproduced signal is reduced.

The present invention is not limited to only the above-described embodiment. For example, the above-described magneto-optical disk capable of light intensity modulation overwriting includes a first layer 41 and a second layer 42.
Although a two-layered magneto-optical disk having an intermediate layer is shown, various multi-layered magneto-optical disks such as a three-layered disk having an intermediate layer can be used. Further, although the magnetization initialization direction (the direction of the magnetization around the recording area) is made to correspond to "0" of the recording data, it is needless to say that it may correspond to "1" of the recording data.

〔The invention's effect〕

As is apparent from the above description, according to the optical recording method and apparatus of the disk-shaped recording medium of the present invention, the intensity of the laser pulse applied during recording of a data recording unit in which the recording layer is in the initial state, The intensity of the laser pulse applied at the time of recording of the data recording unit that is different from the initial state is smaller than the intensity of the laser pulse applied, and the pulse width of the laser pulse applied at the time of recording of the data recording unit at which the recording layer is in the initial state is By performing recording with a pulse width wider than the pulse width of a laser pulse applied when recording a data recording unit that is in a state different from the initial state, the initial state of the data recording unit can be rewritten without erasure, and the reproduction signal can be rewritten. And the initial state is not affected by the fluctuation of laser power, etc. In addition, the pulse width is increased when the laser pulse intensity is low, so that the recording medium irradiated with the laser can be compared with the case where the pulse width is increased when the laser pulse intensity is high. Damage due to temperature rise can be prevented. Therefore, no unerased portion that affects the reproduction signal is generated, and noise during reproduction due to the unerased portion of the previous data is reduced.

[Brief description of the drawings]

FIGS. 1 and 2 are views for explaining an example of a recording method for a magneto-optical disk prior to the description of an embodiment of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of a device for realizing the example, FIG. 4 is a diagram for explaining an embodiment of the present invention,
FIG. 5 is a block diagram showing a schematic configuration of an apparatus for realizing the embodiment of FIG. 4, and FIGS. 6 and 7 are diagrams for explaining the principle of recording operation of light intensity modulation overwriting. FIG. 8 is a view for explaining a conventional overwriting operation, and FIG. 9 is a schematic sectional view of a grooved disk. 10: Magnetic field modulation recording type magneto-optical disk 11, 31 ... Data input terminal 12 ... Magnetic head drive circuit 13 ... Magnetic head 14, 32 ... Data discrimination circuit 15, 37 ... Laser diode drive circuit 22 ... Laser diode 35: Pulse generator for data "1" 36: Pulse generator for data "0" 38: Magnet for applying a recording magnetic field 39 ... Magnet for applying an initializing magnetic field 40: Light intensity modulated recording light Magnetic disk

Continuation of front page (72) Inventor Yoshihiro Tsukamura 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-A-3-242844 (JP, A) JP-A-61-190741 (JP, A) JP-A-2-24801 (JP, A)

Claims (2)

(57) [Claims] 1. An optical recording method for recording data by controlling the intensity of a laser pulse applied in accordance with binary values of recording data for each data recording unit of a recording layer of a disk-shaped recording medium, wherein the recording layer is The intensity of the laser pulse applied at the time of recording of the data recording unit to be in the initial state is smaller than the intensity of the laser pulse applied at the time of recording of the data recording unit to be in a state different from the initial state, and the recording layer is The pulse width of the laser pulse applied when recording the data recording unit in the initial state is made wider than the pulse width of the laser pulse applied when recording the data recording unit in a state different from the initial state. Optical recording method for a disk-shaped recording medium. 2. An optical recording apparatus for recording data by controlling the intensity of a laser pulse applied in accordance with a binary value of recording data for each data recording unit of a recording layer of a disk-shaped recording medium. A laser diode for irradiating the medium with a laser; and a driving unit for generating a laser pulse for driving the laser diode to emit light in accordance with a recording data signal, wherein the driving unit performs data recording in which the recording layer is in an initial state. The intensity of the laser pulse applied during unit recording
The intensity of the laser pulse applied during recording of a data recording unit that is different from the initial state is smaller than the intensity of the laser pulse applied during recording of a data recording unit in which the recording layer is in an initial state. A disk-shaped recording medium for recording data by driving the laser diode with a pulse width wider than a pulse width of a laser pulse applied when recording a data recording unit in a state different from the initial state. Optical recording device.