JPH06150435A - Laser power control for magneto-optical disk device - Google Patents

Abstract

PURPOSE:To easily control a laser power and also to control it minutely by pulse-driving the laser which is used as a light source of a magneto-optical disk device, and controlling the power level while changing the pulse width. CONSTITUTION:The data to be recorded are modulated to a digital mode by an encoder 1, and the modulated signal is converted to a pulse train by a pulse train encoder 2. By a laser diode controller 3 provided with an APC circuit, a laser diode LD 4 in an optical head 10 is controlled for ON/OFF and the magneto-optical disk 5 is irradiated with the laser beam according to the pulse train. The disk 5 is heated by the laser beam to the temperature of two high/ low levels, then the data are recorded. The laser is pulse-driven by a clock period, and the laser beam is modulated so that the L-level part is irradiated with the narrow width pulse and the H-level part is irradiated with the wide width pulse. Thus by pulse-driving the LD 4, the control of laser power is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power level control method for laser light used in an optical modulation overwrite type magneto-optical disk apparatus using a multi-layered magneto-optical disk apparatus.

[0002]

2. Description of the Related Art For example, in an optical modulation type magneto-optical disk apparatus using a two-layered magneto-optical disk, when overwriting is performed, laser light of two power levels of high level / low level, that is, different Data recording is performed by irradiating a laser beam of brightness.

That is, in the double-layered magneto-optical disk, the recording medium is composed of two layers, an auxiliary layer and a recording layer (the Curie point of the recording layer is lower than that of the auxiliary layer and the coercive force is higher than that of the auxiliary layer). The layer passes under the initializing magnet and its magnetization direction is pre-aligned. Then, by irradiating the recording layer with a low-level laser beam, the recording layer is magnetized in the same direction as the auxiliary layer, and by irradiating the recording layer with a high-level laser beam, the recording layer is biased with a magnetic field ( It is magnetized in the direction opposite to the magnetic field of the initialization magnet). In this way, the magnetization direction of the recording layer changes depending on the power level of the laser light, so that the intensity of the laser light is changed to perform data recording.

FIG. 6 is a diagram for explaining an overwrite operation of a light intensity modulation system using a conventional double-layered magneto-optical disk, and is of a binary (1,0) value shown in FIG. 6 (a). The recording data is recorded by irradiating the magneto-optical disk with laser light having the power level shown in FIG. 6B.

That is, when the recording data is "0", a low-level (PL) laser beam is applied to the magneto-optical disk, and when the recording data is "1", a high-level (PH) laser beam is emitted. Data is recorded by irradiating the magneto-optical disk with light.

[0006]

In the case of an optical modulation type magneto-optical disk device using a double-layered magneto-optical disk, data writing is irradiated with laser beams of two power levels, a low level and a high level. There is a need. in this case,
Since the power margin between the low level (PH) and the high level (PL) is small, it is difficult to control and adjust the level, and since continuous irradiation is performed, it is impossible to finely control the medium temperature by the laser light.

The above situation is the same as in the case of a magneto-optical disk device using a four-layer film magneto-optical disk, and it is necessary to irradiate laser light of two power levels of low level / high level at the time of data recording. there were.

The present invention has been made in view of the above problems, and in a magneto-optical disk device that requires laser light of a plurality of power levels during data recording, the magneto-optical disk device can effectively control the laser power. It is an object of the present invention to provide a laser power control method of the above.

[0009]

According to a first aspect of the present invention, there is provided a laser power control method for a magneto-optical disk device, which is a light source in a magneto-optical disk device for irradiating a recording medium with laser light having a plurality of power levels for data recording. The laser is pulse-driven and the pulse width is changed to control the power level.

According to a second aspect of the present invention, there is provided a laser power control method for a magneto-optical disk device, wherein a recording medium is provided with a heating period, a heat retaining period and a cooling period by controlling a pulse width of a laser beam to be irradiated. The laser power control method according to claim 1, wherein recording is performed.

[0011]

In the method of controlling the laser power of the magneto-optical disk device according to the first aspect of the present invention, the power level of the laser light applied to the recording medium is not changed by changing the brightness of the laser light, but by changing the laser power level. This is a method of controlling the power level by keeping the brightness of light constant and changing its pulse width (changing the irradiation time).

By doing so, the power level of the laser light to be applied can be easily controlled and can be finely controlled.

According to a second aspect of the present invention, there is provided a laser power control method for a magneto-optical disk device, wherein a pulse width of a laser beam to be applied is finely controlled, and a period for heating a recording medium, a period for retaining heat, and a period for cooling are provided. Make a record. By doing so, the temperature of the recording medium can be finely controlled, and stable data recording can be performed even at the pit edge.

[0014]

FIG. 1 is a block diagram showing the configuration of an embodiment of a recording system in which the laser power control method of the present invention is used. The method of the invention according to claims 1 and 2 is applied to this recording system.

In FIG. 1, data to be recorded is digitally modulated by an encoder 1. The pulse train encoder 2 converts this modulated signal into a pulse train. APC (Automatic Power Con
A laser diode controller (LD controller) 3 having a controller circuit turns on the laser diode (LD) 4 in the optical head 10 according to the pulse train.
The N / OFF control is performed to irradiate the magneto-optical disk 5 with laser light. The magneto-optical disk 5 is heated by laser light to two levels of high and low levels, and data recording is performed.

The magnetic field head 6 is driven by the magnetic field head driver 7 and applies a recording bias magnetic field to the magneto-optical disk 5. The CPU 8 gives a control command to the magnetic field head driver 7, the LD controller 3 and the servo circuit 9. The servo circuit 9 controls and drives a spindle motor 11 for rotating the magneto-optical disk, a slide motor 13 for the optical head 10, an actuator 14 for focus / tracking, and an actuator 15 for the magnetic field head 6.
The initialization magnet 12 is for aligning the directions of the magnetic fields of the auxiliary layers in the two-layer film (recording layer and auxiliary layer).

The laser power control method of the present invention is
It is mainly applied to the pulse train encoder 2 and the LD controller 3.

2A and 2B are views for explaining the laser power control method in the embodiment of FIG. 1. FIG. 2A shows the case where the conventional method is used, and FIG. 2B shows the method of the present invention. Shows the case of using. In addition, FIG.
It is the figure which expanded a part of pulse waveform in (b).

Hereinafter, with reference to FIGS. 2 (b) and 2 (c),
The control operation of the laser power in this embodiment will be described.

(1) In the present embodiment, as shown in FIG. 2B, the power level (PP) is kept constant and the laser diode (LD) 4 is pulse-driven to change the pulse width corresponding to the recording data. Data is recorded by changing the temperature of the recording medium.

(2) Further, as shown in FIG. 2C, the laser is pulse-driven at the clock cycle (T), and the conventional low level portion is irradiated with a narrow T2 width pulse. As described above, the laser light is modulated so that the conventional high-level portion is irradiated with the T1 width pulse having a wide width.

By thus pulse-driving the laser diode (LD) 4, the laser power can be easily controlled. Further, when the laser diode (LD) 4 is pulse-driven, the power level (PP) is set higher than in the case of continuous irradiation, so that heat is spread in the width direction of the pit and a wide pit width is recorded. Therefore, the C / N can be improved in the case of pulse driving as compared with the case of recording data by continuous irradiation.

Further, this system has an advantage that the temperature control of each level on the recording medium can be easily and independently adjusted by changing the pulse width.

FIG. 3 is a diagram showing a circuit configuration example of the pulse train encoder 2 of FIG.

In FIG. 3, the clock signal is TTL7.
The signals are input to the trigger terminals (B) of the monostable multivibrators 21 and 22 (hereinafter, the “monostable multivibrator” is also simply referred to as “monomulti”) using the 4LS123. Each time the monomulti 21 is triggered, it generates a pulse 1 having a time width T1 according to the time constant determined by the resistor (R1) and the capacitor (C1). Similarly, each time the Mono Multi 22 is triggered, the resistor (R
2) A pulse 2 having a time width T2 corresponding to the time constant determined by the capacitor (C2) is generated.

Pulse 1 is the multiplexer (4051)
The pulse 2 is input to the first channel input terminal of H. 23, and the pulse 2 is input to the 0th channel input terminal of the multiplexer (4051) 23.

Further, the data signal is a multiplexer (4
051) is input to the A terminal of the channel selection terminals (A, B, C) 23, and the B and C terminals are connected to the ground. Therefore, when the data signal is "0", the 0th channel is selected and the pulse 2 is output to the output terminal (CO
Appears in M). When the data signal is "1",
The first channel is selected and pulse 1 appears at the output terminal (COM).

The operation of the circuit of FIG. 3 is shown in the operation timing chart of FIG. The example of FIG. 4 is an example in which the pulse train of FIG. 4E is generated based on the data of FIG. 4A and the clock signal of FIG. 4B.

The timing chart of FIG. 4 will be described below.

(1) From the rising edge of the clock signal, the monomulti 21 outputs the high-level pulse 1 shown in FIG. 4C, and the monomulti 22 outputs the low-level pulse 2 shown in FIG. 4D. To get Pulse width T1, T2
Is optimally set by resistors (R1, R2) and capacitors (C1, C2) connected to the respective monomultis 21, 22.

(2) The pulse 1 and the pulse 2 are switched and switched by the multiplexer 23 according to the data signal to obtain the pulse train shown in FIG.

In the circuit of FIG. 3, the monomulti 21,
Although the pulses 1 and 2 output from 22 are generated at the same frequency as the clock signal, the pulses 1 and 2 may be generated at an integral multiple of the clock frequency in order to control the temperature of the recording medium more finely. . Further, the pulse width may be controlled by combining a plurality of pulse widths.

Next, a second embodiment of the present invention will be described. This embodiment is an embodiment corresponding to the method of the invention described in claim 2.

When pit edge recording is performed on the magneto-optical disk by the optical modulation recording method, the temperature rise is small in front of the pits on the recording medium due to thermal diffusion of the surroundings,
On the contrary, in the rear, the temperature rises largely due to heat conduction from the front. Therefore, the shape of the magnetic domain becomes a teardrop shape.

Therefore, there arises a problem that an accurate edge position cannot be detected during data reproduction. Then, in the case of the overwrite method which requires two levels of laser power for data recording, the temperature control becomes more difficult.

An example in which the method of the present invention is applied in order to effectively perform this pit edge recording is shown below.

FIG. 5 is a diagram showing an example of laser power control for pit edge recording. FIG. 5 (a) shows a first control example, FIG. 5 (b) shows a second control example, and FIG. (C) has shown the 3rd control example.

(1) In the example of FIG. 5A, when the recording data is switched from 0 to 1 at time t1, the temperature of the recording medium is accelerated from the low level temperature to the high level temperature. In addition, the heating unit 51 having a wide pulse width is provided between time t1 and time t2. Then, after heating, a heat retaining portion a52 (between times t2 and t5) that irradiates a pulse required to maintain a high level temperature is provided.
Further, a heat retaining portion b53 for maintaining a low level temperature
(Between times t5 and t8).

(2) In the example of FIG. 5B, the laser power value PP is set to be larger than that of the example of FIG. Then, when the recording data is switched from 0 to 1 at time t1, the pulse width is changed from time t1 to time t2 in order to accelerate the temperature rise of the recording medium from the low level temperature to the high level temperature. A widened heating unit 54 is provided. Then, when the temperature rise in the heating unit 54 is too large, the cooling unit 55 is provided between time t2 and time t3 to lower the temperature so that the medium temperature becomes appropriate.

(3) In the example of FIG. 5C, in order to accelerate the temperature drop of the recording medium from the high level temperature to the low level temperature when the recording data is switched from 1 to 0 at time t5. , The cooling unit 56 between time t4 and time t5.
Is an example in which is provided. In this case, the cooling unit 56 may generate a pulse having a narrower width than that of the heat retaining unit.

As described above, the following effects can be obtained by using the laser power control method of the present invention.

(1) The laser power can be easily controlled when recording data on the magneto-optical disk.

(2) The APC circuit in the LD controller 3 can be simplified, and the laser power can be easily adjusted by changing the pulse width.

(3) Since the laser diode 4 is pulse-driven, C / N is improved.

(4) By controlling the pulse width, fine temperature control of the recording medium becomes possible.

In the embodiment described above, a magneto-optical disk device using a two-layer film magneto-optical disk has been described, but the method of the present invention is not limited to this, and a four-layer film magneto-optical disk is used. The present invention can be applied to all magneto-optical disk devices, such as conventional magneto-optical disk devices, which need to be irradiated with laser light of a plurality of power levels.

[0047]

According to the method of controlling the laser power of the magneto-optical disk device of the first aspect, the power level of the laser light applied to the recording medium is controlled not by changing the brightness of the laser light, but by controlling the laser power. The brightness of the light remains constant,
Since the power level is controlled by changing the pulse width, the laser power can be easily controlled and finely controlled.

According to the method of controlling the laser power of the magneto-optical disk device of the second aspect, the pulse width of the laser light to be applied is finely controlled, and when recording data, a period for heating the recording medium and a period for keeping the temperature thereof warm. Since the data recording is performed while the cooling period is provided, the temperature of the recording medium can be finely controlled and stable data recording can be performed even on the pit edge.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a recording system in which a laser power control method of the present invention is used.

FIG. 2 is a diagram for explaining a laser power control method in the embodiment of FIG.

3 is a diagram showing a circuit configuration example of a pulse train encoder 2 of FIG.

FIG. 4 is an operation timing chart of the circuit of FIG.

FIG. 5 is a diagram showing an example of laser power control for pit edge recording.

FIG. 6 is a diagram for explaining an overwrite operation of an optical modulation method using a conventional two-layer film magneto-optical disk.

[Explanation of symbols]

 1 Encoder 2 Pulse Train Encoder 3 LD Controller 4 LD 5 Magneto-Optical Disk 6 Magnetic Field Head 7 Magnetic Field Head Driver 8 CPU 9 Servo Circuit 10 Optical Head 11 Spindle Motor 12 Initializing Magnet 13 Slide Motor 14, 15 Actuator 21, 22 Monostable Multivibrator 23 Multiplexer

Claims (2)

[Claims] 1. In a magneto-optical disk device for irradiating a recording medium with laser light of a plurality of power levels to record data, a laser as a light source is pulse-driven and its pulse width is changed to control the power level. A laser power control method for a magneto-optical disk device, comprising: 2. The light according to claim 1, wherein the recording medium is provided with a heating period, a heat retaining period, and a cooling period by controlling the pulse width of the laser beam to be irradiated. Laser power control method for magnetic disk device.