JP2539585B2 - Magneto-optical information storage method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical information storage device using the magneto-optical effect, and more particularly to a magneto-optical information storage device capable of applying a stable external magnetic field during recording and erasing.

[0002]

2. Description of the Related Art A magneto-optical information storage device is, for example, an amorphous thin film disk for magneto.
Optical Memory, NHC Broadcasting Science Research Laboratory (Amorphous thin film disk for magneto-opt
ical memory, NHK Broadcasting Science Research
Laboratories) SPIE Vol. 329, p208 Optical Disc Technology
echnology) 1982. Is disclosed in.

This kind of apparatus is composed of a recording / reproducing optical system and an electromagnetic coil, and the electromagnetic coil is installed so as to face a focusing lens with a recording medium sandwiched therebetween.
The magneto-optical information storage device uses a perpendicular magnetization film as an information recording medium, and performs recording by reversing the magnetization direction of the perpendicular magnetization film according to information. The effect of reproduction is that the plane of polarization of incident light rotates in accordance with the direction of magnetization of this perpendicularly magnetized film,
That is, the magneto-optical effect is used.

In this device, information can be erased and information can be rewritten. The recording operation and the erasing operation are performed by fixing the magnetization of the magnetization film by applying a magnetic field from the outside with an electromagnetic coil where the magnetization is once lost by the heat of the laser light spot focused on the magnetization film. To do. The external magnetic field must be applied in opposite directions in the recording operation and the erasing operation, and it is important to increase the switching speed. Therefore, in the magneto-optical information storage device, how to stably apply the external magnetic field is extremely important in terms of speeding up and reliability.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above point, and a stable steady magnetic field is applied at the time of recording or erasing information to perform high-speed and stable recording and erasing. It is an object of the present invention to provide a magneto-optical information storage device that can be implemented.

[0006]

In order to achieve such an object, according to the present invention, an external magnetic field is applied in advance before irradiating a recording medium with an optical pulse for recording or erasing, so that actual recording is performed. The feature is that the external magnetic field is set to reach a sufficiently steady value at the position to be erased. The rise of the magnetic field is determined by the time constant of the coil. However, in general, to obtain a large magnetic field strength,
At the same time as increasing the inductance of the coil, it is necessary to increase the drive current applied to the coil. However, it is very difficult for a coil driver circuit to perform high-speed switching of a large current, and a saturation switch circuit cannot obtain a steady magnetic field faster than the time constant of the coil. Therefore, as in the present invention, the rise time of the magnetic field is taken into consideration at the time of recording and erasing, and a current is passed through the electromagnetic coil before the start of the irradiation of the optical pulse, and the recording and erasing operations can be performed when the magnetic field becomes stable. Be advantageous.

For example, the external magnetic field is applied at least 1 ms or more before the light pulse irradiation. In the case of a sector-managed magneto-optical disk, it is possible for the host controller to easily recognize the sector to be recorded or erased in advance. Therefore, it can be realized very easily by supplying the drive current to the coil before a predetermined number of sectors, which is estimated by the time constant of the coil from the target sector.

[0008]

With the above structure, since the recording and erasing operations can be performed when the magnetic field is stable, stable recording,
Erase operation can be performed.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a schematic structure of a magneto-optical disk device according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a disk-shaped magneto-optical record carrier (hereinafter referred to as a magneto-optical disk), which is rotated by a rotary motor 2.
Reference numeral 3 denotes a magneto-optical head for recording / reproducing / erasing information, which can be moved by the feed motor 4 to an arbitrary radial position of the magneto-optical disk 1, that is, an arbitrary track.

The magneto-optical disk 1 comprises a substrate such as glass or plastic, and a perpendicular magnetization film (for example, TbFe) having a magneto-optical effect provided on the substrate. Information recording / playback / erasure is performed as follows.

A laser beam emitted from a light source 5 such as a semiconductor laser is converted into a parallel light beam by a coupling lens 6 and incident on an objective lens 8 via a beam splitter 7 to form a minute spot on the disc 1. The objective lens 8 is attached to the voice coil 9 so as to move following the vertical shake of the disk 1. If you want to record information. The modulation circuit 11 modulates the drive current of the semiconductor laser 5 with an information signal and irradiates the perpendicular magnetic film on the disk 1 with an optical pulse corresponding to the information to be recorded, and locally raises the temperature of the perpendicular magnetic film. . The temperature rise causes the magnetization of the magnetic film to locally disappear, and a magnetic field in the opposite direction to the surrounding magnetization direction is applied to this portion by the electromagnetic coil 10 so that only the light-irradiated portion has the opposite magnetization. Form an area. In order to erase the already written information, a constant current is passed through the semiconductor laser 5 to irradiate the perpendicular magnetization film with a laser beam, the magnetization of the magnetization film is once lost, and the magnetic field direction generated by the electromagnetic coil 10 is recorded. The reverse magnetization is applied to return the magnetization direction of the perpendicular magnetization film to the same direction as the surrounding unrecorded portion.

Information is reproduced by utilizing the magneto-optical effect represented by the Kerr effect. The Kerr effect is an effect in which the polarization directions of incident light slightly rotate in opposite directions corresponding to the upward and downward magnetizations of the perpendicular magnetization film. The reflected light from the disc 1 passes through the objective lens 8, is separated by the beam splitter 7, and is guided to the analyzer 12. The analyzer 12 is an optical element that passes only a specific polarization component. Therefore, when the light whose polarization plane is rotated depending on the presence or absence of the recording portion is incident due to the Kerr effect, it is converted into a change in the light amount and emitted. The change in light amount is converted into an electric signal by the photodetector 13, and then amplified by the amplifier 14 to a desired level. Reference numeral 15 is a control device for controlling the entire apparatus, including the feed motor 4, the modulation circuit 11, and the electromagnetic coil 1.
The drive circuit 16 of 0, and other control related to information recording / reproducing / erasing operations are performed.

To give a specific numerical example of the external magnetic field, the magnitude of the external magnetic field applied at the time of recording / erasing information is about 200 Oe (oersted) on the surface of the recording film. This magnetic field strength is obtained by passing a current of about 50 mA through an electromagnetic coil having an inductance of 300 mH, and the coil time constant is about 3 ms.

Next, the magneto-optical disk used in the present invention will be described. FIG. 2 shows an example of a disc format. The disc 1 has spiral or concentric circular tracks along its rotation direction, and the track is divided into a plurality of recording areas 21 to 28. These recording areas are generally called sectors, and are the minimum units for writing, reading, and erasing information. Headers 31 to 38 ... Are provided at the beginning of each sector. In each of these headers, the contents such as the track number and the sector number necessary for taking in and out the information in the sector are written in advance as uneven pits.

Next, the operation for recording / reproducing / erasing information in sector units will be described.

FIG. 3 shows an example of a time chart in the case of recording / erasing information in an arbitrary sector in each track with one track of the disk, that is, one track as a basic unit for recording / reproducing / erasing. It is a thing. In FIG. 3, a reproducing operation for one track is performed between the recording operation and the erasing operation. This is a measure for confirming recording or erasing, and at the same time for taking into consideration the rise and fall times of the external magnetic field generated by the electromagnetic coil 10 during recording or erasing. Therefore, of course, if the reproducing operation of one or more tracks is performed during the recording or erasing operation, this object is satisfied.
Reference numeral 41 is a recording mode given from the control device 15. Here, the transition to the recording mode is performed in advance of, for example, one sector of the track on which the recording operation is performed. That is, the recording mode is shifted earlier by the rise time of the magnetic field generated by the electromagnetic coil 10. If the steady rise of the recording magnetic field is slow and a steady magnetic field cannot be obtained in the time of one sector, it is sufficient to shift to the recording mode in advance for two sectors or more. When the recording mode is entered, the coil driving circuit 16 causes the recording magnetic field 4
4 is generated, the coil drive current 43 is applied to the electromagnetic coil 10.
Is applied to If the laser driving pulse 45 is applied to the modulation circuit 11 to modulate the semiconductor laser 5 after the recording magnetic field reaches a steady state, desired information can be stably recorded on the recording film on the disk 1.

When erasing the information already written on the disc 1, the same sequence can be performed. When the controller 15 gives an instruction to shift to the erase mode 42, the coil drive circuit 16 causes the coil drive current 43 in the opposite direction to that in the recording mode to flow to the electromagnetic coil 10. In this case as well, one or more sectors of the track to be erased are preceded by the sector preceding in time, and the erase mode is entered. After the erasing magnetic field has reached a steady state, the laser driving pulse 45 is applied to the modulation circuit 11 so that the semiconductor laser 5
Is modulated, the information is surely erased. The example of FIG. 3 shows a case where a plurality of sectors are continuously erased, during which the laser drive pulse 45 is
It uses a constant level of direct current.

For example, in the case of a monotone disk using a Tb-Fe system amorphous film, the film surface optical power is 5 m during recording.
It is possible to stably perform an external magnetic field of 100 Oe (Oersted) at W, and an external magnetic field of 300 Oe (Oersted) at a film surface optical power of 5 mW during erasing.

Incidentally, the application of the magnetic field is stopped during the reproduction operation. Due to the characteristics of the magneto-optical recording medium, when a medium having a large coercive force is used, it is difficult to erase the information once recorded, but a large power optical pulse is required for recording and erasing. On the other hand, in the case of a medium having a small coercive force, the optical power required for recording and erasing may be small, but on the contrary, the recording state is disturbed by the surrounding magnetic field. Therefore, during the reproducing operation, the application of the magnetic field is stopped so that the latter drawback cannot be compensated and the optical power required for recording and erasing can be reduced.

Next, in order to execute the sequence of FIG.
A more specific configuration example of the logic circuit and a circuit example of the magnetic field generation coil drive circuit 16 will be shown. Various types of circuits have been conventionally known for the semiconductor laser modulation circuit 11, and no special changes or additions are necessary when implementing the present invention.
I will omit the explanation.

FIG. 4 is an example of a logic circuit for executing the sequence of FIG. 3, and is assumed to constitute a part of the control circuit 15. Information given to the logic circuit includes serial data 51 of the current sector number and a delimiter signal of the sector number data 51, that is, a latch signal 52.
And a signal 61 for instructing a mode (recording / reproducing / erasing) for a desired sequter. The serial data 51 indicating the sector number is input to the shift register 53,
It is converted into parallel data 54 by the latch signal 52. Next, it is output after being subtracted by 1 by the subtractor 55. The subtracted data 56 includes a sector number 58 for executing the mode recorded in the memory 57, and a comparator 59.
Matched by. If the sector numbers match,
A signal 60 indicating that they match is output. On the other hand, the mode signal 61 is input to the sector 62 in advance, and when the recording mode is executed, the flip-flop 63 is in the standby state. Further, when executing the erase mode, the flip-flop 64 is in a standby state. If it is in the reproduction mode, both the flip-flops 63 and 64 are reset. If the recording mode is to be executed, the recording mode 41 becomes "H" by the sector number matching signal 60 to the flip-flop 63 in the standby state. The mode is reset when the signal 61 instructing the reproduction mode is input from the upper control circuit 15. When executing the erase mode, the sector number matching signal 6 is sent to the flip-flop 64 in the standby state.
By giving 0, the erase mode 42 is set to "H".

The feature of the logic circuit shown in FIG.
The point 5 is to calculate the sector one sector before the current sector. Note that this subtraction process can also be performed by software for operating a higher-order control circuit.

Next, an example of the coil drive circuit 16 for generating the recording magnetic field and the erasing magnetic field in response to the recording mode 41 or the erasing mode 42 will be described.

FIG. 5 shows an embodiment of the coil drive circuit 16. Positive and negative potentials are set by the variable resistors 71 and 72, respectively. The analog switch 73 incorporates switches 74 and 75 which are opened and closed depending on the recording mode 41 and the erasing mode 42 from the outside.

The recording mode 41 allows the switch 7 to operate.
Consider the case where 4 is closed. When a constant positive potential is applied to the operational amplifier 76, the transistor 77 turns on.
Then, a current value obtained by dividing the positive potential 71 by the value of the resistor 79 flows through the electromagnetic coil 10. When the switch 75 is closed in the erase mode 42, the transistor 78 is turned on, and a current value obtained by dividing the negative potential 72 by the value of the resistor 79 flows through the electromagnetic coil 10 in the opposite direction to that when the recording mode is selected.

When both the recording mode 41 and the erasing mode 42 are "L", the switches 74 and 75 are both open, so that the high resistance 80 causes the positive input terminal of the operational amplifier 76 to become zero volt. No current flows in the electromagnetic coil 10. This state corresponds to the reproduction mode.
The diodes 81 and 82 are respectively transistors 77 and
It acts to neutralize the base-emitter voltage of 78 and eliminate crossover distortion when the transistor switches.

[0028]

According to the present invention, the conventional magnetic field generating means,
That is, it is possible to apply a steady magnetic field in a magnetic field direction corresponding to each of recording of information and erasing of information without special consideration to the electromagnetic coil for generating an external magnetic field and the coil driving circuit, and at high speed. Moreover, it is possible to realize a magneto-optical storage device capable of stable recording and erasing.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a magneto-optical disk device that is an embodiment of the present invention.

2 is a plan view showing an example of a recording format of a disc used in the apparatus shown in FIG.

FIG. 3 is a time chart diagram for explaining information recording / reproducing / erasing operations.

FIG. 4 is a block diagram showing a configuration example of a logic circuit for controlling magnetic field generation.

FIG. 5 is a circuit diagram showing an example of a drive circuit of a magnetic field generating coil.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magneto-optical disk, 3 ... Magneto-optical head, 5 ... Semiconductor laser, 10 ... Electromagnetic coil, 12 ... Analyzer, 15 ... Control circuit, 16 ... Coil drive time, 21-28 ... Sector, 3
1 to 38 ... Header, 41 ... Recording mode, 42 ... Erase mode, 42 ... Erase mode, 55 ... Subtractor, 62 ... Selector.

Claims (4)

(57) [Claims] 1. A method of storing magneto-optical information utilizing the magneto-optical effect.
In the method , when performing a recording or erasing operation, an external magnetic field is applied in advance before irradiating the recording medium with an optical pulse for performing the recording or erasing, and after the irradiation of the optical pulse is finished, the external magnetic field is applied. A magneto-optical information storage method , characterized in that the application of a magnetic field is stopped. 2. The magneto-optical information storage method according to claim 1, wherein the external magnetic field is applied at least 1 ms before the irradiation of the optical pulse. Memory method . 3. A magneto-optical information storage method according to claim 1 or 2, wherein a disc-shaped carrier having a structure in which a track around a disc is divided into a plurality of sectors is used as the recording medium. or the external magnetic field before the predetermined number of sectors to whether the target sector erase, a magneto-optical information storage method that application direction is equal to or to be applied to have opposite directions in recording and erasing . 4. A magneto-optical information storage method according to claim 3, wherein the switching of the application direction of the external magnetic field is performed in units of tracks around the disk, and between the recording operation and the erasing operation. , Magneto-optical information storage method characterized by providing at least a reproducing operation or a standby operation for one round of the disk
Law .