JPH02267756A - Magneto-optical recording and reproducing system - Google Patents

Abstract

PURPOSE:To store more than ternary and to promote recording density of the magneto-optical recording and reproducing system by changing three stages of power at the time of recording using a recording device and a recording medium. CONSTITUTION:A modulation voltage waveform is outputted from a laser diode controller 5 in accordance with an information signal corresponding to a bit of more than ternary information inputted to a magneto-optical recording and reproducing device, and this outputted modulation voltage waveform is inputted to a laser diode driver 4 to be converted into a modulation current waveform. This modulation current waveform is led to a laser diode inside an optical head 3 to obtain a laser output waveform at plural levels on an optical disk 1 to be driven by a motor 2 as a recording medium. Then, the laser power is modulated into three kinds of values of a read level, a write level 1 and a write level 2 to carry out the recording of more than three kinds, thus promoting the recording density.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magneto-optical recording and reproducing system, particularly a magneto-optical recording and reproducing system that uses a recording medium made of a magnetic film. As a high-density recording method, magneto-optical recording is being researched and developed in which bits are written by locally heating the recording medium by irradiating it with laser light and read out using the magneto-optic effect. , amorphous magnetic thin films made of rare earth-transition metal alloys are attracting attention.

However, the recording density of normal magneto-optical recording is limited to a pit pitch of about 1 μm.

Therefore, in order to further increase the recording density, methods are currently being considered, such as reducing the recording beam diameter by decreasing the focusing beam size by shortening the wavelength of the laser beam (1988 Spring 35th Edition). (Refer to Volume 3 of the Proceedings of the Joint Conference on Applied Physics, Vol. 3, page 870).

[Problem to be solved by the invention]

The conventional magneto-optical recording method mentioned above has a bi-center width of 1μ.
There is a drawback that the recording density is limited to approximately m.

An object of the present invention is to provide a magneto-optical recording and reproducing system capable of recording at least 1.5 times as much information as the normal magneto-optical recording system without reducing the bit pitch.

[Means to solve the problem]

The magneto-optical recording and reproducing method of the present invention changes the bit size that can be written on a recording medium made of a magnetic thin film by changing the laser power during writing, making it possible to record information with three or more values on the medium. When reading the bits written on the medium, a beam with a sufficiently large spot diameter is irradiated onto the bits written on the medium, and information with three or more values is detected based on the size of the readable signal.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a magneto-optical recording and reproducing apparatus for explaining one embodiment of the present invention. The present invention provides a method that enables recording of three or more values, but for the sake of simplicity, the case of three-value recording will be explained here as an example.

As shown in FIG. 1, this embodiment has a laser diode controller 5 that outputs a modulated voltage waveform in response to an input information signal corresponding to information of three or more values, and the outputted modulated voltage waveform is input to the laser diode driver 4 and converted into a variable i11 current waveform. This modulated current waveform is guided to a laser diode inside the optical head 3,
A plurality of levels of laser output waveforms are obtained on the optical disc 1 as a recording medium driven by the motor 2.

FIG. 2 is a conceptual diagram of the level of modulated pulses output from the laser diode of the optical head in FIG. 1.

As shown in FIG. 2, this laser power is modulated into three types of values: read level, write level 1, and write level 2.

FIG. 3 is a partially enlarged conceptual diagram of one track showing bits recorded when the modulation pulse in FIG. 2 is irradiated onto the medium.

As shown in FIG. 3, bit 9 is not recorded at all at the read level. On the other hand, at write level 1, relatively small bit 7 is recorded. Furthermore, at write level 2, relatively large bit 8 is recorded.

FIG. 4 is a conceptual diagram showing signals when the bits shown in FIG. 2 are read at read level.

As shown in FIG. 4, when a relatively small bit is recorded at write level 1, the read signal 10 is small compared to a relatively large bit recorded at write level 2. For example, a read completion signal is detected. 'o' if not,
If the smaller read signal 10 is detected, “”1
”, if the larger read signal 11 is detected, “
If it is associated with 2'', three-value recording is possible.

FIG. 5 is a characteristic diagram showing the relationship between the writing laser beam intensity of the optical head in FIG. 1 and the size of the written bit.

As shown in FIG. 5, this characteristic utilizes the fact that the stronger the laser beam intensity, the larger the bit size that can be written on the magnetic recording medium.

That is, this is because the stronger the laser beam intensity, the higher the temperature of the laser irradiation part, the temperature of a wider area becomes equal to or higher than the Curie temperature due to heat conduction, and the magnetization of the area having a wider area is reversed.

FIG. 6 is a diagram showing the relationship between the write bit size and the read signal size in the present invention.

As shown in FIG. 6, when reading, it is utilized that the larger the bit size written, the larger the read signal becomes. By utilizing this phenomenon, it becomes possible to write and read information with three or more values onto a medium.

FIG. 7 is a sectional view of a magneto-optical recording medium for implementing the present invention.

As shown in FIG. 7, this magneto-optical recording medium has a film structure including a dielectric layer 13, a recording/reading layer 14, and a protective film layer 15 on a substrate 12 with groups (grooves). Note that a polycarbonate substrate (PC) with groups is used as the substrate 12, and the outer diameter 1 and inner diameter of this PC substrate are 130φ and 15φ, respectively. A dielectric layer 13. Recording/reading layer 14. The protective film layer 15 may be continuously formed in a vacuum by sputtering. Further, dielectric layers 13 and 14. The protective film layer 15 is made of Si3N4 with a thickness of 800 mm, and the recording/reading layer 14 is made of Si3N4 with a thickness of 1000 mm, Tb 0.25F.
It is formed by using e o, 75Hi.

FIG. 8 is a temperature characteristic diagram of the coercive force of the recording/reading layer of the magnetic recording medium shown in FIG. 1.

As shown in Fig. 8, the Curie temperature of the recording/reading layer is 120''C. An external magnetic field of 4000e is applied perpendicularly to this recording medium, and the linear velocity is 5.6 m/s, IMHz, and the duty ratio is 50%. The reading level of the laser is 1 mW, and the writing level is 6 mW and 10 mW.As a result, the writing level is 6 mW.
The C/N, carrier level, and noise level at 10 mW and 10 mW are shown in Table 1.

Table 1 Next, the three values recorded as bits on the disk are “0”
A device that corresponds to ", '1", and 2" degrees will be explained, and the code conversion method at that time is as follows.

FIGS. 9(a) to 9(d) are signal level diagrams each showing a procedure for converting the read signal in FIG. 1 into a reproduction signal of ternary information.

First, as shown in FIG. 9(a), two slice levels are set. This slice level 1 is a level between the read signal level when recording at 6 mW and the zero level, and slice level 2 exceeds the read signal level when recording at 6 mW, but when recording at 10 mW. The read signal level of is a level that is not exceeded.

Next, as shown in FIGS. 9(b) and 9(c), the timing is set at the same frequency as during recording, and the magnitude relationship between slice level 1 and slice level 2 and the read signal is determined at each timing.

Next, as shown in FIG. 9(d), if the magnitude of the read signal is smaller than slice level 1 at the read timing, it becomes O'', and if the magnitude of the read signal is greater than slice level 1 and slice level 2 If it is smaller, it is set to "1", and if the size of the read signal is larger than slice level 2, it is set to "2°".

When performing ternary recording using the recording apparatus and recording medium described above, the lower recording laser power is 6 mW, the higher recording laser power is 10 mW, the reading laser power is 1 mW, the frequency is IM Hz, and the duty is Ratio 50%
As a result of recording at a linear velocity of 5.6 m/s, a pit error rate of 10-5 to 10-6 was obtained. Furthermore, since the information was recorded using three values, information could be recorded at a recording density 1.5 times higher than when recording using two values.

FIG. 10 is a waveform diagram of a modulated laser power pulse for explaining another embodiment of the present invention.

As shown in FIG. 10, in this embodiment, the write level is set to 5.
This is an example of switching between the second level, that is, the write level (■ to ■) and the zero level. Since the operation and other operations are the same as those of the embodiment described above, the explanation will be omitted.

〔Effect of the invention〕

As described above, the magneto-optical recording and reproducing method of the present invention can perform recording of three or more values and improve recording density by switching the recording power in three stages using a recording device and a recording medium. There is an effect that it can be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a magneto-optical recording and reproducing apparatus for explaining one embodiment of the present invention, FIG. 2 is a conceptual diagram of the level of modulated pulses output from the laser diode of the optical head in FIG. 1, and FIG. The figure is a partially enlarged conceptual diagram of one track showing the bits recorded when the medium is irradiated with modulated pulse recording in Figure 2, and Figure 4 shows the signal when the bits shown in Figure 2 are read at the reading level. Conceptual diagram showing,
FIG. 5 is a characteristic diagram showing the relationship between the writing laser beam intensity of the optical head and the size of the written bit in FIG.
FIG. 6 is a diagram showing the relationship between the size of a write bit and the size of a read signal in the present invention, FIG. 7 is a cross-sectional view of a magneto-optical recording medium for implementing the present invention, and FIG. 8 is similar to FIG. The temperature characteristic diagram of the coercive force of the recording/reading layer of the magneto-optical recording medium shown in FIG. 10 are waveform diagrams of modulated laser power pulses for explaining another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Disk, 2... Motor, 3... Optical head, 4... Laser diode driver, 5... Laser diode controller, 6... One track, 7
... Recording bits corresponding to writing level ■, 8...
- Recording bit corresponding to write level ■, 9... Zero level bit, 10... Read signal of record bit corresponding to write level I, 11... Read signal of record bit corresponding to write level H, 12...
Substrate, 13... Dielectric layer, 14... Recording/reading layer, 15... Protective layer.

Claims (1)

[Claims] In a magneto-optical recording and reproducing method that uses a laser beam to write and erase information on a recording medium made of a magnetic film, the power of the laser beam during recording by an optical head is switched to three or more levels, and information of three or more values is transferred to the recording medium. A magneto-optical recording and reproducing system characterized by being able to write on and reproduce data.