JPH07220317A - Magneto-optical recording/reproducing device and magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To perform at least the quadruple recording with high density by setting the least recording pit length of a recording pattern at or less than 1/4 diameter of a beam spot. CONSTITUTION:When the record signals 2, 1, -1 and -2 are recorded, a magneto-optical recording medium is irradiated by a laser beam of necessary and sufficient intensity PW. At the same time, a modulated magnetic field HW is impressed to the part irradiated by the laser beam. Under such conditions, the drive current used for generation of the field HW is turned into a modulated current waveform so that each record pit string is recorded. Therefore the modulated magnetic fields of different directions are impressed to the part of the recording medium to be irradiated by the laser beam in accordance with the pit pattern to be recorded with necessary and sufficient field intensity HV. In such a way, the information is recorded. Thus the quadruple optical signal levels 2, 1, -1 and -2 are obtained when the record pit strings 1111, 0110 and 0000 having the smallest record pit length set at or less than 1/4 diameter of a beam spot are recorded on the recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording / reproducing apparatus and a magneto-optical recording medium, and in particular, a recording pit is formed by irradiating a light beam and applying a modulation magnetic field according to a recording signal to a light irradiation portion. However, the present invention relates to a magneto-optical recording / reproducing apparatus and a magneto-optical recording medium of a magnetic field modulation system for recording information.

[0002]

2. Description of the Related Art Conventionally, in a magneto-optical recording / reproducing apparatus using a magnetic field modulation method, recording is performed by a method shown in a timing chart of FIG. 6, for example.

A recording signal shown in FIG. 6A is a recording signal obtained by converting binary data to be recorded by a modulation method such as a 2-7 modulation method and further converting it into NRZI. , A recording signal of mark length recording having both trailing edge information. FIG. 6B shows a laser light output when the recording signal is recorded, and outputs a necessary and sufficient recording laser power P _w at a constant intensity during the recording operation. 6C shows the modulation magnetic field applied to the laser light irradiation portion during the recording operation, and FIG. 6D is a schematic view showing a recording pit row formed by the recording operation. 6
The middle part (e) shows a reproduced signal waveform when the recording pit string is reproduced.

The recording operation will be described below with reference to the timing chart of FIG. When a recording signal as shown in (a) of FIG. 6 is input, a value P _w necessary and sufficient for recording the recording laser power intensity is output at a constant intensity. At the same time, according to a recording signal with a magnetic field strength H _w that is necessary and sufficient for recording, a magneto-optical recording medium in which a modulating magnetic field (FIG. 6C) applied in different directions increases its temperature above the Curie point by laser light irradiation. Is applied to the portion irradiated with the laser beam, and recording is performed.
By this recording operation, a recording pit string as shown in FIG. 6D is formed and information is recorded. Here, the shaded portions indicate the recording pits whose magnetization direction is upward, and the open portions indicate the recording pits whose magnetization direction is downward.

FIG. 6 (e) shows a magneto-optical signal obtained when this recording pit pattern ((d) in FIG. 6) is reproduced, and has a level indicated by "0" in FIG. 6 (e). Information is held at the intersection of the reproduced waveform, and the recorded information can be reproduced by performing binarization with a comparator or the like, for example.

[0006]

However, in the above-mentioned conventional example, the directions of magnetization that the magneto-optical recording medium can take by recording are two states of upward and downward as shown in (e) of FIG. The reproduced signal is also processed as binary information, and there has been a problem that there is a limit to high density in binary recording when higher density is intended.

[0007]

A magneto-optical recording / reproducing apparatus of the present invention forms a recording pit by irradiating a magneto-optical recording medium with a light beam and applying a modulation magnetic field to a light-irradiated portion according to a recording signal. The magneto-optical recording / reproducing apparatus for recording information is characterized in that it has means for applying the modulating magnetic field so that the minimum recording pit length becomes ¼ or less of the beam spot diameter.

Further, in the magneto-optical recording / reproducing apparatus of the present invention, the level of the reproduction signal from the magneto-optical recording medium on which the recording pattern is recorded is set so that the minimum recording pit length becomes ¼ or less of the beam spot diameter. It is characterized in that it has a plurality of comparing means for comparing the generated predetermined reference voltage with each other, and means for obtaining at least a quaternary reproduced signal based on the signals from the comparing means.

The magneto-optical recording medium of the present invention is a magneto-optical recording medium in which recording pits are formed by irradiating a light beam and applying a modulation magnetic field according to a recording signal to a light irradiation portion. The minimum recording pit length of is less than 1/4 of the beam spot diameter.

[0010]

According to the present invention, a magnetic field modulation type magneto-optical recording / reproducing apparatus or a magnetic field modulation type magneto-optical recording which irradiates a light beam and applies a modulation magnetic field according to a recording signal to a light irradiation portion to form a recording pit. In the medium, at least four-value recording is possible by setting the minimum recording pit length of the recording pattern to be ¼ or less of the beam spot diameter. Further, the present invention makes it possible to obtain a 4-level reproduction signal output from a recording pattern having a minimum recording pit length of ¼ or less of the beam spot diameter.

[0011]

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

FIG. 1 is a timing chart showing a magneto-optical recording system in a magneto-optical recording / reproducing apparatus according to the present invention.
1A is a recording signal, FIG. 1B is a recording laser power, FIG. 1C is a drive current for generating a modulation magnetic field, FIG. 1D is a modulation magnetic field, and FIG. FIG. 1F shows a magneto-optical signal when the recording pit string is reproduced. Note that, here, the recording signal of FIG. 1A is expressed by a four-value level in order to make it easy to understand the correspondence with the reproduction signal. For example, the binary input signal “11”,
"10", "01", "00" can be made to correspond to the recording signals "2", "1", "-1", "-2" of FIG.

FIG. 2 is a diagram showing the principle of reproducing the recording pattern recorded on the magneto-optical recording medium, and shows the relationship among the light quantity distribution in the beam spot, the recording pit pattern, and the magneto-optical signal level. 2A shows the case of reproducing a four-value input "1", and FIG. 2B shows the case of reproducing a four-value input "-1". Here, the shaded portions in (e) and FIG. 2 in FIG. 1 indicate magnetic domains whose magnetization direction is upward, and the white portions indicate magnetic domains whose magnetization direction is downward.

First, the principle of 4-value recording on a magneto-optical recording medium will be described with reference to FIG.

According to the present invention, when a plurality of recording pits having different magnetization directions are present in one light beam spot, for example, as shown in the recording pit pattern of FIGS. Cause a change in the reproduction signal level, and as shown in the beam spot light quantity distributions of FIGS. 2A and 2B, the light quantity distribution of the light beam spot is a Gaussian distribution and is near the center of the spot. The recording of at least four values is performed by utilizing the large amount of light.

That is, the recording pit string "0110" whose shortest recording pit length is ¼ or less of the beam spot diameter.
2A is irradiated with a light beam having a Gaussian distribution, the amount of light is large in the shaded area near the center of the light spot, which has a magnetic domain with an upward magnetization direction. Since the amount of light is small in the white part near the periphery of the light spot, which has a magnetic domain with a downward magnetization direction, the magneto-optical signal causes interference and the 4-valued magneto-optical signal level "1" is the reproduction signal. Obtained as a level. Also,
FIG. 2B, which is composed of a recording pit string “1001” whose shortest recording pit length is ¼ or less of the beam spot diameter.
When the recording pit pattern of is irradiated with a light beam having a Gaussian distribution of light quantity, a large amount of light is present in the white part near the center of the light spot, which has a magnetic domain with a downward magnetization direction.
Since the amount of light is small in the shaded area near the periphery of the light spot that has a magnetic domain with an upward magnetization direction, the magneto-optical signal causes interference and the 4-level magneto-optical signal level “−1” is the reproduction signal level. Obtained as.

Further, although not shown, from the recording pit pattern consisting of the recording pit string "1111" whose shortest recording pit length is 1/4 or less of the beam spot diameter, a 4-level magneto-optical signal level "" is obtained. 2 "is obtained, and a 4-level magneto-optical signal level of" -2 "is obtained from a recording pit pattern consisting of a recording pit row" 0000 "in which the shortest recording pit length is 1/4 or less of the beam spot diameter. To be

As described above, the recording pit row "11" whose shortest recording pit length is ¼ or less of the beam spot diameter is used.
If 11 "," 0110 "," 1001 ", and" 0000 "are recorded on the magneto-optical recording medium, four levels of magneto-optical signal levels of" 2 "," 1 "," -1 ", and" -2 "are obtained. Obtainable.

Next, four-value recording is performed on the magneto-optical recording medium,
A method of obtaining a reproduction signal will be described with reference to FIG.

The recording signal "2" as shown in FIG.
When “1”, “−1”, and “-2” are recorded, the laser light intensity P _w that is necessary and sufficient as the recording laser light intensity (see FIG.
The magneto-optical recording medium is irradiated with the laser beam of (b)), and at the same time, the modulation magnetic field H _W is applied to the laser light irradiation site (FIG. 1D). In this case, the driving current for generating the modulation magnetic field has a current waveform as shown in FIG. 1C for recording each recording pit row. In this way, a modulation magnetic field whose direction is different depending on the pit pattern to be recorded with a magnetic field intensity H _w necessary and sufficient for recording is applied to the recording laser light irradiation portion of the magneto-optical recording medium, thereby recording information. Is performed. As a result, a recording magnetic domain pit train as shown in FIG. 1E is formed on the magneto-optical recording medium.

FIG. 1 shows a row of recording pits thus recorded.
When reproducing with a light beam having a spot diameter as shown in the middle (e), the reproducing magneto-optical signal level becomes "2" when the recording pit row is "1111" according to the principle of the present invention described above, and the recording pit When the row is “0110”, it becomes “1” due to the interference of the magneto-optical signal in the beam spot, and when the row of recording pits is “1001”, similarly it is “−1” due to the interference of the magneto-optical signal in the beam spot. When the recording pit row is "0000", the magneto-optical signal level is "-2".
As a result, a reproduced magneto-optical signal having four levels as shown in FIG. 1 (f) is obtained. By detecting the four-valued level of this signal, it becomes possible to reproduce the recorded information, and it is possible to provide a magneto-optical recording device capable of recording at a higher density.

FIG. 3 is a diagram showing a schematic structure of a magneto-optical recording / reproducing apparatus of the magnetic modulation type according to the present invention. In FIG. 3, 10 is a magneto-optical disk and 11 is a magneto-optical disk 1.
A spindle motor that rotates 0, and 12 is an optical head that focuses laser light on a disk in a spot shape and detects light reflected from the disk. The optical head 12 is composed of various lenses, PBS and the like. Reference numeral 13 is a semiconductor laser drive circuit, 14 is a floating magnetic head, and 15 is a floating magnetic head drive circuit for driving the floating magnetic head 14. Information is recorded by applying laser light from the optical head 12 to the magneto-optical disk 10.
The magnetic field is applied to the magneto-optical disk 10 by the levitation magnetic head 14 while irradiating the optical disk, and the recorded information is reproduced by irradiating the magneto-optical disk 10 with the laser beam from the optical head 12 to reproduce the Kerr effect of the medium. The rotation of the polarization plane due to is detected as the intensity of light.

FIG. 4 is a diagram showing a signal processing circuit for detecting four-valued levels, and FIG. 5 is a timing diagram of a reproduced signal waveform and a detection synchronization clock.

In FIG. 4, reference numeral 20 denotes an amplifier for amplifying a reproduction signal, and reference numerals 21 to 23 denote non-inverting input terminals to which signals from the amplifier are input, and reference terminals V ₁ , V ₂ and V, respectively, to the inverting input terminals. Reference numeral 24 is a comparator to which ₃ is connected, and reference numeral 24 is a four-value determination circuit to which the outputs of the comparators 21 to 23 are input. The four-value determination circuit 24 is "2", "1", "-".
1 "," -2 "is determined, binarized (1, 1),
The signals (1,0), (0,1), and (0,0) are output. As shown in FIG. 5, the reproduced signal is detected by being divided into four values at a predetermined slice level (V ₁ , V ₂ , V ₃ ).

[0025]

As described above, according to the present invention,
In a magnetic field modulation type magneto-optical recording medium or a magnetic field modulation type magneto-optical recording / reproducing apparatus that irradiates a light beam and applies a modulation magnetic field according to a recording signal to a light irradiation portion to form a recording pit, a minimum recording pattern By setting the recording pit length to be ¼ or less of the beam spot diameter, at least four-value recording becomes possible and high density recording becomes possible. Further, according to the present invention, it is possible to obtain a 4-level reproduction signal output from a recording pattern whose minimum recording pit length is ¼ or less of the beam spot diameter.

[Brief description of drawings]

FIG. 1 is a timing diagram showing a magneto-optical recording system in a magneto-optical recording / reproducing apparatus according to the present invention.

FIG. 2 is a diagram showing the principle of reproducing a recording pattern recorded on a magneto-optical recording medium.

FIG. 3 is a diagram showing a schematic configuration of a magnetic modulation type magneto-optical recording / reproducing apparatus according to the present invention.

FIG. 4 is a diagram showing a signal processing circuit for performing 4-level detection.

FIG. 5 is a timing diagram of a reproduced signal waveform and a detection synchronization clock.

FIG. 6 is a timing chart showing a recording method of a magneto-optical recording / reproducing apparatus according to a conventional magnetic field modulation method.

[Explanation of symbols]

 10 magneto-optical disk 11 spindle motor 12 optical head 13 semiconductor laser drive circuit 14 floating magnetic head 15 floating magnetic head drive circuit 20 amplifiers 21-23 comparator 24 four-value determination circuit

Claims (3)

[Claims] 1. A magneto-optical recording / reproducing apparatus for recording information by forming a recording pit by irradiating a magneto-optical recording medium with a light beam and applying a modulation magnetic field to a light-irradiated portion according to a recording signal. A magneto-optical recording / reproducing apparatus comprising means for applying the modulating magnetic field so that the minimum recording pit length becomes ¼ or less of the beam spot diameter. 2. A level of a reproduction signal from a magneto-optical recording medium on which a recording pattern is recorded such that the minimum recording pit length is 1/4 or less of a beam spot diameter, and a predetermined reference voltage respectively set. A magneto-optical recording / reproducing apparatus having a plurality of comparing means and a means for obtaining a reproduced signal of at least four values based on signals from the comparing means. 3. A minimum recording pit length of a recording pattern in a magneto-optical recording medium having recording pits formed by irradiating a light beam and applying a modulation magnetic field according to a recording signal to a light irradiation portion. A magneto-optical recording medium having a spot diameter of 1/4 or less.