JPH0775087B2 - Magneto-optical memory device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention projects a light beam onto a magneto-optical recording medium to record information on the magneto-optical recording medium, erase and reproduce recorded information, and the like. The present invention relates to a magneto-optical memory device for performing.

[Conventional technology]

A magneto-optical memory device is a magneto-optical recording medium capable of recording and erasing information, from an optical head to a magneto-optical recording medium.
A laser beam focused to a diameter of about μm is projected to record information on a magneto-optical recording medium, read and erase recorded information, and a signal detection circuit detects a reproduction signal obtained from an optical head. A digital reproduction signal is obtained. The signal detection circuit has a peak position detection circuit that detects the peak position of the information pulse in the reproduction signal or an amplitude detection circuit that detects the length and interval of the information pulse. A digital reproduction signal is obtained from the signal.

As shown in FIG. 7, a conventional magneto-optical memory device performs a magneto-optical disk 101 as a magneto-optical recording medium, recording of information on the magneto-optical disk 101, reading of recorded information, erasing and the like. And an optical head 102.

The optical head 102 includes a semiconductor laser 111, a beam splitter (half mirror) 112, an objective lens 113, a half-wave plate 116,
It is composed of an analyzer 117, a condenser lens 114, and a photodetector 115. The light beam emitted from the semiconductor laser 111 passes through a beam splitter (half mirror) 112, is condensed by an objective lens 113, and is irradiated onto the magneto-optical disk 101. The reproduction light reflected by the magneto-optical disk 101 passes through the objective lens 113, and the beam splitter (half mirror) 1
A part is bent at a right angle by 12. This light is 1/2
The polarization direction is tilted at a predetermined angle by the wave plate 116,
The light passes through the analyzer 117, is condensed by the condenser lens 114, and is incident on the photodetector 115. The reproduction light is converted into an electric signal in the photodetector 115 and is sent to the signal detection circuit to reproduce the data.

The above-mentioned magneto-optical disc 101, that is, the magneto-optical recording medium is provided with a magnetic thin film having an easy axis of magnetization in a direction perpendicular to the film surface, and recording on this magneto-optical recording medium is performed as follows. . That is, when the optical thin film of the magneto-optical recording medium is irradiated with the laser light from the optical head 102, the temperature of the portion irradiated with the laser light locally rises and the coercive force decreases. Therefore, when a magnetic field is applied to this portion from the outside, the magnetization can be reversed in a desired direction, and information is recorded by this.

On the other hand, the reproducing operation is performed as follows. That is, when a linearly polarized laser beam, which is weaker than during recording, is projected onto the magneto-optical recording medium, the polarization plane of the reproduction light, which is the reflected light or the transmitted light from the magneto-optical recording medium, depends on the magnetization direction of the magneto-optical recording medium. Rotate a specified angle. This rotation of the plane of polarization is caused by the Faraday effect for transmitted light and the Kerr effect for reflected light. For example, if the vector of the reflected light with respect to a certain magnetization direction of the magneto-optical recording medium is R + and the vector of the reflected light with respect to the magnetization direction which is the opposite of the above magnetization direction is R-, then these reflected light vectors as shown in FIG. The rotation angles of the polarization planes corresponding to the lights R + and R− are + θ _K and −θ _K with respect to the incident polarization plane, respectively. Then, at the detection polarization plane set to 45 ° with respect to the incident polarization plane,
By detecting the detection polarization plane components Rα + and Rα− of the reflected lights R + and R−, a reproduction signal as an electric signal can be obtained. At this time, Rα- is low level,
Rα + becomes high level.

The ninth operation of the magneto-optical memory device based on the above principle is described.
The following is a specific description based on the drawings.

On the magneto-optical recording medium, for example, the recording mark shown in (b) of the digital data (a) shown in FIG. 9 is recorded by magnetization reversal. Here, when the vector of the reflected light from the recording mark is R- and the vector of the reflected light from the non-marked portion other than the recording mark is R +, the optical head 102 that receives the reflected light from the magneto-optical recording medium. From
A reproduction signal (c) is obtained. In this reproduction signal (c), a pulse in the negative direction is generated by the reflected light R- from the recording mark, and becomes a high level by the reflected light R + from the non-mark portion.

Next, in the case where the signal detection circuit has a peak position detection circuit, the digital detection signal (d) in which the peak position in the negative direction coincides with the rising portion is supplied from the signal detection circuit to which the reproduction signal (c) is input. ) Is obtained. On the other hand, when the signal detection circuit has the amplitude detection circuit, the signal detection circuit obtains the digital reproduction signal (e) which becomes high level within a predetermined width with respect to the peak position in the negative direction. The digital data (f) as reproduction information is obtained from the digital reproduction signal (d) or (e).

[Problems to be Solved by the Invention]

However, the above conventional configuration has a problem that it is difficult to increase the recording density and the recording capacity of the magneto-optical recording medium.

That is, in the case of the above configuration, the size of the recording mark must be further reduced in order to increase the recording density of the magneto-optical recording medium. However, the smaller the recording mark, the more difficult the recording on the magneto-optical recording medium becomes. For example, in the case of recording a recording mark by converging laser light on a magneto-optical recording medium, the recording mark is appropriately formed depending on the degree of narrowing down of the laser beam, the characteristics of the magneto-optical recording medium, the ambient temperature and the like. Becomes difficult. Therefore, it is difficult to increase the recording density by reducing the size of the recording mark, and the conventional configuration is unsuitable for increasing the recording density. For convenience of explanation, the recording mark is described as an isolated mark corresponding to one code, but the recording mark is made to correspond to a plurality of codes and is formed to have the same size as the portion other than the recording mark. Similarly, even if
It is insufficient in increasing the recording density.

[Means for Solving the Problems]

In order to solve the above problems, a magneto-optical memory device of the present invention is provided so as to be movable relative to an optical head, and a magneto-optical recording in which a first recording mark and a second recording mark as information are recorded. During the recording operation on the medium and the magneto-optical recording medium, the end portions of the first and second recording marks in the relative movement direction with respect to the optical head are the second digital information of the first and second codes. The first and second recording marks are recorded so as to correspond to the code, and the second recording mark has a portion between both ends corresponding to the second code, and
While recording in a width narrower than the first recording mark, the width is smaller than the width of the first recording mark in the reproducing operation, and
A reproduction signal is output by irradiating a magneto-optical recording medium with a light beam having a focused spot having a diameter larger than the width of a recording mark, and outputting reproduction signal by inputting reproduction light including reproduction information from the magneto-optical recording medium. When reproducing light is input when the beam is applied to the end of the first or second recording mark, it corresponds to the second code by interference of the reproducing light between the first or second recording mark and the non-mark portion. When an information pulse is generated in the reproduction signal and a light beam is applied to a portion between both ends of one second recording mark, the second recording mark and the non-mark portion interfere with each other in the reproduction light, and An optical receiver which outputs a reproduction signal of a level corresponding to the code 2 and outputs a reproduction signal of a level corresponding to the first code when the reproduction light when the light beam is applied to a portion other than the above is input. And de, is compared with a reference value a reproduction signal obtained from the optical head, an end portion of the first recording mark,
And by converting the reproduction signal obtained by irradiating each part of the second recording mark with the light beam into the second code, while converting the reproduction signal obtained by irradiating the other part with the light beam into the first code. , And a signal detection circuit for outputting a digital reproduction signal.

[Work]

According to the above structure, the first recording mark is recorded by the optical head so that the end portion in the relative movement direction with respect to the optical head corresponds to the second code of the digital information including the first and second codes. To be done. In the second recording mark, an end portion in the relative movement direction with respect to the optical head corresponds to the second code, a portion between both end portions of one second recording mark corresponds to the second code, and The width is narrower than one recording mark.

Further, during the reproducing operation, the optical head is irradiated with a light beam having a focused spot having a diameter smaller than the width of the first recording mark and larger than the width of the second recording mark, The optical head outputs a reproduction signal by inputting the reproduction light. The optical head receives the reproduction light when the light beam is applied to the end of the first recording mark and when the light beam is applied to the end of the second recording mark. Information pulses corresponding to the above-mentioned second code are generated in the reproduction signal due to the interference of the recording mark and the non-mark portion in the reproducing light. Further, when the light beam is applied to a portion between both end portions of one second recording mark, reproduction of a level corresponding to the second code is caused by interference of the reproduction light between the second recording mark and the non-mark portion. Output a signal. Further, when the light beam is applied to a portion other than the above, a reproduction signal having a level corresponding to the first code is output.

The signal detection circuit compares the reproduction signal obtained from this optical head with a reference value, and outputs the reproduction signal obtained by irradiating the end portion of the first recording mark and each portion of the second recording mark with the light beam to the second portion. While converting into a code, the reproduction signal obtained by irradiating the other part with the light beam is converted into a first code to output a digital reproduction signal.

By such recording and reproducing operations of the first and second recording marks, a large amount of information can be included in each recording mark, so that the recording density can be increased. Incidentally, by forming the first recording mark to be wider and wider than the diameter of the focused spot in the light beam, and forming the second recording mark to be longer than the diameter of the focused spot,
The above information pulse is easily generated. Further, by forming the first and second recording marks large in this way, it becomes easy to form both recording marks in appropriate shapes.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

The magneto-optical memory device according to the present invention, as shown in FIG. 1, includes a magneto-optical disk 1 as a magneto-optical recording medium, recording of information on the magneto-optical disk 1, reading and erasing of recorded information, and the like. The optical head 2 for performing the reproduction and the signal detection circuit 3 for converting the reproduction signal obtained from the optical head 2 into a digital reproduction signal are provided.

The magneto-optical disk 1 includes a magnetic thin film having an easy axis of magnetization in a direction perpendicular to the film surface, and recording and erasing of the first and second recording marks as information by reversing the magnetization direction are possible. It is movable with respect to the optical head 2.

In the above optical head 2, as shown in FIG.
The laser light emitted from the semiconductor laser 11 passes through the polarization beam splitter 12, is condensed by the objective lens 13, and is incident on the magneto-optical disk 1. The reflected light passes through the objective lens 13 again, and the optical path of a part of the reflected light is dispersed by the polarization beam splitter 12. The polarization beam splitter 12 is arranged so that its polarization plane is perpendicular to the incident polarization plane, and also serves as an analyzer. This reflected light is a condenser lens
The light is collected by 14, converted into an electric signal by the photodetector 15, and sent to the signal detection circuit.

The optical head 2 projects a laser beam as a light beam onto the magneto-optical disk 1 to generate a laser beam, as shown in FIG.
For the digital data (h) as digital information, the recording mark A as the first recording mark shown in (i)
And a recording mark B as a second recording mark is recorded. The end of the recording mark A in the direction of relative movement with the optical head 2, that is, the edge, corresponds to one 1 surrounded by 0. Note that 0 represents the first code and 1 represents the second code. On the other hand, recording mark B
Indicates that the edge portion and the portion between the edge portions correspond to 1, and the recording mark B as a whole corresponds to 1111. The recording mark B is formed to have a narrower width than the recording mark A. On the other hand, the portion between the edge portions of the recording mark A and the non-mark portion other than the recording marks A and B correspond to 0. Further, the recording mark A is formed in an oval shape having a length and width larger than the diameter of the focused spot 4 in the laser beam during reproduction, and the recording mark B is formed longer than the diameter of the focused spot. As a result, the information pulse described later is easily generated.

In addition, the optical head 2 has the recording mark A during the reproducing operation.
Of a laser beam having a focused spot 4 having a diameter smaller than the width of the recording mark B and larger than the width of the recording mark B, and the reflected light is input to output a reproduction signal. ing. Then, only when the reflected light when the laser beam is irradiated to the end of the recording mark A or the recording mark B is input, the recording mark A or B is recorded.
By the interference of the reflected light from the
An information pulse corresponding to 1 as a code is generated in the reproduction signal, and when laser light is applied to a portion between both ends of the recording mark B, the reflected light from the recording mark B and the non-marked portion interferes with each other. , A reproduction signal of a level lower than the reference value is output.

In the present embodiment, as shown in FIG. 3, an analyzer arranged so that the polarization plane of detection is perpendicular to the plane of incident polarization, and a photodetector for converting the output of this analyzer into an electric signal. And the optical head 2 has. Then, when the laser light is applied to the edge portion of the recording mark A or B, the polarization planes of the reflected light from the recording mark A or B and the non-mark portion are in opposite directions at the incident polarization plane of the laser light. By rotating, the detected polarization plane components of both reflected lights become 180 ° out of phase, so that the reproduced signal which is the output of the photodetector may have an information pulse or a part with a level lower than the reference value. Has become.

The signal detection circuit 3 detects the information pulse of the reproduction signal input from the optical head 2 and a portion having a reference value or less between the information pulses as a second code 1, and converts the reproduction signal into a digital reproduction signal. . That is, the signal detection circuit 3
Has a peak position detection circuit for detecting the peak position of the information pulse in the reproduction signal, and an amplitude detection circuit for detecting the length and interval of the information pulse equal to or less than the reference value. A digital reproduction signal can be obtained from the.

In the above configuration, during the recording operation of the present magneto-optical memory device, laser light is projected from the optical head 2 onto the magneto-optical disk 1, and the magnetization reversal of the irradiation portion of the laser light causes the laser light to be projected as shown in FIG. Then, the recording marks A and B shown in (i) are recorded on the magneto-optical disk 1 in correspondence with the digital data (h). At this time, the recording mark A is located at 1 surrounded by 0 in the digital data (h).
Are recorded so as to correspond to the edges. The recording mark B has an edge portion and a portion between the edge portions corresponding to 1, and is recorded in a narrower width than the recording mark A.

On the other hand, during the reproducing operation, laser light having a focused spot with a diameter smaller than the width of the recording mark A and larger than the width of the recording mark B is projected from the optical head 2 onto the magneto-optical disk 1. The reflected light is input to the optical head 2 and a reproduction signal (j) is obtained.

Here, when the laser beam projected from the optical head 2 is applied to the non-marked portion of the magneto-optical disk 1 other than the recording marks A and B, it is reflected according to the magnetization direction of the non-marked portion due to the Kerr effect. The plane of polarization of light rotates. At this time, if the plane of polarization is rotated by + θ _K as shown in FIG. 3, the vector of the reflected light is R +. Since the detection polarization plane of the analyzer is arranged perpendicular to the incident polarization plane of the laser light, Rα +, which is the detection polarization plane component of the reflected light R +, is obtained by the detection by the analyzer, and the photodetector is obtained. The reproduction signal (j) obtained from the above becomes high level.

Further, when the laser light is irradiated between the edge portions of the recording mark A, the recording mark A is magnetization-inverted with respect to the non-mark portion, so that the polarization plane of the reflected light rotates by −θ _K and the reflected light Is R-. Then, Rα−, which is the detection polarization plane component of the reflected light R−, is obtained by detection with the analyzer, and the reproduction signal (j) obtained from the photodetector becomes high level. The level of the reproduced signal (j) at this time is slightly lowered because the reflected light from the non-mark portion interferes with the reflected light from the recording mark A to some extent.

Further, when the laser light is applied to the edge portion of the recording mark A as shown in FIG. 4, the polarization planes of the reflected light from the recording mark A and the non-mark portion rotate by −θ _K and + θ _K , respectively. Therefore, the detected polarization plane components of both reflected lights are 180 ° out of phase with each other. Therefore, the output of the photodetector becomes minimum at the time when the focused spot 4 of the laser light is evenly applied to the recording mark A and the non-mark portion, and the reproduction signal (j)
An information pulse in the negative direction is generated at.

On the other hand, when the laser beam projected from the optical head 2 is applied to the edge portion of the recording mark B on the optical disc 1, as in the case of the recording mark A, the reproduction signal (j) has an information pulse in the negative direction. Occurs. Further, when the laser light is irradiated between the edge portions of the recording mark B, the diameter of the focused spot of the laser light is larger than the width of the recording mark B, so that the reflection from the recording mark B and the non-mark portion is caused. Light interference occurs and the reproduction signal (j) becomes a level lower than the reference value.

Here, FIGS. 5 and 6 show an example of the result of the computer simulation for the reproduced signal.

FIG. 5 is an explanatory diagram showing the relationship between the recording mark C and the focused spot 4 in the computer simulation for the reproduction signal of FIG. In the figure, the recording mark C is
The length is 4 μm, the width is W, and the curved portion of the edge portion is a semicircle having a radius W / 2. The focused spot 4 is a Gaussian beam, and its radius (radius in a circle that becomes 1 / e ² times the beam center intensity) is 0.65 μm. The scanning direction of the focused spot 4 is the major axis direction of the recording mark C, and the distance between the center of the recorded mark C and the center of the focused spot 4 is shown in the upper part of the figure. In addition, the substrate of the optical disc 1 on which the recording mark C is formed has a refractive index of 1.5, the pitch between adjacent tracks in the longitudinal direction of the paper is 1.6 μm, and the aperture ratio of the objective lens is 0.55.
The wavelength of the laser light forming the focused spot 4 is 0.78 μm.

FIG. 6 is a diagram showing simulation results, in which the horizontal axis represents the scanning direction of the focused spot 4, and the distance between the center of the recording mark C and the center of the focused spot 4. The vertical axis represents the intensity of reproduction light that enters the photodetector. The value is set to 1.0 when the focused spot 4 is completely located on a portion other than the recording mark C, and set to 0.0 when the reproduction intensity is 0. In the photodetector, a reproduced signal corresponding to this is obtained. Then, the width W of the recording mark C (and the radius of the curved portion of the edge portion is 2
Double), 0.4μm, 0.6μm, 0.8μm, 1.0μm, 1.4μ
m and 1.8 μm, reproduced waveforms were simulated for these seven types. As a result, W = 1.4μm and 1.8μ
When m, the pulse was remarkable at the edge portion of the recording mark C.

Regarding the width W of the recording mark C (and twice the radius of the curved portion of the edge portion), when W = 1.8 μm and 1.4 μm,
It can be seen that the information pulse is prominent, and even when W = 1.0 μm and 0.8 μm, the pulse at the edge portion still remains and the level of the central portion of the recording mark C gradually decreases.

Further, this simulation was performed under the conditions as described above, but if conditions other than this, such as the refractive index of the substrate, the wavelength λ of the laser light, or the aperture ratio of the objective lens, change, of course, The optimum width of the recording mark C also changes accordingly.

Next, a method of recording by changing the width W of the recording mark C will be described. For example, the focused spots 4 have the same diameter to weaken the strength of the magnetic field applied from the outside. Then, the width of the recording mark C can be reduced for recording. On the contrary, when the magnetic field applied from the outside is increased, the width of the recording mark C is increased.

Further, instead of changing the strength of the magnetic field, the light intensity of the focused spot 4 during recording may be changed. That is, when the light intensity is lowered, the width of the recording mark C becomes smaller, and conversely, when the light intensity is raised, the width of the recording mark C becomes larger.

In the focus servo system for focusing the focused spot 4 on the magneto-optical disk 1, even if the focus point is electrically shifted, the same effect can be obtained. That is, by adding an offset to the focus point, the focused spot 4
Is to spread.

Next, the reproduction signal (j) is input to the signal detection circuit 3, and from the peak position detection circuit, the digital reproduction in which the rising portion coincides with the negative peak position in the information pulse of the reproduction signal (j). The signal (k) is obtained. On the other hand, the amplitude detection circuit obtains a digital reproduction signal (l) which becomes a high level within a predetermined width with respect to a negative peak position in the information pulse of the reproduction signal (j) and a portion having a level lower than the reference value. To be Since the pulses of these digital reproduction signals (k) and (l) correspond to 1 of the digital data (h), both signals (k) and (l) are
Digital data (m) as reproduction information is obtained from (l).

As a configuration for obtaining the digital data (m), an information pulse generated corresponding to the edge portion of the recording marks A and B is used as a reproduction clock, and information is reproduced between the edge portions of the recording mark B. It is also possible to detect by the level of.

Further, in the present embodiment, the configuration is shown in which the polarization plane of the reflected light from the magneto-optical disk 1 is rotated by the Kerr effect to perform the reproduction, but the present invention is not limited to this, and The reproduction may be performed by utilizing the fact that the polarization plane of the transmitted light of the disc 1 rotates due to the Faraday effect.

Further, an example in which the detector polarization plane of the analyzer is perpendicular to the incident polarization plane of the laser light is shown, but in the present invention, the edge portions of the recording marks A and B and the edge portions of the recording marks B are shown. Between the recording marks A and B and the non-marked portion, interference may occur between the reflected light or the transmitted light, and the two need not necessarily be vertical.

〔The invention's effect〕

As described above, the magneto-optical memory device according to the present invention is provided so as to be movable relative to the optical head, and the magneto-optical recording medium on which the first recording mark and the second recording mark as information are recorded, During the recording operation on the magneto-optical recording medium, the ends of the first and second recording marks in the relative movement direction with respect to the optical head correspond to the second code of the digital information composed of the first and second codes. As described above, the first and second recording marks are recorded, and the second recording mark is recorded in a width narrower than the first recording mark while the portion between both ends corresponds to the second code. During playback operation,
The magneto-optical recording medium is irradiated with a light beam having a focused spot with a diameter smaller than the width of the first recording mark and larger than the width of the second recording mark, and reproduction light containing reproduction information from the magneto-optical recording medium. To output a reproduction signal and to input reproduction light when the light beam is emitted to the end portion of the first or second recording mark,
Alternatively, an information pulse corresponding to the second code is generated in the reproduction signal due to the interference of the reproduction light between the second recording mark and the non-mark portion, and the light beam is applied to a portion between both ends of one second recording mark. At this time, due to the interference of the reproduction light between the second recording mark and the non-mark portion, a reproduction signal of a level corresponding to the second code is output, and the reproduction light when the light beam is irradiated to a portion other than the above Is input, an optical head that outputs a reproduction signal of a level corresponding to the first code and a reproduction signal obtained from this optical head are compared with a reference value to compare the end of the first recording mark and the first recording mark. 2 While converting the reproduction signal obtained by irradiating each part of the recording mark with the light beam to the second code, the reproduction signal obtained by irradiating the other part with the light beam is converted into the first code. It is configured to and a signal detecting circuit for outputting a barrel reproduced signal.

Therefore, the end portions of the first and second recording marks and the widths of the second recording marks correspond to the information, and one recording mark can include a large amount of information, so that recording on the magneto-optical recording medium is possible. The density can be increased and the recording capacity can be increased. Further, since the recording density is not increased by simply downsizing the recording marks, it is possible to form the recording marks large and the recording marks are easily formed. Further, for example, the half-wave plate 116 and the analyzer 117 shown in FIG. 7 may be omitted and a polarization beam splitter may be arranged instead of the beam splitter 112. Therefore, the number of parts can be reduced, and the optical system can be simplified.

[Brief description of drawings]

1 to 6 show an embodiment of the present invention. FIG. 1 is a schematic block diagram showing a main part of a magneto-optical memory device, and FIG. 2 is an optical block diagram shown in FIG. FIG. 3 is an explanatory diagram showing a specific configuration of the magnetic memory device, FIG. 3 is an explanatory diagram of a reproducing operation in an optical head, and FIG. 4 is an explanatory diagram showing a relationship between a recording mark and a signal waveform in each part of the magneto-optical memory device. FIG. 5 is an explanatory diagram showing the relationship between the recording mark and the focused spot in the computer simulation for the reproduction signal shown in FIG. 6, and FIG. 6 shows the result of the computer simulation, and the focused spot on the recorded mark. Is a graph showing the relationship between the position of and the reproducing light intensity incident on the photodetector, and FIGS. 7 to 9 show a conventional example.
FIG. 7 is an explanatory diagram showing the structure of the magneto-optical memory device, FIG. 8 is an explanatory diagram of the reproducing operation in the optical head, and FIG. 9 is an explanation showing the relationship between the recording mark and the signal waveform in each part of the magneto-optical memory device. It is a figure. Reference numeral 1 is a magneto-optical disk (magneto-optical recording medium), 2 is an optical head, 3 is a signal detection circuit, and 4 is a focused spot.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Ota, 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture Within the corporation

Claims (1)

[Claims] 1. A magneto-optical recording medium, which is provided so as to be movable relative to an optical head and records a first recording mark and a second recording mark as information, and a recording operation on the magneto-optical recording medium. In the first and second recording marks so that the ends of the first and second recording marks in the relative movement direction with respect to the optical head correspond to the second code of the digital information composed of the first and second codes. The mark is recorded, and the second recording mark has a portion between both ends corresponding to the second code and is recorded in a width narrower than that of the first recording mark. A magneto-optical recording medium is irradiated with a light beam having a focused spot with a diameter smaller than the width of the mark and larger than the width of the second recording mark, and reproduction light containing reproduction information is input from the magneto-optical recording medium. Output a playback signal Along with
When the reproduction light when the light beam is applied to the end of the first or second recording mark is input, the first or second
When an information pulse corresponding to the second code is generated in the reproduction signal due to the interference of the recording mark and the non-mark portion with the reproducing light, and the light beam is applied to a portion between both ends of one second recording mark. , The reproduction signal of the level corresponding to the second code is output due to the interference of the reproduction light between the second recording mark and the non-mark portion, and the reproduction light when the light beam is applied to a portion other than the above is input. Sometimes the above
An optical head that outputs a reproduction signal of a level corresponding to a code, and a reproduction signal obtained from this optical head are compared with a reference value, and a light beam to the end of the first recording mark and each part of the second recording mark A signal detection circuit that outputs a digital reproduction signal by converting a reproduction signal obtained by irradiation to a second code and converting a reproduction signal obtained by irradiation of a light beam to another portion into a first code. A magneto-optical memory device comprising: