JPH06119667A - Information recording and reproducing medium and recording reproducing method and device using the medium - Google Patents

Abstract

PURPOSE:To change the state of only the arbitrary recording layer at the time of recording and to enable the detection of the state of only the arbitrary recording layer at the time of reproducing by using the multilayered recording medium. CONSTITUTION:A silicon nitride layer 102 is formed by a sputtering method on an optical disk substrate 101 having rugged guide grooves. The magneto-optical recording films 103 are then formed of three layers; films 103-1, 2, 3 varying in magnetic characteristics. The thermal magnetic characteristics of respective layer film change the curie temp. and the compensation temp.. The magnetic layers where the magnetization direction is inverted can be specified according to whether the magnetic layers are cooled after heating up to what temp. or not by the thermo-magnetic characteristics in such a manner. Laser pulses are synchronized with a clock and magnetic fields are switched to a desired direction by the contents of the information, by which the magnetization directions of the respective layers are directed at the time of recording with a single light spot. In addition, the respective layers are not continuously recorded with one pulse but the layers be dividedly recorded for each of the respective layers if the recording is executed from the layers of the higher Curie temp. The position accuracy is higher with a sample servo system at this time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing medium such as an optical disk for high density recording / reproducing of digital signals and a recording / reproducing method and apparatus using the same, and more particularly to a multi-level level using a magneto-optical recording system. The present invention relates to an information recording / reproducing medium suitable for high-density recording, and a recording / reproducing method and apparatus using the same.

[0002]

2. Description of the Related Art Heretofore, as a method for recording information multiplexed by a difference in wavelength and polarization of a light source at one point, for example, a technique disclosed in Japanese Patent Laid-Open No. 62-165751 is known. There is. In this technique, each layer of the information recording / reproducing medium is used as a cumulative film obtained by accumulating a plurality of monomolecular films, and when the cumulative film is irradiated with light capable of changing the polarization degree and the wavelength, the state of the specific cumulative film is changed. It is a medium structure that changes.
Further, in JP-A-62-231437, a light absorbing layer of an information recording / reproducing medium is used that absorbs only linearly polarized light in a specific polarization direction, and recording is performed with a focus position of a recording light beam. There is disclosed a method in which the state of only a specific recording layer is changed by aligning with the target layer and rotating the polarization direction of linearly polarized light to align with the light absorption direction of each layer.
Each of the above-mentioned techniques selectively changes the state of only a specific layer of the information recording / reproducing medium depending on the wavelength of light and the degree of polarization. However, the processing at the time of reproduction is not particularly described.

On the other hand, as a multi-layer / multi-value recording method using a magneto-optical recording medium, for example, Multi-Valued Magneto-
Optical Recording in TbZbFe / SiO Compositio
nary Modulated Films, N. Saito, et.al., Proc. Int.
Symp.on Optical Memory, 1989, Japanese Journal
of Applied Physics, Vol.28 (1989) Supp.28-3, pp.343
There is a method described in -347. In this method, four magneto-optical recording layers that are different from each other with respect to temperature are stacked and a modulation magnetic field having different strength is applied to reverse the magnetization direction of the target recording layer. In this method, for example, even when only the magnetization direction of the second layer viewed from the light irradiation side is to be reversed, the recording layer closest to the light irradiation side is also reversed at the same time. Further, during reading, the method is to detect the total Kerr rotation angles of the four layers, and it is not possible to detect the magnetization direction of only an arbitrary recording layer.
Therefore, even when four layers are used, the number of states through recording / reproduction is limited to four levels or less.

[0004]

Multi-valued recording is to record more than two values of "0" and "1" at one point on a recording medium. However, in many conventional multi-value recording methods using a multilayer recording film, it is not possible to selectively change the state of only a specific recording layer. The latter of the above-mentioned conventional techniques corresponds to that example. Further, in the multi-valued recording method using the multilayer recording film in the conventional technique, a value obtained by combining the magnetization directions of all the recording layers is detected at the time of reproduction, and therefore, for example, a state when a medium having four recording layers is used. The number is limited to four. Also, in the case of the method that changes the state of only an arbitrary layer like the former, since the combined value of the states of all layers is detected during reproduction, it is true that only the arbitrary layer is reproduced. There isn't. If each recording layer has a binary state, for example, if the magnetization direction has two states of upward or downward with respect to the thickness direction of the recording film, arbitrary recording of four recording layers If the state of the layers can be changed independently and reproduced (detected) independently, it should be possible to obtain 2 4 power levels, that is, 16 levels of multi-valued levels.
The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above-mentioned problems in the prior art, to use a multilayer recording film medium, and to record only a desired recording layer at the time of recording. Another object of the present invention is to provide an information recording / reproducing medium capable of detecting the state of an arbitrary layer during reproduction by changing the above. Another object of the present invention is to use the above-mentioned information recording / reproducing medium to record / record information having a number of states larger than the number of recording layers.
An object is to provide an information recording / reproducing method and device for reproducing.

[0005]

The above object of the present invention is to provide an information recording / reproducing medium for performing magneto-optical recording / reproducing using a laser beam, the medium having a recording layer comprising a plurality of layers. In an information recording / reproducing medium characterized in that each layer of the recording layer is configured to have different thermomagnetic properties, and a recording / reproducing method using the information recording / reproducing medium, at the time of recording, light spots having different wavelengths corresponding to the number of recording layers are recorded. The temperature of the recording layer is raised to the Curie point by increasing the output of the light spot of the wavelength corresponding to the recording layer to be magnetically reversed by an optical head capable of emitting the magnetic field. Direction, and at the time of reproduction, the magneto-optical effect of an arbitrary recording film is selectively detected by the wavelength of the reproducing light source having a different wavelength for the number of recording layers. And it is achieved by a device.

[0006]

In the information recording / reproducing medium according to the present invention, recording layers having different thermomagnetic properties are laminated as a recording medium structure,
Furthermore, the structure is such that the film thickness is set so as to selectively absorb light of a specific wavelength. As a medium structure for multi-value recording, a structure in which only a specific recording layer changes its state depending on the wavelength of a light source is used. For example, by setting the film thickness of the recording layer to a thickness corresponding to the wavelength of the light source, the heat absorption coefficient of an arbitrary recording layer can be increased. Further, in the information recording / reproducing method according to the present invention, a specific value on a multi-value recordable medium necessary as a necessary component for recording / reproducing multi-valued information on a specific point on the recording medium is specified. By using the sample servo format as a means for recognizing points, even when different recording / reproducing means access points to be recorded or reproduced at different times,
Multi-valued recording / reproduction is enabled by separating or synthesizing a data string with reference to a sample clock or the like.

At the time of recording, a laser optical head capable of emitting light spots having different wavelengths corresponding to the number of recording layers raises the output of the light spot having a wavelength corresponding to the recording layer to be magnetization-reversed, thereby increasing the temperature of the recording layer. After reaching the Curie point, the magnetization direction is fixed to the external magnetic field direction in the cooling process. Here, when reversing the magnetization of another recording layer with respect to the same point (position), the output of the light spot of the second wavelength is increased. Hereinafter, if light spots having different wavelengths for the recording layers are prepared, the state of any recording layer can be similarly changed. A method of raising the temperature of only an arbitrary recording layer with respect to a laser beam spot of a certain specific wavelength can be realized by changing the recording film thickness depending on the corresponding light wavelength. When performing actual data recording / reproducing, it is necessary to align the positions of the laser light spots of multiple wavelengths at the same point (position). This can be achieved, for example, by using a sample servo format disc. The sample servo format is a system in which a recording / reproducing clock is generated based on a signal from a pit that has been built in advance, and a servo area is specified and information is recorded / reproduced by the clock.

The sample servo system itself is a system used in optical disks, but it is also possible to apply the same technique to a tape system to perform the same recording and reproduction. That is, if a preset reference signal is set so that the position on the recording medium can be recognized and set, it is possible to concentrate the operation of different recording means on an arbitrary point based on the reference signal. . This operation corresponds to performing a kind of time correction on many recording means having different positions. Also,
Even when reproducing with light of a wavelength smaller than the number of recording layers at the time of reproduction, it is possible to perform multi-value reproduction without significantly reducing the number of states. For example, when multilevel recording is performed using three recording layers, there are a total of eight states. That is, if the magnetization directions are all upwards, there are 1 case; if only one layer is upwards and the remaining 2 layers are downwards, 3 cases; if only 2 layers are upwards and the remaining 1 layer is downwards, 3 cases; There is one downward direction. If three wavelength lights are used for a recording medium in such a state, all eight states can be detected. Even when two wavelength lights are used, by irradiating one light from one surface of the recording medium and the other light from another surface of the recording medium, it is possible to detect seven states. Detailed description is given in the examples.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. First, the structure of a medium for multilevel recording and the wavelength selectivity at the time of recording / reproducing according to the embodiment will be described. FIG. 8 schematically shows a sectional structure of a magneto-optical disk (hereinafter referred to as “disk”) according to an embodiment of the present invention. This disk was created by the procedure described below. That is, a 600 nm-thickness silicon nitride film 1 is formed on an optical disk substrate 101 having an uneven guide groove by a sputtering method.
02 was formed. Here, pure Si is used as the target, Ar / N ₂ mixed gas is used as the discharge gas, and the discharge gas pressure is 1
Sputtering was performed at 0 mTorr and discharge power density: 6.6 mW / m ² . Next, three layers having different thermomagnetic properties were formed as the magneto-optical recording film 103. The recording material is Tb ₂₄ Fe ₅₈ Co
Focusing on ₁₅ Nb ₃ , Tb 24 at%, 23 at%, 22 at%, Co 15
It was formed by changing at%, 13at%, and 10at%. From the side close to the substrate, there are 103-1, 103-2, 103-3. The film thickness of each layer is 15 nm, and the thermomagnetic characteristics of each film are such that the Curie temperature and the compensation temperature are changed as shown in FIG. With such thermomagnetic properties, it is possible to specify the recording layer in which the magnetization direction is reversed, depending on to what temperature the recording layer is raised and then cooled.

Next, a silicon nitride film 104 was formed to a film thickness of 20 nm. The production conditions are the same as those of the silicon nitride film 102 described above. Finally, the surface of the medium thus formed was protectively coated with the ultraviolet curable resin 105. Recording can be performed on the disc thus created by the following method. Light for recording and reproduction is made incident from the substrate side. First, when recording with a single light spot, there is a method of using a laser pulse having a shape shown in FIG. The disk is irradiated in synchronism with the clock, and in synchronization with each step of the step-like pulse, the direction of the magnetic field is switched to a desired direction according to the content of information, and the direction of magnetization of each layer is directed. In addition, if recording is performed from a layer having a high Curie temperature, each layer may be divided into layers and recorded instead of continuously recording with one pulse. In such a case, the sample servo method is more advantageous than the continuous servo method because the positioning accuracy is higher.

Another example of the media structure is shown below. FIG. 11 is a schematic view showing the cross-sectional structure of the recording film portion of the magneto-optical disk prepared in this example. The disc was created by the procedure described below. A 600-nm-thick silicon nitride film was formed by a sputtering method on an optical disk substrate having an uneven guide groove. Pure Si as the target and Ar as the discharge gas
A / N ₂ mixed gas was used and sputtering was performed at a discharge gas pressure of 10 mTorr and a discharge power density of 6.6 mW / m ² . Next, Tb ₂₄ Fe ₅₈ Co ₁₅ Nb ₃ was used for the recording film. And
The thickness of each layer may be controlled according to the wavelength of light used,
Here, if light with three wavelengths of 680 nm, 530 nm and 430 nm is used, the film thickness of each layer may be 100 nm, 180 nm, 250 nm. The light absorption characteristics of only the recording layer are as shown in FIG. Then, an inorganic dielectric layer having a thickness of 7 nm was formed between the recording layers. This is to cause light to cause multiple interference in each recording layer. Then, the other layers were formed so as to sandwich the recording film as in the previous embodiment. Finally, the surface of the medium thus prepared was protectively coated with an ultraviolet curable resin.

In the medium structure shown in this embodiment, the film thickness of the recording layer is set in accordance with the wavelength of light, so that the thermomagnetic characteristics of the respective recording layers are the same as shown in FIG. I do not care. Furthermore, in order to assist the light wavelength selectivity, it may be considered to slightly shift the thermomagnetic characteristics in each recording layer. Recording is performed on the disc thus created by the following method. Light for recording and reproduction is made incident from both the substrate side and the medium side. Recording may be performed on a layer to be recorded using light having a wavelength that causes multiple interference in that layer, and no recording is performed in other layers because light is not absorbed. Figure 1
The medium having the structure shown in FIG. 1 is a particularly effective structure for the recording / reproducing method in which lights of different wavelengths are incident from both surfaces of the medium. Further, as shown in FIG. 13, the method of changing the absorptance with respect to the wavelength can be similarly applied even when light is incident only from the substrate side as shown in FIG.

Next, an information recording / reproducing method and apparatus using the medium configured as described above will be described. Figure 1
FIG. 6 is a diagram showing a configuration example of an apparatus when an optical disc configured as described above is used as a medium. In the figure,
The disk 1 is a magneto-optical disk having a multi-layer film structure and capable of multilevel recording. The disk 1 is rotated by the spindle motor 2. FIG. 1 shows a case where two independent optical heads of different light sources are used. 2
Since the configurations of the two optical heads are the same, the head configuration on the left side of the drawing will be described here. The light beam emitted from the laser 3 is converted into parallel light by the lens 4, passes through the beam splitter 5, is guided to the lens 7 by the mirror 6, and is condensed on the disk 1. Here, the mirror 6 is
This is a movable mirror for performing tracking in order to position the light spot on a target track on the disk by following the position variation of the disk in the radial direction. The mirror 6
Is also called the galvano mirror. Also, lens 7
Is a movable lens for following an up-and-down swing of the disk 1 and performing an automatic focusing servo so as to always focus on a target recording surface.

The reflected light from the disk 1 passes through the lens 7 again, is reflected by the mirror 6, is reflected by the beam splitter 5, and is condensed by the lens 8 on the detector 9. In FIG. 1, the detection system for tracking and automatic focusing and the drive circuit system for the mirror 6 and the lens 7 are not shown, but these systems may have the configuration used in the conventional sample servo optical disk. Therefore, it is omitted. The coil 10 for the externally applied magnetic field is for generating the externally applied magnetic field when the disk 1 is a magneto-optical disk. The coil 10
In the coil driver 11, the polarity and magnetic field strength are set. Next, a case of recording data will be described.
The recording data 20 is input to the data separator 21. The data separator 21 has a function of separating the input data 20 and distributing it to each optical head. FIG. 2 shows the data separator 21.
3 is a diagram for explaining the function of FIG. As shown in FIG.
When a magneto-optical disc using two layers of perpendicular magnetization films is used as the disc 1, the number of states of information that can be recorded at one point on the disc, which is two different light spots, is determined by the magnetization of each perpendicular magnetization film. Assuming that there are only two states in which the direction is upward or downward in the drawing, there are four ways: upper, upper, lower, lower, lower.

In FIG. 2, this is represented by "0" and "," respectively.
1 "," 2 ", and" 3 "The recording layer A absorbs heat of the wavelength light of the head a, and the recording layer B absorbs heat of the wavelength light of the head b. 2, the applied magnetic field directions on both the head a side and the head b side are set to the lower side, where only the perpendicular magnetization direction at the position cooled after the temperature of the recording layer reaches the Curie point or more is directed downward. In order to record the data "0", it is sufficient that the magnetization direction is upward, so the erased state may be maintained, and the recording pulse need not be applied to either the head a side or the head b side. In order to record the data "1", it is sufficient that the magnetization directions are up and down, so the recording pulse is emitted only on the head b side.
The same applies to 2 "and data" 3. "In addition, in order to erase and erase the data once recorded, the applied magnetic field direction is set to the upper side opposite to the recording mode, and either head a or head b is set. Also, if the recording pulse is irradiated, the magnetization direction is set to the upper side after the erasing regardless of the magnetization direction before the erasing. The number of information states that can be recorded at one point on the disc is 2
There are N powers.

As described above, corresponding to the input data 20,
The function of the data separator 21 is to provide recording pulse data to each optical head. FIG. 3 shows a specific configuration example of the data separator 21. The input data 20 is
It is input to the memory buffer 30. The memory buffer 3
0 has a function of storing the input data 20 and can perform delay time correction on the circuit. The output of the memory buffer 30 described above is input to the decoder 31. The decoder 31 has a function of determining which optical head the recording pulse is to be input to, in accordance with the input data. The simplest configuration is to convert serial data into parallel data in the memory buffer 30, then use ROM (read only memory) as a decoder, input the input data as an address signal, and output the data as the recording pulse data. There is a method used as. The respective outputs of the decoder 31 are output as recording data pulses 22 and 23 via the shift registers 32 and 33. These recording data pulses are supplied to the laser drivers 24 and 25, respectively.
Is input to the disc 1 and the disc 1 is irradiated with light output higher than that in the reproduction mode. The shift registers 32 and 33 described above are
It is used to correct the amount of time shift between the two optical heads.

Further, if the memory buffer 30 is provided with a number of series corresponding to the number of optical heads, the memory buffer 30 can perform time correction. Next, the reproducing system will be described. Similar to the description of the optical head, the reproduction system on the left side of FIG. 1 will be described as an example. In FIG. 2, a polarization plane rotation detection optical system for converting the magneto-optical signal, that is, the upper and lower sides of the magnetization direction recorded on the magneto-optical disk into the magnitude of the light intensity is omitted. The detection optical system is omitted because it can be used with the conventional optical system. The signal received by the photodetector 9 is amplified to a desired signal level by the amplifier 40 and then input to the pit detector 41. Here, a case where a so-called sample servo format in which pits serving as a reference for generating a recording / reproducing clock are preliminarily formed on the disc is used as the disc 1 is used as an example. In the pit detector 41, the recording / reproducing clock is used. It has a function of extracting a pit signal that is a reference for generation.

The pit pulse signal detected by the pit detector 41 is input to a phase locked loop (PLL) 42, and a clock signal for recording / reproduction is generated. on the other hand,
The signal amplified by the amplifier 40 is input to the binarization circuit 43 and converted into a digital signal. In addition, in FIG.
Although 43 is called a binarization circuit, it is more appropriate to call it a digitization circuit because it includes a multi-value level judgment function. Here, the above 2
A clock signal is input from the PLL 42 to the value conversion circuit 43, which means an operation of determining the level of a reproduction signal having an analog value by a clock pulse. In practice, this function can be implemented by an A / D converter. Thereafter, the data stored in the memory 44 is data-synthesized with the reproduction signal from another optical head system by the data synthesizer 45, and the same data 6 as the recording data 20 is recorded.
0 will be played from the disc. Therefore, the function of the data synthesizer 45 is just the opposite function of the data separator 21. The reproduction signal processing system from the other optical head system also has the same configuration and operation. A specific configuration example of the data synthesizer 45 will be described later.

Next, the operation of the above-mentioned reproducing system will be described with reference to FIGS.
It will be explained on the time chart shown in FIG. In FIGS. 4 and 5, the case where the recording medium has a perpendicularly magnetized film having a three-layer structure is taken as an example. When the magnetization directions are set independently for the three layers, the total number of states is from the case where the magnetization directions of all recording layers are upward to the case where the magnetization directions of all recording layers are downward. There are 8 ways. In the figure, in order to facilitate understanding, a case is shown in which multi-valued data from "0" to "7" are recorded in order. In reality, these multi-valued data will be recorded randomly. Here, it is assumed that there are as many optical heads as the number of recording layers, that is, three optical heads are installed and each scans on the same information track. First, a laser having a light source wavelength λ1 is mounted on the optical head a, and the magnetization information of the recording layer A is detected by the wavelength light. A means for detecting only the magnetization information of a specific recording layer for a certain light wavelength can be realized by changing the film thickness of the recording layer in accordance with the wavelength. Specific numerical examples will be described in the medium structure.

Similarly, in the head b in which the laser of wavelength λ2 is mounted, the magnetization information of the recording layer B is detected, and in the head c in which the laser of wavelength λ3 is mounted, the magnetization information of the recording layer C is detected. To be done. FIG. 4 shows reproduced signal waveforms corresponding to the respective wavelengths. In addition, each playback signal waveform,
The binarized signal obtained by slicing at a certain threshold is also shown. The threshold value here is the center level of each reproduced signal waveform. In FIG. 4, it is described that the respective reproduction signal waveforms are detected at the same time. However, in reality, recording and reproduction are performed by different optical heads or different optical spots, and therefore, they are detected by the respective optical heads. It is necessary to correct the generated data sequence to the same time relationship as the recorded data sequence by some method. If a plurality of different light spots can be applied to the same position, ideally, such a time axis correction means is not necessary, but in reality, a slight positional deviation causes a time deviation. Therefore, some kind of time axis correction means is considered necessary. By combining these binarized signals again in the data combiner 45, the recorded eight states are demodulated.

FIG. 5 is an example showing a method of detecting a three-layer multilevel recording state by a reproducing system having a light source of two wavelengths. As described above, if the reproducing system having the three-wavelength light source can reproduce the magnetization directions of the respective recording layers independently, all eight states can be detected. Up to 7 states can be detected by detecting the signal level corresponding to the combined value of the Kerr rotation angles of the recording layer on the center and the recording layer on the incident side from the upper surface and the lower surface of the medium. First, in the light source a, the combined value of the magnetization directions of the recording layer A and the recording layer B can be detected by irradiating light from the upper side in FIG. For example, in "0" and "1", the magnetization direction of both recording layer A and recording layer B is upward, and the corresponding reproduced signal waveform shows the highest level as shown in the figure. "
In 2 "," 3 "," 4 ", and" 5 ", the magnetization directions of the recording layer A and the recording layer B are opposite to each other, so no signal is detected. In" 6 "and" 7 ", The magnetization directions of the recording layer A and the recording layer B are both downward, and the reproduction signal waveform shows the lowest level. Incidentally, the correspondence between the magnetization direction and the reproduction signal waveform level is reversed depending on the setting of the optical system. The reproduced signal waveform thus obtained is binarized by the upper and lower two thresholds, and the binarized signals are "0" and "1", "6" and "6", respectively. When it is 7 ", it goes to" H "level.

Similarly, in FIG. 5, when light is irradiated from the lower side to detect the combined value of the magnetization directions of the recording layer B and the recording layer C, the corresponding reproduced signal waveform and binarized signal are shown in the figure. Like Looking at the binarized signal shown in FIG. 5, the state "2"
And "5" cannot be distinguished because all the binarized signals are "L". However, other states can be determined from the combination of the levels of the binarized signal. Therefore, according to the present embodiment, seven states in which only one state is degenerated can be detected from the reproduced signal waveforms corresponding to the two light sources. According to this method, the number of states obtained by subtracting 1 from 2 N power can be detected by (N-1) light sources for N recording layers in general. By the way, when the combined value of the magnetization directions of all the three recording layers is detected by one light source, all four magnetization directions are upward, all downward, only one upward, and only two upward. Only can be detected. Here, the above-mentioned data synthesizer 45
An example of the configuration will be described. Basically, the data synthesizer 45 has the opposite operation and configuration from the data separator 21. FIG. 6 shows a configuration example of the data synthesizer 45.

The respective data 61 and 63 detected for different light spots are input to the memories 44 and 50, respectively. The outputs 62, 64 of the memory are respectively
It is input to the shift registers 65 and 66. Here, the memories 44 and 50 and the shift registers 65 and 66 function as a kind of buffer for correcting the time difference between the two series of data 61 and 63. Therefore, memory,
The shift register can be completed with one memory. In the following description, unless otherwise specified, it will be referred to as a memory. Each memory is the same as the PLL 42,
The clock generated at 48 causes data to be stored in and retrieved from the memory. When a memory having a sufficiently large capacity is used to store all data for a data processing unit and data is separately fetched from the memory, the data should be fetched from the memory other than the reproduction clock. You may use the clock of. Data sequence 6 for which time axis alignment has been completed in this way
7, 68 are combined by the gate 69 to generate one series of data 60.

In FIG. 6, the data 60 is described by a single signal line, but it is often convenient to perform the subsequent processing with the parallel data as it is. For example, in the case of handling eight kinds of data from "0" to "7", a method of using three data signal lines as signal lines of the data 60 can be considered. FIG. 7 is a supplementary explanatory diagram of the operation of the data separator 21. It is assumed that the data 20 to be recorded on the medium is given as shown in the figure. When the data 20 has eight kinds of state numbers from "0" to "7", it is given by three series of binarized signal data I0 to I2. If three light spots are irradiated on the same position on the disc, the binarized data may be input to each laser drive circuit without time axis correction.
However, it is difficult to accurately align them at the same position, and it is advantageous to separate the light spots from each other by a distance that does not cause thermal interference from the viewpoint of recording temperature control on the medium. Is considered to be. In this case, it is necessary to delay the binarized data by the time interval corresponding to the mutual light spot distance. Binary data S0-S
2 shifts I2 and I1 by an amount corresponding to the spot interval to generate S2 and S1. Further, although a plurality of different optical heads are used in FIG. 1, the same effect can be obtained even with a configuration in which a plurality of optical spot generating means are provided in a single head.

Here, as the above-mentioned shifting means,
When the clock signal can be generated from the disk independently of the data signal as in the sample servo format, the shift register can be used by the clock signal. When an individual head is used, it can be performed by a shift register, but if there is at least one disk of data memory, the data I0 to I2 to be recorded is temporarily stored in this data memory. There is a method of recording on the disk while reading from the above-mentioned data memory based on the address information indicating the position on the disk which is detected by each head as needed. Note that the processing shown in FIG. 5 for reproducing data from two directions of the upper surface and the lower surface of the medium may be the method shown in FIG. However, since the states "2" and "5" in FIG. 5 are read out as the same state, either state may be recorded at the time of recording, but generally, it is unified to either state. It is easier to handle by recording it.

According to the above embodiment, the magnetization direction of any recording layer can be changed by using the recording / reproducing medium having two or more layers of perpendicularly magnetized films having wavelength selectivity. As a result, multi-value recording of three or more values can be performed at the same position. Further, even during reproduction, the information on the magnetization direction of an arbitrary recording layer can be detected by making the thickness of the recording layer correspond to the wavelength. Furthermore, by irradiating the light spots from both the upper and lower surfaces of the recording medium, information recorded on a medium having a larger number of recording layers than the number of light spots can be multi-valued reproduced with almost no degeneracy of the number of states. It will be possible. As a result, although it has been possible to record and reproduce only two values at the same position on the medium in the related art, it becomes possible to easily record and reproduce information of three or more values, so that the recording density is significantly improved. It will be possible.

[0027]

As described above in detail, according to the present invention, by using a multi-layer recording film medium, the state of only an arbitrary recording layer is changed at the time of recording, and the state of any layer is reproduced at the time of reproducing. This has a remarkable effect of realizing an information recording / reproducing medium that can be detected.

[0028]

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a device configuration according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a magnetic field application method and a recording pulse application method during recording.

FIG. 3 is a diagram showing a configuration example of a data separator shown in FIG.

FIG. 4 is a diagram showing a correspondence relationship between a magnetization direction and a reproduction signal waveform in the case of three layers.

FIG. 5 is a diagram showing a correspondence relationship between a magnetization direction in the case of three layers and a reproduced signal waveform in the case of reproducing from both upper and lower surfaces of the recording layer.

FIG. 6 is a diagram showing a configuration example of the data synthesizer shown in FIG. 1.

FIG. 7 is an operation explanatory diagram of the data separator shown in FIG. 1.

FIG. 8 is a cross-sectional view showing a configuration example of a magneto-optical medium according to an embodiment of the present invention.

9 is a diagram illustrating thermomagnetic characteristics of each recording layer having the three-layer structure shown in FIG.

FIG. 10 is a diagram showing an example of a recording pulse shape.

FIG. 11 is a sectional view showing a configuration example of a magneto-optical medium according to another embodiment.

FIG. 12 is a diagram showing an example of thermomagnetic characteristics of a magneto-optical medium.

FIG. 13 is a diagram showing a change in transmittance with respect to a light wavelength of a multilayer structure medium.

[Explanation of symbols]

1: disk, 3, 12: laser, 10, 19: coil, 24, 25: laser driver, 20: data, 21:
Data separator, 45: data synthesizer, 103: recording layer.

Claims (12)

[Claims] 1. An information recording / reproducing medium for performing magneto-optical recording and reproduction by using a laser beam, wherein the medium has a recording layer composed of a plurality of perpendicularly magnetized films, and each layer of the recording layer has thermomagnetic characteristics. An information recording / reproducing medium having a different structure. 2. The thermomagnetic property of the recording layer composed of a plurality of layers is such that at least one physical property value among coercive force temperature change, Curie temperature, and compensation temperature is changed. Information recording / reproducing medium described. 3. The recording layer composed of the plurality of layers is laminated in the thickness direction, and depending on the wavelength of the recording laser light source,
3. The information recording / reproducing medium according to claim 1, wherein any one of the recording layers is made to absorb heat. 4. Each layer of the recording layer composed of the plurality of layers,
4. The information recording / reproducing according to any one of claims 1 to 3, wherein the thickness is such that light causes multiple interference in a layer to be reproduced when using laser light of at least two kinds of wavelengths during reproduction. Medium. 5. The film thickness of each layer of the recording layer composed of the plurality of layers is a film thickness which is transparent to the wavelength of the laser beam used, and more preferably 50 nm or less. Item 5. The information recording / reproducing medium according to any one of items 1 to 4. 6. A recording / reproducing method using the information recording / reproducing medium according to claim 1, wherein upon recording, magnetization reversal is performed by an optical head capable of emitting light spots having different wavelengths corresponding to the number of recording layers. After increasing the output of a light spot having a wavelength corresponding to the recording layer to be made to reach the Curie point of the temperature of the recording layer, the magnetization direction is fixed to the external magnetic field direction during the cooling process, and at the time of reproduction, the recording layer An information recording / reproducing method characterized in that the magneto-optical effect of an arbitrary recording film is selectively detected by the wavelength of a reproducing light source having a different wavelength for several minutes. 7. A recording / reproducing method using the information recording / reproducing medium according to claim 1, wherein the magneto-optical effect of an arbitrary recording film is selectively detected by the wavelength of the reproducing laser light source. And a method for recording and reproducing information. 8. A recording / reproducing method using the information recording / reproducing medium according to claim 1, wherein a combined amount of magneto-optical effects of arbitrary two or more recording layers is set according to a wavelength of a reproducing laser light source. An information recording / reproducing method characterized by selectively detecting. 9. A recording / reproducing apparatus using the information recording / reproducing medium according to claim 1, comprising a detection optical system capable of detecting two or more laser light spots having different wavelengths. An information recording / reproducing apparatus characterized by detecting the magneto-optical effect of different recording films. 10. A recording / reproducing apparatus using the information recording / reproducing medium according to claim 1, wherein when reproducing recorded information, light is introduced from two directions, and the light is introduced from each direction. An information recording / reproducing apparatus characterized in that information of each of at least three recording layers is reproduced by taking a sum of signals obtained from incident light. 11. A recording / reproducing apparatus using the information recording / reproducing medium according to any one of claims 1 to 5, wherein reproduction is performed by irradiating a reproducing laser beam from each of the front and back surfaces of the information recording / reproducing medium. In doing so, the Kerr rotation angle corresponding to the combined value of the magnetization directions of the recording layer closest to the light spot and the intermediate recording layer is detected in the first light spot, and the Kerr rotation angle corresponding to the second light spot is similarly detected. The Kerr rotation angle corresponding to the combined value of the magnetization directions of the recording layer closest to the light spot and the intermediate recording layer is detected, and the state at the recording point is determined based on the detection results of both. Information recording / reproducing apparatus. 12. A recording / reproducing apparatus using the information recording / reproducing medium according to claim 1, wherein the information recording / reproducing medium is preliminarily set so that different laser beam spots act on the same point. An information recording / reproducing apparatus characterized in that a reference clock at the time of recording / reproducing is generated based on the reference signal provided above, and a detection signal by a laser beam spot different depending on the reference clock is synchronized.