JPH04192122A - Information reproducing device - Google Patents

Abstract

PURPOSE:To perform reproducing with good S/N even a fine recording pattern recorded in a magnetic field modulation system by absorbing light of an area where a main spot is overlapped with an auxiliary light spot by means of a light transmission control layer. CONSTITUTION:Light spots 21a and 21b by a light source 8 and a light spot 21c by a light source 32 are formed on a disk 2. Then, light of the light spots 21a and 21b is absorbed by a photochromic layer 2b to change spectral characteristics of light absorption. That is, in the area where the light spots 21a and 21b are overlapped with the light spot 21c, light of the light spot 21c is largely absorbed. As a result, one part of a reproducing light beam is eliminated so that a small reproducing light beam comes to a magneto-optical recording layer. Consequently, since a transfer function of an optical system can drastically be extended in a high region, even a minute recording pattern recorded in the magnetic field modulation system can thus be reproduced in good S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an information reproducing apparatus for reproducing optically recorded information, and particularly to an information reproducing apparatus suitable for reproducing information using a magnetic field modulation method.

[Prior Art] The size of the light spot irradiated onto the information recording medium is determined by the wavelength of the light and the NA of the objective lens that narrows down the light beam.Therefore, in conventional light modulation methods, the spot size is reduced to obtain information. There were naturally limits to high-density recording.

On the other hand, the magnetic field modulation method, which records information using a magnetic field and a light beam, can record recording bits whose length is shorter than the spot size.

FIG. 8 is a configuration diagram showing the magnetic field modulation type disk and its surroundings. In the figure, 107 is a semiconductor laser used as a light source, and the laser beam is collimated by a collimator lens 106 and then converted into a sunlight beam by a beam shaping prism 105. The light also passes through the beam splitter 104, is narrowed down by the objective lens 103, and is focused on the recording layer of the magneto-optical disk 102 as a minute light spot. A magnetic head 101 is arranged on the upper surface of the magneto-optical disk 102, facing an objective lens 103.

On the other hand, the light reflected from the magneto-optical disk 102 is guided to the beam splitter 10B via the objective lens 103 and the beam splitter 104.
separates the reflected light into two, and guides one to the reproduction optical system on the half-wave plate 109 side and the other to the control optical system on the condenser lens 114 side. In the reproduction optical system, the light that has passed through the 1/2 wavelength plate 109 is sent to the beam splitter 11 via the condenser lens 110.
3, where it is further separated into two. The separated lights are received by photodetectors 111 and 112, respectively, and an information signal is obtained from the output of the received light. Further, in the control optical system, the light passing through the condenser lens 114 is separated into two by a beam splitter 115. One of the separated lights is received by the photodetector 116, and the other is received by the knife 116.
17 and is received by a photodetector 118. Then, a servo signal is obtained from the light reception signals of the photodetectors 116 and 118.

Next, when recording information, a laser beam of a constant intensity is irradiated from the semiconductor laser 107, and the magneto-optical disk is
A thermal bias is applied to 02.

As a result, the temperature of the recording layer rises to the Curie point temperature or higher, and in this state, bias magnetism is applied from the magnetic head 101 to the temperature raised region. The bias magnetic field is shown in Figure 9 (a
), it is modulated according to the recording signal, and the direction of magnetization of the recording layer is aligned in the same direction as the direction of the bias magnetic field. Then, at the moment when the temperature of the recording layer becomes below the Curie point temperature, the direction of magnetization is maintained, and domains as shown in FIG. 9(b) are formed. In this case, since the normal light spot has a Gaussian light intensity distribution, the temperature distribution of the heated medium is a smooth temperature distribution that reflects the light intensity distribution, and the shape of the Curie point temperature contour line is not rectangular. Therefore, the recorded domain is shown in Figure 9(a).
As shown, it becomes feather-shaped.

As described above, in the magnetic field modulation method, the size of the recording domain does not depend on the size of the optical spot, but is determined by the scanning speed and the modulation frequency of the magnetic head. Therefore, it is possible to record a domain smaller than the size of the light spot, and the recording density can be further increased.

[Problems to be Solved by the Invention] However, in the conventional magnetic field modulation method described above, the recording domain is smaller than the optical spot for reproduction, so the transfer function of the optical system during reproduction is determined by the spatial frequency determined by the size of the optical spot. In the above case, the signal decreases rapidly, and it is difficult to reproduce a signal with a good S/N ratio.

The present invention has been made to solve these problems, and its purpose is to reproduce information with a good S/N ratio, even for minute recording patterns recorded using the magnetic field modulation method. The goal is to provide equipment.

[Means for Solving the Problems 1] Such an object of the present invention is to provide a light transmission control layer which is located on the light irradiation side of the information recording layer and absorbs light of a predetermined wavelength to change the spectral characteristics of light absorption. a first spot forming means for irradiating, as two adjacent auxiliary light spots, a reproduction auxiliary light beam having the same wavelength as the light absorption wavelength of the light transmission control layer onto an optical information recording medium formed by laminating the light transmission control layer; and second spot forming means for irradiating a main reproduction light beam different from the main light spot as a main light spot so that a part thereof overlaps each of the two auxiliary light spots, and overlaps with the auxiliary light spot of the main light spot. This is achieved by an information reproducing device characterized in that the light transmission control layer absorbs the light in the area.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an optical head optical system according to the present invention.

In FIG. 1, reference numeral 1 denotes a magnetic head disposed on the upper surface of a magneto-optical disk 2, which generates a bias magnetic field modulated in accordance with a recording signal. The magneto-optical disk 2 is rotationally driven by a spindle motor (not shown). The specific structure of the recording layer of the magneto-optical disk 2 will be described in detail later, and an optical head optical system is provided on the lower surface of the magneto-optical disk 2.

In this embodiment, the optical head optical system includes two light sources, a first light source 8 and a second light source 32. First light source 8
This is a light source that emits ultraviolet light for assisting reproduction, and is, for example, a light source that extracts second harmonic light from a semiconductor laser using a non-linear optical crystal.

The light beam from the first light source 8 passes through the phase shift element 5, the polarizing beam splitters 29 and 4, and the objective lens 3, and is irradiated onto the magneto-optical disk 2. The second light source 32 is a light source for recording and reproduction, and uses a semiconductor laser. The laser beam passes through a collimator lens 31, a beam shaping prism 30, polarizing beam splitters 29 and 4, and an objective lens 3, and is irradiated onto the magneto-optical disk 2.

Reference numeral 20 denotes a wavelength selection element that selects the wavelength of the reproduced light beam reflected by the beam splitter 4. This wavelength selection element 20
In this case, only the light beam from the second light source 32 is transmitted, and the light beam from the first light source is cut. The light emitted from the wavelength selection element 20 is
The beam splitter 9 splits the beam into two beams destined for the reproduction optical system and the control optical system. The reproduction optical system and the control optical system are
The structure is the same as the conventional one shown in the figure, and the reproduction optical system is composed of a half-wave plate 10, a condensing lens 11, a beam splitter 12, and photodetectors 13 and 14. In addition, the control optical system includes a condenser lens 15 and a beam splitter 1.
6. It is composed of a knife 17 and photodetectors 18 and 19.

FIG. 2 is a diagram showing the cross-sectional structure of the magneto-optical disk 2 used in this embodiment. 28 in the figure is a transparent substrate, and this substrate side is the incident side of the laser beam.

A photochromic layer 2b, a heat mode recording layer 2c, and a protective film 2d are sequentially formed on the transparent substrate 2a. In addition, in this example, as the heat mode layer 2c,
A magneto-optical recording layer is used.

Generally, the photochromic layer 2b has a property of absorbing light of a specific wavelength and changing the spectral characteristics of light absorption. FIG. 3 shows the change in the characteristics, where a shows the spectral characteristics before the light irradiation, and b shows the change in the spectral characteristics due to the light irradiation. Therefore, by irradiating two lights with different wavelengths, the spectral characteristics of light absorption can be reversibly changed. At this time, since the change in state is caused by absorption of photons, it is thought that the change roughly occurs on the order of the relaxation time of electronic transition, and it is possible to change the state at an extremely high speed. In order to change the spectral characteristics in this way, specifically, when the magneto-optical disk 2 is irradiated with light of the first wavelength, the photochromic layer 2b becomes larger due to absorption of the light of the second wavelength, and the magneto-optical recording layer (Heat mode recording layer) 2c
When the amount of light reaching the optical recording layer 2C decreases significantly and conversely absorbs the light of the second wavelength, the first and second wavelengths and The material of the photochromic layer 2b is selected.

Suitable materials for the photochromic layer 2b include, for example, fulgide, spiropyran, viologen, dihydropyrene, thioindigo, bipyridine, and aziridine. Moreover, ultraviolet light (wavelength is about 360 nm) is used as the first wavelength, and its light source is the first light source 8 shown in FIG. Furthermore, visible light (wavelength is about 600 nm) is used as the second wavelength, and is emitted by the second light source 32.

Next, the operation of this embodiment will be explained. First is the recording operation. Information recording is exactly the same as in the conventional case, and information is recorded by applying a bias magnetic field from the magnetic head 1 and irradiating a laser beam with a constant intensity.

A second light source 32 is used as a light source for recording the transcript. Note that, at the time of recording, the output power of the first light source 8 is set to zero. The laser beam from the second light source 32 is collimated by a collimator lens 31, converted into a circular beam by a beam shaping prism 30, and then irradiated onto the magneto-optical disk 2 via the polarizing beam splitters 29, 4 and the objective lens 3. be done. As a result, the magneto-optical disk 2 is heated to a temperature higher than the Curie point temperature, and a bias magnetic field modulated according to the recording signal is applied from the magnetic head 1 to this heated portion. As a result of the above, the direction of magnetization of the recording layer is oriented in the direction of the bias magnetic field,
A feather-shaped domain is formed.

Next, the playback operation will be explained. The first light source during playback
．． A second light source 8, 32 is used. The ultraviolet light emitted by the first light source 8 passes through the phase shift element 5, the polarizing beam splitters 29 and 4, and the objective lens 3, and is irradiated onto the magneto-optical disk 2.

As shown in FIG. 4, the phase shift element 5 is configured so that the left and right thicknesses differ approximately at the center, and functions to generate a phase difference in the left and right regions 5a and 5b having different thicknesses. The relationship between the thickness difference, wavelength λ3, and refractive index n is β=
λ/n, resulting in a phase difference π.

As a result of producing a phase difference in this way, two first light spots 21a and 21b adjacent in the track direction are formed on the focal plane 21 of the objective lens 3, as shown in FIG. . In addition, in FIG. 5, 3 is an objective lens, and has two regions 3a corresponding to regions 5a and 5b of the phase shift element 5.

It is shown divided into 3b. At this time, areas 3a and 3b
Then, as mentioned above, a phase difference π occurs.

Further, X is the track direction.

On the other hand, at the same time, the second light source 32 emits light, and its light beam is irradiated onto the magneto-optical disk 2 in the same manner as described above. The light spot from this second light source 32 is the second light spot 21
Let it be c. Note that the light intensity of the second light source 32 during reproduction is set to the reproduction power. FIG. 6(a) shows the first light spot 21a of the first light source 8 formed as described above,
21b and the intensity distribution of the second light spot 21c of the second light source 32. FIG. Further, FIG. 6(b) shows the shapes of the first light spots 21a, 21b and the second light spot 21c. First light spot 21a.

21b has a generally arcuate shape that is symmetrical with respect to the y-axis, and the second light spot 21c has a circular shape.

In this way, the first optical substrate 21a is placed on the magneto-optical disk 2.
, 21b and the second light spot 21c, the photochromic layer 2b absorbs the light of the second light spots 21a, 21b as described above, and the spectral characteristics of light absorption change. That is, as shown in FIG. 7(a), a first light spot 21a.

In a region 21e where 21b and the second light spot 21 overlap, a large amount of light from the second light spot 21c is absorbed. As a result, as shown in FIG. 7(b), a region 21f is obtained excluding the overlapping region 21e from the second light spot 21c.
Only the light reaches the magneto-optical recording layer.

The magneto-optical disk 2 reflects the irradiated light as described above, and the reflected light is guided to the wavelength selection element 20 via the objective lens 3 and beam splitter 4. The wavelength selection element 20 is configured to transmit only the light having the wavelength of the second light source 32, so that only the thin linear light spot 21f shown in FIG. 7(b) is transmitted to the reproduction optical system and the control optical system. I am guided. In the reproduction optical system, one of the lights split by the beam splitter 9 is guided to the beam splitter 12 via the 1/2 wavelength plate 10 and the condenser lens 11, as in the conventional case. The beam splitter 12 further splits the light beam into two, and a reproduced signal is obtained from the output of photodetectors 13 and 14 that detect the split light. The other light split by the beam splitter 9 passes through the condenser lens 15 and enters the beam splitter 16, where it is further split into two light beams. One of the divided lights is detected by a photodetector 18 via a knife 17, and the other light is detected by a photodetector 19. Then, as in the conventional case, a servo signal is generated by the output of the photodetectors 18 and 19.

In this embodiment, since the recording domain is reproduced using a thin light spot as shown in FIG. 7(b), the transfer function of the optical system can be significantly extended to high frequencies. . Therefore, even a domain recorded by the magnetic field modulation method as shown in FIG. 9(b), that is, a minute recorded domain, can be reproduced with a good S/N ratio. Furthermore, after reproduction, in preparation for the next information recording, the photochromic layer may be returned to its original state by increasing the light intensity of the second light spot and irradiating the magneto-optical disk again.

In addition, in the above embodiment, an example was shown in which a phase shift element was used to form two first light spots, but the present invention is not limited to this, and for example, an array-shaped element may be used as the first light source. Alternatively, two adjacent light spots may be formed.

[Effects of the Invention] As explained above, according to the present invention, a part of the reproducing light beam is removed and a smaller reproducing light beam is irradiated, so that the transfer function of the optical system is adjusted to a higher frequency range than before. can be significantly extended. Therefore, even if the pattern is as fine as a light spot, recorded information can be reproduced with a good S/N ratio.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a sectional view of an optical information recording medium used in the embodiment, and FIG.
The figure shows the light absorption characteristics of the photochromic layer of the recording medium, Figure 4 is a perspective view of the phase shift element, and Figure 5 is an explanation showing how two light spots are irradiated onto the medium by the phase shift element. FIG. 6 is a diagram showing the light intensity of the first and second light spots and the shape and positional relationship on the medium,
Figure 7 shows the first light spot of the second light spot, which is the main reproduction spot.
An explanatory diagram showing how the area overlapping with the spot is absorbed by the photochromic layer, Figure 8 is a configuration diagram showing the optical head optical system of the conventional magnetic field modulation method, and Figure 9 shows the magnetic field of the magnetic head in the magnetic field modulation method. It is a figure which shows the domain recorded as the same mouth of. 1: Magnetic head 2: Magneto-optical disk 2b: Photochromic layer 2C: Heat mode layer 3: Objective lens 5: Phase shift element 8: First light source
20: Wavelength selection elements 21a, 21b: First spot 21c Second spot 32: Second light source Agent Patent attorney Yohei Yamashita Figure 6 Figure 7

Claims (1)

[Claims] In an optical information recording medium formed by laminating an information recording layer and a light transmission control layer on the light irradiation side that absorbs light of a predetermined wavelength and changes the spectral characteristics of light absorption, the light transmission control layer is a first spot forming means for irradiating a reproduction auxiliary light beam having the same wavelength as the light absorption wavelength as two adjacent auxiliary light spots; and a part of the main reproduction light beam different from the wavelength to the two auxiliary light spots. and a second spot forming means for irradiating as a main light spot so as to overlap each other, and the light transmission control layer absorbs light in an area where the main light spot overlaps with the auxiliary light spot. Information reproducing device.