JP3138650B2 - Optical disc reproducing method and recording method, and optical disc apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an optical disk suitable for high-density recording.
Related to the device .

[0002]

2. Description of the Related Art In an optical disk, a laser beam focused so as to focus on a signal recorded on the optical disk is used to detect a change in reflected light from a recorded signal or a physical quantity such as a Kerr rotation angle. Playing. On optical discs,
Phase change optical disks called PD, DVD-RAM, etc., and magneto-optical disks called MO are roughly classified.

In a phase change optical disk, a guide groove for tracking servo is provided on a substrate made of polycarbonate or the like, and light is directed to either a concave portion (land) or a convex portion (groove) when viewed from the light incident side. The spot is scanned to record and reproduce data. Using a phase change material for the recording film,
The recording data (recording mark) is reproduced by detecting a change in the amount of reflected light at the position of the recording mark.

In a magneto-optical disk, the formation and use of guide grooves are the same as those of the above-mentioned phase change disk. However, a magneto-optical material is used for the recording film, and the reproduction of the recorded mark is performed by detecting a change in a physical quantity called a Kerr rotation angle.

[0005]

In recent years, land / groove recording in which recording marks are formed on both lands and grooves has been proposed in order to increase the density of an optical disk.
What has been recorded only on the land or groove in the past is recorded on both, so simply calculating it doubles the recording capacity.

However, this means that the distance between the grooves forming the recording marks becomes very short, and accordingly, signal leakage (crosstalk) from adjacent grooves (adjacent tracks) cannot be ignored. Is coming.

[0007]

Accordingly, an object of the present invention is to reduce the crosstalk from adjacent tracks caused by the increase in the recording density, so that the effect can be greatly exerted particularly in land / groove recording in which a guide groove exists. An object of the present invention is to provide a reproducing method, a recording method, and an optical disk device.

[0008]

A method of reproducing an optical disk according to the present invention is characterized in that the reproduction is performed without focusing a light spot on a surface on which a signal is recorded.

[0009] The method of reproducing an optical disk according to the present invention comprises:
In the method of reproducing an optical disk having a guide groove, when reproducing a concave groove viewed from a light incident surface, the reproduction is performed by focusing a light spot on a light incident side from a surface on which a signal is recorded. .

[0010] Also, the method for reproducing an optical disk of the present invention comprises:
In the method of reproducing an optical disk having a guide groove, when reproducing a convex groove as viewed from a light incident surface, the reproduction is performed by focusing a light spot on a side opposite to the light incident side from a surface where a signal is recorded. And

[0011] The method for reproducing an optical disk of the present invention comprises:
In a reproducing method of an optical disk having a guide groove and using both the concave groove and the convex groove of the guide groove for reproduction, when reproducing the concave groove viewed from the light incident surface, a signal is recorded. When the light spot is focused on the light incident side from the surface and reproduced, and when the convex groove viewed from the light incident surface is reproduced, the light spot is focused on the opposite side of the light incident side from the surface where the signal is recorded. It is characterized by reproducing.

Also, the method for reproducing an optical disk according to the present invention comprises:
In reproducing method of an optical disk described above, the wavelength of light lambda, and the numerical aperture of the optical head objective lens is expressed as NA, Equation absolute value S is less than the deviation from the recording medium surface of the focal point of the light spot 0. 05λ / (NA) ² ≦ S ≦ 0.4λ / (NA) ² .

[0013] The method of reproducing an optical disk according to the present invention comprises:
In the above-described optical disk reproducing method, the absolute value of the shift of the focal point of the light spot from the recording medium is from 0.3 μm to 1.2 μm.

Further, the recording method of the optical disk of the present invention comprises:
In the above optical disk reproducing method, a focus position is set to a recording surface of the optical disk, that is, a recording medium surface when recording a signal.

Further, the optical disc apparatus of the present invention has a guide groove, and in an optical disc in which both or one of the concave groove and the convex groove of the guide groove is used for reproduction, the concave groove as viewed from the light incident surface. When reproducing a signal, an offset voltage is applied to the focus error signal so that the focal point of the light spot moves to the light incident side from the surface on which the signal is recorded, that is, the recording medium surface, and the convex groove is viewed from the light incident surface. Is reproduced, an offset voltage is applied to the focus error signal so that the focus of the light spot moves to the side opposite to the light incidence side from the surface on which the signal is recorded, that is, the recording medium surface.

Further, according to the optical disk apparatus of the present invention, in the optical disk apparatus described above, an offset voltage is applied to the focus error signal so that the focal position is aligned with the recording surface of the optical disk, that is, the recording medium surface when recording a signal. It is characterized by.

In the optical disk apparatus according to the present invention, when the wavelength of light is expressed as λ and the numerical aperture of the objective lens of the optical head is expressed as NA in the optical disk apparatus described above, the focal point of the light spot deviates from the recording medium surface. The offset voltage is applied to the focus error signal so that the absolute value S of the following equation is added to the following formula: 0.05λ / (NA) ² ≦ S ≦ 0.4λ / (NA) ²

In the optical disk device according to the present invention, in the optical disk device described above, an offset voltage is applied to the focus error signal so that the absolute value of the deviation of the focal point of the light spot from the recording medium becomes 0.3 μm to 1.2 μm. Is added.

[0019]

FIG. 1 is a block diagram showing an embodiment of an optical disk apparatus according to the present invention. Hereinafter, description will be made based on this drawing.

The optical disk device of this embodiment can be roughly divided into an optical head 10 and a controller (control means) 12.
It is composed of The optical head 10 includes an optical system (light spot irradiating means) 16 for irradiating the optical spot 14 with the recording surface on the land L and the groove G with the light spot S;
A photodetector (focus error signal detecting means) 18 for detecting a focus error signal, a tracking error signal, and a reproduction signal from the reflected light of the light spot S returning from the recording surface;
And a lens actuator (focal position varying means) 20 for changing the focal position F of the light spot S with respect to the light spot S.
The controller (control means) 12 controls the groove G based on the focus error signal obtained from the photodetector 18 so that the focus position F is closer to the land L than to the land L.
, The lens actuator 20 is controlled so that the focal position F is farther than the groove G.

The optical system 16 includes a semiconductor laser 161, a beam splitter 162, an objective lens 163, and the like. The photodetector 18 may use any of well-known techniques such as a knife edge method, an astigmatism method, and a critical angle method, and can detect the distance between the focal position F and the recording surface as an analog signal. The controller 12 is composed of, for example, a microcomputer or the like. The controller 12 receives a focus error signal and a tracking error signal, and inputs a lens actuator 20 and a tracking actuator (not shown).
By outputting a control signal to the optical head 10, the position of the optical head 10 is controlled.

Although not shown, the controller 12 includes a land / groove switching unit and a focus offset voltage setting unit. The land / groove switching unit outputs a switching signal for determining whether to reproduce the land L or the groove G to the focus offset voltage setting unit. The focus offset setting unit determines whether the land is the land L or the groove G based on the switching signal, and outputs an offset voltage corresponding to the land L or the groove G.
Add to As a result, optimal reproduction can be performed on each track. A recording signal is also input to the focus offset voltage setting unit. If the recording signal is input, the output is changed to an optimum offset voltage during recording.

FIG. 2 and FIG. 3 are partially enlarged sectional views of the optical disk device of FIG. FIG. 4 is a partially enlarged sectional view of a conventional optical disk device. FIG. 5 is a graph showing an example of the focus offset dependence of the amount of reflected light. Hereinafter, description will be made with reference to FIGS. 2 to 4, the optical disk 14 includes a substrate 141 and a recording film 142. The “focus offset” refers to a distance between the land L or the groove G (recording surface) and the focal position F.

The controller (control means) 12 operates as follows based on the focus error signal obtained from the photodetector 18. As shown in FIG. 2, the lens actuator 20 is controlled so that the focal position F is closer to the land L (so that the focus offset becomes positive), and a signal from the land L is transmitted. Reproduce. As shown in FIG. 3, the lens actuator 20 is controlled so that the focal position F is farther from the groove G (so that the focus offset becomes negative) than the groove G, and a signal is transmitted from the groove G. Reproduce.

Conventionally, as shown in FIG. 4, the focus position F is made coincident with the land L (or groove G) (the focus offset becomes zero), and the focus position F is shifted from the land L (or groove G). The signal was being reproduced. However, when the present inventor examined the dependence of the reflected light quantity on the focus offset, it was found that the reflected light quantity was not the highest when the focus was on the recording film as shown in FIG.

Therefore, in the optical disk device of the present embodiment, a high reflection is achieved by applying an offset to the substrate 141 (see FIG. 2) in the case of the land L and to the recording film 142 (see FIG. 3) in the case of the groove G. The light amount is obtained, that is, the signal output is increased.

In other words, when reproducing the land, the focal position is shifted to the light incident side from the recording surface, and when reproducing the groove, the reproducing method in which the focal position is shifted to the side opposite to the light incident side from the recording surface is used. The signal output can be increased. This means that further densification is possible.

By the way, conventional optical disks use only lands or grooves as recording areas.
Land / groove recording using both of them for recording is actively performed. In the case of land / groove recording, the distance to the adjacent groove (track) is halved, so that the leakage signal (crosstalk) from the adjacent groove increases.
This crosstalk needs to be reduced as much as possible in order to significantly increase data detection errors.

On the other hand, as is apparent from FIG. 5, the behavior of the amount of reflected light with respect to the focus offset is reversed between the land and the groove.

Therefore, if the focus offset position is set on the light incident side of the recording surface and the land is reproduced, a large reproduction signal from the land can be obtained, while a low crosstalk from the adjacent groove can be obtained. In the case of groove reproduction, the same effect can be obtained by setting the focus offset position on the side opposite to the light incident side from the recording surface.

As described above, in the case of land / groove recording, if the above-described reproduction method with the focus offset applied is performed, a reduction in crosstalk can be expected in addition to the amplification of the output signal. This is a very effective method for further densification.

However, when the above-mentioned reproducing method is used, the beam diameter of the reproducing laser beam is slightly larger than the beam diameter at the focal position. On the other hand, when recording, if the beam diameter is large, data already recorded in an adjacent groove may be destroyed. Therefore, at the time of recording,
As shown in FIG. 4, it is preferable to set the focal position to the recording surface.

[0033]

FIG . 6 is a schematic sectional view showing the basic structure of an optical disk used in this embodiment. Hereinafter, description will be made based on this drawing.

The optical disk 30 has an interference film (dielectric film) 34, a recording film 36, and a protective film (dielectric film) on a substrate 32.
Reference numeral 38 denotes a laminated structure. A reflective film or the like may be formed on the protective film 38. As the recording film 36, a magnetic material, a phase change material, or the like can be used.

When the recording film 36 is a magnetic film, the magnetic material does not need to be a single layer, and a multilayer may be used for the purpose of improving the Kerr rotation angle. Further, the magnetic film may be formed directly on the substrate 32. As the magnetic film, an amorphous alloy of a rare earth metal and an iron group transition metal, a periodic multilayer film of an iron group transition metal and a noble metal, a MnBi alloy, an oxide magnetic material, or the like can be used. A film containing TbFeCo as a main component is particularly desirable. Also, Ti, Cr, Ni, T
It is desirable to add one or more corrosion resistance improving elements such as a and Pt.

As the phase change material, a GeSbTe-based compound is desirable. In addition, Al, AlTi
Is desirable.

As the material of the substrate 32, synthetic resin such as polycarbonate and acrylic, glass, and the like can be used, and those coated with resin or the like may be used.
As the shape of the substrate 32, a disk shape or a card shape is used.

As the substrate 32, a substrate having a guide groove was used. Guide groove width is 0.5 for both land and groove
6 μm. Although the cross-sectional shape of the guide groove is relatively close to a rectangle, it is also called a U-shaped groove because it is close to a U-shape. Of course, the groove shape may be a V-shaped V-shaped groove. Also, only the lands or grooves may be V-shaped.

As a first example, a substrate 32 having a diameter of 1
20 mm, track pitch 0.56 μm, substrate thickness 0.6
mm polycarbonate substrate, and the substrate 32
A 160 nm thick ZnS-SiO ₂ film was formed as the interference film 34, a 10 nm thick Ge ₂ Sb ₂ Te ₅ film as the recording film 36, and a 32 nm thick ZnS-SiO ₂ film as the protective film 38. In this case, an AiTi film (not shown) is further formed on the protective film 38 to a thickness of 80 nm.

Data was recorded on this optical disk 30 and reproduced. For recording and reproduction, a wavelength of 640 nm and a numerical aperture (N
A) An optical head of 0.6 was used. The recording mark is 0.37
μm and 1.5 μm were separately recorded, and the signal to noise ratio (CN ratio) was measured for each. In this case, the recording is performed by setting the focal position on the recording film surface. The results are shown in FIGS.

For example, when the focus is shifted by 340 nm to the light incident side, the land is 49 dB for a 0.37 μm recording mark and 60 d for a 1.5 μm recording mark.
The C / N of B is obtained. On the other hand, when the focus is shifted by 340 nm to the side opposite to the light incidence, 0.37 μm in the groove.
A C / N of 48 dB was obtained for the m recording mark, and a C / N of 59 dB was obtained for the 1.5 μm recording mark.

Next, the crosstalk between the land and the groove was measured. A 1.5 μm recording mark was used for the measurement.
A 1.5 μm recording mark is recorded on both adjacent tracks, and the leaked carriers are measured. The crosstalk was obtained by subtracting the carrier in the case where a 1.5 μm recording mark was recorded on its own track from the leaked carrier. FIG. 9 shows the result.

For example, when the focus is shifted by 340 nm to the light incident side, -30 dB crosstalk is obtained in the land. On the other hand, when the focus is even shifted to 340 nm on the side opposite to the light incidence, crosstalk of -29 dB is obtained.

As another example, a silicon nitride film is 80 nm as the interference film 34, a TbTeCo film is 50 nm as the recording film 36, and a silicon nitride film is 80 nm as the trapping film 38.
Were sequentially formed. Experiments similar to those described above were performed, and similar results were obtained.

[0045]

Comparative Example Next, a comparative example will be described with reference to the drawings. In this case, the case corresponding to the conventional example is when the focus offset value in FIGS.

As is evident from FIGS. 5, 7, 8 and 9 ,
It can be seen that providing a focus offset suitable for each of the land and the groove improves both C / N and crosstalk. According to these figures, the preferred form
The range of the scum offset is from 100 nm to 700 nm.
Range. The light used to create these graphs
Spot wavelength (λ), objective lens numerical aperture (NA)
Is λ = 640 nm and NA = 0.6 as described above.
, The preferred focus offset range is λ, N
Expressed using A, this range is 0.05λ / (NA) ² ≦ S ≦ 0.4λ / (NA) ² .

[0047]

According to the present invention, by reproducing a signal in a state where the focus position is closer to the land than the land, the amount of light reflected from the land can be increased, so that the output signal can be increased. Since the amount of reflected light from the groove can be reduced, crosstalk with the groove can be reduced. Also, by reproducing a signal with the focus position farther from the groove than the groove, the amount of reflected light from the groove can be increased, so that the output signal can be increased, and in addition, the amount of reflected light from the land can be reduced. Crosstalk with lands can be reduced. Therefore, the density of the lands and the grooves can be increased more than ever, so that the optical disk can have a further increased capacity.

[Brief description of the drawings]

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

FIG. 2 is a partially enlarged sectional view of the optical disk device of FIG.

FIG. 3 is a partially enlarged sectional view of the optical disk device of FIG. 1;

FIG. 4 is a partially enlarged sectional view of a conventional optical disk device.

FIG. 5 is a graph showing an example of focus offset dependence of the amount of reflected light.

FIG. 6 is a schematic sectional view showing a basic configuration of an optical disk used in an example of the present invention.

FIG. 7 is a graph showing a focus offset dependency of a CN ratio with respect to a 0.37 μm recording mark in the example of the present invention.

FIG. 8 is a graph showing a focus offset dependency of a CN ratio with respect to a 1.5 μm recording mark in the example of the present invention.

FIG. 9 is a graph showing focus offset dependence of crosstalk with respect to a 1.5 μm recording mark in the example of the present invention.

[Explanation of symbols]

 Reference Signs List 10 optical head 12 controller (control means) 14 optical disk 16 optical system (light spot irradiation means) 18 photodetector (focus error signal detecting means) 20 lens actuator (focal position variable means) L land G groove S light spot F focus position

Claims (5)

(57) [Claims] A light spot irradiating means for irradiating a light spot on an optical disk having a recording surface on a land; a focus error signal detecting means detecting a focus error signal from reflected light of the light spot returning from the recording surface; A focus position changing means for changing a focus position of the light spot with respect to the optical disc; and a focus error signal obtained from the focus error signal detection means.
And a control means for controlling the focus position changing means, based on the following : wherein the control means sets the wavelength of light to λ, the objective lens of the optical head
Is expressed as NA, the focal position of the light spot
Assuming that the absolute value of the deviation of the position from the recording surface is S, the absolute value
An offset voltage is applied to the focus error signal so that the value S adds the following equation: 0.05λ / (NA) ² ≦ S ≦ 0.4λ / (NA) ²
And the focal position is incident on a light spot from the land.
Operating the focus position changing means so as to be closer to the side
An optical disk device further comprising an offset adding unit . 2. A light spot irradiating means for irradiating a light spot on an optical disc having a recording surface in a groove; a focus error signal detecting means detecting a focus error signal from reflected light of the light spot returning from the recording surface; A focus position changing means for changing a focus position of the light spot with respect to the optical disc; and a focus error signal obtained from the focus error signal detection means.
And a control means for controlling the focal position variable means, based on the following : wherein the control means sets a wavelength of light to λ, an objective lens of an optical head,
Is expressed as NA, the focal position of the light spot
Assuming that the absolute value of the deviation of the position from the recording surface is S, the absolute value
An offset voltage is applied to the focus error signal so that the value S adds the following equation: 0.05λ / (NA) ² ≦ S ≦ 0.4λ / (NA) ²
And the focus position is shifted into the light spot from the groove.
Move the focus position changing means so as to be farther to the side opposite to the launch side.
An optical disc device further comprising an offset adding means for causing the optical disc device to operate. 3. A light spot irradiating means for irradiating a light spot on an optical disk having a recording surface on lands and grooves; a focus error signal detecting means detecting a focus error signal from reflected light of the light spot returning from the recording surface. a focus position changing means for changing the focal position of the light spot relative to the optical disc, the focus error signal obtained from said focus error signal detection means
And a control means for controlling the focal position variable means, based on the following : wherein the control means sets a wavelength of light to λ, an objective lens of an optical head,
Is expressed as NA, the focal position of the light spot
Assuming that the absolute value of the deviation of the position from the recording surface is S, the absolute value
An offset voltage is applied to the focus error signal so that the value S adds the following equation: 0.05λ / (NA) ² ≦ S ≦ 0.4λ / (NA) ²
Is added to the land, and the focal position is
Focus position so as to be closer to the light spot incidence side from the
Activate the variable means, and focus on the groove.
The position is far from the groove to the opposite side of the light spot incidence side
Offset for operating the focus position varying means so that
An optical disc device , further comprising: 4. The control means controls the focus position variable means based on a focus error signal obtained from the focus error signal detection means so that the focus position coincides with the recording surface when a signal is recorded. An optical disk device according to claim 1, 2 or 3 . 5. The control means applies an offset voltage to the focus error signal so that an absolute value of a shift of a focus position of the light spot from the recording surface is from 0.3 μm to 1.2 μm. Item 4. The optical disk device according to item 1, 2, or 3 .