JP3237287B2 - Optical disc playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus for reproducing an information signal from an optical disk on which recording pits having irregularities are formed in accordance with the information signal.

[0002]

2. Description of the Related Art For example, an optical disk such as a digital audio disk (so-called compact disk) and a video disk has an aluminum reflective film formed on a transparent substrate on which recording pits having embossed pits are formed in advance in accordance with an information signal. It is composed of a film and a protective film or the like formed thereon.

In such an optical disk, a signal is read out, that is, reproduced by irradiating the disk surface with readout light and detecting a large decrease in the amount of reflected light due to diffraction of light at a recording pit formation portion. I have.

In the above-described optical disk, the resolution of signal reproduction is almost determined by the wavelength λ of the light source of the reproduction optical system and the numerical aperture NA of the objective lens.
NA / λ is the reproduction limit.

Therefore, in order to realize a high density in such an optical disk, it is necessary to shorten the wavelength λ of the light source (for example, a semiconductor laser) of the reproducing optical system or to increase the numerical aperture NA of the objective lens. Required.
However, there is naturally a limit in improving the wavelength λ of the light source and the numerical aperture NA of the objective lens, and it is actually difficult to dramatically increase the recording density.

[0006]

Therefore, the applicant of the present invention obtains a resolution exceeding the above-mentioned limits by the wavelength λ and the numerical aperture NA by utilizing the reflectance of the reading spot due to the partial phase change in the scanning spot. (Japanese Patent Application No. 2-94452 (Japanese Unexamined Patent Application Publication No. 3-29263)
No. 2) and Japanese Patent Application No. 3-249511.

FIG. 3 is a schematic sectional view of a main part of one example. This optical disc has a material layer 3 made of a phase-change material that can be crystallized after being melted, on a transparent substrate 2 on which recording pits 1 are formed in accordance with information signals. When irradiating the optical disc with, for example, a reproduction laser beam as readout light, a temperature distribution occurs in a scanning spot of the readout light. As a result, the material layer 3 partially changes from a crystalline state to a molten state to lower the reflectance, and returns to a crystalline state in a state after reading.

Next, a description will be given of a reproducing mode in which the optical disk having such a structure is irradiated with a reproducing laser beam to perform reading, with reference to FIGS. 4A and 4B. In FIG. 4A, SP is a laser spot, which is scanned in a direction indicated by an arrow s opposite to the rotation of the disk indicated by an arrow d.
The dashed line c indicates the center of the track. In FIG. 4A, the recording pits 1 are arranged in the shortest recording cycle q. However, the arrangement interval and the pit length vary according to the recording data.

In FIG. 4B, the horizontal axis indicates the position of the laser spot SP in the scanning direction s. FIG.
Assuming that the optical disk is irradiated with the laser spot SP as shown in A, the light intensity of the laser spot SP has a distribution in which the intensity is highest at the center of the spot as shown by a broken line a. On the other hand, the temperature distribution in the material layer 3 of the optical disk is slightly delayed according to the scanning speed of the laser spot SP as shown by a solid line b, and its peak is a position slightly shifted from the spot center.

Here, as described above, the laser spot S
Assuming that P is scanned in the scanning direction SC as shown in FIG. 4A, the temperature of the optical disk gradually increases from the leading end side of the laser spot SP in the scanning direction, and finally reaches a temperature equal to or higher than the melting point MP of the material layer 3. .

At this stage, the material layer 3 changes from an initial crystalline state to a molten state, and the reflectance changes, for example, the reflectance decreases. Therefore, in the laser spot SP, a hatched area Px where the reflectance is low and reading of the recording pit 1 is impossible, and a reading of the recording pit 1 where the reflectance is high to maintain the crystal state and high. And a region Pz in which is possible.

Therefore, as shown in FIG. 4A, even when, for example, two recording pits 1 exist in the same laser spot SP, the one existing in the area Pz having a high reflectivity is obtained.
Reading is performed only for one recording pit 1, and reading can be performed with ultra-high resolution without being limited by the wavelength λ of the reading light and the numerical aperture NA of the objective lens. Become.

As described above, it is ideal that the reflectivity of the region Px is so low that the reading of the recording pits is impossible, but it is not always sufficient. In such a case, the signals in the area Px and the area Pz are mixedly reproduced.

The above-mentioned optical disk is set so that the reflectance is low when the material layer 3 due to the phase change is in a molten state and is high in the crystalline state.
It is called AD (Front Aperture Detection) type. However, by selecting various conditions such as the configuration and thickness of the phase change material, the material layer 3 may be configured to have a high reflectance in a molten state and a low reflectance in a crystalline state.

Such an optical disk (RAD (Rear Ape)
In the (rture detection) type), reading can be performed only in a region where the reflectance is increased due to a molten state, that is, a region indicated by hatching in FIG. 4A. Therefore, even in the case of the RAD type, it is possible to perform ultra-high-resolution reading similarly to the FAD type, thereby enabling high-density recording.

In this case, as in the case of the optical disk of the FAD type, if the reflectance in the crystalline state is not sufficiently low, the signal from the crystalline region and the signal from the fused region are mixedly reproduced.

As described above, when reproducing an information signal from an optical disc capable of super-resolution (referred to as an SR disc),
For example, if the reflectivity of Px is not sufficiently low with respect to the FAD type SR disk, the information signal is also reproduced in the area Px, and the reproduction signal from Px and the reproduction signal from Pz are mixed, and a desired signal is reproduced. In some cases, super-resolution signal reproduction cannot be performed. In the case of the RAD type SR disk, the same problem may occur if the reflectance of the region Pz is not sufficiently low.

Therefore, the present invention provides an optical disk reproducing apparatus capable of reliably detecting only a signal from a portion having a high reflectance when reproducing a so-called SR disk capable of super-resolution.

[0019]

SUMMARY OF THE INVENTION According to the present invention, there is provided a transparent substrate having recording pits formed thereon in response to an information signal. An optical disk reproducing apparatus for reproducing an optical disk formed, comprising: a light source; an optical system that irradiates a laser beam emitted from the light source onto the optical disk to form a light spot on a recording surface on which recording pits are formed; A detection element for detecting reflected light from the optical disc, the detection element comprises a reflected light area Pc from a readable area forming a light spot obtained by forming an image of reflected light from the optical disc at a confocal position; The size and the position in the direction corresponding to the track direction of the optical disc are set so that only the reflected light area Pc of the reflected light area Pm from the unreadable area is received. It is configured to be formed by.

Further, according to the present invention, of the return light of the optical disk formed on the confocal point in the above-described configuration, only the light returning from a portion having a higher reflectance than a predetermined temperature is detected.

[0021]

When an information signal is detected in the configuration of the present invention described above, it is possible to detect only light from a portion having a high reflectance and obtain a signal in which signals from a portion having a low reflectance are not mixed. Can be.

Still further, in the above-described configuration, of the return light of the optical disk formed on the confocal point, only a light returning from a portion having a high reflectance with a temperature equal to or higher than a predetermined value is detected, for example, a photodetector or the like. The size of the detecting element of
Alternatively, it can be achieved by adjusting the position of the return light in the direction perpendicular to the optical axis.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In the figure, reference numeral 11 denotes an optical disk, which is formed by forming a material layer made of a phase-change material that can change phase by a temperature change on a transparent substrate on which recording pits are formed, for example, as described in FIG. For example, as described above, the so-called FAD type SR disk in which the reflectance decreases in a high-temperature portion in the laser spot and the recording pits in this portion cannot be read out, and only the recording pits ahead in the spot can be read out. Can be used.

In FIG. 1, reference numeral 12 denotes a light source such as a semiconductor laser. The laser light L from the light source 12 is supplied to a collimator lens 13, a diffraction grating 14, a polarizing beam splitter (PBS) 15, a quarter-wave plate 16, and an objective lens 1.
The light is irradiated on the recording surface of the optical disk 11 on which the recording pits are formed.

The laser beam L is diffracted by the diffraction grating 14, but is not shown in the drawing. The reflected light passes through the objective lens 17 and the quarter-wave plate 16, is reflected by the PBS 15, and is further split by the beam splitter 18 at a predetermined ratio. The light transmitted through the beam splitter 18 passes through a cylindrical lens 19 and a condenser lens 20 and is detected by a servo signal detecting element 22 composed of, for example, a photodetector. The focus and tracking error signals are generated from the light received here.

On the other hand, the light reflected by the beam splitter is extracted, for example, in parallel with the transmitted light, and is detected by an information signal detecting element 23 such as a photodetector placed at a confocal position through a condenser lens 21. You.

As described above with reference to FIGS. 4A and 4B, the light L from the light source 12 is
When scanning irradiation is performed on 1, a temperature distribution occurs in the laser spot, and a readable area and an unreadable area appear.

In this case, as shown in FIG. 2 schematically showing the positional relationship between the signal light and the information signal detecting element 24 at the confocal position, the reflected light from the optical disk 11 forms an image at the confocal position. and of the light spot SP ₁ obtained by the reflected light region from readable area on the optical disc 11 (area indicated by Pz in FIG. 4A) P
c, assuming that the reflected light area from the unreadable area (area indicated by Px in FIG. 4A) is Pm, only the reflected light area Pc from this readable area is received by the information signal detection element 23. Next, the size of the information signal detecting element 23 and the position in the direction perpendicular to the optical axis of the detection light are adjusted.

That is, assuming that the optical disk 11 rotates about the dashed line indicated by the arrow c ₁ in FIG. 1 and the light from the light source 12 is scanned in the direction perpendicular to the paper surface as indicated by the arrow s ₁ . By appropriately selecting the size of the information signal detecting element 23 and displacing the position thereof in a direction orthogonal to the paper surface in accordance with the spot position on the disk 11, the material layer of the optical disk 11 has a predetermined temperature. As described above, the configuration can be such that only the reflected light from the area where the readout becomes possible due to the increase in the reflectance is detected.

By adjusting the position of the information signal detecting element 23 as described above, for example, the FAD type S whose reflectance at the molten portion is not sufficiently lower than the reflectance at the crystal portion is obtained.
Even in the case of super-resolution reproduction of an R disk, leakage of a signal from a fused portion can be prevented, only a signal coming from a crystal portion can be extracted, and reproduction characteristics can be improved.

In the above-mentioned example, the present invention is applied to a case where a so-called FAD type super-resolution disc is used in which the reflectivity of a material layer made of a phase change material is low in a molten state and high in a crystalline state. In the case where the invention is applied, as described above, a so-called R in which the material layer has a high reflectance in a molten state and a low reflectance in a crystalline state.
It is needless to say that the present invention can be applied to a case where an AD type super-resolution disc is used, and that various modifications can be made without departing from the configuration of the present invention.

[0032]

As described above, according to the present invention, even when super-resolution reproduction is performed on a super-resolution disc in which the difference between the reflectance in the molten state and the reflectance in the crystalline state cannot be sufficiently obtained, the reflectance can be improved. Information signals reproduced from the lower part are not mixed,
Only the information signal reproduced from the portion having a high reflectance can be reliably detected, and the reproduction characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an explanatory view schematically showing a positional relationship between a signal light and an information signal detection element at a confocal position.

FIG. 3 is a schematic enlarged cross-sectional view showing a configuration of an example of an optical disc.

FIG. 4 is a diagram showing a relationship between a light intensity distribution of a laser spot and a temperature distribution (reflectance) of an optical disk.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording pit 2 Transparent substrate 3 Material layer 11 Optical disk 12 Light source 13 Collimating lens 14 Diffraction grating 15 Deflection beam splitter (PBS) 16 1/4 wavelength plate 17 Objective lens 18 Beam splitter 19 Cylindrical lens 20 Condensing lens 21 Condensing lens 22 Detector for servo signal 23 Detector for information signal

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-292632 (JP, A) JP-A-2-96926 (JP, A) JP-A-4-263151 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G11B ^7/ 00-7/013 G11B 7/24 G11B 7/135

Claims (4)

(57) [Claims] 1. An optical disk reproducing apparatus for reproducing an optical disk comprising a transparent substrate on which recording pits are formed in accordance with an information signal and a material layer whose reflectivity changes when the temperature exceeds a predetermined value is formed. The light source and the laser light emitted from the light source are
Irradiate the disk with the recording pits on the recording surface
An optical system for forming a light spot, and
A detecting element for detecting the reflected light, wherein the detecting element is configured such that the reflected light from the optical disc is confocal.
Readout composing a light spot obtained by imaging at a position
The reflected light area Pc from the possible area and the unreadable area
The reflected light area Pc of the reflected light area Pm from the area
Only the size and the optical disk so that only light is received
An optical disc reproducing apparatus characterized in that a position in a direction corresponding to the track direction is set . 2. An optical disk comprising a transparent substrate on which recording pits are formed in accordance with an information signal and a material layer whose reflectivity is reduced when the temperature exceeds a predetermined value is used. The optical disk reproducing device according to claim 1. 3. An optical disk comprising a transparent substrate on which recording pits are formed in accordance with an information signal and a material layer whose reflectance increases when the temperature rises to a predetermined value or more is used. The optical disk reproducing device according to claim 1. 4. The method according to claim 1, wherein, of the return light of the optical disk imaged on the confocal point, only light returning from a portion having a high reflectance at a temperature equal to or higher than a predetermined value is detected. An optical disc playback device according to claim 1.