JPH06282848A - Optical disc player - Google Patents

Abstract

PURPOSE:To provide an optical disc player which enables accurate detection of a signal alone from a part with a high reflection factor in the reproduction of an SR disc with super higher resolutions. CONSTITUTION:On an optical disc, a transparent substrate 2 having recording pits according to an information signal is provided with a layer 3 whose reflection factor changes, that is, lowers or rises when the temperature is above a specified point. This disc player detects reproduction signal at a confocal position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc reproducing apparatus for reproducing an information signal from an optical disc having recording pits formed by, for example, concave and convex in accordance with the information signal.

[0002]

2. Description of the Related Art Optical discs such as digital audio discs (so-called compact discs) and video discs have an aluminum reflection film formed on a transparent substrate on which recording pits, so-called embossed pits, are formed in advance according to an information signal. A film is formed, and a protective film or the like is formed on the film.

In such an optical disc, a signal is read out or reproduced by irradiating the disc surface with a reading light and detecting a large decrease in the amount of reflected light due to the diffraction of the light at the recording pit formation portion. There is.

By the way, in the above-mentioned optical disc, 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, and the spatial frequency 2
NA / λ is the reproduction limit.

Therefore, in order to achieve high density in such an optical disc, it is necessary to shorten the wavelength λ of the light source (for example, semiconductor laser) of the reproducing optical system or increase the numerical aperture NA of the objective lens. Will be needed.
However, there is a limit to the improvement of the wavelength λ of the light source and the numerical aperture NA of the objective lens, and it is difficult to dramatically increase the recording density by this.

[0006]

Therefore, the present applicant obtains a resolution more than the above-mentioned limits by the wavelength λ and the numerical aperture NA by utilizing the reflectance due to the partial phase change in the scanning spot of the reading light. An optical disc that can be used has been proposed (Japanese Patent Application No. 2-94452 (Japanese Patent Application Laid-Open No. 3-29263).
2), Japanese Patent Application No. 3-249511).

FIG. 3 shows a schematic sectional view of the essential part of an example thereof. This optical disc has a material layer 3 made of a phase-change material that can be crystallized after melting on a transparent substrate 2 on which recording pits 1 are formed by unevenness according to an information signal. When irradiating, for example, a reproduction laser beam as reading light on this optical disk, a temperature distribution is generated in the scanning spot of the reading light. As a result, the material layer 3 partially changes from the crystalline state to the molten state, the reflectance decreases, and the material layer 3 returns to the crystalline state in the state after reading.

Next, a reproducing mode of irradiating the optical disk having such a structure with a reproducing laser beam for reading will be described with reference to FIGS. 4A and 4B. In FIG. 4A, SP is a laser spot, which is scanned in the direction indicated by arrow s, which is the opposite direction to the rotation of the disk indicated by arrow d.
The chain line c indicates the track center. In FIG. 4A, the recording pits 1 are arrayed at the shortest recording cycle q, but it goes without saying that the array interval and the pit length change according to the recording data.

In FIG. 4B, the horizontal axis represents the position of the laser spot SP in the scanning direction s. Figure 4
Considering the state where the optical disc is irradiated with the laser spot SP as shown by 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 disc is slightly delayed according to the scanning speed of the laser spot SP as shown by the solid line b, and its peak is located slightly off 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 disc gradually rises 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 its initial crystalline state to a molten state and its reflectance changes, for example, the reflectance decreases. Therefore, in the laser spot SP, a region Px indicated by hatching that makes it impossible to read the recording pit 1 due to the low reflectance, and a high reflectance because the crystalline state is maintained to read the recording pit 1. And a region Pz capable of

Therefore, even if, for example, two recording pits 1 exist in the same laser spot SP as shown in FIG. 4A, they exist in the region Pz having a high reflectance.
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 or the numerical aperture NA of the objective lens, which enables high-density recording. Become.

As described above, it is ideal that the reflectance of the area Px is so low that the recording pits cannot be read out, but the reflectance is not always sufficiently low. In such a case, the signals of the area Px and the area Pz are mixed and reproduced.

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

Such an optical disc (RAD (Rear Ape
In the (rture detection) type), it is possible to read only a region in which the reflectance is increased in a molten state, that is, a region shown by hatching in FIG. 4A. Therefore, even with this RAD type, it is possible to read out with an ultra-high resolution as in the case of the FAD type, which enables high density recording.

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

As described above, when an information signal is reproduced from an optical disc capable of super-resolution (referred to as SR disc),
For example, in the case of the FAD type SR disk, if the reflectance of Px is not sufficiently low, the information signal is reproduced even in the area Px, and the reproduction signal from Px and the reproduction signal from Pz are mixed and the desired signal is obtained. In some cases, super-resolution signal reproduction may not be possible. Also in 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 disc reproducing apparatus capable of reliably detecting only a signal from a portion having a high reflectance when reproducing a so-called SR disc capable of super-resolution.

[0019]

DISCLOSURE OF THE INVENTION According to the present invention, a material layer whose reflectance changes, that is, decreases or rises when the temperature rises above a predetermined value, is formed on a transparent substrate 2 on which recording pits are formed in accordance with an information signal. In an optical disk reproducing apparatus for reproducing an optical disk formed with No. 3, the reproduction signal is detected at the confocal position, as shown in the configuration diagram of one example in FIG.

Further, according to the present invention, in the above-described structure, only the light returning from a portion having a high reflectance equal to or higher than a predetermined value is detected from the returning light of the optical disk imaged on the confocal point.

[0021]

When the information signal is detected in the above-mentioned configuration of the present invention, it is possible to detect only the light from the portion having high reflectance and obtain the signal in which the signals from the portion having low reflectance are not mixed. You can

Further, in the above-mentioned structure, of the return light of the optical disk imaged on the confocal point, only the light returning from a portion having a high reflectance above a predetermined value is detected, for example, a photodetector or the like. The size of the detector 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 disc, which is formed by forming a material layer made of a phase change material capable of phase change due to temperature change on a transparent substrate on which recording pits are formed, as described in FIG. 3 above. As described above, for example, the so-called FAD-type SR disk in which the reflectance decreases at the high temperature portion in the laser spot and the recording pits in this portion cannot be read, and only the front recording pits in the spot can be read. Can be used.

In FIG. 1, reference numeral 12 indicates a light source such as a semiconductor laser. The laser light L from the light source 12 is collimator lens 13, diffraction grating 14, polarization beam splitter (PBS) 15, quarter wave plate 16 and objective lens 1.
The recording surface of the optical disk 11 on which the recording pits are formed is irradiated through the recording medium 7.

Although the laser beam L is diffracted by the diffraction grating 14, it is omitted in the figure. The reflected light passes through the objective lens 17 and the quarter-wave plate 16, is reflected by the PBS 15, and is further divided into a predetermined ratio by the beam splitter 18. 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 detection element 22 including, for example, a photo detector. Focusing 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 the information signal detecting element 23 such as a photodetector placed at the confocal position through the condenser lens 21. It

As described above with reference to FIGS. 4A and 4B, the light L from the light source 12 is the FAD type optical disk 1.
When 1 is scanned and irradiated, a temperature distribution occurs in the laser spot, and a readable region and a non-readable region 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, in particular, the reflected light from the optical disk 11 is imaged at the confocal position. Of the light spot SP ₁ obtained in this manner, the reflected light area from the readable area (area indicated by Pz in FIG. 4A) on the optical disk 11 is P
c, where Pm is a reflected light region from the unreadable region (region indicated by Px in FIG. 4A), only the reflected light region Pc from this readable region is received by the information signal detection element 23. First, 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, if the optical disk 11 in FIG. 1 rotates about the alternate long and short dash line indicated by arrow c ₁ and the light from the light source 12 is scanned in the direction orthogonal to the paper surface as indicated by arrow s ₁ , By appropriately selecting the size of the information signal detecting element 23 and arranging the position so as to be aligned with the spot position on the disk 11 in a direction orthogonal to the paper surface, the material layer of the optical disk 11 is kept at a predetermined temperature. As described above, it is possible to detect only the reflected light from the region where the reflectance is increased and the reading becomes possible.

By adjusting the position of the information signal detecting element 23 in this way, for example, the reflectance of the melted portion is not sufficiently lower than the reflectance of the crystal portion, which is an FAD type S.
Even in the case of super-resolution reproduction of the R disc, it is possible to prevent the leakage of the signal from the melted portion, extract only the signal coming from the crystal portion, and improve the reproduction characteristic.

In the above example, when a so-called FAD type super-resolution disc is used in which the material layer made of a phase change material has a low reflectance in a molten state and a high reflectance in a crystalline state. This is the case where the invention is applied, but as described above, the so-called R in which the material layer has a high reflectance in the molten state and has a low reflectance in the crystalline state as described above.
Needless to say, the present invention can be applied to the case where an AD type super-resolution disc is used, and various modifications can be made without departing from the structure 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 a sufficient difference between the reflectance in the molten state and the reflectance in the crystalline state is not obtained, Without mixing the information signals reproduced from the lower part,
Only the information signal reproduced from the portion having a high reflectance can be surely detected, and the reproduction characteristic can be improved.

[Brief description of drawings]

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

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

FIG. 3 is an enlarged schematic cross-sectional view showing the 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 disc.

[Explanation of symbols]

 1 recording pit 2 transparent substrate 3 material layer 11 optical disk 12 light source 13 collimating lens 14 diffraction grating 15 deflected beam splitter (PBS) 16 quarter wave plate 17 objective lens 18 beam splitter 19 cylindrical lens 20 condenser lens 21 condenser lens 22 Detecting element for servo signal 23 Detecting element for information signal

Claims (4)

[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 reflectance changes when the temperature reaches a predetermined value or more. An optical disk reproducing apparatus characterized in that a reproduction signal is detected at a confocal position. 2. An optical disk comprising a transparent substrate on which recording pits are formed according to an information signal, and a material layer whose reflectance decreases when the temperature exceeds a predetermined value. The optical disc reproducing apparatus according to claim 1. 3. An optical disk comprising a transparent substrate, on which recording pits are formed according to an information signal, and a material layer whose reflectance increases when the temperature reaches or exceeds a predetermined value. The optical disc reproducing apparatus according to claim 1. 4. The return light of the optical disk imaged on a confocal point, wherein only the light returned from a portion having a high reflectance at a temperature equal to or higher than a predetermined value is detected. The optical disk reproducing device according to item 1.