JPH08297884A - Optical recording medium and reproducing method - Google Patents

Abstract

PURPOSE: To make a disk high density recording and to reproduce excellently recording signals on respective signal recording surfaces without complicating the constitution such as the disk and a pickup, etc., by providing plural signal recording surfaces in layers in the disk. CONSTITUTION: This optical recording medium is constituted so that a reflectance reproducing surface of a first signal recording surface reproduced based on a change in a reflectance and a magneto-optical reproducing surface of a second signal recording surface reproduced based on a magneto-optical effect are formed successively from a substrate side. A laser beam is made incident on the optical recording medium, and the intensities of respective polarization components of reflected light are detected by a first photodetector 19 and a second photodetector 17. Then, when the reflectance reproducing surface of the first signal recording surface is reproduced, a recording signal is reproduced from a sum signal of detection signals of the first, second photodetectors 19, 17. When the magneto-optical reproducing surface of the second signal recording surface is reproduced, the recording signal is reproduced from a difference signal of the detection signals of the first, second photodetectors 19, 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for irradiating an optical recording medium with a laser spot and reproducing a recording signal based on the reflected light. Specifically, it relates to high-density recording / reproducing technology.

[0002]

2. Description of the Related Art Optical recording media are used in various fields such as computer memories and music CDs or MDs.
Widely used. In recent years, there has been a demand for higher density so that it can be used for applications such as moving images with a very large amount of information. In order to increase the density of the optical recording medium, for example, a technique for shortening the wavelength of laser light, a magnetic super-resolution technique for improving the reproducing resolution of the magneto-optical recording medium by a magnetically shielded reproducing layer, and the like have been studied. ing.

As a technique for increasing the density of an optical recording medium, a technique for forming a plurality of signal recording surfaces in layers within the optical recording medium has been studied. For example, SPIE Vol.2338 Optical Data Sto
rage / 1994 / 247p-253p / Multilevel Volumetric Optical
Storage / Kurt A. et.al./ reports the results of recording / reproducing on a write-once type (WO) optical recording film having a layer structure of 100 μm intervals.

[0004]

When two or more signal recording surfaces are formed in a single optical recording medium, reproduction is performed without interference with reflected light from other signal recording surfaces that are not the object of signal reproduction. In order to reduce signal noise, the beam diameter when the laser beam passes through the other signal recording surface must be made sufficiently larger than the information unit of the other signal recording surface.

For that purpose, it is necessary to increase the distance between the signal recording surfaces. However, when the distance between the signal recording surfaces is increased, the distance from the substrate surface greatly differs depending on the signal recording surface, so spherical aberration increases and the laser beam converging points are dispersed in the depth direction. A signal recording surface appears in which the signal cannot be reproduced well. In order to avoid this and reproduce the recorded signals on all the signal recording surfaces satisfactorily, the structure of the optical system including the objective lens must be complicated, resulting in high cost. In addition, the above-mentioned Kurt A. e
In t.al., a technology that solves the problem caused by the above spherical aberration by sandwiching an air layer between the signal recording surfaces of the disc is shown, but in this case, the structure of the disc becomes complicated. There is a problem of doing.

An object of the present invention is to achieve a high recording density of a disc by providing a plurality of signal recording surfaces in layers in the disc. Further, at that time, the purpose is not to complicate the structure of the disk and the configuration of the objective lens and the like. Furthermore, it is an object of the present invention to enable the recorded signals on each signal recording surface to be reproduced well.

[0007]

According to the present invention, there is provided a first signal recording surface on which a recording signal is reproduced based on a change in reflectance,
An optical recording medium in which a second signal recording surface on which a recording signal is reproduced based on the magneto-optical effect is formed in layers in order from the substrate side. Further, it is an optical recording medium in which the first signal recording surface and the second signal recording surface have an interval of 5 μm or more. The first signal recording surface is, for example, a signal recording surface formed by pits. The second signal recording surface is, for example, a magneto-optical recording surface on which a recording signal is reproduced by the differential reproduction method.

The present invention also provides a method of irradiating an optical recording medium with a laser beam and reproducing a recording signal based on the reflected light, wherein the optical recording medium (the optical recording medium according to claim 1 or 2 is used). A laser beam is incident from the substrate side of the recording medium), the reflected light from the optical recording medium is divided into two polarization components orthogonal to each other, and the intensities of the respective polarization components are detected by the first and second photodetectors. When the laser spot is focused on the first signal recording surface to reproduce the recording signal, the recording signal is reproduced based on the sum signal of the first and second photodetectors, and the second signal is reproduced. When the laser spot is focused on the signal recording surface to reproduce the recording signal, the first and second signals are recorded.
Is a reproducing method of an optical recording medium, which reproduces a recording signal based on a difference signal of the photodetector.

[0009]

The laser beam reflected by the optical recording medium is separated into two polarization components which are orthogonal to each other, one polarization is guided to the first photodetector and is detected, and the other polarization is the second light. It is guided to the detector and detected. When the laser spot is focused on the first signal recording surface, the sum of the detection signals of the first and second photodetectors is processed as a reproduction signal. When the laser spot is focused on the second signal recording surface, the difference between the detection signals of the first and second photodetectors is processed as a reproduction signal.

[0010]

EXAMPLE As shown in FIG. 2, in the present optical recording medium, a pit recording surface 31, which is a first signal recording surface, is formed on the laser beam non-incident side of a polycarbonate substrate 31, and the pit recording surface is formed.
An aluminum reflection layer 32 having a thickness of 5 nm is formed on 31 by a sputtering method (input power 200 W, Ar gas pressure 5 mTorr), and a width of 0.9 μm and a track pitch of 1.
An ultraviolet curable resin layer 33 having a thickness of 6 μm and a thickness of 30 μm is formed by the 2P method, and further, SiN having a thickness of 40 nm is formed.
The layer 34, the second signal recording surface of the magnetic layer (T
b ₂₅ Fe ₆₅ Co ₁₀ layer) 35 and a SiN layer 36 having a thickness of 80 nm are sequentially formed by a sputtering method (input power 500 w, Ar gas pressure 5 mTorr), and a UV coating layer 37 is spin-coated thereon as a protective film. 10 μm is applied by the method.

The Al reflective layer 32 is about 1/10 of the thickness of the Al reflective layer on the signal recording surface of the current CD, and therefore the reflectance is about 20% and the transmittance is about 50%. It is lower than the current CD. This is in consideration of the case of reproducing the recording signal of the Tb ₂₅ Fe ₆₅ Co ₁₀ layer 35 which is the second signal recording surface. The reflectance of the Tb ₂₅ Fe ₆₅ Co ₁₀ layer 35 was about 15%. The polycarbonate substrate 31 used was an injection molded product.

Next, the reproducing method will be described. The optical pickup 1 shown in FIG. 1 is similar to an ordinary optical pickup for magneto-optical recording and reproduction. That is, the laser light output from the laser diode 11 is made into a parallel beam by the collimator lens 12, passes through the polarization beam splitter 13, and the objective lens 14
Is focused on the signal recording surface (the magneto-optical reproducing layer which is the second signal recording surface in FIG. 1) and reflected by the signal recording surface, then passes through the objective lens 14 and is reflected by the polarization beam splitter 13. Next, it is separated by the polarization beam splitter 15.
As a result, one polarized light is focused on the detection surface of the first photodetector 19 by the converging lens 18, and the other polarized light is focused by the converging lens 16.
Thus, the detection surface of the second photodetector 17 is focused.

When the laser spot is focused on the second signal recording surface (Tb ₂₅ Fe ₆₅ Co ₁₀ layer 35) as in the case shown in FIG. 1, the first photodetector 19 and the second photodetector 19 Photo detector
The differential signal of the detection signals of 17 is generated by the differential amplifier 22,
It is sent as a reproduction signal to a signal processing unit (not shown) in the subsequent stage.
On the other hand, when the laser spot is focused on the first signal recording surface (Al reflection layer 32), the first photodetector 19 and the second
The sum signal of the detection signals of the photodetector 17 is generated by the amplifier 21 and sent as a reproduction signal to a signal processing unit (not shown) in the subsequent stage.

In the reproducing method of the present embodiment, since the recording signal on the second signal recording surface (Tb ₂₅ Fe ₆₅ Co ₁₀ layer 35) is reproduced by the differential detection method, the first signal recording surface (Al The reflected light at the reflective layer 32) is canceled. Therefore,
A good reproduction signal can be obtained because the reflectance is hardly affected by the first signal recording surface (Al reflective layer 32). In the experiment according to this example, the first signal recording surface (Al reflective layer 32) was used.
Even if the distance between the second signal recording surface and the second signal recording surface (Tb ₂₅ Fe ₆₅ Co ₁₀ layer 35) is set to 5 μm, the influence of the reflected light on the other signal recording surfaces is not recognized and a sufficiently good reproduction signal is obtained. I was able to get it. Although the case where the signal recording surface has two layers has been described above, the same effect can be obtained when a signal is reproduced by a differential reproduction method by providing a magneto-optical recording layer.

[0015]

According to the present invention, when the laser spot is focused on the first signal recording surface, the sum of the detection signals of the first and second photodetectors is signal processed as a reproduction signal, and the second signal is processed.
When the laser spot is focused on the signal recording surface of, the difference between the detection signals of the first and second photodetectors is processed as a reproduction signal, so that interference due to reflection on another signal recording surface occurs. It can be prevented, and a sufficiently good reproduction signal can be obtained. In addition, since the distance between the signal recording surfaces can be made sufficiently small, it is possible to prevent problems due to spherical aberration. Further, the above effects can be obtained without complicating the configuration of the optical disc or the objective lens side.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a reproducing method according to an embodiment.

FIG. 2 is a schematic diagram showing a cross-sectional structure of an optical recording medium of an example.

[Explanation of symbols]

 31 substrate 32 Al reflective layer (first signal recording surface) 33 ultraviolet curable resin layer 34 SiN layer 35 TbFeCo layer (second signal recording surface) 36 SiN layer 37 ultraviolet curable resin layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenji Torazawa 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A first signal recording surface on which a recording signal is reproduced based on a change in reflectance and a second signal recording surface on which a recording signal is reproduced based on a magneto-optical effect are sequentially arranged from the substrate side. An optical recording medium formed in layers. 2. The optical recording medium according to claim 1, wherein the distance between the first signal recording surface and the second signal recording surface is 5 μm or more. 3. An optical recording medium is irradiated with a laser beam,
In a method of reproducing a recording signal based on the reflected light, a laser beam is incident from the substrate side of the optical recording medium according to claim 1 or 2, and the reflected light from the optical recording medium is orthogonal to each other. When the intensity of each polarization component is divided into two polarization components and detected by the first and second photodetectors, and the recording signal is reproduced by focusing the laser spot on the first signal recording surface, When the recording signal is reproduced based on the sum signal of the first and second photodetectors and the recording signal is reproduced by focusing the laser spot on the second signal recording surface, A reproducing method of an optical recording medium, which reproduces a recording signal based on a difference signal of the photodetector of 2.