JP2611681B2 - Optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optically recordable and reproducible optical recording medium having a pregroove and an address pit.

[0002]

2. Description of the Related Art First, a conventional optical recording medium capable of recording and reproduction will be described with reference to FIGS.
7 and 8, reference numeral 1 denotes an optical recording medium (disk).
In FIG. 7, PG is a pre-groove (in FIG. 7, a concentric pre-groove, but a spiral pre-groove close to a circle may be used), SC is a sector of each pre-groove PG, and AP is a pre-groove. The pre-groove PG for indicating the number of the PG and the number of the sector SC
Are address pits formed at the end of each sector SC. The pitch of the pregroove PG is 2.0 μ
m, and its width is 0.8 μm.

As shown in FIG. 8, this optical recording medium 1 has a single-layer or multi-phase low-melting-point metal layer on which a pre-groove PG for optically recording information is formed on a transparent plastic substrate 2 made of acrylic or the like. (Reflective metal layer) 3 is formed. Here, LD is a land portion of the metal layer 3. Reference numeral 4 denotes a protective layer made of plastic and formed on the metal layer 3. In such an optical recording medium 1, a laser beam from a laser light source is scanned while tracking the pre-groove PG of the metal layer 3, and the pre-groove P
Information is optically recorded in G. The recording is performed by irradiating the pre-groove PG with a laser beam, thereby changing the structure of the metal layer 3 and increasing the reflectivity thereof, thereby performing frequency modulation, phase modulation, Recording is performed so as to form a recording track as a row of optical dots by PCM or the like.
Optical dots can also be formed by melting the metal layer 3 with a laser beam to reduce its reflectance, or by exposing another metal layer below it to increase its reflectance. .

Next, a master 1 'for producing the above-mentioned optical recording medium will be described with reference to FIG. FIG.
A is a partial top view of the master 1 ', and B is a partial sectional view thereof. Reference numeral 5 denotes, for example, a glass substrate, wherein the wavelength of the recording and reproducing beams for the optical recording medium 1 is λ, and the refractive index of the light transmitting layer through which the recording and reproducing beams transmit, that is, the transparent substrate 2 is n. When the thickness is λ / (8n)
The photoresist layer 6 is uniformly deposited so that
This is cut to reach the surface of the glass substrate 5, that is, a laser beam is radiated and developed, whereby each of the pregrooves P has a phase depth of λ / (8n).
G 'and address pits AP' are formed.

Thereafter, as is well known in the art, plating is performed on the photoresist layer 6 remaining on the glass substrate 5 of the master 1 ', and a metal master is formed based on the plating. Make a mother. Then, a stamper is formed from the mother, a light-transmissive resin such as acrylic is stamped using the stamper to form a transparent substrate 2, a light-reflective metal layer 3 is formed thereon, and a protective layer is formed thereon. The layer 4 is deposited (see FIG. 8).

[0006]

In the master 1 'of the optical recording medium 1 shown in FIG. 9, the thickness of the photoresist layer 6 applied on the glass substrate 5 is 600.
In addition to the drawbacks of being extremely thin, about 800 °, having a non-uniform thickness and causing pinholes, the pre-groove P
Since both the phase depth of G ′ and the phase depth of the address pit AP ′ are λ / (8n), the following problem occurs. That is, first, the amount of light reflected by the metal layer 3 of the optical recording medium (disk) 1 shown in FIGS. 7 and 8 will be described with reference to FIG. Assuming that the amount of reflected light when the light reflecting metal layer 3 has an ideal mirror surface is I _O , the amount of reflected light I _TOP on the land portion LD of the metal layer 3 is substantially equal to I _O. S _AP indicates a portion where the amount of reflected light is modulated by the address pit AP, and its peak level is defined as I _PP . S _RP indicates the modulation of the amount of reflected light when an information signal is recorded in the pre-groove PG and is reproduced, and I _RP indicates its peak value. The phase depth of the pregroove PG is λ / (8n)
Therefore, the level of the tracking error signal (push-pull signal) becomes large, but on the other hand, the phase depth of the address pit AP becomes λ / similar to that of the pre-groove PG.
(8n), as can be seen from FIG.
It can be seen that the peak value of the reproduction light amount from the address pit AP is extremely small, that is, 20 to 30% of _IO .

Conversely, in order to increase the peak value I _{PP of the} amount of reproduced light from the address pit AP, the address pit AP
If the phase depth of both the pre-groove PG and the pre-groove PG is set to λ / (4n), the level of the tracking error signal decreases, and the degree of modulation of the pre-groove PG increases, thereby lowering the S / N of the reproduction information signal. .

Therefore, in order to satisfy both requirements, at the time of manufacturing the master 1 ′, the λ / (4n)
A thick photoresist layer 6 is deposited and formed.
The phase depth of each pregroove PG 'is λ / (8n),
In the address pit AP ', the phase depth is λ /
(4n) may be considered. But,
In this case, the photoresist layer is formed of a pre-groove PG '.
The process control is difficult because of the half-tone exposure in the part, and the photoresist layer exposed in the half-tone is inconsistent in the development,
When the phase depth of the address pit AP 'becomes non-uniform, recording is performed on the disk 1 made based on this, and when the address pit AP is reproduced from now on, the S of the reproduced signal is
/ N is worse.

Conventionally, information is recorded in the pre-groove PG of the optical recording medium 1, so that the reproduction information signal S
/ N was small, and the possibility of dropout was high.

In view of the foregoing, the present invention provides an optical recording medium having a pre-groove and an address pit, which is optically recordable and reproducible. The present invention intends to propose a device capable of reproducing an information signal having a good S / N, a small dropout, and a good S / N.

[0011]

SUMMARY OF THE INVENTION According to the present invention, when the wavelength of a recording and reproducing beam is λ, and the refractive index of a light transmitting layer through which the recording and reproducing beam passes is n, optical recording and reproducing are performed. A concentric or spiral pre-groove having a phase depth of λ / (8n) is formed on the beam incident surface side of the reproducible recording layer, and λ / ( 4n) An optical type wherein an area in which an address pit having a phase depth of 4n) is formed and an area in which an information signal is continuously recorded and reproduced are provided in the area where the address pit is formed. It is a recording medium.

[0012]

According to the optical recording medium described above, even if the level of the tracking error signal is large and the degree of modulation of the pre-groove PG is slightly varied, the influence on the reproduction information signal is small, and the address pit AP is set to S. / N can be reproduced with good yield, good S / N, and low possibility of dropout. Also, address pit AP
Since the tracking error signal is zero, no disturbance is mixed into the tracking error signal by the address pit AP. Since no information signal is recorded on the pre-groove PG, its width can be reduced, which leads to an improvement in recording density.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of an optical recording medium master according to the present invention will be described below with reference to FIG. 7 and 8, the photoresist layer 6 is formed on the glass substrate 5.
Is formed, and the thickness in this case is λ / (4n). Then, as will become clear from the later description, the photoresist layer 6 is cut by exposure and development until reaching the surface of the glass substrate 5 using two beams as address pits AP '.
G 'is formed at a phase depth of λ / (8n) using a beam having a smaller amount of light than a beam forming the address pit AP'.

The master 1 'thus formed is
The optical recording medium 1 as shown in FIG. That is, a pregroove PG having a phase depth of λ / (8n) is formed on a transparent substrate 2 made of acrylic or the like.
And the low melting point metal layer 3 on which the address pits AP having a phase depth of λ / (4n) are formed. 4 is a protective layer. In this case, the pre-groove PG is formed on the land portion LD of the metal layer 3, the pitch is 2 μm, the interval between the pre-groove PG and the address pit AP is 1 μm,
Each width is 0.5 μm. The information signal is recorded at the center of the land LD of the metal layer 3.

It is needless to say that the beam from the co-optical system during recording and reproduction enters the metal layer 3 of the medium 1 from the transparent substrate 2 side. The amount of reflected light of the optical recording medium 1 thus obtained will be described with reference to FIG. 3. In FIG. 3, portions corresponding to FIG. 10 are denoted by the same reference numerals, and redundant description will be omitted. In this case, the peak level I _PP due to the modulation of the reflected light amount of the address pits is 50 to 60% of I _O , and FIG.
It can be seen that it is significantly larger than in the case of.

The optical recording medium thus formed uses one beam, reproduces the address pits AP on the land LD, detects the tracking error signal, and outputs information to the land LD by dots. The signal is recorded. Further, detection of a tracking error, reproduction of an address pit AP, and recording of an information signal may be performed using three beams. Also at the time of reproduction, the same device can reproduce an information signal that has been phase-modulated or frequency-modulated and PCM-recorded on the land LD.

According to the above-mentioned optical recording medium, even if the level of the tracking error signal is large and the degree of modulation of the pre-groove is slightly varied, the influence on the reproduced information signal is small, and the address pits are reduced by the S / N ratio. An information signal that can be reproduced well, has a good yield, has a good S / N, and has a low possibility of dropout can be reproduced. Also, since the tracking error signal for the address pit is zero, no disturbance is mixed into the tracking error signal by the address pit. Since no information signal is recorded in the pregroove, the width can be reduced, which leads to an improvement in recording density.

Next, an apparatus for manufacturing a master of the above-mentioned optical recording medium will be described with reference to FIG. 7 is a laser light source (e.g., Ar or He-Cd laser light source), than this example is emitted laser beam LB _O S-polarized light,
This is incident on the beam splitter 8 and split into first and second beams LB ₁ and LB ₂ . The optical path of the first beam LB ₁ is deflected by 90 ° by the beam splitter 8, and the optical path of the second beam LB ₂ is deflected by 90 ° by the mirror 9 after going straight.

These first and second beams LB ₁ , LB
₂ is supplied to first and second optical modulators (electro-optical elements) 12 and 13 via lenses 10 and 11, respectively. First
Is supplied with a DC voltage from a DC power supply 14. Pulse signal from the signal source 15 to the second optical modulator 13, i.e., is supplied with an address signal indicating a track number and sector number, the second beam LB ₂ is optically modulated. FIGS. 5 and 6 show the first and second optical modulators 12, 12, respectively.
13 shows the waveform of the beam obtained from FIG. The intensity of the beam for exposing the photoresist layer 6 is weakened by the voltage applied to the first and second optical modulators 12 and 13,
The latter can be adjusted to be stronger.

The first and second optical modulators 12 and 13
S and P-polarized beams LB ₁ and LB ₂ obtained from the mirrors 18 and 19 via convex lenses 16 and 17, respectively.
And its optical path is deflected by 90 °. First
Beam LB ₁ is further reflected by mirror 20 so that
The light is deflected by 0 ° and is incident on the polarization beam splitter 21. Further, the second beam LB ₂ deflected by 90 ° by the mirror 19 is also deflected by the deflection beam splitter 2.
1 is incident.

Then, the first and second beams LB ₁ and LB ₂ emitted from the polarization beam splitter 21 are converted into a convex lens 2.
After the optical paths have been made to 90 ° deflected to the mirror 23 via the 2, focused beam and made incident on the objective lens 24, the beams LB _1, the glass substrate described above LB ₂ is with a spacing of 1 [mu] m 5 Irradiation is performed on the photoresist layer 6 formed thereon, and the photoresist layer 6 is exposed. This exposed photoresist layer 6
By developing, the portion exposed to light is removed, and a pre-groove PG 'and an address pit AP' as shown in FIG. 2 are formed.

According to the optical recording medium master manufacturing apparatus described above, the optical recording medium master can be easily manufactured.

By changing the polarity of the tracking servo circuit, tracking of the optical recording disk according to the present invention using a conventional optical recording / reproducing apparatus is easy.

[0024]

According to the optical recording medium of the present invention described above, when the wavelength of the recording and reproducing beam is λ, and the refractive index of the light transmitting layer through which the recording and reproducing beam passes is n, A concentric or spiral pre-groove having a phase depth of λ / (8n) is formed on the beam incident surface side of the recording layer capable of recording and reproducing information, and a region sandwiched by the pre-groove is formed. , And λ / (4n) address pits are formed, and information signals are recorded. Therefore, the pits have pregrooves and address pits, and can be optically recorded and reproduced. In a recording medium, there is no possibility that disturbance is mixed in the tracking error signal, the level of the error signal is large, the S / N of the reproduced signal of the address pit is good, and the dropout is small. Ku, it is possible to reproduce a good information signal S / N, can be obtained which can improve the recording density. According to the optical recording medium of the present invention, the area where the address pit having the phase depth of λ / (4n) is formed in the area sandwiched by the pregrooves having the phase depth of λ / (8n). And a region where information signals are recorded and reproduced continuously in the area where the address pits are formed. Therefore, as shown in FIG. In recording or reproducing an information signal on or from a recording medium, it is possible to correctly read address information by a beam that scans the area where the address pits are formed. Recording and reproduction operations can be favorably performed in a continuously provided information signal recording and reproduction area.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an optical recording medium according to an embodiment of the present invention.

FIG. 2A is a plan view showing an optical recording medium master according to an embodiment of the present invention. B is a cross-sectional view showing an optical recording medium master according to an example of the present invention.

FIG. 3 is a curve diagram showing characteristics of reflected light of the optical recording medium according to the embodiment of the present invention.

FIG. 4 is a layout diagram showing an optical recording medium master manufacturing apparatus according to an embodiment of the present invention.

5 is a waveform diagram showing a waveform of an output beam of a first optical modulator in the master disc manufacturing apparatus of FIG.

6 is a waveform diagram showing a waveform of an output beam of a second optical modulator in the master disc manufacturing apparatus of FIG.

FIG. 7 is a plan view showing a conventional optical recording medium.

FIG. 8 is a sectional view showing a conventional optical recording medium.

FIG. 9 is a plan view showing a master of a conventional optical recording medium.

FIG. 10 is a sectional view showing a master of a conventional optical recording medium.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical recording medium 2 Transparent substrate as a light transmission layer 3 Reflective metal layer formed on the transparent substrate 4 Protective layer formed on the reflective metal layer PG Pregroove AP Address pit LD Land part

Claims (1)

(57) [Claims] When the wavelength of a recording / reproducing beam is λ and the refractive index of a light transmitting layer through which the recording / reproducing beam passes is n, a beam of a recording layer capable of optically recording / reproducing. A concentric or spiral pre-groove having a phase depth of λ / (8n) is formed on the incident surface side, and λ / (4n) is formed in a region sandwiched by the pre-grooves.
Region address pits are formed to have a phase depth
And information continuously in the area where the address pits are formed.
An optical recording medium, comprising an area for recording and reproducing signals .