JPH09293274A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain RF signals of high quality at an approximately twice higher recording density and a stable track error signal by forming information in the form of phase pits on a disk and selecting the track pitch of information tracks at a prescribed range or below. SOLUTION: The track pitch 6 is so selected as to attain about >=1.1 to <=1.25μm as a condition for forming the phase pits on the polycarbonate substrate 1. Further, the pits are so formed that the shortest mark length 18 attains >=0.6 to <=0.7μm. The pitch depth is determined by applying a resist on a glass master disk at a prescribed thickness and cutting the dried glass master disk to form a stamper. The injection molding of the substrate 1 having 1.2mm thickness is executed by using this stamper. An aluminum reflection film 2 is formed on the side formed with the pits of the injection molded substrate 1. Further, a protective coat 7 for protecting the reflection film 2 is formed at the prescribed thickness, by which the optical recording medium is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a read-only optical recording medium in which information is composed of phase pits.

[0002]

2. Description of the Related Art A conventional compact disc is a read-only optical recording medium recorded as phase pits according to EFM modulation, has a track pitch of 1.6 μm, and has a minimum mark length of 3T pits of 0. 833μ
m to 0.972 μm. Generally, a recording capacity of about 650 MB is available. Recently, in the read-only optical recording medium, a demand for expansion of the recording capacity has increased, and a large capacity standard of 4.7 GB such as DVD has been proposed. However, in order to realize this, securing an inexpensive short wavelength semiconductor laser and an objective lens with a numerical aperture of 0.60, and an inexpensive disk manufacturing process are indispensable. Also, the specifications are quite strict compared to compact discs. For example, 0.60m
It is a structure in which m-thick substrates are bonded together with UV resin, and an assembly process that suppresses warpage of the substrates is required, which includes an extremely complicated process, which greatly affects the yield and supplies low-priced drive devices and disks. Is in a difficult situation.

[0003]

In the manufacture of an optical recording medium having a recording capacity approximately twice that of a conventional compact disk, laser cutting, development, electroconductivity, which is used for manufacturing a compact disk currently in operation, The stamper manufacturing equipment such as electroforming and polishing processes and the substrate injection molding equipment can sufficiently support the high quality RF signal and 3 even if the optical pickup used for reproducing the conventional compact disc is used as it is. It is to realize a disk structure that can obtain a stable track error signal by the spot method or the heterodyne method.

Another object of the present invention is to provide a read-only recording medium having an information density which is approximately doubled and which can be reproduced by an optical pickup used for reproducing a compact disc.

[0005]

In order to solve the above-mentioned problems, according to the present invention, information is formed as phase pits on a disk made of an optically transparent substrate having spirally formed information tracks. Therefore, we propose an optical disk medium in which the track pitch of the information tracks is selected to be approximately 1.1 μm or more and approximately 1.25 μm or less. Further, according to the present invention, it is advantageous that the shortest mark length of the pit is recorded by an EFM signal or an EFM plus signal of about 0.6 μm or more and about 0.7 μm or less.

[0006]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic enlarged cross-sectional view of a part of a disc-shaped optical recording medium according to an embodiment of the present invention cut in the radial direction. According to the present invention, the track pitch 6 is about 1.1 μm or more and about 1.25 μm as a condition for forming the phase pits in the optically transparent polycarbonate substrate 1 having a refractive index of about 1.58.
Make the following selections. Further, according to the present invention, the shortest mark length 18 of 3T of the pit is formed to be about 0.6 μm or more and about 0.7 μm or less. In this evaluation, the pit depth is, for example, 117n, which corresponds to 4.2 wavelengths.
m and the 141 nm thickness corresponding to 1 / 3.5 wavelength are divided into two cases, a glass master is coated with a resist, and the glass master is baked and dried by using an Ar laser cutting device used for manufacturing a compact disc. A stamper was created through cutting, development, electroconductivity, electroforming, and polishing. The pit depth may be made a little shallower in order to detect the push-pull track error signal. The pit opening width 3 and the pit bottom width 4 are adjusted by adjusting the emission power and the objective lens numerical aperture in the laser cutting device, but the shapes of the pit opening width 3 and the pit bottom width 4 are not limited to this. Further, a 1.20 mm thick polycarbonate substrate 1 was injection molded using the stamper. On the injection-molded polycarbonate substrate 1, an aluminum reflective film 2 was formed by a sputtering device on the side where the pits were formed. Further, a protective coat 7 was formed with a spin coater to a thickness of about 12 μm to protect the aluminum reflection film. The signal evaluation of the optical recording medium manufactured through the above-described steps was performed. Table 1 shows data of the examples of the optical recording medium of the present invention. λ is the laser wavelength used.

[0007]

[Table 1]

The optical pickup used for the evaluation is a combination of a 780 nm semiconductor laser used in a compact disc and a finite objective lens with a numerical aperture of 0.45. If The three-spot method and the heterodyne method or the push-pull method can be used to generate the track error signal. In the optical recording medium of the present invention, the pit signal is EFM modulated or E
Recorded according to FM plus modulation. The signal amplitude of 3T with respect to the signal amplitude of 11T is reduced to less than half that of a normal compact disc in any of the optical recording media manufactured in this embodiment. However, all the optical recording media are inexpensive amplitude equalization circuits (SSI programmable filters).
Since the amplitude of 3T can be increased and the effect of inter-pit interference can be sufficiently suppressed by adding, the signal quality satisfying the compact disc standard (block error rate of 3% or less) can be easily obtained. Table 2 shows the results. B
LER is an abbreviation for block error rate, 735
The number of errored blocks in 0 blocks is displayed in percentage. Furthermore, the jitter was also measured. The 3T signal, which is the most severe shortest mark, was investigated instead of the average jitter. In this measurement, the 3T signal is 720
It is a jitter value (standard deviation) when set to kHz. That is, the time width of the 3T pit and space is about 6
The window width Tw is about 231 nsec at 94 nsec. Here, the jitter percentage is expressed as a percentage of the window value of the jitter value. In each disc, BLER is 3% or less and jitter is 30 nsec or less with a considerable margin.

[0009]

[Table 2]

Since most of the optical pickups currently used for reproducing a CD compact disc adopt the 3-spot method, the track error signal by the 3-spot method was also evaluated. FIG. 2 shows the positional relationship between the three spots generated by the diffraction grating and the track (pit row). FIG. 2A shows that the track pitch of the CD according to the present invention is about twice as large as that of the CD and is about 1.1 μm or more and about 1.25 μm.
For example, the positional relationship between the + 1st order light 9, the 0th order light 10 and the −1st order light 11 with respect to the pit 8 in the disk having the track pitch 6 of 1.15 μm is shown below. In the CD pickup, the rotation angle of the diffraction grating is optimized to a track pitch of 1.60 μm, so the phase difference between the cross track signals from the + 1st order light and the −1st order light deviates from 180 degrees, and the track error signal is It will be greatly reduced. But,
When the diffraction grating angle of the pickup is optimized to a track pitch of 1.15 μm, the phase difference between the cross track signals from the + 1st order light and the −1st order light is approximately 180 degrees, and the amplitude of the track error signal becomes maximum. .

In addition, FIG. 2B shows a + 1st order light, a 0th order light and a -1 for a pit 8 having a track pitch of 1.60 μm and a 3T minimum mark length of 0.833 μm to 0.972 μm in a conventional CD disk. The positional relationship of the next light is shown. In the conventional CD head, the rotation angle of the diffraction grating is 1.60.
Since it is optimized for the μm track pitch, the track error signal with the maximum amplitude can be obtained. On the other hand, when the diffraction grating rotation angle of the optical head is about double the capacity of the present invention and the track pitch is optimized to a disk having a track pitch of about 1.1 μm or more and about 1.25 μm or less, for example, 1.15 μm track pitch.
The track error signal amplitude of a CD disc having a 60 μm track pitch is slightly reduced, and the phase difference between the cross track signals from the + 1st order light and the −1st order light is exactly 180 for a disk having a 1.15 μm track pitch. Since the amplitude of the track error signal is maximized, the track following performance of a disc with approximately twice the density can be significantly improved without deteriorating the track following performance of the conventional CD disc. FIG. 3 shows a schematic diagram of a circuit for generating a track error signal by the 3-spot method. 4-split photo detector 1
Obtain the RF output (A + B + C + D) from 2. The focus error signal is similarly generated by the 4-division photodiode 12 using the astigmatism method utilizing the change of (A + C)-(B + D). Generally, an astigmatism is positively used by using a half mirror or a cylindrical lens that is inclined. Photodetector 13 is generated +1
The cross-track signal 15 of the next light and the cross-track signal 16 of the −1st-order light generated by the photodetector 14 are input to the differential amplifier, respectively, and the track error signal TE is input.
Get S. It can be seen that TES provides maximum amplitude when the phase difference between cross-track signals 15 and 16 is 180 degrees. The track error signal when the heterodyne method with one beam was used was also examined. The operation of the heterodyne method will be described with reference to FIG. The focus error signal is generated by the 4-division photodiode 17 using the astigmatism method based on the change of (A + C)-(B + D) as in the three-spot method. The S1 output (A + C)-(B + D) and the S2 output (A + B + C + D) are obtained from the 4-division photodiode 17. The S1 output is also used as the focus error signal as described above. When the focal point of the objective lens and the recording surface of the optical recording medium coincide with each other, the S1 output is zero at the center of the pit and increases when the spot deviates from the center, and the phase varies depending on the direction of deviation. The S2 output is an RF signal generated by the pit, and the signal amplitude becomes maximum at the center of the pit, and monotonically decreases when the spot deviates from the center. By inputting S2 to the falling pulse generation circuit FPG and the rising pulse generation circuit RPG, S3 is input.
And S4 pulse. S3 and S4 function as a sampling pulse, and S1 passing through the gate G1 by S3 is generated by the hold circuit H1 as S5. Similarly, S1 which passed G2 by S4 generates S6 by the hold circuit H2. At this point, S5 and S6 have been converted from the RF band to the track error signal band. Further, by taking the differential signals of S5 and S6, the track error signal TES having no DC component can be obtained. In each of the disks shown in Table 1, the signal amplitude is reduced as compared with the conventional 1.60 μm track pitch, but it is 50% of the conventional one.
The above signal amplitude is obtained and stable tracking control can be performed. Table 3 shows the results regarding the track error signal for the disks shown in Table 1. 1.60 in the tracking method by the three-spot method and the heterodyne method
It is a percentage display for the maximum amplitude obtained on a disc with a μm track pitch.

[0012]

[Table 3]

[0013]

By using the optical recording medium of the present invention, it is possible to effectively use the equipment for manufacturing the conventional compact disk, and to provide a low-cost optical recording medium having a recording capacity approximately twice that of the conventional compact disk. Can be supplied. Also,
A stable track error signal can be obtained even with an optical pickup used for reproducing a conventional compact disc, and a high-quality RF signal can be obtained by a simple method of adding an inexpensive amplitude equalization circuit to a reproducing device. Can get
120 minutes or more of musical sound or 120 minutes or more of MPEG1
Supports video playback.

[Brief description of drawings]

FIG. 1 is a partially enlarged schematic cross-sectional schematic view of an optical recording medium of the present invention cut in a radial direction.

Figure 2: +/- 1 generated by pit train and diffraction grating
It is a figure which shows the positional relationship of secondary light and zero-order light.

FIG. 3 is a block diagram illustrating a generation principle of a three-spot tracking method.

FIG. 4 is a block diagram illustrating the generation principle of the heterodyne tracking method.

[Explanation of symbols]

1 Polycarbonate substrate, 2 Aluminum reflective film,
3 pit opening width, 4 pit bottom width, 5
Pit depth, 6 track pitch, 7 protective coat, 8 pit, 9 + 1st order light, 100
Next light, 11-1 order light, 12 4 division photo detector, 13 photo detector, 14 photo detector, 15 cross track signal, 16
Cross-track signal, 17 4-division photodiode, 18-pit shortest mark length

Claims (2)

[Claims] 1. Information is formed as phase pits on a disc made of an optically transparent substrate having spirally formed information tracks, and the track pitch of the information tracks is approximately 1.1 μm or more and approximately 1. An optical recording medium characterized by being selected to be 25 μm or less. 2. The optical recording medium according to claim 1, wherein the pits of the information track are recorded by an EFM signal or an EFM plus signal having a shortest mark length of about 0.6 μm or more and about 0.7 μm or less. .