JPH09293264A - Optical disk reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low cost reproducing device by combining a semiconductor laser, an objective lens and a diffraction grating. SOLUTION: A pickup is constituted of the semiconductor laser 2, the objective lens 1, a focusing half mirror 4, a tracking diffraction grating 3 and a photodetector 5. Then, the pickup is constituted so as to combine the laser 2 of 760nm < the wavelength < 790nm, the lens 1 of nearly 0.4 < the numerical aperture < nearly 0.47 and the three spots tracking diffraction grating 3. In such a manner, the positional relation in a disk with a narrow track pitch, e.g. 1.15μm when the diffraction grating is adjusted to the disk with a wide track pitch of 1.60μm, and the positional relation in the wide track pitch of 1.60μm when the diffraction grating is adjusted to the wide track pitch of 1.60μm are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc reproducing apparatus composed of information phase pits.

[0002]

2. Description of the Related Art A conventional compact disc is a read-only optical disc medium recorded as phase pits according to EFM modulation, and the track pitch of information tracks formed in a spiral shape is set to 1.6 μm and the shortest mark. The length of the 3T pit is set to 0.833 μm to 0.972 μm. To reproduce such a conventional compact disc, an optical system combining a semiconductor laser with a wavelength of about 780 nm and an objective lens with a numerical aperture of 0.45 is used. The astigmatism method is used for focus control, and the tracking method is used for tracking. The three-spot method is used, and a recording capacity of about 650 MB is generally available.
Recently, even in the case of a read-only optical disk medium, the demand for the expansion of the recording capacity is increasing, so that 4.7 as in the DVD is used.
A large capacity standard called GB has been proposed. However, in order to realize it, it is essential to have a short wavelength semiconductor laser of 630 nm, a large aperture objective lens with a numerical aperture of 0.60, and a substrate thickness of 0.6 mm. In order to be compatible with an optical head using an objective lens and a compact disc with a substrate thickness of 1.2 mm, the specifications are quite strict. For example, it has a structure in which substrates having a thickness of 0.60 mm are adhered with a UV curable resin, and an assembly process for suppressing the warp of the substrates is required, which includes an extremely complicated process, which greatly affects the yield. Supplying low-priced drives and disks is difficult.

[0003]

A conventional compact disc having a track pitch of 1.6 μm, in which information is formed as phase pits on an optically transparent substrate, and a track pitch having a recording capacity about twice that of the conventional compact disc, for example. Is almost 1.
A narrow disk with a size of 1 μm or more and 1.3 μm or less, eg 1.1
An optical pickup that combines a 5-μm disc with a three-spot tracking method equipped with an objective lens and a diffraction grating, which have the same numerical aperture as a compact disc, is used to place a high-quality RF signal and stability on any disc. Disc medium having a disc structure and an optical head capable of obtaining a proper tracking error signal, and reproducible by an inexpensive optical pickup used for reproducing a compact disc, and a reproduction-only disc medium having approximately twice the information density. It is to provide a reproducing apparatus for reproducing the.

[0004]

In order to solve the above-mentioned problems, the present invention reproduces two kinds of optical recording media composed of pit rows having different track pitches, and has a wavelength of 760 nm.
Above 790 nm semiconductor laser and numerical aperture 0.4
In an optical information detection device in which an objective lens of 5 or more and 0.47 or less and a diffraction grating are combined, a disk having a narrower track pitch is irradiated to generate +/− 1
The reproducing apparatus is arranged so that the diffraction grating is arranged so that the phase difference of the cross-track signal of the secondary reflected light becomes approximately 180 degrees. As another means, the diffraction grating is set to an angle that gives a tracking signal of + 1 / -1 order light obtained at a narrower track pitch to give 50% or more of a tracking signal of + 1 / -1 order light obtained at a wider track pitch. This is to supply a reproducing device to be arranged.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Table 1 shows an example of two types of disk specifications having different recording capacities used in the present invention. In Table 1, the disc is formed in a spiral shape by modulating information as phase pits on an optically transparent substrate.
The D disc has a track pitch of 1.6 μm and the double-density optical disc has a capacity of about 2
1 shows a disk having a track pitch of approximately 1.1 μm or more and approximately 1.3 μm or less, which is an embodiment of the present invention in which recording is performed with double the high density. Both disk substrate thickness is 1.2mm
It is. It is necessary to reproduce these two types of discs with the same reproducing device.

In order to solve the above problems, the present invention provides a wavelength 7
A semiconductor laser of 60 nm or more and 790 nm or less, a finite objective lens with a numerical aperture of approximately 0.45 or more and approximately 0.47 or less, and 3
This is realized by an optical information detection device using an optical pickup in which a diffraction grating for spot tracking is combined. In addition to the three-spot method, the heterodyne method can be used in the present invention for generating the tracking signal. The pit signal recorded on the optical disk medium of the present invention complies with EFM modulation. The reproduction signal amplitude of the minimum pit 3T with respect to the signal amplitude of 11T is reduced to 50% or less in the double-density optical disc as compared with the normal compact disc. However, all the optical recording media are inexpensive amplitude equalization circuits (SSI).
The 3T amplitude can be increased by adding a programmable filter manufactured by the company, and the effect of pit-to-pit interference can be sufficiently suppressed, so that a signal quality that satisfies the compact disc standard (block error rate 3% or less) can be easily obtained. To be

[0007]

[Table 1]

Next, the tracking signals of the two types of disks shown in Table 1 were evaluated. As a tracking method, the three-spot method adopted in most compact disk player optical pickups was evaluated. FIG. 1 is a block diagram of an optical pickup by the three-spot method using a diffraction grating used in an embodiment of the present invention.
In FIG. 1, the pickup includes a semiconductor laser 2, an objective lens 1, an obliquely tilted half mirror 4 for generating astigmatism for focusing, a diffraction grating 3 for tracking, and a photodetector 5.

FIGS. 2A and 2B show the positional relationship between the three spots generated by the diffraction grating and the disc tracks (pit rows) having two kinds of track pitches. FIG. 2A shows a positional relationship in a disc having a narrow track pitch, for example, 1.15 μm when a diffraction grating is adjusted to a disc having a wide track pitch of 1.60 μm, and FIG.
FIG. 6 is a plan view showing a positional relationship in a wide track pitch of 1.60 μm when a diffraction grating is adjusted to a wide track pitch of 0 μm. FIG. 3 shows a configuration diagram of a tracking signal forming circuit by the three-spot method. In FIG. 3, the RF output (A + B + C + D) is obtained from the four-division photo detector 12. The focus signal is also 4
By the divided photodiode 12, (A + C)-(B +
It is generated by using the astigmatism method utilizing the change of D).
The + 1st order light crosstrack signal 15 generated by the photodetector 13 and the −1st order light crosstrack signal 16 generated by the photodetector 14 are input to a differential amplifier, respectively, to obtain a tracking signal TES. It can be seen that the tracking signal TES gives the maximum amplitude when the phase difference between the cross track signals 15 and 16 is 180 degrees.

Next, the tracking error signal by the three-spot method was evaluated for two kinds of disks, which are one of the embodiments of the present invention shown in Table 1. The optical pickup used is an embodiment of the present invention and has a wavelength of 760 nm or more.
A semiconductor laser having a wavelength of 90 nm or less and a numerical aperture of about 0.
This is a combination of a finite system objective lens of 45 or more and approximately 0.47 or less and a diffraction grating for three-spot tracking.

Evaluation Experiment 1 (where the angle of the diffraction grating is 1.60 μm)
Pickup optimized for a disc with a wide track pitch of m): In this case, the phase difference between the cross track signals 15 and 16 from the + 1st order light and the -1st order light with respect to the pits in the 1.6μm track pitch disc is accurate. 18
It is 0 degrees. On the other hand, however, the phase difference between the cross track signals 15 and 16 from the + 1st-order light and the -1st-order light with respect to the pits in the disc having the narrower track pitch, for example, 1.15 μm, is largely deviated from 180 degrees. In this case, it was found that the tracking control of the double-density disc becomes unstable.

Evaluation experiment 2 (when a disc having a narrow track pitch of the diffraction grating, for example, a pickup optimized for a 1.15 μm track pitch is used): In this case, +1 for a pit in the disc having a 1.15 μm track pitch. The phase difference between the cross track signals 15 and 16 from the secondary light and the primary light is exactly 180 degrees. However, when the signal amplitude of the tracking signal was measured using a wider disc having a track pitch of 1.60 μm, it was 30% compared with the case where the track was adjusted to a track of 1.6 μm.
Although it is reduced to some extent, it has been found that there is no problem in tracking control of a disc having a track pitch of 1.60 μm.

From the above experiment, the redundancy in the tracking signal is practically required, and therefore even when reproducing a disc having a track pitch of 1.60 μm.
It is desirable to secure 50% or more of the maximum amplitude of the tracking signal obtained at a track pitch of 1.60 μm. In this case, the signal amplitude is reduced as compared with the conventional optical pickup in which the rotation angle of the diffraction grating is adjusted at the track pitch of 1.60 μm so that the tracking signal is maximized, but the signal amplitude of 50% or more of the conventional one is obtained. As a result, a 1.60 μm disk can be stably controlled for tracking.

Further, an embodiment of the present invention will be shown. The rotation angle of the diffraction grating shown in FIG. 1 is adjusted so that the phase difference between the cross track signals 15 and 16 from the + 1st order light and the −1st order light with respect to the pits in the disc having a narrow track pitch is approximately 180 degrees. Good. In that case, + for the pits on the disc with a wider track pitch of 1.6 μm
Cross-track signals 15 and 16 from primary light and -primary light
Although the phase difference of is deviated from 180 degrees and the tracking signal amplitude is slightly reduced, the signal amplitude for the disc having a narrower track pitch can be greatly improved.

Next, a track error signal using the one-beam heterodyne method was also investigated. FIG. 4 is a schematic circuit diagram for explaining the operation principle of the heterodyne method. 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. S1 output (A + C)-(B + D) from the 4-division photodiode 17 and S
2 outputs (A + B + C + D) are obtained. 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. The S3 and S4 pulses are obtained by inputting S2 to the falling pulse generation circuit FPG and the rising pulse generation circuit RPG. S3 and S4 function as sampling pulses, and S3 causes gate G1
After passing S1, S5 is generated by the hold circuit H1. 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 tracking 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 50% or more of the conventional signal amplitude is obtained and stable tracking control can be performed.

[0016]

By using the optical recording medium of the present invention, it is possible to reproduce a conventional compact disc and a disc having a recording capacity approximately twice that of the conventional compact disc, by using the same optical system as that of the conventional compact disc. A low-cost reproducing device can be supplied. That is, even if the conventional optical pickup is used, a stable tracking signal can be obtained, and a high-quality RF signal can be obtained by a simple method of adding an inexpensive amplitude equalization circuit to the reproducing apparatus, and the RF signal of 120 minutes or more can be obtained. It is possible to realize a music sound or an MPEG1-compliant video reproduction of 120 minutes or more.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration diagram of an optical pickup by a three-spot method using a diffraction grating used in the present invention.

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 principle of generating a tracking signal by the 3-spot method.

FIG. 4 is a block diagram illustrating a principle of generating a tracking signal by the heterodyne method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Objective lens 2 Semiconductor laser 3 Diffraction grating 4 Half mirror 5 Photodetector 6 Disk 7 Actuator 8 Pit 9 + 1st order light 10 0th order light 11 -1st order light 12 4 split photodetector 13 Photodetector 14 Photodetector 15 and 16 Cross Track signal 17 4-division photodiode

Claims (6)

[Claims] 1. A disc having a wide track pitch with an information track pitch of 1.6 μm formed in a spiral shape on which information is formed as phase pits on an optically transparent substrate, and the capacity is about twice that of the disc. A disk having a narrow track pitch recorded at a high density and having a track pitch of approximately 1.1 μm or more and approximately 1.3 μm or less is used, and a semiconductor laser having a wavelength of approximately 760 nm or more and a wavelength of 790 nm or less and a numerical aperture of approximately 0.
An optical reproducing device characterized by reproducing by an optical information detecting device using an optical head in which a finite objective lens of 45 or more and approximately 0.47 or less is combined. 2. The head according to claim 1, further comprising a head in which the rotation angle of the diffraction grating is adjusted so that the tracking signals from the narrow track pitch disc and the wide track pitch disc are substantially the same. Optical regenerator. 3. The light whose rotation angle is adjusted so that the phase difference between the cross track signals from the + 1st order light and the −1st order light with respect to the pits on the disc having the narrower track pitch is approximately 180 degrees. The optical reproducing apparatus according to claim 1, further comprising a head. 4. A difference signal of +/− 1st-order reflected light generated by a diffraction grating by irradiating the disk with the narrower track pitch is obtained with the wider track pitch +1.
The optical reproducing apparatus according to claim 1, further comprising an optical head in which the rotation angle of the diffraction grating is adjusted to an angle that gives 50% or more of the difference signal of the / -1st order light. 5. The optical disk reproducing apparatus according to claim 1, further comprising means for reproducing the optical disk by a 3-spot tracking method. 6. The optical disk reproducing apparatus according to claim 1, further comprising means for reproducing the optical disk in a heterodyne system.