JP2001126277A - Optical disk reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk reproducing method which is capable of dealing with low density reproduction and high density reproduction without changing a beam spot size. SOLUTION: A beam spot 4 is emitted so as to be caught to the edge of a pit 52 formed on an optical disk 50, and a reproduced RF signal without a fold phenomenon is obtained from the photoelectric conversion signal of the reflected beam of the beam spot 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing method capable of reproducing high-density information and ensuring compatibility with information recorded at low density.

[0002]

2. Description of the Related Art In order to realize an optical disk having a high recording density, it is a general method to reduce the track pitch and, accordingly, the width of pits formed on the optical disk. In addition, when a reproduction signal is obtained from an optical disk, it is necessary to irradiate the optical disk with a light beam having a diameter suitable for the pit width (about half the width of the pit).

However, if a reproduction signal is to be obtained from an optical disk having a low recording density with a light beam having the above-mentioned diameter, in other words, an optical disk having pits whose width is larger than the diameter of the light beam, the following method is required. Such a problem arises.

That is, since most of the light beam irradiates the inside of the pit, the reflection and diffraction effect of the light due to the edge is lost. As a result, the reflected light of the light beam increases at the center of the pit, The aliasing occurs in the reproduced signal.

Therefore, conventionally, for example, Japanese Patent Application Laid-Open No. 8-102
As described in Japanese Patent Application Laid-Open No. 079/079, when reproducing an optical disk with a low recording density, a method of providing an aperture and enlarging a laser beam spot is described, or described in JP-A-9-185833 or JP-A-10-208276. Like N
A method has been proposed in which a lens having a different A is switched, or a laser beam spot is enlarged by limiting the aperture using a hologram or the like.

[0006]

However, in the above configuration, the former requires an expensive optical element such as a non-linear optical filter, and the latter requires a pickup structure when switching lenses. When the hologram is used, there is a problem that the efficiency of using the laser beam is deteriorated due to the diffraction loss caused by the hologram.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a method of reproducing an optical disk having a simple configuration and capable of effectively using a laser beam.

[0008]

In order to solve the above-mentioned problems, a method for reproducing an optical disk according to the present invention is characterized in that when reproducing information recorded at a low density, a light beam is formed on an optical disk from an on-track state by a predetermined amount. In the case of reproducing the information recorded at a high density, the light beam is irradiated in an on-track state, and the photoelectric conversion signal of the reflected light of the light beam is used as a reproduction signal. The photoelectric conversion signal of the reflected light of the light beam is used as a reproduction signal.

In another method of reproducing an optical disk according to the present invention, a predetermined interval is provided in a radial direction of the optical disk,
The first light beam in the on-track state and the second and third light beams in the off-track state by a predetermined amount are applied to both sides of the first light beam, respectively. Is reproduced as a reproduction signal using the photoelectric conversion signal of the reflected light of the second and third light beams. When information recorded at high density is reproduced, the reflection of the first light beam is performed. A reproduction signal is obtained by using a photoelectric conversion signal of light.

Further, when the photoelectric conversion signal of the reflected light of the first light beam contains a crosstalk component, the crosstalk component is canceled using the photoelectric conversion signal of the reflected light of the second and third light beams. It is characterized by the following.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 shows a configuration of an apparatus for executing a method of reproducing an optical disk according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a laser light source, and a laser beam emitted from the laser light source 1 is applied to an optical disk 50 via a half mirror 2 and an objective lens 3 to form a beam spot 4. This reflected light is again transmitted through the objective lens 3 and the half mirror 2
The light enters the divided photodetector 5. The photoelectric conversion signals output from the four channels of the four-split photodetector 5 are input to a tracking error signal generation circuit 6 to obtain a tracking error signal 7. The tracking error signal 7 is input to the tracking control / drive circuit 8 and
Is controlled by controlling the actuator 9 on which
The position of the beam spot 4 is controlled in a direction perpendicular to the scanning direction 51, and the beam spot 4 is irradiated on a pit 52 formed on the optical disk 50.

Numeral 10 denotes an offset adding means for adding a predetermined offset to the tracking control / drive circuit 8 to make the beam spot 4 off-track from the center of the pit 52.

The tracking error signal generating circuit 6 may be based on the push-pull method or may be based on the phase difference method.

On the other hand, the reproduction signal 11 is obtained by adding the photoelectric conversion signals output from the four channels of the four-divided photodetector 5 by the full addition circuit 12.

In the first embodiment configured as described above, a reproduction method at the time of low-density reproduction will be described. FIG. 2A shows the reproduction signal 11 when the beam spot 4 is on track with respect to the pit 52, assuming that the diameter of the beam spot 4 is equal to the width of the pit 52.
Of the pit 52 and the beam spot 4 in the scanning direction 5
This is shown in comparison with the positional relationship according to No. 1, and in this case, as described in the related art, a folding phenomenon occurs at the center of the pit.

On the other hand, FIG. 2B shows an arrangement in which the tracking control / drive circuit 8 shown in FIG.
, A predetermined offset is added, and beam spot 4
Shows the waveform of the reproduced signal 11 when the pit 52 is in the off-track state, in comparison with the positional relationship between the pit 52 and the beam spot 4 in the scanning direction 51. In this case, the beam spot 4 By being off-track, since the light is irradiated to the edge portion 53 of the pit 52, the light reflection / diffraction effect is not lost even at the center of the pit. Therefore, the reproduction signal 11
Does not cause the aliasing phenomenon, and can be used as a reproduced RF signal.

In FIG. 2B, the beam spot 4
Is off-track so as to irradiate the edge portion 53 of the pit 52, but it may be off-track so as to irradiate the edge portion 54 of the pit 52. In this case, the polarity of the offset applied to the tracking control / drive circuit 8 may be set to be opposite to the control center.

Next, a reproduction method at the time of high-density reproduction according to the first embodiment will be described. FIG. 2C shows that the diameter of the beam spot 4 is the same as in the low-density reproduction, and the pit 5
When the width of No. 2 is halved compared to the low-density reproduction,
The waveform of the reproduction signal 11 when the beam spot 4 is in the on-track state with respect to the pit 52 is shown in comparison with the positional relationship between the pit 52 and the beam spot 4 in the scanning direction 51. Unlike the low-density reproduction, in this case, the relation between the diameter of the beam spot 4 and the width of the pit 52 is in a state where a sufficient light reflection / diffraction effect is obtained. However, there is no aliasing phenomenon, and therefore, a reproduced RF signal can be obtained.
Therefore, the beam spot 4 does not need to be in an off-track state with respect to the pit 52. In other words, there is no need to add an offset to the tracking control / drive circuit 8 during high-density reproduction.

At the time of low-density reproduction, the beam spot 4
The ratio between the offset amount applied to the tracking control / drive circuit 8 for off-tracking and the maximum value of the tracking error signal (corresponding to the amplitude of the tracking error signal obtained when the tracking control loop is opened) is 30%.
More preferably, it is 50% or less. The basis of this numerical value is the offset amount corresponding to the off-track amount for obtaining a sufficient light reflection / diffraction effect for 30%, and the upper limit offset value for achieving the stable tracking control for 50%. Quantity.

As described above, according to the first embodiment, a simple method without changing the beam spot diameter, that is,
It is possible to cope with low-density reproduction and high-density reproduction only by the presence or absence of an offset added to the tracking control / drive circuit.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described. FIG. 3 shows Embodiment 2 of the present invention.
1 shows a configuration of an apparatus for carrying out a method of reproducing an optical disk in the first embodiment, in which a laser beam emitted from a laser light source 1 is divided into three light beams by a diffraction grating 20 and is transmitted through a half mirror 2 and an objective lens 3. Then, the light is irradiated onto the optical disk 50 as a first beam spot 4a, a second beam spot 4b, and a third beam spot 4c.

The reflected light from the beam spots 4a, 4b and 4c passes through the objective lens 3 and the half mirror 2 again, and is divided into a four-divided photodetector 5a and photodetectors 5b and 5c.
Respectively. As in the first embodiment, the photoelectric conversion signals output from the four channels of the four-segment photodetector 5a on which the reflected light of the beam spot 4a is incident are input to the tracking error signal generation circuit 6 and the tracking error signal 7 is obtained. The tracking error signal 7 is input to a tracking control / drive circuit 8, and by controlling an actuator 9 on which the objective lens 3 is mounted, the position of the beam spots 4a, 4b and 4c is controlled in a direction perpendicular to the scanning direction 51. The light is irradiated onto pits 52 formed on the optical disk 50. Here, the first beam spot 4a is set so as to be in an on-track state.
The second and third beam spots 4b and 4c are irradiated on both sides of the first beam spot 4a so as to be off-track by a predetermined amount.

In the second embodiment, three reproduction signals can be obtained. That is, the photoelectric conversion signals output from the four channels of the four-divided photodetector 5a are
, The reproduced signal 11a obtained by photoelectric conversion by the photodetector 5b.
b, a reproduction signal 11c photoelectrically converted by the photodetector 5c.

In the second embodiment configured as described above, a reproduction method at the time of low-density reproduction will be described. FIG. 4A shows a case where the diameters of the beam spots 4a, 4b, and 4c are assumed to be equal to the width of the pit 52, and the three beam spots are formed on the optical disk 50 when the optical disk 50 is irradiated. The positional relationship with the pits 52 is shown, and the waveforms of the reproduced signals 11a, 11b, and 11c when simultaneously scanned in the scanning direction 51 are shown in comparison. The three beam spots 4a, 4b, 4
The reason why c is irradiated at regular intervals in the direction of the scanning direction 51 and in the direction perpendicular thereto is due to the function of the diffraction grating 20 shown in FIG.

Since the beam spots 4a, 4b, 4c are also arranged at regular intervals in the scanning direction 51, actual reproduction signals 11a, 11b, 11c have a time difference determined by the scanning speed and the interval. In FIG. 4A, the time difference is omitted for simplicity.

In the waveform of the reproduced signal 11a, since the diameter of the beam spot 4a is equal to the width of the pit 52, the light reflection / diffraction effect is lost, and a folding phenomenon occurs. However, the waveforms of the reproduced signals 11b and 11c have a sufficient light reflection / diffraction effect because the beam spots 4b and 4c are radiated to the edge portions of the pits 52. As a result, the reproduced signals have no aliasing phenomenon. Moreover, the waveforms of the reproduced signals 11b and 11c are the same.

Thus, in the low-density reproduction according to the second embodiment, the reproduction signal 11b or the reproduction signal 1
1c can be used as a reproduced RF signal.

The addition signal of the reproduction signal 11b and the reproduction signal 11c may be used as the reproduction RF signal. However, in this case, since the beam spots 4b and 4c are arranged at a constant interval in the scanning direction 51, at the time of addition, the reproduction signal 11b and the reproduction signal 11b are reproduced by using a delay means having a predetermined delay time. It is necessary to correct the time difference that occurs between the signals 11c. If the beam spots 4b and 4c can be arranged in a direction perpendicular to the scanning direction 51 depending on the configuration of the optical system, it is not necessary to correct the time difference by the delay means, and the simplest is possible. A simple addition process is sufficient.

The reproduction RF signal obtained by adding the reproduction signal 11b and the reproduction signal 11c is the reproduction signal 11
Compared to a case where either one of the reproduction signal b and the reproduction signal 11c is used as a reproduction signal, the reproduction signal can be a reproduction signal whose amplitude has been improved twice, and a reproduction RF signal having an advantageous S / N can be obtained.

Next, a reproduction method at the time of high-density reproduction according to the second embodiment will be described. FIG. 4B shows that the diameters of the beam spots 4a, 4b, and 4c are the same as those at the time of low-density reproduction, and the width of the pits 52 is half that at the time of low-density reproduction. 5 shows a positional relationship with a pit 52 formed on the optical disk 50 when the light is irradiated on the optical disk 50, and at the same time, in the scanning direction 51.
2 shows the waveform of the reproduced signal 11a when scanning is performed.

Since the portion irradiated with the beam spots 4b and 4c is between the track scanned by the beam spot 4a and its adjacent track, the light reflection / diffraction effect cannot be obtained, and the reproduced signals 11b and 11c cannot be reproduced. It is merely a DC-like signal, and cannot obviously be a reproduced RF signal. However, by assumption, beam spot 4
Since the relationship between the diameter of “a” and the width of the pit 52 is such that a sufficient light reflection / diffraction effect is obtained, the reproduced signal 11a has no aliasing phenomenon as shown in FIG.
It can be an F signal.

Next, the density is further increased, that is, the pits 52 are formed.
The reproduction method at the time of high-density reproduction according to the second embodiment when the track pitch is small, although the width is the same, will be described. FIG. 5 shows the track pitch shown in FIG.
Beam spots 4a, 4a,
The positional relationship between 4b and 4c and pits 52 formed on the optical disk 50 is shown. According to FIG. 5, it is apparent that the crosstalk component of the adjacent track is mixed in the reproduction signal 11a by the beam spot 4a.
It is often inappropriate to use a as a reproduction RF signal.
In this case, the crosstalk component is canceled by the following method, and a higher quality reproduced RF signal can be obtained. That is, the reproduction signals 11b and 11c obtained from the beam spots 4b and 4c irradiated on the track adjacent to the track scanned by the beam spot 4a are added at an appropriate ratio, and the addition result is used as the reproduction signal 11a obtained from the beam spot 4a. What is necessary is just to subtract.

When the reproduced signals 11b and 11c are added at an appropriate ratio, a means for correcting the time difference generated between the reproduced signals 11b and 11c is required, as described above.

As described above, according to the second embodiment, it is possible to cope with low-density reproduction and high-density reproduction with a simple method, and easily realize a means for canceling crosstalk from an adjacent track. can do.

[0036]

As described above, according to the present invention,
It is possible to cope with low-density reproduction and high-density reproduction with a simple method, and it is possible to obtain a high-quality reproduction RF signal while ensuring compatibility with optical disks having different recording densities.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an apparatus for performing a method of reproducing an optical disk according to a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram of an apparatus for implementing a method of reproducing an optical disc in Embodiment 2 of the present invention.

FIG. 4 is an operation explanatory diagram according to Embodiment 2 of the present invention.

FIG. 5 is an operation explanatory diagram when the track pitch is further smaller in the second embodiment of the present invention;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Half mirror 3 Objective lens 4, 4a, 4b, 4c Beam spot 5, 5a Quadrant photodetector 5b, 5c Photodetector 6 Tracking error signal generation circuit 7 Tracking error signal 8 Tracking control / drive circuit 9 Actuator 10 Offset addition means 11, 11a, 11b, 11c Reproduction signal 12 Full adder circuit 20 Diffraction grating 50 Optical disk 51 Scanning direction 52 Pits 53, 54 Edge portion

Claims (6)

[Claims] When reproducing information recorded at a low density, a light beam is irradiated onto an optical disk in a state where it is off-track by a predetermined amount from an on-track state, and photoelectric conversion of reflected light of the light beam is performed. When a signal is used as a reproduction signal and information recorded at high density is reproduced, the light beam is irradiated in an on-track state, and a photoelectric conversion signal of reflected light of the light beam is used as a reproduction signal. Method of reproducing an optical disk. 2. The method according to claim 1, wherein the off-track state is achieved by adding a predetermined offset amount to a tracking control unit. 3. The method according to claim 2, wherein the predetermined offset amount is not less than 30% and not more than 50% of a maximum value of the tracking error signal. 4. A first light beam in an on-track state and a second light beam in a state of off-track by a predetermined amount on both sides of the first light beam at predetermined intervals in a radial direction of the optical disk. When the information recorded at a low density is reproduced by irradiating the second and third light beams, a photoelectric conversion signal of the reflected light of the second and third light beams is used as a reproduction signal, and the recording is performed at a high density. Reproducing the reproduced information by using a photoelectric conversion signal of the reflected light of the first light beam as a reproduction signal. 5. The tracking error signal is generated from reflected light of the first light beam.
The method for reproducing the optical disc according to the above. 6. When a crosstalk component is included in a photoelectric conversion signal of the reflected light of the first light beam, the crosstalk component is canceled by using a photoelectric conversion signal of the reflected light of the second and third light beams. The method for reproducing an optical disk according to claim 4, wherein: