JP4692684B2 - Optical disc apparatus and optical disc reproducing method - Google Patents

Description

  The present invention relates to laser waveform control during information reproduction in an optical disc apparatus.

  In an optical disc apparatus that reads mark / space information recorded on an optical disc using a laser beam output from a laser diode, it is important to determine mark / space binarization information without error. However, the laser light has a problem that noise such as mode hop noise and return light noise occurs.

  As a technique for reducing these noises, Patent Document 1 discloses a technique called high-frequency superposition. As a method for controlling the laser power during reproduction, Patent Document 2 discloses a technique called APC (Auto Power Control).

JP 2000-149302 A JP 2005-216395 A

  In recent years, optical discs with different standards such as CD, DVD, Blu-Ray Disc (hereinafter referred to as “BD”), and HD-DVD have been put on the market. Although these optical discs are not compatible, in consideration of user convenience, an optical disc device that supports recording / reproduction of CD, DVD, BD and an optical disc device that supports recording / reproduction of CD, DVD, HD-DVD have appeared. ing. However, an optical disc apparatus that supports both BD and HD-DVD recording / reproduction has not yet appeared.

  One possible reason for this is that an optical disc conforming to the BD standard (hereinafter referred to as “optical disc 1”) and an optical disc conforming to the HD-DVD standard (hereinafter referred to as “optical disc 2”) are as shown in FIG. There may be differences in the standards. Of these, the problem that is considered to be particularly problematic is the relationship between the wavelength of the laser light specified by the standard (both 405 nm) and the lens aperture ratio (BD: 0.85, HD-DVD: 0.65).

When the wavelength of the laser beam is λ and the lens aperture ratio is NA, the spot diameter of the laser beam on the optical disk is
(Λ / NA) (Formula 1)
The spot area of the laser beam on the optical disk is proportional to
(Λ / NA) ² (Formula 2)
It is known to be proportional to That is, the spot area on the optical disc differs between the BD standard and the HD-DVD standard. In the BD standard and the HD-DVD standard, the power of the laser beam per unit area is made substantially equal by making the reproduction laser power value different from 0.3 mW and 0.5 mW.

  Here, if the superposed high frequency characteristics (amplitude, frequency) are fixed to reduce the noise of the laser beam, suitable reproduction can be performed for one optical disc, but reproduction for the other optical disc is appropriate. In other words, there is a problem that the recorded data is destroyed, specifically, the recorded data is destroyed.

  The above problem is solved by the invention described in the claims.

The present invention, on the optical disc having a plurality of recording layers open mouth index different recording data erasure due to excessive laser power irradiated to the optical disc information recording surface during information reproduction, or to reduce the destruction of the information recording film it can.

1 is a configuration diagram of an optical disk apparatus according to a first embodiment. Internal configuration diagram of the laser driver in the first embodiment The figure which shows the relationship between the aperture ratio NA of a laser beam, the spot diameter R formed on an optical disk, and the spot area S The figure which shows the parameter of two types of optical discs with the same reproduction laser wavelength and different aperture ratios The figure which shows the relationship between laser drive current and the light emission power of the laser by this drive current The schematic diagram which shows the laser emission waveform with respect to the optical disk 2 in a 1st Example The schematic diagram which shows the laser emission waveform with respect to the optical disk 1 in a 1st Example Optical disc playback process start flowchart in the first embodiment Configuration diagram of optical disk apparatus according to third embodiment Laser power control circuit and laser driver internal configuration diagram in the third embodiment Optical disc playback process start flowchart in the third embodiment Optical disc playback process start flowchart in the fourth embodiment The internal block diagram of the laser driver in 2nd Example

  First, the cause of the above-mentioned problem will be examined in detail.

As in the relationship between the BD standard and the HD-DVD standard, the optical disc standards having the same laser light wavelength but different lens aperture ratios are the optical disc 1 and the optical disc 2, respectively, and the relationship between these lens aperture ratios NA ₁ and NA ₂ If NA ₁ > NA ₂ , the relationship between the spot areas S ₁ and S ₂ of the laser beam on each optical disc and the reproduction laser powers P ₁ and P ₂ is expressed by the following two equations.

S ₁ <S ₂ (Formula 3)
P ₁ <P ₂ (Formula 4)
Consider an optical disk apparatus capable of reproducing both the optical disks 1 and 2.

  From (Equation 4), it can be seen that this optical disk apparatus needs to switch the reproduction laser power between when reproducing the optical disk 1 and when reproducing the optical disk 2.

At this time, if a high frequency having a suitable amplitude with respect to the optical disc 2 is superimposed upon reproduction of the rewritable optical disc 1, the irradiation energy per unit area reaches the erasing power of the optical disc 1, and recorded data may be erased. is there. That is, for a large spot area S ₂ on the optical disk 2 be a high-frequency amplitude setting value that does not cause a problem, a problem arises for small spot area S ₁ on the optical disk 1.

This is because the energy per unit area given by the high-frequency peak power superimposed on the reproduction laser power P ₁ is equivalent to the energy per unit area given by the erasing laser power for the optical disc 1, and the recorded data is erased. It is thought that it is. This is considered to be the cause of the above-mentioned “problem that the recorded data of the other optical disk is destroyed by excessive laser power irradiation”.

  On the other hand, when focusing on a specific laser, it has been found that the optimum amplitude and frequency of the high frequency to be superimposed in order to reduce laser noise depend on the laser power. That is, it has been found that it is preferable to change the amplitude and frequency of the high frequency when the value of the laser power is changed.

  From the above, even if two types of optical disc standards using lasers of the same wavelength are used, if the NA is different, that is, if the reproduction laser power needs to be changed, the high frequency superposition characteristics (amplitude, frequency) are also changed. Found that there is a need to do.

  An embodiment for solving such problems will be described in detail below.

  The optical disc apparatus of the first embodiment will be described with reference to FIG. Laser light emitted from the laser 108 is irradiated to a predetermined radial position of the recording medium 101 through the collimator lens 105 and the objective lens 103. The reflected light of the laser light is condensed by the condenser lens 106 via the beam splitter 104 and converted into an electric signal (hereinafter referred to as “signal”) by the photoelectric conversion element 107. The obtained signal is decoded by the demodulation circuit 111 through the I / V conversion circuit 109 and the signal processing circuit 110, and is sent to the upper host 115 through the microcomputer 114.

  At the time of discriminating the optical disc, a signal necessary for discriminating the optical disc (hereinafter referred to as “optical disc discrimination signal”) is input from the signal processing circuit 110 to the optical disc discrimination circuit 112. The optical disc discrimination signal is a signal whose signal output differs depending on the optical disc structure, and includes, for example, a focus error signal and a tracking error signal.

  The optical disc discrimination result output from the optical disc discrimination circuit 112 is input to the microcomputer 114 via the data bus 116. The microcomputer 114 controls the signal processing circuit 110, the demodulation circuit 111, the laser driver 113, the spindle motor 102, and the like based on the determination result of the optical disk so as to be optimal for the determined optical disk.

  A detailed configuration of the laser driver 113 in the optical disk apparatus of FIG. 1 will be described with reference to FIG. A variable current source 201 is controlled by the microcomputer 114 via the data bus 116. Reference numeral 202 denotes a first high-frequency current generation circuit (hereinafter referred to as “OSC1”), which sets the amplitude and frequency of the high frequency output from the OSC1 to “HFamp1” and “HFfreq1”, respectively. Reference numeral 203 denotes a second high-frequency current generation circuit (hereinafter referred to as “OSC2”), which sets the amplitude and frequency of the high-frequency output from the OSC2 to “HFamp2” and “HFfreq2”, respectively. A signal selection circuit 204 selects one of the output of OSC 1 and the output of OSC 2 and outputs the selected signal to the adder 205, and is controlled by the microcomputer 114 via the data bus 116. Reference numeral 205 denotes an adder that adds the outputs of the variable current source 201 and the signal selection circuit 204, and the output of the adder 205 becomes a laser drive current output 117 that is an output of the laser driver 113.

  The relationship between the lens aperture ratio NA, the spot diameter R formed on the optical disc, and the spot area S will be described with reference to FIG. As described in (Formula 1), the spot diameter R is inversely proportional to the aperture ratio NA, and this relationship is indicated by a solid line 301. Further, as described in (Equation 2), the spot area S is inversely proportional to the square of the lens aperture ratio NA, and this relationship is indicated by a solid line 302.

  FIG. 6 shows the relationship between the laser emission waveform, the emission power, and the drive current value when the optical disc 2 is reproduced. In a period 601 where no high frequency is superimposed, the laser power is P2, and the DC laser drive current is C2.

  In the period 602 in which the high frequency is superimposed, the signal selection circuit 204 in FIG. 2 selects and outputs the output of the OSC2. In order for the average laser power in the period 602 to be equal to the power P2 in the period 601, it is necessary to set C2 'that satisfies the following relationship in the variable current source 201 in FIG.

Cpk2 = C2 ′ + HFamp2 (Formula 5)
C2 = C2 ′ + (HFamp2 / HFfreq2) (Formula 6)
FIG. 7 shows the relationship between the laser emission waveform, the emission power, and the drive current value when the optical disc 1 is reproduced. In a period 701 in which no high frequency is superimposed, the laser power is P1 and the DC laser drive current is C1. The relationship between P1, C1 and P2, C2 in FIG.
P1 <P2 (Formula 7)
C1 <C2 (Formula 8).

  Since reproduction of the optical disk 1 and optical disk 2 uses a laser having the same wavelength and an optical pickup having the same optical path length, the signal selection circuit 204 in FIG. 2 selects the output of the OSC 2 even during the period 702 during which high frequency superimposition is performed. And output. In order for the average laser power in the period 702 to be equal to the power P1 in the period 701, C1x that satisfies the following relationship needs to be set in the variable current source 201 in FIG.

Cpk2 ′ = C1x + HFamp2 (Equation 9)
C1 = C1x + (HFamp2 / HFfreq2) (Formula 10)
Here, as shown in FIG. 4, since the light spot area with respect to the optical disk 1 is about 0.6 times the light spot area with respect to the optical disk 2, if the same laser power is irradiated, the area per unit area of the optical disk 1 The laser power is 1 / 0.6≈1.7 times that of the optical disc 2. Since the reproduction laser power C1 (0.3 mW) is set to about 0.6 times the reproduction laser power C2 (0.5 mW), if attention is paid to the average reproduction laser power C1 and C2, the laser power per unit area is Almost equal.

  However, comparing the effect of HFamp2 superimposed in the period 702 on the increase in laser power per unit area and the effect of HFamp2 superimposed in the period 602 on the increase in laser power per unit area, the former is larger. Therefore, the laser power per unit area in the high frequency peak portion of the period 702 may be larger than the laser power per unit area in the high frequency peak portion of the period 602. That is, depending on the set value of HFamp2, there is a possibility of irradiating the recording film of the optical disc 1 with an excessive laser power, which may cause destruction of recorded data or deterioration of the optical disc recording film at a portion 705 in FIG. There is.

  In order to avoid such a problem, the signal selection circuit 204 in FIG. 2 selects the output of the OSC 1 so that the relationship between the laser emission waveform, the emission power, and the drive current value in the period 703 is selected during reproduction of the optical disc 1. Output. At this time, “HFamp1” and “HFfreq1” output by OSC1 are set as follows.

HFamp1 = HFamp2 × (P1 / P2) (Formula 11)
HFfrq1 = HFfrq2 (Formula 12)
When the average emission power P1 and the average drive current C1 are realized so as to satisfy this condition, the laser emission waveform by high frequency superposition is similar to the period 602 in FIG. 6 as shown in the period 703 in FIG. The laser power per unit area of Ppk1 and Ppk2 in FIG. 6 can be made substantially the same.

  FIG. 5 is a diagram showing the relationship between the laser drive current and the laser emission power by the laser drive current (hereinafter referred to as “I / L relationship”). A solid line 501 indicates the relationship between the average laser power and the average laser drive current during a period in which a high frequency is not superimposed on the laser drive current, such as the period 603 in FIG. 6 and the period 704 in FIG. A solid line 502 indicates the relationship between the average laser power and the average laser drive current during a period in which a high frequency is superimposed on the laser drive current, such as the period 602 in FIG. 6, the period 702 in FIG. 7, and the period 703, for example. Further, a solid line 503 indicates the relationship between the peak power value of high frequency superposition and the laser driving current at that time.

  When the laser light emission waveform at the time of high frequency superposition is made similar in the period 602 and the period 703, each power value such as an average value of the high frequency peak laser power to be superposed in a region where the laser power changes linearly with respect to the drive current. Ride on the same straight line. Therefore, the I / L relationship of each level of Ppk1 and Ppk2 is derived in advance, and the laser power and laser drive current value of each level may be set according to the laser spot diameter on the recording surface of the optical disk to be reproduced. .

  FIG. 8 shows a flowchart of the processing of this embodiment. When an optical disk is loaded in the optical disk apparatus (step 801), the optical pickup head is moved to a predetermined reproduction position to prevent destruction of recorded data on the optical disk (step 802), (Expression 13), (Expression 14) (Expression) The reproduction setting for the optical disk 2 in 15) is performed (step 803), and it is determined whether the optical disk is the optical disk 2 (step 804). At this time, the signal selection circuit 204 in FIG. 2 selects and outputs the output of the OSC2.

Aperture ratio = NA2 (Formula 13)
Reproduction power = P2 (Formula 14)
High frequency superimposed peak power = Ppk2 (Equation 15)
The reason for discriminating the type of the optical disk in the reproduction setting for the optical disk 2 is that the light spot diameter with respect to the optical disk 2 is larger than the light spot diameter with respect to the optical disk 1, so This is because the laser power is reduced and destruction of recorded data can be avoided.

  If it is determined in the determination step 804 that the optical disc is the optical disc 2 (step 805), data reproduction processing is started with the settings of (Equation 5) and (Equation 6) (step 807).

When it is determined in the determination step 804 that the optical disc is not the optical disc 2, that is, when it is determined that the optical disc is the optical disc 1 (step 806), the reproduction conditions of the optical disc 1 are (Equation 9) (Equation 10) and
Aperture ratio = NA1 (Formula 16)
Reproduction power = P1 (Formula 17)
High frequency superposition peak power = Ppk1 (Equation 18) is set, and reproduction processing is started (step 807).

  In the present embodiment, the optical disk 1 conforming to the BD standard and the optical disk 2 conforming to the HD-DVD standard are exemplified as optical disks having the same laser wavelength to be reproduced and different reproduction laser spot areas. Needless to say, the present invention can also be applied.

  In this embodiment, the amplitude “HFamp1” of the high-frequency superimposed signal of the optical disc 1 is calculated by (Equation 11). 1. In the case of a rewritable optical disc, the high frequency superimposed peak power Ppk1 is equal to or less than the erasing power. In the case of a read-only or once-recorded optical disc, HFamp1, which is a power at which the high frequency superimposed peak power Ppk1 does not destroy the data recording film, may be set.

  In FIG. 2, the OSC1 (202), the OSC2 (203), and the signal selection circuit 204 are provided inside the laser driver 113. However, any or all of these may be provided outside the laser driver 113. . According to this configuration, effects such as downsizing the laser driver and reducing the amount of heat generated can be obtained.

  Further, the processing in step 802 in FIG. 8 may be omitted. As a result, the disc discrimination time can be shortened.

  Further, in step 803 in FIG. 8, the optical disc is determined after the high frequency superimposition is set, but the optical disc may be determined without superimposing the high frequency. In this case, the reproduction power P2 and the high frequency peak power Ppk2 may be set in step 805.

  Next, a second embodiment will be described with reference to FIG. In this embodiment, in place of FIG. 2 of the first embodiment having a plurality of high frequency generation circuits (OSC1, OSC2) inside the laser driver, the high frequency current amplitude and high frequency can be set from the outside of the laser driver. And a high frequency generation circuit 1301, which is characterized in that the amplitude and frequency of the high frequency to be superimposed can be changed according to the optical disc discrimination result. The configuration of the optical disk apparatus according to this embodiment is the same as that of the first embodiment shown in FIG.

  FIG. 13 is a diagram showing an internal configuration of the laser driver 113 of this embodiment. Description of portions 201 and 205 common to FIG. 2 of the first embodiment is omitted. A high frequency oscillation circuit 1301 is provided with a current amplitude control circuit 1302 for controlling a high frequency current amplitude and a frequency control circuit 1303 for controlling a high frequency, which are controlled by a microcomputer 114 via a data bus 116. The The control values of the variable current source 201 and the current amplitude control circuit 1302 are set so that the average of the reproduction laser power becomes the optimum reproduction laser power according to the type of the optical disc discriminated by the optical disc discrimination circuit 112.

  For example, when the optical disc is determined to be the optical disc 1, the setting of the current amplitude control unit 1302 is set to HFamp1, and when the optical disc is determined to be the optical disc 2, the setting of the current amplitude control unit 1302 is set to HFamp2. At this time, if all the settings of the frequency control unit 1303 are set to HFfrq2 = HFfreq1, the same effect as that of the first embodiment can be obtained.

  Next, a third embodiment of the present invention will be described.

  FIG. 9 is a block diagram of an optical disk apparatus according to the third embodiment of the present invention. Elements equivalent to those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted. Reference numeral 901 denotes a monitor diode that detects the laser emission power in order to perform APC control. The signal band of the monitor diode is sufficiently low with respect to the high frequency superimposed on the reproduction laser beam. A signal 902 detected by the monitor diode 901 is input to the laser power control circuit 903. Details of the laser power control circuit 903 and the laser driver 905 are shown in FIG. The same elements as those in FIG. 13 of the second embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the laser power control circuit 903, the reproduction laser power target value corresponding to each optical disk is set in the reproduction power target value generation circuit 1001 by the microcomputer 114 according to the optical disk determination result by the optical disk determination circuit 112. A difference between the set value and the monitor diode output 902 is calculated by a subtractor 1002 to obtain a difference value 904. A reproduction laser drive current is generated based on the difference value 904 via the amplifier 1003. Further, in the high frequency current generation circuit 1004, the amplitude set value is controlled by the variable gain amplifier 1005 controlled by the output of the difference value 904 with respect to the amplitude value set in the high frequency amplitude control circuit 1302 by the output of the optical disc discrimination circuit 112. To do. The coefficient ratio of the variable gain amplifier with respect to the difference value 904 may be, for example, the ratio between the solid line 502 and the solid line 503 in FIG. 5 of the first embodiment. As a result, it is possible to achieve appropriate high-frequency superposition corresponding to the optical disc playback power while correcting changes in the I / L relationship due to temperature changes inside the optical disc device and around the laser, and deterioration over time, and data errors during playback can be realized. Erasure can be prevented.

  FIG. 11 shows a flowchart of the processing of this embodiment. When the optical disk is loaded (step 1101), the target value setting of the reproduction power target value generation circuit 1001 is set to P1 or P2 in FIG. 5, and the amplitude and frequency settings of the high-frequency current generation circuit 1004 are set to the first and optical disks 2. The common setting, which is a setting corresponding to the blue laser in this embodiment, is turned off, and the output of the high-frequency current generation circuit 1004 is turned off by turning off the switch 1006 in FIG. In this state, the signal quality (S / N) is deteriorated because laser noise is superimposed on the reproduction signal. However, the focus error signal and tracking error signal mainly used for optical disc discrimination have a sufficiently low signal bandwidth of several kHz, Improvement of signal quality is relatively easy with a low-pass filter (LPF) or the like. If a signal with improved quality is used in this way, it is possible to discriminate an optical disc having the same performance as that of an optical disc by a reproduction waveform subjected to high-frequency superposition as in the first embodiment. By not performing high frequency superposition in this way, it is possible to avoid erroneous erasure of recorded data on the optical disc and deterioration of the optical disc recording film when the peak power of laser emission at the time of high frequency superposition is excessive. it can. In this state, optical disc discrimination is executed (step 1102), and if the optical disc is determined to be the optical disc 2 (Yes in step 1103), the target value of the playback power target value generation circuit 1001 in FIG. (1105). When it is determined that it is not the optical disk 2, that is, when it is determined that it is the optical disk 1 (No in step 1103), the target value of the reproduction power target value generation circuit 1001 in FIG. 10 is set to the reproduction power P 1 of the optical disk 1. (1104). Next, the output of the high-frequency current generation circuit 1004 is turned on by the switch 1006 (step 1106), and the reproduction process is started (step 1107).

  FIG. 12 shows a processing flow in the fourth embodiment of the present invention. The circuit configuration of this embodiment is the same as that of the third embodiment, and a description thereof will be omitted. In the present embodiment, a case is considered in which a multilayer optical disc that reproduces information using a blue laser has different aperture ratios NA during reproduction. Preparation for playback of the layer to be played back (hereinafter referred to as “target layer”) when the optical disc is loaded (step 1201) or when the optical disc playback layer is switched (step 1202). NA of the target layer = NAt. Pt is set to the target value of the reproduction power target value generation circuit 1001 in FIG. 10 (step 1203). At this time, the switch 1006 in FIG. 10 is turned off, and the output of the high-frequency current generation circuit is turned off. Next, the focus is drawn toward the target layer (step 1204). When the focus pull-in to the target layer is confirmed, the aforementioned switch 1006 is turned on to turn on the output of the high-frequency current generation circuit (step 1205). Thereafter, tracking pull-in is performed (step 1206), and reproduction processing is started (step 1207). Thereby, at the time of focus pull-in, it is possible to prevent the recorded data of the layers other than the target layer or the recording film from being deteriorated due to the peak power of the high frequency superimposition.

  In each of the above embodiments, the case where a high-frequency signal is superimposed on the laser drive signal at the time of reproduction is illustrated, but the reproduction power level when reproducing for servo signal generation at the time of recording or at the time of forming a space during recording. Needless to say, the invention described in the above embodiment can be applied to the case of emitting the light.

  In the above-described embodiments, the characteristics of the high-frequency signal superimposed on the laser drive signal during reproduction are switched. However, depending on the case, the output of the high-frequency signal may be stopped, that is, a high-frequency signal with zero amplitude may be used. It is not limited to the waveforms shown in FIGS.

DESCRIPTION OF SYMBOLS 101 ... Recording medium, 102 ... Spindle motor, 103 ... Objective lens, 104 ... Beam splitter, 105 ... Collimator lens, 106 ... Condensing lens, 107 ... Photoelectric conversion element, 108 ... Laser, 109 ... IV conversion element, 110 ... Signal Processing circuit 111... Modulation circuit 112. Optical disc discrimination circuit 113. Laser driver 114 114 Microcomputer 115 Host host 116 Data bus 201 Variable current source 202 203 203 1001 High frequency current generation Circuit 204, signal selection circuit, 205, adder, 901, monitor diode, 903, laser power control circuit, 1001, reproduction power target value generation circuit, 1002, subtractor, 1003, 1005, amplifier, 1006, switch, 1302 ... High-frequency current amplitude controller, 303 ... high-frequency current frequency control unit

Claims (5)

  An optical disc for reproducing information from an optical disc having a first recording layer provided at a first distance from the surface of the optical disc and a second recording layer provided at a second distance from the surface of the optical disc A device,
  A laser that emits laser light of a predetermined wavelength;
  An objective lens that focuses laser light of a predetermined wavelength irradiated from the laser onto the first recording layer and the second recording layer;
  When reproducing the information recorded on the first recording layer, the information recorded on the second recording layer is reproduced by superimposing a high frequency of the first amplitude on the laser beam emitted from the laser. A high frequency generation circuit that switches from the first amplitude to a second amplitude smaller than the first amplitude, and superimposes the high frequency of the second amplitude on the laser light emitted from the laser;
  When reproducing the information recorded on the first recording layer, control to irradiate the first recording layer with a first laser power with a laser beam superimposed with a high frequency of the first amplitude, When reproducing the information recorded on the second recording layer, a laser beam on which the high frequency of the second amplitude is superimposed is changed from the first laser power to the second laser power smaller than the first laser power. A laser power control circuit that controls to irradiate the second recording layer with the second laser power.
  An optical disc apparatus, wherein a ratio of the first amplitude to the first laser power is substantially equal to a ratio of the second amplitude to the second laser power.   Information recorded on the first recording layer provided at a first distance from the surface of the optical disk having a plurality of recording layers, and a second information provided at a second distance from the surface of the optical disk. A method for reproducing an optical disc, wherein information recorded on a recording layer is reproduced by irradiating the first recording layer and the second recording layer with laser light,
  When reproducing the information recorded on the first recording layer, a high frequency with a first amplitude is superimposed on the first laser beam, and a high frequency with the first amplitude is superimposed with a first laser power. Reproducing information recorded on the first recording layer by irradiating the first recording layer with the first laser beam,
  When reproducing the information recorded on the second recording layer, the high frequency of the second amplitude is switched from the first amplitude to the high frequency of the second amplitude smaller than the first amplitude. The laser beam is superposed on the second laser beam, and the second laser power is switched from the first laser power to a second laser power smaller than the first laser power, and the high frequency of the second amplitude is superposed on the second laser power. Reproducing information recorded on the second recording layer by irradiating the second recording layer with the second laser beam,
  A method of reproducing an optical disc, wherein a ratio of the first amplitude to the first laser power is substantially equal to a ratio of the second amplitude to the second laser power.   An optical disc for reproducing information from an optical disc having a first recording layer provided at a first distance from the surface of the optical disc and a second recording layer provided at a second distance from the surface of the optical disc A device,
  A laser that emits laser light of a predetermined wavelength;
  An objective lens that focuses laser light of a predetermined wavelength irradiated from the laser onto the first recording layer and the second recording layer;
  When reproducing the information recorded on the first recording layer, the information recorded on the second recording layer is reproduced by superimposing a high frequency of the first amplitude on the laser beam emitted from the laser. A high-frequency generation circuit that superimposes a high-frequency wave having a second amplitude smaller than the first amplitude on a laser beam emitted from the laser;
  When reproducing the information recorded on the first recording layer, control to irradiate the first recording layer with a first laser power with a laser beam superimposed with a high frequency of the first amplitude, When reproducing the information recorded on the second recording layer, the second laser power smaller than the first laser power is used as the second laser power to superimpose the high-frequency wave having the second amplitude. A laser power control circuit that controls to irradiate the recording layer of
  An optical disc apparatus, wherein a ratio of the first amplitude to the first laser power is substantially equal to a ratio of the second amplitude to the second laser power.   Information recorded on the first recording layer provided at a first distance from the surface of the optical disk having a plurality of recording layers, and a second information provided at a second distance from the surface of the optical disk. A method for reproducing an optical disc, wherein information recorded on a recording layer is reproduced by irradiating the first recording layer and the second recording layer with laser light,
  When reproducing the information recorded on the first recording layer, a high frequency with a first amplitude is superimposed on the first laser beam, and a high frequency with the first amplitude is superimposed with a first laser power. By irradiating the first recording layer with the first laser beam, the information recorded on the first recording layer is reproduced,
  When reproducing the information recorded on the second recording layer, a high frequency of the second amplitude smaller than the first amplitude is superimposed on a second laser beam, and the information is more than the first laser power. Information recorded on the second recording layer by irradiating the second recording layer with the second laser light on which the high frequency of the second amplitude is superimposed with a small second laser power. Play and
  A method of reproducing an optical disc, wherein a ratio of the first amplitude to the first laser power is substantially equal to a ratio of the second amplitude to the second laser power.   A plurality of recording layers, and information recorded on a first recording layer provided at a first distance from the surface of the optical disc and a second information provided at a second distance from the surface of the optical disc. An optical disc having information recorded on two recording layers,
  When information recorded on the first recording layer is reproduced from the optical disc, a high frequency with a first amplitude is superimposed on a first laser beam, and a high frequency with the first amplitude is applied with a first laser power. The information recorded in the first recording layer is reproduced by irradiating the first recording layer with the first laser beam on which is superimposed,
  When the information recorded on the second recording layer is reproduced from the optical disc, a high frequency having the second amplitude smaller than the first amplitude is superimposed on a second laser beam, and the first The second recording layer is irradiated with the second laser light on which the high frequency of the second amplitude is superimposed with a second laser power that is smaller than the laser power, so that the second recording layer is irradiated to the second recording layer. The recorded information is played back,
  An optical disc, wherein a ratio of the first amplitude to the first laser power is substantially equal to a ratio of the second amplitude to the second laser power.

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