KR100772414B1 - Optical Information recording and reproducing apparatus and driving method of the same - Google Patents

Abstract

Disclosed are an optical information recording and reproducing apparatus having a compatibility including a next generation DVD and a driving method thereof.

The disclosed optical information recording and reproducing apparatus comprises: a first semiconductor laser for recording and reproducing; And a second semiconductor laser that radiates a laser beam having a wavelength longer than the emission wavelength of the first semiconductor laser to perform reproduction only. The second semiconductor laser includes a minimum T (T is a time width of one channel pit length) during optical disk reproduction. ) Is pulsed by a clock cycle less than the division by an integer of two or more, releasing an output greater than the continuous maximum rating.

Description

Optical information recording and reproducing apparatus and driving method of the same

1 is a block diagram showing a reproduction unit of the optical information recording and reproducing apparatus according to the first embodiment of the present invention;

2 is a schematic diagram illustrating pulse driving conditions of a semiconductor laser,

3 is a schematic diagram illustrating driving pulses of a semiconductor laser,

4 is a flowchart for reading a signal from an optical disc,

5 is a block diagram showing a first modification in the first embodiment,

6 is a block diagram showing an optical information recording and reproducing apparatus according to the second embodiment,

7 is a block diagram showing an optical information recording and reproducing apparatus according to the third embodiment,

8 is a schematic diagram illustrating driving pulses of a semiconductor laser according to a third embodiment,

9 is a block diagram showing a compatible optical information recording and reproducing apparatus according to the embodiment of the present invention.

<Explanation of symbols for main parts of the drawings>

8 ... optical pickup 10 ... semiconductor laser

14 ... monitor diode 16 ... objective lens

18 ... optical disk 20 ... light receiving element

30 ... Operator 32 ... LPF

The present invention relates to an optical information recording and reproducing apparatus and a driving method thereof, and more particularly, to an optical information recording and reproducing apparatus using an optical disc as a recording medium and a driving method thereof.

Background Art Optical information recording and reproducing apparatuses compatible with DVD (Digital Versatile Disc) and CD (Compact Disc) are widely used. In addition, a next generation DVD using a blue semiconductor laser has been developed as a large-capacity optical information recording and reproducing apparatus. In this case, there is a strong demand for an optical information recording and reproducing apparatus further equipped with compatibility with the next generation DVD.

In order to realize a recording capacity of 15 GB (one layer) or more in a next-generation DVD, an optical system using a blue semiconductor laser having a central emission wavelength around 405 nm, an objective lens OL having a high aperture number (for example, 0.65 to 0.85), Development is underway due to the need for a video encoding scheme and the like.

In order to increase the recording capacity, the emission wavelength of the semiconductor laser is set to 405 nm, and a high aperture objective lens is used to reduce the spot diameter of the laser beam emitted from the semiconductor laser. Such an objective lens is commonly included, and the optical system is complicated to ensure compatibility with an optical disk such as a DVD or a CD. Aperture limiting, aberration correction, and beam splitters for changing the optical path by reflecting and transmitting laser beams having different wavelengths are required. Since light attenuation is caused every time these optical component elements are transmitted, the more complicated the optical system, the more it arrives on the optical disk, and thereafter, less light is reflected and incident on the photodetector for reproduction.

In this case, recording is not necessary for all standard optical discs. Therefore, in the semiconductor laser corresponding to the optical disc standard for reproduction only, there is sufficient light output necessary for the reproduction purpose. In this case, the attenuation of the light due to the optical components arranged in order to ensure compatibility with the next-generation DVD is large, and the light output may be insufficient in the conventional semiconductor laser. However, although a higher power semiconductor laser can be newly designed, it is more reasonable if the current semiconductor laser can be handled well by, for example, pulse driving.

One disclosed example of a technique for pulse driving a semiconductor laser is disclosed in Japanese Patent Laid-Open No. 2001-331960. However, the above-described disclosure reduces the average power consumption by pulse driving so that the battery can be used for a longer time, and is not intended to obtain high output.

SUMMARY OF THE INVENTION An object of the present invention is to improve the problems of the above-described conventional optical information recording and reproducing apparatus, and an object of the present invention is to have a compatibility including a next-generation DVD capable of obtaining a sufficient laser beam output by improving a method of driving a semiconductor laser. An optical information recording and reproducing apparatus and its driving method are provided.

In order to achieve the above object, the optical information recording and reproducing apparatus according to the first embodiment of the present invention comprises: a first semiconductor laser for recording and reproducing; And a second semiconductor laser that radiates a laser beam having a wavelength longer than the emission wavelength of the first semiconductor laser to perform reproduction only, wherein the second semiconductor laser has a minimum T (T is a time of one channel pit length) during optical disk reproduction. And pulse driven by a clock cycle smaller than the value obtained by dividing the width by an integer of 2 or more.

In order to achieve the above object, an optical information recording and reproducing apparatus according to a second embodiment of the present invention comprises: a first semiconductor laser for recording and reproducing; A second semiconductor laser that emits only a reproduction by emitting a laser beam having a wavelength longer than the emission wavelength of the first semiconductor laser; A light receiving element for detecting a reflected beam from the optical disk; And a low pass filter into which the electric signal converted by the light receiving element is input, wherein the second semiconductor laser is smaller than a value obtained by dividing the minimum T (T is the time width of one channel pit length) at the time of optical disc reproduction by an integer of 2 or more. The low pass filter is pulse driven by a small clock period, and the low pass filter is characterized by having a cutoff frequency equal to or less than half the clock frequency of pulse driving the second semiconductor laser.

In order to achieve the above object, an optical information recording and reproducing apparatus according to a third embodiment of the present invention comprises: a first semiconductor laser for recording and reproducing; A second semiconductor laser that emits only a reproduction by emitting a laser beam having a wavelength longer than the emission wavelength of the first semiconductor laser; And a light-receiving element for detecting the reflected beam from the optical disk, wherein the second semiconductor laser has a clock period smaller than a value obtained by dividing the minimum T (T is the time width of one channel pit length) at the time of optical disk reproduction by an integer of 2 or more. And the light receiving element has a cutoff frequency of not more than one half of the clock frequency for pulse driving the second semiconductor laser.

In order to achieve the above object, a method of driving an optical information recording and reproducing apparatus according to an embodiment of the present invention includes optical information recording having a first semiconductor laser for recording and reproducing, and a second semiconductor laser for reproducing only. A reproducing apparatus, wherein the second semiconductor laser is pulse-driven at a clock cycle smaller than the minimum T (T is the time width of one channel pit length) at the time of optical disc regeneration divided by an integer of 2 or more, so that an output larger than the continuous maximum rating is obtained. To be released.

Hereinafter, an optical information recording and reproducing apparatus and a driving method thereof according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals denote like elements, and detailed descriptions thereof will be omitted.

1 is a block diagram showing a main portion of a reproduction unit in the optical information recording and reproducing apparatus according to the first embodiment of the present invention.

The semiconductor laser 10 is exclusively for reproduction, and emits a laser beam having a wavelength corresponding to an optical disc standard such as CD or DVD, for example, and is driven by the LD pulse driving circuit 54. The driving conditions of the semiconductor laser 10 will be described later.

The laser beam, which is the pulse output from the semiconductor laser 10, is branched by the half mirror 12 or the like and incident on the monitor diode 14, and then converted into a current and input to the sampling circuit 50. The sampling circuit 50 detects the peak value of the input pulse. The output of the sampling circuit 50 is input to the APC (Automatic Power Control) circuit 56 and controls the LD pulse drive circuit 54 so that the pulse output of the semiconductor laser 10 is maintained at a predetermined value.

The laser beam from the semiconductor laser 10 having a predetermined pulse output is converged by the objective lens 16 to form a spot on the optical disk 18. The beam reflected from the optical disc 18 returns to the optical system and then enters the light receiving element 20 composed of the multi-division regions. The light receiving element 20 is composed of a multi-division region for detecting the focusing error signal FE, the tracking error signal TE, and the RF signal, respectively.

The beam incident on the multi-division region is converted into an electrical signal, and then the calculation is performed by the calculator 30 according to a predetermined calculation formula. The coil 22 is moved in the vertical direction with respect to the optical disk 18, and the focus servo is turned ON based on the calculation result of the FE with respect to the focusing point. Similarly, the tracking servo is turned ON based on the result of the TE operation. The RF signal is then received from the rotating optical disk 18.

An information signal on the optical disc 18 is input to each calculator 30. In the present embodiment, since the input to the light receiving element 20 is a pulse, it is preferable that a LPF (Low Pass Filter) 32 is inserted after each calculator 30 to smooth the signal. Each signal smoothed in the LPF 32 is input to a voltage control led amplifier (VCA) 34. The signal output from each VCA 34 is input to the digital equalizer 36 and then sent to a pulse width modulator (PWM) 38. In this case, the cutoff frequency of the LPF 32 is preferably equal to or less than one half the clock frequency of the LD drive pulse.

The focusing signal FOCS is output from the PWM 38 to the coil 22, and the tracking signal TRKG is output to the coil 24. The spindle motor control signal SPDL and the drive signal CARG of the drive device are output.

As the modulator 42 connected to the PLL (Phase Locked Loop) 40, for example, a modulator corresponding to the code recording method by EFM (Eight to Fourteen Modulation) called 8-14 modulation in the case of a CD is used. do.

The disc discrimination signal is generated by the disc discrimination circuit 44 from the FE, TE, and RF signals and input to the CPU (Central Processing Unit) 46. The CPU 46 is also connected to the servo controller 52, the LD pulse driving circuit 54, the RAM (Random Access Memory) 48, and the like to control the entire optical information recording and reproducing apparatus.

Next, pulse driving conditions of the semiconductor laser 10 will be described.

In general, the maximum rated power of a semiconductor laser for DVD having a center wavelength of 650 nm and a semiconductor laser for reproduction (or CD-ROM) having a center wavelength of 780 nm is 5 mW or 7 mW or less. In DVD, CD, and these compatible optical disc standards, optical pickups are feasible with this maximum rated output.

For example, when a 780 nm semiconductor laser for CD is employed, the transmittance of 780 nm light for each optical component is set to 70%, respectively, and the number of optical components is set to five. At this time, after the objective lens, in order to obtain CW = 0.5 mW so as to correspond to CD RW having a low reflectance, light output with P1 = 0.5 / (0.7 × 0.7 × 0.7 × 0.7) = 4.25 (mW) is required. In this case, if the maximum rating of a semiconductor laser is 5 mW, it is fully possible.

Recently, however, there has been a demand for a compatible optical optical information recording device including a next-generation DVD having a center wavelength of 405 nm. In this case, it is very difficult to maintain high transmittance for all three wavelengths. For example, even when designed to have a transmittance of 90% at 405 nm, it is often 50% at 780 nm. In addition, the phase and the like must be adjusted for each wavelength, and the number of optical components passing through each wavelength inevitably increases.

For example, in the case of using a semiconductor laser of 5 mW output of 780 nm wavelength, assuming that the number of optical components passing through is six and the transmittances are 70, 60, 70, 50, 70, and 60%, respectively, P2 = 5 x 0.7 x 0.6 x 0.7 x 0.5 x 0.7 x 0.6 = 0.31 (mW). By the way, this optical output may not be able to fully reproduce. If 0.5 mW is required for reproducing on an optical disc, the rated power of the required semiconductor laser is P3 = 0.5 / (0.7 x 0.6 x 0.7 x 0.5 x 0.7 x 0.6) = 8.1 (mW). Therefore, the power required for regeneration is insufficient in the reproducing semiconductor laser whose maximum rated output is 7 mW. If CW power is used at 8 mW, catatrophic optical damage (COD) tends to occur due to temperature rise or the like in the cross section of the semiconductor laser, and the performance of the semiconductor laser is not stabilized, which may shorten the life of the semiconductor laser.

Using a semiconductor laser with a larger maximum rated power is solved, but it is very cost effective if a semiconductor laser can be used so far.

In order to suppress COD in the semiconductor laser cross section and to obtain a higher output, it is preferable to pulse-drive the semiconductor laser under appropriate conditions. (In this case, since the output from the light receiving element becomes a pulse, a signal constituting the optical information device. Circuits involving processing need to be newly designed.)

2 is a graph showing an example of pulse driving conditions.

The semiconductor laser, which was a CW output = 5 mW output, can be driven, for example, by a pulse drive with a pulse output Ppulse of about 10 mW. In this case, even when the continuous maximum rated output Pcw is 5 mW, the semiconductor laser can output above the continuous maximum rating by pulse driving under the following conditions. This is because the temperature rise can be suppressed by pulse driving, and the COD of the pulse can be made higher.

The clock period t _LD of the pulses may be a positive integer multiple of the channel clock period according to the write modulation method. The clock period t _LD is preferably equal to or less than an integer greater than 2 of 2T at the disc double speed. Where T is the time width of the channel pit length. 3T is in a range of about 14ns to about 694ns, depending on the speed of the optical disk, as shown in FIG. In addition, as shown in Fig. 3, the first start of the pulse for driving the laser can also detect the pit edge of the signal recorded on the disk and synchronize it in a circuit not shown on the pit edge.

Here, the operation in the case of reading the signal from the optical disc will be described in more detail.

4 is a flowchart showing an operation of reading a signal from an optical disc. The optical pickup (8 in FIG. 1) in the optical information recording and reproducing apparatus moves to the inner circumference of the optical disk (18 in FIG. 1) (step S200). A pulse voltage is applied to the semiconductor laser (10 in FIG. 1) (step S202). The focus coil (22 in FIG. 1) is moved up and down in the vertical direction with the optical disk 18 so that the reflected light from the optical disk 18 is detected by the light receiving element (20 in FIG. 1) (step S204).

FE, TE, and RF signals are obtained by calculating the converted currents from the beams respectively incident in the multi-division region. At this time, it is determined whether or not the optical disk is set in the apparatus by the FE level (step S206). If the FE level is NO, the optical disc 18 is inserted.

If the FE level is YES, the peak value of the FE is read and the gain of the VCA is adjusted by comparison with the set value (step S210). Next, the focus servo is turned ON at the focusing point (step S212).

Subsequently, the spindle motor is rotated (step S214), the peak value of TE is read out, and the gain of the VCA (34 in Fig. 1) is adjusted by comparison with the set value (step S216). If the tracking servo is turned on and the track is turned on, the tracking servo is turned off (step S218). Next, an RF signal is received (step S220), and preparation for reproduction procedure is complete | finished.

Fig. 5 is a block diagram showing a first modification of the first embodiment.

The CPU 46 determines whether or not to pulse-drive the semiconductor laser 10 in accordance with the type of the optical disk 18, and reproduces by driving the pulse only when the light output of the semiconductor laser 10 should be large. In this case, the switch 60 in FIG. 5 may be connected to the output terminal side of the LPF 32. On the other hand, when there is no need for pulse driving including when the optical disk 18 is discriminated, the switch 60 is connected to the output terminal of the calculator 30. In this way, only the signals that must pass through the LPE for various standards of the optical disk 18 can select the optimal RF signal, FE, and TE detection method through the LPE.

6 is a block diagram showing a main portion of a reproduction unit of the optical information recording apparatus according to the second embodiment.

In this case, electric signals in the multi-division regions constituting the light receiving element 20 are input to each LPF 32. In this figure, a total of six signals of four signals in a four-division region provided near the center part mainly for detecting FE, and two signals from two regions provided at both ends of the four-division region mainly for detecting TE. Are each entered as LPF. The output of the LPF is input to the calculator 30. In this case, the input to the arithmetic circuit shown by the broken line can be selected from the six signals based on the error detection method. Also in this embodiment, the pulse signal is smoothed by the LPF 32 and then input to the calculator 30. In addition, if the LPF composed of the inductance L, the capacitor, and the capacitor C is formed of an OEIC (Opto-Electric Integrated Circuit) integrated with the light receiving element 20, miniaturization and high performance can be achieved. In addition, the presence or absence of the pit is determined by the received light signal of the reflected light of the pulsed light beam from the reproducing semiconductor laser, and the LPE can be omitted by predicting that the sampling period following the pulse waveform has zero intervals and pits is also present. do.

In the above embodiment, the pulse signal was smoothed by LPF. However, the pulse signal can be smoothed by means other than this.

7 is a block diagram showing a main portion of a reproduction unit of the optical information recording apparatus according to the third embodiment.

In this embodiment, the frequency band of the light receiving element 20 is set to be less than 1/2 of the clock frequency of the driving pulse as shown in FIG. Thus, by making the light receiving element 20 narrow, it can be made into the signal which has continuity compared with a pulse signal. In addition, although LPF can also be used together, LPF in this case may be LPF by which the number of steps was reduced compared with the 1st Example. As a result, the price can be reduced.

In the monitor diode 14, the frequency band is set to, for example, less than half the clock frequency of the drive pulse, so that the sampling circuit 50 can be eliminated. In this case, it can be automatically controlled to a predetermined pulse output by the average value of the pulse outputs from the second semiconductor laser received by the monitor diode.

FIG. 9 is a schematic diagram showing an optical information recording and reproducing apparatus provided with a reproducing section illustrated in FIG. 1 using a pulse driving semiconductor laser.

In this figure, the semiconductor laser is pulse driven, for example, having a center wavelength of 780 nm or 650 nm. Although the chip 80 of the semiconductor laser, the chip 94 of the light-receiving element, the diffraction grating 92, and the like are the hologram unit 96 arranged in the same package, the optical pickup 9 having a regeneration-only function is shown in FIG. ) Has almost the same function as the optical pickup 8 illustrated in FIG. 1.

Further, after the laser beam from the blue semiconductor laser 82 passes through the prism 88, the aperture is limited by the collimator lens 86 and the hologram element 90, and the light is condensed by the objective lens 16 and the optical disk. It enters into (18). On the other hand, the 780 nm or 650 nm semiconductor laser or the 780 nm and 650 nm two-wavelength semiconductor laser, after passing through the prism 88, restricts the opening by the collimator lens 86 and the hologram element 90, and covers each disk. The condensing angle is changed to a thickness of 0.6 mm and 1.2 mm, and the light is collected by the objective lens 16 and incident on the optical disk 18. The reflected light of 650 nm or 780 nm is returned to the hologram unit 96 through the prism 88, diffracted and spectroscopically diffracted by the diffraction grating 92 to enter the light receiving element 94. The blue light is bent by the prism 88 to enter the OEIC 84 which is a light receiving element. In this case, for example, blue light records and reproduces, but only 780 nm for CD (including CD-ROM and the like) or 650 nm for DVD is dedicated to reproduction.

In order to ensure compatibility with the next-generation DVD standard using the blue semiconductor laser 82 (405 nm) in this figure, optical components such as the prism 88 and the aperture limiting element 90 are newly required. Each device needs to transmit or reflect three wavelengths of 405 nm, 650 nm and 780 nm. For this reason, it is difficult to optimize transmittance and reflectance for each wavelength, and it is hard to design by optimally optimizing any one wavelength or two wavelengths, and the reflectance and transmittance | permeability for each wavelength fall. As a result, the light output of 780 nm or 650 nm band on the optical disk 18 is insufficient in CW (continuous wave) operation. However, the semiconductor laser disposed in the hologram unit 96 is pulse driven, and the pulse peak light output is made larger than the maximum rated light output at the time of CW driving, thereby ensuring a pulse peak light output sufficient for reproduction.

Further, there is provided an optical information recording and reproducing apparatus provided with the reproducing sections of the first to third embodiments, which are controlled by detecting sampling reference signals generated at the pit edges on the optical disc.

Further, the light disk reflection light of the pulsed light beam from the second semiconductor laser is received by the light receiving element. An optical information recording and reproducing apparatus provided with a reproducing section for judging the presence or absence of a pit by this light reception signal, predicting that there is a pit also in the subsequent sampling period when there is a pit, and preventing misdetection.

In the above, embodiment of this invention was described, referring drawings. However, the present invention is not limited to these embodiments.

For example, various design changes made by those skilled in the art regarding the size, shape, arrangement, and the like in components such as a semiconductor laser, an LPF, an LD pulse driving circuit, an optical component, and a light receiving element, which constitute the optical information recording and reproducing apparatus, are also described. It is included in the present invention as long as it does not depart from the gist of the matter.

As described above, the optical information recording and reproducing apparatus and the driving method thereof according to the present invention provide a high output semiconductor such as a compatible optical information recording and reproducing apparatus including a next-generation DVD by pulse driving a semiconductor laser to implement high output. A conventional semiconductor laser can be used for an optical information recording and reproducing apparatus that requires a laser, which not only makes manufacturing cost low, but also enables the semiconductor laser to be driven more stably.

The optical information recording and reproducing apparatus and the driving method thereof according to the present invention have been described with reference to the embodiments shown in the drawings for clarity, but these are merely exemplary, and those skilled in the art can various modifications and It will be appreciated that other equivalent embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

Claims (22)

A first semiconductor laser for recording and reproducing; A second semiconductor laser for performing only regeneration; And the second semiconductor laser is pulse-driven by a clock cycle smaller than a value obtained by dividing the minimum T (T is the time width of one channel pit length) by an integer of 2 or more during optical disc reproduction. The method of claim 1, A light receiving element for detecting a reflected beam from the optical disk; And a low pass filter to which the electric signal converted by the light receiving element is input. And the low pass filter has a cutoff frequency equal to or less than one-half the clock frequency for pulse driving the second semiconductor laser. The method of claim 2, And an arithmetic unit connected between the light receiving element and the low pass filter. The method of claim 3, A switch selectively connected to an output of the operator and an output of the low pass filter; And a VCA connected to an output terminal of the switch. The switch directly connects the output terminal of the calculator and the VCA when the second semiconductor laser is not pulse driven, and connects the output terminal of the low pass filter and the VCA when the second semiconductor laser is pulsed. An optical information recording and reproducing apparatus. The method of claim 2, And an arithmetic unit connected to an output terminal side of said low pass filter. The method of claim 1, And a light receiving element that detects the reflected beam from the optical disk. And the light receiving element has a cutoff frequency of not more than 1/2 of a clock frequency for pulse-driving the second semiconductor laser. The method according to any one of claims 1 to 6, And the second semiconductor laser emits a laser beam having a wavelength longer than the emission wavelength of the first semiconductor laser. The method according to any one of claims 1 to 6, And the second semiconductor laser is pulse driven by a clock cycle which is a positive integer multiple of the channel clock cycle according to the recording modulation scheme. The method according to any one of claims 1 to 6, Further equipped with a monitor diode, And the pulse output from the second semiconductor laser is automatically controlled to a predetermined pulse output by sampling by the monitor diode. The method according to any one of claims 1 to 6, Further equipped with a monitor diode, The optical information recording and reproducing apparatus is automatically controlled to a predetermined pulse output by an average value of pulse outputs from the second semiconductor laser received by the monitor diode. The method according to any one of claims 1 to 6, An optical information recording and reproducing apparatus, which is controlled by detecting a sampling reference signal generated at a pit edge on an optical disk. The method according to any one of claims 1 to 6, The presence or absence of a pit is determined by the light-receiving signal of the reflected light of the pulsed light beam from the second semiconductor laser. Recording and playback device. A driving method of an optical information recording and reproducing apparatus having a first semiconductor laser for recording and reproducing and a second semiconductor laser for reproducing only, The second semiconductor laser is pulse-driven at a clock cycle smaller than a minimum T (T is the time width of one channel pit length) divided by an integer of 2 or more during optical disc reproduction, so that a pulse output larger than the continuous maximum rating is emitted. A driving method of an optical information recording and reproducing apparatus. The method of claim 13, And a pulse signal reflected and detected by the optical disk is cut off at less than one-half of the clock frequency of the pulse for driving the second semiconductor laser. The method of claim 13, A drive method for an optical information recording and reproducing apparatus, characterized in that the type of optical disc is determined and pulse driven only when the output of the second semiconductor laser should be larger than a predetermined output. The method of claim 15, Only when the second semiconductor laser is pulse driven, the pulse signal reflected and detected by the optical disk is cut off at less than one-half of the clock frequency of the pulse driving the second semiconductor laser. Driving method of a recording / playback apparatus. The method according to any one of claims 13 to 16, And the second semiconductor laser emits a laser beam having a wavelength longer than the emission wavelength of the first semiconductor laser. The method according to any one of claims 13 to 16, And driving the second semiconductor laser pulse by a clock cycle which is a positive integer multiple of the channel clock cycle according to the recording modulation scheme. The method according to any one of claims 13 to 16, And a pulse output from the second semiconductor laser is automatically controlled to a predetermined pulse output by sampling with a high speed monitor diode. The method according to any one of claims 13 to 16, A pulse output from the second semiconductor laser is received by a monitor diode and automatically controlled to a predetermined pulse output by an average value. The method according to any one of claims 13 to 16, And the second semiconductor laser is controlled by detecting a sampling reference signal generated at the pit edge on the optical disk. The method according to any one of claims 13 to 16, The presence or absence of a pit is determined by the light-receiving signal of the reflected light of the pulsed light beam from the second semiconductor laser, and the optical information predicts that there is a pit even in the case where the pulse waveform has a zero section and a pit. Driving method of a recording / playback apparatus.

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