Patent Publication Number: US-6222814-B1

Title: Recording/reproducing apparatus and method for phase-change optical disc

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a phase-change drive of a high transfer rate, and more particularly, to a phase-change optical disc drive with a semiconductor laser power control and a method of writing/reading a phase-change optical disc at a high transfer rate by controlling the laser power of the semiconductor laser. 
     2. Description of Related Art 
     Typical phase-change optical discs in which information can be rewritten include a so-called DVD-RAM. DVD-RAM adopts an EFM (Eight-to-Fourteen Modulation) method for signal modulation to drive a semiconductor laser to emit multi-pulses for generation of recording waveforms for marks of 3T to 11T. 
     FIG. 1 is a timing chart of recording waveforms in DVD-RAM. As shown, a mark 3T is written with a single light pulse while a mark 11T is recorded with nine light pulses. Each light pulse is immediately followed by a bias power  2  set to a lower value than a bias power  1  corresponding to an erasure power to control the crystallization speed of the phase-changed recording medium. Further, both leading and trailing pulses have a period of about 1T, and they are generated with predetermined time delays (T SFP  and T SLP  in FIG.  1 ), respectively, from the clock pulse. 
     DVD-RAM uses a clock frequency of 29 MHz (user transfer rate of 11 Mbps). Both the leading and trailing pulses have a width of about 35 ns. The recording power of these light pulses is detected by a laser power monitoring detector, and then sampled and given a predetermined value, thus the recording pulse is controlled to always have a constant power. For example, the peak power is controlled by sampling the light power of the leading or trailing pulse, and the bias power  1  is controlled by sampling the light output of the multi-pulse. Note that the bias power  2  is controlled by sampling a reproducing output detected by an RF signal detector. 
     For a phase-change optical disc drive of a higher transfer rate than the normal one of DVD-RAM, however, it is necessary to increase the clock frequency. For a clock frequency of 100 MHz (use transfer rate of 38 Mbps), for example, the leading and trailing pulses will have a width of less than 10 ns, so it will be difficult to accurately sample the light output for controlling the recording power. Furthermore, wen the light pulse is less than 10 ns in width, it will easily be affected by noise component and also a sufficient band of the optical system cannot be assured, so that the recording power cannot be controlled. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing a phase-change optical disc writing/reading apparatus and method in which a laser power of a semiconductor laser can be accurately controlled even at the time of writing or reading a phase-change optical disc at a high transfer rate. 
     The above object can be attained by providing a phase-change optical disc drive in which a data of nT in pulse width is recorded with a multi-pulse generated from a semiconductor laser, including a number (n−1) of pulses and which shifts at a minimum of three levels, comprising according to the present invention: 
     means for detecting a laser power of the semiconductor laser; and 
     means for generating, when in a power control mode, an output control pulse larger in pulse width than the multi-pulse to drive the semiconductor laser to generate a light pulse based on the output control pulse, sampling and holding, based on the output control pulse, the laser power detected by the detecting means, and controlling the laser power of the semiconductor laser so that the sampled and held laser power has a predetermined value. 
     When in the power control mode, the phase-change optical disc drive generates, when in the power control mode, an output control pulse larger in pulse width than the multi-pulse, drives the semiconductor laser based on the output control pulse to generate a light pulse, samples and holds, based on the output control pulse, the laser power detected by the detecting means, and controls the laser power of the semiconductor laser so that the sampled and held laser power has a predetermined value. 
     The above object can also be attained by providing a method of recording a data of nT in pulse width with a multi-pulse generated from a semiconductor laser, including a number (n−1) of pulses and which shifts at a minimum of three levels, comprising, according to the present invention, the steps of: 
     generating, when in a power control mode, an output control pulse larger in pulse width than the multi-pulse; 
     driving the semiconductor laser to generate a light pulse based on the output control pulse; 
     detecting a laser power of the semiconductor laser; 
     sampling and holding the detected laser power; and 
     controlling the laser power of the semiconductor laser so that the sampled and held laser power has a predetermined value. 
     When in the power control mode, an output control pulse larger in pulse width than the multi-pulse is generated, and the semiconductor laser is driven based on the output control pulse to emit a light pulse, the laser power detected by the detecting means is sampled and held based on the output control pulse, and the laser power of the semiconductor laser is controlled so that the sampled and held laser power has a predetermined value. 
     These objects and other objects, features and advantages of the present intention will become more apparent from the following detailed description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a timing chart of recording waveforms in DVD-RAM; 
     FIG. 2 is a schematic block diagram of a phase-change optical disc drive according to the present invention; 
     FIG. 3 illustrates the construction of an aspheric two-group objective lens unit used in the phase-change optical disc drive in FIG. 2; 
     FIG. 4 schematically illustrates the construction of an optical disc compatible with the phase-change optical disc drive in FIG. 2; 
     FIG. 5 is a schematic block diagram of a recording pulse generation circuit used in the phase-change optical disc drive in FIG. 2; 
     FIG. 6 is a timing chart showing the relationship between a master clock, NRZI (No Return to Zero Inverse) signal, recording signals Data  1 , Data  2  and Data  3 , output control signal Data  3 ′, NRZI pulse and a multi-pulse; 
     FIG. 7 is a schematic block diagram of a recording output control circuit used in the phase-change optical disc drive in FIG. 2; and 
     FIG. 8 is a schematic block diagram of a semiconductor laser drive circuit used in the phase-change optical disc drive in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 2, there is illustrated the rewritable phase-change optical disc drive according to the present invention. The optical disc drive uses a large numerical-aperture (NA) two-group objective lenses  21  and  23  as shown. 
     The phase-change optical disc drive according to the present invention includes an optical head  10 , recording pulse generation circuit  30  to generate a recording pulse, recording output control circuit  50  to control the recording pulse output and a semiconductor laser drive circuit  70  to drive a semiconductor laser  3  which will be discussed later. 
     In the phase-change optical disc drive, the optical disc  1  is spun at a constant angular velocity, for example, by a spindle motor  2  while the information recording surface of the optical disc  1  is being scanned with a laser light by the optical head  10 , to optically record/reproduce information through the ( 1 , 7 ) modulation. 
     The semiconductor laser (LD)  3  is included in the optical head  10  to generate a reading/writing laser light for irradiation onto the optical disc  1 . The laser light from the semiconductor laser  3  is formed to be a parallel beam by a collimator lens  4 , passes through a side spot generating diffraction grating  5 , and through a beam splitter  6  and quadrature wavelength plate (QWP)  7  and then it is incident upon an aspheric two-group objective lens  20  which will focus the laser light on the information recording surface of the optical disc  1 . A part of the laser output from the semiconductor laser  3  is reflected by the beam splitter  6  and led to a laser power monitoring detector  9  through a condenser lens  8 . The reflected light from the optical disc  1  (namely, reproduced signal) is reflected by the beam splitter  6  and led to the detection light path while a part of the reflected light is reflected by a beam splitter  11 , passed through a condenser lens  12  and cylindrical lens  13  and incident upon a servo signal detector  14  where it is converted to a current while the rest of the reflected light from the optical disc  1  is passed through lenses  15  and  16  and incident upon an RF signal detector  17  where it is converted to a current. In the optical head  10 , the astigmatism is used to generate a focus error signal and also the differential pushpull method is used to generate a tracking error signal. In this embodiment, the two signal detectors  14  and  17  are used to detect servo error signal and reproduced RF signal, respectively. However, these signals can also be detected by a single detector. 
     As shown in FIG. 3, the aspheric two-group objective lens unit  20  includes a first electromagnetic actuator  22  to drive a first lens  21 , and a second electromagnetic actuator  24  to drive a second lens  23 . The second electromagnetic actuator  24  is movable in the optical-axial and tracking directions. The second lens  23  is mounted on the second electromagnetic actuator  24 . The second lens  23  has an NA of about 0.5. The first lens  21  is provided above the second lens  23  and mounted on the first electromagnetic actuator  22  independent of the second electromagnetic actuator  23 . The first lens  21  can be positioned on the optical axis. 
     The first lens  21  is movable together with the second lens  23  in the tracking direction to follow up with the tracking servo control. A light beam from the semiconductor laser  3  is passed through these two objective lenses  23  and  21  by which it is focused on the phase-change information recording surface of the optical disc  1 . The effective NA of the two-group objective lenses  23  and  21  is about 0.85. 
     As the NA of the objective lenses increases, the skew tolerance of ordinary optical disc drive decreases. The wave front aberration due to disc skew (in X direction) can be represented using a Saidel&#39;s polynominal expression as follows: 
     
       
           W ( x,y )= W   22   X    2   +W   31    x ( X    2   +y   2 ) 2   
       
     
     where W 22 : Astigmatism, W 31 : Next coma and W 51 : Quinary coma. Of these terms, the most dominant one W 31  can be given in the following expression: 
     
       
           W   31 =( n   2 −1) n   2 sin θcos θ/2( n   2  −sin 2 θ) 2/5 ·tNA 3 /λ 
       
     
     where n: refractive index of the disc substrate and t: Disc substrate thickness. When the skew angle is as small as less than 1°, the refractive index n is approximately a cube of the NA and proportional to the disc substrate thickness t. 
     Therefore, for the optical disc drive using the aspherical two-group objective lenses  23  and  21  whose NA is about 0.85, the disc substrate must be as thin as about 0.1 mm to assure a same skew tolerance as that of DVD-RAM. 
     On the other hand, to form a phase-change recording medium on the disc substrate, a first dielectric layer (ZnS—SiO 2 ), recording layer (Ge 2 Sb 2 Te 5 ), second dielectric layer (ZnS—SiO 2 ) and a aluminum reflective layer are formed in this order on a disc substrate. However, it is difficult to form the above layers on a disc substrate of 0.1 mm in thickness on which addresses and sector marks have been pre-formatted by embossing. To solve this problem, the optical disc  1  for use with the phase-change optical disc drive according to the present invention is produced by providing an aluminum reflective layer  1 B, second dielectric layer  1 C (ZnS—SiO 2 )a, recording layer  1 D (Ge 2 Sb 2 Te 5 ), first dielectric layer  1 E (ZnS-SiO 2 ) and finally a disc protective layer  1 F of 0.1 mm in thickness on a pre-formatted disc substrate  1 A of 1.2 mm in thickness, as shown in FIG.  4 . The order of forming the layers is opposite to that in production of the conventional optical disc. 
     The recording pulse generation circuit  30  generates recording signals Data  1 , Data  2  and Data  3  for generation of light pulses and an output control signal Data  3 ′. 
     More particularly, the recording pulse generation circuit  30  comprises a recording signal generation circuit  31  as shown in FIG.  5 . The recording signal generation circuit  31  generates five kinds of recording signals including the above recording signal Data  1 , NRZI (No Return to Zero Inverse) pulse enable signal, leading pulse enable signal, pulse train enable signal, and trailing pulse enable signal. 
     The recording signal generation circuit  31  is switched between recording and reproduction modes by a CPU (not shown). When in the recording mode, this recording signal generation circuit  31  generates the above-mentioned five recording signals based on, for example, a 100-MHz master clock shown in FIG.  6 (A) and NRZI signal shown in FIG.  6 (B). The circuit  31  further comprises a channel clock sync pattern detection circuit  31   a  which judges, based on the NRZI signal, the length of the recording marks 3T to 11T, adjusts the delay time of each of variable delay elements  34 ,  37 ,  40  and  42  and thus determines a width of each pulse. The channel clock sync pattern detection circuit  31   a  similarly adjusts the delay time of each of variable delay elements  32 ,  35 ,  38  and  43  according to the judged recording mark length and thus sets a position of each pulse. The recording signal generation circuit  31  supplies the recording signal Data  1  to the variable delay element  32 , NRZI pulse enable signal to a D flip-flop  33  and variable delay element  34 , leading pulse enable signal to a D flip-flop  37  and variable delay element  37 , pulse train enable signal to a D flip-flop  39 , and the trailing pulse enable signal to a D flip-flop  41  and variable delay element  42 . 
     The variable delay element  32  delays the recording signal Data  1  a predetermined time and supplies it to the recording output control circuit  50 . The recording signal Data  1  is a logic signal which is at H (high) level when the recording signal generation circuit  31  is in the recording or reproduction mode, and at L (low) level when no laser output is existent, as shown in FIG.  6 (C). 
     Receiving the NRZI pulse enable signal from the variable delay element  34  as a reset signal, the D flip-flop  33  clears the NRZI pulse enable signal from the recording signal generation circuit  31  and supplies it to the variable delay element  35  which will delay the NRZI pulse enable signal a predetermined time and supplies it as an output control signal Data  3 ′ (NRZI pulse) to an OR gate  45  and recording output control circuit  50 . The output control signal Data  3 ′, namely, the NRZI pulse, is the NRZI signal in FIG.  6 (B) delayed a predetermined time as shown in FIGS.  6 (F) and  6 (G). When the NRZI pulse length is 2T, 3T or 8T, its width is 2T NRZIPW , 3T NRZIPW  or 8T NRZIPW , respectively, which is determined by the variable delay element  34 . The rise time of the NZRI pulse is delayed 2T NRZIPS , 3T NRZIPS or 8T NRZIPS  from the NRZI signal of 2T, 3T or 8T, respectively, which is determined by the variable delay element  35 . These NRZI pulses are used as output control pulse. 
     Receiving the leading pulse enable signal from the variable delay element  37  as a reset signal, the D flip-flop  36  clears the leading pulse enable signal from the recording signal generation circuit  31  and supplies it to the variable delay element  38  which will delay the leading pulse enable signal a predetermined time and supplies it to an OR gate  44 . 
     Receiving the master clock from the variable delay element  40  as a reset signal, the D flip-flop  39  clears the pulse train enable signal from the recording signal generation circuit  31  and supplies it to the OR gate  44 . The variable delay element  40  will delay the master clock from the recording signal generation circuit  31  a predetermined time and supplies it to the D flip-flop  39 . 
     Receiving the trailing pulse enable signal from the variable delay element  42  as a reset signal, the D flip-flop  41  clears the trailing pulse enable signal from the recording signal generation circuit  31  and supplies it to the variable delay element  43  which will delay the trailing pulse enable signal a predetermined time and supplies it to the OR gate  44 . 
     The OR gate  44  provides a logical sum of the pulses as the recording signal Data  3  and supplies it to the OR gate  45  and recording output control circuit  50 . The recording signal Data  3  consists of a leading pulse, a train of n−1 pulses and a trailing pulse for a recording mark having a length nT (n: integer from 2 to 8 and T: channel clock width), as shown in FIG.  6 (E). Note that for a recording mark having a length 2T, the recording signal Data  3  consists only of the leading pulse. 
     The OR gate  45  provides a logical sum of an inverted pulse of the output control signal Data  3 ′ and the recording signal Data  3 , and supplies it as a recording signal Data  2  to the recording output control circuit  50 . The recording signal Data  2  is as shown in FIG.  6 (D). 
     When supplied with the recording signals Data  1 , Data  2  and Data  3  via the recording output control circuit  50 , the semiconductor laser drive circuit  70  drives the semiconductor laser  3  to generate a laser light according to the multi-pulse shown in FIG.  6 (H). 
     The aforementioned construction of the recording pulse generation circuit  30  is just an example, and it may be configured otherwise if it can generate the recording signals Data  1 , Data  2  and Data  3  and the output control signal Data  3 ′ shown in FIGS.  6 (C) to  6 (F). 
     As shown in FIG. 7, the recording output control circuit  50  comprises a photoelectric transducer circuit  51  which transduces a current detected by the laser power monitoring detector  9  shown in FIG. 2 to a voltage to provide a LD control signal LDC, sample and hold circuits  52 ,  53  and  54  which sample and hold the LD control signal LDC, APC circuit  55  to control the signal level of the LD control signal LDC, delay elements  56  and  57  to delay a predetermined signal, sampled and held pulse select circuit  58  (will be referred to as “S&amp;H select circuit” hereinbelow) which selects and provides a sampled and held pulse from the predetermined signal, data selector  59  which selects a desired one of the recording signals Data  1  to output control signal Data  3 ′ and supplies it to the semiconductor laser drive circuit  70 , and a CPU (Central Processing Unit)  60  which controls the above circuits. 
     The photoelectric transducer circuit  51  supplies the sample and hold circuits  52 ,  53  and  54  with an LD control signal LDC obtained through the photoelectric transduction. The LD control signal LDC is detected a multi-pulse output obtained by the laser power monitoring detector  9 . 
     The sample and hold circuits  52 ,  53  and  54  sample the LD control signal LDC when the sampled and held pulse supplied from the S&amp;H select circuit  58  is at H level, and hold the LD control signal LDC when the sampled and held pulse is at L level. The sample and hold circuits  52 ,  53  and  54  supply such LD control signals LDC (LDC  1 , LDC  2  and LDC  3 , respectively) to the APC circuit  55 . 
     The APC circuit  55  controls the LD control signals LDC  1 , LDC  2  and LDC  3  separately to a predetermined level and supplies them to the semiconductor laser drive circuit  70 . The levels of the LD control signals LDC  1 , LDC  2  and LDC  3  are set by the CPU  60 . 
     The LD control signal LDC  1  designates a reproduction power (“read power” in FIG. 6) at the time of data reproduction and an erasure power (“bias power 1” in FIG. 6) to erase data at the time of data recording. The LD control signal LDC  2  designates a cooling power (“bias power 2” in FIG. 6) at the time of data recording. The LD control signal LDC  3  designates a peak power (“peak power” in FIG. 6) at the time of data recording. 
     The S&amp;H select circuit  58  provides a predetermined sampling pulse to the sample and hold circuits  52 ,  53  and  54  under the control of the CPU  60 . The S&amp;H select circuit  58  supplies the sample and hold circuits  52 ,  53  and  54  with a L- or H-level sampling pulse, inverts an NRZI signal supplied via the delay element  56  and supplies it to the sample and hold circuit  53 , and supplies the sample and hold circuit  54  with the output control signal Data  3 ′ (NRZI pulse) supplied via the delay elements  56  and  57 . 
     Under the control of the CPU  60 , the data selector  59  selects recording signals Data  1  to output control signal Data  3 ′ and provide them as LD recording signals LD Data  1  to  3  or the LD recording signals LD Data  1  to  3  set to a predetermined level. 
     For example, when in the recording power control mode, the data selector  59  provides the recording signal Data  1  as LD recording signals LD Data  1 , the LD recording signal LD Data  2  set to H level, and the output control signal Data  3 ′ as LD recording signal LD Data  3 . When in the ordinary recording mode, the data selector  59  provides the recording signal Data  1  as LD recording signal LD Data  1 , the recording signal Data  2  as LD recording signal LD Data  2 , and the recording signal Data  3  as LD control signal LDC  3 . When in the reproduction mode, the data selector  59  provides the recording signal Data  1  as LD recording signal LD Data  1  and the recording signal Data  1  as LED recording signal LD Data  1  and the LD data signal  2  set to L level. At this time, the data selector  59  will provide no LD control signal LDC  3 . When the semiconductor laser is off, the data selector  59  does not provide the LD recording signals LD Data  1  and  3  but provides the LED recording signal LD Data  2  set to L level 
     When in the recording power control mode, the recording output control circuit  50  will adjust the LD control signals LDC  1 , LDC  2  and LDC  3  as will be described below. 
     First, the data selector  59  provides the recording signal Data  1  as LD recording signal LD Data  1  and fixes the LD recording signals LD Data  2  and  3  to L level. The S&amp;H select circuit  58  supplies the sample and hold circuit  52  with a sampled and held pulse at H level. The sample and hold circuit  52  supplies the APC circuit  55  with the LD control signals LDC from the photoelectric transducer circuit  51 . The APC circuit  55  will set the LD control signal LDC  1  from the sample and hold circuit  52  to a predetermined level under the control of the CPU  60 . After a level is set for the LD control signal LDC  1 , the S&amp;H circuit  58  supplies the sample and hold circuit  52  at the enable terminal thereof with sampled and held pulse at L level. Thus, the LD control signal LDC  1  is fixed at L level. 
     Next, the data selector  59  provides the recording signal Data  1  as LD recording signal LD Data  1  and the output control signal Data  3 ′ as LD recording signal LD Data  3 , and fixes the LD recording signal LD Data  2  to H level. The S&amp;H select circuit  58  supplies an inverted one of the NRZI signal to the enable terminal of the sample and hold circuit  53 . Therefore, the sample and hold circuit  53  samples an output of the bias power  1  part and supplies it as LD control signal LDC  2  to the APC circuit  55 . Thus, the bias power  1  being a laser power of the multi-pulse is sampled by the sample and hold circuit  53  and controlled by the APC circuit  55  as will be discussed later. 
     The S&amp;H select circuit  58  supplies an inverted one of the output control signal Data  3 ′ (NRZI pulse) to the enable terminal of the sample and hold circuit  54 . Therefore, the sample and hold circuit  54  samples the peak power of the multi-pulse and supplies it as LD control signal LDC  3  to the APC circuit  55 . That is, the peak power being a laser power of the multi-pulse is sampled by the sample and hold circuit  54  and controlled by the APC circuit  55  as will be discussed later. 
     Since the bias power  2  of the multi-pulse has a same power as the read power, it is controlled based on a detected output of the RF signal during reproduction. The time of delay by the delay elements  56  and  57  corresponds to the time of delay by the semiconductor laser  3  and laser power monitoring detector  9  shown in FIG.  2 . 
     The APC circuit  55  sets the LD control signals LDC  2  and LDC  3  to a predetermined level under the control of the CPU  60 . The S&amp;H select circuit  58  supplies the sample and hold circuits  53  and  54  with an L-level sampled and held pulse and fixes the LD control signals LDC  2  and LDC  3  to the L level. 
     After the LD control signals LDC  1  to LDC  3  are set, the recording output control circuit  50  shifts to the ordinary recording mode. At this time, the data selector  59  will provide the recording signal Data  1  as LD recording signal LD Data  1 , the recording signal Data  2  as LD recording signal LD Data  2 , and the recording signal Data  3  as LD recording signal LD Data  3 . 
     As having been described in the foregoing, when in the recording power control mode, the recording output control circuit  50  supplies the semiconductor laser drive circuit  70  with the NRZI pulse shown in FIG.  6 (G) as LD recording signal LD Data  3 , the semiconductor laser  3  is caused to generate a light beam according to the NRZI pulse. The recording output control circuit  50  samples and holds, according to the NRZI pulse, a peak power of a light beam detected by the laser power monitoring detector  9 , so it is possible to control the laser beam power even for a multi-pulse of less than 10 ns in width. After completion of this light beam power control, data is recorded. 
     As shown in FIG. 8, the semiconductor laser drive circuit  70  comprises three current sources  71 ,  72  and  73  to supply a drive current to the semiconductor laser  3 . In the semiconductor laser drive circuit  70 , the current sources  71 ,  72  and  73  are selectively controlled according to three kinds of LD recording signals LD Data  1  to  3  supplied from the recording output control circuit  50  and LD control signals LDC  1  to LDC  3  corresponding to the LD recording signals to form a light waveform for the semiconductor laser  3 . 
     The LD control signal LDC  1  controls the operation of the first current source  71 , the LD control signal LDC  2  controls the operation of the second current source  72  and the LD control signal LDC  3  controls the operation of the third current source  73 . Each of the LD control signals LDC is set to a predetermined value by the recording output control circuit  50 , so that each of the currents from the first to third current sources  71  to  73  are set to a constant value. The semiconductor laser drive circuit  70  drives the semiconductor laser  3  to generate a multi-pulse according to the LD recording signals LD Data  1  to LD Data  3 . 
     As having been described in the foregoing, the phase-change optical disc drive according to the present invention can sample and hold a peak power of a light beam detected by the laser power monitoring detector  9  according to the NRZI pulse when in the recording power control mode even for data recording at a user transfer rate higher than 30 Mbps, thereby controlling the laser power. Therefore, even during data recording in which the laser power may possibly vary under the influence of the return light from the optical disc  1 , it is possible to stably control the peak power, bias power  1  and bias power  2  of the multi-pulse. 
     To implement the present invention, a recording output sampling area has to be provided on the optical disc  1  to control each output of the multi-pulse by generating an appropriate NRZI pulse (for example, repetition of a 3 T pattern). 
     However, the above recording output sampling area may also be buried in an ordinary recorded data to set and control a recording power without any special area provided on the optical disc  1 . In this case, the multi-pulse and NRZI pulse are different from each other in the rates at which the optical disc  1  is heated or cooled. For aligning the leading and trailing edges of a recording mark with each other between the heating and cooling, appropriate methods of temperature compensation are available. The phase-change optical disc drive according to the present invention can control the pulse width to a predetermined value by the variable delay elements  34 ,  37 ,  40  and  42 , respectively, and also the pulse position to a predetermined position by the variable delay elements  32 ,  35 ,  38  and  43 , respectively. Namely, since the pulse width and laser irradiation position of the NRZI pulse and multi-pulse can be controlled correspondingly to recording marks 2T to 8T, respectively, the leading and trailing edges of the recording marks can be accurately controlled. That is, the quality of a reproduced signal will not be deteriorated. 
     It should be noted that the present invention is not limited only to the embodiment having been described in the foregoing. For example, the NRZI pulse is used as output control signal, but it may be a pulse having a larger width than the multi-pulse. Also, the present invention may easily be built along with a wider-band and high-speed APC circuit in a large scale integrated circuit, thereby permitting to design a more compact circuit. 
     As having been discussed in the foregoing, the recording/reproducing apparatus and method for a phase-change optical disc can control the multi-pulse power even at a high transfer rate by generating an output control pulse having a larger width than the multi-pulse when in the power control mode, causes the semiconductor laser to generate a light pulse according to the output control pulse, samples and holds the laser power detected by the detecting means according to the output control pulse and controlling the laser power of the semiconductor laser so that the sampled and held laser power has a predetermined value.