JP2009245557A - Information recording method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording method capable of improving its direct overwriting characteristics, and to provide an information recording device using the same. <P>SOLUTION: In an information recording method which uses short-pulse light using relaxation oscillation of a semiconductor laser, the direct overwrite characteristics are improved by using light having a cooling pulse driven by a current smaller than the light-emitting threshold current of the semiconductor laser after the last recording pulse of a short pulse train recording a predetermined length of a mark, and further having a boost pulse driven by a current larger than an erase pulse drive current at the head of the erase pulse. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an information recording method for recording information on a recording medium having a recording layer with a laser beam from a light source, and an information recording / reproducing apparatus such as an optical disk drive device using the recording method.

  One of the optical recording media that records light by irradiating the recording medium with light and forming optically distinguishable marks by the generated heat, utilizing the phase change between crystalline and amorphous due to heat Thus, there is a phase change medium for recording.

  The recording film of the phase change type medium is a crystal in a steady state, but the region irradiated with light is heated, melted, and then cooled to cause a phase change to amorphous.

  Information can be recorded by forming an amorphous portion as a mark using this principle.

  In such a phase change type medium, a PWM (Pulse Width Modulation) system that corresponds to binary information for recording the start and end positions of the mark is effective in improving the recording density.

  In general, when applying the PWM method to an optical disc, in order to reduce the heat storage effect associated with light irradiation, when forming a long mark, use a light pulse divided into a plurality of light instead of a single light pulse. So-called multi-pulse recording is performed.

  As a more advanced example, even in high-speed recording with high linear density and narrow track pitch, the use of sub-nanosecond-class short light pulses using relaxation oscillation for unit mark formation eliminates thermal interference and recrystallization. A system that enables high-quality recording has already been proposed by a development group including the present inventors.

  In addition, it is known that at the time of rewriting (overwriting), it is possible to directly overwrite the previous recording area by irradiating the space portion with an erasing power smaller than the recording power.

Japanese Patent Application Laid-Open No. 2004-228561 describes that the overwrite characteristic is improved by adding an erase head pulse to the head of the erase power.
JP 2006-209935 A

  However, simply adding the leading pulse as in the method described in Patent Document 1 increases wasteful energy input, and the deterioration of the recording film is promoted by increasing the number of times of overwriting. There is a fear. Therefore, in the method described in Document 1, it is necessary to optimize the recording waveform in consideration of the characteristics of the medium during high-speed recording.

  In phase change recording technology, it is known that rapid cooling (cooling) after heating is important for mark formation. In particular, in order to support high-speed recording, a short sub-nanosecond class recording pulse is used. In the case of rapid heating, it is known that if the cooling period is not sufficient, the cooling is insufficient and the mark formation is liable to occur. That is, the setting of the cooling period is important in order to maintain the initial recording characteristics.

  On the other hand, since the cooling period is required to reduce the laser power below the erasing power, the longer the cooling period after the recording pulse, the longer the erasing power start time is delayed, the non-erasing area is enlarged, There is a possibility that the recording mark of the previous recording will be erased and the direct overwrite characteristic is deteriorated.

  An object of the present invention is to provide an information recording method capable of improving the direct overwrite characteristic and an information recording apparatus using the recording method.

  The present invention has been made based on the above problems, and in an information recording method using short pulse light using relaxation oscillation of a semiconductor laser, the recording pulse at the end of a short pulse train for recording a mark of a predetermined length is recorded. Using light having a cooling pulse driven with a driving current smaller than the emission threshold current of the semiconductor laser and a boost pulse driven with a driving current larger than the erasing pulse driving current at the head of the erasing pulse The present invention provides an information recording method characterized by recording information on a recording medium.

  According to the embodiment of the present invention, a sufficient cooling period is provided, and the head of the erase area is expanded by adding light emission for a short period of time that is larger than the erase power to the head of the subsequent erase power. Even when overwriting is repeated, it is possible to reduce the deterioration of the reproduction signal due to unerased recorded marks.

  That is, the direct overwrite characteristic is improved, and a recording mark that can obtain a stable reproduction signal is formed even when overwriting is repeated.

  The overall operation and detailed operation of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an example of the configuration of an information recording / reproducing apparatus (optical disc drive) to which the present invention can be applied.

  The information recording / reproducing apparatus (optical disc drive) records information on the recording surface of the information recording medium (optical disc) 100 or reproduces information recorded on the recording surface.

  The recording surface of the optical disc 100 has grooves concentrically or spirally formed. The concave portion of the groove is called a land, the convex portion is called a groove, and one round of the group or land is called a track.

  User data is recorded by forming recording marks by irradiating intensity-modulated laser light along tracks (grooves only or grooves and lands). Data reproduction is performed by irradiating a laser beam having a weaker read power than that at the time of recording along the track and detecting a change in reflected light intensity due to a recording mark on the track.

  The recorded data can be erased by irradiating a laser beam of erase power stronger than the read power along the track to crystallize the recording layer.

  The optical disk 100 is rotated at a predetermined speed by the spindle motor 63.

  A rotation angle signal is output from a rotary encoder 63A provided in the spindle motor 63. The rotation angle signal is generated, for example, 5 pulses when the spindle motor 63 makes one rotation. The spindle motor control circuit 64 determines the rotation angle and rotation speed of the spindle motor 63 from the rotation angle signal.

  Information recording / reproduction with respect to the optical disc 100 is performed by an optical pickup (Pick Up Head, PUH) 65.

  An optical pickup (PUH, hereinafter simply referred to as an optical head) 65 is connected to a feed motor 67 via a gear and a screw shaft, and this feed motor 67 is controlled by a feed motor control circuit 68. When the feed motor 67 is rotated by the feed motor drive current from the feed motor control circuit 68, the optical head 65 moves in the radial direction of the optical disc 100.

  The optical head 65 is provided with an objective lens 70 supported by a wire or a leaf spring (not shown) so as to be movable by a predetermined distance in the direction orthogonal to the recording surface of the optical disc 100 and in the radial direction of the optical disc 100. The objective lens 70 can be moved in the focusing direction (the direction orthogonal to the recording surface, that is, the optical axis direction of the objective lens 70) by driving the drive coil 72, and the tracking direction (the radius of the optical disc 100) by driving the drive coil 71. Direction, that is, a direction orthogonal to the optical axis of the objective lens 70).

  The laser modulation control circuit 75 provides a write signal to a laser diode (laser light emitting element) 79 based on recording data supplied from the host device 94 via the interface circuit 93 during information recording (mark formation). To do.

  Laser light generated by the laser diode 79 enters the half mirror 96. The half mirror 96 branches the laser beam generated by the laser diode 79 by a certain ratio.

  A monitor light detector (FM-PD) 95 constituted by a photodiode receives a part of the laser light from the half mirror 96. The monitor light detector (FM-PD) 95 detects partial light proportional to the irradiation power of the laser light, and supplies a light reception signal to the laser modulation control circuit 75.

  The laser modulation control circuit 75 is based on the intensity of the reflected laser beam received by the monitor light detector 95, and the laser power during reproduction and the laser power during recording set by the main processing block 90 including the central processing unit (CPU). Further, the laser diode 79 is controlled so that the laser power at the time of erasing can be appropriately obtained.

  The laser diode 79 generates laser light in accordance with the drive current supplied from the laser modulation control circuit 75. Laser light emitted from the laser diode 79 is irradiated onto the optical disc 100 via the collimator lens 80, the half prism 81, and the objective lens 70. The reflected light from the optical disk 100 is guided to the photodetector 84 through the objective lens 70, the half prism 81, the condenser lens 82, and the cylindrical lens 83.

  The photodetector 84 is composed of, for example, four-divided photodetection cells, and detection signals from these photodetection cells are output to the RF amplifier 85. The RF amplifier 85 processes a signal from the photodetection cell, a focus error signal FE indicating an error from the in-focus position, a tracking error signal TE indicating an error between the laser beam spot center and the track center, and the photodetection cell. A reproduction signal that is a full addition signal of the signals is generated.

  The focus error signal FE is supplied to the focus control circuit 87. The focus control circuit 87 generates a focus drive (control) signal according to the focus error signal FE. The focus drive signal is supplied to the drive coil 71 in the focusing direction. Thus, focus servo is performed in which the laser beam is always just focused on the recording film of the optical disc 100.

  The tracking error signal TE is supplied to the track control circuit 88. The track control circuit 88 generates a track driving signal according to the tracking error signal TE. The track drive (control) signal output from the track control circuit 88 is supplied to the drive coil 72 in the tracking direction. As a result, tracking servo is performed in which the laser beam always traces the track formed on the optical disc 100.

  By performing the focus servo and the tracking servo, the full addition signal RF of the output signal of each light detection cell of the light detector 84 includes a record mark formed on the track of the optical disc 100 corresponding to the record information. Changes in the reflected light from are reflected. This signal is supplied to the data reproduction circuit 78. The data reproduction circuit 78 reproduces recorded data based on the reproduction clock signal from the PLL circuit 76.

  When the objective lens 70 is controlled by the tracking control circuit 88, the feed motor 67, that is, the optical head (PUH) is arranged by the feed motor control circuit 68 so that the objective lens 70 is positioned in the vicinity of a predetermined position in the optical head 65. The position of 65 is also controlled.

  A spindle motor control circuit 64, a feed motor control circuit 68, a laser control circuit 73, a PLL (Phase Locked Loop) circuit 76, a data reproduction circuit 78, a focus control circuit 87, a track control circuit 88, an error correction circuit 62, etc. It is controlled by the main processing block (CPU) 90 via the (Bus) 89. A CPU (main arithmetic processing block) 90 controls the overall operation of the recording / reproducing apparatus in accordance with an operation command provided from the host device 94 through the interface circuit 93. In addition, the CPU 90 uses a RAM (Random Access Memory) 91 as a work area, appropriately refers to the parameters for each device recorded in the nonvolatile memory (NV-RAM) 99, and records them in a ROM (Read Only Memory) 92. A predetermined operation is performed according to a control program including the program according to the present invention. Needless to say, the error correction circuit 62 performs error correction of the reproduction signal.

  The wavelength λ of the laser light output from the laser diode (semiconductor laser element) 79 is, for example, 450 nm (nanometers) or less, and preferably 405 ± 5 nm.

The numerical aperture NA (numerical aperture) of the objective lens 70 is, for example, 0.6 to 0.65, and the pitch (interval) TP of tracks (guide grooves) formed on the optical disc 100 and the shortest mark described later. When the wavelength of the laser beam output from the laser diode 79 is λ between the length L (2T) and the shortest mark length L,
λ / (4 × NA) ≦ L ≦ λ / (2.5 × NA)
It is preferable that

The wavelength of the laser beam output from the laser diode 79 is λ between the pitch (interval) TP of tracks (guide grooves) formed on the optical disc 100 and the shortest mark length L (2T) described later. When the track pitch TP is
λ / (2 × NA) ≦ TP ≦ λ / (1.3 × NA)
It is preferable that

  FIG. 2 shows an example of the configuration of the laser drive circuit in the information recording / reproducing apparatus shown in FIG.

  FIG. 2 shows a write strategy (recording waveform (laser light) optimization) circuit 7503 for generating a recording waveform from a recording clock and recording data, a peak (PEAK / WRITE) power, an erase (ERASE) power, and a read (READ). DAC (D / A converter) units 7504 to 7507 for setting indication values of individual drive currents to be supplied to the laser diode 79 in order to enable laser emission of power and bias (BIAS) power, peak power, An interface for interpreting control signals from the current sources 7508 to 7511 and the signal bus 89 for the erase power, read power, and bias power, and controlling the entire drive current supplied from the laser modulation control circuit 75 to the laser diode 79 ( I / F) portion 7501 is included.

  Although not described in detail, the write strategy circuit 7503 includes a PLL (Phase Locked Loop) circuit and a modulation circuit. The PLL circuit receives the recording clock and generates a timing signal necessary for the modulation circuit. The modulation circuit interprets the recording data, generates a recording waveform according to a control signal including strategy information such as a pulse width and edge timing set by the internal bus 7502, and sets the timing for turning on / off each of the current sources 7508 to 7511. Decompose into the timing signal shown.

  The timing signal is connected to the selector 7512, and each current source 7508 set so that a different current value is output by each current setting DAC 7504 to 7507 to which the current command value is set by the internal bus 7502 according to the timing signal. The intensity of the laser drive current supplied to the laser element 79 is generated by turning on / off .about.7511. This achieves intensity modulation of the irradiation power during recording.

  In the embodiment of the present invention, the pulse width and the current value are supplied as control signals from the CPU 90 to the laser modulation control circuit 75 through the signal bus 89.

  The pulse width and current value are sent to the write strategy circuit 7503 and the individual current setting DACs 7504 to 7507 via the interface circuit 7501 and the internal bus 7502.

  In the example of FIG. 2, the erase boost pulse current source and the current setting DAC are used in common with the PEAK current source 7504 and the PEAK current setting DAC (current source) 7508 that are the same as the PEAK pulse. Needless to say, the erase boost current source and the current setting DAC (current source) may be provided separately.

  Next, a calibration process performed for a recording process using a sub-nano class pulse laser beam, that is, a laser beam that is an extremely short-time emission generated by relaxation oscillation, according to an embodiment of the present invention will be described with reference to FIG. Will be described.

  In order to perform recording processing using pulsed laser light, that is, laser light that is emitted in a very short period (sub-nanoclass) generated by relaxation oscillation, the write strategy is determined by the write strategy circuit 7503 described with reference to FIG. is necessary.

  For this reason, for example, by supplying a predetermined control signal to the laser modulation control circuit 75 connected to the CPU 90 through the signal bus 89, the calibration is executed as follows.

  According to the flowchart shown in FIG. 3, first, initial setting conditions prepared in the optical disc 100 or the servo driver 30 are read (step S11). Next, based on the read initial setting value, for example, one peak current and drive pulse width are temporarily determined from among five types of peak current values and drive pulse widths (step S12).

  Next, for the spatial frequency transfer characteristics of the optical pickup head used for recording / reproduction, a signal containing a long mark that provides a sufficient degree of modulation is used as the recording signal, and the peak current is calibrated so that the degree of modulation is sufficient. (Step S13). Here, the long mark with a sufficient degree of modulation is 11T, but this is possible as long as it is one of 6T to 13T as an example. T represents one clock cycle, and the shortest mark is 2T.

  Subsequently, the laser beam for reading written on the optical disc 100 is irradiated with the laser beam including the relaxation oscillation emitted at the above value to detect the reflected light (step S14), and based on the detection result. The write strategy (optimization of recording waveform (laser light)) is determined.

  For example, the peak current to be set is gradually increased to determine whether or not the amplitude of the detection signal of the reflected light is maximized (step S15), and the peak current value when the amplitude is maximized is written. It is determined as the peak current value of the strategy and is stored in a storage area not described in detail of the write strategy circuit 7503 (step S16).

  Next, a recording signal in which a shortest mark and a sufficiently long mark are mixed, for example, any one of 6T to 13T, for example, an 11T mark, a space and a 2T mark which is the shortest mark, a mixed signal of spaces, etc. Perform pulse width calibration. That is, trial writing is performed on the optical disc 100 with the laser beam having the relaxation oscillation emitted at this value for the temporarily determined pulse width (step S17).

  Subsequently, in step S12, a laser beam for reading is irradiated onto a region written on the optical disc 100 by laser light having relaxation oscillation, and the reflected light is detected (step S18).

  Hereinafter, the asymmetry of the reproduction signal (an index for evaluating whether the center level of each T signal is at the same level) is calculated, and the pulse width is adjusted to be approximately zero (step S19). The pulse width at the time is determined as a strategy and stored in a storage area (not described in detail) of the write strategy circuit 7503 (step S20).

The asymmetry is a signal obtained by detecting the amplitude level on the positive side (upper side) with the peak level detection circuit with reference to 0 V in a state where the reproduction RF signal is AC-coupled by passing through a high-pass filter. Value), and the signal detected by the bottom level detection circuit with the amplitude level on the negative side (lower side) with respect to 0V as A2 (usually a negative value)
Asymmetry value = (A1 + A2) / (A1-A2)
It is preferable to use the value represented by (asymmetry value).

  Here, as a method for determining the pulse width, the signal level from the reproduction signal level of the unrecorded area to the amplitude center of the detection signal when the 11T continuous pattern is used as the recording pattern is the reproduction signal level of the unrecorded area. To a signal level that is approximately twice the signal level up to the amplitude of the detection signal when a continuous pattern of the shortest mark length (2 clocks when 2T, 1T is used as a clock) is used as a recording pattern. The same effect can be obtained by searching for the pulse width, determining this pulse width as a strategy, and storing it in a storage area such as the write strategy section 41.

  As described above, the strategies used for the relaxation vibration recording process are the pulse edge timing for each recording mark length and the edge timing applied for each front / rear mark length / space length and recording mark length as in the conventional recording process. It is characteristic that it is defined only by the shortest pulse width, not by the compensation value.

  The write strategy obtained in this way and stored in the write strategy unit 41 is read out during the data recording process under the control of the control unit 31. In the recording process using the relaxation oscillation of the optical laser, the peak current value and the erase current value are determined based on the read write strategy, and the recording process to the optical disc is performed (step S21).

  In general, the relaxation oscillation is useful for generating a steep pulse having a recording pulse length shorter than 1 ns (nanosecond), and a pulse of a laser driving current supplied to the laser diode 79 as a recording pulse. The rise / fall time is less than 100 ps (picoseconds).

As a condition for causing relaxation oscillation, as shown in FIGS. 4A and 4C, the drive current is shown in FIG. 4A when the bias current I _bi and the peak current I _pe are considered. Thus, the bias current I _bi set to a level slightly higher than the threshold current Ith at which the laser diode 79 starts laser oscillation is first generated, and the laser diode 79 is preliminarily driven. Thereafter, a peak current I _pe for obtaining a desired peak power is applied at a time A until it is lowered to the bias current I _bi at a time B. Thus, by applying the peak current I _pe from time A to time B, laser output (time change in laser emission light intensity) as shown in FIG. 4B is obtained.

That is, until the time A when the magnitude of the laser drive current is the bias current I _bi , the intensity of the emitted light is such that the laser light output from the laser diode 79 cannot record data on the optical disc 100. Although the power is very low, the peak current I _pe is applied, and the intensity of the laser light is increased to the recording power. Needless to say, after time B, the intensity of the emitted light again becomes low power.

  When the intensity of the emitted light is observed in more detail, in FIG. 4B, when the intensity is raised to the recording power at time A, the intensity instantaneously increases until the steady recording power is stabilized. You can see how it falls (arrow c in the figure). This is due to the relaxation oscillation of the laser diode 79. In normal recording pulse generation, control is performed so that this relaxation oscillation is minimized.

  In this way, relaxation oscillation is a transient oscillation phenomenon that occurs when the drive current suddenly increases from a certain level to a certain level that greatly exceeds the threshold current in the semiconductor laser.

  Note that the relaxation vibration becomes smaller every time the vibration is repeated, and the vibration is eventually stopped.

  In the optical recording apparatus of the present invention, this relaxation vibration is actively used for recording.

  That is, although it is originally a relaxation vibration that should be suppressed, the “pulse length is short” and “energy amount (integral value of laser power as optical output) peculiar to the relaxation vibration are recorded on the recording film of the optical disc 100. It is an object of the present invention to obtain “stable” a steep recording pulse having a short pulse length by utilizing the fact that “the recording level may be changed”.

  As shown in FIG. 4C, when a drive current having a predetermined characteristic is supplied to the laser diode 79 from the laser modulation control circuit 75, a laser with high peak level is accompanied by vibration as seen in FIG. Output is obtained for only a short time.

More specifically, a bias current I _bi set to a level lower than the threshold current I _th is supplied to the laser diode 79, and at a predetermined timing, that is, time A, the laser diode 79 suddenly rises with a rise time earlier than normal recording pulse generation. In addition, the drive current is raised to a peak current level I _pe higher than the threshold current I _th , and the bias current I _{bi is} at time D after a short time of nanosecond (ns) level shorter than the normal recording pulse generation. Return to.

  In this case, as can be seen in FIG. 4D, laser output (time change in laser emission light intensity) is obtained.

That is, in FIG. 4D, the laser diode 79 does not start laser oscillation until the time A when it is driven by the bias current I _bi lower than the threshold current I _th , and the level is negligible. Thus, light emission as a light emitting diode is to some extent. After that, when current is suddenly applied at time A, relaxation oscillation occurs and the emitted light intensity also rises rapidly.

Hereinafter, the amplitude of the relaxation oscillation gradually converges to a steady level. However, by setting a predetermined time, that is, time C, and setting the drive current to I _bi that is lower than the threshold current I _th , a laser beam having a certain energy amount can be obtained. can get. Note that time C is the timing at which the pulse of the second period of the relaxation oscillation is generated, as is apparent from FIGS. 4C and 4D.

  As described above, the pulse due to relaxation oscillation has a feature that the emitted light intensity increases in a very short time compared to a normal recording pulse, and the emitted light intensity decreases at a certain period determined by the structure of the semiconductor laser. ing. Therefore, by using a pulse due to relaxation oscillation as a recording pulse, it is possible to obtain short pulse light having a short rise / fall time and a strong peak intensity, which cannot be obtained with a normal recording pulse.

  Next, an outline of a recording process using a sub-nano class pulse laser beam, that is, a short laser beam generated by relaxation oscillation will be described with reference to FIGS. 5A to 5E are timing charts showing one form of each signal when the 2T mark and the 3T mark of the optical disc apparatus are formed. FIG. 5A shows 1T, that is, the clock CLK.

When forming the 2T mark, one pulse is supplied from the laser modulation control circuit 75 to the laser diode 79 as shown in FIG. In FIG. 5C, the pulse width T _W , the peak current I _PEAK , the bias current I _BIAS , and the erase current I _ERASE are shown. When forming a 3T mark, two pulses are supplied from the laser modulation control circuit 75 to the laser diode 79.

  As shown in FIG. 5D, the laser light output from the laser diode 79 shows a very steep power in a pulse shape, and several vibration waveforms, that is, from FIG. 4A to FIG. The relaxation vibration explained using the above is seen.

  What should be noted here is that the laser light output by using the relaxation oscillation method according to one embodiment of the present invention is very low, in terms of power consumption, approximately 1/5 compared to a known method. Recording processing is possible with less energy. That is, as an example, in the conventional driving method, energy of about 300 pJ (picojoule) is required to record a 4T mark with a peak power of 10 mw, a current value of 80 mA, and a multipulse width of 30 ns. By using relaxation oscillation, the energy of pulsed laser light with relaxation power having a peak power of 40 mw, a current value of 150 mA, and a signal time width of 1.5 ns is 20 pJ. When recording a 4T mark, a recording pulse (laser beam) is used. In the case of three, the required energy is about 60 pJ (picojoule), and recording of a 4T mark is possible with a very small energy of about one fifth.

  By the way, in the example shown in FIGS. 5A to 5E, in the period until the erase pulse is output subsequent to the write pulse, that is, in the region until the erase pulse is output after the write pulse. 6 (A) or 6 (B) schematically shows a recrystallization region accompanying melting of the periphery (FIG. 6 (A)), a non-heated region accompanying laser OFF (FIG. 6 (B)). Has been confirmed to occur. This means that when direct overwrite recording is repeated, the reproduction signal may be deteriorated as an unerased area.

Therefore, in order to suppress the appearance of the recrystallization region / non-heated region shown in FIGS. 6A and 6B, the binarized recording data (NRZI) is changed from FIG. As shown in the drive current for driving the laser diode 79 and the optical output waveform, the write pulse peak current is I _p , the erase current is I _e , and the bias current is the cooling period for the last pulse of the write pulse. I _b , the current in the cooling period is I _c , the boost current is I _bst , the oscillation threshold current of the laser diode 79 is I _th, and for each current value,
_{I b = I c <I th} <I e <I bst ≦ I p ··· (1)
It is preferable to add light emission by the boost current I _bst determined by giving the relationship of the above formula (1), that is, a boost pulse. More specifically, for example, when forming a 4T recording mark, the pulse width of the recording pulse is T _w , the pulse width of the cooling pulse is T _c , the pulse width of the boost pulse is T _bst , and the channel clock interval is T, As the pulse width relationship,
T _bst ≦ T _w <1.5 ns (nanoseconds)
0.8T < _Tc
As a result, as shown in FIG. 6C, a recrystallization region as shown in FIG. 6A and a non-heated region as an unerased region as shown in FIG. 6B are generated. Can be suppressed.

  That is, at the time of recording (PEAK / WRITE = write pulse output), the write strategy generation unit 7503 detects the channel clock WCLK and the binarized recording data WDATA, and preset timing (pulse width / number of pulses) through the internal bus 7502. ) Generates a timing signal for controlling the selector 7512.

When writing the 4T recording mark shown in FIG. 7A, considering only during WRITE, the switch (READ_SW, in the selector 7512) connected to the READ current source 7510 is turned off, and the BIAS timing of FIG. At (T _bst ), the switch (PEAK_SW, in selector 7512 / ERASE_SW, same) connected to PEAK current source 7508 and ERASE current source 7509 is turned off, and the connection switch (BIAS_SW, same) to bias current source 7511 is turned on. . Further, as shown in FIG. 7C, at the timing of PEAK (LD output), PEAK_SW (in the selector 7512) is turned on and ERASE_SW (same) is turned off. At this time, by turning on BIAS_SW (same as above), a current obtained by adding the PEAK current and the BIAS current is obtained. Note that if only the PEAK current source bears the peak power, BIAS_SW may be turned off.

Hereinafter, after a predetermined pulse width time T _w has elapsed, turn off again PEAK_SW, in the supplies only BIAS current into the laser diode 79, an extremely short period of time the light pulses with the relaxation oscillation can be obtained.

  Therefore, a recording mark (see FIGS. 5C to 5E) is recorded on the disk 100 for each unit pulse, with one light pulse in the very short period as a unit pulse.

The pulse width T _w, by being set between the relaxation oscillation 1-5 cycles, no thermal interference, regardless of the moving velocity of the medium, it is possible to stable recording mark formation. In this embodiment, the recording mark formed by the unit pulse is the shortest length mark. However, it is also conceivable that the mark formed by a plurality of unit pulses is the shortest length mark.

Hereinafter, the re-BIAS current portion, generally output bias pulse of 1T period, is output PEAK current again pulse width (period) _{T w.}

  Accordingly, when recording a 4T mark, three unit pulses are emitted at 1T intervals.

  That is, when the shortest mark length based on the recording modulation system is 2T, the shortest mark is represented by an optical pulse of M (M: 1 or more) ultrashort time, and the recording mark is NT (N: integer, T: In the case of (channel clock width), a recording mark is formed by the shortest mark continuous with (N-1) 1 channel clock intervals. Therefore, when the shortest mark length is 3T, the shortest mark is represented by one short light pulse, and when the recording mark is NT (N: integer, T: channel clock width), (N-2) 1 It can be represented by the shortest consecutive marks with a channel clock interval.

  On the other hand, after the last pulse is output from the series of recording pulses, the process proceeds to the BIAS current section again as a cooling period for cooling. Here, after the elapse of time Tc, the process proceeds to the PEAK current period (PEAK pulse output) as an erase boost pulse. The PEAK pulse is a pulse for erasing and has a role different from that of the conventional PEAK pulse for forming a mark. However, when the circuit shown in FIG. 2 is used, the circuit scale can be reduced. Therefore, since it is assumed that the same current source and DAC (D / A converter) as the PEAK current are used, a pulse having the same current value as the PEAK pulse is output.

Thereafter, after the pulse width time T _{bst has} elapsed, the process _proceeds to the erase current portion (erase pulse output).

  By setting such recording waveform (peak current supply) and cooling period, it is a rewritable phase change recording medium, which has excellent recording characteristics even under conditions of high linear velocity, high linear density, and narrow track pitch. And overwrite characteristics are obtained.

  More specifically, in short pulse recording using relaxation oscillation of a semiconductor laser, a cooling pulse having a power level smaller than the erasing power is provided after the last recording pulse of a short pulse train for recording a mark of a predetermined length. Furthermore, the direct overwrite characteristic can be improved by adding a boost pulse having a power level larger than the erase power to the head of the erase power.

If the driving current pulse width of the cooling pulse is T _c and the channel clock width T, preferably,
T _c > 0.8T
It is.

Also, _assuming that the drive current of the boost pulse is I _bst , the boost pulse width is T _bst , the drive current of the recording pulse is I _p , and the pulse width is T _w ,
I _bst ≦ I _p and T _bst ≦ T _w .

In addition, the drive current pulse width T _w of the recording pulse,
T _w <1.5 ns (nanoseconds)
It is.

  FIG. 8 shows the relationship between the cooling pulse width (Tc) and bER (bit error rate) when repeated recording (direct overwrite) is continued an arbitrary number of times. That is, in FIG. 8, as bER is smaller, the error rate in repeated recording is reduced, and the recrystallization region and the non-heated region as shown in FIGS. 6A and 6B are suppressed. Indicates.

  In addition, FIG. 8 shows bER when the number of repetitions (direct overwrite (DOW)) is five, and the cooling pulse width is within a range of 0.8T to 1.13T, regardless of the number of repetitions. It is recognized that the unerased residue is sufficiently suppressed.

  FIG. 9 shows a difference in bER between the current overwrite recording described with reference to FIGS. 4 and 5 and the proposed overwrite recording, that is, the bER is improved by the proposed overwriting regardless of the number of repeated recordings. Show.

Of course, the bER deteriorates abruptly when the direct overwriting is repeated, but the bER changes by about 1.0 × 10 ⁻⁶ by adopting the proposed overwriting.

  As described above, by using one of the embodiments of the present invention, a sufficient cooling period is provided, and light emission for a short time with a power larger than the erasing power is added to the head of the subsequent erasing power to By enlarging the head, it is possible to suppress the amount of input heat, and it is possible to reduce the deterioration of the reproduction signal due to unerased recorded marks even when overwriting is repeated.

  That is, the direct overwrite characteristic is improved, and a recording mark that can obtain a stable reproduction signal is formed even when overwriting is repeated.

  Note that the present invention is not limited to any of the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in any of the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows an example of the information recording / reproducing apparatus (optical disc drive) which can apply this invention. Schematic which shows an example of the laser drive circuit in the information recording / reproducing apparatus shown in FIG. FIG. 3 is a flowchart for explaining an example of a calibration process performed for a recording process using laser light, which is light emission for a very short time caused by relaxation oscillation using the laser driving circuit shown in FIG. 2. FIG. 3 is a schematic diagram for explaining an example of a laser driving method for causing relaxation oscillation using the laser driving circuit shown in FIG. 2. FIG. 3 is a schematic diagram for explaining an example of a recording process using a laser beam generated by relaxation oscillation using the laser drive circuit shown in FIG. 2. FIG. 6 is a schematic diagram illustrating a characteristic example of a recording mark that may be generated by the recording process illustrated in FIG. 5 and an example of a recording mark according to the present proposal. Schematic explaining the example of the recording pulse of this proposal, a cooling pulse, an erase pulse, and an erase boost pulse (off pulse). The graph explaining the relationship between the proposed cooling pulse width and the bit error rate during direct overwrite. The graph explaining the extent to which a bit error rate is improved by using the cooling pulse and erase boost pulse of this proposal.

Explanation of symbols

  62 ... Error correction circuit, 63 ... Spindle motor, 63A ... Rotary encoder, 64 ... Spindle motor control circuit, 65 ... Optical head, 67 ... Feed motor, 68 ... Feed motor control circuit, 70 ... Objective lens, 71, 72 ... Drive Coil, 75 ... Laser modulation control circuit, 76 ... PLL circuit, 78 ... Data recovery circuit, 79 ... Laser diode, 80 ... Collimator lens, 81 ... Half prism, 82 ... Condensing lens, 83 ... Cylindrical lens, 84 ... Light detection 85 ... RF amplifier, 87 ... focus control circuit, 88 ... tracking control circuit, 89 ... signal bus, 90 ... central processing unit, 91 ... RAM, 92 ... ROM, 93 ... interface circuit, 94 ... host device, 95 ... monitor light detector, 96 ... half mirror, 99 ... nonvolatile memory, 100 ... light Disk, 7501 ... I / F (interface) section, 7502 ... internal bus, 7503 ... write strategy circuit, 7504 ... peak power DAC, 7505 ... erase power DAC, 7506 ... read power DAC, 7507 ... bias power DAC, 7508 ... peak Power current source, 7509 ... Erase power current source, 7510 ... Read power current source, 7511 ... Bias power current source, 7512 ... Selector.

Claims (13)

In an information recording method using short pulse light using relaxation oscillation of a semiconductor laser,
There is a cooling pulse driven by a drive current smaller than the emission threshold current of the semiconductor laser behind the last recording pulse of a short pulse train that records a mark of a predetermined length, and an erase pulse is driven at the beginning of the erase pulse. An information recording method, wherein information is recorded on a recording medium using light having a boost pulse driven by a driving current larger than the current. When the driving current pulse width of the cooling pulse is T _c and the channel clock width is T,
T _c > 0.8T
2. The information recording method according to claim 1, wherein When the drive current of the boost pulse is I _bst , the boost pulse width is T _bst , the drive current of the recording pulse is I _p , and the pulse width is T _w ,
I _bst ≦ I _p and T _bst ≦ T _w
The information recording method according to claim 1, wherein: A drive current pulse width T _w of the recording pulse,
T _w <1.5 ns
The information recording method according to claim 1, wherein: When the wavelength of the laser beam is λ and the numerical aperture of the objective lens for condensing the laser beam is NA, the shortest mark length L is
λ / (4 × NA) ≦ L ≦ λ / (2.5 × NA)
The information recording method according to claim 1, wherein the following condition is satisfied. When the wavelength of the laser beam is λ and the numerical aperture of the objective lens for condensing the laser beam is NA, the track pitch TP is
λ / (2 × NA) ≦ TP ≦ λ / (1.3 × NA)
The information recording method according to claim 1, wherein the following condition is satisfied.   The information recording method according to claim 1, wherein a wavelength λ of the laser beam is 450 nm or less. A light source that outputs light of a predetermined wavelength;
The light source includes a first pulsed light having a power level lower than an erasing power for erasing a mark already recorded on the recording medium, a second pulsed light having a power level larger than the erasing power, A driving circuit for supplying a driving current so that a third pulsed light having a power level larger than that of the second pulsed light can be output;
A control circuit that instructs the drive circuit to output the first to third pulses;
An information recording apparatus comprising:   The control circuit causes the drive circuit to output the first pulse after the last pulse of the third pulse and output the second pulse at the head of the erase pulse. The information recording apparatus according to claim 8. The control circuit continuously outputs the second pulse and the first pulse to the drive circuit after the last pulse of the third pulse and between the erase pulse. An information recording apparatus comprising: The control circuit is configured such that when the drive current pulse width of the first pulse is T _c and the channel clock width is T with respect to the drive circuit,
T _c > 0.8T
The information recording apparatus according to claim 8, wherein the first pulse is output so as to fall within the range. The control circuit, for the drive circuit, _sets the drive current of the second pulse to I _bst , the pulse width of the second pulse to T _bst , the drive current of the third pulse to I _p , and the first pulse 3 of the pulse of the pulse width when a T _w,
I _bst ≦ I _p and T _bst ≦ T _w
The information recording apparatus according to claim 8, wherein the second pulse is output so that Wherein the control circuit to the drive circuit, the pulse width T _w of the drive current of the third recording pulse,
T _w <1.5 ns
The information recording apparatus according to claim 8, wherein the third pulse is output so that

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