JP4338569B2 - Laser power control method and laser power control apparatus - Google Patents

Description

  The present invention relates to a laser power control apparatus and a laser power control method.

  In recent years, demand for rewritable optical disk devices has increased in the fields of computer auxiliary storage devices and consumer video recorders. In order to form a recording mark on an optical disc, a semiconductor laser light source is generally used. In order to form a good recording mark, the semiconductor laser needs to emit light in pulses. For example, as shown in FIG. 6, in forming a recording mark, a semiconductor laser emits multipulse light by modulating the intensity between peak power and bottom power. In order to form the recording space, the semiconductor laser is caused to emit light continuously for a predetermined time with a bias power. In order to ensure stable recording performance, it is necessary to accurately control these laser powers. However, the power characteristics of semiconductor lasers are greatly affected by the ambient temperature. Therefore, even if the power is set once before recording and a constant driving current is supplied, the power is not kept constant, and the power fluctuates due to the temperature rise of the semiconductor laser main body or peripheral devices.

  As a means for avoiding power fluctuations, power calibration at regular intervals is effective. For example, in an optical disc format having a sector structure, a laser control area for calibrating the laser power is provided once per sector. In this case, power fluctuation can be avoided by performing power calibration in the laser control region every time the light spot passes through the laser control region.

Hereinafter, a power calibration method in the laser control region in the prior art will be described with reference to FIG.
(A) When the light spot reaches the laser control region, a constant current Iop1 is supplied to the laser. The laser power P1 at this time is detected as a laser power detection voltage Vm1 by a laser power detection means including a light receiving element and a current-voltage conversion circuit.
(B) Next, a constant current Iop2 is supplied to the laser. The laser power P2 at this time is detected as a detection voltage Vm2 by the laser power detection means. The laser power detection voltages Vm1 and Vm2 thus obtained are converted into laser powers P1 and P2 by an arithmetic processing circuit.
This makes it possible to obtain the relationship of the laser power to the laser drive current during calibration as shown in FIG. 10 (hereinafter this relationship is referred to as “laser IL characteristics”). Therefore, if the laser is driven with a drive current corresponding to the desired power in the recording area, the laser can be driven with the desired power (hereinafter, this method is referred to as “continuous (DC) light emission method”).

  There is a problem with this continuous light emission method. When the frequency characteristic of the light receiving element is low, it is necessary to drive the laser at a constant value for a long time in order to stabilize the laser power detection voltages Vm1 and Vm2. When light is continuously emitted at a power P2 that is about the recording peak power with respect to the power P1 that is about the erasing power, the recording film on the optical disk is continuously irradiated with high power, and the recorded recording is performed. The film deteriorates. When the recording film is repeatedly irradiated with high power continuously for a long time every time data is rewritten, there is a problem that the recording film deteriorates not only in the laser control area but also in the data recording area. In addition, since light emission is repeated at a high power continuously for a long time for each laser control region, the life of the semiconductor laser is likely to be shortened.

  As a method for avoiding the above problems, for example, a method as disclosed in Patent Document 1 is disclosed. Hereinafter, the power calibration method in the laser control region in Patent Document 1 will be described with reference to FIGS.

FIG. 11 is a block diagram showing the configuration of the laser control device in Patent Document 1. In FIG. FIG. 12 is an operation sequence diagram thereof.
(A) When the light spot reaches the laser control region, the laser drive circuit 140 supplies a drive current Iop1 to the laser to perform continuous (DC) light emission with the bias power P1.
(B) The light emission power at this time is detected by the laser power detection means 100. The laser power detection unit 100 includes a light receiving element 101, a current-voltage conversion circuit 102, a peak detection circuit 116, a bottom detection circuit 115, and a multiplexer 117.
(C) The multiplexer 117 controls the peak detection voltage y output from the peak detection circuit 116, the bottom detection voltage x output from the bottom detection circuit 115, and the through output x of the current-voltage conversion circuit 102 from the outside. The configuration is such that it is selected by the signals v and w.
(D) In continuous (DC) light emission with the erasing power P1, the through output x is selected by the multiplexer 117, and Vm1 is output as the laser power detection voltage.

(E) Subsequently, pulsed emission is performed between the recording peak power P3 and the bottom power P3 by supplying the laser with currents switched by the driving currents Iop2 and Iop3.
(F) The light emission power at this time is detected by the laser power detection means 100. At this time, the current-voltage conversion circuit 102 outputs a switching waveform between Vm2 and Vm3 as a through output x. The peak detection circuit 116 outputs a peak detection output y that holds the peak level Vm2 of the through output x for a certain period. Further, the bottom detection circuit 115 outputs a bottom detection output y that holds the bottom level Vm3 of the through output x for a certain period. The multiplexer 117 appropriately selects the peak detection output y and the bottom detection output y, and outputs Vm2 and Vm3 as laser power detection voltages.
The laser power detection voltages Vm1, Vm2, and Vm3 thus obtained are converted into digital values by the AD conversion circuit 121, and converted to laser powers P1, P2, and P3 by the arithmetic processor 125. The arithmetic processor 125 makes it possible to obtain the laser IL characteristics.

  With the above configuration, the peak detection circuit 116 holds the peak level Vm2 for a certain period, so that the same output as the detection output obtained by continuously driving the semiconductor laser for a long time can be obtained. In this method, since the semiconductor laser emits pulses, the laser power applied to the recording film is reduced compared to the continuous (DC) emission method, so that damage to the recording film is reduced and the life of the semiconductor laser is further reduced. Can be reduced.

JP 2000-244054 A

  However, there is a problem with the above method. The output of the current-voltage conversion circuit is used when higher-speed recording is attempted or when the laser power detector requires high-precision DC characteristics and the frequency characteristics of the current-voltage conversion circuit cannot be secured sufficiently. Does not reach Vm2 and Vm3, and the power detection accuracy decreases. When the width of pulsed light emission is increased for the purpose of reaching the output of the current-voltage conversion circuit to Vm2 and Vm3, damage to the recording film, reduction in the life of the semiconductor laser, etc., as in the continuous (DC) light emission method A malfunction occurs.

  An object of the present invention is to provide a semiconductor laser power control method capable of accurately controlling the laser power to a desired level even when the frequency characteristics of the laser power detection means cannot be sufficiently ensured.

An apparatus for controlling the power of a laser to be recorded on an optical disc having a data recording area and a laser control area according to the present invention, using the laser control area ,
A multi-pulse emission section in which a pulse current that is intensity-modulated between a peak value current and a bottom value current at the time of forming a recording mark on the optical disc is supplied to the laser to cause the laser to emit light, and the multi-pulse emission section. Before, a formatter having a test emission pattern including a bottom value continuous light emission section for continuously supplying the bottom value current to the laser for a predetermined time to continuously emit the laser ;
Based on the test light emission pattern transmitted from the formatter, a laser driving unit that supplies a current to the laser to emit test light;
A laser power detector that receives the test emission pattern of the laser and converts it into an electrical signal to obtain a light detection signal ;
A multipulse average value detection value is calculated from an average value of the light detection signals in the multipulse light emission section, and a bottom detection value is calculated from the light detection signal in the bottom value continuous light emission section. Based on the detection value and the bottom detection value, a characteristic of the light emission power of the laser with respect to the current to be supplied, and a calculation unit that controls the supply current to the laser based on the characteristic,
The test emission pattern includes a bias value continuous emission period in which a bias value current at the time of recording space formation is continuously supplied to the laser for a predetermined time between the bottom value continuous emission period and the multi-pulse emission period. Further including
In the calculation unit, further calculating a bias detection value based on the light detection signal in the bias value continuous light emission section, based on the bias detection value, the multi-pulse average value detection value, and the bottom detection value, Obtaining the characteristics of the laser emission power with respect to the supplied current,
The test emission pattern includes an extinguishing section that turns off the laser with substantially no current supplied before the bottom value continuous emission section,
The calculation unit detects an offset based on a detection value of the light detection signal in the extinction section,
In the data recording area, a frame data area in which a mark whose length is limited based on a predetermined modulation rule is recorded, and a mark that is longer than the longest mark in the frame data area is recorded. A frame sync area for identifying the head position,
The time width Tmp of the multi-pulse light emitting section is relative to the time width Tmax of the longest recording mark of data in the frame sync area and the wobble period Twbl on the recording track of the optical disc.
Tmax <Tmp <Twbl / 2
The filling,
The time width Tb of the bottom value continuous light emission section is:
Tmax <Tb <Twbl
The filling,
The time width Te of the bias value continuous light emission section is:
Tmax <Te <Twbl / 2
The filling,
The time duration T0 of the unlit section is
Tmax <T0 <Twbl
The filling,
For the time width Tapcare for scanning the laser control region,
Tmp + Tb + Te + T0 <Tapcarea
Meet .

Furthermore, before Symbol test emission pattern, instead of the off period, it is preferable to further include a spontaneous emission light-emitting section to emit light in spontaneous emission light by supplying a current of less than the laser threshold current to the laser. In this case, the calculation unit detects an offset based on a detection value of the light detection signal in the spontaneous emission light emission section.

In the laser power control method according to the present invention, in the spontaneous emission light emission period, the current I _led supplied to the laser is about the threshold current Ith of the laser.
Ith / 4 ≦ I _led <Ith
It is preferable to satisfy.

Further, in the spontaneous emission light emission section, the current I _led supplied to the laser is about the threshold current Ith of the laser.
Ith / 4 ≦ I _led ≦ Ith × 3/4
It is preferable to satisfy.

Furthermore, in the spontaneous emission light emission period, it is more preferable that the current I _led supplied to the laser is ½ of the substantial threshold value Ith with respect to the threshold current Ith of the laser.

A method for controlling the power of a laser to be recorded on an optical disc having a data recording area and a laser control area according to the present invention, using the laser control area ,
A multi-pulse emission section in which a pulse current that is intensity-modulated between a peak value current and a bottom value current at the time of forming a recording mark on the optical disc is supplied to the laser to cause the laser to emit light, and the multi-pulse emission section. Before, a step of emitting a test light emission pattern in the laser including a bottom value continuous emission section for supplying the bottom value current to the laser continuously for a predetermined time to continuously emit the laser; and
Receiving the test emission pattern of the laser and converting it to an electrical signal to obtain a light detection signal ;
A multipulse average value detection value is calculated from an average value of the light detection signals in the multipulse light emission section, and a bottom detection value is calculated from the light detection signal in the bottom value continuous light emission section. Obtaining a characteristic of light emission power of the laser with respect to a current to be supplied based on a detection value and the bottom detection value ;
Controlling the current supplied to the laser based on the characteristics of the light emission power relative to the current supplied to the laser;
Including
In the step of emitting the laser, the test emission pattern to be used supplies a bias value current at the time of recording space formation to the laser continuously for a predetermined time between the bottom value continuous emission period and the multi-pulse emission period. Further including a continuous emission section of a bias value for continuously emitting light,
In the step of obtaining the light emission power characteristic of the laser, a bias detection value is further calculated based on the light detection signal in the bias value continuous light emission section, the bias detection value, the multipulse average value detection value, and the Based on the bottom detection value, obtain the characteristics of the emission power of the laser with respect to the supplied current,
In the step of causing the laser to emit light, the test light emission pattern to be used includes an extinguishing period in which the laser is extinguished with the supplied current substantially zero before the bottom value continuous emission period,
In the step of obtaining the light emission power characteristics of the laser, an offset is detected based on the detection value of the light detection signal in the extinguishing section,
In the data recording area, a frame data area in which a mark whose length is limited based on a predetermined modulation rule is recorded, and a mark longer than the longest mark in the frame data area is recorded, A frame sync area for identifying the head position,
The time width Tmp of the multi-pulse light emitting section is relative to the time width Tmax of the longest recording mark of data in the frame sync area and the wobble period Twbl on the recording track of the optical disc.
Tmax <Tmp <Twbl / 2
The filling,
The time width Tb of the bottom value continuous light emission section is:
Tmax <Tb <Twbl
The filling,
The time width Te of the bias value continuous light emission section is:
Tmax <Te <Twbl / 2
The filling,
The time duration T0 of the unlit section is
Tmax <T0 <Twbl
The filling,
For the time width Tapcare for scanning the laser control region,
Tmp + Tb + Te + T0 <Tapcarea
Meet.

Furthermore, in the laser power control method according to the present invention, in the step of emitting the laser, the test emission pattern to be used is replaced with the extinguishing section, and a current less than a threshold current for laser emission is supplied to the laser to spontaneously emit. It is preferable to further include a spontaneous emission light emitting section that emits light. In this case, in the step of obtaining the light emission power characteristic of the laser , the offset can be detected based on the detection value of the light detection signal in the spontaneous emission light emission section.

  In the laser power control method according to the present invention, the average value of the multi-pulse emission section is detected, and the laser power is controlled based on this average value detection information. However, each power value of the optical pulse can be controlled with high accuracy.

In the laser power control method according to the present invention, the laser is spontaneously emitted by supplying a current that is less than the threshold current to the test emission pattern during the extinction period in which the current to be supplied is substantially zero and the laser is extinguished. A spontaneous emission light emitting section for emitting light is provided. The offset can be detected based on the detection value of the light detection signal in the extinguishing period or the spontaneous emission light emission period . Therefore, if this value is used, even if the light receiving element of the laser detection means or the current-voltage conversion circuit causes a temperature drift due to a change in the ambient temperature, the offset due to the temperature drift can be calibrated, and each power value can be calibrated. Detection accuracy is improved.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, substantially the same members are denoted by the same reference numerals.

(Embodiment 1)
FIG. 1 is a block diagram of a laser power control apparatus according to Embodiment 1 of the present invention. This laser power control apparatus includes a laser drive circuit 140 that drives by supplying a current to the laser 150, a laser power detection unit 100 that detects light emission of the laser 150, a formatter 130 that generates a recording signal and a test light emission pattern, And an arithmetic unit 120. Hereinafter, each part which comprises this laser power control apparatus is demonstrated.

First, the laser drive circuit 140 that causes the laser 150 to emit light will be described. The laser drive circuit 140 includes a bottom current source 141, a bias current source 142, and a peak current source 143, and switches 144, 145, and 146 that open and close according to the bottom modulation signal, the bias modulation signal, and the peak modulation signal, respectively. In order to form the recording mark, it is necessary to cause the laser 150 to emit multipulse light between the peak power and the bottom power as shown in FIG. On the other hand, to form a recording space, the laser 150 needs to emit light with a bias power. Hereinafter, the operation of the laser driving circuit 140 will be described with reference to the block diagram of FIG. 1 and the operation sequence diagram of FIG.
(A) First, when light is emitted with bottom power, the bottom current source 141 is controlled to be turned on by the formatter 130 by a bottom modulation signal. Further, the set current (IinB) of the bottom current source 141 is input from the arithmetic processor 125 to the bottom current source 141 so that the bottom power becomes a desired value.
(B) When the light is emitted with the bias power, the bias current source 142 is controlled to be added to the bottom current source 141 by the bias modulation signal from the formatter 130. Further, the setting current (IinE) of the bias current source 142 is input from the arithmetic processor 125 to the bottom current source 141 so that the bias power becomes a desired value when the bias current source 142 and the bottom current source 141 are added. .
(C) Further, when emitting light at peak power, the peak current source 143 is controlled to be added to the bias current source 142 and the bottom current source 141 by the peak modulation signal and the bias modulation signal from the formatter 130. Further, the set current (IinP) of the peak current source 143 is set to the peak current source so that the peak power becomes a desired value when the peak current source 143, the bias current source 142, and the bottom current source 141 are added from the arithmetic processor 125. 143 is input.
By the operation as described above, the modulation current is supplied to the laser 150, and the laser 150 can emit pulses.

This laser power control device outputs a specific light emission pattern for the purpose of calibrating the power of the laser 150 when scanning of the laser control area provided in the recording track is started, and the relationship between the laser drive current and the light emission intensity. (Hereinafter, this relationship is referred to as “IL characteristic”) (hereinafter, this operation is referred to as “test light emission”). As shown in the operation sequence diagram of FIG. 3, the test light emission is caused to turn off the laser for a time width T0, then continuously (DC) light emission for the time width Tb at the bottom power, and then continuously light emission for the time width Te at the bias power, Thereafter, the light emission is performed with a specific light emission pattern in which light is emitted by a multi-pulse for a time width Tm (hereinafter, this light emission pattern is referred to as a “test light emission pattern”). When the detection window width of the recording mark is Tw, the longest mark length of the recording mark is _Tmax, and the wobble period on the recording track is _Twbl , the extinction period T0 is
T0 = T _wbl
And
In addition, the time width Tb of the bottom power emission section is
Tb = 30Tw
And
In addition, the time width Te of the bias power emission section is
Te = 16Tw
And
In addition, the time width Tmp of the multi-pulse emission section is
Tmp = 16Tw
And

Further, it is assumed that the _IL characteristic of the laser is generally predicted in advance before the test light emission, and from this characteristic, the laser drive current I _testB corresponding to the desired bottom power and the laser drive current corresponding to the desired bias power are obtained. It is _assumed that I _testE and a laser drive current I _testP corresponding to a desired peak power are expected. Therefore, the current of each current source in the test light emission is set as follows.
First, the set current value I _inB of the bottom current source 141 is
I _inB = I _testB
Is set.
The set current value I _inE of the bias current source 142 is
I _inE = I _testE −I _testB
Is set.
The set current value I _inP of the peak current source 143 is
I _inP = I _testP −I _testE
Is set.
The current supplied from the laser driving circuit 140 to the laser 150 is set by the above procedure. By supplying a current set from the laser driving circuit 140 to the laser 150, the laser 150 emits light and generates an optical pulse.

  Next, the laser power detection means 100 for detecting the light pulse generated from the laser 150 will be described. The laser power detection means 100 includes a light receiving element 101, a current-voltage conversion circuit 102, a sample hold circuit (SH0) 110, a sample hold circuit (SH1) 111, a sample hold circuit (SH2) 112, a low pass filter 114, a sample hold. A circuit (SH3) 113 is provided. When receiving the laser beam, the light receiving element 101 outputs the laser power as a current. The output current of the light receiving element 101 is converted into a voltage value by the current-voltage conversion circuit 102.

Hereinafter, the operation of the laser power detection unit 100 when the test emission pattern is emitted from the laser 150 will be described with reference to the block diagram of FIG. 1 and the operation sequence diagram of FIG.
(A) In the light-off period in the test light emission pattern, the sample hold circuit (SH0) 110 holds the output voltage of the current-voltage conversion circuit 102 according to the sample hold signal S0, and outputs a 0 mW level detection voltage Vm0.
(B) Thereafter, in the bottom power emission period, the sample hold circuit (SH1) 111 holds the output voltage of the current-voltage conversion circuit according to the sample hold signal S1, and outputs the bottom power detection voltage Vmb.
(C) Thereafter, in the bias power emission period, the sample hold circuit (SH2) 112 holds the output voltage of the current-voltage conversion circuit in accordance with the sample hold signal S2, and outputs the bottom power detection voltage Vme.
(D) Thereafter, in the multi-pulse emission section, the output of the current-voltage conversion circuit 102 is band-limited by the low-pass filter 114 so that a voltage corresponding to the average value of the multi-pulse emission can be obtained. The sample hold circuit (SH3) 113 holds the voltage corresponding to the average value of the multi-pulse emission thus obtained in accordance with the sample hold signal S3, and outputs the multi-pulse average value detection voltage Vma.

Further, the calculation unit 120 will be described. The arithmetic unit 120 includes AD conversion circuits 121, 122, 123, 124, an arithmetic processor 125, and DA conversion circuits 131, 132, 133.
(A) The 0 mW level detection voltage Vm0, the bottom power detection voltage Vmb, the bias power detection voltage Vme, and the multi-pulse part average power detection voltage Vma obtained by the laser power detection means 100 are the AD converter circuits (AD0) 121, (AD1) 122, (AD2) 123, and (AD3) 124 are input to digital values such as 0 mW level detection value Dm0, bottom power detection value Dmb, bias power detection value Dme, and multi-pulse part average power detection value Dma, respectively. Is converted to
(B) Further, the arithmetic processor (DSP) 125 performs offset calibration of the laser power detection means using the 0 mW level detection value Dm0 and converts it to a power value. That is, a value obtained by subtracting Dm0 from Dmb is converted into bottom detection power _PmonB , and a value obtained by subtracting Dm0 from Dme is converted into bias detection power _PmonE , and a value obtained by subtracting Dm0 from Dma is converted to multipulse average detection power _PmonA. The
(C) Thereafter, the arithmetic processor 125 obtains the IL characteristics of the laser at this point in the procedure described below, and converts the set current to the laser drive circuit 140 in terms of voltage so as to emit light at a desired laser power. decide. The procedure for determining the set current value of each current source 141, 142, 143 of the current supplied to the laser drive circuit 140 in the arithmetic processor 125 will be described later.
(D) Next, the set current value I _inB of the bottom current source 141 is set via the DA conversion circuit 131 based on the voltage conversion value of each set current value determined by the arithmetic processor 125, and the DA conversion circuit 132 is The set current value I _inE of the bias current source 142 is set via the DA converter circuit 133, and the set current value I _inP of the peak current source 143 is set via the DA converter circuit 133.

Hereinafter, how the arithmetic processor 125 determines the set current values of the current sources 141, 142, and 143 of the current to be supplied to the laser driving circuit 140 will be described.
FIG. 4 is an example of the IL characteristic of the laser. From the bottom detection power _PmonB , the bias detection power _PmonE, and the drive currents _ItestE and _ItestB during the test light emission, the _IL characteristics of the laser are shown in FIG. 4 where the laser power is y and the drive current is x. As shown
y = η1 × x + b1
It is expressed by a linear function.
Here, using P _monB and P _monE ,
η1 = (P _monE −P _monB ) / (I _testE −I _testB )
b1 = ( _PmonB * _{ItestE- PmonE} * _ItestB ) / ( _{ItestE- ItestB} )
It becomes.
Therefore, if the desired bottom power is P _refB , the bottom power drive current IB is
IB = (P _refB −b1) / η1
Is determined.
Also, _assuming that the desired bias power is _PrefE , the bias power drive current IE is
IE = (P _refE −b1) / η1
Is determined.

_Further , the peak detection power P _monP is _obtained from the multipulse average detection power P _monA and the bottom detection power P _monB by the following calculation. When the duty of the multi-pulse part is d, the multi-pulse average detection power P _monA is expressed by the following equation.
P _monA = P _monP × d + P _monB × (1-d)
Therefore, the peak detection power P _monP is
_{P monP = (P monA -P monB} × (1-d)) / d
As required.
Then, from the relationship between the detection powers P _monP and P _monB and the drive currents I _testP and I _testB , the laser _IL characteristic is as _follows , _assuming that the laser power is y and the drive current is x, as shown in FIG.
y = η ₂ × x + b ₂
It is expressed by a linear function.

In FIG. 4, the _IL characteristic of the laser is shown as a straight line having the same slope over the entire range of the drive current equal to or higher than the threshold value Ith, but this is only an ideal example. Since in practice I-L characteristics of the laser may change by the scope of the drive current I, the drive current from the _{I testB} the inclination in the range of _{I Teste} and eta _1, the driving current _{I testB} ranging _{I testP} It has a slope and η _2.
Here, when expressed using the detected powers P _monP and P _monB ,
η2 = (P _monP −P _monB ) / (I _testP −I _testB )
b2 = ( _PmonB * _{ItestP- PmonP} * _ItestB ) / ( _{ItestP- ItestB} )
It becomes.
Therefore, when the desired peak power is P _refP , the peak power drive current IP is
IP = (P _refP −b2) / η2
Is determined.

By the above calculation, as shown in FIG. 2, the set current value I _inB of the bottom current source 141 is I _inB = IB
Updated to
The set current value I _inE of the bias current source 142 is I _inE = IE−IB
Updated to
The set current value I _inP of the peak current source 143 is I _inP = IP−IE
Updated to

  As described above, the laser power control apparatus according to the first embodiment detects the average value of the multi-pulse emission section in the laser control region and controls the laser power based on this average value detection information. Even when the frequency characteristics of the detection means 100 cannot be sufficiently ensured, it is possible to control each power value of the optical pulse with high accuracy.

  In addition, the laser power control apparatus according to the first embodiment has a light-off section in which the laser 150 is turned off for a certain period in the laser control region. In this extinguishing section, the output of the current-voltage conversion circuit 102 of the laser power detection means 100 is acquired as a 0 mW detection value, that is, an offset value. Therefore, if this value is used, offset calibration can be performed even when the light receiving element 101 of the laser power detection means 100 and the current-voltage conversion circuit 102 cause a temperature drift due to a change in ambient temperature and an offset occurs. Therefore, the detection accuracy of each power value is improved.

FIG. 5 is a flowchart of a method for controlling the power of the laser according to the first embodiment. The laser power control method will be described below.
(A) In the formatter 130, a pulse current between a peak value current and a bottom value current at the time of recording mark formation is supplied to pulse the laser 150, and a bottom value current is continuously generated for a predetermined time. A test light emission pattern including a bottom value continuous light emission section for supplying and continuously emitting light to the laser 150 is provided. The test light emission pattern is transmitted from the formatter 130 to the laser driving circuit 140 to cause the laser 150 to emit light along the test light emission pattern (S01). The test light emission pattern may further include a constant value light emission section of a bias value that emits light when the recording space is formed.
(B) The laser power detection unit 100 receives the test light emission pattern of the laser 150 and converts it into an electrical signal to obtain a light detection signal (S02).
(C) The computing unit 120 calculates the multi-pulse average value detection value from the average value of the light detection signals in the multi-pulse light emission interval, calculates the bottom detection value from the light detection signal in the bottom value continuous light emission interval, Based on the pulse average value detection value and the bottom detection value, the characteristics of the laser emission power with respect to the supplied current are obtained (S03). In addition, a bias detection value is further calculated based on the light detection signal in the constant value light emission section of the bias value, and a current supplied based on the bias detection value, the multi-pulse average value detection value, and the bottom detection value is calculated. You may make it acquire the characteristic of the light emission power of a laser.
(D) Further, the arithmetic unit 120 controls the current supplied to the laser 150 based on the characteristics of the light emission power of the laser 150 with respect to the supplied current (S04). As a result, calibration can be performed even if the laser power fluctuates due to a temperature change or the like.

Here, the multi-pulse light emission section Tmp and the bias light emission section Te are set to 16 Tw, which has the following reason.
(1) In order to improve the detection accuracy of the average value of the multipulse part, it is better to emit multipulse light as long as possible. That is, it is possible to achieve both the stabilization of the average value of the multipulse part and the reduction of the residual ripple by making the multipulse light emission for a long time. Therefore, it is conceivable to emit multi-pulse light having the same length as that when recording the longest recording mark. For example, when the recording code is a (1,7) modulation system, the longest mark is 8T, and a longer 9T mark and 9T space pair identifies the start position of each frame on the format “frame sync”. Is recorded. Therefore, in the test light emission pattern, it is conceivable that the time width Tmp of the multi-pulse light emission section and the time width Te of the bias light emission section are set to 9 Tw. In such a case, this pattern is mistaken as a frame sync during disk reproduction. There is a possibility of detection. Therefore, for the purpose of avoiding erroneous detection with the frame sync and further improving the detection accuracy of the average value of the multi-pulse part, a recording mark longer than the longest recording mark length T _max including the frame sync (16 Tw in this embodiment) It is preferable to emit light.
(2) Since the test light emission must be completed within the laser control region, _assuming that the passing time of the laser control region is T _apcarea , the time width Te of the multi-pulse light emission interval Tmp and the bias light emission interval is T _max. <Tmp <T _apcarea
T _max <Te <T _apcarea
It is preferable to satisfy. Furthermore, since the multi-pulse emission section and the bias emission section are preferably included in the test emission pattern in one laser control area,
Tmp + Te <T _apcarea
It is preferable to satisfy.

Furthermore, in order to improve the detection accuracy of the multipulse part average value and bias power, it is preferable to increase the time width Tmp of the multipulse light emission section and the time width Te of the bias light emission section. But these should not be longer than necessary. This is because if a recording spot or recording space is formed in the groove portion of the recording track when the light spot is deviated from the center of the recording track due to some malfunction of the optical disk apparatus, the groove portion is damaged, resulting in the recording track The wobble extraction performance may be degraded. Therefore, when the wobble period of the recording track is T _wbl , the time width Tmp of the multi-pulse light emission section and the time width Te of the bias light emission section are T _max <Tmp <T _wbl / 2.
T _max <Te <T _wbl / 2
It is preferable that
For example, when the optical disk is T _{wbl ≈69} Tw,
T _max <Tmp <34 Tw
T _max <Te <34Tw
It is preferable that

  Further, since the bottom power is detected every time it passes through the laser control region, the detection accuracy of the bottom power can be improved. Furthermore, since the detection of peak power is also detected using the detection value of bottom power, the detection accuracy of bottom power can be improved.

Here, the time width Tb of the bottom power emission section is 30 Tw. There are the following reasons for this.
(1) In order to perform detection after the bottom power has settled, it is preferable that the time width Tb is longer than the longest recording mark _Tmax . As a result, even when test light emission is performed immediately after the transition from the playback state to the recording state, the transient that occurs when transitioning from the playback state to the recording state is avoided, and detection is performed after the bottom power has settled. Since this can be done, the detection accuracy of the bottom power is improved.
(2) As described above, the longer the time width Tb of the bottom power emission section, the better the detection accuracy of the bottom power. However, since the laser power is weak during this time, tracking control is performed on the optical disc. The signal of S / N ratio deteriorates. When the sampling frequency of the tracking error signal is 200 kHz, the time width Tb of the bottom power emission section is preferably 5 μs or less. In effect, the test emission itself must be completed in the laser control region, and T _max <Tb <T _apcarea when T _{apcarea is} approximately 5 μs or less than 5 μs.
It is preferable that In consideration of using the bottom power emission section and the extinction section in combination, substantially, T _max <Tb <T _wbl
More preferably. Furthermore, since the multi-pulse emission section and the bottom power emission section are preferably included in the test emission pattern in one laser control area,
Tmp + Te <T _apcarea
It is preferable to satisfy.

In addition, here, the time width T0 of the extinguishing section is set to T _wbl , for the following reason.
(1) In order for the laser to transition from the light emitting state to the extinguished state and the 0 mW level to settle, it is better that the extinguishing period is longer. The period for setting the 0 mW level depends on the characteristics of the laser drive circuit, and the time width T0 of the extinguishing section is preferably longer than the longest recording mark _Tmax .
(2) On the other hand, it is preferable that the extinguishment section is long as described above. However, since the laser power is weak during this period, a signal for tracking control on the optical disk is lost. When the sampling frequency of the tracking error signal is 200 kHz, the time width Tb of the bottom power emission section is preferably 5 μs or less. In addition, since the test light emission must be completed in the laser control region, if T _{apcare is} approximately 5 μs or less than 5 μs, T _max <T 0 <T _apcare
It is preferable to satisfy. Furthermore, considering that the bottom power emission _{period and the extinction period} are used in combination, substantially T _max <T0 <T _wbl
More preferably.

  In the first embodiment, in the test light emission, the light is first turned off, the light is continuously emitted for the time width Tb at the bottom power, the light is continuously emitted for the time width Te by the bias power, and the light is emitted for the time width Tm by the multi-pulse thereafter. The test light emission pattern is configured with. When the test light emission patterns are performed in this order, the change amount of the crest value becomes the smallest in the light emission transition state, which is most advantageous from the viewpoint of the settling time of the current-voltage conversion circuit 102. Therefore, it is preferable to perform the test light emission in this order.

  In addition, the laser power control method of the first embodiment provides an extinguishing section in which the laser is extinguished for a certain time in the laser control area. In this extinguishing section, the output of the current-voltage conversion circuit of the laser detection means is acquired as a 0 mW detection value. Therefore, if this value is used, even when the light receiving element of the laser detection means or the current-voltage conversion circuit causes a temperature drift due to a change in the ambient temperature, the offset due to the temperature drift can be calibrated. Therefore, the detection accuracy of each power value is improved.

(Embodiment 2)
FIG. 7 is an operation sequence diagram of the laser power control method according to the second embodiment of the present invention. Compared with the laser power control method according to the first embodiment, the laser power control method according to the present embodiment supplies a current less than the threshold current Ith in the test light emission pattern instead of the extinguishing period, and spontaneously emits the laser. The difference is that a spontaneous emission light emitting section for emitting light is provided. In the first embodiment, for the purpose of calibrating the offset of the light receiving element 101 of the laser power detection means 100 and the current-voltage conversion circuit 102, the extinguishing section is provided in which the current supplied to the laser is substantially zero and the laser is extinguished. . On the other hand, as shown in FIG. 4, the laser shows a spontaneous emission light emitting region that emits spontaneous emission for a supply current less than the threshold current Ith. Therefore, as shown in FIG. 7, instead of turning off the laser, spontaneous emission light is emitted for a time width T0 in the spontaneous emission region (LED emission region), and the offset is calibrated with the detection value at this time as 0 mW level. Use as a thing. FIG. 8 is a diagram showing the relationship between the supply current (drive current) to the semiconductor laser element using the GaN blue-violet laser, the light output from the semiconductor laser element, and the light intensity detected by the light receiving element. Note that, in the spontaneous emission light emitting region, only weak light with low coherence propagates to the light receiving element 101. Therefore, as shown in FIG. However, it is possible to obtain substantially the same effect as turning off the laser 150. Further, since the laser driving circuit 140 continues to output a constant current that is less than the threshold current Ith but not zero, the transition from the spontaneous emission light emission period to the laser emission area can be smoothly performed.

Table 1 shows the relationship between the supply current (drive current) to the semiconductor laser element in FIG. 8, the light output from the semiconductor laser element, and the light intensity detected by the light receiving element (a value converted to the objective lens output).

Next, a preferable range of the supply current I _led to the laser in the spontaneous emission light emission section will be described with reference to FIG. When the current (threshold current) at the boundary between the spontaneous emission light emitting region and the laser emitting region of the laser is Ith, the supply current I _led to the laser needs to be less than the threshold current Ith.
Iled <Ith
In addition, in order that the transition to the laser emission can be smoothly performed after the spontaneous emission light emission period, the drive stage transistor of the laser drive circuit 140 is not cut off.
Ith / 4 ≦ I _led
It is preferable to satisfy.
Therefore, as shown in FIG. 8, a preferable range Δ1 of the supply current I _led to the laser is
Ith / 4 ≦ I _led <Ith
Represented as:

Furthermore, in this spontaneous emission light emitting region, in order to obtain an effect almost equivalent to turning off the laser,
I _led ≦ Ith × 3/4
It is preferable to supply a current I _led satisfying the above condition to the laser.
Therefore, a more preferable range Δ2 of the supply current I _led to the laser is
Ith / 4 ≦ I _led ≦ Ith × 3/4
Represented as: I _led is more preferably set to Ith / 2.

  When the temperature drift of the laser power detection unit 100 is large, the offset can be appropriately calibrated by providing the spontaneous emission light emission section in the test emission pattern.

  In each embodiment of the present invention, it is assumed that a rewritable optical disk is used, and light is emitted with a bias power to form a recording space. However, the present invention is not limited to such a case. For example, in the case of adapting to a write-once type optical disc, it is not necessary to emit light with a bias power that forms a recording space. In such a case, the bias power emission section may be omitted in the test emission pattern.

  Further, in each embodiment of the present invention, a test light emission is performed in a laser control area provided on a recording track of an optical disc to calibrate the laser power. However, the present invention is not limited to this configuration, and a configuration may be adopted in which a test light emission is performed in a rewritable sector to calibrate the laser power without providing a laser control area on the optical disc, and then the rewritable sector is rewritten. .

  As described above, the laser power control method according to each embodiment of the present invention detects the average value of the multi-pulse emission region in the laser control region and controls the laser power based on this average value detection information. Even when the frequency characteristics of the laser power detection means cannot be sufficiently secured, it is possible to control each power value of the optical pulse with high accuracy.

It is a block diagram which shows the structure of the laser power control apparatus in Embodiment 1 of this invention. It is an operation | movement sequence diagram of the laser drive circuit in Embodiment 1 of this invention. It is an operation | movement sequence diagram of the laser power control apparatus in Embodiment 1 of this invention. It is a figure which shows the light emission characteristic of the laser with respect to a drive current. It is a flowchart of the laser power control method which concerns on Embodiment 1 of this invention. It is a figure which shows a response | compatibility with the recording pulse waveform and recording mark of an optical disk recording / reproducing apparatus. It is an operation | movement sequence diagram of the laser power control apparatus which concerns on Embodiment 2 of this invention. It is a figure which shows the optical output of the semiconductor laser in Embodiment 2 of this invention, and the light intensity which a light receiving element detects. It is an operation | movement sequence diagram in the laser control method in a prior art. It is a figure which shows the relationship (IL characteristic) of the drive current of a laser and laser emission intensity in a prior art. It is a block diagram which shows the structure of the laser control apparatus in patent document 1 of a prior art. It is an operation | movement sequence diagram of the laser control apparatus in patent document 1 of a prior art.

Explanation of symbols

100 Laser power detection means 101 Light receiving element 102 Current-voltage conversion circuit 110 Sample hold circuit SH0
111 Sample hold circuit SH1
112 Sample hold circuit SH2
113 Sample hold circuit SH3
114 Low-pass filter 120 Operation unit 121 AD conversion circuit AD0
122 AD conversion circuit AD1
123 AD conversion circuit AD2
124 AD conversion circuit AD3
125 arithmetic processor (digital signal processor)
130 Formatter 131 DA Conversion Circuit DA1
132 DA converter circuit DA2
133 DA conversion circuit DA3
140 Laser drive circuit 141 Bottom current source 142 Bias current source 143 Peak current sources 144, 145, 146 Switch 150 Laser

Claims (7)

An apparatus for controlling the power of a laser to be recorded on an optical disc having a data recording area and a laser control area, using the laser control area ,
A multi-pulse emission section in which a pulse current that is intensity-modulated between a peak value current and a bottom value current at the time of forming a recording mark on the optical disc is supplied to the laser to cause the laser to emit light, and the multi-pulse emission section. Before, a formatter having a test emission pattern including a bottom value continuous light emission section for continuously supplying the bottom value current to the laser for a predetermined time to continuously emit the laser;
Based on the test light emission pattern transmitted from the formatter, a laser driving unit that supplies a current to the laser to emit test light;
A laser power detector that receives the test emission pattern of the laser and converts it into an electrical signal to obtain a light detection signal;
A multipulse average value detection value is calculated from an average value of the light detection signals in the multipulse light emission section, and a bottom detection value is calculated from the light detection signal in the bottom value continuous light emission section. Based on the detection value and the bottom detection value, a characteristic of the light emission power of the laser with respect to the current to be supplied, and a calculation unit that controls the supply current to the laser based on the characteristic ,
The test emission pattern includes a bias value continuous emission period in which a bias value current at the time of recording space formation is continuously supplied to the laser for a predetermined time between the bottom value continuous emission period and the multi-pulse emission period. Further including
In the calculation unit, further calculating a bias detection value based on the light detection signal in the bias value continuous light emission section, based on the bias detection value, the multi-pulse average value detection value, and the bottom detection value, Obtaining the characteristics of the laser emission power with respect to the supplied current,
The test emission pattern includes an extinguishing section that turns off the laser with substantially no current supplied before the bottom value continuous emission section,
The calculation unit detects an offset based on a detection value of the light detection signal in the extinction section,
In the data recording area, a frame data area in which a mark whose length is limited based on a predetermined modulation rule is recorded, and a mark longer than the longest mark in the frame data area is recorded, A frame sync area for identifying the head position,
The time width Tmp of the multi-pulse light emitting section is relative to the time width Tmax of the longest recording mark of data in the frame sync area and the wobble period Twbl on the recording track of the optical disc.
Tmax <Tmp <Twbl / 2
The filling,
The time width Tb of the bottom value continuous light emission section is:
Tmax <Tb <Twbl
The filling,
The time width Te of the bias value continuous light emission section is:
Tmax <Te <Twbl / 2
The filling,
The time duration T0 of the unlit section is
Tmax <T0 <Twbl
The filling,
For the time width Tapcare for scanning the laser control region,
Tmp + Tb + Te + T0 <Tapcarea
Laser power control device that satisfies The test emission pattern further includes a spontaneous emission light emitting section that emits spontaneous emission light by supplying a current less than a laser threshold current instead of the extinction section ,
The laser power control apparatus according to claim 1 , wherein the calculation unit detects an offset based on a detection value of the light detection signal in the spontaneous emission light emission section. In the spontaneous emission light emitting section, the current Iled supplied to the laser is about the threshold current Ith of the laser.
Ith / 4 ≦ Iled <Ith
The laser power control apparatus according to claim 2 , wherein: In the spontaneous emission light emitting section, the current Iled supplied to the laser is about the threshold current Ith of the laser.
Ith / 4 ≦ Iled ≦ Ith × 3/4
The laser power control apparatus according to claim 2 , wherein: 3. The laser power control apparatus according to claim 2 , wherein the current Iled supplied to the laser in the spontaneous emission light emission section is ½ of the substantial threshold value Ith with respect to the threshold current Ith of the laser. A method for controlling the power of a laser to be recorded on an optical disc having a data recording area and a laser control area, using the laser control area ,
A multi-pulse emission section in which a pulse current that is intensity-modulated between a peak value current and a bottom value current at the time of forming a recording mark on the optical disc is supplied to the laser to cause the laser to emit light, and the multi-pulse emission section. Before, a step of emitting a test light emission pattern in the laser including a bottom value continuous emission section for supplying the bottom value current to the laser continuously for a predetermined time to continuously emit the laser; and
Receiving the test emission pattern of the laser and converting it to an electrical signal to obtain a light detection signal;
A multipulse average value detection value is calculated from an average value of the light detection signals in the multipulse light emission section, and a bottom detection value is calculated from the light detection signal in the bottom value continuous light emission section. Obtaining a characteristic of light emission power of the laser with respect to a current to be supplied based on a detection value and the bottom detection value;
Controlling the current supplied to the laser based on the characteristics of the light emission power relative to the current supplied to the laser ;
Including
In the step of emitting the laser, the test emission pattern to be used supplies a bias value current at the time of recording space formation to the laser continuously for a predetermined time between the bottom value continuous emission period and the multi-pulse emission period. Further including a continuous emission section of a bias value for continuously emitting light,
In the step of obtaining the light emission power characteristic of the laser, a bias detection value is further calculated based on the light detection signal in the bias value continuous light emission section, the bias detection value, the multipulse average value detection value, and the Based on the bottom detection value, obtain the characteristics of the emission power of the laser with respect to the supplied current,
In the step of emitting the laser, the test emission pattern to be used includes an extinguishing period in which the laser is extinguished with the supplied current substantially zero before the bottom value continuous emission period,
In the step of obtaining the light emission power characteristics of the laser, an offset is detected based on the detection value of the light detection signal in the extinguishing section,
In the data recording area, a frame data area in which a mark whose length is limited based on a predetermined modulation rule is recorded, and a mark longer than the longest mark in the frame data area is recorded, A frame sync area for identifying the head position,
The time width Tmp of the multi-pulse light emitting section is relative to the time width Tmax of the longest recording mark of data in the frame sync area and the wobble period Twbl on the recording track of the optical disc.
Tmax <Tmp <Twbl / 2
The filling,
The time width Tb of the bottom value continuous light emission section is:
Tmax <Tb <Twbl
The filling,
The time width Te of the bias value continuous light emission section is:
Tmax <Te <Twbl / 2
The filling,
The time duration T0 of the unlit section is
Tmax <T0 <Twbl
The filling,
For the time width Tapcare for scanning the laser control region,
Tmp + Tb + Te + T0 <Tapcarea
Laser power control method that satisfies In the step of emitting the laser, the test light emission pattern to be used further includes a spontaneous emission light emitting section for supplying a current less than a threshold current for laser emission to the laser to emit light by spontaneous emission instead of the extinguishing section. ,
The laser power control method according to claim 6 , wherein in the step of obtaining the light emission power characteristic of the laser, an offset is detected based on a detection value of the light detection signal in the spontaneous emission light emission section.

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