Optical recorder and laser power control method

An optical recording apparatus which obtains the most appropriate recording laser power state in real time according to an environmental mark-generation condition. When data is recorded (marks and spaces are generated) by emitting pulse-train-manner laser outputs to an organic-pigment recording medium, a space-period signal value corresponding to a space period is detected in a reflected-light information signal to estimate a first-pulse signal value corresponding to a first pulse. In addition, a second-and-subsequent-pulse signal value corresponding to second and subsequent pulses is detected in the reflected-light information signal. The ratio between the estimated first-pulse signal value and the detected second-and-subsequent-pulse signal value is obtained, and the obtained ratio and a reference ratio are used to generate a laser-power compensation signal to control the power of the laser outputs.

TECHNICAL FIELD

The present invention relates to optical recording apparatuses for recording into recording media such as optical disks, and laser-power control methods.

BACKGROUND ART

CD-type and DVD-type optical disks have been widely known as optical recording media. Especially as write-once media and rewritable media, media for which data recording can be performed at a user side, and recording apparatuses have also been spread.

For example, CD-Rs (compact discs recordable) and DVD-Rs (digital versatile discs recordable) are typically used as write-once media. In the disks, organic pigment films are used as disk recording layers, and pits (marks) are formed by organic-pigment changes when a laser is emitted to data tracks formed as pre-grooves.

When data is recorded in such recording media, if laser power is optimized, pits are successfully formed and therefore, the quality of a reproduced signal is improved when reproduction.

To this end, when an organic-pigment-film recording medium is loaded into an optical recording apparatus, or immediately before recording is started, test writing is executed several times at a predetermined area (test-writing area) of the recording medium while laser power is slightly being changed, to determine the recording laser power which makes the quality of a reproduced signal best in the area. The asymmetry or the jitter of a reproduced RF signal is, for example, used as an evaluation function to evaluate the quality of the reproduced signal.

The most appropriate laser power is obtained before a recording operation, and so-called APC (automatic laser-power control) is applied during recording to output a laser at the most appropriate power. Therefore, a successful recording operation is allowed.

However, the obtained most appropriate laser power is just for the test-writing area.

On the disk, recording-film unevenness may occur from the center to the peripheral of the disk due to a recording-film forming process in manufacturing the recording medium.

Further, the wavelength of a laser output from a semiconductor laser device generally fluctuates according to the temperature. The wavelength of the laser emitted to the surface of a recording medium changes the optical absorption efficiency of the recording medium. In other words, even if the laser output power is constant, the energy received by the recording film of the disk is changed due to a change in laser wavelength, and therefore, the state of a pit mark generated by the energy is also changed. In summary, even if the recording laser power is output at the most appropriate value, a mark to be generated may be shifted from the most appropriate mark state.

With these points being taken into consideration, the most appropriate laser power obtained by power calibration performed at the test-writing area on the disk at a point of time is not necessarily the most appropriate recording laser power for the entire area of the disk or under every environmental condition, which includes temperature changes.

In other words, even when a laser is output by an APC operation at the most appropriate laser power obtained by power calibration, this does not necessarily mean that the most-appropriate recording operation (pit forming operation which causes a high-quality reproduction signal to be obtained during reproduction) is always implemented.

When an APC operation is performed which employs only the most appropriate recording power obtained in the test-writing area as a target value, if the quality margin of a reproduced signal is taken into account in a system, it may be effective to suppress the fluctuation of the light absorption efficiency of the recording medium as much as possible, or to employ a laser driving apparatus which has a laser in which the fluctuation of the wavelength is unlikely to occur when the temperature is changed or which has a temperature control mechanism. These measures are, however, technically complicated and disadvantageous in terms of cost.

The above problem may be avoided by proposing a format in which the deterioration of reproduced-signal quality is assumed in advance. This proposal, however, leads in an opposite direction for optical recording/reproduction systems for which higher density is strongly demanded.

DISCLOSURE OF INVENTION

Under the above situation, an object of the present invention is to allow a recording operation to be always executed at the most appropriate laser power to obtain a high-quality reproduced signal.

To this end, an optical recording apparatus according to the present invention includes recording processing means for applying encoding processing to data to be recorded to generate encoded data and for generating laser driving pulses used for executing pulse-train-manner laser outputs, according to the encoded data; recording-head means for emitting the laser outputs to the recording medium according to the laser driving pulses to execute recording of a data string formed of a mark and a space on the recording medium; reflected-light information signal detection means for detecting a reflected-light information signal obtained when the recording-head means emits the laser outputs; signal-value detection means for detecting a space-period signal value corresponding to a period of the space and a second-and-subsequent-pulse signal value corresponding to second and subsequent pulses in the pulse-train-manner laser outputs, in the reflected-light information signal detected by the reflected-light information signal detection means; estimation means for estimating a first-pulse signal value corresponding to a first pulse in the pulse-train-manner laser outputs by using the space-period signal value detected by the signal-value detection means; calculation means for obtaining the ratio between the second-and-subsequent-pulse signal value detected by the signal-value detection means and the first-pulse signal value obtained by the estimation means and for generating a laser-power compensation signal by using the obtained ratio and a reference ratio; and laser-power control means for controlling the power of the laser outputs according to the laser-power compensation signal sent from the calculation means.

In this case, the recording medium has an organic pigment film as a recording layer.

Further, the signal-value detection means further detects the first-pulse signal value corresponding to the first pulse in the pulse-train-manner laser outputs, and the estimation means corrects the first-pulse signal value estimated by using the space-period signal value, by using the first-pulse signal value detected by the signal-value detection means.

The first-pulse signal value is the peak, the center value, or the modulation value of the reflected-light information signal, corresponding to the first pulse in the pulse-train-manner laser outputs.

The second-and-subsequent-pulse signal value is the peak, the center value, the bottom value, the average, or the modulation value of the reflected-light information signal, corresponding to the whole or part of the second and subsequent pulses in the pulse-train-manner laser outputs.

The calculation means stores in advance the most appropriate ratio between the first-pulse signal value and the second-and-subsequent-pulse signal value according to each of various conditions related to a recording operation, and selects a ratio suited to the current condition among the stored ratios to use it as the reference ratio.

A laser-power control method according to the present invention is for an optical recording apparatus which applies pulse-train-manner laser outputs to a recording medium having an organic pigment film to record data. A space-period signal value corresponding to a period of the space and a second-and-subsequent-pulse signal value corresponding to second and subsequent pulses in the pulse-train-manner laser outputs are detected in a reflected-light information signal obtained during the laser outputs; a first-pulse signal value corresponding to a first pulse in the pulse-train-manner laser outputs is estimated by using the detected space-period signal value; the ratio between the detected second-and-subsequent-pulse signal value and the estimated first-pulse signal value is obtained; a laser-power compensation signal is generated by using the obtained ratio and a reference ratio; and the power of the laser outputs is controlled according to the laser-power compensation signal.

Pit marks are formed more quickly with respect to laser emission on recording media having organic pigment films than on, for example, recording media having general phase-change recording films. In other words, an effect of the pit mark being recorded by the current laser illumination appears on reflected light obtained by the laser illumination. “Pit marks are formed more quickly,” described above, means that pit marks are generated so “quickly” that the pit mark being recorded changes the quantity of reflected light of the recording laser.

For such recording media, a mark-generation state can be monitored in real time by reflected-light information. Therefore, reflected-light information which includes mark-generation information is observed during recording, it is determined almost at the same time whether the recording power currently being output is most appropriate for mark generation, and if the recording power is shifted from the most appropriate state, a shift compensation is fed back to a laser-power control system to control the laser power so as to be the most appropriate state.

BEST MODE FOR CARRYING OUT THE INVENTION

As an optical recording apparatus and a laser-power control method according to an embodiment of the present invention, a disk drive apparatus (recording and reproduction apparatus) for DVD-Rs and its laser-power control operation will be taken as examples and described. Descriptions will be given in the following order.

1. Pulse-Train Recording Method and RF Signal

2. Structure of Disk Drive Apparatus

6. Various Modifications

1. Pulse-Train Recording Method and RF Signal

The disk drive apparatus according to the present embodiment records and reproduces data into and from recording media having an organic pigment film, such as DVDRs, and emits a laser by a so-called pulse train method when recording.

A pulse-train-manner laser emission driving method used when recording and a reflected-light information signal, which is an RF signal, observed during a recording operation with laser outputs will be first described to explain the principle of laser-power control, described later, executed in the disk drive apparatus according to the present embodiment.

When recording, data to be recorded is encoded to finally generate an NRZI-method run-length-limited code.

For example,FIG. 1(a) shows a data track on a disk in a simplified manner. To form a data track having marks M and spaces SP in this way, a data stream shown inFIG. 1(b) is output from an encoding system as encoded data.

In this case, an encoded data stream which forms a 8 T mark (pit), a 3 T space, a 3 T mark, a 4 T space, and a 6 T mark is indicated (where T means the unit of length corresponding to a channel bit) as an example.

For the encoded data shown inFIG. 1(b), so-called pulse-train-manner laser driving pulses like those shown inFIG. 1(c) are generated as a signal for actually executing laser outputs.

In other words, laser driving pulses (writing pulses) having a recording level are intermittently output according to the lengths of pits to be formed during a period in which marks M are formed, and laser driving pulses having a reproduction level are consecutively output during a period corresponding to spaces SP.

Various waveforms of the laser driving pulses can be considered, and this case shows just one example. In this case, a writing pulse rises about 1.5 T later than when the encoded data rises, and lasts for a period of 1.5 T . Then, writing pulses having a period of 0.5 T continue with a period of 0.5 T sandwiched by adjacent writing pulses, until the encoded data falls.

Therefore, to form an 8 T mark, as shown in the figure, after a 1.5 T reading level, a 1.5 T writing pulse is output, and then, five 0.5 T writing pulses are output with 0.5 T read levels sandwiched therebetween.

To form a 6 T mark, after a 1.5 T reading level, a 1.5 T writing pulse is output, and then, three 0.5 T writing pulses are output with 0.5 T read levels sandwiched therebetween.

To form a 3 T mark, a 1.5 T writing pulse output after a 1.5 T reading level is sufficient for a 3 T period, there is no subsequent 0.5 T writing pulses.

Since laser output is performed by such laser driving pulses, laser power increases intermittently during pit forming periods.

When such pulse-train-manner laser outputs are performed, an RF signal detected as light reflected from the organic-pigment-film disk is as shown inFIG. 1(d).

More specifically, a first pulse has a relatively large amplitude, a second pulse has a smaller amplitude than the first pulse, and third, fourth, and subsequent pulses have almost the same amplitude as the second pulse.

For convenience of description, pulses observed in the RF signal are called first pulses P#1, second pulses P#2, third pulses P#3, . . . , and an n-th pulse P#n, as shown inFIG. 2.

In addition, the peak of the amplitude of a pulse is called “PK,” the bottom value thereof is called “BT,” and the center value thereof is called “CT.” For example, the peak of the first pulse P#1is expressed as “PK1,” the peak of the second pulse P#2is expressed as “PK2,” and so on.

In the same way, the bottom value “BT” and the center value “CT” of the first pulse P#1are called “BT1” and “CT1,” the bottom value “BT” and the center value “CT” of the second pulse P#2are called “BT2” and “CT2,” and so on.

Laser outputs usually have a relatively low level corresponding to a read level at periods where no mark M is generated on disk tracks, that is, where spaces SP are made. The level of the RF signal, corresponding to the periods of the spaces SP, namely, the quantity of reflected light, is called “LSP.”

Further, the average of the second pulse P#2to the n-th pulse P#n is called “av.” The average of the peak PK2of the second pulse P#2to the peak PKn of the n-th pulse P#n is called “avPK.” The average of the bottom value BT2of the second pulse P#2to the bottom value BTn of the n-th pulse P#n is called “avBT.” The average of the center value CT2of the second pulse P#2to the center value CTn of the n-th pulse P#n is called “avCT.”

As shown inFIG. 1andFIG. 2, the first pulse P#1has a large amplitude, and the second pulse P#2and subsequent pulses have relatively small amplitudes in the RF signal. This is because, since the generation of a mark is instantaneously started by laser emission caused by the first writing pulse in laser driving pulses, the second pulse P#2and subsequent pulses in the RF signals have reduced amounts of reflected light due to the effect of the mark being formed. Namely, the RF signal, especially the second pulse P#2and subsequent pulses, shows information affected by the mark being formed. In other words, the RF signal can be an information signal by which a mark generation state is monitored in real time.

FIG. 3toFIG. 6show RF-signal waveforms observed when various levels of recording laser power were used.

The figures show RF signals corresponding to the total quantity of light of a main beam having a DC component. Signals obtained from an RF-signal photodetector when an optical system emits pulse-train-manner lasers to a DVD-R are current-to-voltage converted, and amplified by an RF matrix amplifier to acquire the RF signals.

When the peak PK1of the first pulse P#1and the peaks PK2, . . . , and PKn of the second pulse P#2and subsequent pulses in each RF signal are observed, it is found from the experimental results that the peaks PK2, . . . , and PKn of the second pulse P#2and subsequent pulses were almost not changed under a certain recording condition (a determined recording medium, a determined optical system, and a determined linear velocity).

It is confirmed especially from the comparison betweenFIG. 3andFIG. 4that the ratios of the peak PK1of the first pulse P#1and the peaks PK2, . . . , and PKn of the second pulse P#2and subsequent pulses were changed according to the magnitude of the quantity of light emitted on the recording medium.

In addition, it is also found that the quality of a reproduction RF signal became best in that recording area if the ratio of the peak PK1and the peak PK2was a certain constant value during recording, when the quality was evaluated by a jitter.

From these findings, it is understood that a feedback function can be implemented that allows recording power most suitable for generating marks to be output in an environment when an RF signal is monitored during recording; the ratio of, for example, the peak PK1and the peak PK2is calculated; and if the ratio is shifted from the value (reference value measured in advance in various conditions) regarded as that which provides the best recording condition, a compensation is given to a laser-power control system.

FIG. 7shows the relationship between recording laser power and normalized amplitudes obtained from the experiments. Normalized amplitudes are the values obtained by dividing the amplitudes by the amplitude (peak) of the first pulse P#1, that is, the ratio therebetween.

The figure show the peaks PK1of the first pulses P#1, the normalized peaks (PK2/PK1) of the second pulses P#2, the normalized peaks (PK3/PK1) of the third pulses P#3, the normalized bottom values (such as BT3/PK1) of the third pulses P#3(and subsequent pulses), the normalized center values (such as CT3/PK1) of the third pulses P#3(and subsequent pulses), and the normalized modulation values (such as (PK3−BT3)/PK1) of the third pulses P#3and subsequent pulses in a laser-power range of 2 mW to 5 mW.

It is assumed that the reproduction RF signal has the best quality in a predetermined linear-velocity condition of the system when the average recording power is about 2.8 mW.

For example, it can be considered that the normalized peak of the second pulse P#2is reduced from 0.80 as the recording power is gradually increased, and the mark generation state becomes best when the normalized peak is settled at about 0.63.

From this phenomenon, it is understood that, if energy required for generating marks is insufficient due to an environmental temperature change or film unevenness on the medium, the normalized peak of the second pulse shows a value larger than 0.63, such as 0.70.

In other words, when the ratio (P2/P1), which is a normalized value, is monitored during recording; and an instruction for increasing the recording power to return the value to the normal value is given to the laser control system to actually increase the laser power, the normalized peak of the second pulse returns to 0.63, and the mark generation condition also becomes best in the environment.

Conversely, if the energy required for generating a mark is excessive, when the normalized amplitude of the second pulse is monitored and a difference with the target value of 0.63 is fed back to the laser control system, a mark is always generated in the best condition.

When a ratio to be detected is called B/A, the ratio (PK2/PK1) between the peak PK1of the first pulse P#1and the peak PK2of the second pulse P#2is used as the ratio B/A to be detected, in the foregoing description. It is understood fromFIG. 7that the normalized peaks, the normalized bottom values, the normalized center values, and the normalized modulation values of the third pulse P#3and subsequent pulses are also changed linearly to some extent in a range of, for example, 2 mW to 3 mW (where it is assumed that there exists the most suitable laser power).

Therefore, it is considered that, in addition to the ratio between the peak PK1of the first pulse P#1and the peak PK2of the second pulse P#2, the ratio between the peak PK1and the peak PK3(or PK4, . . . ), the ratio between the peak PK1and the center value CT2(or CT3, . . . ), the ratio between the peak PK1and the bottom value BT2(or BT3, . . . ), the ratio between the peak PK1and the average av (or avPK, avCT, or avBT), the ratio between the peak PK1and the modulation value (PK2−BT2, or PK3−BT3, . . . ), and so on can be used for laser-power feedback control in the same way.

When normalization is performed by using the center value CT1of the first pulse P#1, it is considered that the same results are obtained. Therefore, the center value CT1or the modulation value (PK1BT1) may be used as the value A, instead of the peak PK1.

In other words, the ratio B/A to be detected can be PK3/PK1, BT2/PK1, CT2/PK1, avPk/PK1, or various others in addition to PK2/PK1.

Since there exists no second and subsequent pulses during a 3 T -mark generation period as understood fromFIG. 1, the value B is not obtained. Therefore, an operation for obtaining the ration B/A is not performed during the 3 T -mark generation period.

A structure and operation according to the present embodiment will be described later. A fundamental idea of operations is that a ratio observed in the RF signal, that is, a ratio B/A, is detected, where a value A indicates a signal value (such as PK1or CT1) related to the first pulse, and a value B indicates a signal value (such as PK2, PK3, CT2, CT3, BT2, BT3, av, or avPK) related to the second and subsequent pulses, and laser-power feedback control is performed according to the ratio, as described above (although the value A is compensated in the present embodiment, as described later).

In the present embodiment, as in an optical recording apparatus for organic-pigment-film recording media, it is assumed that a mark generation speed is faster than in usual phase-change media during a recording process, and luminous flux having recording power is obtained on an RF photodetector as reflected light from the surface of a medium, indicating the generation state of a mark to be changed by its energy, which passes through a returning path in the optical system.

It is further assumed that pulse-train-manner laser emission is employed in order to form marks at accurate positions by avoiding heat interference on a recording medium, in a high-density recording system.

In a so-called APC laser control method, which has been used conventionally, an APC photodetector monitors (front monitoring) part of outgoing luminous flux to obtain a change caused by an environmental temperature change or during aging in the I-L (current and optical output) characteristic of a semiconductor laser, the quantity of the outgoing light is estimated, and the estimated quantity is compared with the recording-power target value specified in advance to feedback the state to a laser driving circuit system.

To accurately obtain pulse-train-manner optical-recording waveforms, a circuit for sampling a monitoring signal of the quantity of outgoing light at timing corresponding to the pulse width is required. With this, even if an environmental temperature is changed, or aging occurs, the outgoing laser power is always maintained at a constant level.

This is just for controlling the laser output level so that it is the most suitable level. Factors which affect mark generation other than the I-L characteristic of the semiconductor laser, such as recording film unevenness or a change in the energy absorption efficiency of the recording medium caused by wavelength fluctuation due to a temperature change, described above, cannot be covered.

In the present embodiment, reflected light which includes mark-generation information is observed by the RF photodetector during recording; it is determined almost at the same time whether the recording power currently being output is most suitable for mark generation; and if the recording power is shifted from the most suitable state, a compensation is fed back to the laser-power control system to control the power of the semiconductor laser. Therefore, laser-power control which covers all factors which affect mark generation, such as recording film unevenness or a change in the energy absorption efficiency due to waveform fluctuation, can be implemented.

More specifically, a signal measured by the RF photodetector is observed at timing slightly delayed with respect to the pulse-train-manner outgoing luminous flux output from the semiconductor laser, due to a go-and-return optical length, photoelectric-conversion time, and transmission time, in a state limited by the frequency characteristics of the optical system and the electrical system. When the signal is sampled at suitable timing corresponding to pulse periods to obtain the ratio between measured amplitudes, it is determined whether a mark has been generated successfully. In other words, when the obtained ratio is compared with a target ratio value, a feedback control signal is obtained for laser-power control.

As described above, the ratio B/A is detected, and laser-power feedback control is performed according to the ratio. This method is effective just under a system condition in which the most appropriate recording laser power falls in a range of 2 to 3 mW. More specifically, as understood fromFIG. 7, since a change in normalized values, that is, a change in the ratio B/A, is linear in the range of 2 to 3 mW, control for increasing or reducing laser power according to the comparison between the ratio B/A and a reference ratio is allowed.

It is found fromFIG. 4,FIG. 5, andFIG. 6that there is no conspicuous difference among the differences between the peaks of the first pulses P#1and the peaks of the second pulse P#2and subsequent pulses when the laser power is equal to or more than 3 mW.

As shown inFIG. 7, normalized values (B/A) do not show definite changes in a zone where the laser power is equal to or more than 3 mW. Therefore, even if the ratio B/A is compared with a reference ratio, a desirable direction (increase or reduction) cannot be determined for laser power control, and appropriate laser power control cannot be

Consequently, the above fundamental idea can be an effective laser-power control method in recording systems where the most appropriate laser power falls in a range of 2 to 3 mW, but the idea needs to be further developed in recording systems where the most appropriate recording laser power can be 3 mW.

With recording conditions such as a medium type, a recording density, and a linear velocity being taken into account, it is necessary to assume that there are recording systems where the most appropriate recording laser power is 3 mW.

Based on the above-described background, it is considered that a laser-power control operation, described later, according to the present embodiment is applied to a case in which recording is performed at a high linear velocity according to a system condition, and a case in which a write strategy is employed to have a relatively-large-width first pulse. It is assumed that, when the laser power reaches the most appropriate recording power, an effect of mark generation extends to the quantity of reflected light corresponding to the first pulse.

In the above-described fundamental idea, whether a mark has been successfully generated is determined by checking the ratio B/A, where the value A (value not affected by a mark-generation state) indicates the quantity of reflected light corresponding to the first pulse P#1and is used as a reference, and the value B (value affected by the mark-generation state) indicates the quantity of reflected light corresponding to the second pulse P#2and subsequent pulses. The reason why the ratio B/A is not changed at 3 mW or more, for example, as shown in the experimental results ofFIG. 3toFIG. 6is that the first pulse P#1itself in the RF signal is affected by a pit mark generated instantaneously by the laser illumination corresponding to the first pulse, and the amplitude corresponding to the reflected light is suppressed.

When the quantity of reflected light corresponding to the first pulse P#1in the RF signal is affected by a mark-generation state in this way, the value A, which serves as a reference value corresponding to the quantity of light not affected by a mark, becomes indefinite, and as a result, it is difficult to indicate the state of the most appropriate recording power only by the ratio B/A.

Therefore, in operations according to the present embodiment, a value A′ obtained by compensating the value A, which is the quantity of reflected light corresponding to the first pulse P#1, for a portion affected by a mark generation, and laser power control is performed according to the ratio B/A′.

FIG. 8shows the peak PK1of the first pulse P#1in an RF signal and a compensated peak PK1′, which indicates the peak PK1compensated as to have no effect of mark generation, both obtained when the recording laser power is changed. The compensated peak PK1′ linearly changes in proportion to the recording laser power.

FIG. 8also shows a normalized value PK2/PK1, which indicates the peak PK2of the second pulse P#2, normalized by the peak PK1, and a compensated normalized value PK2/PK1′, which indicates the peak PK2of the second pulse P#2, normalized by the compensated peak PK1′.

It is found that the compensated normalized value PK2/PK1′ is changed in a certain direction with respect to the recording laser power. In other words, it is understood that, even when the laser power becomes equal to or larger than, for example, 3 mW, the compensated normalized value PK2/PK1′ functions as information by which a mark generation state can be determined.

FIG. 9shows the characteristics of compensated normalized values corresponding to the normalized values shown inFIG. 7, that is, the characteristics obtained when the normalization reference is changed from the peak PK1to the compensated peak PK1′.

It is understood from the figure that each compensated normalized value shows a specific tendency with respect to changes in the recording laser power, and more precisely, the value is reduced as the recording laser power increases.

Therefore, each of compensated normalized values PK2/PK1′, PK3/PK1′, BT3/PK1′, CT3/PK1′, and (PK3−BT3)/PK1′, corresponding to the ratio B/A′, can be used for the same laser power control as in the above-described fundamental idea.

As the value B in the ratio B/A′, any of the peaks PK2, PK3, . . . , the center values CT2, CT3, . . . , the bottom values BT2, BT3, . . . , the averages, av, avPK, avCT, and avBT, the modulation values (PK2−BT2), (PK3−BT3), . . . corresponding to the second pulse P#2and subsequent pulses needs to be used in the same way as described in the above fundamental idea.

As the value A′, a compensated center value CT1′ or a compensated modulation value (PK1−BT1)′ may be used, in addition to the compensated peak PK1′, obtained by compensating the peak PK1of the first pulse P#1.

The value A′, for example, the compensated peak PK1′ of the first pulse P#1, is obtained in the following way.

Since the compensated peak PK1′ is set to a value not affected by a mark-generation state, a value not affected by the mark-generation state is first observed. More specifically, the amplitude of an RF signal, corresponding to a space SP period, that is, the quantity LSP shown inFIG. 2, of reflected light needs to be detected at a space period.

The above-described APC control regulates the laser output with respect to a recording power (corresponding to the peak of a pulse train) and a reproduction power (corresponding to a level at a space period), both specified as laser power.

When the quantity LSP of reflected light is detected at a space period as a value not affected by the mark-generation state, the quantity of reflected light, which serves as a value not affected by the mark-generation state, that is, the compensated peak PK1′, can be estimated by using a specified ratio between the recording power specified in the APC system and a power at a space area.

Since a first-pulse waveform is observed as a slightly drooped waveform due to the optical pickup, the state of a recording medium, and the restrictions of the frequency characteristics of electric circuit systems, when calibration is performed at a low recording power state where the quantity of reflected light corresponding to the first pulse P#1is obviously not affected by mark generation, the compensated peak PK1′ serving as a more precise reference value can be obtained in some cases.

When the compensated peak PK1′ obtained in this way is used as the value A′ and the ratio B/A′ is calculated, even if the recording laser power becomes high to some extent, only the changes caused by mark generation, of the quantities of reflected light corresponding to the second pulse P#2and subsequent pulses can be taken while the changes are not affected by the change caused by an organic-pigment film unevenness on the recording medium, of the quantity of the entire reflected light.

Therefore, when the shift of the detected ratio B/A′ against a target ratio between the value A′ and the value B, indicating the most appropriate recording state and obtained in advance correspondingly to various recording conditions, is calculated and fed back to the laser control system, even if the first pulse P#1in an RF signal is affected by mark generation, the most appropriate recording power for mark generation can be obtained precisely.

2. Structure of Disk Drive Apparatus

A specific structure and operation according to the present embodiment will be described below.

A disk drive apparatus serving as an embodiment of an optical recording apparatus according to the present invention is, for example, an apparatus for recording and reproducing data into and from DVD-Rs. Compensation control with the ratio (B/A′) of sample values of an RF signal, as described above, is performed in addition to APC control in laser-power control. It is assumed in the most fundamental processing that the ratio between the compensated peak PK1′ of the first pulse P#1and the peak PK2of the second pulse P#2is used as the ratio (B/A′), where PK1′ serves as the value A and PK2serves as the value B.

Various other ratios can be used, and they will be described laser in modifications.

FIG. 10shows the entire structure of a disk drive apparatus30according to the present embodiment.FIG. 11illustrates the structure of a main part related to laser-power control in the structure shown inFIG. 10.

As shown inFIG. 10, a disk100, such as a DVD-R, is mounted on a turntable7, and rotated by a spindle motor6at a constant linear velocity (CLV) in a recording/reproduction operation.

An optical pickup1reads pit data recorded in tracks, track wobbling information, and land-prepit information. Pits recorded as data on tracks formed as grooves are so-called pigment-change pits.

In the pickup1, a laser diode4serving as a laser light source, a photodetector5for detecting reflected light, an objective lens2serving as an output end of laser light, and an optical system24for illuminating a disk recording surface through the objective lens2and for leading reflected light therefrom to the photodetector5are provided.

A monitor detector22for receiving part of the output light from the laser diode4is also provided therein.

The structure inside the pickup1is shown inFIG. 11in an outlined manner. Laser light output from the laser diode4is led to the objective lens2by the optical system24, which has a grating plate (not shown), a collimator lens24a, a retardation plate (not shown), a PBS (polarized beam splitter)24b, and a multi-lens (not shown), and is emitted on the disk100. Light reflected therefrom is detected by the photodetector5.

Part of the laser light output from the laser diode4is also led to the monitor detector22, and its detection light is used for an APC operation, described later.

The laser diode4outputs laser light having a wavelength of 650 nm or 635 nm. The optical system has an NA of 0.6.

The objective lens2is held by a two-axis mechanism3in a movable manner in a tracking direction and a focus direction.

The pickup1is held by a sled mechanism8in a movable manner in a disk radius direction as a whole.

The laser emission of the laser diode4of the pickup1is driven by a driving signal (driving current) sent from a laser driver18.

As shown inFIG. 10, the information of light reflected from the disk100is detected by the photodetector5, converted to an electric signal corresponding to the quantity of received light, and sent to a matrix circuit9.

The matrix circuit9is provided with a current-to-voltage conversion circuit and a matrix calculation/amplification circuit for the output current of a plurality of light receiving elements serving as the photodetector5, and generates necessary signals by matrix calculation processing.

For example, an RF signal corresponding to reproduced data, a focus-error signal FE for servo control, and a tracking-error signal TE are generated.

In addition, a push-pull signal P/P related to wobbling of land prepits and grooves is generated.

The RF signal output from the matrix circuit9is sent to a binarizing circuit11, the focus-error signal FE and the tracking-error signal TE are sent to a servo circuit14, and the push-pull signal P/P is sent to an address decoder26.

The RF signal is also sent to a pulse sampling section25, and is used for processing for laser-power compensation control, described later.

The address decoder26uses the push-pull signal P/P to extract land-prepit information, to generate a wobbling clock synchronized with track wobbling, and to decode address information pre-formatted on the disk100. The decoded address information is sent to a system controller10.

The generated wobbling clock is sent to the address decoder26and to a spindle servo circuit23. An encoding clock is generated from the wobbling clock, and sent to a encoding/decoding section12.

The RF signal obtained by the matrix circuit9is binarized in the binarization circuit11, and sent to the encoding/decoding section12.

The encoding/decoding section12is provided with a functional block serving as a decoder during reproduction and a functional block serving as an encoder during recording.

During reproduction, demodulation processing for the run-length-limited code, error correction processing, deinterleaving are performed as decoding processing to obtain reproduced data.

The encoding/decoding section12generates a reproduction clock synchronized with the RF signal by a PLL process, and executes the above-described decoding processing with the reproduction clock, during reproduction.

During reproduction, the encoding/decoding section12accumulates data decoded as described above in a buffer memory20.

As a reproduction output of the disk drive apparatus30, the data buffered in the buffer memory20is read and sent.

An interface section13is connected to an external host computer80, and performs communications with the host computer80for recording data, reproduction data, and various types of commands.

During reproduction, the reproduction data decoded and stored in the buffer memory20is sent to the host computer80through the interface section13.

A read command, a write command, and other signals are sent from the host computer80to the system controller10through the interface section13.

During recording, the host computer80sends recording data. The recording data is sent from the interface section13to the buffer memory20and buffered therein.

In this case, the encoding/decoding section12executes encoding processing which includes error-correction-code addition, interleaving, sub-code addition, and run-length-limited code modulation for recording data for the disk100, as encoding processing for the buffered recording data.

The encoding/decoding section12uses an encoding clock synchronized with the wobbling clock, as a reference clock for the encoding processing.

NRZI-format recording data generated in the encoding processing executed by the encoding/decoding section12is converted to pulse-train-manner recording pulses (Laser driving pulses) by a write strategy21, and sent to the laser driver18.

The write strategy21also executes recording compensation, namely, fine adjustment of the most suitable recording power and adjustment of a laser-driving-pulse waveform according to the characteristics of a recording layer, the spot shape of the laser light, and a recording linear velocity.

The laser driver18gives driving current according to the received laser driving pulses to the laser diode4for laser emission driving. With this, pit marks (pigment change pits) are formed on the disk90according to recording data.

An APC circuit (auto power control)19is a circuit section for controlling the laser output such that it is constant irrespective of the temperature while monitoring the laser output power by the output of the monitor detector22. The target value of the laser output is given by the system controller10, and the APC circuit controls the laser driver18such that the laser output level has the target value.

A detailed example structure of the APC circuit will be described later by referring toFIG. 11.

The servo circuit14generates various servo driving signals, a focus driving signal, a tracking driving signal, and a sled driving signal, from the focus-error signal FE and the tracking error signal TE sent from the matrix circuit9, and executes a servo operation.

More specifically, the servo circuit14generates the focus driving signal FD and the tracking driving signal TD according to the focus-error signal FE and the tracking-error signal TE, and sends them to a two-axis driver16. The two-axis driver16drives a focus coil and a tracking coil in the two-axis mechanism3of the pickup1. With this, a tracking servo loop and a focus servo loop are generated by the pickup1, the matrix circuit9, the servo circuit14, the two-axis driver16, and the two-axis mechanism3.

The servo circuit14also turns off the tracking servo loop and outputs a jump driving signal to the two-axis driver16in response to a track jump instruction sent from the system controller10to execute a track jump operation.

The servo circuit14further generates the sled driving signal according to a sled-error signal obtained as a low-frequency component of the tracking-error signal TE and access execution control made by the system controller10, and sends the signal to a sled driver15. The sled driver15drives the sled mechanism8according to the sled driving signal. The sled mechanism8includes a mechanism, although not shown, formed of a main shaft for holding the pickup1, a sled motor, and a transmission gear. When the sled driver15drives the sled mechanism8according to the sled driving signal, predetermined slide movement of the pickup1is performed.

The spindle servo circuit23performs control so as to CLV rotate the spindle motor6.

The spindle servo circuit23obtains the wobbling clock as the information of the current rotation speed of the spindle motor6when data recording, and compares it with CLV reference speed information to generate a spindle-error signal SPE.

Since the reproduction clock (clock serving as decoding-processing reference) generated by the PLL in the encoding/decoding section12serves as the information of the current rotation speed of the spindle motor6when data reproduction, the clock is compared with the predetermined CLV reference speed information to generate a spindle-error signal SPE.

The spindle servo circuit23sends a spindle driving signal generated according to the spindle-error signal SPE to a spindle motor driver17. The spindle motor driver17applies, for example, a three-phase driving signal to the spindle motor6according to the spindle driving signal to CLV rotate the spindle motor6.

The spindle motor23also generates a spindle driving signal according to a spindle kick/brake control signal sent from the system controller10, and makes the spindle6perform operations, for example, start rotating, stop rotating, accelerate rotating, or decelerate rotating by using the spindle motor driver17.

The above-described various operations in the servo systems and the recording and reproduction system are controlled by the system controller10formed of a microcomputer.

The system controller10executes various types of processing according to commands sent from the host computer80.

When the host computer80sends a read command which requests the transmission of data recorded in the disk100, for example, seek-operation control is first performed with a specified address being set to the target. More specifically, an instruction is sent to the servo circuit14to make the pickup1perform an access operation with the address specified by a seek command being set to the target.

Then, operation control required for sending data in a specified data area to the host computer80is performed. In other words, the required data is read from the disk100, decoded, buffered, and sent.

When the host computer80sends a write command, the system controller10first moves the pickup1to an address where data is to be written. Then, the system controller10makes the encoding/decoding section12apply the encoding processing to the data sent from the host computer80, as described above.

Laser driving pulses are sent from the write strategy21to the laser driver18, as described above, to perform recording.

A memory27collectively indicates a ROM, a RAM, and a non-volatile memory used by the system controller10for processing. The memory27may be a memory built in the system controller10, formed of the microcomputer.

The memory27is used as a working area for calculations and storage of a program, various coefficients, and constants required for a control operation in the disk drive apparatus. In the present embodiment, various system conditions (such as a medium type and a linear velocity) and the ratios (PK2/PK1′) most suited thereto are stored in a non-volatile area of the memory27as information for a laser-power compensation operation, described later. For example, the most suitable ratios are experimentally obtained under various system conditions before the apparatus is shipped from the factory, and the experimental results are stored as a data table.

In summary, the reproduction operation and the recording operation of the disk drive apparatus30can be described as follows:

Servo Operation

A signal detected by the pickup1is converted to servo-error signals, such as the focus-error signal FE and the tracking-error signal TE, in the matrix circuit9, and sent to the servo circuit14. The driving signals FD and TD output from the servo circuit14drive the two-axis mechanism3of the pickup1to perform focus servo and tracking servo.

Data Reproduction

A signal detected by the pickup1is converted to an RF signal in the matrix circuit9, and sent to the encoding/decoding section12. The encoding/decoding section12reproduces a channel clock and performs decoding according to the channel clock. Decoded data is sent to the interface section13.

Rotation Control

The channel clock reproduced by the encoding/decoding section12is sent to the spindle servo circuit23, and the rotation of the disk100is controlled thereby.

Address Reproduction

An address is included in the RF signal, decoded by the encoding/decoding section12, and sent to the system controller10.

Laser Control

The APC circuit19performs control so as to maintain a constant laser output, according to an instruction of the system controller10.

Servo Operation

The same operation as in reproduction is performed. The matrix circuit9or the servo circuit14performs compensation such that an increase in gain caused by an increase in laser power does not occur.

Data Recording

Channel coding, such as ECC addition, re-arrangement, and modulation, is applied by the encoding/decoding section12to data received through the interface section13. The data, to which the channel coding has been applied, is converted to laser driving pulses suited to the disk100in the write strategy21, and applied to the laser diode4of the pickup1through the laser driver18(APC circuit19).

Rotation Control

The wobbling clock is generated from the push-pull signal P/P output from the matrix circuit9, sent to the spindle servo circuit23, and used for constant-linear-velocity (CLV) rotation control.

Address Reproduction

The land-prepit information is detected from the push-pull signal P/P output from the matrix circuit9. The detected land-prepit information is decoded to generate an address, and read by the system controller10.

The encoding clock is also generated from the push-pull signal P/P, and sent to the encoding/decoding section12.

A structure used for laser-power control in the present embodiment will be described below by referring toFIG. 11. Since laser-power compensation performed during recording is a point in operations in the present embodiment, the following description will be made for recording operations.

As it is understood from the above description made by referring toFIG. 10, when laser driving pulses, that is, a combination pattern of a specified laser-driving-current value and a modulated signal, are input to the laser driver18from the write strategy21during recording, the laser diode4emits laser light, and the objective lens2condenses the laser light as an optical spot and projects at a predetermined area on the disk100through the above-described optical system24.

The detector22for front monitoring receives part of outgoing luminous flux, and detects the quantity of light to estimate the quantity of the emitted light of laser power.

The luminous flux condensed on the disk100is returned to the optical system24as reflected light (reproduction signal) while reflecting a mark generation state on the disk, and finally projected on the RR-signal photodetector5divided into multiple pieces.

The APC circuit19includes, for example, a current/voltage conversion section19a, a sample/hold circuit19b, an A/D converter19c, a laser-power controller19d, a target-value holding section19e, a D/A converter19f, and a timing generator19g, as shown inFIG. 11.

The timing generator19goutputs various timing signals according to encoded data, namely, a signal serving as the source of laser driving pulses, output from the encoding/decoding section12to control the operation timing of the sample/hold circuit19b, the A/D converter19c, and the laser-power controller19d.

Pulse-train-manner laser emission is performed during recording. The APC circuit19monitors recording-level laser power to maintain it at the target value.

A signal (current corresponding to the quantity of received light) sent from the monitor detector22is converted to a voltage at the current/voltage conversion section19a, and sent to the sample/hold circuit19b. Since pulse-train-manner laser emission is performed, the sample/hold circuit19bsamples and holds the signal at for period where a pulse-train pulse width is maintained, namely, a period where a recording-power laser output is applied, at appropriate timing according to a timing signal sent from the timing generator19g.

The voltage held and output is converted to a digital value by the A/D converter19c, and sent to the laser-power controller19das the current estimated laser power.

The laser-power controller19dcompares a laser-power target value specified in the target-value holding section19ewith the estimated laser power to superpose the quantity corresponding to the difference therebetween onto the current indication, and sends it to the laser driver18through the D/A converter19f. The system controller10sets a target laser-power value in the target-value holding section19e.

With such an operation in the APC circuit19, a function for maintaining the laser output power at the target value is obtained.

As described before, the operation performed by the APC circuit19is to control the laser output at a constant level, and does not optimize the recording power with factors, such as laser-wavelength fluctuation and recording-film unevenness, being taken into account.

In the present embodiment, a structure for laser-power compensation is further provided. More specifically, an RF signal is sampled to obtain a ratio, and laser-power compensation is performed according to the ratio.

As shown inFIG. 11, the matrix circuit9is provided with a current/voltage conversion section9aand an RF matrix amplifier9bas a structure for obtaining an RF signal. With these components, an RF signal is generated according to the quantity of reflected light detected by the photodetector5.

The RF signal obtained in the matrix circuit9is sent to the pulse sampling section25. The pulse sampling section25performs sampling required for calculating the ratio.

In the present embodiment, it is assumed that the ratio B/A′ obtained for the RF signal is set to the ratio PK2/PK1′ between the compensated peak PK1′ of the first pulse P#1and the peak PK2of the second pulse P#2.

The compensated peak PK1′ is obtained from the quantity LSP of reflected light detected in the RF signal, corresponding to a space period, as described above, and the setting ratio between the recording-power target value and the reproduction-power target value, specified in the APC circuit19.

Therefore, the pulse sampling section25is configured such that the quantity LSP of reflected light is sampled in the RF signal. A structure for sampling the peak PK2as the value B is also provided.

More specifically, a peak holding circuit25a2and an A/D converter25b2corresponding to the peak PK2of the second pulse P#2, and a sample-and-hold circuit25dfor performing sampling at a space period and an A/D converter25eare provided. In addition, a timing generator25cis also provided.

To obtain the compensated peak PK1′ of the first pulse P#1, it is necessary to obtain at least the quantity LSP of reflected light at a space period. When the peak PK1of the first pulse P#1is actually obtained, the compensated peak PK1′ can be corrected to a further more appropriate value. To this end, as shown in the figure, a peak holding circuit25a1 and an A/D converter25b1 corresponding to the peak PK1of the first pulse P#1are also provided.

The timing generator25csends a signal shown inFIG. 12(d), which indicates a sampling period corresponding to a period of the first pulse P#1in an RF signal shown inFIG. 12(c), to the peak holding circuit25a1according to the encoded data shown inFIG. 12(a) sent from the encoding/decoding section12to hold and output the peak during the period. The timing generator25calso applies timing control to the A/D converter25b1so as to convert the held and output peak to a digital value.

The timing generator25cfurther sends a signal shown inFIG. 12(e), which indicates a sampling period corresponding to a period of the second pulse P#2in the RF signal, to the peak holding circuit25a2 to hold and output the peak during the period. The timing generator25calso applies timing control to the A/D converter25b2so as to convert the held and output peak to a digital value.

The timing generator25cfurther sends a signal shown inFIG. 12(f), which indicates a sampling period corresponding to a space period in the RF signal to the sample-and-hold circuit25dat a point of time, such as when a laser-power compensation operation is started, to hold and output the peak in the period. The timing generator25calso applies timing control to the A/D converter25eso as to convert the held and output peak to a digital value.

With these operations, the A/D converter25b1 outputs the peak PK1as the digital value, and the A/D converter25b2outputs the peak2as the digital value. In addition, the A/D converter25eoutputs the quantity LSP of reflected light as the digital value. Each digital value can be sent to the system controller10at a necessary point of time.

Since the pulse-train-manner laser driving pulses shown inFIG. 12(b) are generated according to the encoded data shown inFIG. 12(a), the timing generator25ccan obtain the timing of the first-pulse P#1period, the second-pulse P#2period, and the space period in the RF signal shown inFIG. 12(c) from the encoded data. Actually, there is a delay caused by processing in the optical system24and the matrix circuit9between laser-output timing and timing when the pulse sampling section25receives the RF signal, which is reflected-light information. Therefore, the timing generator25cgenerates timing signals for sampling periods with the delay being taken into account.

The system controller10reads the peaks PK1and PK2and the quantity LSP of reflected light at the space period, calculates the ratio, and compares the calculated ratio with a reference ratio to generate a laser-power compensation signal.

InFIG. 11, functional blocks for generating such a laser-power compensation signal are shown inside the system controller10.

A sampled-value input section10a, an estimation calculation section10b, a compensation calculation section10c, a compensation-reference holding section10d, and a compensated-first-pulse-value estimation section10eare provided. Actually, these sections need to be implemented by software in the system controller10.

Detailed processing examples will be described by referring toFIG. 13andFIG. 14. The sampled-value input section10areads the peak PK2as the value B, and sends it to the estimation calculation section10b. When the sampled-value input section10areads the peak PK1and the quantity LSP of reflected light at the space period, the sampled-value input section10asends them to the compensated-first-pulse-value estimation section10eas information for obtaining the compensated peak PK1′ (value A′).

The compensated-first-pulse-value estimation section10eassociates the quantity LSP of reflected light at the space period with the ratio of (recording power)/(reproduction power) in the APC circuit19, that is, the target ratio which the system controller10has specified for the APC circuit19, to estimate the peak PK1′ (value A′) not affected by mark generation, of the first pulse P#1.

The compensated-first-pulse-value estimation section10ealso corrects the estimated peak PK1′ by using the received peak PK1.

The estimation calculation section10buses the peak PK2sent from the sampled-value input section10aas the value B and the compensated peak PK1′ sent from the compensated-first-pulse-value estimation section10eas the value A′ to calculate a ratio, that is, B/A′ (PK2/PK1′), as an estimate of the current laser power.

The compensation-reference holding section10dholds the most appropriate PK2/PK1′ value (hereinafter called a reference ratio) corresponding to the current recording conditions, including the current linear velocity. For example, among the most appropriate ratios for recording conditions, stored in the memory27shown inFIG. 10as the table, as described above, the most appropriate ratio corresponding to the current conditions has been loaded.

The compensation calculation section10ccompares the ratio calculated by the estimation calculation section10bwith the reference ratio held by the compensation-reference holding section10dto generate the laser-power compensation signal.

The laser-power compensation signal is sent to the laser-power controller19din the APC circuit19. The laser-power controller19dcompensates, for example, the target value stored in the target-value holding section19eand used for the laser-power regulation control, described above, according to the laser-power compensation signal.

The target value itself stored in the target-value holding section19emay be updated by the laser-power compensation signal.

With such a structure, in the present embodiment, the ratio serving as a recording-power estimate is calculated almost at the same time when recording, from the correlation of the amplitudes of the RF signal corresponding to the pulse-train-manner waveform. The ratio is compared with the reference ratio to calculate a value used for compensating the recording power. The operation in the APC loop is compensated. With this, feedback for most-appropriate recording-power control is implemented with a mark generation state on the disk100being taken into account.

A specific example of the laser-power compensation processing performed in the system controller10, that is, the processing executed by the functional blocks shown inFIG. 11inside the system controller10, will be described by referring toFIG. 13.

Steps shown inFIG. 13correspond to the functional blocks shown inFIG. 11as follows:

In the recording-laser-power compensation processing, the system controller10first checks various system conditions related to a recording operation in step F101. More specifically, the system controller10checks a medium type, a recording linear velocity, and a recording-power target value.

Next, in step F102, the system controller10reads the quantity LSP of reflected light at the space period from the pulse sampling section25.

Then, in step F103, the system controller10calculates the compensated peak PK1′, that is, the value A′, from the quantity LSP of reflected light and a system condition (specified ratio between the recording-power target value and the reproduction-power target value).

In step F104, a reference ratio (B/A′)ref suited to the system conditions checked in step F101is read from the data table stored in the memory27.

With this, a preparation for the compensation processing has been finished, and a compensation calculation process starts at step F105.

In step F105, the peak PK1of the first pulse P#1output from the A/D converter25b1 is read.

In step F106, the peak PK2of the second pulse P#2output from the A/D converter25b2is read as the value B.

In step F107, the compensated peak PK1′ (value A′) calculated in step F103is corrected by using the peak PK1read in step F105. This correction is made for non-uniform reflectivity on the disk100.

For example, the peak PK1of the first pulse P#1in the RF signal is changed with respect to the recording laser power as shown inFIG. 8. Therefore, the peak PK1can be estimated from the current recording laser power according to the characteristic shown inFIG. 8. If there is a difference between the estimated peak PK1and the peak PK1actually detected, it can be determined that the difference is caused by non-uniform reflectivity of the disk.

Consequently, the estimated compensated peak PK1′ can be adjusted to a value in which the non-uniform reflectivity is taken into account when the compensated peak PK1′ is multiplied by the ratio corresponding to the difference.

In step F108, the ratio B/A′ is calculated.

In step F109, the calculated ratio B/A′ is compared with the reference ratio (B/A′)ref.

When the ratio B/A′ is larger than the reference value (B/A′)ref, the processing proceeds to step F111, and the value obtained by increasing the current recording-power target value, that is, the recording-power target value held by the target-value holding section19eof the APC circuit19, by 0.5 mW is set to a new compensated recording-power target value.

Then, in step F112, the new recording-power target value is sent to the laser-power controller19das a laser-power compensation signal, and the APC loop is made to execute laser power control by using the new recording-power target value. Then, the processing returns to step F105.

When the ratio B/A′ is smaller than the reference value (B/A′)ref in step F109, the processing proceeds to step F110, and the value obtained by reducing the current recording-power target value, that is, the recording-power target value held by the target-value holding section19eof the APC circuit19, by 0.5 mW is set to a new compensated recording-power target value.

Then, in step F112, the new recording-power target value is sent to the laser-power controller19das a laser-power compensation signal, and the APC loop is made to execute laser power control by using the new recording-power target value. Then, the processing returns to step F105.

After the processing returns to step F105, the same processes are repeated.

In summary, the ratio B/A′ is compared with the reference ratio (B/A′)ref, and the recording-power target value in the APC loop is increased or reduced by 0.5 mW at a time such that the ratio B/A′ converges almost at the reference ratio (B/A′)ref.

When the ratio B/A′ becomes almost equal to the reference ratio (B/A′) ref at a point of time in step F109, the recording-power-target-value compensation processing is terminated.

As described above, according to the processing example shown inFIG. 13, the recording-power target value used as the reference in the APC circuit19is compensated according to the comparison between the ratio B/A′ and the reference value (B/A′)ref such that the ratio B/A′ finally matches the reference ratio (B/A′)ref, that is, the recording laser power reaches the most appropriate recording laser power.

With such laser-power compensation processing being performed, the actual recording power is controlled so as to be most appropriate for the current recording-operation environment. With this, the laser output can be controlled for laser wavelength fluctuation due to the temperature dependency of the I-L characteristic of the laser diode4or aging, a change in the energy absorption efficiency of the disk100due thereto, and a change in the most appropriate recording power due to the film unevenness of the disk100. Therefore, the most appropriate mark-generation operation is implemented, and the quality (jitter and others) of an RF signal is improved when reproduction.

Further, non-uniform reflectively is also handled, and the most appropriate control is allowed.

FIG. 14shows a processing example which can be employed in stead of that shown inFIG. 13, as recording-power compensation processing.

Since steps F201to F208are the same as steps F101to F108shown inFIG. 13, a description thereof is omitted.

In the processing example shown inFIG. 14, after the ratio B/A′ is calculated in step F208, (B/A′)/(B/A′)ref is calculated in step F209.

Then, in step F210, it is determined whether (B/A′)/(B/A′)ref is “1” or not. When it is not “1” (does not fall in an area where it is regarded as “1”), the processing proceeds to step F211.

In step F211, a ratio α corresponding to the shift of the ratio B/A′ against the reference ratio (B/A′)ref is calculated.

FIG. 15shows the relationship between the recording power, and the ratio B/A′ and the reference ratio (B/A′)ref obtained from the table data. Under the current system conditions, it is assumed that recording power Pref shown in the figure is the most appropriate. In this case, according to the calculated ratio B/A′, the current power is estimated as recording power Po shown in the figure with the system conditions being taken into consideration.

In the above description, the ratio α is specified in Pref=(1+α)Po, and indicates the increase ratio of the current recording-power target value to the new compensated recording-power target value.

After the ratio α is calculated, the value obtained by multiplying the current recording-power target value, that is, the recording-power target value held by the target-value holding section19eof the APC circuit19, by (1+α) is set to a new compensated recording-power target value in step F212.

Then, in step F213, the new recording-power target value is sent to the laser-power controller19das a laser-power compensation signal, and the APC loop is made to execute laser power control by using the new recording-power target value. The processing returns to step F205.

In such compensation processing, if algorithm used for calculating the ratio α for compensation is ideal and the recording-power target value reaches the most appropriate value by one compensation operation, the processing may be finished at step F213. When a condition that the algorithm is not always ideal is taken into account, however, it is preferred that the processing return to step F205, the determination at step S210be repeated, and the compensation processing be finished after it is confirmed that the laser power sufficiently approaches the most appropriate state, that is, (B/A′)/(B/A′)ref reaches “1” (or falls in an area in which it is regarded as “1”).

Even with such laser-power compensation processing, the laser output can be controlled for a change in the energy absorption efficiency of the disk100due laser wavelength fluctuation and a change in the most appropriate recording power due to the film unevenness of the disk100. Therefore, the most appropriate mark-generation operation is implemented, and the quality (jitter and others) of an RF signal is improved when reproduction.

A still another example of a recording-power compensation operation will be described by referring toFIG. 16andFIG. 17.

In the processing examples shown inFIG. 13andFIG. 14, the estimated compensated peak PK1′, serving as the value A, is corrected by using the peak PK1actually detected.

When the non-uniformity of reflectivity on the disk100is not large or is as small as it can be ignored, it is not necessary to further correct the estimated compensated peak PK1′ according to the detected peak PK1.

The processing example shown inFIG. 17omits such correction of the compensated peak PK1′.

Therefore, since it is not necessary to detect the peak PK1in this case, the pulse sampling section25has a structure shown inFIG. 16. In other words, the peak holding circuit25a1and the A/D converter25b1corresponding to the first pulse P#1are omitted from the structure shown inFIG. 11.

In addition, the sampled-value input section10aof the system controller10needs to send the received peak PK2of the second pulse P#2to the estimation calculation section10bas the value B, and needs to send the received quantity LSP of reflected light at a space period to the compensated-first-pulse-value estimation section10e.

A flowchart shown inFIG. 17indicates the processing shown inFIG. 14from which the steps F205and F207are omitted.

Step F305inFIG. 17is the same as step F206inFIG. 14.

Since the process of each step inFIG. 17overlaps with that inFIG. 14, a description thereof is omitted.

According to such a processing example, the simplified structure of the pulse sampling section25and a reduction in the processing load of the system controller10are obtained as advantages, in addition to laser-power optimization.

6. Various Modifications

The disk drive apparatus30and the laser-power compensation operation thereof have been described in the embodiment. The present invention is not limited to the above embodiment, and various modifications can be considered.

In the above-described embodiment, the compensated peak PK1′ obtained by compensating the peak PK1of the first pulse P#1serves as the value A′, the peak PK2of the second pulse P#2is sampled and used as the value B, and PK2/PK1′ is used as the ratio B/A′.

However, the ratio B/A′ is not limited to this ratio, and can be other various ratios as described above.

For example, when the average avPK of the peaks of the second pulse P#2and subsequent pulses is used as the value B, the pulse sampling section25needs to be configured as shown inFIG. 18.

More specifically, in this case, the pulse sampling section25is provided with a sample-and-hold circuit25dand an A/D converter25eas a structure for obtaining the quantity LSP of reflected light at a space period, used for estimating the value A′.

The pulse sampling section25is also provided with a peak holding circuit25a2and an A/D converter25b2corresponding to the peak PK2, a peak holding circuit25a3and an A/D converter25b3corresponding to the peak PK3, . . . , and a peak holding circuit25a(n) and an A/D converter25b(n) corresponding to the peak PKn are provided as structures for sampling the peaks PK2, PK3, . . . , and PKn of the second pulse P#2and subsequent pulses, which are used for obtaining the average avPK as the value B.

When the peak PK1of the first pulse P#1is sampled to adjust the value A′ as shown inFIG. 13andFIG. 14, a peak holding circuit25a1and an A/D converter25b1corresponding to the peak PK1are provided. When the processing shown inFIG. 17is employed, however, the peak holding circuit25a1and the A/D converter25b1are unnecessary.

The timing generator25csends a signal shown inFIG. 19(d), indicating a sampling period corresponding to a period of the first pulse P#1in an RF signal shown inFIG. 19(c) according to encoded data shown inFIG. 19(a) sent from an encoding/decoding section12, to the peak holding circuit25a1to hold and output the peak in the period. In addition, the timing generator25cperforms timing control such that the A/D converter25b1converts the held and output peak to a digital value.

The timing generator25calso sends a signal shown inFIG. 19(e), indicating a sampling period corresponding to a period of the second pulse P#2in the RF signal to the peak holding circuit25a2to hold and output the peak in the period. In addition, the timing generator25cperforms timing control such that the A/D converter25b2converts the held and output peak to a digital value.

The timing generator25cfurther sends a signal shown inFIG. 19(f), indicating a sampling period corresponding to a period of the third pulse P#3in the RF signal to the peak holding circuit25a3to hold and output the peak in the period. In addition, the timing generator25cperforms timing control such that the A/D converter25b3converts the held and output peak to a digital value.

Although not shown in the figure, the timing generator25cgenerates signals indicating sampling periods for the fourth pulse P#4to the n-th pulse P#n and signals for controlling A/D conversion timing.

Furthermore, the timing generator25csends a signal shown inFIG. 19(g), which indicates a sampling period corresponding to a space period in the RF signal to the sample-and-hold circuit25dat a point of time, such as when a laser-power compensation operation is started, to hold and output the peak in the period. The timing generator25calso applies timing control to the A/D converter25eso as to convert the held and output peak to a digital value.

With this, the A/D converter25eoutputs the quantity LSP of reflected light as the digital value, and a sampled-value input section10ain a system controller10reads the quantity LSP of reflected light as information used for calculating compensated peak PK1′ (value A′).

The A/D converter25b1outputs the peak PK1as the digital value, and the sampled-value input section10ain the system controller10reads the peak PK1as information used for adjusting the calculated compensated peak PK1′ (value A′).

The A/D converters25b2to25b(n) also input the peaks PK2, . . . , and PKn of the subsequent pulses to the sampled-value input section10a. The sampled-value input section10aobtains the average avPK thereof by the calculation of (PK2+PK3+. . . +PKn)/n, and sets the calculated average avPK in the value B.

Then, an estimation calculation section10bneeds to obtain the ratio B/A′ from the values A′ and B, and a compensation calculation section10cneeds to generate a laser-power compensation signal in the same way as described above. In other words, the processing shown inFIG. 13,FIG. 14, orFIG. 17needs to be performed.

FIG. 20shows a case in which the bottom values BT2and BT3of the second pulse P#2and the third pulse P#3are used as the value B. A figure showing the structure of a pulse sampling section25is omitted. In this case, a bottom holding circuit for the second pulse P#2and a bottom holding circuit for the third pulse P#3in addition to a sample-and-hold circuit25dfor the quantity LSP of reflected light at a space period (and a peak holding circuit25a1for the first pulse P#1if a process for adjusting A′ is performed), and A/D converters corresponding thereto need to be provided.

A timing generator25coutputs signals which specify sampling periods as shown inFIG. 20(d),FIG. 20(e),FIG. 20(f), andFIG. 20(g) to sample the peak PK1, the bottom values BT2and BT3, and the quantity LSP of reflected light at predetermined points of time.

With this, a sampled-value input section10ain a system controller10receives the peak PK1, the bottom values BT2and BT3, and the quantity LSP of reflected light. The sampled-value input section10areads the peak PK1and the quantity LSP of reflected light for calculating and adjusting the value A′, and also reads the bottom values BT2and BT3as the value B. Either the bottom value BT2or the bottom value BT3may be used as the value B. Alternatively, the average (BT2+BT3)/2 may be used as the value B.

FIG. 21shows a case in which the center values of the second pulse P#2and subsequent pulses are used as the value B. A figure showing the structure of a pulse sampling section25is omitted. In this case, peak holding circuits for the second pulse and subsequent pulses P#2to P#n, bottom holding circuits for the second pulse and subsequent pulses P#2to P#n in addition to a sample-and-hold circuit25dfor the quantity LSP of reflected light at a space period (and a peak holding circuit25a1for the first pulse P#1if a process for adjusting A′ is performed), and A/D converters corresponding thereto need to be provided.

A timing generator25coutputs signals which specify sampling periods as shown inFIG. 21(d),FIG. 21(e),FIG. 21(f), andFIG. 21(g) to sample the peak PK1, the peak values and bottom values of the periods of the second pulse and subsequent pulses P#2to P#n, and the quantity LSP of reflected light at predetermined points of time.

With this, a sampled-value input section10ain a system controller10receives the peak PK1, the peak and bottom values of the second pulse P#2and subsequent pulses, and the quantity LSP of reflected light. The sampled-value input section10areads the peak PK1and the quantity LSP of reflected light for calculating and adjusting the value A′. The sampled-value input section10aalso calculates center values CT(2−n) by dividing the sums of the peak and bottom values of the second pulse P#2and subsequent pulses by 2 and uses them as the value B.

FIG. 22shows a case in which the average av of all sampled values of the second and subsequent pulses P#2to P# is used as the value B. A figure showing the structure of a pulse sampling section25is omitted. In this case, sampling circuits for the second and subsequent pulses P#2to P#n in addition to a sample-and-hold circuit25dfor the quantity LSP of reflected light at a space period (and a peak holding circuit25a1for the first pulse P#1if a process for adjusting A′ is performed), and A/D converters corresponding thereto need to be provided.

A timing generator25coutputs signals which specify sampling periods as shown inFIG. 22(d),FIG. 22(e), andFIG. 22(f) to sample amplitudes at intervals of predetermined sampling periods in the zone of the second pulse P#2to the n-th pulse, and the quantity LSP of reflected light at predetermined points of time.

With this, a sampled-value input section10ain a system controller10receives the peak PK1, the sampled values of the second pulse P#2and subsequent pulses, and the quantity LSP of reflected light. The sampled-value input section10areads the peak PK1and the quantity LSP of reflected light for calculating and adjusting the value A′. The sampled-value input section10aalso calculates the average av by dividing the sum of the sampled values of the second pulse P#2and subsequent pulses by the number of samples and uses it as the value B.

FIG. 23shows a case in which the bottom values of the second and subsequent pulses P#2to P# are used as the value B. A figure showing the structure of a pulse sampling section25is omitted. In this case, bottom holding circuits for the second and subsequent pulses P#2to P#n in addition to a sample-and-hold circuit25dfor the quantity LSP of reflected light at a space period (and a peak holding circuit25a1for the first pulse P#1if a process for adjusting A′ is performed), and A/D converters corresponding thereto need to be provided.

A timing generator25coutputs signals which specify sampling periods as shown inFIG. 23(d),FIG. 23(e), andFIG. 23(f) to sample the peak PK1, bottom values in the zone of the second pulse P#2to the n-th pulse, and the quantity LSP of reflected light at predetermined points of time.

With this, a sampled-value input section10ain a system controller10receives the peak PK1, the bottom values of the second pulse P#2and subsequent pulses, and the quantity LSP of reflected light. The sampled-value input section10areads the peak PK1and the quantity LSP of reflected light for calculating and adjusting the value A′, and uses the bottom values of the second pulse P#2and subsequent pulses as the value B.

As described above, various items can be used as the values A′ and B used for obtaining the ratio B/A′. The compensated values of the center value CT1or the modulation value (PK1−BT1) of the first pulse P#1, that is, a center value CT1′ or a modulation value (PK1−BT1)′, may be used as the value A′.

Further various items may be used as the value B, such as the peaks, the bottom values, the center values, the average, or the modulation values (peak−bottom value) corresponding to the second pulse P#2and subsequent pulses.

The reference ratio (B/A′)ref stored in the memory27in advance as table data needs to correspond to the values A′ and B. When the compensated center value CT1′ of the center value CT1of the first pulse P#1is used as the value A′ and the center value CT2of the second pulse P#2is used as the value B, for example, a reference ratio (B/A′)ref needs to be the most appropriate CT2/CT1′ value.

In the embodiment, the disk drive apparatus is the recording and reproduction apparatus which handles DVD-Rs. The disk drive apparatus can also be a recording apparatus which handles other types of recording media.

From the point of view of the operational principle of the present invention, the present invention can be preferably applied to disk drive apparatuses which handle recording media having an organic pigment film, which has a quick mark-generation response to laser illumination. The present invention can also be preferably applied to recording apparatuses which handle not recording media having an organic pigment film but recording media having a quick mark-generation response to laser illumination, that is, recording media in which reflected light includes an effect of generated marks.

The disk drive apparatus30shown inFIG. 10is connected to the host computer80. An optical recording apparatus according to the present invention can be an apparatus not connected to the host computer80or others. In this case, an operation section and a display section are provided and a data input-and-output interface section has a different structure from that shown inFIG. 10. In other words, recording and reproduction needs to be performed according to user's operations, and a terminal section for inputting and outputting various data needs to be formed.

As understood from the above description, according to the present invention, when data is recorded (a data string is generated by marks and spaces) in an organic-pigment recording medium by pulse-train-manner laser outputs, for example, a space-period signal value corresponding to a space period is detected in a reflected-light information signal to estimate a first-pulse signal value corresponding to a first pulse in the pulse-train-manner laser outputs. A second-and-subsequent-pulse signal value corresponding to second and subsequent pulses in the pulse-train-manner laser outputs is also detected in the reflected-light information signal. The ratio between the estimated first-pulse signal and the detected second-and-subsequent-pulse signal value is obtained, and a laser-power compensation signal is generated by using the obtained ratio and a reference ratio to control laser output power. This means that a recording state itself, that is, pit mark generation, is observed to compensate laser power. The laser power is compensated to be most appropriate with all environmental conditions (all factors that affect mark generation) at the point of recording being taken into account. More specifically, the laser power is controlled for a change in the energy absorption efficiency of the recording medium caused by wavelength fluctuation due to the temperature dependency of the I-L characteristic of the semiconductor laser or aging, and film unevenness on a surface of the recording medium.

Therefore, the most appropriate mark-generation operation is always implemented, and the quality (jitter and others) of an RF signal is improved when reproduction.

When the first-pulse signal value corresponding to the first pulse of the pulse-train-manner laser outputs is detected in the reflected-light information, and the first-pulse signal value estimated by using the space-period signal is corrected by using the first-pulse signal value detected by the signal detection means, the estimated first-pulse signal is changed to the most appropriate value generated with reflectivity unevenness on the recording medium being taken into account. With this, more appropriate laser power control is implemented.

It is preferred in the above-described laser-power compensation processing that the peak, the center value, or the modulation value of the reflected-light information signal, corresponding to the first pulse in the pulse-train-manner laser outputs be used as the first-pulse signal value, and the peak, the center value, the bottom value, the average, or the modulation value of the reflected-light information signal, corresponding to the whole or part of the second and subsequent pulses in the pulse-train-manner laser outputs be used as the second-and-subsequent-pulse signal value.

When the most appropriate ratio between the first-pulse signal value and the second-and-subsequent-pulse signal value is stored in advance according to each of various conditions related to a recording operation, and a ratio suited to the current condition is selected among the stored ratios and used as the reference ratio, various recording conditions, such as a medium type, a linear velocity, and target laser power, can be appropriately handled.