JP3922242B2 - Optical disc recording method - Google Patents

Description

  The present invention relates to an optical disk that records information by irradiation with an energy beam, and more particularly to a technique for optimizing a recording power level.

  An optical disc apparatus is an information recording / reproducing apparatus characterized by non-contact, large capacity, high-speed access, replaceable and low-cost media, and as a recording / reproducing apparatus for digital audio signals and digital video signals by utilizing these characteristics, Alternatively, it is widely used as an external storage device for computers.

  Currently used optical disks include a read-only disk in which information is recorded in advance with concave and convex pits, such as a CD-ROM (Compact Disc) and DVD-ROM, and a CD-R, CD-RW, or DVD-ROM. There are recordable discs such as a RAM that allow the user to record arbitrary information by changing the physical state of the information recording film of the disc by irradiating an energy beam.

  By the way, in order to record information on the latter recordable disc, it is essential to irradiate an energy beam having an appropriate power level according to the physical characteristics of the recording film of the disc.

However, the appropriate value of the recording power level depends not only on the characteristics of the disk, but also on the characteristics of the optical disk device, such as the emission timing (recording strategy) of the energy beam and the shape of the energy beam spot. In addition, since it is necessary to consider a power level calibration error between optical disc apparatuses, conventionally, an appropriate recording power level is detected for each optical disc apparatus by so-called test writing, and writing processing is performed at the power level. I came.
A series of operations for detecting the optimum power level by trial writing is called OPC (Optimum Power Control).

  Usually, the OPC executes writing of a predetermined signal pattern while changing the power level in an OPC area defined as a standard for each disk, obtains a power level satisfying a predetermined evaluation index, and further Correction processing is performed using a predetermined coefficient for the level to obtain an optimum power level. Currently, evaluation indexes generally used include β (index related to RF signal asymmetry) used in CD-R and the like, and γ (related to modulation degree of RF signal) used in CD-RW and the like. These indices are recorded on the disk in advance as disk information, or are stored as parameters in the memory on the disk device side.

As an OPC using the modulation degree m of the RF signal, in addition to the above method using γ, a method using the product (P × m) with the corresponding power level P as an evaluation value (hereinafter referred to as κ method) is known. It has been. This method is effective in that the use of linear approximation can reduce the number of measurement samples and can be expected to improve accuracy. (For example, Patent Document 1)
Hereinafter, the κ method will be described. FIG. 1 is an example of a characteristic curve showing the relationship between the power level P and the modulation degree m. Here, the modulation degree m is approximated by the following equation as a function of the power level P.

m = msat × (1−Pthr / P)
Here, when both sides are multiplied by P, the following formula is obtained, and the evaluation value (P × m) on the left side and the power level P are approximated by a straight line. Pthr means a straight P-intercept.

P × m = msat × (P−Pthr)
An example of a characteristic curve showing the relationship between the power level P and the evaluation value P × m is shown in FIG.

By the way, as shown in FIG. 1, the sensitivity of the modulation degree change with respect to the power level change is low in the vicinity of the optimum power level Popt. For OPC, the higher sensitivity is desirable in terms of measurement accuracy, and since it is desirable to perform measurement with as low power as possible because the laser has an output limit, a predetermined coefficient ρ is introduced,
Ptarget = Popt / ρ
Define the power level defined in. The ratio of Ptarget and Pthr is
κ = Ptarget / Pthr
Define as

  The following procedure is known as OPC when Ptarget, ρ, and κ are given as disc information. That is, writing is performed in a predetermined signal pattern while changing the power level in the vicinity of Ptarget, for example, in the range of Ptarget ± 30%, in the OPC area of the disc. A modulation factor mi corresponding to each power level Pi is measured, and an evaluation value Pi × mi is calculated. Pthr is obtained by linearly approximating the relationship between P and P × m. Popt is obtained by multiplying the obtained Pthr by κ, and further by ρ.

  Further, a relational expression between the evaluation value P × m and the power level P is obtained in a plurality of measurement ranges in the vicinity of Ptarget (for example, the measurement target is slightly higher power side and slightly lower power side than Ptarget, respectively) Means for improving accuracy by performing predetermined calculation processing are known.

JP 2002-298357 A (pages 3 to 4)

  However, depending on the characteristics of the recording film of the optical disc, it has been found that the characteristic curve between the power level P, the modulation degree m, and the evaluation value (P × m) may deviate greatly from the above approximation. .

  3 and 4 show examples of characteristic curves showing the relationship between the power level P and the evaluation value (P × m) in the optical disc having the recording film characteristics. FIG. 3 is a reference device, and FIG. 4 shows the characteristics of a device with a large power calibration deviation. In this example, the linearity of the evaluation value (P × m) with respect to the power level P is poorer than before, and the characteristic curve bends at a predetermined power level. In the reference device, Ptarget is slightly smaller than the bending point. Is given to the low power side. In the above-described κ method, linear approximation is performed in a predetermined range centered on Ptarget. In this case, linear approximation is performed in a range including the bending point. For this reason, the approximate straight line (inclination msat and intercept Pthr) differs greatly with a slight deviation of Ptarget.

Here, as shown in FIG. 4, assuming that OPC is executed in an optical disk apparatus whose power level calibration is shifted, the optical disk apparatus intends to emit light at Ptarget, but in actuality, the reference apparatus. The light emission is equivalent to Ptarget_B.
From the approximate straight line obtained from the range centered on Ptarget in the optical disc apparatus, the intercept Pthr ′ is obtained, and further, Popt ′ = ρ · κ · Pthr ′ is obtained as the optimum power. Since the inclination of the approximate line is obtained differently from the reference device, the difference between κ · Pthr ′ and Ptarget ′ is large, and as a result, the difference between Popt ′ and the actual optimum power level is also large. In such a combination of an optical disc and an optical disc apparatus, the recording process is performed at a power level Popt ′ different from the actual optimum recording power level, which may cause a problem of quality deterioration of recorded information marks. The more Popt ′ deviates from the optimum power, the higher the possibility of recording mark quality degradation.

  The present invention has been made in view of the above. Since the power level dependency characteristic of the modulation degree is different from the conventional one, the linearity of the evaluation value (P × m) in the κ method with respect to the power level P is higher than the conventional one. An optical disk recording method capable of satisfactorily optimizing the power level even for a scarce optical disk is proposed.

  An object of the present invention is an optical disc recording method for recording a signal by irradiating an optical beam with an optical beam, recording the signal by irradiating the optical disc with a power level changed, and reproducing and modulating the signal. Measure the degree of power, determine a target power level related to the target degree of modulation from the degree of modulation, record a signal by irradiating the optical disk with a light beam having a power level within a predetermined range from the target power level, The degree of modulation is measured by reproduction, and the power level is determined by approximating the relationship between the power level of the predetermined range and the product of the power level of the predetermined range and the modulation degree by a linear function, and This is solved by an optical disk recording method in which a signal is recorded by irradiating a level light beam.

  More specifically, in the present invention, an optical disc recording method in an optical disc apparatus that records information by irradiating an optical disc with an energy beam having a predetermined power level is configured according to the following procedure.

  That is, a predetermined signal pattern is recorded in the OPC area of the optical disc while appropriately changing the power level P. A signal recorded at each power level Pi is reproduced, and a modulation degree mi (= Ipp / Itop) defined by a ratio between the amplitude Ipp and the maximum value Itop of the reproduction signal is measured, thereby obtaining a predetermined target modulation degree mtarget. A corresponding target power level Ptarget ′ is obtained.

  A predetermined signal pattern is recorded while the power level P is appropriately changed within a predetermined range about the target power level Ptarget ', and the degree of modulation mj of the signal recorded at each power level Pj is measured. The relationship between the power level P and the product of the power level P and the modulation factor m (P × m) is approximated by a linear function, an intercept Pthr ′ of the approximate expression is obtained, and multiplied by a predetermined coefficient to obtain the optimum power The level Popt 'was determined. Further, information is recorded on the optical disc by irradiating the energy beam with the optimum power level.

  Further, the disc information of the optical disc is reproduced, and the target modulation degree mtarget is determined based on parameters recorded in advance as the disc information.

  According to the present invention, the power level of the light beam can be determined more appropriately.

  Hereinafter, an optical disk recording method as an embodiment of the present invention will be described with reference to the drawings. First, the configuration of the optical disc apparatus according to the present embodiment will be clarified, and then the optical disc recording method as the present embodiment in the optical disc apparatus will be described.

  FIG. 5 is a block diagram showing a configuration example of the optical disk apparatus according to the embodiment of the present invention.

  The optical disc apparatus 1 includes an optical disc rotating mechanism 11 that holds an optical disc 10 and can rotate at a predetermined speed, an optical pickup 12 for recording and reproducing information on the optical disc 10, and the optical pickup 12 to the optical disc 10 And an optical pickup feeding mechanism 13 that can be positioned at a predetermined position in the radial direction.

  The first optical pickup 12 includes a laser light source 2 that emits light at a wavelength λ corresponding to the optical disc 10, an objective lens 3 that forms a light spot with a predetermined NA on the predetermined information recording surface of the optical disc 10 with high aberration, An objective lens actuator 4 that displaces the objective lens 3 in the focus direction and the tracking direction, a light detector 5 that detects the amount of light reflected from the optical disk 10 and converts it into an electrical signal, and light that detects the amount of light emitted from the laser light source 2 A detector 6 and a laser driving circuit 7 for causing the laser light source 2 to emit light at a predetermined power level and a predetermined timing are provided.

  A reproduction signal generation circuit 21 generates a reproduction signal of information recorded on the optical disc 10 from the output signal of the photodetector 5.

The servo signal generation circuit 22 generates predetermined servo signals such as a focus error signal and a tracking error signal from the output signal of the photodetector 5 based on a predetermined detection method.
The system control circuit 20 has a function of controlling the operation of the entire optical disc apparatus 1 and drives the optical disc rotation mechanism 11 via the servo control circuit 23 to control the rotation of the optical disc 10 at a predetermined rotational speed. Further, the optical pickup feeding mechanism 13 is driven to position the optical pickup 12 at a predetermined position in the radial direction of the optical disk. Further, the objective lens 3 is positioned at a predetermined position via the objective lens actuator 4 based on each servo signal output from the servo signal generation circuit 22.

The system control circuit 20 causes the laser light source 1 to emit light at a predetermined power level via the laser driving circuit 7 based on the output of the photodetector 6.
In the present embodiment, the laser drive circuit 7 is mounted on the optical pickup 12. However, the present invention is not limited to this, and the laser drive circuit 7 may be mounted on a fixed circuit board.
Next, the optical disk recording method of the present embodiment in the optical disk apparatus described above will be described. FIG. 6 is a flowchart showing an OPC processing procedure in the optical disc recording method according to the present embodiment.

The system control circuit 20 positions the optical pickup 12 in the disc information recording area of the optical disc 10 by driving the optical pickup feeding mechanism 13 and the objective lens actuator 4, and the disc information is output from the reproduction signal generation circuit 21. Get OPC parameters. In this embodiment, the OPC parameters are the above-described coefficient κ, coefficient ρ, target power level Ptarget, and target modulation degree mtarget. (Step 100)
The system control circuit 20 moves the optical pickup 12 to an unused area of the OPC area provided on the optical disk 10. If there is no unused area, and the optical disk 10 is a rewritable type, an erasing process is performed by irradiating a laser beam with an appropriate power level to secure an empty area. When the optical disk 10 is a write-once type, it is processed as being unrecordable. (Step 101)
Based on the target power level Ptarget, the power level P is set to a power level corresponding to 70% of Ptarget, for example, and a predetermined pattern signal, for example, a random signal is recorded on the optical disc 10 for a predetermined length. The power level P is changed, for example, set to a value P + ΔP increased by ΔP corresponding to 10% of Ptarget, and a predetermined pattern is recorded again. The power level change and recording process are repeated until the power level P reaches a predetermined level, for example, a power level corresponding to 130% of Ptarget. (Step 102)
The track on which the test writing process has been performed is reproduced. The envelope of the reproduction signal corresponding to each power level Pi is detected, the amplitude Ipp and the maximum level Itop are measured, and the modulation factor mi defined by the following equation is calculated. (Step 103)
mi = Ipp / Itop
Based on the relationship between P and m obtained in step 103, a power level Ptarget ′ corresponding to the target modulation degree mtarget obtained from the disc information is obtained. For example, mtarget and m are sequentially compared to obtain the maximum mn satisfying m <mtarget and the minimum mm satisfying m> mtarget, and using Pn and Pm corresponding to each degree of modulation, the following equation is obtained by linear interpolation. Ptarget ′ can be determined. (Step 104)
Ptarget ′ = Pn + mtarget × (Pm−Pn) / (mm−mn)
The test writing process is performed again while moving to a track where test writing can be performed again, and the power level is changed sequentially in the same manner as in step 102 based on Ptarget ′ obtained in step 104. The range of the power level is, for example, a range from 90% to 110% corresponding to Ptarget ′. (Step 105)
Similarly to step 103, the signal of the track on which trial writing has been performed in step 102 is reproduced, and the degree of modulation mj corresponding to each power level Pj is measured. (Step 106)
An evaluation value (P × m) is calculated for P and m in the predetermined range obtained in step 106, and the relationship between the evaluation value (P × m) and the power level P is expressed, for example, by the least square method as follows: To obtain a slope msat ′ and an intercept Pthr ′. (Step 107)
P × m = msat ′ × (P−Pthr ′)
Finally, the optimum power level Popt ′ is determined by multiplying Pthr ′ obtained in step 106 by the coefficient κ and the coefficient ρ acquired as OPC parameters. (Step 108)
The present invention is not limited to the procedure specifically shown in this embodiment, and an appropriate algorithm may be used in each step. For example, in order to obtain the intercept Pthr ′, accuracy may be improved by performing a plurality of linear approximations in a plurality of ranges including Ptarget ′ and adopting an average value.

  Alternatively, in order to obtain Ptarget ′, in this embodiment, a procedure for performing comparison of the measurement and the target modulation degree after one-time recording is shown. For example, power level setting, recording, modulation degree measurement, target modulation You may comprise by making a series of operation | movement of a comparison with a degree loop.

  FIG. 7 is an example of a characteristic curve with poor linearity between the power level P and the evaluation value P × m shown in FIGS. 3 and 4, and the present invention described above in an apparatus with a large power calibration deviation. The case where OPC is performed based on the procedure is shown.

  Since the range for performing the linear approximation is determined based on mtarget, even if there is a power calibration deviation, the slope of the approximate straight line can be obtained approximately equal to the reference device in consideration of the power calibration ratio. As a result, κ · Pthr ′ and Ptarget ′ are approximately equal, and Popt ′ is approximately equal to the optimum power level.

  FIG. 8 shows a specific example of a characteristic curve of a power level P having poor linearity and an evaluation value P × m in an apparatus having a large power calibration deviation. The optical disk has the characteristic that there are two bending points. In this apparatus, the optimum power level Pjb at which the reproduction performance (jitter) of the recording mark is optimum is 3.9 mW. Further, the OPC parameters of the optical disc determined by the reference device were as follows.

Coefficient κ = 1.17
Coefficient ρ = 1.20
Target power Ptarget = 2.67 mW
Target modulation degree mtarget = 0.21
The results of performing OPC based on the procedure of the present invention using the above OPC parameters are as follows. However, here, the accuracy of OPC is defined as the ratio between the optimum power Popt ′ obtained by OPC and the actual optimum power Pjb.

Measurement target power Ptarget ′ = 3.22 mW
Section Pthr ′ = 2.79 mW
κ · Pthr '= 3.26mW
Optimal power level Popt '= 3.92 mW
Accuracy Popt '/ Pjb = 100%
On the other hand, when a linear approximation is performed in a range with the target power Ptarget approximately at the center based on the conventional procedure, the OPC has the following results.

Section Pthr ′ = 2.47 mW
κ · Pthr '= 2.89mW
Optimal power level Popt '= 3.47mW
Accuracy Popt '/ Pjb = 89%
Incidentally, the accuracy required for OPC is, for example, 95% to 105%, although it depends on the system design of the optical disk apparatus. By applying the OPC of the present invention, it is possible to obtain the optimum power with high accuracy even for an optical disk having characteristics that cannot be obtained with the conventional OPC by the κ method.

  As described above, according to the present embodiment, an optical disc having a large power calibration deviation compared to an optical disc having a characteristic in which the relationship between the power level P and the evaluation value P × m, which has not been considered in the past, is poor in linearity. Even in the case of an apparatus, the optimum power level can be determined with high accuracy by determining the range of linear approximation based on the target modulation degree mtarget, which is disk information, in OPC using the κ method.

It is a figure of an example of the characteristic curve which shows the relationship between the power level P and the modulation degree m. The relationship between the power level P and the evaluation value P × m is an example of a characteristic curve with good linearity, and is a diagram showing a case where OPC is performed in the reference device. It is a figure which shows the case where the relationship between the power level P and evaluation value Pxm is an example of a characteristic curve with poor linearity, and OPC is performed in the reference device. The relationship between the power level P and the evaluation value P × m is an example of a characteristic curve with poor linearity, and is a diagram showing a case where OPC is performed by a conventional procedure in an apparatus having a large power calibration deviation. It is a block diagram which shows the structural example of the optical disk apparatus based on the Example of this invention. It is a figure of the flowchart which shows the process sequence of OPC in the optical disk recording method as an Example of this invention. The relationship between the power level P and the evaluation value P × m is an example of a characteristic curve with poor linearity, and is a diagram showing a case where OPC is performed by the procedure of the present invention in an apparatus having a large power calibration deviation. It is a figure of the specific example of the characteristic curve of power level P with poor linearity and evaluation value Pxm in an apparatus with large power calibration deviation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical disk apparatus, 2 ... Laser light source, 3 ... Objective lens, 4 ... Objective lens actuator, 5 ... Photo detector, 6 ... Photo detector, 7 ... Laser drive circuit, 10 ... Optical disk, 11 ... Optical disk rotation mechanism, 12 DESCRIPTION OF SYMBOLS ... Optical pick-up, 13 ... Optical pick-up feeding mechanism, 20 ... System control circuit, 21 ... Reproduction signal generation circuit, 22 ... Servo signal generation circuit, 23 ... Servo control circuit.

Claims (5)

An optical disk recording method for recording a signal by irradiating an optical disk with a light beam,
Recording a signal by irradiating the optical disk with a light beam with a changed power level,
Reproduce the signal and measure the modulation factor,
A target power level associated with the target modulation degree is determined from the modulation degree;
A signal is recorded by irradiating the optical disk with a light beam having a power level within a predetermined range from the target power level,
Reproduce the signal and measure the modulation factor,
A power level is determined by approximating the relationship between the power level of the predetermined range and the product of the power level of the predetermined range and the modulation factor by a linear function,
A method of recording an optical disk, comprising: irradiating the optical disk with a light beam of the power level to record a signal.   2. The optical disc recording method according to claim 1, wherein the target modulation degree is recorded in advance on an optical disc or stored in an optical disc apparatus.   2. The optical disc recording method according to claim 1, wherein the power level in the predetermined range is a power level in a range substantially centered on the target power level. An optical disk recording method for recording information by irradiating an optical disk with an energy beam,
Recording a signal pattern while appropriately changing the power level of the energy beam in the power calibration area of the optical disc,
Play back the recorded signal and measure the degree of modulation, which is the ratio of the amplitude and maximum value of the playback signal,
A target power level corresponding to the target modulation degree is obtained using the modulation degree,
A predetermined signal pattern is recorded while appropriately changing the power level within a predetermined range about the target power level;
Measure the degree of modulation of the signal recorded at the power level;
Approximating a relationship between the power level and the product of the power level and the modulation factor by a linear function, and determining an optimum power level based on the approximation formula;
An optical disk recording method, wherein information is recorded by irradiating an energy beam of the optimum power level. 5. The optical disc recording method according to claim 4, wherein the disc information of the optical disc is reproduced, and the target modulation degree is determined based on a parameter recorded in advance in the disc information.

Images