JP2012022733A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of controlling recording power more accurately than ever before in a walking OPC.SOLUTION: Test data is recorded in a predetermined area while changing recording power prior to data recording to an optical disk 10, and the recording power corresponding to a β value showing asymmetry of an amplitude of data obtained by reproducing the test data is set as the optimal recording power. The data recording is intercepted at every first interval, and the optimal recording power is corrected so that the β value measured at a recording terminal corresponds to the target β value. The data recording is intercepted after a second interval, and an amount of change with time of the β value is calculated using a β value obtained by measuring again at the same recording terminal and a past β value, followed by further correction of the optimal recording power using a power correction amount corresponding to the amount of change with time.

Description

  The present invention relates to an optical disc apparatus, and more particularly to adjustment of recording power.

  In an optical disc apparatus capable of recording data, a technique is known in which the β value is measured in order to stably maintain the recording signal quality, and the recording power is controlled so that the β value becomes a target value.

  In Patent Document 1 below, recording is interrupted at regular intervals or at regular intervals, the recording end portion is reproduced, the β value at the recording end portion is measured, and the β value obtained by measurement and the target β In so-called walking OPC that adjusts the recording power by comparing with the value, the reciprocal of the change ratio of the β value to the recording power is calculated as a correction coefficient based on the β value for a plurality of times, and after correction using the correction coefficient Is disclosed, and the recording power is corrected based on the calculated corrected recording power.

JP 2008-77714 A

  Since the β value is a parameter representing the asymmetry of the amplitude and has a strong correlation with the recording power, it is generally considered that the recording power should be controlled so that the measured β value matches the target β value. The value varies depending on the environmental temperature, the wavelength and temperature of the laser diode of the optical pickup, in-plane sensitivity unevenness and warpage, scratches, dirt, servo system control errors, changes over time, etc. Almost no consideration.

  That is, in the conventional walking OPC, recording is interrupted and the β value at the end of recording is measured and compared with the target β value. This measured β value is the β value immediately after the recording is interrupted and changes with time. Therefore, if the recording power is corrected based on the measured β value, there is no guarantee that the recording power is optimized. In other words, in the conventional walking OPC, it is difficult to optimize the recording power because the recording power is corrected based on a temporary value or a temporary value of β value that can change with time.

  An object of the present invention is to measure the β value and improve the accuracy when optimizing the recording power based on the β value obtained by the measurement, thereby improving the data recording quality. To provide an apparatus.

  The present invention is an optical disc apparatus, comprising a measuring means for measuring an asymmetry of amplitude of data recorded on an optical disc, and a plurality of β values obtained at different timings for the same data portion. and a setting means for setting a recording power for recording data according to the amount of change with time.

  In one embodiment of the present invention, the setting means includes an optimum recording power setting means for setting an optimum recording power for the data portion so that a β value obtained at a certain timing matches a target β value; A temporal change amount calculating means for calculating a temporal change amount, a power correction amount calculating means for calculating a power correction amount corresponding to the temporal change amount, and a correcting means for correcting the optimum recording power using the power correction amount; Have

  In another embodiment of the present invention, the data portion is a recording end portion when data recording is interrupted at every first interval or every first time after the start of data recording, and the optimum recording power setting means Sets the optimum recording power so that the first β value, which is the β value at the end of recording immediately after the interruption of data recording, coincides with the target β value, and the temporal change amount calculating means includes the first β value and Then, after the second interval after the start of data recording or after the elapse of the second time, the amount of change with time is calculated from the second β value which is the β value at the recording end portion.

  In another embodiment of the present invention, the power correction amount calculating means uses the relationship between the recording power obtained by measurement on the optical disc and the β value, and the power correction amount according to the temporal change amount. Calculate the amount.

  The present invention is also an optical disc apparatus, wherein the test data is recorded in a predetermined area while changing the recording power prior to data recording on the optical disc, and the asymmetry of the amplitude of the data obtained by reproducing the test data Means for setting the recording power at which the β value indicating the target β value coincides with the target β value, means for recording data on the optical disc with the optimum recording power, and data recording at every first interval or every first time , The first correction means for correcting the optimum recording power so that the β value measured at the end of recording coincides with the target β value, the storage means for storing the β value, and the corrected optimum recording power Means for resuming data recording in step (b), the β value obtained by suspending data recording after the second interval or after the elapse of the second time and measuring again at the recording end portion, and the storage means A second correction unit that calculates a temporal change amount of the β value using the stored β value and further corrects the corrected optimum recording power using a power correction amount corresponding to the temporal change amount; It is characterized by that.

  In one embodiment of the present invention, the second correction unit calculates the power correction amount according to the amount of change with time, using a relationship between a recording power obtained by reproducing the test data and a β value. To do.

  According to the present invention, the recording power is optimized with higher accuracy than before, thereby improving the data recording quality.

It is a block diagram of an optical disk device. It is a graph which shows a time-dependent change of (beta) value. It is a graph (logarithm display) which shows a time-dependent change of (beta) value. It is a flowchart which shows recording power control. It is a graph which shows the relationship between recording power and (beta) value. It is explanatory drawing which shows the time change of recording power.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, the basic principle of this embodiment will be described.

In the present embodiment, as a premise thereof, recording is interrupted at regular intervals or at regular intervals, the recording end portion is reproduced, the β value at the recording end portion is measured, and the β value obtained by measurement is A so-called walking OPC is performed in which the recording power is adjusted by comparing with the target β value. Here, the β value is one of the parameters for evaluating the asymmetry of the amplitude, and is defined by the CD-R standard or the DVD standard. Specifically, with respect to the peak level P and bottom level B of the envelope value of the AC signal that is AC-coupled, and A1 = PC and A2 = CB with respect to the AC center level C of the RF signal,
β = (A1-A2) / (A1 + A2)
Defined by

  In walking OPC, recording is interrupted and data at the end of recording is reproduced to obtain a measured β value, and this is compared with a target β value to adjust recording power. However, since the measured β value is generally a value immediately after the recording is interrupted and the β value can change with time, the measured β value becomes a temporary or temporary value of the β value that changes with time. .

  Therefore, in the present embodiment, immediately after the recording is interrupted, the data at the recording end portion is reproduced to obtain the β value, and the data of the same portion is reproduced again after a predetermined time has elapsed to obtain the β value again. Then, the state of the β value with time is grasped from a plurality of β values obtained by measuring the same data at different times, and the recording power is corrected based on the time change.

  In the present embodiment, since the β value is measured again for the same data after a predetermined time has elapsed, it is possible to correct the recording power in consideration of the temporal change of the β value.

  Here, the recording power to be corrected in consideration of the temporal change of the β value is a recording power that is corrected at any time by the walking OPC. That is, the recording power is interrupted immediately before by the walking OPC and is corrected based on the β value of the immediately preceding recording end portion. In this embodiment, the recording power corrected in this way is further changed to the β value. Is corrected again based on the change with time.

  The correction method of this embodiment will be schematically described.

  The recording power at a certain timing is P0. Recording is interrupted after a certain interval or after a certain time, and the data at the end of recording is reproduced to obtain the β value. At this time, the data at the end of recording is d0, and the β value is β0 (t0). β0 (t0) means a β value acquired in the data d0 at a certain time t0. It is assumed that the recording power P0 is corrected to the recording power P1 based on β0 obtained by measurement.

  Next, recording is interrupted again after a certain interval or after a certain time, and the data at the end of recording is reproduced to obtain the β value. At this time, the data at the recording end is d1, and the β value is β1. It is assumed that the recording power P1 is corrected to the recording power P2 based on β1 obtained by measurement. At this time, not only the recording end part d1 but also the past recording end part d0 that has already been reproduced once is reproduced to obtain the β value. The β value at this time is β0 (t1). β0 (t1) means a β value acquired in the data d0 at another time t1 different from a certain time t0. Since the β value changes with time, β0 (t0) and β0 (t1) are different from each other. In general, the larger the time difference between t0 and t1, the greater the difference between β0 (t0) and β0 (t1). Then, Δβ = β0 (t1) −β0 (t0), which is a change in β value with time, is calculated, and a change ΔP in recording power corresponding to this Δβ is obtained and added to the recording power P2. That is, the recording power at this time is P2 + ΔP. Note that the recording power P2 is a recording power corrected based on the β value of the immediately preceding data d1.

  As the time difference between the time t1 and the time t0 is larger, the change with time of β becomes larger and it becomes easier to acquire a more definite β value. Therefore, when data is recorded from the inner periphery to the outer periphery of the optical disc, it is desirable to set the data d0 in the inner periphery and acquire β0 (t1) when data is recorded in the outer periphery. . In this case, the accuracy of optimizing the recording power is improved toward the outer periphery.

  The recording power change ΔP corresponding to Δβ can be obtained in advance from a relational expression between the known β value and the recording power P. That is, ΔP corresponding to Δβ may be obtained when the relational expression between β value and recording power P is β = β (P). This relational expression β = β (P) is preferably a relational expression of β after a sufficient time has elapsed and the recording power P, but is not necessarily limited thereto, and β and It may be a relational expression with the recording power P. The reason is that the relational expression only needs to have the accuracy necessary to calculate ΔP corresponding to Δβ. Specifically, the slope in the relational expression is important, and the intercept is irrelevant. That's why.

  Next, a specific configuration and operation of the present embodiment will be described.

  FIG. 1 shows the overall configuration of the optical disc apparatus according to this embodiment. An optical disk 10 such as a CD, DVD, or Blu-ray is driven by a spindle motor (SPM) 12. The spindle motor SPM 12 is driven by a driver 14, and the driver 14 is servo-controlled by a servo processor 30 so as to have a desired rotation speed.

  The optical pickup 16 includes a laser diode (LD) for irradiating the optical disk 10 with laser light and a photodetector (PD) that receives reflected light from the optical disk 10 and converts it into an electrical signal, and is disposed opposite to the optical disk 10. . The optical pickup 16 is driven in the radial direction of the optical disk 10 by a sled motor 18 constituted by a stepping motor, and the sled motor 18 is driven by a driver 20. The driver 20 is servo-controlled by the servo processor 30 similarly to the driver 14. The LD of the optical pickup 16 is driven by a driver 22, and the driver 22 is controlled by an auto power control circuit (APC) 24 so that the drive current becomes a desired value. The APC 24 and the driver 22 control the light emission amount of the LD according to a command from the system controller 32. In FIG. 1, the driver 22 is provided separately from the optical pickup 16, but the driver 22 may be mounted on the optical pickup 16.

  When data recorded on the optical disk 10 is reproduced, a laser beam of reproduction power is irradiated from the LD of the optical pickup 16, and the reflected light is converted into an electric signal by the PD and output. A reproduction signal from the optical pickup 16 is supplied to the RF circuit 26. The RF circuit 26 generates a focus error signal and a tracking error signal from the reproduction signal and supplies them to the servo processor 30. The servo processor 30 servo-controls the optical pickup 16 based on these error signals, and maintains the optical pickup 16 in an on-focus state and an on-track state. Further, the RF circuit 26 supplies an address signal included in the reproduction signal to the address decoding circuit 28. The address decoding circuit 28 demodulates the address data of the optical disk 10 from the address signal and supplies it to the servo processor 30 and the system controller 32.

  The address signal is, for example, a wobble signal, and address data is obtained by extracting the wobble signal from the reproduction signal and decoding it. Further, the RF circuit 26 supplies the reproduction RF signal to the binarization circuit 34. The binarization circuit 34 binarizes the reproduction signal and supplies the obtained signal to the encoding / decoding circuit 36. The encode / decode circuit 36 demodulates the binary signal and corrects errors to obtain reproduction data, and outputs the reproduction data to a host device such as a personal computer via the interface I / F 40. When the reproduction data is output to the host device, the encoding / decoding circuit 36 temporarily stores the reproduction data in the buffer memory 38 and outputs it.

  When data is recorded on the optical disk 10, data to be recorded from the host device is supplied to the encode / decode circuit 36 via the interface I / F 40. The encode / decode circuit 36 stores data to be recorded in the buffer memory 38, encodes the data to be recorded, and supplies the data to the write strategy circuit 42 as modulated data. The write strategy circuit 42 converts the modulation data into, for example, a multi-pulse (pulse train) according to a predetermined recording strategy, and supplies it to the driver 22 as recording data. Since the recording strategy affects recording quality, optimization is performed prior to data recording. The laser light whose power is modulated by the recording data is irradiated from the LD of the optical pickup 16 and the data is recorded on the optical disk 10. The recording power at the start of data recording is adjusted by trial writing test data using a PCA (Power Calibration Area) formed on the inner circumference side of the optical disc 10 by OPC (Optical Power Control). . After recording the data, the optical pickup 16 reproduces the recorded data by irradiating a laser beam with a reproduction power, and supplies it to the RF circuit 26. The RF circuit 26 supplies the reproduction signal to the binarization circuit 34, and the binarized data is supplied to the encode / decode circuit 36. The system controller 32 controls the operation of the entire system, drives the sled motor 18 via the servo processor 30, and controls the position of the optical pickup 16.

  When recording data on the optical disc 10, the system controller 32 executes walking OPC separately from OPC before data recording. That is, recording is interrupted at regular intervals or at regular intervals, the recording end portion is reproduced, the β value at the recording end portion is measured, and the β value obtained by measurement is compared with the target β value. Correct the recording power. At this time, the walking OPC is executed, and the β value of the data reproduced in the past is measured again every predetermined time, and the β value obtained by the measurement is compared with the β value obtained in the past in the same data. Then, the change Δβ is calculated. Then, the recording power change ΔP corresponding to the β value aging change Δβ is calculated, and the recording power is further corrected by reflecting this ΔP in the recording power.

FIG. 2 shows the time change of the β value obtained by reproducing the data recorded in a certain part of the optical disc 10. In the figure, the horizontal axis is the elapsed time (sec) from the end of recording, and the vertical axis is the β value. The β value changes (decreases) relatively steeply immediately after the end of recording, and then changes (decreases) gently. Such a change in β value with time is considered to be mainly caused by a thermal change in the recording film of the optical disc 10. The time change of the β value obtained by actual measurement is specifically shown as follows. Incidentally, the optical disk used for the measurement is DVD + R, and the recording speed is 6 times faster than CLV (constant linear velocity).
Elapsed time (sec) β (%)
0.797 0.27
5.922 -0.14
10.937-0.37
20.89 -0.47
30.906 -0.58
60.922 -0.74
120.89 -0.86
300.906 -1.07
600.922 -1.31
1200.922 -1.54
1800.906 -1.72
3600.937 -2.05

FIG. 3 shows the time change of the β value when the time axis in FIG. 2 is logarithmic. As shown in the figure, the β value changes almost linearly with time (logarithm),
β = −0.2648Ln (t) +0.3161
Can be approximated by the following linear expression. The coefficient of determination ^{R 2} is 0.983. This means that the β value at an arbitrary time interval can be estimated by acquiring the β value at a constant time interval. It also means that a β value after a sufficient time has elapsed, for example, a β value after an hour has elapsed since the end of recording can be estimated. In the present embodiment, the recording power change ΔP corresponding to the difference value Δβ between the β value at a certain time and the β value after a certain time has elapsed from this time is calculated for data at a certain part of the optical disc 10. However, since the change with time of β can be approximated by a linear expression as shown in FIG. 3, Δβ may be calculated by estimating the β value when a sufficient amount of time has elapsed (for example, one hour after a certain time). .

  FIG. 4 shows a flowchart for controlling the recording power in the present embodiment. First, prior to recording, OPC is executed in the PCA area of the optical disc 10 to calculate the optimum recording power P0 at the start of recording (S101). Specifically, test data is written on a trial basis while changing the recording power stepwise, and the β value at each recording power is measured. Then, the recording power at which the measured β value is at or near the target β value is set as the initial optimum recording power (S101). The initial optimum recording power is P0.

  Next, user data is recorded in the data area of the optical disc 10 with the initial optimum recording power P0 obtained by OPC (S102). Then, the system controller 32 determines whether or not a certain interval has elapsed after the start of recording (S103). This fixed interval may be any of the number of addresses, the number of tracks, and the number of sectors. It may be a physical distance. Further, it may be determined whether a certain time has passed instead of a certain interval. If the fixed interval has not elapsed, data is continuously recorded with the current optimum recording power P0. On the other hand, if the predetermined interval has elapsed, recording is interrupted (S104), the data at the end of recording is reproduced, and the β value is measured (S105). The measured β value is stored in the memory of the system controller 32 and is compared with the target β value to calculate a power correction amount such that the measured β value matches the target β value. The power correction amount is P1. Then, the current optimum recording power is corrected to P0 + P1 with this power correction amount (S106).

  The optimum recording power is sequentially corrected by executing the above processing at regular intervals. Then, while executing such walking OPC, in parallel with this, it is determined whether or not a predetermined time has elapsed since the start of recording (S107). This certain time is a time for detecting a change in β value with time, and is a timing different from the certain time that is the timing for executing the walking OPC. This fixed time can be, for example, 5 minutes or 10 minutes. If the predetermined time has not elapsed, the recording is performed as it is (S108), but if the predetermined time has elapsed, the β value of the recording portion where the β value has been measured in the past is measured again (S110). Then, the measured β value stored in the memory measured in the past with respect to the same recording portion is compared with the newly measured β value, and a change Δβ of the β value with time is calculated, and according to this Δβ. The calculated power correction amount is calculated (S111). This power correction amount is assumed to be P2.

  FIG. 5 shows the relationship between the β value and the recording power for calculating the power correction amount P2 corresponding to the time-dependent change Δβ of the β value. In the figure, the horizontal axis represents the β value (%), and the vertical axis represents the recording power (mW). In the processing of S101, the test data is test-written by changing the recording power in various steps, and the test data is reproduced and the β value is measured. Therefore, the relationship between the β value and the recording power can be acquired. In general, the recording power and the β value can be approximated by a linear function. For example, as shown in FIG. 5, the recording power P can be approximated to 0.2133β + 20.946. Of course, this is a relational expression using the β value immediately after recording. From such a relational expression, the recording power change ΔP corresponding to Δβ can be calculated, and the recording power change ΔP is set as the power correction amount P2. For example, the power correction amount corresponding to Δβ = 1% is 0.2133 mW. Note that a and b of the recording power P = aβ + b, which is a linear function, vary depending on conditions such as recording speed, disk temperature, and write strategy.

  After calculating the power correction amount P2 taking into account the change in β value with time, the newly calculated power correction amount is added to the current optimum recording power P0 + P1, and the optimum recording power P0 + P1 + P2 is newly set, and recording is performed. Is resumed (S108). The above process is repeated until the recording is completed (S109).

  FIG. 6 schematically shows changes in the optimum recording power in the present embodiment. The horizontal axis represents time (sec) from the start of recording, and the vertical axis represents recording power (mW). The initial optimum recording power P0 is determined by OPC, and data recording is started. Walking OPC is executed at time t1 after the start of data recording, and the optimum recording power is corrected from P0 to P0 + P1. Then, data recording is resumed at the optimum recording power P0 + P1 corrected from time t2.

  Walking OPC is executed again at time t3 after the start of data recording, and the optimum recording power is corrected from P0 + P1 to P0 + P1 + P1 '. On the other hand, at this timing, when the power correction amount P2 corresponding to the time-dependent change Δβ of the β value is calculated at the same time, the optimum recording power at this time is further corrected to P0 + P1 + P1 ′, and data recording is performed at time t4 as P0 + P1 + P1 ′ + P2. To resume. In the figure, the optimum recording power P0 + P1 + P1 ′ when the correction according to the present embodiment is not performed is indicated by a broken line, and the optimum recording power P0 + P1 + P1 ′ + P2 when the change in β value with time is taken into consideration as in the present embodiment is indicated by a solid line. .

  As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment, A various deformation | transformation is possible.

  For example, in this embodiment, the recording power correction timing by walking OPC and the recording power correction timing in consideration of the time-dependent change of the β value are the same. It may be. For example, referring to FIG. 6, the recording power may be corrected at the timing between time t2 and time t3 in consideration of the change with time of the β value. However, since both the walking OPC and the correction of the recording power in consideration of the β value change with time are to temporarily interrupt the recording process, both timings coincide with each other in order to shorten the total recording time. It is suitable.

  Further, in the present embodiment, the β value of the same recording region can be measured twice or more at different timings, and the recording power can be sequentially corrected in accordance with the change over time of the obtained β value. For example, with respect to a certain recorded region, the β value obtained by measuring at time t1 is β (t1), the β value obtained by measuring at time t2 is β (t2), and obtained at time t3. If the β value is β (t3), first, the recording power is corrected by a power correction amount corresponding to Δβ = β (t2) −β (t1), and then Δβ = β (t3) −β (t2). For example, the recording power is corrected by a corresponding power correction amount. Of course, as described above, β (t1), β (t2), and β (t3) are defined as a function of changes over time of β, and β (t) that is a β value at an arbitrary time t is calculated. , Δβ = β (t) −β (t1) may be used to correct the recording power with a power correction amount.

Further, in the present embodiment, the recording power is corrected in consideration of the change with time of the β value obtained at a certain recording site, but the recording site does not have to be one location, and a plurality of locations may be provided. In this case, the power correction amount can be an average value of the β value correction amounts obtained at a plurality of locations. For example, β values are measured at recording sites R1 at times t1 and t2 to obtain β1 (t1) and β1 (t2), and β values are measured at recording sites R2 at times t3 and t4 to obtain β2 (t3), When β2 (t4) is acquired and β values are measured at time t5 and t6 at the recording site R3 to obtain β3 (t5) and β (t6), Δβ1 = β1 (t2) −β1 (t1) The power correction amount is ΔP1, Δβ2 = β2 (t4) −β2 (t3) is a power correction amount ΔP2, Δβ3 = β3 (t6) −β3 (t5) is a power correction amount ΔP3, and ΔP = The power correction amount is obtained by (ΔP1 + ΔP2 + ΔP3) / 3. Or
Δβ = {β1 (t2) −β1 (t1) + β2 (t4) −β2 (t3) + β3 (t6) −β3 (t5)} / 3
Thus, an average value of the β value with time can be obtained, and a power correction amount corresponding to this can be obtained.

In either case, the optimum recording power is
Optimum recording power = initial optimum recording power set by OPC + power correction amount by walking OPC + power correction amount corresponding to the change with time of β value.

  Further, the amount of change over time of the β value obtained by measurement is stored in the memory of the system controller 32 for each disk manufacturer, for each recording speed, and for each recording temperature, and the time-dependent change stored in the memory at the next recording is stored. The initial optimum recording power obtained by OPC may be corrected by obtaining a power correction amount corresponding to the amount.

  10 optical disc, 16 optical pickup, 32 system controller.

Claims (6)

An optical disk device,
Measuring means for measuring β value indicating the asymmetry of the amplitude of the data recorded on the optical disc;
Setting means for calculating the amount of change over time of a β value from a plurality of β values obtained at different timings for the same data portion, and setting recording power for recording data according to the amount of change over time When,
An optical disc apparatus comprising: The apparatus of claim 1.
The setting means includes
Optimum recording power setting means for setting the optimum recording power so that the β value obtained at a certain timing matches the target β value for the data portion;
A time variation calculation means for calculating the time variation;
Power correction amount calculating means for calculating a power correction amount according to the amount of change over time;
Correction means for correcting the optimum recording power using the power correction amount;
An optical disc apparatus comprising: The apparatus of claim 2.
The data portion is a recording end portion when the data recording is interrupted at every first interval or every first time after the start of data recording,
The optimum recording power setting means sets the optimum recording power so that a first β value, which is a β value at the recording end portion immediately after interruption of data recording, matches the target β value,
The time variation calculation means calculates the time variation from the first β value and a second β value that is a β value at the recording end portion after a second interval after the start of data recording or after a second time has elapsed. An optical disc apparatus characterized by the above. The apparatus according to any one of claims 2 and 3,
The power correction amount calculation means calculates the power correction amount according to the amount of change with time, using the relationship between the recording power obtained by measurement on the optical disc and the β value. . An optical disk device,
Recording the test data in a predetermined area while changing the recording power prior to recording the data on the optical disc, and the β value indicating the asymmetry of the amplitude of the data obtained by reproducing the test data matches the target β value Means for setting the power to the optimum recording power;
Means for recording data on the optical disc with the optimum recording power;
First correction means for interrupting data recording at every first interval or every first time and correcting the optimum recording power so that the β value measured at the end of recording coincides with the target β value;
Storage means for storing the β value;
Means for restarting data recording with the corrected optimum recording power;
Data recording is interrupted after the second interval or after the second time has elapsed and the β value obtained by measuring again at the recording end portion and the β value stored in the storage means are used to change over time. Second correction means for calculating the amount and further correcting the corrected optimum recording power using a power correction amount corresponding to the amount of change with time;
An optical disc apparatus comprising: The apparatus of claim 5.
The optical disc apparatus characterized in that the second correction means calculates the power correction amount according to the amount of change with time, using the relationship between the recording power obtained by reproducing the test data and the β value.

Images