JP2012089192A - Optical information recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical information recording method hardly affected by overwriting frequency and capable of setting an optimum recording power.SOLUTION: In a predetermined test area of an optical disk, test data is recorded with a plurality of recording power and in direct overwriting. The test data is reproduced to measure a modulation degree, and a relational expression of recording power and a modulation degree is calculated. A plurality of relational expressions are acquired by executing calculation processes of that relational expression in the same test area a plurality of times. A recording power corresponding to an intersection among graphs according to the each relational expressions is determined, and based on that recording power, a recording power at the time of the recording is determined.

Description

  The present invention relates to a data recording method for a rewritable optical disc, and more particularly to a method for calculating an optimum recording power.

  When recording on an optical disk using laser light, it is important to set the output power (recording power) of the laser light at the time of recording to an optimum value for the characteristics of the optical disk. Therefore, usually, test recording is performed prior to the actual recording of data on the optical disc, and the optimum recording power is obtained as a result of the test recording. In this test recording, test data is recorded with a plurality of recording powers in a predetermined test writing area provided on the inner periphery of the optical disc. Then, a reproduction signal of data recorded with each recording power is detected to obtain an optimum recording power. Thereafter, during the actual recording of data, data recording is performed using the optimum recording power. Such a method is called OPC (Optimum Power Control).

  In the phase change rewritable Blu-ray Disc (BD-RE), the optimum recording power Pwo is calculated using a technique called the κ method shown below as described in the standards and patent documents 1 and 2. It has been proposed.

  In the κ method, first, data necessary for setting the optimum recording power is obtained from a predetermined area of the optical disk. The data acquired here includes a reference recording power Ptarget, a constant ρ, and a constant κ.

  At the time of test recording, test data is recorded in a random pattern while the recording power Pw is sequentially switched in a predetermined range centered on the reference recording power Ptarget. Next, the recorded test data is reproduced, and the modulation m (Pw) of the reproduced RF signal is measured for each recording power Pw. The modulation degree m is defined by the ratio of the magnitude of the maximum amplitude to the signal level of the maximum amplitude in the RF signal. Next, Pthr is obtained by the equation (1).

Pthr = (Mmax−m (Pw)) × Pw / Mmax (1)
Here, Pthr means an intercept of an approximate line corresponding to the recording start power in the graph showing the relationship of the evaluation index of (modulation m (Pw) × recording power Pw) to the recording power Pw. Then, the optimum recording power Pwo is obtained by the following equation (2).

Pwo = ρ × κ × Pthr (2)
Here, κ is a constant that defines the relationship between Ptarget and Pthr, and there is a relationship of Ptarget = κ × Pthr. Ρ is a constant that defines the relationship between Ptaget and Pwo, and there is a relationship of Pwo = ρ × Ptarget.

JP-A-2005-149538 JP 2008-16165 A

  However, the κ method may not always provide an appropriate recording power Pwo. In the Blu-ray Disc standard, when an area in which data has already been recorded is to be overwritten, the data area is not erased once by laser irradiation with an erasing power weaker than the recording power Pwo. A technique called direct over write (DOW) is used in which writing is performed by irradiating a laser beam with the recording power Pwo and the erasing power corresponding to each of the data strings. The applicant has experimented and investigated the change in SER (Signal Error Rate) with respect to the number of overwriting (DOW number) (hereinafter referred to as “DOW characteristic” as necessary). It was found that the DOW characteristics were better when recording was performed with a recording power slightly lower than Pwo. In other words, it was found that the DOW characteristics are not optimal with the recording power Pwo obtained by the κ method. The reason why such a phenomenon occurs is estimated as follows. In other words, as the number of overwriting (DOW times) increases, areas with different number of phase changes are scattered in the recording area. As a result, the relationship between the recording power Pw and the modulation factor m (Pw), which is a reference for calculating the optimum recording power Pwo, also changes as the overwriting is repeated. On the other hand, in the algorithm of the κ method, it is calculated mathematically approximated on the assumption that the graph indicating the relationship of the evaluation index of (modulation m (Pw) × recording power Pw) to the recording power Pw is a straight line. Therefore, it is considered that an error with the actual optical disk characteristic has been noticeably caused by an increase in the number of overwriting (the number of DOW).

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical information recording method in which an optimum recording power can be set with little influence of overwriting.

  In order to achieve the above object, the present invention provides an optical information recording method for recording information by irradiating a rewritable optical disk with laser light, and performing direct overwriting while changing the laser power stepwise in the test area of the optical disk. The writing step for writing the test pattern is repeatedly performed in the same test area a plurality of times, and the measurement step for reading the written test pattern and measuring the degree of modulation at each laser power is performed after the two or more writing steps, respectively. In addition, a relational expression calculation step for calculating a relational expression for deriving a modulation degree for the laser power based on each measurement result for each measurement time, and calculating a laser power at which the modulation degree for the laser power is equal between the relational expressions, Data recording based on the calculated laser power Characterized in that a optimum recording power calculating step of calculating an optimum recording power in.

  According to the present invention, since the relationship between the recording power and the modulation degree is considered from the measurement result while considering the change with respect to the overwriting frequency, and the relationship between the recording power and the modulation degree is directly evaluated from the measurement result, The influence is small, and a more appropriate optimum recording power can be obtained.

  In the above invention, it is preferable that the number of overwriting in each writing step to be measured in the measuring step includes an exponentially increasing number from the smallest. More specifically, it is preferable that the writing step to be measured in the measuring step includes all or at least two of the writing steps of 0 times, 1 time, and 10 times.

  In the optimum recording power calculation step, when a plurality of laser powers having the same degree of modulation are calculated, it is preferable to calculate an average value or a median value of the laser powers as the optimum recording power. A case where the maximum value or the minimum value of the laser power is calculated as the optimum recording power is also conceivable. In other words, any value that falls within the range from the minimum value to the maximum value of the laser power can be usually adopted as a preferable optimum recording power. Which one is adopted may be arbitrarily selected according to the medium characteristics of the optical disk.

  As described above, according to the present invention, the relationship between the recording power and the modulation factor is directly evaluated from the measurement result while considering the change with respect to the number of overwriting times. Therefore, the influence of the number of overwriting is small, and a more appropriate optimum recording power can be obtained.

System configuration diagram of optical information recording / reproducing apparatus Diagram explaining the degree of modulation Graph explaining DOW characteristics Flowchart explaining OPC process in optical information recording / reproducing apparatus

  An optical information recording / reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a system configuration diagram of an optical information recording / reproducing apparatus. In FIG. 1, only the configuration according to the present invention is shown, and other configurations are omitted. In this embodiment, a BD-RE will be described as an example of a phase change rewritable optical disk.

  As shown in FIG. 1, an optical information recording / reproducing apparatus 100 records and reproduces data by irradiating a phase change rewritable optical disk 10 with a laser beam 20, and is connected to an external device such as a personal computer. It is a device that transmits and receives data. The optical information recording / reproducing apparatus 100 includes an optical pickup head 200 that emits and receives laser light 20. The optical pickup head 200 includes a laser diode 201, a collimator lens 202, a beam splitter 203, an objective lens 204, a detection lens 205, and a photodiode 206. The optical information recording / reproducing apparatus 100 also includes an LD driving unit 310 that drives the laser diode 201, an equalizer 320 that performs equalization processing such as PRML processing on the reproduction signal from the photodiode 206, and data demodulation. A data demodulating circuit 330 that performs processing, a modulation degree measuring unit 340 that measures a value necessary for calculating a modulation degree from the reproduced RF signal, and a servo control circuit that performs track king control of the optical pickup head 200 350, a control circuit 400 that comprehensively controls the operation of the entire apparatus, a nonvolatile data storage unit 450 that stores various data referred to from the control circuit 400, and an interface 500 with an external device. Yes. The control circuit 400 includes a recording power calculation unit 410 that calculates an optimum recording power based on the modulation degree and the recording power.

Here, the modulation degree will be described with reference to FIG. The modulation degree m is defined by the ratio of the maximum amplitude magnitude I _8pp to the maximum amplitude signal level I _8H in the reproduction RF signal. That is, the modulation degree m = (I _8pp / I _8H ). Therefore, the modulation degree measurement unit 340 measures I _8H and I _8pp and outputs them to the recording power calculation unit 410 of the control circuit 400.

  As will be described later, the recording power calculation unit 410 performs an OPC (Optimum Power Control) process to calculate the optimum recording power Pwo. The operation of the recording power calculation unit 410 will be described later. The data storage unit 450 stores various information related to the write strategy, various information necessary for OPC processing, and the like. Examples of these data include various pulse width correction data used in the write strategy, erasing power calculation constant ε, start recording power during test data recording during OPC processing, recording power increase width, recording power increase The number of steps, the number of overwrites (DOW number) for measuring the modulation degree, and the like can be mentioned. Here, it is preferable that these data sets are stored in advance for each type of known optical disc 10 and a set of standard setting values (default values) is stored.

  When data recording is performed on the optical disc 10 using the optical information recording / reproducing apparatus 100, the control circuit 400 applies the error correction coding and 1-7PP modulation to the recording data, thereby creating a recording pattern. Generate. The LD driving unit 310 generates a recording pulse by applying a write strategy to the recording pattern, and drives the laser diode 201 using the recording pulse. The recording laser light 20 emitted from the laser diode 201 is applied to the optical disk 10 rotating at a constant linear speed or a constant rotational speed via a collimator lens 202, a beam splitter 203, and an objective lens 204. As a result, a recording pattern consisting of a mark / space sequence corresponding to desired recording data is recorded on the optical disc 10.

  On the other hand, when data reproduction is performed, the control circuit 400 controls the LD driving unit 310 to output with reproduction power. The reproducing laser light 20 emitted from the laser diode 201 is irradiated to the optical disk 10 rotating at a constant linear speed or a constant rotational speed through a collimator lens 202, a beam splitter 203, and an objective lens 204. Reflected light from the optical disk 10 is received by the photodiode 206. The received reflected light is converted into an electrical signal by the photodiode 206 and output to the modulation degree measurement unit 340 and the equalizer 320 as a reproduction RF signal. The equalizer 320 and the data demodulation circuit 330 perform PRML equalization processing and 1-7PP demodulation processing on the reproduced RF signal, and are decoded by the control circuit 400.

  Next, OPC (Optimum Power Control) in the optical information recording / reproducing apparatus 100 according to the present embodiment will be described in detail. First, the principle of the present invention will be described with reference to FIG. The solid line graph of FIG. 3 shows the degree of modulation m (Pw) when recording is performed by changing the recording power Pw in a predetermined step, and the overwrite count (DOW count) is 0, 1 and 10 respectively. This is a case of times. As shown in FIG. 3, it can be seen that the relationship between the recording power Pw and the modulation factor m (Pw) differs depending on the number of overwrites (the number of DOWs). Further, it can be seen that the graphs showing the relationship between the recording power Pw and the modulation degree m (Pw) intersect, in other words, there is a recording power Pw having the same modulation degree m (Pw).

  On the other hand, the dotted line graph of FIG. 3 is a graph showing SER (Pw) when recording is performed with the recording power Pw being changed in a predetermined step, and the number of overwrites (DOW number) is the same as the degree of modulation m (Pw) described above. Represents the cases of 0 times, 1 time and 10 times, respectively. Comparing the two graphs, it can be seen that the SER is excellent around the recording power corresponding to the intersection of the graphs of the modulation degree m (Pw).

  The present invention has been made paying attention to such DOW characteristics, and calculates the optimum recording power based on the characteristic change with respect to the number of overwrites (DOW number) regarding the relationship between the recording power Pw and the modulation factor m (Pw). It is. Specifically, test data is recorded at a plurality of recording powers Pw in the same test area, and the recording data is measured for reproduction / modulation to obtain a relational expression between the recording power Pw and the modulation m (Pw). The measurement process is performed at a plurality of different overwriting times. Specifically, it is preferable that the number of overwriting at the time of the measurement process is increased exponentially in ascending order. More specifically, the number of overwriting at the time of the measurement process is 0 times, 1 time, 10 times write processing, or at least 2 times of 0 times, 1 time, 10 times write processing. It is preferable to carry out during one treatment. This is because the relationship between the recording power Pw and the degree of modulation m (Pw) changes greatly between the initial writing and when writing is performed at least once, and changes after the writing is performed once or more. This is because the rate is reduced. In the present embodiment, as in the graph shown in FIG. 3, the measurement process is performed when the number of overwrites is 0, 1, and 10. That is, three relational expressions between the recording power Pw and the modulation degree m (Pw) are acquired.

  The relational expression between the recording power Pw and the modulation degree m (Pw) may be expressed in any form and form as long as the intersection point in the case of a graph can be calculated. Actually, the data obtained from changing the recording power Pw at the time of test recording stepwise is discrete. Therefore, as shown in the graph of FIG. 3, there can be considered a method of expressing the recording power Pw, the modulation degree m (Pw), and the relational expression by a discontinuous straight line connecting the data. In this case, there is an advantage that it is easy to check the existence of an intersection between graphs and to calculate the coordinates thereof, that is, to calculate the optimum recording power Pwo. As another form / form of the relational expression, there is a function that approximates the graph of the non-continuous straight line. In the present invention, after calculating a plurality of relational expressions, the recording power Pw at the intersection when each relational expression is graphed, in other words, the recording power Pw having the same degree of modulation m (Pw) between the relational expressions is optimally recorded. Set as power Pwo. In the subsequent actual recording, the optimum recording power Pwo is used as a reference for mark recording.

  Here, when there are two or more points where the degree of modulation m (Pw) with respect to the recording power Pw is equal when there are graphs of a plurality of relational expressions, the optimum recording power Pwo is determined using various methods described below. Is calculated. For example, a method of calculating an average value of recording power Pw related to a plurality of intersections, a method of employing a median value, a method of employing a maximum value, a method of employing a minimum value, and the like can be mentioned.

  Next, a specific operation of OPC in the optical information recording / reproducing apparatus 100 according to the present embodiment will be described in detail with reference to the flowchart of FIG. Here, in the data storage unit 450, the start recording power at the time of test data recording in the OPC process is 3.00 [mW], the increase amount of the recording power is 0.5 [mW / step], and the number of steps of the recording power increase. Is 11 [step], and the number of overwriting (DOW times) for measuring the modulation degree is recorded as 0th, 1st, and 10th data.

  First, when the optical disc 10 is set in the optical information recording / reproducing apparatus 100, the recording power calculation unit 410 reads the media ID from the optical disc 100 (step S1), and data corresponding to the media ID is stored in the data storage unit 450. (Step S2). If it is not stored, the following processing is continued using the default value, or OPC is not performed (end without performing recording).

  Next, the recording power calculation unit 410 reads various data corresponding to the media ID or default values for the various data from the data storage unit 450 (step S3), and then the recording power calculation unit 410 performs OPC processing. The optical pickup head 200 is moved to a predetermined test area address (step S5). Note that the test area used here has no data recorded, in other words, the overwrite count (DOW count) is zero. Next, the recording power calculation unit 410 records test data while changing the recording power based on the various data read in step S3 (step S6). Here, when the overwriting number (DOW number) is the predetermined overwriting number (0 times, 1 time, 10 times) read in step S3, the recorded test data is read and the modulation degree m (Pw) with respect to the recording power Pw is read. Is measured (steps S7 and S8). This process is repeated until the maximum number of overwriting times (10 times in the present embodiment) in the same test area (steps S4 to S9).

  Next, the recording power calculation unit 410 calculates a relational expression between them based on the degree of modulation m (Pw) with respect to the recording power Pw measured in step S8, and at different overwriting times (0, 1, 10). The intersection between the relational expressions is calculated (step S10). Next, the recording power calculation unit 410 calculates the optimum recording power Pwo from the recording power Pw corresponding to the intersection (step S11). Next, the recording power calculation unit 410 sets the recording power and the erasing power during the main recording based on the optimum recording power Pwo (step S12).

  If there is no unrecorded area in the test area on the optical disc 10, the OPC process may be performed after irradiating a predetermined erasing power to erase already recorded test data.

  As described above, according to the optical information recording / reproducing apparatus 100 according to the present embodiment, the relational expression between the recording power Pw and the modulation factor m (Pw) at the time of test recording is directly based on the change with respect to the overwrite count (DOW count). Since the optimum recording power Pwo is obtained, the influence of the number of overwriting (DOW times) is small, and data recording with a more appropriate optimum recording power Pwo can be performed.

  Although one embodiment of the present invention has been described in detail above, the present invention is not limited to this. For example, in the above embodiment, the reading process is performed only when the modulation factor is measured for the test data writing. However, the reading process may be performed for each test data writing.

  In the above-described embodiment, various data used in the OPC process are stored in advance in the data storage unit 450, but may be stored in advance in a predetermined area of the optical disc 10.

  DESCRIPTION OF SYMBOLS 10 ... Optical disk, 100 ... Optical information recording / reproducing apparatus, 200 ... Optical pick-up unit, 201 ... Laser diode, 202 ... Collimator lens, 203 ... Beam splitter, 204 ... Objective lens, 205 ... Detection lens, 206 ... Photodiode, 310 ... LD drive unit, 320 ... equalizer, 330 ... data demodulation circuit, 340 ... modulation degree measurement unit, 350 ... servo control circuit, 400 ... control circuit, 410 ... recording power calculation unit, 450 ... data storage unit, 500 ... inter face

Claims (5)

In an optical information recording method for recording information by irradiating a rewritable optical disc with laser light,
The write step of writing a test pattern with direct overwriting while changing the laser power stepwise in the test area of the optical disc is repeated several times in the same test area,
Performing a measurement step of reading the written test pattern and measuring the degree of modulation at each laser power after each of the two or more writing steps;
A relational expression calculating step for calculating a relational expression for deriving the degree of modulation with respect to the laser power based on each measurement result;
A step of calculating an optimum recording power for calculating the optimum recording power at the time of actual recording of data based on the calculated laser power, and calculating a laser power at which the degree of modulation with respect to the laser power is equal between the relational expressions. Optical information recording method. 2. The optical information recording method according to claim 1, wherein the number of overwriting in each writing step to be measured in the measuring step includes one that exponentially increases in ascending order. The optical information recording method according to claim 1, wherein the writing step to be measured in the measuring step includes all or at least two of the writing steps of overwriting times of 0 times, 1 time, and 10 times. 4. In the optimum recording power calculation step, when a plurality of laser powers having the same degree of modulation are calculated, an average value of laser powers is calculated as the optimum recording power. The optical information recording method as described. 4. The median value of the laser power is calculated as the optimum recording power when a plurality of laser powers having the same degree of modulation are calculated in the optimum recording power calculation step. 5. The optical information recording method as described.

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