WO2005104101A1

WO2005104101A1 - Method and apparatus for determining an erasing power of a rewritable optical disc

Info

Publication number: WO2005104101A1
Application number: PCT/IB2005/051149
Authority: WO
Inventors: Fulong Tang; Benno Tieke; Jochen Hellmig; Jing Tao; Geert Langereis
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-04-23
Filing date: 2005-04-08
Publication date: 2005-11-03
Also published as: CN1691150A; TW200636695A

Abstract

The present invention provides a method for determining the erasing power of rewritable optical disk and the apparatus thereof. The method comprises the steps: setting up a plurality of erasing test powers firstly; then testing optical disk writing using a designated writing power of optical disk together with the plurality of erasing test powers of optical disk respectively to obtain the parameters corresponding to every erasing test power of optical disk, the parameters representing the effects of erasing optical disk, such as the data-to-clock jitter; and then determining an erasing power used for said rewritable optical disk by establishing the corresponding variation relation between the parameters and the erasing test powers of optical disk according to the plurality of erasing test powers of optical disk and said corresponding parameters.

Description

METHOD AND APPARATUS FOR DETERMINING AN ERASING POWER OF A REWRITABLE OPTICAL DISC

BACKGROUND ART The present invention relates to a field of optical storage, in particular to a method and apparatus for determining an erasing power of a rewritable optical disc. With the fast development of digital information technology, optical discs have become more and more important information storage mediums owing to the advantages such as large capacity, portability, low cost, and non-contact access, etc. Optical discs include read-only optical discs (mainly CD-ROM), recordable optical discs (e.g., CD-R, DVD-R) and erasable-and-rewritable optical discs (e.g., CD-RW, DVD-RW). The erasable-and-rewritable optical discs mainly include Magneto-Optical (MO) discs and Phase-Change disc. The recording principle of a Phase-Change disc is achieved by making use of the phase change of the structure of the material of the optical disc recording layer. The general material of the optical disc recording layer has different phases under different temperatures. Under normal temperatures, the atoms of the material of the optical disc recording layer are arranged regularly, i.e., they exhibit crystalline. If the material of the optical disc recording layer is heated to make the temperature thereof higher than its melting point, the atoms thereof are scattered irregularly; if the material of the recording layer is cooled quickly at this time, the atoms thereof would not be restored to their regular arrangement and their irregular distribution under the high temperature would be maintained, i.e., they are in a non-crystalline state; while if the material of the recording layer is cooled slowly, there would be enough kinetic energy and time for the atoms to be arranged regularly , i.e., to exhibit crystalline. On the basis of the above-mentioned phase change principle, if the recording layer of the optical disc is irradiated with laser light of high power and short pulse, and the highest temperature is higher than the melting point of the material, and the temperature thereof is made to increase and decrease quickly and instantly, the material of the recording layer at the irradiated site will become non-crystallized. This process is the data writing process while the laser light power is called writing power. When the recording layer of the optical disc is irradiated with laser light pulses of low power to make the temperature change thereof be between the melting point and the crystallizing temperature and remain for a longer time, the material of the recording layer at the irradiated site will become crystallized. This process is called data erasing process while the laser light power is called erasing power. During the practical Phase-Change disc recording, the writing and erasing of data are accomplished by directly rewriting, that is, no special erasing of the existing data on the optical disc will be performed, instead, the existing data is erased while writing data. The writing power and erasing power directly affect the effect of optical disc writing and erasing and also directly affect the magnitude of the data-to-clock jitter recorded on the optical disc. If the data-to-clock jitter is greater, there will be error codes. An optical disc with good rewriting performance requires particular optimum writing power and erasing power. Therefore, optical disc write strategies such as the optimized writing power Pw corresponding to the optical disc and the erasing/writing power ratio (ε=Pe/Pw) for determining the erasing power, etc., are stored in the ATIP (Absolute Time In Pregroove) information or ADIP (Absolute Address In Pregroove) information of the Phase-Change optical disc provided by the manufacturers. When writing information on the optical disc, the optical disc recording device first read the Pw value in the ATIP or ADIP information stored in the optical disc, and correct it with the optimum Power Control (OPC) program, then obtain the erasing power value from the erasing/writing power ratio (ε=Pe/Pw). However, the erasing power determined from the ATIP or ADIP information of the optical disc is only an erasing power obtained from a general ratio ε and is not the optimum erasing power under specific writing conditions, so the optimum erasing effect cannot be guaranteed. Therefore, there will be a lot of residual signals that cannot be erased, which will affect the rewriting effect of the optical disc. In addition, some optical discs that do not contain optical disc write strategies might also enter the market, thus it is impossible to obtain the corresponding writing power value and the corresponding erasing power value from such optical discs, accordingly. The optical disc recording device could only use the default erasing power when writing on the optical disc, while the default erasing power might be greatly different from the optimum erasing power that could be used under the specific writing condition. In some cases, the optical disc recording device will not be able to rewrite the optical disc because of failing to get the erasing power. Therefore, a method and apparatus that could determine the erasing power of a Phase-Change optical disc under the specific writing condition; are needed.

CONTENTS OF THE INVENTION The present invention provides a method and apparatus for determining an optical disc erasing power of a rewritable optical disc under a specific writing condition in order to improve the erasing effect when rewriting an optical disc and overcome the defects of the prior art. The present invention provides a method for determining an optical disc erasing power of a rewriting optical disc, comprising steps: setting a plurality of optical disc erasing test powers; performing optical disc writing tests by respectively using a specific optical disc writing power and the plurality of optical disc erasing test powers to obtain parameters corresponding to the optical disc erasing test powers, the parameters reflect the effect of erasing optical disc data, such as data-to-clock jitters; and determining a corresponding variation relationship between the plurality of optical disc erasing test powers and the parameters according to the plurality of optical disc erasing test powers and the parameters to determine an optimized optical disc erasing power for erasing data of the rewritable optical disc. Preferably, the optimum erasing power under a specific writing condition could be determined according to the corresponding relationship. The present invention also provides an apparatus for determining an optical disc erasing power of a rewritable optical disc, comprising: means for setting an optical disc erasing test power to perform optical disc writing test with a specific optical disc writing power; means for acquiring parameter corresponding to the optical disc erasing test power according to the optical disc writing test, wherein the parameter reflecting the effect of optical disc erasing; and means for determining a corresponding variation relationship between the optical disc erasing test power and the parameter according to the parameter and the optical disc erasing test power to determine an optimized optical disc erasing power for erasing data of the rewritable optical disc. Preferably, the optimum erasing power under a specific writing condition could be determined according to the corresponding relationship. By means of the method and apparatus provided by the present invention, the optical disc writing system determines an erasing power that suits the specific writing condition when no optimum erasing power is provided in the optical disc or the provided erasing power is not ideal, so as to make the rewriting of the optical disc more reliable. Other objects and achievements of the invention will become apparent from the following description made with reference to the accompanying drawings and the claims, and a more comprehensive understanding of the invention will also be obtained. DESCRIPTION OF FIGURES The present invention is explained in detail through the embodiments with reference to the figures, wherein: Fig. 1 is a block diagram of the device for determining an erasing power of a rewritable optical disc according to one embodiment of the present invention; Fig. 2 is a flow chart of the method for determining an erasing power of a rewritable optical disc according to one embodiment of the present invention; Fig. 3 is a relationship diagram showing the relationship between the erasing/writing power ratio (Pe/Pw) and the average data-to-clock jitter when writing an optical disc for the first time according to one embodiment of the present invention; Fig. 4 is a relationship diagram showing the relationship between the erasing/writing power ratio (Pe/Pw) and the average data-to-clock jitter when writing an optical disc for the third time according to the embodiment of Fig. 3; Fig. 5 is a relationship diagram showing the relationship between the erasing/writing power ratio (Pe/Pw) and the average data-to-clock jitter when writing an optical disc for the 9th time according to the embodiment of Fig. 3; and Fig. 6 is a relationship diagram showing the relationship between the erasing/writing power ratio (Pe/Pw) and the average data-to-clock jitter when writing an optical disc for the 500th time according to the embodiment of Fig. 3. Throughout the drawings, the same reference numerals indicate similar or same features and functions. The present invention will be further explained in the following in conjunction with specific embodiments with reference to the drawings. MODE OF CARRYING OUT THE INVENTION Fig. 1 is a block diagram of an apparatus 100 for determining the erasing power of the rewritable optical disc according to one embodiment of the present invention. The apparatus comprises a setting device 120 for setting a plurality of optical disc erasing test powers which will be used to perform optical disc writing test with a specific optical disc writing power respectively. The optical disc erasing test powers could be set on the basis of some conventional methods and data settings, for example, they can be set on the basis of the writing power provided in the optical disc or in a optical disc recording device and the commonly used ratio between the < writing power and the erasing power, etc. The apparatus 100 also comprises an acquiring device 140 for acquiring a corresponding data-to- clock jitter according to one optical disc writing test. The apparatus 100 further comprises a determining device 160 for determining a corresponding relationship between the data-to-clock jitter and the optical disc erasing test power, so as to determine an optical disc erasing power for erasing data of the rewritable optical disc. Generally speaking, at least three groups of corresponding optical disc erasing test powers and jitters are needed for determining the relationship between the data-to-clock jitter and the optical erasing power. Therefore, usually at least three optical disc erasing test powers are set so as to perform optical disc writing test. The determined relationship between the data-to-clock jitter and the optical disc erasing power includes the parabolic relationship between the jitter and the optical disc erasing power, and it could also include a parabolic relationship between the jitter and the ratio between the optical disc erasing power and the specific optical disc writing power. On the basis of an extreme value corresponding to the minimum jitter in the parabolic relationship, the optimum erasing power under a specific writing condition could be determined and be set as the erasing power when writing the optical disc. Fig. 2 is a flow chart of the method for determining an erasing power of a rewritable optical disc according to one embodiment of the present invention. This embodiment takes a 32x CD-RW Phase-Change optical disc writing as an example, the rewriting speed of the optical disc is 19.2Mbit/s and the reading speed is 14.52Mbit/s. Firstly, the optical disc recording device sets at least three different optical disc erasing test powers Pe (step S200). The optical disc erasing test powers are set according to the optical disc writing powers. The optical disc writing power could be either the default writing power or a value close to the default writing power. For example, the present embodiment specific the writing power Pw=40mw. According to experiments, it is preferable that the relationship between the optical disc erasing power and writing power satisfies Pe/Pw=0.2, so that the range of the optical disc erasing power could be centered at 8mw with a deviation around 30%. For instance, three erasing powers could be set, i.e., Pe=7mw, 8mw and 9mw, accordingly, three ratios of Pe/Pw could be obtained, i.e., 0.175, 0.2 and 0.225. Next, an optical disc writing test is performed using the specific optical disc writing power and the at least three optical disc erasing test powers

(step S210). Subsequently, a data-to-clock jitter of the writing test is obtained (step S220). The optical disc recording device rewrite the optical disc with the above-mentioned three groups of writing powers and erasing powers, respectively, and the data-to-clock jitter could be measured by a measuring device according to a conventional method. For each group of writing power and erasing power, a leading jitter and a trailing jitter could be obtained. The measuring device will automatically calculate the root mean square values of the leading jitter and the trailing jitter so as to obtain three average jitters, i.e., 2.572, 2.608 and 2.712, accordingly. Then, the relationship between the average jitter and the erasing/writing power ratio is calculated by parabola so as to obtain a parabolic equation between the jitter and erasing/writing power ratio (step

S240). In the present embodiment, put the data of the three groups of average jitters and the erasing/writing power ratios into the general parabolic equation, y=ax²-bx+c, wherein x is the value of Pw/Pe, and y is the average jitter. By solving the equation, the values of the coefficients a, b and c are obtained and thereby the parabolic equation is calculated. For example, the parabolic equation obtained according to the above available data is y=53.937x²-18.77x+4.2045. Of course, more than three erasing powers could be set so as to obtain more erasing/writing power ratios and to obtain more average jitter, accordingly, the parabolic equation obtained could be more accurate. Moreover, the parabolic equation could also be solved according to the relationship between the trailing jitter and the erasing /writing power ratio. Next, the optimized erasing/writing power ratio is obtained based on the parabolic equation (step S260). If the optical disc is rewritten with the optimum writing power and erasing power, the average jitter of data-to-clock will be the smallest, which means that the rewriting effect of the optical disc is very good, thus the method of deriving the parabolic equation is used to obtain the optimized erasing power. Deriving the parabolic equation y= 53.937x²-18.77x+4.2045 and making the derived first degree polynomial be 0, i.e., 107.874x-18.77=0. By solving this equation, x=0.18 is obtained, i.e.,

Pe/Pw=0.18. The optimized erasing power could also be obtained by directly calculating x= | b/2a | . Finally, since Pe/Pw=0.18, the optimized erasing power Pe=0.18x40=7.20mw (step S280). In the present embodiment, the optical disc is rewritten with one fixed writing power and three varying erasing powers to calculate an optimized erasing power. In order to obtain an optimum erasing power, a plurality of different writing powers could be set to perform a plurality of direct rewriting on one optical disc to obtain a plurality of optimized erasing powers, thereby, the optimum optical disc erasing power could be obtained. For instance, in the following example, under the premise that both the optical disc types and rewriting speeds are the same, three writing powers are set, with which one optical disc will be directly rewritten for a plurality of times respectively. Fig. 3 is a relationship diagram showing the relationship between the erasing/writing power ratio (Pe/Pw) and the average data-to-clock jitter when writing an optical disc for the first time according to one embodiment of the present invention. It could be seen from the figure that the X- coordinate represents Pe/Pw and the Y-coordinate represents the average jitters. Three writing powers 40mw, 43mw and 46mw are set respectively, and a plurality of erasing powers which correspond to the writing powers are set. The optical disc is written with the writing powers and erasing powers as set respectively. The erasing power optimizing method could be used for obtaining the curve corresponding to each of the writing powers, wherein the writing power of 40mw corresponds to the rhombic-dot curve, the writing power of 43mw corresponds to the quadrate-dot curve and the writing power of 46mw corresponds to the triangular-dot curve. Then these curves are calculated with parabola and the parabolic equations of the three curves are obtained, which are respectively such as: y=53.937x²-18.77x+4.2045; y=62.156x²-21.416x+4.2459; y=79.135x²-27.228+4.6052. The method of obtaining the parabolic equation could take three dots from each parabolic curve and put the three dots, i.e., three groups of Pe/Pw values and average jitters into the general parabolic equation of y=ax²-bx+c, wherein x represents the value of Pe/Pw, and y represents the average jitter. By solving the equations, the values of coefficients a, b and c are obtained, thereby the parabolic equation could be calculated. After solving the parabolic equation, the value of Pe/Pw to which the smallest jitter corresponds could be obtained, thereby the optimized erasing power could be obtained. Generally, the optical disc that is written for the first time is an empty optical disc, so the erasing power has not been used, accordingly, it is unknown which erasing power is the optimum one and thus several rewritings are needed. Fig. 4 is a relationship diagram showing the relationship between the erasing/writing power ratio (Pe/Pw) and the average data-to-clock jitter when writing an optical disc for the 3rd time according to the embodiment of Fig. 3. Fig. 5 is a relationship diagram showing the relationship between the erasing/writing power ratio (Pe/Pw) and the average data-to-clock jitter when writing an optical disc for the 9th time according to the embodiment of Fig. 3. Fig. 6 is a relationship diagram showing the relationship between the erasing/writing power ratio (Pe/Pw) and the average data-to-clock jitter when writing an optical disc for the 500th time according to the embodiment of Fig. 3. It could be seen from the figures that although these parabolas are somewhat different, the Pe/Pw to which the minimum average jitter corresponds are very close to each other, and the specific values could be seen in the following table 1. Table 1 is a table of the optimized erasing/writing power ratio (Pe/Pw) obtained from the data of Figs. 3-6. The table shows that, when taking the writing power of 40mW as an example, the optimized erasing/writing power ratio (Pe/Pw) obtained from the first rewriting is 0.17, the optimized erasing/writing power ratio (Pe/Pw) obtained from the third rewriting is 0.19, the optimized erasing/writing power ratio (Pe/Pw) obtained from the 9th rewriting is 0.20 and the optimized erasing/writing power ratio (Pe/Pw) obtained from the 500th rewriting is 0.22. The optimized erasing/writing power ratio is influenced by the Direct overwrite curve, i.e., the parabolic tendency. Experiments show that the optimized erasing/writing power ratios obtained from the 3rd to the 500th rewritings are very close to each other. Thus if the erasing/writing power ratio calculated from the 3rd direct rewriting is used as the optimized erasing/writing power ratio, the errors of the Pe/Pws obtained in other cases will be within 10%. Therefore, it is not necessary to perform so many rewritings to obtain the optimized erasing power, and the optimized erasing power could substantially be obtained from the 3rd rewriting. Table 1 : the optimized erasing/writing power ratios (Pe/Pw) obtained from the data of Figs. 3-6.

Note: AJ is the average jitter. While the invention has been described in conjunction with specific embodiments, many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the invention is intended to include all such alternatives, modifications and variations when they fall within the spirit and scope of the appended claims.

Claims

What is claimed is:

1. A method for determining a erasing power of rewritable optical disk, comprising steps: (a) setting up a plurality of erasing test powers of optical disk; (b) testing optical disk writing using said plurality of erasing test powers of optical disk together with a designated writing power of optical disk respectively to obtain parameters corresponding to every erasing test power of optical disk, the parameters representing the effects of erasing optical disk data; and (c) establishing the corresponding variation relation between erasing test powers of optical disk and said parameters according to said plurality of erasing test powers and said parameters, thereby to determine an optimized erasing power of optical disk for erasing the data of said rewritable optical disk .

2. The method according to claim 1 , wherein said writing power of optical disk in step (b) includes a default writing power of optical disk.

3. The method according to claim 1 or 2, wherein one or more of said plurality of erasing test powers of optical disk in step (a) is set up according to said writing power of optical disk.

4. The method according to claim 1 , wherein said parameter includes a data-to-clock jitter.

5. The method according to claim 4, wherein said jitter includes a data-to-clock average jitter.

6. The method according to claim 1 , wherein said corresponding variation relation includes: a corresponding variation relation between the ratios of erasing test powers of optical disk to the designated writing powers of optical disk and the parameters.

7. The method according to claim 6, wherein the corresponding variation relation between the ratios of erasing test powers of optical disk to said designated writing powers of optical disk and the jitters includes: a parabola relation between the ratios of erasing test powers of optical disk to said designated writing powers of optical disk and the jitters.

8. The method according to claim 7, wherein step (c) includes determining an erasing power of optical disk according to the extremum of the established parabola relation.

9. The method according to claim 1 , wherein said a plurality of erasing test powers of optical disk in step (a) include at least three erasing test powers of optical disk.

10. An apparatus for determining the erasing power of rewritable optical disk, comprising: means for setting up a plurality of erasing test powers of optical disk to test optical disk writing using them together with a designated writing power of optical disk; means for obtaining the parameter corresponding to said erasing test power of optical disk according to said optical disk writing test, the parameter representing the effect of erasing optical disk data; and means for determining an optimized erasing power of optical disk for erasing the data of said rewritable optical disk by establishing the corresponding variation relation between erasing test powers of optical disk and said parameters according to said plurality of erasing powers of optical disk and said corresponding parameters.

11. The apparatus according to claim 10, wherein said parameters obtained by the obtaining means include data-to-clock jitters.

12. The apparatus according to claim 11 , wherein said corresponding variation relation includes the corresponding relation between the ratios of erasing powers of optical disk to said designated writing powers of optical disk and the jitters.

13. The apparatus according to claim 12, wherein said corresponding variation relation between the ratios of erasing powers of optical disk to said designated writing powers of optical disk and the jitters includes the parabola relation between said ratios and said jitters.

14. The apparatus according to claim 13, wherein said determining means determines an erasing power of optical disk according to the extremum of said parabola relation.

15. An optical disk writing system, comprising: an optical disk writing device for writing optical disk; and a device for determining the erasing power of rewritable optical disk, comprising: means for setting up a plurality of erasing test powers of optical disk to test optical disk writing using them together with a designated writing power of optical disk by said optical disk writing device; and means for obtaining the parameter corresponding to every erasing test power of optical disk according to said optical disk writing test, the parameter representing the effect of erasing optical disk data; and means for determining an optimized erasing power of optical disk for erasing the data of said rewritable optical disk by establishing the corresponding relation between said parameters and said erasing test powers of optical disk according to said obtained parameters and erasing test powers of optical disk.

16. The system according to claim 15, wherein said parameter includes a data-to-clock jitter.

17. The system according to claim 16, wherein said corresponding variation relation includes a corresponding relation between the ratios of erasing powers of optical disk to said designated writing powers of optical disk and the jitters.