Method Of Optimizing The Write Power For Recording Marks In An Information Layer Of A Record Carrier And Recording Device Using Such An Optimizing Method

Abstract

The present invention relates to a method of optimizing the write power for recording marks in an information layer of a record carrier by irradiating the information layer with a (pulsed) radiation beam, said information layer having a phase that is reversibly changeable between a first (for example a crystal) phase and a second (for example an amorphous) phase. Since the methods known for 1 T write strategies generally cannot be used for nT write strategies, n being an integer greater than 1, a new method is proposed comprising the steps of: recording (S 1) a pattern of test marks including short marks having a predetermined short nominal runlength onto the record carrier by applying at least three different write powers, measuring (S2) the runlengths of said recorded short marks obtained by applying the at least three different write powers, and determining (S4) an optimum write power on the basis of the deviations of the measured runlengths from the nominal runlength of said short marks.

Description

The invention will now be explained in more detail with reference to the accompanying drawings, in which

FIG. 1 shows curves of the write power plotted against the modulation for different parameters settings of a 2 T write strategy,

FIG. 2 shows curves of the write power plotted against the jitter of 3 T marks for different 2 T write strategies,

FIG. 3 shows curves of the difference (Δ3TRL) between a measured 3 T runlength and a nominal 3 T runlength plotted against the 3 T land jitter for different write strategies,

FIG. 4 is a flowchart illustrating a method according to the invention,

FIG. 5 shows curves of the difference (Δ3TRL) between measured 3 T runlengths and nominal 3 T runlengths plotted against the write power for different write strategies, and

FIG. 6 shows curves of the modulation plotted against the difference (Δ3TRL) between measured 3 T runlengths and nominal 3 T runlengths for different write strategies.

FIG. 1 shows the curves of the modulation versus the write power for four parameter settings (numbered 1 to 4) of a 2 T write strategy (WS). Apparently, the modulation is only a function of the write power. It appears not to depend on the details of other WS parameters since the four different parameters settings give exactly the same modulation.

However, for a certain write power the resulting jitter of the 3 T marks (especially the land jitter) varies considerably as a function of the applied write strategy (see FIG. 2). For example, at 42 mW, write strategies 2 and 3 give a land jitter of 28 ns, whereas write strategies 1 and 4 result in a land jitter of 33 ns. Moreover, the optimum write power for each write strategy may be considerably different, e.g. 36 mW for WS 4 and 40 mW for WS 2. It is noted that the attainable bottom jitter (i.e. the lowest jitter value of a curve) is very similar for all write strategies. However, this bottom jitter is, for different write strategies, achieved for different write power values and thus at different modulation values.

Another problem, which is apparent from FIG. 2 is that the curve of the jitter vs. the write power is asymmetrical, with a steep increase on the low-power side and a shallow increase on the high-power side. Generally, such an asymmetrical curve is not ideal for optimizing the write strategy parameters; a symmetrically shaped parabolic curve would be preferred.

A third problem for 2 T write strategies is that the number of WS parameters may be large, and the parameter settings are critical at a given write power. Some of the parameters, especially those related to the shorter marks such as 3 T marks, have to be defined with a high timing resolution (for example a timing resolution of up to 1/16 T). The resulting jitter, especially the land jitter, may be very sensitive to these parameters, as is apparent from FIG. 2. The solution to the problem of write strategy parameter, and especially write power, optimization described above is to look for an underlying important parameter indicative of the recording performance. This parameter is the length of the recorded 3 T mark or, more generally, the length of the shortest mark allowed by the applied modulation method, or at least of the short marks. It appears that the jitter (which is the most important parameter indicative of the recording performance; a low jitter is preferred) is high when the length of the recorded 3 T marks is not correct.

If the curve of the 3 T land jitter is plotted against the difference between the measured 3 T runlength and the nominal 3 T runlength (Δ3TRL), all curves for different parameters settings of a 2 T write strategy become a parabola (see FIG. 3). A similar bottom jitter (i.e. the lowest jitter value of the parabolic curve) can be found for all different write strategy parameter settings if the write power changes. Furthermore, all parabolas for the different write strategies are scaled to the same “generic” parabola (see FIG. 3).

FIG. 3 illustrates that the optimization of write power, or more generally of the WS parameters, becomes straightforward when using the relation between the 3 T land jitter and the 3 T mark length. It is noted that the pit jitter remains almost constant when the writing power changes. Therefore, it is not required to consider the pit jitter in this optimization process (although this pit jitter may be considered also).

By measuring three points one can already derive the three parameters of a parabolic curve. Measuring of more points will improve the accuracy of the parabolic curve. The resulting parabola curve readily enables the optimum write power (to be used for recording marks having a low jitter) for a set of 2 T write strategy parameters to be derived.

As described, the land jitter vs. Δ3TRL curves scale to the same basic curve. All different write strategies result in a similar bottom jitter value for a similar Δ3TRL, and therefore for a similar recorded 3 T mark length. Generally, the bottom jitter is found to be equal to zero for a Δ3TRL. For the different 2 T WS parameter settings in FID. 3, however, the Δ3TRL corresponding to the lowest jitter (i.e. the bottom jitter) is around 0.5 ns. Therefore, it is possible to optimize for a certain target Δ3TRL value close to, but not exactly equal to, zero (in this case 0.5 ns).

Based on the observations above, an example of a possible OPC method according to the invention for determining the optimum write power for a given 2 T write strategy by measuring of Δ3TRL will be discussed below, with reference to a flowchart shown in FIG. 4. In a first step S1, a drive writes random test marks on three tracks of the record carrier (for example in a specially reserved Power Calibration Area) using three different write power values around a default write power value, while using a default parameter setting for the remaining parameters of the write strategy. The default write power value may be obtained from a previous optimization process or from a number of experiments using the same type of record carrier. Said random test marks include at least a number of the shortest allowed marks (for example 3 T marks for recordable or rewritable CD and DVD type record carriers).

Subsequently (step S2), the runlength of said written shortest marks is measured for each of the three different write powers. Optionally, the resulting modulations of said written shortest marks are measured at the same time.

From the difference Δ3TRL between the measured runlengths and the nominal runlength of said shortest marks (3 T marks), (part of) a parabolic curve of the write power versus Δ3TRL is determined, as is shown in FIG. 5. Optionally, if the modulations were measured in step S2, a further curve of Δ3TRL versus modulation is determined, as shown in FIG. 6. The latter curve can be used in an optional step S3 to determine those Δ3TRL values, and thus implicitly those write powers, which result in a sufficiently high modulation of the recorded marks (as specified in the relevant standard). Alternatively, or in addition, a curve of the write power versus the modulation of the recorded marks as shown in FIG. 1 can be obtained and used to determine those write powers which result in a sufficiently high modulation.

In the next step S4, the optimum write power is determined. A method of determining the optimum write power is based on the derived parabolic curve of the write power versus Δ3TRL as shown in FIG. 5. The write power is derived from this parabolic curve, which is expected to result in the optimum Δ3TRL. The optimum Δ3TRL itself is either set to 0 ns, or to a value previously determined as the Δ3TRL for which the jitter is expected to be minimal, for example based on the parabolic curve of Δ3TRL versus (land) jitter as shown in FIG. 3, which illustrates that the jitter is lowest for Δ3TRL 0.5 ns. The write power thus determined is then used as the optimum write power for the optimum parameter setting of the given 2 T write strategy.

This optimum write power is now used in step S5 to write data. When subsequently a “walking OPC” procedure is applied, the runlengths of at least the shortest marks in the written data are measured again in step S6. The Δ3TRL can then again be determined for the measured runlengths, and the new Δ3TRL can then again be compared with the optimum Δ3TRL so as to adjust, if necessary, the optimum write power in step S7. Fluctuations of stack thickness and material composition in the record carrier or drive or temperature variations may cause changes in the optimum write power for different areas of a disc. It is thus possible to adjust the write power for such fluctuations and variations during the process of writing data in that such a “walking OPC” procedure is carried out. After normal data (i.e. data not specifically intended for the OPC procedures) have been written on a disc, the drive measures the Δ3TRL, compares it with the optimum value, and adjusts the write power.

It should be noted that either a single writing step for writing test patterns or two separate writing steps for writing test marks may be used for the above-mentioned combined measurement of the mark lengths and the (optional) measurement of the modulation of the recorded marks in step S2. Furthermore, the invention is not limited to 2 T write strategies, but may be generally applied to any nT write strategy, n being an integer greater than 1. The invention is not limited to any particular type of record carrier, but may be applied to any recordable or rewritable type of record carrier, such as any CD, DVD, or BD type of record carrier. For some types of record carriers, the shortest allowed marks may be not 3 T marks, but, for example, 2 T marks, as is the case for BD record carriers. It is further possible to use and measure not only the runlength of the shortest marks, but also the runlengths of longer marks which can then be taken into account for determining the optimum write power. For example, not only the 3 T marks may be used, but also the somewhat longer 4 T and 5 T marks. The pattern of test marks must then be adapted accordingly.

Claims

1. Method of optimizing the write power for recording marks in an information layer of a record carrier by irradiating the information layer with a radiation beam, said information layer having a phase that is reversibly changeable between a first phase and a second phase, comprising the steps of: recording (S1) a pattern of test marks at least comprising short marks having a predetermined short nominal runlength onto the record carrier by applying at least three different write powers,measuring (S2) the runlengths of said short marks recorded through the application of the at least three different write powers,determining (S4) an optimum write power on the basis of the deviations of the measured runlengths from the nominal runlength of said short marks.

2. Method as claimed in claim 1, wherein the optimum write power is determined on the basis of the deviations of the measured runlengths from the nominal runlength of said short marks, such that the difference between a measured runlength and the nominal runlength of said short marks is substantially zero.

3. Method as claimed in claim 1, wherein the optimum write power is determined on the basis of the deviations of the measured runlengths from the nominal runlength of said short marks, such that the jitter of said short marks is minimal.

4. Method as claimed in claim 1, wherein, in said step of recording a pattern of test marks (S1), shortest marks having the shortest runlength allowed by an applied modulation method are recorded, and wherein the runlengths of said shortest marks are measured and used for determining the optimum write power.

5. Method as claimed in claim 1, wherein, in said step of recording a pattern of test marks (S1), the test marks are recorded in that at least three different write powers around a default optimum write power are applied.

6. Method as claimed in claim 1, further comprising the steps of: recording (S5) marks including short marks onto the record carrier by applying the determined optimum write power,measuring (S6) the runlengths of said short marks thus recorded by means of the determined optimum write power,adjusting (S7) the optimum write power on the basis of the difference between the measured runlengths and the nominal runlength of said short marks.

7. Method as claimed in claim 1, further comprising the steps of: measuring (S2) the modulations of said recorded short marks recorded by means of the at least three different write powers,checking (S3) whether the applied write powers result in a modulation of the recorded short marks that lies above a predetermined threshold modulation.

8. Recording method for recording marks representing user data in an information layer of a record carrier by irradiating the information layer with a radiation beam, said information layer having a phase that is reversibly changeable between a first phase and a second phase, comprising the steps of: optimizing the write power for recording said marks by a method as claimed in claim 1, so as to obtain an optimum write power, andrecording said marks representing user data by applying said optimum write power.

9. Recording method for recording marks representing user data in an information layer of a record carrier by irradiating the information layer with a radiation beam, said information layer having a phase that is reversibly changeable between a first phase and a second phase, comprising the steps of: optimizing the write power for recording said marks by regularly carrying out a method as claimed in claim 6 to adjust the optimum write power regularly during said recording.

10. Device for optimizing the write power for recording marks in an information layer of a record carrier by a method as claimed in claim 1, comprising recording means for recording a pattern of test marks at least comprising short marks having a predetermined short nominal runlength onto the record carrier by applying at least three different write powers,measuring means for measuring the runlengths of said short marks recorded by the application of the at least three different write powers, anddetermining means for determining an optimum write power on the basis of the deviations of the measured runlengths from the nominal runlength of said short marks.

11. Recording device for recording marks in an information layer of a record carrier by irradiating the information layer with a radiation beam, comprising a device for optimizing the write power for recording marks in an information layer of a record carrier as claimed in claim 10.

12. Recording device as claimed in claim 11, further comprising further recording means for recording marks including short marks onto the record carrier by applying the determined optimum write power,further measuring means for measuring the runlengths of said short marks recorded by means of the determined optimum write power, andadjusting means for adjusting the optimum write power on the basis of the deviation of the measured runlengths from the nominal runlength of said short marks.

13. Recording device as claimed in claim 12 adapted for optimizing the write power for recording said marks by regularly carrying out a method as claimed in claim 6 for regularly adjusting the optimum write power.