JP2005251391A - Information recording method and information recording and reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording method and an information recording and reproducing apparatus in which information is recorded in an information recording medium so that a reproduced signal property is good and compatibility is improved. <P>SOLUTION: Recording light is modulated in a pulse state, and information constituted of a plurality of codes having time width of integral multiple of a reference clock period T is recorded in the information recording medium in accordance with the information. Recorded information is reproduced from the information recording medium, first asymmetry is calculated using difference between a reproduced signal central level of a 2T code and a reproduced signal central level of a 3T code, second asymmetry is calculated using difference between a reproduced signal central level of the 2T code and a reproduced signal central level of the sparsest code, third asymmetry is calculated using difference between a reproduced signal central level of the 3T code and a reproduced signal central level of the sparsest code (ST003, ST004). A pulse shape of the recording light is varied so that the first to the third asymmetry become respectively 15% or less (ST010). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an information recording medium such as an optical disc capable of recording / reproducing information, a method for evaluating a reproduction signal of the information recording medium, an information recording method for recording information on the information recording medium, and an information recording / reproducing apparatus.

  Conventionally, there is a thermal recording medium as a write-once or rewritable information recording medium. This is to record information by heating and cooling the information recording medium. A typical example is a phase change medium. In this method, information is recorded using a difference in phase of a medium, that is, a difference in physical properties due to a difference between amorphous and crystal, for example, a difference in reflectance. For example, in an optical disk apparatus using a phase change medium, the medium is crystallized over the entire surface by initialization in advance, and an amorphous recording mark is formed by irradiating a strong laser beam in a pulsed form.

  This is because the medium is melted by the strong laser beam, and then the laser beam is weakened to rapidly cool and become amorphous. On the other hand, information reproduction is performed by irradiating a medium with a weak laser beam at a certain level, and converting the reflectance change due to the amorphous part and the crystal part, which are recording marks, into an electric signal for reading.

  There is a DVD-RAM (ISO / IEC16824) as an optical disk using a phase change medium that has recently been put into practical use. In this DVD-RAM, information is recorded and erased by switching the output level of the laser beam to be irradiated. Information is recorded as a plurality of recording marks on a recording track of the optical disc, and each recording mark is formed by irradiating the recording track with a plurality of laser pulses. The recording waveform of this laser pulse is generally called a write strategy. The write strategy indicates a laser modulation method or a recording waveform when a mark is recorded on the optical disc, and is defined for each length of the recording mark.

  The DVD-RAM write strategy has three or four levels of light output. That is, the peak power for heating and melting the medium above the melting temperature, the bias power 1 (erasing power) for holding the medium at the crystallization temperature for the crystallization holding time, and the molten medium is rapidly cooled to be amorphous. The bias power 2 and the bias power 3 are In the DVD-RAM, the size and shape of the mark to be recorded are accurately adjusted by adjusting these light output levels.

  In the case of DVD-RAM, the light output level defined by the write strategy is constant regardless of the width of the mark or space. Therefore, unlike a mark surrounded by a long space, a recording mark surrounded by a short space transmits the amount of heat for recording the immediately preceding and immediately following marks, and the recording mark is recrystallized due to the amount of heat, or the melted portion is There is a problem of thermal interference such as enlargement. In the DVD-RAM, the change is corrected by widening or narrowing the pulse width according to the space width before and after this problem, thereby obtaining a desired mark shape.

  On the other hand, asymmetry is defined in DVD-RAM as one of evaluation methods for recorded signals. The asymmetry defined in the DVD-RAM is to evaluate the difference between the reproduction waveform center level of the most dense pattern and the reproduction waveform center level of the least dense pattern of recorded data.

  As described above, in the DVD-RAM, a change in the recording mark area due to thermal interference is dealt with by adjusting the write strategy. As an adjustment procedure and method at this time, for example, there is a method disclosed in Japanese Patent Laid-Open No. 2000-36115. In this publication, a test pattern is recorded before actual user data is recorded, and a write strategy (pulse width) is adjusted. At this time, the test pattern uses the most dense pattern and the least sparse pattern of the modulation system to be used, and the pulse width is adjusted so that the difference between the center levels of these reproduction signals becomes zero.

  As described above, in DVD-RAM, as an evaluation index of a reproduction signal, the difference between the center level of the most dense pattern and the center level of the most sparse pattern is defined as asymmetry. By making this asymmetry below the standard value, the balance of the amplitude direction of the densest signal with respect to the envelope of the information reproduction signal is maintained, and the reproduction characteristics and compatibility of the information recording medium are improved. However, when information recording is densified, the influence of thermal interference increases, and the balance in the amplitude direction may be greatly lost not only in the close-packed pattern but also in other patterns. In such a case, it becomes difficult to reproduce information, and compatibility of the information recording medium is lost.

  Furthermore, although asymmetry is defined in DVD-RAM, there is a problem that the write strategy adjustment procedure for optimizing this asymmetry has not been clarified.

  Moreover, although the jitter of random data including the most dense pattern is used as an index for determining the write strategy, the recording of information is increased in density, and the reproduction signal processing method is different from the slice method such as PRML. When the method is used, it becomes difficult to measure the jitter of a signal including a close-packed pattern. Therefore, there is a problem that the write strategy cannot be determined using this jitter as an index.

  Japanese Patent Laid-Open No. 2000-36115, as a write strategy adjustment method using asymmetry, records test data of a combination pattern of the densest and the least sparse code and writes the write strategy, particularly the pulse, so that the center level of the reproduced signal is aligned. A method for adjusting the width is disclosed. However, even this method cannot cope with the problem of thermal interference caused by the above-described increase in density. Also, the correction method only corrects the pulse width uniformly, but in high-density recording with large thermal interference, it is difficult to adjust the asymmetry while forming the recording mark with high accuracy only by this correction. There's a problem.

  An object of the present invention is to provide an information recording method and an information recording apparatus for recording information on an information recording medium so that reproduction signal characteristics are good and compatibility is high.

  In order to achieve the above object, an information recording method according to an embodiment of the present invention is an information recording method for recording information on an information recording medium capable of recording and reproducing information, and is an integral multiple of a reference clock period T. And recording the information on the information recording medium, and reproducing the recorded information from the information recording medium. Calculating a first asymmetry using a difference between the reproduction signal center level of the 2T code and the reproduction signal center level of the 3T code, a reproduction signal center level of the 2T code, and a reproduction signal center level of the least-sparse code; And calculating the second asymmetry using the difference between them and the third asymmetry using the difference between the reproduction signal center level of the 3T code and the reproduction signal center level of the least-sparse code. That the method, as the first to third asymmetry is 15% or less, respectively, and a step of changing the pulse shape of the recording light.

  As described above, according to the present invention, a method for clearly evaluating the reproduction signal quality of an information recording medium, an information recording medium having good reproduction characteristics and high compatibility, an information recording / reproducing apparatus for recording information on the recording medium, And an information recording method are provided.

  Embodiments of the present invention will be described in detail with reference to the drawings. The following description is an embodiment of the present invention and does not limit the method and apparatus of the present invention.

  FIG. 1 shows a schematic diagram of a recording waveform of laser light and a track on which information is recorded in the information recording apparatus of the present embodiment. The recording waveform is roughly divided into a recording portion 001 and an erasing portion 002. If the recording medium is a phase change medium, the recording film is heated and rapidly cooled by a plurality of heating pulses, and amorphous recording marks 004 are formed on the recording track. Ideally, the front end position of the recording mark 004 is determined in proportion to the rising position of the heating pulse. Similarly, the rear end position of the recording mark 004 is determined in proportion to the falling position of the heating pulse.

  Accordingly, in order to move the front end position of the recorded mark backward, it is only necessary to shift the rising position of the heating pulse backward. The recording portion 001 is irradiated with a plurality of heating pulses. By changing the width of each pulse, the mark shape such as the horizontal width of the recording mark 004 can be controlled. In the erase portion 002, the recording light is kept at a constant level. As a result, the recording medium is maintained at the crystallization temperature and crystallizes. The portion 003 between the crystallized recording mark 004 and the recording mark 004 is called a space.

  FIG. 2 shows an embodiment of a write strategy which is a correspondence relationship between a recording waveform and a signal to be recorded. If the period of the reference clock is T, FIG. 2A shows a recording waveform for recording a 2T mark, and FIG. 2B shows a recording waveform for recording a 9T mark. In the erase portion 002, the power of the recording light is kept at Bp1. In the recording portion 001, the power of the recording light rises to Pp and then falls to the erasing power Bp2 or the erasing power Bp3 for cooling. In the recording portion 001, each pulse is divided into a first pulse 005, an intermediate pulse 006, and a final pulse 007 according to its function. The width of each pulse is defined by each variable of delay time Tsfp, Tefp, Tsmp, Temp, Tslp, Telp, and Tlc shown below with respect to the rising edge of the NRZI signal or the rising position of the reference clock. The number of intermediate pulses is determined by the length of the code to be recorded.

Tsfp: start pulse start time with respect to rising of NRZI signal,
Tefp: start pulse end time with respect to the rising edge of the NRZI signal,
Tsmp: intermediate pulse start time with respect to the reference clock,
Temp: each pulse width of the intermediate pulse,
Tslp: last pulse start time with respect to the reference clock,
Telp: end pulse end time with respect to the reference clock,
Tlc: Time during which the erasing power Bp2 is supplied after the last pulse Next, a method for evaluating the reproduction signal will be described.

  FIG. 3 shows a reproduction signal waveform, that is, an eye pattern, of user data (random data) recorded using the above write strategy. Here, the shortest code (mark or space) used for data modulation is 2T, and the longest code is 13T. The signal having the smallest amplitude in the eye pattern is a 2T mark and 2T space reproduction signal. Hereinafter, a continuous signal of 2T mark and 2T space is expressed as 2T pattern. Further, the highest level of the 2T pattern reproduction signal is defined as I2H, and the lowest level is defined as I2L. The next largest amplitude signal is a 3T mark and 3T space reproduction signal. Similarly to the 2T pattern, I3H and I3L are defined for the 3T pattern reproduction signal. The amplitude of the 3T pattern is defined as I3. On the other hand, the signal having the largest amplitude is a reproduction signal of 13T mark and 13T space. Similarly to the 2T pattern, I13H and I13L are defined for the reproduction signal of the 13T pattern. The amplitude of the 13T pattern is defined as I13.

Here, the definition of two asymmetry that is an evaluation index of the reproduction signal in the present embodiment will be described. Asymmetry 1: AS2T13T, which is the first asymmetry, is an asymmetry of a 2T pattern with respect to the envelope of the entire random data, and is defined as follows.

AS2T13T = {(I13H + I13L) / 2− (I2H + I2L) / 2}} / I13 × 100% (1)
The second asymmetry, asymmetry 2: AS2T3T, is an asymmetry of a 3T pattern and a 2T pattern that are considered to be particularly susceptible to discrimination, and is defined as follows.

AS2T3T = {(I3H + I3L) / 2− (I2H + I2L) / 2}} / I3 × 100% (2)
Here, (I13H + I13L) / 2 is the central level of I13, (I3H + I3L) / 2 is the central level of I3, and (I2H + I2L) / 2 is the central level of I2.

  Furthermore, the third asymmetry, asymmetry 3: AS3T13T, is a 3T pattern asymmetry with respect to the 13T pattern envelope, and is defined as follows.

AS3T13T = {(I13H + I13L) / 2− (I3H + I3L) / 2}} / I13 × 100% (3)
The asymmetry defined by the formula (1) has been used conventionally. On the other hand, in this embodiment, the asymmetry of formula (2) and formula (3) is newly defined. The asymmetry 2 defined by the equation (2) is a code of the shortest code that is particularly likely to cause an identification error and a code of the next length among the codes used in the modulation law, in this case, the signal levels of the 2T code and the 3T code. It can be used to evaluate the deviation. Here, the modulation law is a law applied when information is recorded on an optical disc, and the information is modulated into a signal having an integer multiple of T as shown in FIG. . For example, in a conventional DVD-ROM, 8-16 modulation is used as a modulation rule.

  The fact that asymmetry 2 is close to 0 means that the reproduction signals of 2T code and 3T code have an ideal relationship in the amplitude direction. Therefore, if this asymmetry 2 is close to 0, the identification error is low in an optical disc recorded with high density. In particular, the effect is high in an optical disc using an identification method using a plurality of identification threshold values in the amplitude direction such as a PRML (partial response maximum likelihood) identification method. Furthermore, a medium on which a signal with asymmetry 2 close to 0 is recorded is a highly compatible medium because the signal is close to the ideal state.

  Asymmetry 3 defined by equation (3) evaluates the difference in signal level between the longest code among the codes used in the modulation law and the longest code after the shortest code, here the 13T code and the 3T code. Can be used. In an optical disk that performs high-density recording, a 2T code signal, which is the densest code, has a very small amplitude and may be difficult to measure. On the other hand, the amplitude of the signal of the 3T code is sufficiently smaller than that of the 13T code, and the amplitude is larger than that of the signal of the 2T code. Therefore, if this asymmetry 3 is used for signal evaluation, the same effect as the asymmetry 1 which is the definition of conventional asymmetry can be obtained relatively easily. The most sparse code used for the measurement of asymmetry 1, 2, 3 is not limited to the 13T code, and a code of 8T or more can be used.

  Next, the measurement result representing the relationship between the asymmetry defined above and the error rate of the reproduction signal will be described.

  FIG. 4 shows an embodiment of an optical disk apparatus used for measurement. The optical pickup 46 performs focusing and tracking with a weak laser emission power for data reproduction by a servo circuit 49 and an actuator driver 47 under the control of the CPU 42 to generate a light beam spot on the recording track of the optical disc 40.

  This optical disk apparatus uses a PRML identification method for signal processing of the signal processing circuit 52. Further, in the evaluation index measurement circuit 48, in addition to asymmetry 1, asymmetry 2, and asymmetry 3, second harmonics, cancellation ratio, C / N (carrier / noise), modulation degree, error rate, estimated error rate described below, S1, S2, S3, etc. can be measured. The CPU 42 has a function of determining the write strategy from the value of the measured evaluation index according to the write strategy determination procedure described below and setting the recording waveform generation circuit 41. The test data storage device 43 can store test data as shown in FIGS. 14, 15, 17A and 19A, which will be described later. This test data is input to the recording waveform generation circuit 41 when the switch 45 is switched to the test data storage device 43 side by the CUP 42. The recording waveform generation circuit 41 outputs a recording signal having a waveform corresponding to the set write strategy. This recording signal is amplified by the LD driver 44 and drives a laser diode (not shown) provided in the optical pickup 46. As a result, a mark is recorded on the optical disk. The switch 45 is normally connected to the user interface 53, and the input user data is recorded on the optical disc.

  FIG. 5 shows measurement results of error rate (bER) of asymmetry 1, asymmetry 2 and the reproduction signal when the erasing power Bp1 is changed. At this time, all variables other than the erase power Bp1 in the write strategy are fixed. Therefore, changing the erase power Bp1 is equivalent to changing the Pp / Bp ratio, which is the ratio of the recording power Pp and the erase power Bp1. From the measurement results, it can be seen that asymmetry 1 and asymmetry 2 change in the positive direction as the erasing power Bp1 is increased. It can also be seen that the error rate of the reproduction signal is the best at Bp1 = 2.4 mW. Focusing on the asymmetry at this time, asymmetry 2 is almost 0, while asymmetry 1 is about 3%. Therefore, it can be said that the asymmetry 2 is an evaluation index that is more sensitive to the error rate of the reproduction signal than the asymmetry 1.

  Further, FIG. 6 shows error rate measurement results of asymmetry 1, asymmetry 2 and the reproduction signal when the time Tsfp is changed. At this time, all variables other than Tsfp in the write strategy are fixed. Therefore, increasing the time Tsfp is equivalent to shortening the width of the leading pulse. From the measurement results, it can be seen that as the time Tsfp is increased, the asymmetry changes in the negative direction. It can also be seen that the error rate of the reproduction signal is the best at time Tsfp = 1.15 [T]. Focusing on the asymmetry at this time, asymmetry 2 is almost 0, while asymmetry 1 is about 8%. Therefore, from this result, it can be said that asymmetry 2 is an evaluation index that is more sensitive to the error rate of the reproduction signal than asymmetry 1.

  Further, similar experiments were conducted for the times Telp and Tlc. From these results, it was concluded that the asymmetry 2 is an evaluation index that is more sensitive to the error rate of the recording / reproducing signal than the asymmetry 1. was gotten.

  From these results, it can be said that the asymmetry requires the following conditions with respect to the standard value (%) of asymmetry in order to keep the error rate of the reproduction signal below a specified value and maintain the compatibility of the information recording medium.

-Standard value A <Asymmetry 1 <Standard value B (4)
-Standard value C <Asymmetry 2 <Standard value D (5)
{Standard value B − (− Standard value A)} ≧ {Standard value D − (− Standard value C)}
... (6)
That is, it can be said that high compatibility can be realized if the information recording medium satisfies this condition. Furthermore, it is known from experimental experience that a highly compatible signal can be recorded when the standard values A and B are 5 to 15% and the standard values C and D are 3 to 15%.

  Next, the second harmonic, which is another evaluation index of the recording / reproducing signal, will be described. The second harmonic is a signal component that appears at twice the carrier frequency when an nT pattern, which is a pure tone signal such as an nT mark nT space (n is an integer), is recorded and reproduced. The large second harmonic indicates that the recorded signal has asymmetric distortion or the duty is shifted.

  Subsequently, the result of an experiment representing the relationship between the second harmonic and the error rate of the recording / reproducing signal will be described. FIG. 7 shows the measurement results of the second harmonic and the error rate of the recording / reproducing signal when the time Temp is changed. When the time Temp is 0.4 [T], the error rate of the recording / reproducing signal is the smallest. At this time, the second harmonic is also minimum, and it can be seen that the second harmonic is suitable as an evaluation index of the recording / reproducing signal.

  A description will be given of a write strategy determination method focusing on the above experimental results. FIG. 8 is a flowchart of the write strategy determination method according to the first embodiment of the present invention.

  In the first step (ST001), the initial values (Pp0, Bp10, Bp20, Bp30, Tsfp0, Tefp0, Tsmp0, Temp0, Tslp0, Telp0, Tlc0) are set. Further, the values of the erasing powers Bp21 and Bp31, the relational expressions of Bp21 and Bp31, the time Tefp1, Tslp1, or the relational expressions thereof are determined.

  In the second step (ST002), the value of the erase power Bp11 is determined. This value is determined by using the erasure ratio and the modulation degree of the signal as an index so that a sufficient margin can be secured between them. Here, the degree of modulation is a value obtained by normalizing the amplitude of a reproduction signal of information constituted by marks on a medium with a reference value such as a signal intensity obtained when the mirror surface is reflected. Further, as an index for improving the same effect as this, a jitter value when a pattern not including the closest code is recorded / reproduced may be used.

  In the third step (ST003), the value of the recording power Pp1 is determined. This value is determined so that the asymmetry value is equal to or less than the standard value using the signal asymmetry as an index. Further, as an index for improving the same effect, a signal error rate or an estimated bER proposed in the applicant's previous application (Japanese Patent Application No. P2002-69138) may be used.

  In the fourth step (ST004), times Tsfp1, Telp1, and Tlc1 are determined. This value is determined so that the asymmetry value is equal to or less than the standard value using the signal asymmetry as an index.

  In the fifth step (ST005), the time Temp1 is determined. This value is determined so that the second harmonic is sufficiently small using the second harmonic of the signal as an index. In addition, as an index for improving the same effect, the signal error rate, the estimated bER proposed in the applicant's previous application (Japanese Patent Application No. P2002-69138), or the asymmetry of a pure tone signal with a code of 5T or more is used. Also good.

  In the sixth step (ST006), a compensation table for times Tsfp and Telp that adaptively correspond to the pattern of the signal to be recorded is determined.

  In the seventh step (ST007), the value of the erase power Bp12 is determined. This value is determined using the signal error rate or estimated bER as an index.

  In the eighth step (ST008), the value of the recording power Pp2 is determined. This value is determined using the signal error rate or estimated bER as an index.

  In the ninth step (ST009), the compensation tables for times Tsfp and Telp adaptively corresponding to the signal pattern to be recorded again are updated.

  In the tenth step, the reproduction signal is evaluated based on the final evaluation index. Here, if the evaluation result is equal to or less than the specified value, the set value at this time is set as the final write strategy. If the evaluation result exceeds the prescribed value, the write strategy setting is resumed by going back the steps. As the final evaluation index, a signal error rate or an estimated bER is used.

  Next, a detailed write strategy determination method in each step will be described.

  The initial value of each variable in the first step (ST001) is a value specified in advance by the media manufacturer based on the media characteristics such as the thermal analysis result, and the manufacturer of the apparatus based on the recording / reproduction characteristics of the device. Or a value designated by the evaluator according to the characteristics of the medium based on past experience. These initial value information, medium information, and the like are recorded as physical format information in the lead-in area of the optical disk shown in FIG. 26, for example, and can be obtained by reproducing the information.

  Furthermore, in this step, Bp21, Bp31, which are values of erasing power Bp2, Bp3 for proceeding to the next step, or a relational expression is determined based on the initial value. There are two methods of determination. One is a method of fixing the erasing powers Bp2 and Bp3 with initial values in the following steps. In this case, the erasing powers Bp2 and Bp3 are not changed from the initial values in subsequent steps. Another method is a method of calculating the Bp10 / Bp20 ratio and the Bp10 / Bp30 ratio from the erase powers Bp10, Bp20, and Bp30 given as initial values, and fixing this ratio in the subsequent steps. In this case, when the erasing power Bp1 is changed in the subsequent steps, the erasing powers Bp2 and Bp3 are also changed accordingly. These two methods are selectively used depending on the characteristics of the medium.

    Similarly, the values of the times Tefp1, Tsmp1, Tslp1, or the relational expressions of Tef1, Tsfp1 are determined. There are two methods for determination. The first method is a method of fixing all values with initial values. Another method is to calculate the width of the first pulse (Tefp0-Tsfp0) and the width of the final pulse (Telp0-Tslp0) from the initial values, and fix this width in the subsequent steps. In this case, Tefp1 and Tslp1 are also changed as the times Tsfp1 and Telp1 are changed. These two methods are selectively used depending on the characteristics of the medium.

  In the second step (ST002), the erasing power Bp1 is determined so that the power margin of the erasing characteristic at the time of overwriting can be maximized and a sufficient degree of signal modulation can be secured. The values determined in the first step are used for values other than the erasing power Bp1.

  Here, the erase ratio is defined as follows as an evaluation index of the erase characteristic. The rate of decrease from the amplitude of the nT pattern before overwriting to the amplitude after overwriting when the mT pattern is overwritten on the signal of the nT pattern is defined as an nT overwrite (OW) mT erasure ratio. A method for determining the erase power Bp1 in the second step will be described below.

  FIG. 9 shows a flowchart of the first erasing power Bp11 determination method. In step ST101, the erase power Bp1a is determined by the following equation from the initial value Bp10 of the erase power Bp1.

Bp1a = (Bp10−A / 2) + n × (A / N) (7)
Here, A: evaluation range of Bp1, n: number of repetition steps, N: maximum number of repetition steps In step ST102, the nT pattern is overwritten on the same track 10 times. In step ST103, the amplitude information of the recorded and reproduced nT pattern is measured by a spectrum analyzer or the like, and the value is stored. In step ST104, the mT pattern is overwritten once on the same track as in step 102. In step ST105, the information recorded in the track is reproduced, the amplitude information of the reproduced nT pattern is measured by a spectrum analyzer or the like, and the value is stored. In step ST106, nTO. Is calculated from the ratio of the two amplitude information stored in step ST103 and step ST105. W. Calculate and store mT erasure ratio. If n ≦ N (Yes in step ST107), the flow returns to step ST101, the erase power Bp1a is increased by A / N, and steps ST102 to ST107 are executed again. In this way, steps ST101 to ST106 are repeated while increasing the erase power Bp1a by A / N until n = N.

  At this time, the nTO. W. When the mT elimination ratio is plotted, a curve as shown in FIG. 10 is obtained. Here, the evaluation of the erasing characteristics is performed in order from the lowest power. In step ST108, a predetermined nTO. W. Two powers mTBp1H and mTBp1L which are intersections with the standard threshold of the mT erasure ratio are determined. Further, the erasing power Bp11 is determined using the following equation, and this is determined as the value of the erasing power Bp1.

Bp11 = (mTBp1H + mTBp1L) / 2 (8)
Here, m is the closest code used for the modulation law, and n is the longest code satisfying n ≠ m × 2 × k (k: natural number) among the codes used for the modulation law.

  As the second erasing power Bp11 determination method, as shown in FIG. W. In addition to mT erasure ratio, nTO. W. The (m + 1) T erase ratio may be measured to determine the erase power Bp11.

Bp11 = ((m + 1) TBp1H + mTBp1L) / 2 (9)
As a third erasing power Bp11 determination method, there is a method of evaluating a signal modulation degree together with an erasing ratio. In this determination method, as in the first determination method, the power margin of the erase characteristic is measured. Further, overwriting of the nT pattern is performed 10 times while changing the erasing power Bp1a in the same order, and the degree of signal modulation or C / N is measured. The measurement results are shown in FIG. Here, from the erasing characteristics calculated in FIG. 10 or FIG. 11 and the result of FIG. 12, the erasing power Bp1a at which the erasing rate is highest in the range where the decrease in the modulation degree is within 1 dB from the saturated portion is taken as the value of the erasing power Bp11 decide.

  As another method, nTO. W. There is a method using jitter and bER in addition to the mT erasure ratio.

  As the fourth erasing power Bp11 determination method, the pure tone jitter of the kT pattern and the (m + 1) T pattern is measured in the same order as in the first determination method, while changing the erasing power Bp1a, and the most jitter power is determined. The erasing power Bp1 is determined so that the margin becomes larger, and this is set as the value of the erasing power Bp11 to complete the determination process. Here, k is a least-sparse code used for the modulation law.

  In the third step (ST003), the recording power Pp is determined so that the asymmetry of the reproduction signal is less than the standard value. Also in this step, as in the second step, the test data is recorded and the evaluation index is measured while the recording power Pp is changed in order from low power to high power. Here, the values determined in the second step are used as the values of the erasing powers Bp1, Bp2, and Bp3. As the pulse width, the value determined in the first step is used.

  Asymmetry evaluation index in the third step, asymmetry 1, asymmetry 2, and asymmetry 3 defined above can be used. Further, since detailed asymmetry correction is performed again in the fourth step, in this step, for example, only asymmetry 1 or asymmetry 3 for adjusting the overall balance may be corrected.

  In this case, asymmetry is measured by, for example, recording random data, and detecting the values of I13H, I13L, I2H, and I2L shown in FIG. 3 from the A / D conversion result and the decoding result of the reproduced signal waveform, This can be done by performing the calculation using the above equation (1).

  If it is difficult to directly measure asymmetry, the method shown in FIG. 13 can be used. The signal shown in FIG. 13 is a signal to which duty feedback is applied so that the center of the signal automatically becomes the slice level SL. The high level A1 and low level A2 of this signal are measured to obtain the following value S1.

S1 = {(A1-SL) + (A2-SL)} / (A1-A2)
... (10)
By correcting this value to 0, it is possible to obtain substantially the same effect as when asymmetry 1 is set to 0. This method can also be applied to the case where the slice level SL is 0, that is, a DC cut signal. As test data to be recorded at this time, random data similar to user data may be used. For example, data combining two types of patterns for measuring asymmetry as shown in FIG. 14, hT and kT may be used. Here, h is the most dense code and k is the least sparse code.

  Also, the hT pattern and kT pattern as shown in FIG. 15 are recorded and reproduced independently as test data, respectively, and the center voltage of the hT pattern and kT pattern is measured, and then this difference ΔV is used as an evaluation index. Even if this is corrected to 0, the same effect as that of setting asymmetry 1 to 0 can be obtained.

  FIG. 16A shows the state of change in the set value of the recording power Pp obtained in the third step and the evaluation index (asymmetry 1, S, ΔV). The values PpH and PpL of the recording power Pp at the intersection of the upper and lower limits of the standard value and the measured value are calculated from FIG. 16A, and the recording power Pp is determined according to the following equation.

Pp = (PpH + PpL) / 2 (11)
Further, similar results can be obtained by plotting the value obtained by taking the absolute value of asymmetry 1 as an evaluation index as shown in FIG.

  Alternatively, the value may be determined as the recording power Pp when the standard value is satisfied without using Equation (11).

  In the fourth step (ST004), times Tsfp1, Telp1, and Tlc1 are determined so as to further correct the symmetry of the reproduction signal. In this step, for example, the test data is recorded and the evaluation index is measured while changing the value of the time Tsfp from a large value to a small value in order. Here, the value determined in the third step is used as the value of the recording power Pp, and the value determined in the second step is used as the values of the erasing powers Bp1, Bp2, and Bp3. As the pulse width, the value determined in the first step is used.

  Asymmetry 1 and asymmetry 2 defined above can be used as the asymmetry evaluation index in the fourth step. Further, in this step, detailed asymmetry correction can be performed, and rough correction is completed in the third step. Therefore, for example, only the highly sensitive asymmetry 2 is corrected as an evaluation index here. It may be.

  In this case, asymmetry is measured by, for example, detecting the values of I3H, I3L, I2H, and I2L from the A / D conversion result and the decoding result of the reproduced signal waveform, and performing the calculation using the above equation (2). It becomes possible.

  On the other hand, when it is difficult to directly measure asymmetry, the method shown in FIG. 17 can be used. In this case, a pattern in which qT and (q + 1) T marks and spaces appear at random as shown in FIG. 17A is used as test data. However, q is a dense code. Further, the signal shown in FIG. 17B is a signal obtained by recording the signal of FIG. 17A and applying duty feedback so that the reproduction signal at the time of reproduction is centered at the slice level SL. The high level B1 and low level B2 of this signal are measured, and the following value S2 is obtained.

S2 = {(B1-SL) + (B2-SL)} / (B1-B2)
(12)
By correcting this value to 0, it is possible to obtain substantially the same effect as when asymmetry 2 is set to 0. Further, this method can be applied to a case where the slice level is 0, that is, a DC cut signal.

  In addition, the qT pattern and the (q + 1) T pattern are recorded and reproduced independently as test data, respectively, the center voltages of the qT pattern and the (q + 1) T pattern are measured, and the difference ΔV is used as an evaluation index. Even if this is corrected so as to be 0, the same effect as when asymmetry 2 is set to 0 can be obtained.

  FIG. 18A shows the set values of the times Tsfp, Telp, and Tlc obtained in the fourth step and the change state of the evaluation indices (asymmetry 2, S2, ΔV). For example, values TsfpH and TsfpL of the time Tsfp at the intersection of the upper and lower limits of the standard value and the measured value are calculated from FIG. 18A, and the time Tsfp is determined according to the following equation.

Tsfp1 = (TsfpH + TsfpL) / 2
... (13)
Alternatively, when the standard value is satisfied without using Equation (13), the value may be determined as the recording power Pp.

  As another evaluation index, a signal error rate or an estimated bER may be used. Also in this case, if the signal is evaluated while changing the time Tsfp from the largest value to the smallest value in the same manner as the asymmetry, a graph as shown in FIG. 18 is obtained. Here, the value of the intersection with the standard threshold for the evaluation index is defined as TsfpH and TsfpL. Tsfp1 is determined by equation (13).

  Times Telp and Tlc are determined in a similar manner.

  In the fifth step (ST005), the time Temp1 is determined so that the distortion of the reproduction waveform of the long mark becomes small. In the fifth step, test data is written on a trial basis and an evaluation index is measured while changing the time Temp from a small value to a large value. Here, the value determined in the third step is used as the value of the recording power Pp, and the value determined in the second step is used as the values of the erasing powers Bp1, Bp2, and Bp3. The values determined in the first step are used for the times Tefp, Tsmp, and Tslp, and the values determined in the fourth step are used for the times Tsfp, Telp, and Tlc.

  The second harmonic can be used as the evaluation index in the fifth step. The test data uses an sT pattern. Here, s is a least-sparse code or a relatively long code, for example, a code of 5T or more.

  If it is difficult to directly measure the second harmonic, the sT pattern may be recorded and reproduced as shown in FIG. 19, and S3 may be evaluated according to the following equation.

S3 = {(C1-SL) + (C2-SL)} / (C1-C2)
(14)
By correcting this value to 0, it is possible to obtain substantially the same effect as reducing the second harmonic.

  FIG. 20 shows the set value of the time Temp1 obtained in the fifth step and the state of change of the evaluation index. Here, FIG. 20A shows the case where S3 is used as the evaluation index, and FIG. 20B shows the case where the second harmonic is used as the evaluation index. From FIGS. 20A and 20B, the upper and lower limits of the evaluation index or the time TempL and TemppH of the intersection of the threshold and the measured value are calculated, and Temp is determined according to the following equation.

Temp1 = (TempH + TempL) / 2 (15)
Alternatively, the value may be determined as Temp1 when the standard value is satisfied without using Equation (15).

  The signal error rate or estimated bER may be used. Also in this case, if the signal is evaluated while changing the time Temp from a small value in order to a large value, a graph as shown in FIG. 20A is obtained.

  In the sixth step (ST006), a compensation table is determined. In this step, the times Tsfp and Telp are adaptively set in accordance with the combination of consecutive spaces and mark codes or the arrangement of marks and spaces so as to remove the non-linearity of the reproduction signal, that is, the difference from the ideal waveform. The table shown in FIG. 21 is for setting values of mark times Tsfp and Telp to be recorded corresponding to the immediately preceding space or the immediately following space, and is called a compensation table.

  In the seventh step (ST007), a random signal is recorded, and fine adjustment of Bp1 is performed using an error rate of the reproduction signal that is the final evaluation index or an evaluation index highly correlated therewith, for example, estimated bER. The random signal is overwritten 10 times while changing the value of Bp1, and the evaluation index is evaluated each time. Also, the value of Bp1 is increased in order from the smallest. FIG. 22 shows the measurement results. From the curve in FIG. 22, Bp12L and Bp12H that are intersections with the standard threshold are determined, and Bp12 is determined from the following equation.

Bp12 = (Bp12H + Bp12L) / 2 (16)
In the eighth step (ST008), a random signal is recorded, and fine adjustment of the recording power Pp is performed using an error rate of the reproduction signal as a final evaluation index or an evaluation index highly correlated with the error rate, for example, estimated bER. The random signal is overwritten 10 times while changing the value of the recording power Pp, and the evaluation index is evaluated each time. Further, the value of the recording power Pp is increased in ascending order. FIG. 23 shows the measurement results. From the curve in FIG. 23, Pp2L that is an intersection with the standard threshold is determined, and Pb2 is determined from the following equation.

Pp2 = Pp2L × α (17)
Here, α is a coefficient determined by the characteristics of the medium, and is a value recorded in the physical format information of the lead-in area 50 or the like.

  In the ninth step (ST009), the compensation tables for times Tsfp and Telp are recalculated. In this step, the compensation amount is determined in the same manner as in the sixth step.

  In a tenth step (ST010), an error rate of a random signal recorded using the finally determined write strategy and an evaluation index correlated therewith are measured. If this value is better than the standard value, the write strategy determined in the above step is set as the final determined value of the write strategy. If the evaluated value is worse than the standard value, the process returns to the previous step and the determination of the write strategy is resumed. If the target optical disk is a land-and-groove recording optical disk, the same process is performed for the land and groove.

  The write strategy determination method according to the present embodiment does not use the jitter of the signal including the closest code as an evaluation index at any stage. Therefore, it is possible to adapt to high-density recording in which the signal amplitude of the most dense code is small and binarization and jitter measurement cannot be performed by the slice method. Also, signal asymmetry is reduced by adjusting both the recording power and the pulse width during the process. As a result, a high effect can be obtained even when applied to an identification method that uses information in the amplitude direction, such as a PRML identification method.

  In addition, a more ideal signal can be recorded by using asymmetry 2 which is the asymmetry of the next dense code and the closest code defined in the present application. In particular, since the finer adjustment is possible by changing the pulse width than by changing the recording power, the recording power is evaluated and determined by asymmetry for balancing the entire random signal, and the pulse width is determined by asymmetry 2. Thus, it is possible to make an adjustment that balances the overall balance and the balance of the signal of the closest code and the next code for any medium.

  Further, by providing a process for adjusting the time Temp, which is the width of the intermediate pulse, by evaluating the second harmonic and the error rate, it is possible to remove the asymmetry of the relatively long recording mark. As a result, a high effect can be obtained even when applied to an identification method that uses information in the amplitude direction, such as a PRML identification method.

  Also, before determining the compensation table corresponding to the arrangement of marks and spaces having various lengths as in step ST006, asymmetry and asymmetry of the mark before and after are removed, the compensation table is determined. In addition, it is possible to determine the compensation table normally without converging on non-ideal results or divergence. That is, it is possible to determine an optimal pulse shape in a shorter time and more simply.

  For this reason, by using this write strategy determination method, it is possible to record information with good reproduction characteristics and high compatibility even with respect to an optical disc that performs high-density recording.

  Next, a second embodiment of the write strategy determination method will be described. FIG. 24 shows a flowchart of the present embodiment. In this embodiment, the second and third steps (ST202, ST203) are different from the second and third steps (ST002, ST003) in the first embodiment, and the other steps are the same.

  In the first step (ST201), the initial values are set for all the parameters of the recording power Pp, the erasing power Bp1, Bp2, Bp3, the time Tsfp, Tefp, Tsmp, Temp, Tslp, Telp, and Tlc, as in the above-described step ST001. (Pp0, Bp10, Bp20, Bp30, Tsfp0, Tefp0, Tsmp0, Temp0, Tslp0, Telp0, Tlc0) are set. Further, the values of the erasing powers Bp21 and Bp31, the relational expressions of the erasing powers Bp21 and Bp31, Tefp1, Tslp1, or the relational expressions thereof are determined.

  In the second step (ST202), the value of the recording power Pp1 is determined. This value is determined based on the amplitude, C / N, or modulation degree of the signal. At this time, a signal is recorded on the adjacent track, and the recording power Pp1 in consideration of crosstalk and cross erase can be determined.

  In the third step (ST203), the value of the erase power Bp11 is determined. This value is determined so that the asymmetry value is equal to or less than the standard value using the signal asymmetry as an index. Further, a signal error rate or estimated bER may be used as an index for improving the same effect.

  In the fourth step (ST204), times Tsfp1, Telp1, and Tlc1 are determined. This value is determined so that the asymmetry value is equal to or less than the standard value using the signal asymmetry as an index.

  In the fifth step (ST205), the time Temp1 is determined. This value is determined so that the second harmonic is sufficiently small using the second harmonic of the signal as an index. Further, as an index for improving the same effect, signal error rate, estimated bER, or asymmetry of a pure tone signal having a code of 5T or more may be used.

  In a sixth step (ST206), Tsfp1 and Telp1 compensation tables adaptively corresponding to the signal pattern to be recorded are determined.

  In the seventh step (ST207), the value of the erase power Bp12 is determined. This value is determined using the signal error rate or estimated bER as an index.

  In the eighth step (ST208), the value of the recording power Pp2 is determined. This value is determined using the signal error rate or estimated bER as an index.

  In the ninth step, the Tsfp1 and Telp1 compensation tables adaptively corresponding to the signal pattern to be recorded again are updated.

  In the tenth step (ST210), the reproduction signal is evaluated based on the final evaluation index. Here, if the evaluation result is equal to or less than the specified value, the set value at this time is set as the final write strategy. If the evaluation result exceeds the prescribed value, the write strategy setting is resumed by going back the steps. As the final evaluation index, a signal error rate or an estimated bER is used. In this way, the write strategy determination process according to the second embodiment is completed.

  In the first embodiment described above, the erasing power Bp1 is determined mainly with respect to the erasing characteristics, and the recording power Pp is determined mainly with respect to asymmetry. Therefore, in some cases, the signal modulation degree (amplitude) is not ideal. There was a case of convergence. Depending on the characteristics of the medium, there is a medium with a relatively large erase characteristic margin and a narrow modulation degree margin. In addition, the degree of signal modulation may be defined due to the effects of crosstalk and cross erase of signals recorded on adjacent tracks. In such a case, as shown in the second embodiment, the modulation level of the signal is determined by adjusting the recording power Pp first, and then the erasing power Bp1 is determined. Further, the signal asymmetry is greatly affected by the ratio of the erasing power Bp1 and the recording power Pp. Therefore, the asymmetry can be accurately reduced by fixing the recording power Pp and changing the erasing power Bp1.

  Next, a third embodiment of the write strategy determination method will be described. FIG. 25 shows a flowchart of the write strategy determination method. In this embodiment, the second and third steps (ST302, ST303) are different from the second and third steps (ST002, ST003) in the first embodiment, and the other steps are the same.

  In the first step (ST301), as in step ST001 described above, the initial values (all the parameters of the recording power Pp, the erasing power Bp1, Bp2, Bp3, the time Tsfp, Tefp, Tsmp, Temp, Tslp, Telp, and Tlc are set ( Pp0, Bp10, Bp20, Bp30, Tsfp0, Tefp0, Tsmp0, Temp0, Tslp0, Telp0, Tlc0). Further, the values of the erasing powers Bp21 and Bp31, the relational expressions of the erasing powers Bp21 and Bp31, Tefp1, Tslp1, or the relational expressions thereof are determined.

  In the second step (ST302), the value of Pp / Bp11 is determined. This value is determined so that the asymmetry value is equal to or less than the standard value using the signal asymmetry as an index.

  In the third step (ST303), the value of the recording power Pp1 is determined. At the same time, the value of the erasing power Bp11 is determined from Pp / Bp11. This value is determined on the basis of the signal amplitude, C / N or modulation factor and erasure ratio. A signal error rate or estimated bER may be used as an index for improving the same effect. At this time, a signal is recorded on the adjacent track, and the recording power Pp1 in consideration of crosstalk and cross erase can be determined.

  In the fourth step (ST304), times Tsfp1, Telp1, and Tlc1 are determined. This value is determined so that the asymmetry value is equal to or less than the standard value using the signal asymmetry as an index.

  In the fifth step (ST305), the time Temp1 is determined. This value is determined so that the second harmonic is sufficiently small using the second harmonic of the signal as an index. Further, as an index for improving the same effect, signal error rate, estimated bER, or asymmetry of a pure tone signal having a code of 5T or more may be used.

  In the sixth step (ST306), compensation tables for Tsfp1 and Telp1 that adaptively correspond to the pattern of the signal to be recorded are determined.

  In the seventh step (ST307), the value of the erase power Bp12 is determined. This value is determined using the signal error rate or estimated bER as an index.

  In the eighth step (ST308), the value of the recording power Pp2 is determined. This value is determined using the signal error rate or estimated bER as an index.

  In the ninth step (ST309), the compensation table for Tsfp1 and Telp1 adaptively corresponding to the pattern of the signal to be recorded again is updated.

  In the tenth step (ST310), the reproduction signal is evaluated based on the final evaluation index. Here, if the evaluation result is equal to or less than the specified value, the set value at this time is set as the final write strategy. If the evaluation result exceeds the prescribed value, the write strategy setting is resumed by going back the steps. As the final evaluation index, a signal error rate or an estimated bER is used. In this way, the write strategy determination process according to the third embodiment is completed.

  In a general medium, the signal asymmetry is greatly influenced by the ratio of the erasing power Bp1 and the recording power Pp. However, when the ratio of the erasing power Bp1 and the recording power Pp is kept constant, the absolute value changes. Also has a feature that the asymmetry does not change much.

  In the first embodiment, after determining the erasing power Bp1 based on the erasing characteristics, the recording power Pp is determined by asymmetry. For this reason, in some cases, the recording power Pp becomes a relatively large value, the mark to be recorded becomes large, and there is a possibility that the erasing characteristic is deteriorated with the previously determined erasing power Bp1. On the other hand, in the third embodiment, the ratio between the erasing power Bp1 and the recording power Pp is determined first, and then the absolute value is changed while the ratio is maintained, so that the modulation degree, erasing ratio, crosstalk, etc. The most balanced light strategy for cross erase can be determined.

  The signal asymmetry is highly dependent on the ratio of the first and second levels, the erasure characteristics depend on the erasing power, the modulation factor depends on the recording power, and the jitter of a single frequency signal depends on both powers. I know you will.

  To optimize asymmetry, adjust the ratio of erase power to recording power, and optimize the absolute value of the first and second levels to optimize the erase characteristics, modulation depth, or single frequency signal jitter. By determining the value, it is possible to determine the optimum pulse level with higher accuracy in a shorter time.

The schematic diagram which shows the track | truck where the recording waveform and information of the laser beam were recorded as a mark. The figure for demonstrating the write strategy which shows the correspondence of the NRZI signal waveform which shows information, and a recording waveform. The figure which shows the reproduction signal waveform, ie, eye pattern, of the user data recorded using the write strategy. The figure which shows one Example of the optical disk apparatus based on this invention. The figure which shows the asymmetry 1 and the asymmetry 2 at the time of changing erasing power Bp1, and the error rate (bER) measurement result of a reproduction signal. The figure which shows the error rate measurement result of the asymmetry 1, the asymmetry 2, and the reproduction | regeneration signal at the time of changing time Tsfp. The figure which shows the result of the measurement of the secondary harmonic at the time of changing Temp and the error rate of a recording / reproducing signal. The flowchart which shows the write strategy determination method which concerns on a 1st Example. The flowchart which shows the 1st erasing power Bp11 determination method. Erase power Bp1 and nTO. W. The figure which shows mT erasure | elimination ratio as a relationship. The figure for demonstrating the 2nd erasing power Bp11 determination method. The figure for demonstrating the 3rd erasing power Bp11 determination method. The figure which shows the other method for measuring an asymmetry. The figure which shows the other method of measuring an asymmetry. The figure which shows the other method of measuring an asymmetry. The figure which shows the setting value of recording power Pp, and the state of a change of an evaluation parameter | index (asymmetry 1, S, (DELTA) V). The figure which shows the other method of measuring an asymmetry. The figure which shows the setting value of time Tsfp, Telp, and Tlc, and the state of a change of an evaluation parameter | index. The figure which shows the other method of measuring a secondary harmonic. The figure which shows the setting value of time Temp1, and the state of a change of an evaluation parameter | index. The figure which shows the compensation table for setting the value of the time Tsfp of the mark recorded corresponding to the space immediately before or the space | interval immediately after, and Telp. The figure which shows the relationship between erasing power Bp1 and an evaluation parameter | index (error rate, estimated bER). The figure which shows the relationship between recording power Pp and an evaluation parameter | index (error rate, estimated bER). The flowchart which shows the 2nd Example of the write strategy determination method. The flowchart which shows the 3rd Example of the write strategy determination method. The figure which shows the structure of an optical disk simply.

Claims (2)

An information recording method for recording information on an information recording medium capable of recording and reproducing information,
According to information composed of a plurality of codes having a time width that is an integral multiple of the reference clock period T, modulating the recording light in pulses, and recording the information on an information recording medium;
Reproducing the recorded information from the information recording medium;
Calculating a first asymmetry using a difference between a reproduction signal center level of 2T code and a reproduction signal center level of 3T code;
Calculating a second asymmetry using a difference between the reproduction signal center level of the 2T code and the reproduction signal center level of the least-sparse code;
Calculating a third asymmetry using a difference between the reproduction signal center level of the 3T code and the reproduction signal center level of the least-sparse code;
Changing the pulse shape of the recording light so that the first to third asymmetry values are each 15% or less;
An information recording method characterized by comprising: An information recording apparatus for recording information on an information recording medium capable of recording and reproducing information,
Means for modulating recording light in a pulsed manner in accordance with information composed of a plurality of codes having a time width that is an integral multiple of the reference clock period T, and recording the information on an information recording medium;
Means for reproducing recorded information from the information recording medium;
Means for calculating the first asymmetry using the difference between the reproduction signal center level of the 2T code and the reproduction signal center level of the 3T code;
Means for calculating a second asymmetry using the difference between the reproduction signal center level of the 2T code and the reproduction signal center level of the least-sparse code;
Means for calculating a third asymmetry using a difference between the reproduction signal center level of the 3T code and the reproduction signal center level of the least-sparse code;
Means for changing the pulse shape of the recording light such that the first to third asymmetry values are each 15% or less;
An information recording apparatus comprising:

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