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Researchers Submit Patent Application, "Information Recording Method, Information Recording Apparatus, Information Recording Medium, and Medium...

February 11, 2014



Researchers Submit Patent Application, "Information Recording Method, Information Recording Apparatus, Information Recording Medium, and Medium Estimating Method", for Approval

By a News Reporter-Staff News Editor at Information Technology Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors MORIMOTO, Yoshitaka (Kodaira, JP); ETO, Soichiro (Tokyo, JP); WATANABE, Koichi (Hachioji, JP), filed on May 10, 2013, was made available online on January 30, 2014.

The patent's assignee is Hitachi-LG Data Storage, Inc.

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to an information recording method which determines a recording waveform of a light beam at a time of recording information by irradiating light to an optical disc and records the information using the light beam, an information recording apparatus which records information on an optical information recording medium, an information recording medium and a medium evaluating method.

"Currently, as an optical disc that is an optical information recording medium, a CD (Compact Disc), a DVD (Digital Versatile Disc), a BD (Blu-ray Disc), a BDXL.TM., and the like have been commercialized and widely spread in use. These optical discs include various kinds of discs such as a ROM (Read Only Memory) type which is dedicated for reproduction, a R (Recordable) type which is a re-recordable type, a RE (Rewritable) type which is a rewritable type.

"A laser beam is irradiated to the optical disc to perform information recording and reading on the optical disc. An area is formed in which a state of a recording film material is changed by heat of the laser beam, whereby information recording is performed. An area where the state is changed is referred to as a mark, and another area where the state is not changed is referred to as a space. As the recording film, a phase-change material, an organic dye, and an alloy and an oxide of inorganic material are used. A mark edge recording is used as an encoding method in the CD, the DVD, the BD, and the BDXL.TM., and information is recoded as an edge position of a mark.

"In the recording, it is necessary to control the heat that is generated by irradiation of a laser beam so as to form a mark of any length in the recording film. Therefore, the laser beam at a time of recording is controlled in various waveforms depending on a mark length to be formed. FIGS. 1A and 1B are examples of laser emitting waveforms to be used when marks of 2T to 5T (T is a channel bit length) are formed. These are recording waveforms to be used in BDXL.TM. specification, FIG. 1A is referred to as an N-1 strategy, and FIG. 1B is referred to as a castle strategy. In the N-1 strategy, a mark of a length of NT is recorded using (N-1) pulses. The first pulse in a pulse train is referred to as a first pulse, and the last pulse in the pulse train is referred to as a last pulse. The pulse between the first pulse and the last pulse is referred to as a multi-pulse. In a case of 4T mark, the number of the multi-pulse is one. The number of the multi-pulse is increased by one, as the subsequent mark length is increased by 1T. A pulse of 2T mark has only the first pulse. A pulse of 3T mark has only the first pulse and the last pulse. Both the pulses of 2T mark and 3T mark do not respectively include the multi-pulse. On the other hand, in the castle strategy, each waveform is mainly configured of either only first pulse or both of the first pulse and the last pulse without the multi-pulse, and the waveform between the first pulse and the last pulse is kept at a constant power. Since a pulse having a short width is not used in the waveform, the waveform is suitable for recording at high speed.

"With respect to a laser beam power in each strategy, the N-1 strategy uses four kinds of powers, that is, a recording power (Pw), a space power (Ps), a bias power (PBW), and a cooling power (Pc), whereas the castle strategy uses four kinds of powers, that is, an intermediate power (Pm), in addition to the Pw, the Ps, and the Pc. Here, in the RE type optical disc, the Ps is referred to as an erase power (Pe). The Pw has a maximum power level in a pulse train, and is used to mainly cause a state change by inputting energy to the recording film. The Ps is the power level to be irradiated to a part that becomes a space, and is used mainly in preheating to form a next mark. The Pe in the RE type optical disc plays a role to return the mark that is already recorded to a space, in addition to the preheating. The Pc is the power level right after the last pulse, and mainly plays a role to block heat diffusion to the subsequent mark recording part in the R type optical disc, and a role to rapidly cool the recording film in order to form the mark in the RE type optical disc.

"Although the recording of the optical disc is performed using the aforementioned recording waveforms, the recording waveforms are different depending on the type of the optical disc and the recording layer. This is resulted from that the material of the recording film and the formation mechanism of a mark are different. Therefore, the recording waveform is prepared for each type of the optical disc and recording layer. As indexes for defining the recording waveform, there are dTtop, Ttop, TMP, dTLP, TLP, dTc, dTS, and dTE for defining the pulse width, and the like, in addition to the aforementioned various power levels Pw, Pm, Ps, Pe, Pc, and PBW. The dTtop indicates the start end position of the first pulse, the Ttop indicates the time width of first pulse, the TMP indicates the time width of the multi-pulse, the dTLP indicates the start end position of the last pulse, the TLP indicates the time width of the last pulse, the dTS indicates the start position of the Ps, and the dTE indicates the start position of the Pe. These parameters are set in 1/16 unit of the channel bit according to the BD specification, and are set in 1/32 unit of the channel bit according to BDXL.TM. specification.

"The recording waveform in each optical disc and the recording layer is mainly prepared by an optical disc maker, and the determined recording waveform is converted into the index of the recording waveform and is recorded in the management region of the optical disc. Accordingly, in a case of recording information on the optical disc using a drive that is an optical information recording and reading apparatus, the drive obtains the recording waveform of the optical disc from management information on the optical disc, and thus starts the recording without adjustment of the recording waveform. Here, even in the same type of optical disc, there may be a difference in an optimum recording waveform for each optical disc, especially, in a power level of a laser due to variations in production. Further, even in a case of using the same optical disc, the optimum recording may not be performed in the same recording waveform, especially in the power level of the same laser, due to the individual differences of drives. In order to correspond to the individual differences of the optical discs and the drives, the drive has means for adjusting the recording waveform. As one of adjustment methods, there is a method to optimize the laser power level called OPC (Optimum Power Control). This enables to realize a proper recording without being affected by the individual differences of the optical discs and the drives.

"The adjustment of the recording waveform in the aforementioned optical disc maker and the drive is performed by evaluating the quality of the recording signal in each recording waveform. As evaluation indexes of the recording signal, there are a Jitter of evaluating the aged fluctuation in the mark edge, bER (bit Error Rate) of evaluating the decoded result of a reading signal, SER (Symbol Error Rate), and the like. Further, as an index of evaluating the reading signal quality based on PRML to be used in reading signal processing of BDLX.TM., i-MLSE (Integrated-Maximum Likelihood Sequence Error Evaluation) is disclosed in Pamphlet of International Publication WO2010-001588. i-MLSE is an index of statistically evaluating an error amount of a target waveform and a reading signal waveform that are predicted at a time of decoding. Besides this, SbER (Simulated bit Error Rate) is disclosed in JP-A-2004-253114. SbER is an index of quantifying an estimation value of an error probability from an error amount of the target waveform and the reading signal waveform. Furthermore, L-SEAT (run-length-Limited Sequence Error for Adaptive Target) which is an index of evaluating a shift of an edge position of a recording mark is disclosed in US 2010-0260025. L-SEAT is a value that is obtained by calculating the error amount of the reading signal waveform and Left target waveform and Right target waveform that are assumed in a case where the edge is shifted in the left or right with respect to the target waveform, before and after each edge of each mark length. Since the shift amount of the mark edge can be evaluated using L-SEAT, L-SEAT is suggested as an adjustment index of the recording waveform in BDXL.TM. specification."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Here, a signal recorded on the optical disc is agedly deteriorated. For this reason, it is necessary to adjust a recording waveform in order to suppress the deterioration in a recording signal on an optical disc. In order to confirm a difference in signal deterioration characteristics depending on the recording waveform, in the optical disc of BDXL.TM. specification, two types of recording signal are prepared such that their i-MLSE are equivalent to each other immediately after the recording. The recording signals are prepared based on the castle strategy in FIG. 1B, and the parameter values thereof are illustrated in FIGS. 2A and 2B. The main difference between recording signal A (Write strategy-A: WS-A) and the recording signal (WS-B) is signal modulation. The signal modulation for A and B is 50% and 60%, respectively. FIG. 3 shows a result of measuring the deterioration characteristic after a thermostatic oven acceleration test is performed with respect to the signal recorded using the recording waveform. The thermostatic oven acceleration test is a testing which utilizes aggravated condition of heat, humidity, etc. to speed up the normal aging processes of the optical disc. agedFrom FIG. 3, it is found that immediately after the recording, i-MLSE in two recording signals are almost same, but the deterioration rate of the recording signal A is faster than that of the recording waveform B. Due to the fact, it found difficult to determine the optimal recording signal enabling to suppress the deterioration of the optical disc for the long term storage by using i-MLSE. It is resulted from that i-MLSE is not an index reflecting the deterioration characteristic of the signal. In addition, since indices such as L-SEAT, SbER, bER, SER, and Jitter cannotreflect the deterioration characteristic it is apparent that it is not possible to determine the recording waveform which suppresses the deterioration of the recording signal by adjusting the recording waveform based on the indices. From the above, in a case of using the adjustment index of the recording waveform in the related art, it is difficult to determine the recording waveform which suppresses the deterioration of the recording signal.

"Therefore, in an agedaged deterioration of a recording signal, the adjustment of the recording waveform is performed based on the fluctuation amount of the mark edge position, focused on that the fluctuation of the mark edge position is increased. Specifically, the recording waveform is adjusted such that the fluctuation amount becomes minimum or a threshold value or less.

"Hereinafter, indexes reflecting deterioration characteristics of an optical disc are described.

"In order to describe deterioration cause of the optical disc, a thermostatic oven acceleration test is performed, and the change in the recording mark size, the movement (shift) of the average position of the mark edge, and the fluctuation of the mark edge position according to the agedaged deterioration are measured. The result is illustrated in FIG. 4. In FIG. 4, .beta. is an index of evaluating a ratio of the mark length of a short mark and that of a long mark. Further, L-SEAT shift and L-SEAT jitter are indexes disclosed in US2010/0260025, and respectively represent indexes for evaluating the shift and the fluctuation of the mark edge position. Here, since L-SEAT is an index that is directly calculated from the reading signal, it is necessary to notice that the L-SEAT is an index which is affected by the noise of the reading system. When comparing the increase amount .DELTA. of each evaluation index before and after the acceleration test, it is possible to confirm that the L-SEAT shift does not change and the increase of .beta. is small, whereas the L-SEAT jitter is remarkably increased. From this fact, it is possible to confirm that the fluctuation amount of the mark edge position is increased, in the aged deterioration of the recording signal.

"Therefore, using simulation, the effect of fluctuation in the mark edge position affecting the reading signal quality is considered. For the purpose of comparison, calculation even for a case where the mark length is uniformly increased in the entire mark length is performed. Since the uniform increase in the mark length results in a change in a ratio of the mark length of a short mark and the mark length of a long mark, this corresponds to a change of .beta.. The result of calculating a relationship between the fluctuation amount of the mark edge position and i-MLSE is illustrated in FIG. 5A, and the result of calculating a relationship between the increase amount of the mark length and i-MLSE is illustrated in FIG. 5B. Since i-MLSE is rapidly increased according to the increase in the fluctuation amount of the mark edge position, it is possible to confirm that the fluctuation in the mark edge position remarkably deteriorates the signal quality (FIG. 5A). On the other hand, since i-MLSE rarely changes according to the increase in the mark length, it is found that the contribution of .beta. change due to the deterioration in the signal quality is small (FIG. 5B). From the above result, it is found that the agedaged deterioration in the recording signal quality is due to an increase in the fluctuation in the mark edge position. From the above fact, it is found that the recording waveform is adjusted such that the fluctuation amount of the mark edge position becomes small, thus it is possible to suppress the deterioration in the recording signal.

"Here, although L-SEAT Jitter is used in a method of evaluating the fluctuation amount of the mark edge position, since the L-SEAT Jitter is affected from various noises of a readingreading system, the L-SEAT Jitter is not an index of correctly reflecting the fluctuation amount of the mark edge position. Therefore, an index capable of evaluating the fluctuation amount of the mark edge position, without being affected by various noises of the reading system has been proposed. Hereinafter, a description of the proposed evaluation index will be given. FIG. 6 is a schematic diagram illustrating a change in a signal level in a case where the position of the mark edge is moved. Since the change in the signal level in the mark edge (step response) is substantially linear, it is known that the change amount of the signal level is proportional to the move amount of the mark edge position and the maximum amplitude of the step response in a case where the mark edge position is moved. That is, it is found that a value, in which the change amount of the signal level derived from the movement of the mark edge position is normalized by the maximum amplitude of the recording signal, represents the move amount of the mark edge position without depending on a reflectance, a modulation degree of a signal, and a reading system. Using this characteristic, the fluctuation amount of the mark edge position is to be evaluated by an index in which the fluctuation amount of the signal level derived from the fluctuation of the mark edge position is normalized by the maximum amplitude of the step response. Since it is confirmed that the proposed evaluation index is not affected by the reading system, the evaluation indexes variation of severalreading powers are measured, and the result of the measurement is illustrated in FIG. 7. In this measurement, the same signal is used for this measurement Since the proposed evaluation index has a constant value irrespective of that SNR (Signal to Noise Ratio) of the reading signal changes according to the change in the reading power, it is possible to confirm that the evaluation index accurately reflects the fluctuation amount of the mark edge position, without being affected from the reading system.

"From the above result, the recording waveform which suppresses the deterioration in the recording signal can be determined by evaluating the fluctuation amount of the mark edge position and adjusting the recording waveform such that the evaluation index becomes small, using the aforementioned evaluation index.

"Here, the calculation of the evaluation index of the fluctuation amount of the mark edge position is not limited to the description above. For example, if the difference of the fluctuation amount of the mark edge position depending on the recording waveform in the same medium is compared, the signal amplitude used in normalization is not limited to the maximum amplitude of the step response, but the signal amplitude may be the signal amplitude of the same signal length in each recording waveform. Further, if the fluctuation amount of the mark edge position between different mark lengths is compared, the index in which the aforementioned evaluation index is multiplied by the measured signal length may be calculated. Further, in a case of calculating the evaluation index of the fluctuation amount of the mark edge position using the fluctuation amount of the time direction derived from the fluctuation of the mark edge position, the fluctuation amount of the time direction may be normalized with the maximum amplitude of the step response. As described above, there are many variations in the evaluation index of the fluctuation amount of the mark edge position depending on the purpose. Therefore, hereinafter, an index of evaluating the fluctuation amount of the mark edge position is integrally referred to as an edge fluctuation amount. The edge fluctuation amount is an index of quantifying the fluctuation amount of the mark edge position, and indicating an index used in quality determination of the recording waveform in the determination of the recording waveform which suppresses the deterioration of the recording signal. Further, hereinafter, the fluctuation amount of the signal level derived from the fluctuation of the mark edge position that is used in the calculation of the edge fluctuation amount is a level fluctuation amount, and the fluctuation amount of the time direction derived from the fluctuation of the mark edge position is referred to as a time fluctuation amount.

"By an adjustment method of a recording waveform of the present invention based on an edge fluctuation amount, the recording waveform which suppresses an aged deterioration of the recording signal can be determined and the extension of the life span of the recording signal is realized.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1A is an exemplary diagram illustrating a recording waveform and definition of index of determining the recording waveform in an N-1 strategy, and FIG. 1B is an exemplary diagram illustrating a recording waveform and definition of index of determining the recording waveform in a castle strategy.

"FIG. 2A is an exemplary diagram illustrating index values of determining a waveform structure of a recording waveform A, and FIG. 2B is an exemplary diagram illustrating index values of determining a waveform structure of a recording waveform B, based on the castle strategy.

"FIG. 3 is an exemplary diagram illustrating a result of measuring a change of i-MLSE due to a thermostatic oven acceleration test in the recording signal of the recording waveform A and the recording waveform B.

"FIG. 4 is an exemplary diagram showing a result of measuring changes of L-SEAT jitter, .beta., L-SEAT shift jitter, and L-SEAT shift due to a thermostatic oven acceleration test.

"FIG. 5A is an exemplary diagram illustrating a result of calculating a relationship between fluctuation amount of a mark edge position and i-MLSE, and FIG. 5B is an exemplary diagram illustrating a result of calculating a relationship between an increase amount of a mark length and i-MLSE.

"FIG. 6 is a schematic diagram illustrating a relationship between a fluctuation of a mark edge value and a fluctuation of a signal level.

"FIG. 7 is an exemplary diagram illustrating a relationship between an evaluation index of the fluctuation amount of the mark edge position and reading power used for measuring.

"FIG. 8 is an exemplary block diagram illustrating a main configuration of an optical disc apparatus relating to an embodiment of the present invention.

"FIG. 9 is an exemplary block diagram illustrating a main configuration of a controller of the optical disc apparatus relating to the embodiment of the present invention.

"FIG. 10 is an exemplary diagram illustrating a result of measuring edge fluctuation amounts of recording signals of recording waveforms A, B, C, D, E, and F.

"FIG. 11A is an exemplary diagram illustrating index values of determining a waveform structure of a recording waveform E, and FIG. 11B is an exemplary diagram illustrating index values of determining a waveform structure of a recording waveform F.

"FIG. 12 is an exemplary diagram illustrating a result of measuring changes of i-MLSE due to the thermostatic oven acceleration test, in recording signals of a recording waveform A, a recording waveform B, and a recording waveform E.

"FIG. 13 is an exemplary flowchart illustrating steps of a method of determining a recording waveform which suppresses deterioration of the recording signal.

"FIG. 14 is an exemplary flowchart illustrating steps in a case of introducing an acceleration test to a method of determining a recording waveform which suppresses deterioration of the recording signal.

"FIG. 15 is an exemplary diagram illustrating a result of measuring a change of an edge fluctuation amount due to the thermostatic oven acceleration test in the recording signal of the recording waveform E and the recording waveform F.

"FIG. 16 is an exemplary diagram illustrating a result of measuring a change of i-MLSE due to the thermostatic oven acceleration test in the recording signal of the recording waveform E and the recording waveform F.

"FIG. 17 is an exemplary diagram illustrating a relationship between a signal length and a signal amplitude in a recording signal of BDXL.TM. specification.

"FIG. 18A is an exemplary diagram illustrating a superimposed signal generated from a reading signal of a single periodic pattern of a 8T signal, and FIG. 18B is an exemplary diagram illustrating a superimposed signal generated from a reading signal of a single periodic pattern of a 2T signal.

"FIG. 19 is an exemplary diagram of a result of measuring changes of L-SEAT jitter and .beta. due to a reading light acceleration test in a recording signal of a recording waveform C.

"FIG. 20 is an exemplary diagram of a result of measuring SNR and the edge fluctuation amount of a signal which is recorded while changing recording power in the recording waveform E.

"FIG. 21 is an exemplary diagram illustrating a result of measuring a change of i-MLSE due to the thermostatic oven acceleration test in recording signals of a recording waveform E and a recording waveform E'.

"FIG. 22 is an exemplary diagram illustrating a configuration of an optical disc relating to an embodiment of the present invention.

"FIG. 23 is an exemplary diagram illustrating information that is included in DI (Disc Information) of the optical disc relating to an embodiment of the present invention.

"FIG. 24 is an exemplary diagram illustrating a result of calculating an edge fluctuation amount and a life span of a recording signal of each of optical discs 1 to 10."

For additional information on this patent application, see: MORIMOTO, Yoshitaka; ETO, Soichiro; WATANABE, Koichi. Information Recording Method, Information Recording Apparatus, Information Recording Medium, and Medium Estimating Method. Filed May 10, 2013 and posted January 30, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3396&p=68&f=G&l=50&d=PG01&S1=20140123.PD.&OS=PD/20140123&RS=PD/20140123

Keywords for this news article include: Information Technology, Hitachi-LG Data Storage Inc., Information and Data Storage.

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