JP4431827B2 - Information recording method and recording power determination method - Google Patents

Description

  The present invention relates to an information recording method for optical information, and more particularly to an information recording method and information recording medium for high-density optical information.

  In recent years, not only computer information but also information such as voice, still images, and moving images has been digitized, and the amount of information handled has become extremely large. Accordingly, it is necessary to increase the capacity of the optical recording medium for storing such information. Such optical recording media include a read-only information recording medium, a write-once information recording medium capable of additional recording, and a rewritable information recording medium capable of rewriting information. Examples of the rewritable information recording medium include a magneto-optical recording medium and a phase change optical recording medium. Examples of the write-once information recording medium include an organic dye-based optical recording medium containing an organic dye in a recording layer. . In particular, with respect to organic dye-based optical recording media, CD-Rs that perform recording and reproduction with a laser beam having a wavelength of about 780 nm have spread worldwide, and more recently, recording and reproduction with a laser beam having a wavelength of about 650 nm have been performed. The DVD-R and DVD + R performed are showing signs of widespread use following the CD-R.

  This method of recording information on a write-once optical recording medium changes the optical characteristics and shape of the organic dye and its surrounding substrate material and metal reflective film by irradiating the recording layer containing the organic dye with intense laser light. This is done by causing a difference in reflectance between the unrecorded state and the recorded state. So far, many methods have been proposed for optimizing strategies (pulse emission waveform rules) in order to obtain good recording quality. As partly shown in the DVD-R standard and the like, in mark length modulation recording (a method of recording by modulation of mark and space signals) for high-density information recording, incident laser light for optical recording is multiplexed. A method for controlling the timing of the edge of a recording mark by pulsing has been established and has been put to practical use in DVD-R and DVD + R (for example, see Patent Document 1).

JP 2001-176072 A (paragraph 0017 etc.)

  A method for dramatically increasing the capacity of an optical recording medium so far has been to shorten the laser light wavelength (λ) and increase the numerical aperture (NA) of the objective lens to increase the recording spot diameter (laser wavelength). Techniques such as reducing / NA) have been performed. With such a technology, DVD-RAM and DVD-RW having a capacity seven times that of a conventional CD-R have been commercialized. Since the amount of information tends to increase in the future, for example, in order to record high-quality video information for 2 hours or more, a capacity of 15 GB or more is required with a CD size of 12 cm in order to increase the capacity of optical recording media. The medium to have is anxious. As a method of obtaining such a large-capacity medium, the oscillation wavelength of the recording / reproducing laser beam is further shortened. That is, development is proceeding to an optical recording medium that can be recorded and reproduced using a laser beam having a wavelength of 405 nm in place of the semiconductor laser beam having a wavelength of 640 nm to 680 nm used in the current DVD.

  Furthermore, as a next-generation DVD technology, a 1-7 modulation method has been proposed in which 1-bit data is replaced with a 7-bit data string for recording. That is, in the next-generation DVD technology, EFM (8-14) modulation, which has been used in the CD standard in the past, in order to further increase the efficiency of recording a huge amount of information and meet the demand for larger capacity of optical recording media. Alternatively, the 1-7 modulation method is employed instead of the 8-16 modulation method in which 8-bit data is replaced with a 16-bit data string for recording.

  By the way, in the case of this 1-7 modulation method, the mark length of the 2T signal, which is the shortest mark, is about 1/3 of the laser spot diameter, so that it depends on the recording / reproducing light applied to the optical recording medium. Almost no signal amplitude can be obtained. For this reason, the information of the recorded 2T signal is read according to fluctuations in signal level, that is, asymmetry.

  Further, in the case of the 1-7 modulation method, in order to perform high-density recording, for example, the mark length of the 2T signal, which is the shortest mark, is about 1/3 of the laser spot diameter. The mark length of a large 3T signal is about ½ of the laser spot diameter. In this way, the recorded information is read by the fluctuation of the signal level, that is, asymmetry in the case of a 2T signal for which the signal amplitude cannot be obtained, while in the case of a signal of 3T or more, the signal is read. By performing reading based on the amplitude, higher density recording than before can be performed.

  In particular, in the case of a write-once type optical recording medium having an organic dye recording layer, it is usually difficult to form a short recording mark as compared with a recording layer containing a phase change material. For this reason, as described above, when an extremely small recording mark such as a 2T signal is formed, there is a problem that the asymmetry does not become nearly zero, and an error in reading recorded information occurs.

The present invention has been made to solve such technical problems.
That is, an object of the present invention is to provide an information recording method for recording a recording mark having a signal length smaller than the spot diameter of a laser beam at a high density on an optical recording medium.
Another object of the present invention is to provide an information recording medium suitable for recording a recording mark having a signal length smaller than the laser beam spot diameter at a high density.

  For this purpose, according to the present invention, there is provided a method for recording information on an information recording medium having a recording layer, wherein the recording power for recording a signal having a predetermined signal length on the recording layer by laser light is increased. Recording power for recording a signal whose signal length is ½ or less of the spot diameter of the laser beam on the recording layer based on the power calibration step to be determined and the recording power determined by the power calibration step. An information recording method comprising: a complementing step for performing the complementing.

  In the supplementing step in the information recording method to which the present invention is applied, a signal whose signal length is ½ or less of the spot diameter of the laser beam is recorded in advance in a test writing area provided in the recording layer, and is recorded. It is preferable to have a process of repeating the calibration operation so that the asymmetry of the RF signal reproduced from the mark becomes substantially zero. That is, by performing such processing, in addition to calibration for recording a signal whose signal length is larger than ½ of the laser beam spot diameter, the signal length is ½ or less of the laser beam spot diameter. Calibration for recording a signal is performed a plurality of times.

  Further, the complementary step in the information recording method to which the present invention is applied is a signal whose signal length is ½ or less of the spot diameter of the laser beam, depending on the recording speed when the signal is recorded on the information recording medium. It is preferable to perform a process of complementing the recording power for recording the image. That is, the laser light irradiation conditions differ depending on the recording speed.

  On the other hand, for a plurality of recording speeds, a signal having a predetermined signal length and recording power are calibrated in advance, for example, recording power of 2T signal and 3T signal (where T is a one-channel clock). It is conceivable to obtain the ratio of. In this case, the complementing step can calculate the recording power at a predetermined recording speed based on the recording power of the signal recorded at the reference recording speed and having a signal length of ½ or less of the spot diameter of the laser beam. It becomes possible.

  In the supplementing step in the information recording method to which the present invention is applied, the recording power for recording the signal whose information signal length is 1/3 or less of the spot diameter of the laser beam on the recording layer by the laser beam is complemented. When applied to the case, for example, in order to form extremely small marks such as 2T signals, the problem that it is impossible to record in a predetermined asymmetry only by the length of the pulse is solved, and even the shortest mark is accurately detected. An information recording method that can be formed can be provided.

Moreover, it is preferable that the laser beam used in the information recording method to which the present invention is applied is pulsed irradiation that is intermittently applied to the recording layer of the information recording medium at a predetermined interval.
Further, the laser beam is irradiated with (n-1) or (n-2) (one is when n is 2) recording pulses, and the laser beam has a length nT (however, n is an integer of 2 or more, and T is a 1-channel clock.). Such pulse irradiation is particularly effective for high-density recording in which, for example, a mark having a diameter of 1/2 or less of the laser spot diameter, which is considered as one of the next generation DVD technologies, is formed.

  Further, the recording layer of the information recording medium preferably contains an organic dye. That is, according to the information recording method to which the present invention is applied, a 2T signal can be efficiently recorded on a write-once optical recording medium having an organic dye layer in which a short recording mark is difficult to be formed as compared with a recording layer containing a phase change material. Thus, extremely small recording marks can be formed.

On the other hand, according to the present invention, there is provided a substrate and a recording layer provided on the substrate on which information is recorded by irradiation with laser light, and the signal length is ½ or less of the spot diameter of the laser light. There is provided an information recording medium having a predetermined area in which data of recording power for recording a signal on a recording layer with a laser beam is recorded.
In such a predetermined area, for example, information on complementation of the recording power of the recording mark of a signal length that can be predicted to some extent by the physical properties of the organic dye constituting the recording layer, the shape of the guide groove formed in the substrate, etc. Recording in advance before use by the user is effective as a means for shortening the time required for calibration.

In such a predetermined area, it is preferable that data of optimum recording power for recording a signal whose signal length is ½ or less of the spot diameter of the laser beam is recorded.
Furthermore, data for recording a signal whose signal length is ½ or less of the spot diameter of the laser beam is recorded in the predetermined area according to the recording speed when information is recorded by the laser beam. It is preferable. That is, since the recording power of the laser beam varies depending on the recording speed (linear velocity), the data for recording a signal whose signal length is ½ or less of the spot diameter of the laser beam for each recording velocity (linear velocity). However, being recorded in advance before being used by the user is an effective method for shortening the time required for calibration.

  Further, it is preferable that data for recording a signal whose signal length is ½ or less of the spot diameter of the laser beam with the laser beam at a reference recording speed is recorded in the predetermined region. For example, by using the ratio between the recording speed (linear velocity) and the reference velocity, a signal whose signal length is ½ or less of the spot diameter of the laser beam is recorded for each different recording velocity (linear velocity). Data relating to the complement of recording power can be calculated.

On the other hand, the predetermined area of the information recording medium to which the present invention is applied is preferably formed in the recording layer.
Further, such a predetermined area is formed on the substrate in the stamper cutting process when manufacturing the information recording medium, and for recording a signal whose signal length is ½ or less of the laser beam spot diameter. Preferably the data is embedded.

  Furthermore, according to the present invention, there is provided a method for determining a recording power for recording information on an information recording medium having a recording layer, for recording a signal having a predetermined signal length on the recording layer by a laser beam. In order to record a signal having a signal length of ½ or less of the spot diameter of the laser beam on the recording layer based on the power calibration step for determining the recording power and the recording power determined by the power calibration step. And a supplementing step for supplementing the recording power.

  According to the present invention, an optical information recording method for recording optical information having a recording mark length smaller than the laser spot diameter on an optical recording medium at a high density can be obtained.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described below with reference to the accompanying drawings.
FIG. 1 is a diagram for explaining an information recording medium for recording information by an information recording method to which the present embodiment is applied. FIG. 1 shows a write-once optical recording medium 100 provided with a recording layer containing an organic dye as an information recording medium. The optical recording medium 100 includes a first substrate 101 made of polycarbonate resin, a first intermediate layer 102 formed in order on the first substrate 101, a first recording layer 103, a first reflective layer 104, 1 cover layer 105, and the same configuration, that is, the second substrate 106, the second intermediate layer 107, the second recording layer 108, the second reflective layer 109, and the second cover layer 110, , Another substrate having a structure in which the first cover layer 105 and the second cover layer 110 are bonded to each other with the adhesive layer 111 interposed therebetween.

The first substrate 101 and the second substrate 106 are manufactured by injection molding. For example, a groove width (WG) 200 nm, a land width (WL) 225 nm, a track on the surface of a polycarbonate resin plate having a diameter of 120 mm and a thickness of 0.6 mm. Grooves with a pitch (W) of 0.425 μm are formed. On the first substrate 101 and the second substrate 106, disc recognition information, address information and the like are recorded in advance by wobbles in the grooves. These disc recognition information and address information can also be formed by premarks. A groove was used as an information recording track. For example, the first intermediate layer 102 and the second intermediate layer 107 are formed to a thickness of 20 nm using ZnS—SiO ₂ as a target in an argon gas. The first intermediate layer 102 or the second intermediate layer 107 can also use SiO ₂ .

  The first recording layer 103 and the second recording layer 108 are prepared by, for example, dissolving 0.5 g of an organic dye represented by the following formula in 40 g of octafluoropentanol in a carbostyryl compound, and dissolving this at 40 ° C. for 30 minutes. After ultrasonic dispersion, the mixture is filtered through a 0.2 μm filter, spin-coated at 1300 rpm, and dried in an oven at 80 ° C. for 30 minutes.

  As the organic dye contained in the first recording layer 103 or the second recording layer 108, for example, a compound represented by the following formula can be used. Further, the first recording layer 103 or the second recording layer 108 can also use other recording layer materials such as a phase change recording material and a magneto-optical material.

  The first reflective layer 104 and the second reflective layer 109 are provided on the first recording layer 103 and the second recording layer 108, respectively, by sputtering. The first cover layer 105 and the second cover layer 110 are formed by, for example, spin-coating a precursor of an ultraviolet curable resin on the first reflective layer 104 and the second reflective layer 109, respectively, and curing them by ultraviolet irradiation to obtain a thickness of 0. .1 mm is formed. For the adhesive layer 111, a slow-acting ultraviolet curable adhesive is used.

  Next, a method for recording information on the optical recording medium 100 will be described. As a method for recording information on the optical recording medium 100, information is recorded by irradiating the first recording layer 103 or the second recording layer 108 with a pulse of laser light 112. Specifically, the recording mark of length nT (where n is an integer of 2 or more and T is a 1-channel clock) has (n-1) recording pulses or recording pulses (n-2). The first recording layer 103 or the second recording layer 108 is formed by irradiating the number of pulses (provided that the number is 1 when n is 2). Such pulse irradiation of laser light is called (n-1) strategy or (n-2) strategy. When information is recorded on a write-once optical recording medium containing an organic dye, the heat storage effect of the optical disk is used. This is known as a method for avoiding the formation of a recording mark longer than the pulse width of the irradiated laser beam. Table 1 shows an example of a multi-pulse train of pulse irradiation for forming recording marks having a length of 2T to 8T.

  FIG. 2 is a diagram for explaining a recording control pulse of pulse irradiation for forming a recording mark having a length of 8T. In the recording control pulse shown in FIG. 2, Pw (recording power) is variable, Pb (bias power) is set to 0.2 mW, and a single pattern is used as the recording pattern. As shown in FIG. 2, the recording control pulse is divided into three parts, the first pulse is FRP (first pulse), and the last pulse of the recording power pulse following this FRP is one MLP (multi-pulse). ), And the last pulse is ENP (final pulse), and the respective pulse widths are TTop, Tmp, and Tlp. The delay of each pulse from the reference clock is TSFP, TSMP, TSLP.

  The conditions for recording information on the optical recording medium 100 include four recording speeds (linear velocities) of the optical recording medium 100: 4 m / s, 6 m / s, 9 m / s, and 12 m / s. The 1-channel clocks T at (linear velocity) are 22.5 ns (4 m / s), 15 ns (6 m / s), 10 ns (9 m / s), and 7.5 ns (12 m / s), respectively. The semiconductor laser used has a wavelength of 405 nm and N / A = 0.65. The laser spot diameter is 405 / 0.65 = 623 nm.

Next, calibration of a predetermined signal length of the recording mark and the recording power (Pw) of the laser beam will be described.
In this embodiment, when recording a signal on an optical recording medium having a recording layer, trial writing is performed in advance before recording the actual signal, and then the portion of the trial writing is reproduced, and the signal of the reproduced signal is reproduced. Based on the quality, calibration is performed to obtain an optimum recording power for recording an actual signal. For example, in the case of a CD-R, a test writing area called PCA (Power Calibration Area) is provided on the innermost periphery of the optical recording medium. The calibration operation is referred to as OPC (Optimum Power Control). In order to perform this OPC, in the case of a CD-R drive, first, a test signal (EFM: Eight to Fourteen Modulation) is applied to a PCA provided on an optical recording medium by changing the power of laser light in several steps or continuously. ) Is written. Next, the portion written in the PCA is reproduced, and the position where the optimum writing has been performed is obtained from the signal quality of the reproduced RF signal. The laser power at the time when the signal at that position is recorded is set as the optimum recording power. The signal quality of the RF signal is checked by detecting the asymmetry (asymmetry) of the RF signal.

  FIG. 5 is a diagram for explaining asymmetry (asymmetry). FIG. 5A shows a case where the recording power is insufficient, FIG. 5B shows a case where the recording power is appropriate, and FIG. 5C shows a case where the recording power is excessive. The horizontal axis of FIG. 5 is time (t), the vertical axis is a high frequency signal (reproduced signal) (HF Signal), A1 indicates the level of the upper envelope, and A2 indicates the level of the lower envelope. The reproduction signal is detected by a signal called a high-frequency signal (HF Signal 1).

In order to detect asymmetry, an upper envelope level A1 is reached for each recording power by a predetermined detection circuit (not shown) based on an RF signal obtained by irradiating an optical recording medium with a reproducing laser beam. The detected top peak and the bottom peak reaching the level A2 of the lower envelope are detected. Next, an asymmetry (β) value defined by the following equation is calculated for each recording power by a predetermined arithmetic circuit (not shown).
β = (A1 + A2) / (Al−A2)

  As shown in FIG. 5A, when the recording power is insufficient, the upper envelope level A1 and the lower envelope level A2 are both shifted downward. On the other hand, as shown in FIG. 5C, when the recording power is excessive, both the upper envelope level A1 and the lower envelope level A2 are shifted upward. As described above, the asymmetry (β) value is defined as an amount obtained by normalizing the shift amount by the signal amplitude. Therefore, if the recording power is appropriate, the asymmetry (β) value is substantially zero (β≈0). In this case, the recording power is determined as the optimum recording power. Therefore, if actual recording is performed in the data recording area using this optimum recording power, recording and reproduction can be performed in the best state.

  The calibration reproduces a recording mark of a predetermined signal length recorded on the optical recording medium 100 by the recording control pulse of pulse irradiation shown in Table 1, and asymmetry (β for the 8T signal of the reproduction signal obtained from each recording mark. ) And the recording power for recording each recording mark. The reproduction signal was measured with a disk characteristic measuring machine (DDU-1000 manufactured by Pulstec). Measurement conditions were such that the optical recording medium 100 was rotated so as to have a linear velocity of 6 m / s, semiconductor laser light having a wavelength of 405 nm was condensed by an objective lens having a numerical aperture of 0.65, and was reproduced with a reproduction power of 0.2 mW. The reproduction signal was recorded by inputting desired waveform data from the personal computer to the multi-signal generator, and outputting the target signal from the multi-signal generator to the DDU-1000.

  The noise in the unrecorded state was measured with a spectrum analyzer for the noise level of the reproduction signal at a frequency of 12 MHz. Here, RBW (resolution bandwidth) is 30 kHz, VBW (video bandwidth) is 100 Hz, and as a result, the measured value of the noise level is −75.0 dBm.

  FIG. 3 is a graph for explaining the result of calibration between a predetermined signal length of a recording mark and Pw (recording power) of a laser beam at a recording speed (linear velocity) of 6.0 m / s. FIG. 3A is a graph in which the asymmetry (β) of the signal of the recording mark having each signal length with respect to the 8T signal is plotted with respect to the recording power, and FIG. It is the graph which plotted C / N ratio of the signal of the recording mark which has with respect to recording power.

  According to FIGS. 3A and 3B, a 5T to 8T signal having a signal length larger than ½ of the spot diameter of the laser beam has a C / N ratio and a recording power of 5.0 mW to 5 m. A peak is shown in the range of 0.5 mW, and the asymmetry (β) with respect to the 8T signal is substantially the same within 0% ± 5% at the total recording power. Next, the 4T signal having a signal length that is 2/3 of the spot diameter of the laser beam has a peak C / N ratio in the recording power range of 5.0 mW to 5.5 mW, and asymmetry (β) for the 8T signal. However, in the range of the recording power of 4.0 mW to 6.0 mW, the values substantially coincide with each other within 0% + 5%, and become 10% or more at a high power of 6.5 mW or more.

  On the other hand, a 3T signal having a signal length of about ½ or less of the spot diameter of the laser beam has a maximum C / N ratio at a recording power of 6.0 mW, and an asymmetry (β) for the 8T signal has a recording power of 5 mW or less. In this range, the asymmetry (β) fluctuates significantly to -5%, and the asymmetry (β) becomes 0% at a recording power of 6.0 mW. Furthermore, the 2T signal having a signal length of about 1/3 of the spot diameter of the laser beam is maximum when the C / N ratio is 7.0 mW or more, and the asymmetry (β) for the 8T signal is different from that of the 3T signal. The recording power becomes 0% at 6.5 mW or more.

  From the results shown in FIGS. 3A and 3B, the asymmetry (β) with respect to the 8T signal is 0% for the 2T signal and the 3T signal having a signal length of ½ or less of the spot diameter of the laser beam. It can be seen that the recording power becomes different from other 4T to 8T signals. This is based on the result of calibration between a predetermined signal length of the recording mark and the recording power of the laser beam in order to accurately record the 2T signal, the 3T signal, and the other 4T to 8T signals. It shows that the recording power for recording the signal and the 3T signal needs to be complemented for each signal.

  As a result, in recording of an optical recording apparatus for forming a recording mark having a signal length nT, the top power calibration of pulse irradiation is performed for each recording mark, and the shortest is at least smaller than 1/2 of the spot diameter of the laser beam. By separately complementing the recording power of the mark and the next largest short mark, the asymmetry (β) of the signal to be recorded can be matched, and as a result, the recording marks of all signal lengths nT can be obtained. It can be recorded accurately.

  Next, the same verification was performed by changing the recording speed (linear velocity), and the optimum recording power of the 2T signal and 3T signal at each recording velocity (linear velocity) was measured. The results are shown in Table 2.

  Table 2 shows the optimum recording power at which the asymmetry (β) of the 2T signal and the 3T signal is about 0% at each recording speed (linear velocity). From the results in Table 2, it can be seen that the optimum recording power ratio between the 2T signal and the 3T signal at each recording speed (linear speed) is substantially the same. Therefore, when recording a mark (2T signal and 3T signal) whose signal length is smaller than ½ of the spot diameter of the laser beam, the supplement of the recording power is performed at a reference recording speed (linear velocity). Based on the recording power, it can be seen that the calculation can be performed using numerical values roughly calculated by a predetermined calculation formula.

Therefore, in order to accurately record all of the 2T signal to 8T signal for each recording speed (linear velocity), the result of calibration between the recording mark having a predetermined signal length and the recording power of the laser beam. From the above, it can be seen that it is necessary to supplement the recording power for recording the 2T signal and the 3T signal, respectively. It can also be seen that the recording method of the present embodiment is effective even under various conditions with different recording speeds (linear velocities).
Further, as described above, as described above, as described above, calibration at a plurality of recording speeds (linear velocities) is performed, and recording power for recording 2T signals and 3T signals is complemented, and It is effective to use a numerical value roughly calculated by a predetermined calculation formula based on the recording power at the recording speed (linear velocity).

  As described above, when optical information having a recording mark length smaller than the spot diameter of the laser beam is recorded at a high density on the optical recording medium, calibration for complementing the recording power is performed whenever necessary. Is ideal. This is when the applied laser power differs due to the accuracy error of the pickup installed in the drive, the environmental temperature, etc., or when it is difficult to maintain a uniform condition due to variations in the quality of the produced media. It is valid.

However, information on the recording power supplement of the mark length that can be predicted to some extent depending on the physical properties of the organic dye constituting the recording layer and the shape of the guide groove formed on the substrate is preliminarily used before the user uses the information recording medium. Recording in the predetermined area is an effective method for shortening the time required for calibration.
It is also possible to record all the information relating to the complement of the recording power obtained by the calibration performed at a plurality of recording speeds (linear velocities). Thereby, the time required for calibration can be further shortened.

  In general, in DVD-R and the like, information on recording power of various media manufacturers is stored in the memory of the drive, and each time data is written, the media information is read and the recording conditions corresponding to the media information are set to the initial laser. After setting the power and performing OPC (Optimum Power Control) using the test area, data is written with the recording power obtained by calibration.

  On the other hand, in the information recording method to which the present embodiment is applied, calibration is further performed on recording marks (2T and 3T) whose signal length is ½ or less of the spot diameter of the laser beam, and 2T signal and 3T By supplementing the recording power for recording the signal, the asymmetry (β) of the 2T mark and the 3T mark can be reduced to about 0%.

  In such an information recording medium that records information on the recording layer by pulse irradiation of laser light, data relating to complementation of the recording power of a recording mark having a signal length of ½ or less of the spot diameter of the laser light, As a method for manufacturing an information recording medium recorded in a predetermined area, there are the following two methods. As a first method, there is a method of embedding the above-described data in a stamper cutting process when manufacturing a substrate of an information recording medium. As a second method, there is a method in which an information recording medium having a recording layer is prepared, and then the above-described data is recorded on the recording layer by an appropriate method.

FIG. 4 is a flowchart showing the flow of the recording power determination work procedure by the information recording method to which the present embodiment is applied. First, initial conditions (information stored in the disk or drive) are read (step 101), and then the recording power of the longest mark is provisionally determined (step 102). Next, power calibration of the (n + 1) T signal is performed. First, the (n + 1) T signal asymmetry (beta) _{(A 1)} were measured (step 103), the asymmetry of the (n + 1) T signal (beta) _{(A 1)} is substantially zero _{(A 1} ≒ 0) (Step 104), (n + 1) T signal recording power (P ₁ ) is determined (step 105). Subsequently, power calibration of the shortest mark (nT) is performed. First, the asymmetry (β) (A ₀ ) of the nT signal is measured (step 106), and is repeated until the asymmetry (β) (A ₀ ) of the nT signal becomes substantially zero (A ₀ ≈0) (step 107). The shortest mark (nT) recording power (P ₀ ) is determined (step 108).

  After determining the recording power of the recording mark having each signal length, it is important to correct the recording power while detecting the writing state and optimize the recording power when actually writing data. It is. By doing so, the recording marks can be formed stably. As a method for detecting the writing state, it is effective to detect recording return light by so-called running OPC and correct the recording power in accordance with the writing state. Also in this case, if the complementary conditions for the 2T signal and 3T signal with respect to the recording power are set in advance, the asymmetry (β) of the 2T signal and 3T signal is always optimally about 0% even during data writing. It becomes possible to do.

  In the present embodiment, the interval between the recording pulses is adjusted so that the recording pulses are at equal positions, but a good result can be obtained even when the intervals between the recording pulses are different. In this embodiment, laser light having a wavelength of 405 nm is used. However, similar results can be obtained by using a laser having a longer wavelength, for example, a laser having a wavelength of about 650 nm, about 780 nm, or about 830 nm. In the present embodiment, a numerical aperture of 0.65 is used, but the same result can be obtained even if a numerical aperture of 0.45 to 0.7 is used. Similar results can be obtained by combining two or more lenses and using a lens having a numerical aperture of 0.7 or more. A combination of a lens with NA = 0.85 and a laser with a wavelength of 405 nm enables high-speed and high-density recording. Furthermore, the same effect can be obtained in near-field recording using evanescent light with an effective NA of 1 or more in combination with SIL (Solid Immersion Lens) or the like.

  As an application example of the present invention, for example, it is effective when performing high density recording of 1.5 biT / m or more. The shortest mark length is 0.20λ / NA (μm) to 0.5λ / NA (μm) (NA (aperture ratio) = 0.65 to 0.85, λ (recording / reproducing wavelength) = 0.40 to 0. This is particularly effective when performing 1-7 modulation random mark length modulation recording defined by.

It is a figure explaining the information recording medium which records information with the information recording method to which this Embodiment is applied. It is a figure explaining the recording control pulse of the pulse irradiation which forms the recording mark of length 8T. It is a graph explaining the result of calibration with the predetermined signal length of a recording mark, and Pw (recording power) of a laser beam. FIG. 3A is a graph in which the asymmetry of the recording mark signal having each signal length with respect to the 8T signal is plotted with respect to the recording power, and FIG. 3B is a recording mark having each signal length. 3 is a graph in which the C / N ratio of the signal is plotted with respect to the recording power. It is a flowchart which shows the flow of the determination work procedure of recording power. It is a figure explaining asymmetry (asymmetry). FIG. 5A shows a case where the recording power is insufficient, FIG. 5B shows a case where the recording power is appropriate, and FIG. 5C shows a case where the recording power is excessive.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Optical recording medium, 101 ... 1st board | substrate, 102 ... 1st intermediate | middle layer, 103 ... 1st recording layer, 104 ... 1st reflection layer, 105 ... 1st cover layer, 106 ... 2nd board | substrate, 107 ... 2nd Intermediate layer 108 ... second recording layer 109 ... second reflective layer 110 ... second cover layer 111 ... adhesive layer 112 ... laser light

Claims (8)

A method of recording information on an information recording medium having a recording layer,
A first power calibration step of determining a first recording power for recording on the recording layer of the recording marks with laser light having a predetermined recording mark length,
Based on the first recording power determined by the first power calibration step, a recording mark whose recording mark length is ½ or less of the spot diameter of the laser beam is recorded on the recording layer by the laser beam. a second power calibration step of determining a second recording power to the possess,
In the first power calibration step, the first test writing is performed on the test writing area provided in the recording layer, the first test writing is reproduced, and the RF reproduced from the first test writing is reproduced. Detecting a first asymmetry of a signal and determining the first recording power based on the first asymmetry;
In the second power calibration step, a second test writing is performed in a test writing area provided in the recording layer, the second test writing is reproduced, and an RF signal obtained from the second test writing is obtained. The second asymmetry is detected, a calibration operation is repeated so that the second asymmetry becomes substantially zero, and based on the first recording power determined in the first power calibration step. And determining the second recording power . Said second power calibration process in accordance with the recording speed when recording the record mark on the information recording medium, respectively, the recording mark recording mark length is 1/2 or less of the spot diameter of the laser beam The information recording method according to claim 1, wherein the second recording power for recording is determined . In the second power calibration step, predetermined recording is performed based on the second recording power of the recording mark , which is recorded at a reference recording speed and whose recording mark length is ½ or less of the spot diameter of the laser beam. The information recording method according to claim 1, further comprising a process of calculating the second recording power at a speed. It said second power calibration process, the recording mark length of information, a second recording for recording the recording mark is less than 1/3 of the spot diameter of the laser beam on the recording layer by the laser beam The information recording method according to claim 1, wherein power is determined .   2. The information recording method according to claim 1, wherein the laser beam is pulsed irradiation that is intermittently applied to the recording layer at a predetermined interval.   The laser beam is applied to the recording layer with (n-1) or (n-2) (n is 1 when n is 2), and the recording layer has a length nT (where 2. The information recording method according to claim 1, wherein n is an integer of 2 or more, and T is a one-channel clock.   The information recording method according to claim 1, wherein the recording layer contains an organic dye. A method for determining a recording power for recording information on an information recording medium having a recording layer,
A first power calibration step of determining a first recording power for recording on the recording layer of the recording marks with laser light having a predetermined recording mark length,
Based on the first recording power determined by the first power calibration step, a recording mark whose recording mark length is ½ or less of the spot diameter of the laser beam is recorded on the recording layer by the laser beam. A second power calibration step for determining a second recording power for performing ,
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In the first power calibration step, the first test writing is performed on the test writing area provided in the recording layer, the first test writing is reproduced, and the RF reproduced from the first test writing is reproduced. Detecting a first asymmetry of a signal and determining the first recording power based on the first asymmetry;
In the second power calibration step, a second test writing is performed in a test writing area provided in the recording layer, the second test writing is reproduced, and an RF signal obtained from the second test writing is obtained. The second asymmetry is detected, a calibration operation is repeated so that the second asymmetry becomes substantially zero, and based on the first recording power determined in the first power calibration step. Determining the second recording power; and determining the recording power.

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