JP2005122881A - Optical recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording method capable of expanding a linear velocity margin of a phase-change type optical recording medium. <P>SOLUTION: To deal with different linear velocities on a phase-change type recording medium, a clock cycle is changed according to a linear velocity V, and a pulse division parameter in a recording laser pulse is changed. When the mark of a length nT is formed, laser power is divided into m pulses by alternately setting the period α<SB>i</SB>T (1≤i≤) of applying recording power Pw and the period β<SB>i</SB>T of applying bias power P<SB>b</SB>. In this division, the combination of αiT and βiT is variable corresponding to the linear velocity V. The method is suitably used for a CD-E or the like employing mark length modulation recording in which a linear velocity varies. The recording layer of a specific composition is disclosed to be suited to the method. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical recording method. More specifically, the present invention relates to a recording method capable of widening the recordable linear velocity for a phase change optical recording medium capable of recording, erasing and reproducing information by irradiation with a laser beam or the like.

  2. Description of the Related Art In recent years, an optical disk using a laser has been actively developed as a recording medium that meets the demand for an increase in the amount of information and high recording / reproducing density. There are two types of recordable optical discs: a write-once type that can be recorded only once, and a rewritable type that can be recorded and erased any number of times. Examples of the rewritable optical disk include a magneto-optical recording medium using a magneto-optical effect and a phase change medium using a reversible change in crystal state. The phase change medium does not require external magnetism, and can be recorded / erased only by power modulation of laser light. Furthermore, there is an advantage that one-beam overwrite is possible, in which erasing and re-recording are performed simultaneously with a single beam. In a phase change recording method capable of overwriting one beam, a recording mark is generally formed by amorphizing a minute portion of the recording film on the order of μm, and erasing is performed by crystallizing the recording mark. . As a recording layer material used in such a phase change recording method, a chalcogen-based alloy thin film is often used. For example, a Ge-Te system, a Ge-Te-Sb system, an In-Sb-Te system, a Ge-- Examples thereof include Sn—Te alloy thin films.

  In general, a rewritable phase change recording medium uses two different levels of laser light power in order to realize two different states (crystallization and amorphization). This method will be described by taking as an example a case where an amorphous mark is formed from the crystallized initial state, and this is crystallized again to erase the amorphous mark. Crystallization is performed by heating the recording layer portion to a temperature sufficiently higher than the crystallization temperature of the recording layer and lower than the melting point. In this case, the recording layer is sandwiched between dielectric layers, or an elliptical beam that is long in the beam moving direction is used so that the cooling rate is slow enough to allow sufficient crystallization. On the other hand, the amorphization is performed by heating the recording layer to a temperature higher than the melting point and quenching. When performing a one-beam overwrite on a normal phase change medium, a recording pulse is modulated between a recording laser power and an erasing laser power of a lower power to record a past amorphous material. Record while erasing the mark. In this case, the dielectric layer also has a function as a heat dissipation layer for obtaining a sufficient cooling rate (supercooling rate) in the recording layer. Furthermore, in order to prevent the deformation accompanying the melting / volume change of the recording layer in the heating / cooling process as described above, the thermal damage to the plastic substrate, or the deterioration of the recording layer due to moisture, The dielectric layer has an important role. In general, the material of the dielectric layer is optically transparent to laser light, has a high melting point / softening point / decomposition temperature, is easy to form a film, has an appropriate thermal conductivity, etc. Selected from the viewpoint of

In the phase change medium, the thermal characteristics at the time of recording and erasing are greatly affected by the scanning speed of the laser beam, that is, the linear velocity. Therefore, when creating the phase change medium, in order to improve the recording and erasing characteristics. Therefore, it is necessary to optimize the recording layer composition or the layer structure of the medium in accordance with the disk linear velocity at the time of recording / erasing of the target recording apparatus. Amorphous marks are formed by cooling the recording layer once melted with the recording power at a speed equal to or higher than the critical cooling rate (Mitsubishi Kasei R & D Review vol.4 No2 p68-81). This cooling rate depends on the linear velocity when the same layer structure is used. In other words, the cooling rate increases at high linear speeds, and the cooling rate decreases at low linear speeds. In order to confirm this, the ZnS: SiO ₂ mixed film is 100 nm on the polycarbonate substrate, the GeSbTe recording layer is 25 nm, the ZnS: SiO ₂ mixed film is 20 nm, and the Al alloy film, which is the layer structure used in the examples of the present invention. The heat distribution simulation using a general difference method was performed on a disk formed with a thickness of 100 nm sequentially. In this case, the calculated recording power (level) Pw and base power (level) Pb are irradiated, the recording layer is heated to the maximum temperature of 1350 ° C., and then the melting point (600 ° C. in the process of temperature drop). The critical cooling rate in the vicinity was examined at a position advanced by 0.1 μm from the pulse irradiation start position. As a result, when the linear velocity was 10 m / s or more, it was several K / nsec or more, 4 m / s was 2.2 K / nsec, and 1.4 m / s was 0.9 K / nsec.

  On the other hand, in order to erase the amorphous mark, it is necessary to keep the recording layer at a temperature higher than its crystallization temperature and lower than its melting point for a certain period of time. On the contrary, this heat retention time tends to be short at a high linear velocity and long at a low linear velocity. Therefore, in a recording apparatus with a relatively high linear velocity, when the light beam is irradiated, the thermal distribution of the recording layer in the irradiated portion becomes relatively steep in time and space, so that the unerased at the time of erasure Is concerned. In order to cope with such a recording apparatus, the recording layer is made of a compound having a relatively fast crystallization so that crystallization, that is, mark erasing can be performed in a relatively short time, or the layer structure is difficult to escape heat as a whole. Or On the other hand, in a recording apparatus having a relatively low linear velocity, the cooling rate is slow as described above, and there is a concern about recrystallization during recording. Therefore, in order to cope with a recording apparatus with a relatively low linear velocity, a composition with a relatively slow crystallization in the recording layer is used as a method for preventing recrystallization during recording mark formation in order to obtain a target mark length. Or a layer structure that allows heat to escape easily.

Specifically, in a high linear velocity medium, the heat insulating layer between the recording layer and the reflective layer is thickened to make it difficult for heat to escape, or a material such as a GeSbTe alloy is used as the material. in devising such use is made of easily crystallized composition on GeTe-Sb ₂ Te ₃ line. On the other hand, in the case of low linear velocity, the thermal insulation layer is made thin so that heat can escape easily, or more Sb is used than in the case of using the high linear velocity medium, and it is difficult to crystallize during re-solidification. Some ideas are made.

  By adopting the recording layer composition as described above or optimizing the layer structure, it is possible to record, erase and reproduce information with good characteristics with the target driving device. However, media optimized for recording devices with relatively high linear velocities have high crystallization speeds, so it is difficult to form amorphous bits due to recrystallization in areas where linear velocities are low. Can not. On the other hand, when the medium is adjusted to a low linear velocity, the composition / layer structure is such that an amorphous bit can be easily formed. In the end, the linear velocity margin could not be greatly expanded only by optimizing the recording medium.

  In recent years, in order to shorten the time spent for recording and erasing, the linear velocity of the medium at the time of recording and erasing has increased, but on the other hand, there is a demand for recording information in real time. For example, it is a case of recording video, music, etc. In this case, it is essential to record in real time. In this case, there is also a demand for recording at a high speed for editing the information after recording in real time. Furthermore, the same recording medium can be used at a relatively low linear velocity (for example, 1.2 m / s to 1.4 m / s and up to 4-6 times speed thereof) such as a recordable CD, and the current light. It is particularly preferable as a recording medium for multimedia if it can be properly used for both high linear velocity applications such as a magnetic disk (about 10 m / s or more). However, if the recording is performed at a linear velocity significantly lower than the original linear velocity in which the layer structure and recording layer composition of the recording medium are optimized in order to satisfy such requirements, the target mark length can be recorded. In some cases, information could not be recorded. In a phase change recording medium, generally, an amorphous mark is formed by irradiating a minute portion of a recording layer with a laser to melt the minute portion and then rapidly cooling it. Is relatively small, as described above, it is considered that recrystallization occurs after recording melting, and it becomes difficult to form a sufficient amorphous mark. When the reproduction waveform of the recording mark recrystallized after melting is observed, it becomes as shown in FIG. 1, and referring to FIG. 2 showing the state of the amorphous film portion, recrystallization is large in the first half of the recording mark, It can be seen that the amorphous part is formed relatively well in the latter half of the mark. This is because, by continuous irradiation of the laser beam corresponding to the recording power, heat from the laser irradiation to the region corresponding to the second half of the mark is conducted to the region corresponding to the first half of the once melted mark, and as a result, It can be explained that the first half is recrystallized without being rapidly cooled. In this case, in the latter half of the mark, the laser beam corresponding to the recording power is not irradiated immediately after that, so there is no extra heat conduction, and the melted portion becomes a good amorphous. Considering the above, once the recording pulse is divided by once reducing the power after the recording power irradiation is started, the temporal temperature change of the recording layer becomes rapid cooling, and the deterioration of the mark due to recrystallization at the time of recording occurs. It can be inferred that it can be suppressed.

  Examples of the recording method in consideration of the above are disclosed in JP-A-2-165420, JP-A-4-221735, JP-A-5-62193, JP-A-5-325258, JP-A-1-116927, and JJAP. vol.30 No.4 (1991) p677-681 etc., and those using off-pulses, the 40th Japan Applied Physics Related Association Spring Lecture 29a-B-4, JP-A-7-37251, JP-A-6-4867, JP-A-1-253828, JP-A-1-150230, JP-A-1-3153030, JP-A-4-313816, JP-A-2-199628, JP-A-63-113938 Each publication is listed. However, these methods are effective when recording at a linear velocity within a certain range because the pulse division method is constant, but good recording may not be possible under conditions where the linear velocity is greatly different. In many cases, as long as a certain pulse division method is used, the range of linear velocities that can be handled by a specific medium is limited.

  In order to solve the above problems, the present inventors here propose a pulse division method in accordance with the linear velocity. The inventors of the present invention have devised that heat is quickly released from the recording layer and becomes amorphous easily as the speed decreases, and the pulse division method can be specified in accordance with the linear velocity. That is, the gist of the present invention is not the recording pulse dividing method itself, but the pulse dividing method changing method according to the linear velocity. According to the present invention, it is possible to widen the use margin of the linear velocity of a specific single disk.

In the first aspect of the recording method of the present invention, the laser power of the irradiation light is set between the recording power Pw, the erasing power Pe, and the bias power Pb (where Pb ≦ Pe) according to the clock period T. Optical recording method for recording or erasing data by mark length modulation recording method by forming or erasing a plurality of optically identifiable amorphous marks by modulating the optical information recording medium In
In forming an amorphous mark having a length nT (where n is an integer of 2 or more, and the minimum and maximum possible values of n are n _min and n _max , respectively)
Α ₁ T, α ₂ T,..., Α _m T and the period during which the bias power Pb is applied are β ₁ T, β ₂ T,. ..., Β _m T, and laser power application periods are sequentially α ₁ T, β ₁ T, α ₂ T, β ₂ T,..., Α _m T, β _m T (where k is (An integer from 0 to 2, j being a real number from 0 to 2, m = n−k, n _min −k ≧ 1, α ₁ + β ₁ +... + Α _m + β _m = n−j) Thus, the period during which the recording power Pw is applied is divided into m pulses for irradiation,
The linear velocity V when irradiating the irradiation light onto the recording medium is variable within the range of V _L ≦ V ≦ V _h , with the maximum linear velocity V _h and the minimum linear velocity V _L being set,
The clock cycle T is made variable according to the change of the linear velocity V,
Where i is an integer of 1 ≦ i ≦ m, the application period width of each of the divided recording powers Pw is α _i T, the application period width of each bias power is β _i T, and 2 ≦ i ≦ m−1. Α _i + β _i = 1.0 in _i satisfying
For all i, α _iL ≦ α _i1 ≦ α _i2 ≦ α _ih and α _iL <α _ih when V _L <V ₁ <V ₂ <V _h ,
Further, α _1h > α _ih (2 ≦ i ≦ m) is _satisfied , and α _ih = 0.5 in i of 2 ≦ i ≦ m.

In the second aspect of the recording method of the present invention, the laser power of the irradiation light is set according to the clock period T, the recording power Pw, the erasing power Pe, and the bias power Pb (where Pb / Pe ≦ 0.25). In this way, a plurality of optically distinguishable amorphous marks having different lengths are formed or erased on the optical information recording medium, and data is recorded by the mark length modulation recording method. In the optical recording method for erasing,
In forming an amorphous mark having a length nT (where n is an integer of 2 or more, and the minimum and maximum possible values of n are n _min and n _max , respectively)
Α ₁ T, α ₂ T,..., Α _m T and the period during which the bias power Pb is applied are β ₁ T, β ₂ T,. ..., Β _m T, and laser power application periods are sequentially α ₁ T, β ₁ T, α ₂ T, β ₂ T,..., Α _m T, β _m T (where k is (An integer from 0 to 2, j being a real number from 0 to 2, m = n−k, n _min −k ≧ 1, α ₁ + β ₁ +... + Α _m + β _m = n−j) Thus, the period during which the recording power Pw is applied is divided into m pulses for irradiation,
The linear velocity V when irradiating the irradiation light onto the recording medium is variable within the range of V _L ≦ V ≦ V _h , with the maximum linear velocity V _h and the minimum linear velocity V _L being set,
The clock cycle T is made variable according to the change of the linear velocity V,
i as integer 1 ≦ i ≦ m, the divided application period widths of the individual recording power Pw and alpha _i T, the linear velocity V is V _L, when the _{V 1, V 2, V h} α i _Is α _iL , α _il , α _i2 , α _ih respectively.
For all i, α _iL ≦ α _i1 ≦ α _i2 ≦ α _ih and α _iL <α _ih when V _L <V ₁ <V ₂ <V _h ,
Further, α _1h > α _ih (2 ≦ i ≦ m) is _satisfied , and α _ih = 0.5 in i of 2 ≦ i ≦ m.

  By using the recording method of the present invention, it is possible to widen the linear velocity margin of the medium, in particular, the margin on the low linear velocity side, without changing the material of the medium, and overwrite recording is possible in a wide linear velocity range. Become. In addition, while the recording data format is compatible, the same medium can be used for various drives with different linear velocities during recording, and there is no need to optimize for each linear speed. The problem can be solved.

  Recording methods with almost constant linear velocity include general CLV (Constant Linear Velocity), ZCLV (Zoned CLV) with constant linear velocity in each zone (supervised by Morio Onoe, Optical Disc Technology, Radio Technology Co., Ltd.) ). In the ZCLV format, the linear velocity slightly changes in the zone, but the linear velocity is maintained almost constant as a whole. Nowadays, it is a known technique to change the linear velocity of CD between 1 × speed (1.2 m / s to 1.4 m / s).

For example, let T _h be the clock cycle employed at a certain maximum linear velocity V _h . If you specify n, determines the mark length to be recorded by nT _h. In order to record a mark having the same length at a low linear velocity V, the clock period T should be calculated as (V _h / V) × T _h, and a mark having the same length should be obtained by the nT pulse. Adjustment of the clock period T in this way according to the linear velocity has already been generally performed. However, in practice, a desired mark length cannot always be obtained by increasing the mark length by thermal diffusion or shortening the mark length by recrystallization. Such a phenomenon is particularly likely to occur when the minimum linear velocity V _L is a low linear velocity of 4 to less than 6 m / s. Therefore, the temperature distribution in the recording layer is adjusted by dividing the recording pulse and shortening each divided pulse width. This mark length modulated recording method is shown in FIG. Examples of modulation schemes that use such mark length modulation include 1-7 modulation and EFM modulation. In these mark length recordings, the starting end position and the trailing end position of the recording mark correspond to the recording data, which is particularly important.

In the present invention, parameters m = n−k, n−j = (α ₁ + β ₁ +... + Α _m + β _m ), n _min −k ≧ 1 that determine the pulse division method corresponding to the linear velocity. As a condition, a configuration is adopted in which at least one of α _i T and Pb is variable according to the following rule to widen the applicable linear velocity of the same medium. That is, in the present invention, when the linear velocity is small and the cooling rate is slow, the pulse width α _i T at which the recording power Pw is turned on is shortened, the off time β _i T is lengthened, or recording is performed. By lowering the laser beam power (bias power) Pb _i applied during the period β _i T during which the power Pw is off as the linear velocity decreases, the heat buildup within one mark is suppressed and the cooling rate is increased. Prevent recrystallization. Alternatively, in addition to these, one of the recording pulses divided to record one mark is irradiated between the divided recording pulses in order to suppress reheating by the subsequent recording pulse. By controlling the light energy, the cooling rate of the region melted for forming the amorphous mark is controlled. More specifically, in the linear velocity range (V _{L to} V _h ) for recording information on the phase change optical recording medium, linear velocities V ₁ and V ₁ satisfying V _L <V ₁ <V ₂ <V _{h. In 2} , for all i with 1 ≦ i ≦ m,
α _iL ≦ α _i1 ≦ α _i2 ≦ α _ih (1)
Is established. Here, α _iL , α _i1 , α _i2 , and α _ih are the divided individual pulse widths for V _L , V ₁ , V ₂ , and V _h , respectively.

Instead of or in addition to the above, the ratio Pb _i / Pe of each bias power Pb _i and erasing power Pe in the β _i T period is θ _i, and θ _iL , θ _i1 , θ _i2 and θ _ih Is θ _i for V _L , V ₁ , V ₂ and V _h , respectively,
θ _iL ≦ θ _i1 ≦ θ _i2 ≦ θ _ih (2)
It can be.

In any of the above cases, at least at V _L ,
α _iL <α _ih (3)
Or
θ _iL <θ _ih (4)
To hold for at least one i. However, as a matter of course, the recording power Pw and the erasing power Pe take different values depending on individual linear velocities.

In particular, Pe is selected as a power capable of erasing an amorphous mark when only that is irradiated in a direct current only once. More specifically, Pe is DC-directed on a mark recorded at a single frequency (duty ratio 50%) such that f _max = 1 / (2n _max T) or f _min = 1 / (2n _min T). Pe is selected such that the carrier level attenuation of the erased signal is about 20 dB or more when irradiated. Alternatively, on a mark recorded with a single frequency of f _max = 1 / (2n _max T) (duty ratio 50%), a single frequency of f _min = 1 / (n _min T) (duty ratio 50%) When the signal is overwritten (in this case, the recording pulse may or may not be divided, but modulation is performed with binary values of Pw and Pe), the carrier level of f _{min and} the carrier of f _max erased are erased. Select Pe so that the level difference is about 20 dB or more. Pw is selected so that the C / N ratio (Carrier to Noise ratio) of the recording signals of f _max and f _min is about 45 dB or more.

  It is known to change Pw, Pe, and the clock cycle T according to the linear velocity at the time of recording. However, as in the present invention, the present inventors first propose to change the pulse division method according to the linear velocity and according to a certain rule. The parameters describing these pulse division methods may be changed continuously according to the linear velocity, but may be changed stepwise for each range of a constant linear velocity.

In the optical recording method described above, the bias power Pb _i in the β _i T period when the recording power is turned off takes an arbitrary value less than or equal to the power Pe necessary for erasure when performing normal three-value modulation recording (FIG. 4). In addition, the value of Pb _i may change during β _i T to take several levels. In this case, the heat distribution can be finely controlled, the shape of the amorphous mark can be adjusted, and the jitter of the recording signal can be improved. Further, since it becomes more rapid cooling, the recrystallized region can be reduced, and the recording sensitivity may be improved. Here, when Pb _i becomes 0, the servo signal cannot be obtained and the tracking servo is not applied. On the other hand, if Pb _i exceeds Pe, the recording layer is melted, so that erasure becomes impossible. Eventually, Pb _i is preferably greater than 0 and less than Pe.

At a high linear velocity where V is 10 m / s, it is particularly desirable to use a medium that can be overwritten with Pb = Pb = Pe (constant). This is because at a high linear speed, the clock cycle is short and the Pb switching circuit needs to have a high response speed. However, when used at a low linear velocity, the clock cycle is long and the demand for the response of the pulse control circuit is relaxed. Therefore, in order to adjust the shape of the amorphous mark, Pb is not a single value. The combination of several types is sometimes preferable although it complicates the circuit. In the pattern for the 4T mark illustrated in FIG. 5B, the case where 0 <Pb <Pe is first taken and then Pb = Pe is changed during the period β _i T is given. In the pattern illustrated in FIG. 5A, an example is given in which Pb = Pe is first taken and then Pb <Pe is changed. In this way, Pb _i is a plurality of values Pb _iJ in β _i T (where β _i = Σ _J β _iJ , Pb _iJ is a bias power value taken in a section β _iJ T obtained by further dividing β _i ) In place of θ _i ,
θ _i = Σ _j (Pb _ij β _ij T) / (Pe · β _i T)
And (2) and (4) are satisfied.

  In the above optical recording method, since the laser power immediately before the mark tip portion is the erasing power and the temperature hardly rises normally, the pulse width of the leading divided pulse may be longer than the following pulse in some cases. An example of this is shown in FIG. Further, the rising edges of the individual divided recording pulses do not necessarily have to be synchronized with the clock cycle. However, in order to simplify the pulse control circuit, it is desirable to synchronize. In this case, however, shifting only the rising edge of the first pulse or the last pulse for one mark length from the clock period T by at most T is effective in correcting the thermal interference between different marks. Furthermore, in order to suppress thermal interference with the preceding mark, it is effective to provide an off-pulse section immediately before the leading pulse of the succeeding mark (before 2T time at the maximum), although it is complicated. An example of this is shown in FIG.

The recording power Pw does not depend on the pulse length nT at each linear velocity, and is constant between the individual pulses divided within one mark, thereby simplifying the pulse control circuit. This is desirable. However, it is sometimes effective to change the recording power of the subsequent pulse stepwise from the recording power of the first pulse in one mark, in particular, to lower the recording power of the subsequent pulse. In some cases, further, when recording an nT mark, when a pulse train of a laser power for a pulse length nT necessary, that is, (α ₁ + β ₁ +... + Α _m + β _m ) = n is applied. The heating time becomes too long, and a mark longer than the required length may be written. In that case, (α ₁ + β ₁ +... + Α _m + β _m ) = n−j (j is a real number in the range of 0 <j ≦ 2), and accordingly, the pulse division number m = n− k may be changed. FIG. 7 illustrates a pattern in which β _i (1 ≦ i ≦ m−1) is constant and only β _m is different as an example. In this case, by adjusting β _m , n−j can be changed to obtain a desired mark length nT.

As described above, there are at least two parameters of the pulse division method to be changed according to the linear velocity. Among these parameters, the number of pulse divisions m = n−k, the pulse length n−j, and α _i + β _i Is constant regardless of the linear velocity, and the linear velocities V ₁ and V ₂ satisfying V _L <V ₁ <V ₂ <V _h are such that all of the equations (1) to (4) are satisfied. This is desirable for simplifying the control circuit. Even more desirably, at the maximum linear velocity V _h used,
α _1h = 0.5, 1.0, or 1.5, and β _1h = α _ih = 0.5 (2 ≦ i ≦ m)
And at all linear velocities,
α _i + β _i = 1.0 (2 ≦ i ≦ m)
And In this way, the rise of each recording pulse is synchronized with the reference clock, apart from a certain delay. Therefore, the design of the pulse control circuit is further facilitated. Here, at the linear velocity V in the range of the linear velocity V _L ≦ V <V _h , the lower the linear velocity, the shorter the pulse width and the recrystallization should be prevented. However, if the pulse width is too short, the recording sensitivity deteriorates, which is not preferable. Therefore, in practice, it is preferable to set a lower limit of 0.05 <α _i .

  The present invention is intended for mark length modulation recording, but is not limited to the mark end detection method. That is, either simple slice by DC level or peak detection by double differentiation as disclosed in Jpn.J.Appl.Phys., Vol.31 (1992), 584-589pp may be used. Further, a method of detecting the mark end separately at the mark front end and the rear end as disclosed in the same document is also effective.

An optical recording medium to which the present invention can be applied is a so-called phase change recording medium, which is of a type in which an amorphous recording mark is formed with the crystalline state set to an unrecorded state. An example of the configuration of this type of phase change medium is shown in FIG. Of course, the present invention is not limited to this layer structure. In FIG. 8, on a substrate 1, a lower protective layer 2, a phase change recording layer 3, an upper protective layer 4, a reflective layer 5 made of metal or semiconductor, and a protective layer 6 made of ultraviolet light or a thermosetting resin are sequentially formed. Is formed. Each layer indicated by reference numeral 2-5 is a thin film that is usually formed by sputtering. In general, the focused light for recording / reproducing is transmitted through the transparent substrate 1 and applied to the recording layer 3. The recording layer 3 is locally heated and melted by the irradiation of the recording power Pw, rapidly cooled by turning off the focused light irradiation light, and becomes amorphous when solidified. The amorphous mark is heated to a temperature below the melting point and above the crystallization temperature by irradiation with Pe, recrystallized and erased. Recording layer materials that can be overwritten based on such a principle include GeSbTe alloys (in particular, pseudo binary alloys of GeTe and Sb ₂ Te ₃ ), Ag in the vicinity of the eutectic composition of Sb ₇₀ Te ₃₀ , and the like. Examples include those to which Cu, Au, Ge, Pd, Pt and the like are added. In these alloys, the crystallization speed and the amorphous forming ability, or the crystallization temperature are controlled by controlling the amount of Sb in particular, and optimization is performed according to the linear velocity used. For example, when Sb is added to a GeTe—Sb ₂ Te ₃ pseudo binary alloy, the amorphous forming ability increases, and the crystallization speed decreases, so that the direction of low linear velocity is achieved. Further, by controlling the thickness of the recording layer 2 and the protective layer 4 and the thermal conductivity of the protective layers 2, 4 and the reflective layer 5, it is possible to control the supercooling speed of the melted region formed during recording. It is possible to control to adapt to. For example, if the thermal conductivity of the protective layer is increased, or if the thickness of the recording layer and the upper protective layer is 15-30 nm and thermal diffusion from the recording layer to the reflective layer is promoted, amorphous formation is promoted. , Low linear speed direction.

A specific application example of the present invention is a recordable compact disc (CD-E). In CD-E, V _L = 1.2 to 1.4 m / s, and it is desirable that recording / reproduction can be performed at 1 × speed and at 2, 4 and 6 × speeds. Such a method of using CD-E has not been publicized, but is currently on the market, write-once recordable CDs (CD-R, CD-Recrordable) are 1-6 times faster. It is desirable to be able to record at a wide linear velocity. In this case, as a preferable pulse division method, first, EFM modulation of m = n, n−1, or n−2 is adopted as the mark length modulation method, and V is V _L , 2V _L , 4V _L, or 6V. _{Assume that} a finite number of values of _L can be taken. Α _1h = 1.5 or 1.0, β _1h = α _ih = 0.5 (2 ≦ i ≦ m) at a linear velocity of 2 V _L or more, and α _i + β _i−1 = 1.0 (2 ≦ i ≦ m). Furthermore, the linear velocity 2V _L in _{Pb i = Pr ± 0.5mW (1} ≦ i ≦ m, Pr reproduction light power), the linear velocity V _h = 4V _L or _{6V L Pb i = Pe ± 0.5mW} ( 1 ≦ i ≦ m) and linear velocity V _L , the recording pulse division method is set in accordance with the linear velocity so that 0.05 <α _i <0.5 (2 ≦ i ≦ m) and α _1L ≦ α _1h. Change it. However, β _m ≠ 0.5 (can be 0). That is, the off-pulse period at the end of each mark can be set to a time different from the off-pulse period in the mark. In this way, a single type of medium can be used for various drive devices that perform recording at various linear velocities.

As a CD-E recording medium suitable for the optical recording method, more specifically, at least a lower dielectric protective layer on the substrate, {(GeTe) _y (Sb ₂ Te ₃ ) _1-y } _1-x Sb _x (0 ≦ x <0.1, 0.2 <y <0.9) A recording layer, an upper dielectric protective layer, and a metal reflective layer are provided in this order, and the recording layer thickness is 15-30 nm. Examples thereof include a phase change medium having a layer thickness of 10-30 nm. Alternatively, the recording _{layer, M y (Te 1-x} Sb x) 1-y (0 ≦ y <0.3,0.5 <x <0.9, M = In, Ga, Zn, Ge, Sn , Si, Co, Cr, Cu, Ag, Au, Pd, Pt, S, Se, and O). JP-A-4-221735 and JP-A-5-62193 are prior applications of a method relating to a phase-change recording medium using a GeSbTe recording layer that is rewritable particularly at a CD linear velocity. The recording method to be divided is shown. However, the pulse division method at the 2 × speed 2V _L is not even suggested, and the linear velocity dependency problem that occurs when recording at 2, 4, 6 × speed is not mentioned at all. Furthermore, there is no disclosure of a method for overcoming the linear velocity dependency by changing the recording pulse division method according to a certain rule. An example of a CD-E medium using an AgInSbTe recording layer is disclosed in Japanese Patent Application Laid-Open No. 7-37251 and a conference presentation by the inventors (International symposium on Optical Memory, 1995, Knanazawa, Japan, No. P-33). And a recording method thereof. However, there is no disclosure about the linear velocity dependency problem and its solution.

In the above example, for mark length modulation recording where the minimum linear velocity V _L is in the range of 1.2 to 1.4 m / S, m is selected as m = n, n−1, or n−2, It is selected that the speed V is based on a finite number of values of V = V _L , 2V _L , 4V _L , or 6V _L , and in each linear speed V, α _i is in the range of 2 ≦ i ≦ m. When + β _i = 1.0 and i is in the range of 1 ≦ i ≦ m, Pb _i = Pr ± 0.5 mW, and when the linear velocity V decreases, α _i decreases monotonously for all i Can be configured. In this case, β _m ≠ 0 is preferable from the viewpoint of tracking servo.

  Another effective use of the present invention is to eliminate the linear velocity dependency caused by the linear velocity difference between the inner and outer circumferences of a phase change disk rotating at a constant angular velocity (CAV). That is, in a medium having a large radius such that the radius of the inner and outer circumferences of the recording area is twice or more, a linear velocity difference of twice or more occurs on the inner and outer circumferences. In order to overcome the dependence on the linear velocity, it is difficult to change the recording layer composition and the layer configuration on the inner and outer circumferences, requiring special devices at the time of manufacturing. Therefore, by changing the recording pulse division method according to the present invention in accordance with the linear velocity of the inner and outer circumferences, information can be recorded without any inconvenience over the entire disk surface even in a medium that is uniform in the radial direction. For example, in a normal ZCAV (Zoned CAV) type medium, the recording pulse division method may be changed in conjunction with the switching of the reference clock period at the radial position.

In order to use the optical recording method of the present invention more simply and effectively, information relating to pulse division is recorded in advance on the disc to be used, for example, with uneven pit information. The pulse division information is described, for example, so as to change the combination of the above parameters (Pw, Pe, Pb, m, j, k, α _i , β _i ) according to the linear velocity used. It is preferable that In this description, a dividing method is described only with respect to linear velocities at V _L and V _h at linear velocities V in the range of V _L ≦ V ≦ V _h , and for V in between, parameters for V _L and V _h are described. Can be interpolated and used. In the CD-E, information on the pulse division may be previously written on the substrate by frequency modulation of a meandering groove in the lead-in area. The disk drive device automatically reads a pulse division method written in advance on the disk and automatically executes a pulse division scheme for recording at a specified pulse division method and linear velocity. By adopting such a disk drive device, the linear velocity dependency is different from each other, but even when a plurality of phase change media having the same recorded information format coexist in the market, the compatibility is taken. Is possible. In other words, according to the present invention, when recording is performed on a specific phase change medium with a disk drive device that employs only a specific fixed pulse division method, recrystallization occurs and normal marks are not recorded. The problem can be solved.

As described above, in the present invention, the pulse division method is changed in accordance with the linear velocity, so that even if recording is performed in a condition where the linear velocity is greatly different, for example, a linear velocity range of V _h ≧ 2V _L , A good temperature distribution can be created, and recrystallization at a low linear velocity and unerased residue at a high linear velocity can be suppressed. Can be used at linear speed.

Embodiment Examples (Examples) of the present invention are shown below, but the present invention is not limited to the following examples.
In the following examples and comparative examples, recording (one-beam overwriting) was performed using an optical disk drive tester manufactured by Pulstec Corporation equipped with a 680 nm laser diode and an optical lens with NA = 0.60. The reproduction light power Pr was 1.0 mW and constant regardless of the linear velocity. The clock cycle T is assumed to be inversely proportional to the linear velocity, and T = 143 nsec (7 MHz) at the time of recording at 1.4 m / s, and T = 20.0 nsec at 10 m / s.

Example 1 and Comparative Examples 1 and 2 As Example 1, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ [mol%] layer was 100 nm and a Ge _22.2 Sb _22.2 Te _55.6 [at%] layer was 25 nm on a polycarbonate substrate. , (ZnS) ₈₀ (SiO ₂ ) ₂₀ [mol%] layer 20 nm, Al alloy layer 100 nm sequentially laminated by magnetron sputtering method, and a disk made by providing an ultraviolet curable resin 4 μm thereon. It was. First, evaluation was performed using a repetitive pattern including a pattern of 3T / 9T / 7T / 9T / 11T / 9T (an underlined portion corresponds to a mark and an ununderlined portion corresponds to a space between the marks). After overwriting several times under appropriate conditions, the mark length was detected by slicing at the center level of the peak wave height value of the 11T / 9T signal amplitude in the reproduction signal. For detection, use a time interval analyzer (TIA, manufactured by Hewlett-Packard, E1725A) and a simple method (a simple peak detection method disclosed in Jpn.J.Appl.Phys., Vol.31 (1992), 584-589pp, etc.). Using.

A pattern as shown in FIG. 9A at a linear velocity of 10 m / s, that is, m = n−j, j = 0 (because Pe = Pb, j = 0.2 is the same), α ₁ = 1. 5. A pulse division method using β ₁ = 0.5 and α _i = β _i = 0.5 (i ≧ 2) was used (see, for example, Proc. Int. Symp. On Optical Memory, 1991, 291-296pp) ). Overwriting was performed at Pw = 12.0 mW and Pe = 4.0 mW, and a good reproduction waveform like the oscillograph shown in FIG. 10A was obtained. Similarly, by adjusting the clock cycle according to the linear velocity and selecting appropriate Pw and Pe, overwriting was attempted in the range up to 20 m / s, and all recorded good recording waveforms. Further, good mark length jitter of less than 10% of T was obtained with 3T, 7T, and 11T mark lengths.

As Comparative Example 1, with the same configuration, the pulse division pattern was not changed by the linear velocity, only the clock cycle T was adjusted, and overwriting was attempted at 1.4 m / s. In this case, it is impossible to record 7T and 11T marks in any combination of Pw and Pe. FIG. 10B shows an example of the waveform (relatively better example). It is considered that when the mark length is long, the first half of the mark is recrystallized due to residual heat during recording of the second half of the mark, and the amorphous mark cannot be recorded. Furthermore, as Comparative Example 2, in order to optimize for 1.4 m / s, the composition of the recording layer was set to Ge ₂₃ Sb ₂₈ Te ₄₉ , which was Sb richer than the previous example. Although formed, since the crystallization speed was slow, the erasure ratio of the amorphous mark was insufficient at 10 m / s, which was not suitable for overwriting.

Therefore, in the most difficult case, in order to perform good recording even at 1.4 m / s on a medium for high linear velocity used at 10-20 m / s, according to the gist of the present invention, the pulse division method is as follows. Tried to optimize.
Example 2 Using a disc optimized for a linear velocity of 10-20 m / s, overwriting with the above-described repeated mark length pattern was attempted at a linear velocity of 1.4 m / s. m = n, j = 0.2, Pe = 4 mW, Pb is constant as Pb = Pb _i = 0.2 mW, and the width Tp of n divided recording pulses for forming an nT mark is Tp = α _i T was kept constant, and the recording power Pw was made variable. This pulse pattern is shown in FIG. When Tp ≧ 50 nsec, the film was hardly amorphized, and the mark end itself could not be detected by TIA. FIGS. 11A and 11B show the Pw dependence of the mark length and mark length jitter for each nT mark (3T, 7T, 11T) when Tp is further shortened. When Tp = less than 30 nsec (that is, less than 0.21T), an appropriate mark length corresponding to the recording mark nT and good jitter of less than 0.1T were selected at Pw = 14 to 17 mW. Note that at Tp = 12 nsec (0.084T), Pw needs to be Pw> 16 mW or more, and the above tester was insufficient in sensitivity.

In this embodiment, the beta _i, except beta _n are all equal, is adjusted only beta _n such that j = 0.2.
Example 3 Pb and Pw were variable under the conditions of Tp = 20 nsec (α _i = 0.14), m = n, j = 0.2, and Pe = 4.0 mW. FIGS. 12A and 12B show the dependency of mark length and mark length jitter on Pw and Pb, as in FIGS. 11A and 11B. If Pb was smaller than about 1 mW, good jitter of about 0.1 T or less was obtained at Pw = 14 to 17 mW. Even when 0 <Pb <Pr, there was no effect on the tracking servo or the like. Even if Pb = 0.2 mW and Pb is lower than Pr, the tracking servo cannot be removed within this time.

From Examples 2 and 3, when using in a wide range of linear velocities of 1.4 m / s to 20 m / s, it is necessary to reduce α _i and decrease Pb, particularly on the low linear velocity side. It was found that good results were obtained when used in combination.
Example 4 When Tp = 20 nsec (α _i = 0.14T), Pb = 0.2 mW, Pe = 4 mW, the mark length and mark length jitter Pw when m = n or m = n−1 The j dependency is shown in FIG. 13 (when m = n) and FIG. 14 (when m = n−1), respectively. The mark length strongly depends on n−j = Σ (α _i + β _i ). It can be seen that there is an optimum point in the range of j = 0.2 to 0.7 for both m = n and m = n−1. In the case of m = n−1, it is preferable that m is constant in the range of 1.4 m / s to 20 m / s, and only n−j and α _i need to be changed according to the linear velocity. This is because, as the pulse control circuit, it is preferable in terms of the circuit configuration that m can be made constant rather than the case where m changes according to the linear velocity. In addition, by obtaining good results using a repetitive pattern including mark lengths of n = 3, 7, and 11, a pattern including all mark lengths of n = 3 to 11 is employed. For example, a compact disc In the EFM modulation method used in (CD), this means that overwriting is possible over a wide range of linear velocities. However, 3T, which is the shortest mark length at T = 143 nsec, corresponds to 0.6 μm, which is higher in density than the current CD. However, even if this is 0.8 to 0.9 μm, which is the same as that of the current CD, overwriting can be performed with a wide range of linear velocities in the same manner if the pulse width is slightly optimized. On the other hand, the shortest mark length is further reduced. For example, the same applies to mark length modulation recording on a digital video disk. Rather, when the mark length is shorter, recrystallization is less likely to occur, so the problem relating to the linear velocity dependency is reduced. The pulse division method of the present invention can also be applied to such a high-density recording medium.

[Example 5] The above repetitive pattern is overwritten on the phase change medium at an intermediate linear velocity between 10 m / s and 1.4 m / s. For example, recording at 2.8 m / s is performed. It was. As a result, in a pulse division pattern with Tp = 15-20 nanoseconds, j = 0.2, m = n, Pe = 4 mW, and Pb = 0.2 mW, Pw = about 15 mW or more, an appropriate mark length and 0 Good jitter of less than 1T was obtained. Therefore, the same pattern can be applied to the medium of the present embodiment at least at 1-2 times the CD linear velocity. On the other hand, at 5.6 m / s, which is about 4 times the CD linear velocity, when m = n−1, j = 0.0, Pb = Pe, Tp = 20 nsec, Pw = 16 mW and Pe = 4 mW. Good jitter of 0.1 T or less was obtained.

[Embodiment 6] The present invention can also be applied to cases where the pulse length modulation method is different between the high linear velocity and the low linear velocity. In the sixth embodiment, in the range of 10-20 m / s, (1, 7) RLL (run-length) consisting of mark lengths of n = 2 to 8 used in computer peripheral devices and optical recording media. -limited), and at 1.4 m / s, an attempt was made to overwrite using EFM modulation. In this case, the mark end detection circuit becomes easier when the clock cycle T is constant. However, it is not always necessary to agree exactly. Since the physical minimum mark length is the lower limit of the linear density determined by the physical characteristics of the medium, it is better to make it constant. Therefore, it is effective to change the clock cycle so that both the shortest mark 2T in the (1, 7) modulation and the 3T mark in the EFM modulation are 0.6 μm. FIGS. 15A to 15C show eye patterns at linear speeds of 10 m / s (EFM modulation), 5.6 m / s (EFM modulation), and 1.4 m / s (1-7 modulation), respectively. It was. As shown in the figure, a good waveform was obtained at each linear velocity, and the mark length jitter was less than 0.1 T even at the shortest mark.

[Example 7] As the recording medium, an AgInSbTe alloy thin film was used for the recording layer, and the same layer structure as that of Example 1 was prepared. For recording, a semiconductor laser with a wavelength of 780 nm and an optical lens with NA = 0.55 were used. At a CD double linear velocity of 4.8 m / s, recording was performed with a pattern of Pw = 12 mW, Pe = 6 mW, and Pb = Pr = 0.8 mW by the pulse division method shown in FIG. 16 with respect to the EFM modulation method. A good eye pattern was obtained. That is, the jitter of each mark was less than 10% of the clock period. When this medium was recorded with the same pulse division method and the clock cycle was doubled at CD 1 × speed, recrystallization was remarkable and a good eye pattern could not be selected. However, when α _i is 0.33 (2 ≦ i ≦ m, α ₁ is not changed at 1.0), Pw = 11 mw, Pe = 5 mW, and Pb = Pr = 0.8 mW, a good eye pattern is obtained. was gotten.

The graph which shows the reflective characteristic of the conventional amorphous mark. The typical top view which shows the structure of the amorphous mark of FIG. The wave form diagram which illustrates the pulse pattern in the mark length modulation system which records an nT mark. The wave form diagram which illustrates the pulse pattern in the mark length modulation employ | adopted by this invention. (A) And (b) is a wave form diagram which illustrates the pulse pattern which records 4T mark, respectively. (A) And (b) is a wave form diagram which illustrates a pulse pattern when changing a pulse application period, respectively. The wave form diagram which illustrates the pulse pattern employ | adopted by the Example of this invention. FIG. 3 is a cross-sectional view showing a layer structure of a recording medium employed in the present invention. (A) And (b) is a wave form diagram of the pulse pattern respectively employ | adopted by the Example of this invention. (A) And (b) is an oscillograph photograph which shows the reproduction | regeneration waveform of Example 1 and the comparative example 1, respectively. (A) And (b) is a graph which shows the recording power dependence of the mark length and jitter in Example 2, respectively. (A) And (b) is a graph similar to FIG. 11 (a) and (b) in Example 3, respectively. (A) And (b) is a graph similar to FIG. 11 (a) and (b) in Example 4, respectively. (A) And (b) is the same figure as FIG. 13 at the time of m = n and m = n-1 in Example 4, respectively. (A)-(c) is an oscillograph photograph which shows the reproduced eye pattern in EFM modulation or 1-7 modulation, respectively. FIG. 10 is a waveform diagram showing a recording waveform pattern in Example 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower protective layer 3 Recording layer 4 Upper protective layer 5 Reflective layer 6 Protective layer

Claims (10)

The optical information recording medium is optically modulated by modulating the laser power of the irradiation light between the recording power Pw, the erasing power Pe, and the bias power Pb (where Pb ≦ Pe) according to the clock period T. In an optical recording method for forming or erasing a plurality of identifiable amorphous marks having different lengths and recording / erasing data by a mark length modulation recording method,
In forming an amorphous mark having a length nT (where n is an integer of 2 or more, and the minimum and maximum possible values of n are n _min and n _max , respectively)
Α ₁ T, α ₂ T,..., Α _m T and the period during which the bias power Pb is applied are β ₁ T, β ₂ T,. ..., Β _m T, and laser power application periods are sequentially α ₁ T, β ₁ T, α ₂ T, β ₂ T,..., Α _m T, β _m T (where k is (An integer from 0 to 2, j being a real number from 0 to 2, m = n−k, n _min −k ≧ 1, α ₁ + β ₁ +... + Α _m + β _m = n−j) Thus, the period during which the recording power Pw is applied is divided into m pulses for irradiation,
The linear velocity V when irradiating the irradiation light onto the recording medium is variable within the range of V _L ≦ V ≦ V _h , with the maximum linear velocity V _h and the minimum linear velocity V _L being set,
The clock cycle T is made variable according to the change of the linear velocity V,
Where i is an integer of 1 ≦ i ≦ m, the application period width of each of the divided recording powers Pw is α _i T, the application period width of each bias power is β _i T, and 2 ≦ i ≦ m−1. Α _i + β _i = 1.0 in _i satisfying
For all i, α _iL ≦ α _i1 ≦ α _i2 ≦ α _ih and α _iL <α _ih when V _L <V ₁ <V ₂ <V _h ,
Further, α _1h > α _ih (2 ≦ i ≦ m), and α _ih = 0.5 in i of 2 ≦ i ≦ m. An optical information recording medium is obtained by modulating the laser power of the irradiation light between the recording power Pw, the erasing power Pe, and the bias power Pb (where Pb / Pe ≦ 0.25) according to the clock period T. In an optical recording method for forming or erasing a plurality of optically identifiable amorphous marks, and recording / erasing data by a mark length modulation recording method,
In forming an amorphous mark having a length nT (where n is an integer of 2 or more, and the minimum and maximum possible values of n are n _min and n _max , respectively)
Α ₁ T, α ₂ T,..., Α _m T and the period during which the bias power Pb is applied are β ₁ T, β ₂ T,. ..., Β _m T, and laser power application periods are sequentially α ₁ T, β ₁ T, α ₂ T, β ₂ T,..., Α _m T, β _m T (where k is (An integer from 0 to 2, j being a real number from 0 to 2, m = n−k, n _min −k ≧ 1, α ₁ + β ₁ +... + Α _m + β _m = n−j) Thus, the period during which the recording power Pw is applied is divided into m pulses for irradiation,
The linear velocity V when irradiating the irradiation light onto the recording medium is variable within the range of V _L ≦ V ≦ V _h , with the maximum linear velocity V _h and the minimum linear velocity V _L being set,
The clock cycle T is made variable according to the change of the linear velocity V,
i as integer 1 ≦ i ≦ m, the divided application period widths of the individual recording power Pw and alpha _i T, the linear velocity V is V _L, when the _{V 1, V 2, V h} α i _Is α _iL , α _il , α _i2 , α _ih respectively.
For all i, α _iL ≦ α _i1 ≦ α _i2 ≦ α _ih and α _iL <α _ih when V _L <V ₁ <V ₂ <V _h ,
Further, α _1h > α _ih (2 ≦ i ≦ m), and α _ih = 0.5 in i of 2 ≦ i ≦ m. 3. The optical recording method according to claim 2, wherein α _i + β _i = 1.0 in _i satisfying 2 ≦ i ≦ m−1. The optical recording method according to claim 1, wherein α _1h = 0.5. 5. The optical recording according to claim 1, wherein α _i is constant and α ₁ > α _i with respect to i in a range of 2 ≦ i ≦ m. Method. Mark length modulation recording in which the maximum linear velocity V _h is in the range of 2 to 6 times the minimum linear velocity V _{L in} the range of 1.2 to 1.4 m / s,
m is selected as m = n, n-1 or n-2,
The linear velocity V is selected to be based on a finite number of values of V = V _L , 2V _L , 4V _L , or 6V _L ,
At each linear velocity V, α _i + β _i = 1.0 when i is in the range of 2 ≦ i ≦ m, and Pr is the reproducing light power when i is within the range of 1 ≦ i ≦ m, and Pb _i = Pr ± 0.5 mW
6. The optical recording method according to claim 1, wherein α _i monotonously decreases for all i when the linear velocity V decreases. 7. 7. β _i takes a constant value with respect to i in the range of 1 ≦ i <m, and β _m is different from the constant value and can be zero. The optical recording method according to any one of the above. Mark that the maximum linear velocity V _h to be used is in the range of 2 to 6 times the minimum linear velocity V _{L in} the range of 1.2 to 1.4 m / s, and m = n, n−1, or n−2. Using long modulation EFM modulation,
The linear velocity V is selected as a finite number of values of V _L , 2V _L , 4V _L or 6V _L ,
When the linear velocity V is 2 V _L or more, α _1h = 1.5 or 1.0, and in the range of 1 ≦ i ≦ m, β _1h = α _ih = 0.5 (2 ≦ i ≦ m)
For all linear velocities V, in the range of 2 ≦ i ≦ m, α _i + β _i-1 = 1.0,
When the linear velocity V is 2V _L and i is in the range of 1 ≦ i ≦ m, Pr is the reproduction light power, Pb _i = Pr ± 0.5 mW,
When the linear velocity V is V _L and i is in the range of 1 ≦ i ≦ m, 0.05 <α _i <0.5 and α _1L ≦ α _1h ,
The optical recording method according to claim 1, wherein Pb _i = Pe at the linear velocity V _h . The optical recording method according to claim 8, wherein β _m ≠ 0.5. The optical information recording medium is variable among Pw, Pe, Pb, m, j, k, α _i and β _i so as to select one from a plurality of pulse division methods according to the linear velocity V used. The optical recording method according to claim 1, wherein the optical recording method is a medium formed by recording a combination of information to be recorded as pulse division information.

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