JP2007004983A - Recording method for write-once type optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a write-once type high-density optical recording medium enabling high-speed recording, and to form a space favorably especially between recording marks. <P>SOLUTION: An irreversible recording mark is formed by applying a laser beam having a wavelength of a range of 200 to 450mm to the recording layer of a write-once type optical recording medium. After a laser beam of predetermined write power Pw is applied in order to form the recording mark, a laser beam of a power level P1 of a range of a track tracing limit value lower than read power Pr set to read the recording mark to 0.4mW is applied for predetermined time, and a recording mark having at least a shortest recording mark length among the recording marks set less than a 0.35 times a laser spot diameter and a width of the shortest recording mark set equal to or higher than a 0.7 times the shortest mark length, is formed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a recording method for a write once optical recording medium.

  At present, in the optical recording medium market, rewritable optical recording media and so-called write-once optical recording media that cannot be rewritten are in circulation. Since the rewritable optical recording medium can be rewritten literally many times, the same optical recording medium can be repeatedly used with only necessary information. On the other hand, write-once optical recording media are characterized by the fact that data cannot be rewritten and, conversely, “data is not tampered with”, so that their usefulness for distribution, storage, or backup is recognized.

  In recent years, in the field of multimedia-compatible optical recording media, recording at higher density and higher speed is required, and similar requirements are also applied to write-once type optical recording media.

  In the rewritable optical recording medium, it is necessary to strictly control the specifications related to time, such as the cooling rate, and the recording strategy becomes more complicated as the recording speed increases and the recording density increases. In the past, write-once optical recording media have not had a complicated recording strategy. However, in view of further increases in density and speed in the future, it has become clear that sufficient characteristics cannot be obtained with a recording strategy used in a conventional write-once type optical recording medium. Here, the recording strategy means a power control pattern of laser light for recording. In general, a laser beam for recording is not continuously irradiated in accordance with the length of a recording mark (particularly when recording is performed on an optical recording medium using a phase change material). As described in JP-7176, in order to control the recording mark shape, it is possible to irradiate a laser beam as a pulse train composed of a plurality of pulses and to strictly control the width of each pulse in the pulse train. Many. In this case, a specific configuration of pulse division is generally referred to as a recording strategy.

  The present invention has been made to solve such a conventional problem, and in particular, recording on a write-once type optical recording medium capable of maintaining the space between the recording marks in a clean unrecorded portion. It aims to provide a method.

  The object is achieved by the present invention shown in the following (1) to (3).

  (1) A recording mark can be formed by irradiating a recording layer of a write-once type optical recording medium with a laser beam having a wavelength in the range of 200 to 450 mm, and a predetermined light is used to form the recording mark. After irradiating the laser beam with the power Pw, the laser beam with the power level P1 in the range of the track trace limit value to 0.4 mW lower than the read power Pr set for reading the recording mark is irradiated for a predetermined time, Of the recording marks, at least the shortest recording mark length is less than 0.35 times the laser spot diameter, and the shortest recording mark width is 0.7 times or more the shortest mark length. A recording method for a write once optical recording medium.

  (2) In (1), before irradiating the predetermined write power Pw to form the recording mark, 1.1 Pr to 0... 0 higher than the read power Pr and lower than the write power Pw. 4. A recording method for a write-once optical recording medium, wherein a laser beam having a power level P2 in the range of 4Pw is irradiated.

  (3) In (1), after laser light having a power level P1 lower than the read power Pr is irradiated for a predetermined time, it is further higher than the read power Pr and lower than the write power Pw. A recording method for a write-once type optical recording medium, wherein a laser beam having a power level P2 in the range of 1 Pr to 0.4 Pw is irradiated.

  In the present invention, after irradiating a laser beam having a predetermined write power Pw to form a recording mark, a laser beam having a power level P1 in the range of a track trace limit value lower than the read power Pr to 0.4 mW is irradiated. It is configured to do. As a result, there is a high possibility that the problem will occur when high-density recording is performed at high speed, in particular, excessive heat from the laser beam remains near the end of a long recording mark. It is possible to effectively prevent the problem that spaces (portions where no recording marks are formed) cannot be formed cleanly.

  In addition, before irradiating the write power Pw for forming the recording mark, the laser beam having the power level P2 in the range of 1.1 Pr to 0.4 Pw higher than the read power Pr and lower than the write power Pw is applied. By doing so, it is possible to compensate for a decrease in recording sensitivity that occurs during high speed recording. Thereby, in order to achieve particularly high density recording, a recording mark whose shortest recording mark length is less than 0.35 times the laser spot diameter and whose shortest recording mark width is 0.7 times or more of the shortest mark length is recorded. It is possible to form more reliably, and it is possible to solve the decrease in recording sensitivity that occurs when the pulse length during formation is shortened. The irradiation at the power level P2 may be after the irradiation at the power level P1.

  According to the present invention, an optical recording medium suitable as a multimedia-compatible recording medium can be obtained because high-speed and high-density recording is possible at a low cost.

  According to the present invention, recording at high speed becomes possible. In addition, since the mark / space edge portion, which is a problem in increasing the density at the time of high-speed recording, can be kept clear, it is possible to compensate for a decrease in recording sensitivity caused by high-speed recording. Furthermore, by adjusting the maintenance time of this low power level, it is possible to better cope with high-speed recording including low-speed recording.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  As shown in FIG. 1, a high-speed and high-density write-once optical recording medium (hereinafter referred to as an optical recording medium) 10 to which a recording method according to the present invention is applied includes a reflective layer 14 and a second dielectric layer on a support base 12. 16, a recording layer (laminated recording layer) 18, a first dielectric layer 20, and a light-transmitting cover layer 22 are provided in this order, and a blue laser having a wavelength of 405 nm, for example, from a recording laser light source 24. By irradiating the recording layer 18 with light through the light-transmitting cover layer 22, the reflectance of the irradiated region is changed, and this is used as a recording mark.

  At least one of the recording layers 18 preferably employs one of the highly reflective metals such as Al, Ag, Au, and Cu as the main component metal. Specific combinations include Al-Sb, Al-Ca, Al-Ce, Al-La, Al-Se, Au-Ce, Au-La, Au-Si, Au-Ge, Si-Cu, and Ge-Cu. Etc.

  Among them, in particular, Al and Ag have high reflection characteristics even with respect to lasers of blue or lower, so that it is easy to adjust the reflectance by changing the film thickness of the sub-recording layer, and the reflectance of the unrecorded portion Can be set higher than the reflectance after the recording mark is formed, which is more preferable.

  Furthermore, a combination that forms an intermetallic compound having a higher melting point than any of the sub-recording layers or any of the main component metals is more preferable.

  When the recording layer 18 is irradiated with blue laser light as recording light, the main component metals contained in the first and second sub recording layers 18A and 18B are diffused and mixed in the irradiated region. The reaction product generated by further layering changes the reflectivity of the irradiated area, so that it can be recognized as a recording mark. Since the reaction in which the two main component metals are diffused and mixed is irreversible, the recording layer 18 can perform write-once type optical recording.

  The thickness of the recording layer 18, that is, the total thickness of the first and second sub recording layers 18A and 18B is 3 to 50 nm, preferably 5 to 20 nm. Qualitatively, if the recording layer 18 (sub-recording layers 18A and 18B) is too thin, it is difficult to ensure a sufficient difference in reflectance between recording marks before and after recording, while the recording layer 18 is too thick. Then, since the heat capacity becomes large, the recording sensitivity is lowered.

  The thickness of each of the sub recording layers 18A and 18B is appropriately determined so that a recording mark having high thermal stability and a large reflectance difference is formed. For example, when an Al-based sub-recording layer and an Sb-based sub-recording layer are combined, it is considered that an intermetallic compound in which Al and Sb are combined at a ratio of 1: 1 is formed. It is preferable to set the thickness of each recording layer so that the ratio (atomic ratio) to Sb does not deviate significantly from 1: 1.

The first and second dielectric layers 20 and 16 are made of various dielectric materials such as oxide, sulfide, nitride, fluoride, carbide, or a mixture thereof. Specifically, in this sample, the first and second dielectric layers 20 and 16 are both formed by sputtering using a ZnS—SiO ₂ target (ZnS: 80 mol%, SiO ₂ : 20 mol%). is doing.

  The first dielectric layer 20 has a thickness of 5 to 200 nm and is provided so as to sandwich the recording layer 18 together with the second dielectric layer 16. The second dielectric layer 16 has a thickness of 5 to 200 nm and is provided on the reflective layer 14.

  The first and second dielectric layers 20 and 16 serve not only to protect the recording layer 18 from water vapor or other gases, but also by adjusting the thickness of the first and second dielectric layers 20 and 16 so as to cause the laser beam to interfere with the recording layer 18. Thus, it is possible to adjust the reflectance at an unrecorded portion 18 or to increase the difference in reflectance before and after optical recording.

  The support base 12 is made of polycarbonate having a thickness of 1.1 mm, for example.

  The reflective layer 14 is formed by, for example, forming a silver alloy layer on the support base by sputtering or the like, and has a thickness of about 10 to 200 nm. The reflection layer 14 is located behind the recording layer 18 when viewed from the laser beam incident side, and gives a return light to the recording layer 18 to increase the difference in reflectance before and after recording. This contributes to increasing the recording sensitivity. The reflective layer 14 is made of a metal (including a semimetal) film, a dielectric multilayer film, or the like. In this sample, the reflective layer 14 is formed of an alloy AgPdCu whose main component is silver having a thickness of 100 nm. However, the reflective layer 14 is not necessarily essential.

  The light transmissive cover layer 22 is formed on the first dielectric layer 20 by a spin coating method, or is formed by adhering a previously formed sheet-like member. For example, an ultraviolet curable resin layer, It consists of a polycarbonate sheet. The thickness of the light-transmitting cover layer 22 is the numerical aperture (NA) of the objective lens 26 when the recording layer 18 is irradiated with blue laser light having a wavelength of 405 nm, for example, the total thickness with the first dielectric layer 20. Is selected so that the blue laser light can be condensed on the recording layer 18. In this sample, it was about 100 μm.

  Of the optical recording medium 10 to which this embodiment is applied, in the case of the recording layer 18 including the first sub recording layer 18A mainly composed of Al and the second sub recording layer 18B mainly composed of Sb, the above recording is performed. When the thermal stability of the reaction product in the recording mark formed on the layer 18 (that is, the thermal stability after recording) is such that the first and second sub-recording layers 18A and 18B are simply laminated at the unrecorded portion. The main characteristic is that it is higher than the thermal stability (that is, the thermal stability before recording).

  More specifically, the main component metals of the first and second sub-recording layers 18A and 18B when irradiated with laser light are in a state of being diffused and mixed, and are present as intermetallic compounds. Even if no intermetallic compound is generated, it is considered that at least the main component metals are present as a mixture in a bonded state. Since the reaction product generated by the mixing irreversibly changes the reflectance of the irradiated region, this change in reflectance can be used as a recording mark.

  The melting point of Al is 660 ° C., and the melting point of Sb is 631 ° C. Both of them are well above 500 ° C., are thermally stable by themselves, and can be melted by laser light irradiation. In addition, the reaction between Sb and Al can produce a stable intermetallic compound AlSb (melting point: 1060 ° C.) having a sufficiently higher melting point than that of each simple substance and whose crystal structure does not change between low and high temperatures. The intermetallic compound such as AlSb does not need to be crystal-grown and can be recorded even in a microcrystalline state that cannot be detected by electron diffraction.

  In view of this phenomenon, when the recording layer 18 is irradiated with a laser beam having a write power Pw capable of forming a recording mark, A) In the region where the recording layer 18 is not mixed, the mixing is performed. It occurs and the reflectance changes (recording becomes possible). On the other hand, B) In the area where the recording mark is already formed, the reflectance does not change due to the irradiation of the recording light. It can be said that it is an ideal characteristic as a write-once type.

  Therefore, even if the optical recording medium 10 is stored in a high temperature environment after recording, the recording mark made of the reaction product hardly changes and is stable. In addition, the recording mark hardly changes even by continuous reproduction, and the reproduction durability is excellent. Furthermore, even if the reflectance after recording mark formation is set to be low and the light absorption after recording mark formation is increased, the thermal stability of the recording mark is high. It will not deteriorate.

  In addition, since the thermal stability of the recording mark is high, the phenomenon of erasing the recording mark on the adjacent track during recording (cross erase) does not substantially occur. Therefore, the recording track pitch can be narrowed, which is effective for high-density recording (described later).

  FIG. 2 shows an example of a recording strategy for forming a recording mark. FIG. 2 shows an example in which a relatively long recording mark R is formed. However, the example of FIG. 2 exaggerates the qualitative concept, and the size and number of each pulse, the maintenance time, and the like do not necessarily match those in reality.

  FIG. 2A shows the most basic example of this embodiment. In this example, a switching configuration of write power Pw and bias power Pb is basically adopted as a strategy at the time of recording, and a laser beam having a predetermined write power Pw for forming a recording mark R thereon (example in the figure). Then, after irradiating FP and three MPs), a configuration is added in which laser light having a power level P1 lower than read power (laser power set to read the recording mark R) Pr is irradiated for a predetermined time T1. ing.

  When high-density recording is performed and the recording transfer speed is high, the heat of the laser beam remains excessively near the end of the long recording mark R, and the rear portion of the recording mark is caused by this residual heat. Tends to be a shape with a trailing edge, and the edge of the rear part of the mark is distorted. At this time, there is a problem that the mark portion enters the space up to the next recording mark and the space cannot be formed cleanly. In particular, in mark edge recording, since the mark / space boundary is unclear, the Jitter value of the signal deteriorates and an error is likely to occur.

  However, such a problem can be prevented from occurring by maintaining the power level P1 lower than the read power Pr for the predetermined period T1 in the last part of the recording mark formation.

  By using such a strategy, the write-once type achieves high-density recording in which the shortest mark (space) length is less than 0.35 with respect to the spot diameter (defined by the laser wavelength λ / the numerical aperture NA of the lens). An optical recording medium can be obtained. Specifically, when the laser wavelength is 405 nm and the numerical aperture of the lens is 0.85, the shortest mark length is less than 167 nm.

  The maintenance time T1 of the power level P1 is suitably in the range of 0.2 to 1.0 times the passage time of the shortest mark (space) length, more preferably in the range of 0.3 to 0.8 times. However, the bias power Pb and the power level P1 may be matched, and the maintenance time T1 may be longer than the length of the longest space.

  Specifically, the power level P1 is suitably in the range of the track trace limit value to 0.4 mW. Since the limit value of the track trace is about 0.08 mW at present, more preferably, 0.1 mW to 0.3 mW is the optimum range at present. If the hardware trace capability improves in the future, the lower limit may be lowered accordingly.

  FIG. 2B is based on the configuration of FIG. 2A, and is higher than the read power Pr before irradiating a predetermined write power Pw to form the recording mark. Laser light having a power level P2 lower than the write power Pw is irradiated. When recording at high speed, it is effective to set the laser power P2 higher than the read power Pr and perform preheating from the viewpoint of the rise time of the laser beam or the recording sensitivity. In particular, when the power level P1 lower than the read power Pr is maintained after the recording mark is formed as in this embodiment, the rising portion of the next recording mark can be formed satisfactorily.

  The power level P2 is higher than the read power Pr but sufficiently lower than the write power Pw. This is to prevent an unintended recording mark from being formed on an unrecorded portion due to the laser beam irradiation at the power level P2. Specifically, a range of 1.1 Pr to 0.4 Pw is appropriate, and a range of 1.2 Pr to 0.3 Pw is more preferable.

  The maintenance time T2 of the power level P2 is preferably in the range of 0.2 to 1.0 times the passing time of the shortest mark length, but may be the power level of P2 immediately after irradiation of P1 (FIG. 2D).

  As shown in FIG. 2C, in FIG. 2B, the bias power Pb at the time of recording mark formation may be made to coincide with the power level P1 (Pb = P1).

  FIG. 2D shows the bias power Pb for forming the recording mark in FIG. 2C set to a value slightly lower than the power level P2 (Pb≈P2). By doing so, the shape of the intermediate portion of the recording mark can be adjusted to a shape closer to a straight line. In particular, by setting the power level of Pb to a value that is the same as or slightly lower than P2, the write power can be set low, and the decrease in recording sensitivity that is disadvantageous during high-speed recording can be compensated.

  In any of the cases (A) to (D), it is basically possible to cope with variable speed recording by changing only the frequency and the write power Pw while using the recording strategy of the same pattern. Can do. In this case, in particular, if the values of the bias power Pb and the power levels P1 and P2 are changed and set in accordance with the recording transfer speed, the recording mark R is further prevented from becoming a teardrop type or a reverse teardrop type. Can be fine-tuned precisely.

  In particular, when recording is performed in a drive device capable of performing trial writing on the optical recording medium 10 prior to recording of information, the value of the bias power Pb and recording mark formation are performed during the trial writing. By adjusting the maintenance time T1 of the power level P1 immediately after that, the maintenance time T2 of the power level P2, etc., good recording characteristics can be obtained at any recording transfer speed between 35 Mbps and 100 Mbps. The times T1 and T2 may be changed independently.

  By the way, in this embodiment, as shown in FIG. 3, the shape of the shortest recording mark R1 is not an ellipse like the conventional recording mark Ro, but a shape close to a perfect circle. In FIG. 3, an example of dimensions when forming a DVD-R recording mark is shown for reference.

  As described above, the optical recording medium 10 does not require deformation of the groove portion when forming the recording mark R1 in combination with the effect of the basic recording method. Therefore, there is no problem even if it is recorded outside.

  For this reason, even when the recording density is high, the track pitch is narrowed and the group width is narrow, the shortest mark has a shape close to a perfect circle, and the conventional width is 0.5 (times) or less of the shortest mark length. It can be 0.7 or more, more preferably 0.8 or more.

  In order to bring the shortest recording mark closer to a perfect circle, the write power is increased and the pulse width is shortened. Specifically, the laser pulse with the write power Pw was irradiated in the range of 0.3 to 0.7 (times) the transit time of the shortest mark length. In this embodiment, the transit time of the shortest mark length is Laser irradiation is performed in the range of 0.05 to 0.3. By doing in this way, as shown in FIG. 3, when having the same circumferential length, a larger reproduction signal can be obtained, and CNR (carrier to noise ratio) can be improved. In addition, when a reproduction signal having the same size as the conventional one is sufficient, higher density recording is possible.

  When the write power is increased to bring the shortest recording mark closer to a perfect circle in this way, the power level P1 set to a value lower than the above-described “read power Pr set when reading the recording mark”. The configuration of irradiating the laser beam of "is more advantageous in that the space can be formed cleanly." Further, “a configuration in which a laser beam having a power level P2 higher than the read power Pr and lower than the write power Pw is irradiated before the predetermined write power Pw is irradiated to form a recording mark” This also contributes more favorably to compensating for the power shortage caused by shortening the pulse width. Of course, these configurations may be adopted at the same time.

  The operation of the recording method of the optical recording medium 10 according to this embodiment will be described.

  The recording marks of the recording layer (laminated recording layer) 18 of the optical recording medium 10 to which this embodiment is applied are basically formed by predetermined diffusion / mixing of the main component metals in the sub-recording layer by irradiation with laser light. Therefore, high-speed recording can be easily performed by adjusting the heat amount control. Further, since a metal material having a high thermal conductivity is used for the laminated recording layer, it is not necessary to consider the influence of large thermal interference generated in an optical recording medium using a dye material. Therefore, it is most suitable as an additional type optical recording medium for realizing the recording method according to the present invention.

  By using the recording strategy as shown in FIGS. 2A to 2D described above, the mark / space edge portion, which is a problem in high density recording at high speed recording, can be kept clear and high speed recording can be performed. Can compensate for the decrease in recording sensitivity.

  In this way, high-speed and high-density recording, which was difficult with a write-once type optical recording medium, is possible.

  Particularly, since the laser beam having the power level P1 in the range of the track trace limit value to 0.4 mW lower than the read power Pr is irradiated after irradiating the laser beam with the write power Pw (even if a long recording mark is formed). In this case, the influence of residual heat can be minimized, and a space up to the next recording mark can be left in a clean unrecorded portion. Further, even if the write power Pw is set large so as to form the shortest recording mark in a shape close to a perfect circle, the influence of the residual heat can be eliminated satisfactorily. The space up to the recording mark can be left in a clean unrecorded part.

  In the above embodiment, when information is specifically recorded on the optical recording medium 10, the wavelength of the laser beam is set to a blue wavelength of 405 nm. Rather, it can be said that the advantages of the present invention can be fully utilized only in high-speed recording under such conditions.

Example of Al / Sb An optical recording medium was prepared with the configuration shown in FIG. 1 and evaluated for high-density and high-speed recording.

  The support base 12 was a 1.1 mm polycarbonate substrate on which a group having a track pitch of 0.32 μm and a group width of 0.13 μm was formed, and the thickness of the light-transmitting cover layer 22 was 100 μm.

  Other layers were formed by sputtering under the following conditions.

Electrostatic layer: ZnS + SiO ₂ (80:20 mol%)
First dielectric 20: 60 nm
Second dielectric 16: 105 nm
First sub-recording layer 18A: AlCr (98: 2 at.%) 4 nm
Second sub recording layer 18B: Sb 6 nm
Reflective layer 14: AgPdCu (98: 1: 1 at.%) 100 nm

  Using an evaluation device with a laser beam wavelength of 405 nm and an objective lens group having a numerical aperture NA of 0.85, the recording linear velocity is changed by 70 Mbps equivalent ((1,7) RLL modulation method, channel clock 132 MHz fixed, format efficiency 80%). As a result, the shortest mark (2T) length was changed, a random signal was recorded, and the reproduction Jitter value was evaluated.

  The multi-pulse strategy used for recording is (n-1) type, 2T is a FP (first pulse) 1 pulse, 5T is a FP and MP (multi-pulse) 3 pulses, a total of 4 pulses. Using.

  Using the strategy having the shape shown in FIG. 2A, Pr = Pb: 0.5 mW, Pw: 6.0 mW, and the respective pulse lengths are TFP: 0.3 T (0.15), TMP: 0 .25T, T1: 1T (0.5) (ratio to the shortest mark length).

  At this time, P1 is 0.1 mW and 0.5 mW (P1 = Pr comparative example), and the results of evaluation using the clock jitter value of the signal are shown in Table 1.

  It can be seen that by using a recording strategy for irradiating a power level P1 lower than the read power for a predetermined time, the jitter value is lowered and the signal characteristics are improved. It can also be seen that the difference is particularly noticeable when the shortest mark length is shortened to a high recording density.

  The recording layer of the sample in which a single signal of 2T (shortest mark) mark and space was recorded at 10.6 m / s was peeled from the substrate and the cover layer, and the shape of the recording mark was observed by TEM. The recording mark width has reached 150 nm (about 0.9 times the recording mark length), and the mark is almost a perfect circle.

  The recording signal was evaluated for the same sample using the recording strategy having the shape shown in FIG.

  P2 = Pb: 1 mW, P1: 0.1 mW, each pulse length and other conditions were the same as those described above, and a random signal was recorded at a recording linear velocity of 10.6 m / s and evaluated.

  The optimum write power was reduced to 5.0 mW (Jitter 7.6%), and the recording sensitivity could be improved from 6.0 mW to 1.0 mW.

Example of Si / Cu An optical recording medium was prepared with the configuration shown in FIG.

  The supporting substrate and the light-transmitting cover layer were the same as those in Example 1.

  Other layers were formed by sputtering under the following conditions.

Electrostatic layer: ZnS + SiO ₂ (80:20 mol%)
First dielectric 20: 22 nm
Second dielectric 16: 28 nm
First sub recording layer 18A: Si 5 nm
Second sub recording layer 18B: Cu 6 nm
Reflective layer 14: AgPdCu (98: 1: 1 at.%) 100 nm

  Using an evaluation device with a laser beam wavelength of 405 nm and an objective lens group having a numerical aperture NA of 0.85, the recording linear velocity is changed at an equivalent of 35 Mbps ((1, 7) RLL modulation method, channel clock 66 MHz fixed, format efficiency 80%). As a result, the shortest mark (2T) length was changed, a random signal was recorded, and the reproduction jitter value was evaluated.

  Using the strategy having the shape shown in FIG. 2A, Pr = Pb: 0.5 mW, Pw: 5.0 mW, and the length of each pulse is TFP: 0.3T (0.15), TMP: 0 .25T, T1: 1T (0.5) (ratio to the shortest mark length).

  Table 2 shows the results of evaluation using the clock jitter value of the signal in the same manner as in Example 1, with P1 being 0.1 mW and 0.5 mW (P1 = Pr comparative example).

  It can be seen that the jitter value is lowered and the signal characteristics are improved by using a recording strategy in which a power level P1 lower than the read power is irradiated for a predetermined time as in the first embodiment. It can also be seen that the difference is particularly noticeable when the shortest mark length is shortened to a high recording density.

Sectional drawing which expands and shows typically the high-speed write-once type optical recording medium to which the present invention is applied Pulse waveform diagram showing an example of a recording strategy when a recording mark is formed on the high-speed write-once optical recording medium Explanatory drawing which showed the formation method of the shortest recording mark in the said embodiment compared with the past.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Low speed-high-speed write-once type optical recording medium 12 ... Support base | substrate 14 ... Reflective layer 16 ... 1st dielectric material layer 18 ... Recording layer 18A ... 1st subrecording layer 18B ... 2nd subrecording layer 20 ... 2nd dielectric material layer 22 ... Light-transmitting cover layer

Claims (3)

By irradiating the recording layer of the write-once type optical recording medium with a laser beam having a wavelength in the range of 200 to 450 mm, an irreversible recording mark can be formed,
After irradiating a laser beam with a predetermined write power Pw to form the recording mark, a power level in the range of the track trace limit value to 0.4 mW lower than the read power Pr set to read the recording mark P1 laser beam is irradiated for a predetermined time,
Among the recording marks, at least the shortest recording mark length is less than 0.35 times the laser spot diameter, and the shortest recording mark width is 0.7 times or more the shortest mark length. A recording method for a write-once optical recording medium. In claim 1,
Before irradiating the predetermined write power Pw to form the recording mark, the power level P2 is in the range of 1.1 Pr to 0.4 Pw that is higher than the read power Pr and lower than the write power Pw. A recording method for a write once optical recording medium, characterized by irradiating a laser beam. In claim 1,
After performing laser beam irradiation at a power level P1 lower than the read power Pr for a predetermined time,
A recording method for a write-once optical recording medium, wherein laser light having a power level P2 in the range of 1.1 Pr to 0.4 Pw higher than the read power Pr and lower than the write power Pw is irradiated.

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