JPH11339268A - High density optical recording method and medium thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an optical medium which contains dyestuff in its recording layer to perform satisfactory high density recording that comprises formation of pits, each having a smaller diameter than the laser spot diameter. SOLUTION: This recording medium is provided on a transparent substrate with a recording layer and a metallic reflection layer. In this recording method, mark edge recording is performed in such a way that the correlation of the minimum pit length Pmin with (r) ((r) is λ/NA (where λ is a recording wavelength (μm) and NA is the numerical aperture of a pickup objective lens)) meets the relation 0.35r<=Pmin<=0.45r, and when laser beam irradiation for forming a pit of length of Mi[T] (Mi[T] is the length of a pit (i); represented with a clock cycle T as units, (i) is a positive integer, and M1<M2<...<Mi<...<Mn), while placing a space of Lj[T] between the pit (i) and its preceding pit (where Lj[T] is the length of the space, represented with by clock time T as the unit, (j) is a positive integer, and L1<L 2<...<Lj<...<Lm), is performed in such a way as to meet the following relation ti(L1)<ti(L 2)<=...<=ti(Lj)<=...<=ti(Lm), and when an irradiation time ti[T] is ti(Lj) (where ti[T] is the irradiation time for forming the pit (i), represented with the clock cycle T as units, and ti(Lj) is ti[T] at the placing of the space of Lj[T] between the pit (i) and its preceding pit); and 0.01T<=Δtij<=0.2T (when Δtij=ti(Lj)-ti(L1), and (Js) for all with j>=2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording an optical recording medium having a recording layer containing a dye and a reflective layer on a transparent substrate, and more particularly to an optical recording method capable of recording at high density.

[0002]

2. Description of the Related Art A recordable optical recording medium in which a dye is used as a recording layer and a metal reflective layer is provided on the recording layer to increase the reflectance is disclosed in, for example, Optical Data Storage 1989.
Technical Digest Series Vol. 145 (1989), a medium using a cyanine dye or a phthalocyanine dye in the recording layer is available on the market as a CD-R medium. These media are characterized in that they can be recorded with a 780 nm semiconductor laser and can be reproduced by a commercially available CD player or CD-ROM player equipped with a 780 nm semiconductor laser. Also, 635
A DVD-R having a capacity of 3.95 GB on one side, which can be recorded / reproduced by a semiconductor laser of up to 650 nm and can be reproduced on a commercially available DVD player or DVD-ROM player, is already on the market. Furthermore, although the recording capacity is different from that of DVD-R, a read-only DV having 4.7 GB per side is used.
D media is also available on the market. At present, it is important to improve the quality of a recording signal for a DVD-R having a capacity of 3.95 GB, and a recordable optical recording medium having the same recording capacity as the read-only DVD medium is required. .

The beam spot diameter used for recording on the DVD-R is smaller than the beam spot diameter used for recording on a conventional CD-R.
The recording density is higher than the increase in recording density predicted from the reduction ratio of the beam spot diameter.
Therefore, during recording, pits smaller than the beam spot diameter must be accurately formed as compared with the case of CD-R. However, there is a problem that thermal interference between pits at the time of recording and the influence of the spread of the recorded pit to an adjacent track (crosstalk) are large, so that the jitter of the shortest pit becomes high and high-density recording becomes difficult. is there. Therefore, when the recording density is higher than the beam spot diameter, it is important to reduce the problems described above.

A method for performing high-density recording on an optical recording medium using a dye for the recording layer is disclosed in Japanese Patent Publication No. 4-49525. However, this publication only describes a method for reducing crosstalk, and does not disclose any method for suppressing jitter deterioration due to thermal interference between pits. Also, Japanese Patent Application Laid-Open
No. 83573 discloses a method of changing the beam irradiation time according to the length of the interval between pits. However, it does not disclose any conditions for forming pits smaller than the beam spot diameter in an optical recording medium having a dye in the recording layer.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of suppressing high jitter due to thermal interference between pits and enabling high-density optical recording even if the recording density is increased with respect to the recording beam diameter. That is.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies with the aim of solving the above-mentioned problems, and as a result, have completed the present invention. That is, the present invention, on a transparent substrate having a groove, a recording layer containing a dye that absorbs laser light directly or through another layer,
In an optical recording medium having a metal reflective layer directly on the recording layer or via another layer, the shortest pit lengths Pmin and r
= Λ / NA [λ is the recording wavelength (μm), NA is the numerical aperture of the objective lens of the pickup], but 0.35r ≦ Pmin ≦ 0.
When performing mark edge recording satisfying 45r, the length of the pit is Mi [T] (the length expressed by the clock interval time T, i
Is an integer), and the length of the interval between pits immediately before the pit is Lj
[T] (j is an integer), and M1 <M2 <... <Mi <... <Mm L1 <L2 <... <Lj <... <Lm, and the length of Mi after the interval of Lj A laser beam irradiation time ti [T] for forming a pit of a height ti (L
j), ti (L1) <ti (L2) ≤ ... ≤ti (Lj) ≤
... ≤ti (Lm), and .DELTA.tij = ti (Lj) -ti (L1
), 0.0 for all j ≧ 2
The present invention relates to a high-density optical recording method that satisfies 1T ≦ Δtij ≦ 0.2T, and a high-density recording medium having recording recorded by the method described above.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The recording method of the present invention is a high-density optical recording method capable of suppressing jitter deterioration due to thermal interference between pits even if the recording density is increased with respect to the recording beam diameter. Very good even when performing mark edge recording in which the length Pmin and r = λ / NA (λ is the recording wavelength (μm), NA is the numerical aperture of the objective lens of the pickup) satisfy 0.35r ≦ Pmin ≦ 0.45r. This is a recording method that can obtain a proper reproduction signal.

[0008] As a recording method for an organic dye-based optical recording medium, there is a recording method for CD-R. This means that for a recording code pulse width of 3T, 4T, 5T,... 11T (T is a clock interval time) in the EFM signal, recording laser pulses having a length of 2T, 3T, 4T,. Irradiation, a so-called (n-1) T strategy, is a basic recording method. However, with this recording method,
The shortest pit length is 0.45 × λ / NA [λ is the recording wavelength (μ
m), NA is not high when high-density recording is performed to form smaller pits smaller than or equal to the numerical aperture of the objective lens of the pickup.

The pits formed after the shortest pit interval are apt to open due to the influence of heat generated during the formation of the pits recorded before the interval, but as the pit interval increases, the pits increase. Are difficult to open, and as a result, the pit length may be uneven. In order to prevent such non-uniform pit lengths, it can be prevented to some extent by using pulse-divided basic recording laser pulses as shown in FIG.

According to the recording method of the present invention, the length of the pit is set to Mi.
[T] (the length represented by the clock interval time T, i is an integer), and the length of the inter-pit interval immediately before the pit is Lj [T].
(J is an integer), and M1 <M2 <... <Mi <... <Mm L1 <L2 <... <Lj <... <Lm, and a pit having a length of Mi after the interval of Lj The laser beam irradiation time ti [T] for forming
j), ti (L1) <ti (L2) ≤ ... ≤ti (Lj) ≤
... ≤ti (Lm), and .DELTA.tij = ti (Lj) -ti (L1
), 0.01T ≦ Δtij ≦ 0.2T is satisfied for all j ≧ 2, thereby enabling high-density optical recording. That is, the recording method is characterized in that a laser beam irradiation time for forming a pit after the shortest pit interval is shorter than an irradiation time for forming other pits. According to the recording method of the present invention, pit size non-uniformity is corrected, so that recording with extremely good jitter can be performed.

Here, Δtij is optimized in consideration of the recording laser pulse width with respect to the recording code pulse width, the dye type, the dye film thickness, the substrate groove shape, and the like. Is likely to be non-uniform, which is not preferred. Conversely, if it is smaller than 0.01 T, the effect of the present invention tends to be extremely small, which is not preferable. The laser beam irradiation time ti for forming a pit having a pit length Mi is the total time during which the laser beam is output when the pulse is divided as shown in FIG. Usually, the adjustment of Δtij is performed at the first rising edge of the laser beam. If the shortest pit length is 0.35 × λ / NA or less, the signal amplitude of the shortest pit length becomes small, and good recording becomes impossible.

The recording method according to the present invention is, for example, shown in FIG.
Although it can be applied to basic recording pulses as shown in FIGS. 1A and 1B, from the viewpoint of removing thermal interference as much as possible in high-density recording, it is shown in FIGS. Such a recording pattern is preferable. The signals to be recorded include an EFM signal suitable for mark edge recording,
(8-16) Modulated signal, (2-7) Modulated signal, (1-
7) Modulation signals and the like. The laser wavelength used for recording is 0.635 to 0.6 which is usually used for DVD.
A laser having a thickness of 6 μm is used, but the present invention is also applicable to a green to blue-violet laser of 0.550 μm or less.

The recording medium used in the present invention contains a dye in the recording layer. The dye used in the recording layer is selected from the viewpoints of recording sensitivity, reflectance, presence / absence of waveform distortion, high density recording characteristics and the like. is important. Specific examples of the pigment satisfying the above properties, for example, porphyrin pigment, polymethine pigment, cyanine pigment, pyromethene pigment, azo pigment,
Examples include naphthoquinone-based dyes and the like and metal complexes thereof.

In the recording medium used in the present invention, a recording layer containing the above-mentioned dye is provided directly on the substrate or via another inorganic or organic layer (undercoat layer). The thickness of the recording layer is 40 nm to 300 nm, preferably 60 nm to 200 nm. The method for providing the recording layer includes, for example, a spin coating method, a dipping method, a spraying method, and a vapor deposition method, and the spin coating method is preferable. In the recording medium used in the present invention, an intermediate layer may be provided between the recording layer containing the dye and the reflective layer in order to improve the characteristics such as the reflectance, the degree of modulation, and the jitter. Materials for forming the intermediate layer include inorganic dielectrics, polymers,
Dyes and the like.

In the recording medium used in the present invention, a reflection layer is provided on the recording layer. As a material for the reflective layer,
Metals such as gold, silver, aluminum, copper, and platinum, and alloys containing these metals are used. From the viewpoint of reflectance and durability, gold, aluminum, silver, and alloys containing these metals as main components are desirable. The thickness of the reflective layer is usually 40
nm to 300 nm, preferably 60 nm to 200 nm. Examples of a method for forming the reflective layer include a vacuum deposition, a sputtering method, and an ion plating method.

In the recording medium used in the present invention, the numerical aperture of the objective lens is preferably 0.6 or more. In this case, the thickness of the substrate is set to 0.5 to 0.5 in order to reduce aberration.
About 0.8 mm is desirable. At this time, in order to improve the strength and mechanical properties of the medium, the two sheets are bonded together using an adhesive. In bonding, without forming a protective layer on the reflective layer, or after forming the protective layer,
Can be laminated. The optical recording medium thus obtained can perform stable recording and reproduction even at a high recording density compared to the laser beam spot diameter.

[0017]

EXAMPLES The present invention will be described below in more detail with reference to examples, but embodiments of the present invention are not limited thereto.

Example 1 An azo dye having a thickness of 160 nm was formed as a recording layer by spin coating on a grooved surface of an injection-molded polycarbonate substrate having a spiral groove having a thickness of 0.6 mm and a diameter of 120 mm. On top of this recording layer,
A silver thin film having a thickness of 100 nm was formed as a reflective layer by a sputtering method. Next, an ultraviolet curable adhesive was applied on the reflective layer. The same 0.6 mm substrate as described above was superimposed on this adhesive, rotated at high speed to remove excess adhesive, and then irradiated with ultraviolet light to be bonded to produce an optical recording medium. The optical recording medium is placed on a turntable and rotated at a linear speed of 3.8 m / s.
semiconductor laser with lasing wavelength of nm and NA of 0.6
Using a drive equipped with an optical head consisting of a zero objective lens, record an 8-16 modulation signal with a minimum pit length of 0.40 μm while controlling the laser beam to focus on the recording layer on the groove through the substrate. did. At this time, as a basic recording pattern, a pulse pattern as shown in FIG.
Recording was performed by setting Δti2 to 0.07T and Δtij (j ≧ 3) to 0.1T for i. Next, the recorded signal was read by the same drive. Note that when reading, an equalization process was performed. At the optimum recording power at which the jitter is minimized, the jitter value is 6% of the channel bit clock, and extremely good recording,
I was able to play.

Examples 2 to 4 and Comparative Examples 1 to 3 Recording and reproduction were performed on the media prepared in Example 1 using the optical system and conditions shown in Table 1. The results are summarized in (Table 1).

[0020]

[Table 1] As is clear from Table 1, good recording and reproduction were possible in the example of the present invention, but jitter was large in the comparative example, and stable reproduction was not possible.

[0021]

According to the method of the present invention, in an optical recording medium containing a dye in a recording layer, good recording can be performed with respect to high-density recording in which pits smaller than a laser beam spot diameter are formed. It is now possible.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a relationship between a recording code pulse and a recording laser pulse.

Claims (2)

[Claims] 1. A recording layer containing a dye that absorbs laser light directly or through another layer on a transparent substrate having a groove, and a metal layer directly or through another layer on the recording layer. Pit length Pmin and r = λ / NA [λ is the recording wavelength (μm), NA
Is the numerical aperture of the objective lens of the pickup], but 0.35r ≦
When performing mark edge recording that satisfies Pmin ≦ 0.45r, the length of the pit is Mi [T] (the length represented by the clock interval time T, i is an integer), and the length of the pit interval immediately before the pit is Lj [T] (j is an integer), and M1 <M2 <... <Mi <... <Mm L1 <L2 <... <Lj <... <Lm The laser beam irradiation time ti [T] for forming a pit having a length is set to ti (L
j), ti (L1) <ti (L2) ≤ ... ≤ti (Lj) ≤
... ≤ti (Lm), and .DELTA.tij = ti (Lj) -ti (L1
), 0.0 for all j ≧ 2
A high-density optical recording method, wherein 1T ≦ Δtij ≦ 0.2T is satisfied. 2. A high-density recording medium having a recording recorded by the method according to claim 1.