JPH0935269A - Recording method for optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make possible optical recording of high sensitivity having few jitter by dividing a mark length into plural numbers of pulses and projecting a bias power lower than a recording power at the OFF time of the recording power in the recording of the mark length. SOLUTION: At the time of recording a signal having a mark length nT (n: natural number, T: reference clock period) in a write-once type medium by projecting a light beam, the mark length nT is divided into plural numbers of recording pulses. A power Pw is a recording power for forming a pit in a recording layer, a bias power Pb is applied in the OFF time interval of Pw in the mark and temp. distribution in one mark is properly controlled. By representing a reproducing pulse required for tracking by Pr, irradiation is performed by setting the powers so as to be Pw>Pb>Pr. Consequently, the recording method of the write-once type medium of high sensitivity having few jitter is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording method for a write-once type optical information recording medium suitable for documents and image files capable of recording and reproducing information at high density and at high speed.

[0002]

2. Description of the Related Art As a write-once type optical recording medium in which a thin film formed on a substrate is irradiated with a laser beam to form holes (pits), it has a lower melting point and lower thermal conductivity than before. T which can make holes with low recording power
e thin film is known (Appl. Phys. Let.
t. , 34 (1979), p. 835).

Furthermore, S is added to Te to increase stability over time.
e, Sb, Cu, Pb and other alloy thin films (H.W.
atanabe et al. , SPIE, vol.
1499 (1991), 21-28) and plasma-polymerized films containing these metals and further containing carbon, nitrogen, fluorine, oxygen, etc., reactive sputtered films, etc. (JP-A-53-31104). JP-A-58-54338, JP-A-57-98394, and JP-A-62-252
543, JP 63-160027, JP 6
3-95983).

A recording medium having a recording layer made of a dye or a mixture of a dye and a polymer has also been proposed. In addition, 2
Alloy-forming type (K. Watanabe et al., J. App when the metal or semiconductor thin film of the layer is melted)
l. Phys. , Vol. 54 (1983), 12
56-1260, or M.I. Matsubara
et al. , Jpn. J. Appl. Phys. ,
vol. 32 (1993), 5234-5237),
Alternatively, a phase-change type (K.-C. Pan) utilizing high-speed crystallization of a stable amorphous recording film near room temperature is used.
et al. , USP4960680, or
M. Takenaga et al. , J. et al. App
l. Phys. , Vol. 54 (1983), 53
76-5380, or T.I. Nishida et
al. , SPIE, vol. 2338 (199
4), 114-120) are also proposed.

These alloy-forming type or phase change type write-once mediums are better than the punching or deformation type mediums.
Since the recording pit shape can be made small and a rim is not formed on the peripheral portion of the pit, it is suitable for high density recording, particularly mark length recording. These write-once recording media use a physical phenomenon that is irreversible and the state after recording is extremely stable, and therefore has excellent stability over time and is highly reliable as a recording medium that cannot be tampered with because it cannot be rewritten. Has been obtained and has already been put to practical use as a document file and an image file.

The recording method of the write-once medium may be so-called mark position recording or mark length recording. In any case, in order to achieve higher density, it is required to obtain a sufficient signal-to-noise ratio (SN ratio) even if the size of the pit is reduced, and to reduce the pit interval. .

The size of the pit is such that the diameter of the focused light beam is reduced and the temperature distribution generated in the light beam irradiation region is utilized to cause a hole or deformation only in the high temperature region of the central portion. Alternatively, by inducing alloying and crystallization, it is possible to form a pit having a diameter of 0.5 μm or less, for example.

[0008]

However, it is usually difficult to obtain a good jitter at the mark end by simply modulating the mark length recording in accordance with the mark length in recording the mark length. In particular, when a long mark is recorded with a single recording pulse, heat is likely to be accumulated at the trailing end of the recording mark and the mark width tends to be widened.

Since the effect varies depending on the mark length, the jitter at the rear end of each mark is apt to be deteriorated. In view of such a situation, as shown in FIG. 1, when the recording power Pw for mark length recording is applied, the mark length nT
The irradiation is not performed with a single pulse having a time width tw according to (n: natural number, T: reference clock cycle), but tw is divided and irradiated as several pulses to improve the pit shape. It is widely known that is effective.

However, since the recording power is turned off in the mark, there is a problem in that the average light energy irradiated within one mark is lowered and the recording sensitivity is lowered.
Furthermore, if the spacing between these pits (shortest mark spacing) is reduced in order to increase the recording capacity, even if adjacent pits that are formed successively in terms of time are separated spatially, There is a problem that residual heat in the pit formation process affects the subsequent pit formation process, that is, thermal interference.

Due to the thermal interference effect, the following pit becomes large, and its center position shifts forward (HS.
ugiyama et al. , Proc. Int.
Symp. On Optical Memory (19
91), 219-224). When such a pit is read, so-called jitter and peak shift increase, which leads to an increase in error rate.

Conventionally, in a magneto-optical medium having a large thermal conductivity of a recording layer and a remarkable thermal interference effect, an attempt to positively limit / control the thermal interference effect has been proposed. For example,
Do not change the recording layer material, try to control the thermal diffusion amount by changing the material thickness of the protective layer and the reflection layer that sandwich the recording layer, or divide the recording power during recording, or change the bias power. There have been attempts to change the size and turn it off (K. Shimazaki et al.,
J. Magn. Soc. Jpn. , Vol. 19
(1995), suppl. S1, 347-35
0).

Such an attempt has also been proposed for a rewritable phase change medium (K. Nishiuchi).
et al. , Proc. Int. Symp. on
Optical Memory (1991), 291
-296, or H.264. Kobori et a
l. , SPIE, vol. 2338 (1994),
127-131).

However, in the write-once medium, such an attempt was completely unsatisfactory. Since the write-once medium does not perform erasing or overwriting, it can be said that no study has been made from the viewpoint of controlling / optimizing the bias power closely related to these operations.

A recording method proposed by the present inventors for the purpose of reducing thermal interference between marks, in which a bias power different from the reproduction power is applied between the marks during recording (Japanese Patent Laid-Open No. 6-251376, Japanese Patent Laid-Open No. 6-251376). 7-08547
8), but further improvement is desired in order to perform mark length recording with higher density.

[0016]

The present inventors can dramatically improve the recording density of a write-once recording medium for recording a mark length on a write-once recording medium for recording by irradiation of a light beam. As a result of extensive studies on the recording method, when the recording power is Pw and the reproducing power required for tracking is Pr, the mark length nT (n is a natural number,
(T is a reference clock cycle), when recording with the recording power Pw by the light beam is divided into a plurality of recording pulse trains shorter than nT, and the recording power Pw in the recording mark is turned off. Light power is Pw>Pb> Pr in time
It was found that the temperature distribution within one mark can be appropriately controlled by the recording method characterized by irradiating the bias power Pb as described above, and as a result, peak shift and jitter can be reduced, and the present invention has been reached. .

A change in laser light power in the recording method of the present invention is schematically shown in FIG. Pr is a laser light power necessary for reproducing or tracking information, and it is desirable that Pr is a power that does not cause deformation or deterioration of the recording layer even if the recording layer is repeatedly irradiated. Usually 10 ⁷
It is required to be able to withstand repeated playback, and is generally 1 m
The power is W or less.

Pw is a recording power for locally forming holes, deformation, alloying, or crystallization in the recording layer to form pits. The temperature of the recording layer is the melting point of the recording layer, the decomposition temperature, It is selected so as to reach a sufficiently high temperature with respect to any or all of the softening point and the crystallization temperature. In mark length recording, normally n of the reference clock cycle T is used.
A (natural number) times finite number of mark lengths nT are used.

When performing mark length recording in optical recording,
It is widely known that it is better to divide the recording light beam into a plurality of beams rather than irradiating with a single nT pulse length, and it is applied to various write-once media. However, in these pulse division recording methods, the recording pulse divided as shown in FIG.
The light beam power was basically the same as the reproduction light power Pr (M. Matsubara et al., Jp.
n. J. Appl. Phys. , Vol. 32 (19
93), 5234-257, or T.W. Nis
hida et al. , SPIE, vol. 23
38 (1994), 114-120).

According to the pulse division method of the present invention, as shown in FIG. 2, a recording signal pulse for recording a mark of length nT (n: natural number of 2 or more, T: reference clock period) is

[0021]

[Formula 1] α1T / β1T / α2T / β2T /.../ αmT / βmT

(Where αiT is the time for applying the recording power Pw, βiT is the time for turning off Pw, and α1 + β1 + ·
... + αm + βm = n−j (0 ≦ j ≦ 2), where m = n−k when the minimum value of n that the mark can take is nmin
N as in (k = 0, 1, 2) and nmin-k ≧ 1)
In the recording method in which the pulse is divided into −k pulses, the bias power Pb that satisfies Pr <Pb <Pw is applied during the time βiT.

Generally, in mark length recording without pulse division, the shorter the mark length, the higher the power required for recording. It is desirable that the bias power Pb is set so that the bias power Pb does not have a sufficient recording power for recording the mark length corresponding to the off pulse time βiT. For example, when the off-pulse time is 0.5T in FIG. 2, the bias power Pb is recorded in a repeating pattern of 0.5T mark length / longest mark interval,
When the C / N ratio (carrier to noise ratio) was measured, C
It is preferable to set the / N ratio to be sufficiently lower than the recording power at which the ratio rises and is saturated.

When the bias power Pb becomes higher than that, an off-pulse period is provided and recording is performed with residual heat,
There is a risk of impairing the original effect of pulse division, which is to prevent unnecessary heat accumulation. More preferably, when the longest mark length in the mark length recording is n1T, and the lowest recording power required for recording a repetitive pulse train of the longest mark length and interval without dividing the recording power is Pw1, Is set to Pw> Pb ≧ Pw1.

This is because if the power of Pb is too low, the sensitivity is lowered. In the above pulse division method, especially when the recording signal pulse is α1 + β1 = n0 = 2
There are division methods satisfying the conditions of 4, 1 ≦ α1 <n0, αi <1.0 (2 ≦ i ≦ m). This is because the recording pulse at the beginning of the pulse divided into a plurality of the above division methods is
This division method is characterized in that the pulse width is divided longer than the subsequent pulse, but since the laser power immediately before the mark is the erasing power and the temperature usually does not rise easily at the tip of the mark, the pulse of the first divided pulse It may be beneficial to have the width be longer than the pulse that follows (FIG. 3).

The rising edges of the individual divided recording pulses are not necessarily synchronized with the clock cycle, but are preferably synchronized with each other in order to simplify the pulse control circuit. However, even in that case, it is necessary to shift only the rising edge of the first pulse or the last pulse for one mark length from the clock cycle within a range of, for example, 20% of T in order to correct thermal interference between different marks. effective.

In the recording method of FIG. 2, the bias power Pbr applied between recording marks is the reproduction power required for tracking during recording, but it is not necessarily the same as the reproduction power Pr used during information reproduction. There is no.
As Pbr, select a power that does not cause an optically readable physical change in the recording layer by one irradiation to positively heat the recording layer and is sufficiently larger than Pr. You can

Since Pbr is irradiated only between the marks during recording, in the write-once medium, the same track is irradiated only once during recording. Therefore, it is not necessary to worry that the recording layer is deteriorated by the repeated irradiation of Pbr. Therefore, at least Pr <Pb <P
As long as the condition of w1 is satisfied, there is no fear of giving an image to the recording layer by one irradiation.

Here, if the power becomes Pr or less, the servo signal cannot be obtained and tracking servo may not be applied, which is not preferable. Although the mechanism of controlling the thermal interference effect by the irradiation of the bias power Pbr is not always clear, in general, the thermal conductivity of the recording layer has temperature dependency, and the higher the temperature in a metal, the smaller it becomes. The thermal interference between adjacent pits can be controlled.

The heat flow from the preceding pit to the subsequent pit is proportional to the temperature gradient, but this can also be controlled by reducing the temperature distribution between adjacent pits by bias power. In the present invention, as shown in FIG. 4, a constant time t after forming Pbr with Pw divided by the mark length nT.
Blocking only d and reducing it to Pr is also effective in suppressing thermal interference between adjacent pits. Thereby, the heat transfer from the preceding pit to the following pit can be substantially blocked.

[0031]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the present embodiment, the write-once medium of the type in which the dye is used as the recording layer and the bit is formed by its decomposition or alteration is used, but the present invention is not limited to the type of the recording layer, and the irradiation light A so-called heat mode write-once, in which energy is absorbed in the recording layer and converted into heat energy, thereby locally raising the recording layer temperature and inducing physical or chemical changes to form bits It is effective for all types of media. It does not depend on the modulation method of mark length recording.

Example 1, Comparative Examples 1 and 2 A metal-containing dye layer having a structure represented by the following formula (1) was formed on a polycarbonate resin substrate having spiral grooves with a pitch of 1.39 mm provided on the surface thereof. It was formed by a spin coating method.

[0033]

Embedded image

As the mark length recording method, it is assumed that recording is performed by the EFM modulation method used for compact discs. The longest mark length and the shortest mark length are
11T and 3T. However, the linear velocity of the disc is 1
At 1.2 m / s, the reference clock period is 14.5 nsec
(Frequency 69.1 MHz).

Recording and reproduction were performed using an optical head having a wavelength of 780 nm and an objective lens having a numerical aperture of 0.55. As shown in FIG. 5, the recording pulse was divided into (n-1) T pulses each having a head pulse of 1.5T. The subsequent pulse width and the off pulse width were both 0.5T.

The reproducing light power Pr was set to 1.0 mW. First, when recording with a pulse width of 0.5T, 10 m
Recording was not possible even with W. On the other hand, the longest mark length is 11T
Was recorded without pulse division, C at 5 mW
/ N ratio began to rise.

Therefore, with the bias power Pb = 6 mW, the recording power Pw of the C / N ratio and the mark length jitter at the longest mark length 11T where the jitter is most likely to be deteriorated.
The dependence was measured. The same measurement was performed in Comparative Example 1 without pulse division and in Comparative Example 2 with the bias power between the divided pulses reduced to Pr.

The results are summarized in FIGS. 6 (a) and 6 (b).
Comparing the recording powers with the C / N ratio of 50 dB, the recording sensitivity was improved to 6.5 mW in Comparative Example 1, slightly less than 9 mW in Example 1, and 10.5 mW in Comparative Example 2 compared to Comparative Example 2. . Further, regarding the mark length jitter, in Example 1, the recording power at which the jitter was reduced to 4 nsec was 1
0 mW, Comparative Example 1 has a high sensitivity,
mW, 15 mW in Comparative Example 2, and the widest recording power margin was obtained in Example 1.

[0039]

According to the present invention, it is possible to provide a recording method with high sensitivity and little jitter.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a conventional pulse division method.

FIG. 2 is an explanatory view schematically showing a change in laser light power in the method of the present invention.

FIG. 3 is an explanatory view schematically showing a change in laser light power in the method of the present invention.

FIG. 4 is an explanatory view schematically showing a change in laser light power in the method of the present invention.

FIG. 5 is an explanatory diagram schematically showing the division time of laser light power in Example 1.

FIG. 6 is a C / N ratio in Example 1 and Comparative Examples 1 and 2;
Graph showing changes in jitter

[Explanation of symbols]

Pw recording power Pr reproducing power nT mark length (n is a natural number, T is a reference clock period) Pb bias power

Claims (3)

[Claims] 1. A mark length nT when a recording power is Pw and a reproducing power required for tracking is Pr in a recording method in which mark length recording is performed on a write-once medium for recording by irradiation of a light beam. (N is a natural number,
(T is a reference clock cycle), when recording with the recording power Pw by the light beam is divided into a plurality of recording pulse trains shorter than nT, and the recording power Pw in the recording mark is turned off. In time, the optical power is Pw>Pb> P
A recording method for an optical information recording medium, which comprises irradiating a bias power Pb of r. 2. When the minimum recording power required to record the longest mark length in the mark length recording by continuous irradiation without dividing the recording power is Pw1,
The recording method for the optical information recording medium according to claim 1, wherein Pw> Pb ≧ Pw1. 3. The recording method for an optical information recording medium according to claim 1, wherein the recording power Pbr irradiated between the marks when the mark length recording is performed is Pb>Pbr> Pr.