JP2924758B2 - Optical information recording / erasing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recording and erasing a signal on a rewritable optical information recording medium, and more particularly to a method for overwriting a signal.

[0002]

2. Description of the Related Art Phase change between amorphous and crystal, such as a chalcogenide glass thin film based on tellurium or selenium,
Alternatively, a so-called phase-change optical recording in which a phase change between crystals such as an InSb, AgZn thin film or the like is applied to a recording layer of an optical information recording medium and a small signal mark is recorded, reproduced, erased, and rewritten using a laser beam. Techniques are known.

[0003] Further, the magnetization direction of the ferromagnetic thin film is reversed using a laser beam with the help of an external magnetic field,
A so-called magneto-optical recording technique for reading this out by the magnetic Kerr effect is already known.

Further, a laser beam pulse-modulated between a recording level (peak value) and an erasing level (bias value) as shown in FIG. 2 on a phase-change type recording medium. Is also known, in which a new signal is directly recorded on a previously written signal while erasing the already written signal, that is, a so-called single laser beam overwriting method (Japanese Patent Application Laid-Open No. 56-1981). 145
530).

That is, a part irradiated with high laser power is melted and then rapidly cooled to become amorphous, while a part irradiated with low laser power is annealed near the vitrification temperature without exceeding the melting point. Crystallizes. It has been reported that if this process occurs regardless of the state before the laser beam irradiation, that is, whether it is amorphous or crystalline, overwriting can be performed with a single laser spot.

[0006]

However, the overwriting function with a single laser spot can simplify the optical system and shorten the access time for rewriting (if the rotation speed is the same) to half. Although it has advantages such as possible, on the other hand, there has been a problem that the length of a recording mark is longer than that in a case where recording is simply performed without overwriting.

This means that jitter tends to occur at the recording position of the recording mark. In other words, the conventional overwriting method has not yet sufficiently responded to a recording method in which both the rising and falling positions of the recording mark need to be strictly determined, such as the PWM recording method.

Accordingly, an object of the present invention is to provide an optical information recording / erasing method for suppressing jitter in a recording mark.

[0009]

According to the present invention, the intensity of light is
With pulse modulated between a frequency f ₁ corresponding to the information signal with the power level P ₁ and power level P ₂ (where,
P ₁ is the power level that can also be instantly melt the irradiated portion in the case of irradiation with modulated light, P ₂ has not power level that even when irradiated with unmodulated light to melt the irradiated portion And P ₁ > P ₂ ), at least the power level P
In the portion forming the recording mark by performing a _first irradiation, the laser beam higher than the frequency f _1, a pulse train formed by superposing a frequency f ₂ which is independent of the information signal, the laser power and power level P ₁ Irradiation is performed by modulating the power level between P ₀ (where P ₂ > P ₀ ). At this time, when the power level is converted from P ₁ to P ₂ , the power level must always pass through the power level P ₀ , The pulse width corresponding to the frequency f ₂ is
The irradiation power from P ₁ corresponding to the frequency f ₁ to P _2, there
There has a structure of an optical information recording and erasing method of the longest immediately after switching from the P ₂ to P _1.

When a high frequency is superimposed on the recording frequency f ₁ and the laser power is switched between P ₁ and P ₂ , the temperature is once reduced to the reproduction light level, so that the temperature rise / cooling profile by irradiation can be further improved. Can be controlled precisely.

That is, by forming the irradiation light into a pulse train,
It is possible to suppress the phenomenon that the mark shape exhibits teardrop-shaped distortion due to the accumulation of heat at the rear part of the recording mark.

In addition, when the power level is switched, the power is once passed through the P ₀ level, thereby reducing the influence of heat conduction and suppressing a change in mark shape due to a thermal interference effect between marks. That is, the recording mark can be formed at a desired position at a desired length.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, problems in the conventional method are analyzed, and then the present invention is described.

The problem in the above-mentioned conventional method is a phenomenon peculiar to so-called "heat mode recording". That is,
Amorphous / crystalline, phase-change type recording media applying the phase change between crystals, and magneto-optical recording media applying the magnetic Kerr effect of a ferromagnetic thin film all convert the absorbed light into heat. Transformation is caused by heat.
Therefore, if the balance between the generation of heat and the diffusion of heat differs depending on the irradiation time (pulse width) of irradiation light and / or the intensity of irradiation light, the size of the recording mark naturally changes.

With the model shown in FIG. 3 (a), the time-dependent change of the heating and cooling was calculated. Furthermore, recording was actually performed, and the recorded marks were observed. The structure of the recording medium 1 is a structure usually used for a rewritable optical disk. 130m in diameter
A 90 nm thick GeTe thin film sandwiched between upper and lower 100 and 200 nm ZnS thin films is formed on a polycarbonate substrate having a thickness of 1.2 mm and a thickness of 1.2 mm. On top of that, the same plate as the base material is bonded using an adhesive.

The recording medium 1 is rotating at a speed of 22.5 m per second. The track 2 of the recording medium 1 is irradiated with pulse light 3 (when there is no bias light) or pulse light 4 (when there is bias light). 20m peak power
W and the bias power are 10 mW. The irradiation pulse width is 88.8 nsec. During the irradiation with the pulse light 3 or 4, the recording medium 1 moves a minute distance of 2.0 μm.

FIG. 3B shows the calculation results of the temperature change at the track center at the recording start point (irradiation start point), the recording end point (irradiation end point), and the intermediate point therebetween.

This shows the following. That is: 1) When there is bias power, the temperature rise at the irradiation start point is faster and the ultimate temperature is higher than when there is no bias power. Therefore, the portion before the irradiation start point (the portion to which the bias light is applied) is melted considerably widely.

This is because heat is conducted from a portion irradiated with the bias light, and the temperature of a portion where a recording mark is to be formed (a portion to be irradiated with peak power) is raised in advance. It is thought to be.

2) However, at the intermediate point, there is almost no difference in the profile of the heating and cooling between the two. This corresponds to the fact that the effect of the preliminary heating with the bias light is reduced because the temperature rise approaches the saturation in the middle part of the irradiation part.

3) Next, at the recording end point (irradiation end point), when there is bias light, the temperature is less likely to decrease than when there is no bias light, in other words, the cooling rate is low, and It has been kept in a molten state for a long time.

This is because, when there is bias light, irradiation is continued at the bias level even after irradiation at the peak level.

From the above, the following can be said. As described above, when the bias light is present, a recording mark that is elongated back and forth is formed as compared with the case where the bias light is not present. If the peak power is simply reduced in order to solve this, the temperature at the center decreases and the mark width decreases.

FIG. 4 shows the result of observing the shape of the mark 12 actually recorded on the track 5 using an electron microscope. (a) when there is no bias light, (b) has a bias light component, and when the peak power is aligned with (a), (c) is (b)
Has a bias light component similar to
This is the case where it is lower than (b).

In the figure, point 6 represents the point at which the laser beam 7 switches from off to on, or from the bias level 10 to the peak level 9, and point 8 conversely from on to off, or from the peak level to the bias level. Represents a point that has been converted to a level.

From this, it was found that in the case of (b) with the bias light, a recording mark longer than before and after the peak power was on was formed, that is, positioning was difficult. Also reduced peak power
In the case of (c), it was confirmed that only a thin mark was formed on the whole.

FIG. 1 shows an example of a modulation waveform of irradiation light when the optical information recording / erasing method of the present invention is performed. The features are as follows from 1 to 3.

1. Laser power, at a frequency f ₁ corresponding to the information signal to be recorded, is pulse-modulated between a peak level P ₁ and a bias level P _2.

2. Further independent of the information signal, a sufficiently high frequency f ₂ is superimposed than the frequency f _1. Therefore, the laser power, a peak level P ₁ or bias level P _2, is pulse-modulated between a reproducing light level P _0.

3. Duration of the pulse train produced by the frequency f ₂ (pulse duration) is a maximum immediately after the laser power is changed in correspondence with the frequency f _1, converges to a constant value by sequentially decreased. That is, the peak power P ₁ bias power P ₂ or, conversely, is largest immediately after the change from the bias power P ₂ to the peak power P _1, also the peak power P ₁ from a bias power P ₂ or peak power P _1, From bias power P
_It becomes the smallest just before returning to ₂ .

4. When switched from the peak power P ₁ to the bias power P _2, also when switching from the bias power P ₂ to the peak power P _1, the power level is via a time P _0.

[0032] Once that is through the P _0, suppressing to a minimum the influence of the bias light. FIG. 7 is a reference diagram.

According to this method, as described below, the length of the recording mark can be accurately determined to a predetermined length. That is, it is possible to strictly determine the rising position and the falling position of the signal during recording.

FIG. 5 shows the temperature change on the track at the irradiation end portion when overwriting is performed by the optical information recording and erasing method of the present invention shown in FIG. This is an example of a model calculation. 6 times the frequency f ₂ is f _1, the power level P ₁ was set to twice the P _2. The duty of the pulse width was set to 90%, 80%, 70%, 60%, 60%, and 60% in order from the first pulse.

It is expected that the melting time will be shorter than in the example of FIG. 3 and will not affect the rear part. FIG. 6 shows the observation results of the recording marks. It can be seen that a recording mark of a predetermined length is formed.

It is preferable that the value of f ₂ is at least twice, and preferably four times or more, f ₁ as compared with f ₁ because the temperature rise becomes smooth. In addition, the width of each pulse at that time is preferably wider at first and gradually narrower, since it is necessary to make the gradient of the temperature distribution uniform. However, the pulse width also converges to a constant value due to the need to maintain a certain temperature after a certain pulse irradiation.

[0037]

According to the present invention, an overwriting method with high signal quality, that is, with less jitter at the position of a recording mark can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a state of a modulated pulse train of a laser beam applied to an optical information recording / erasing method of the present invention.

FIG. 2 is a diagram showing a modulation method of a conventional overwrite method.

3 (a) is a perspective view of a recording medium and an irradiation pulse waveform diagram used for examining a temporal change in heating and cooling by a conventional overwriting method or a recording method, and FIG. 3 (b) is a conventional overwriting method. Or a diagram showing a temporal temperature change received by an irradiation unit when light is irradiated by a recording method.

FIG. 4 is a diagram showing an observation result of a recording mark formed when light is irradiated by a conventional overwriting method or a recording method.

FIG. 5 is a diagram showing the relationship between the erasing rate and the erasing light power when the optical information recording / erasing method of the present invention is applied.

FIG. 6 is a diagram showing a result of observing a temporal temperature change applied to an irradiation unit and a shape of a formed recording mark when the optical information recording / erasing method of the present invention is applied.

FIG. 7 is a reference diagram showing a state of a modulated pulse train of laser light.

Claims (6)

(57) [Claims] 1. The light intensity is changed between a power level P ₁ and a power level P ₂ (where P ₁ >) at a frequency f ₁ corresponding to an information signal.
And pulse modulation between P _2), an optical information recording medium to a method of overwriting recording information signals, the power level P _1, even in the case of irradiating while modulating light,
The irradiation part is set to a power level capable of instantaneously melting, and the power level P ₂ is set even if the light is irradiated without modulation.
Set the power level it is not possible to melt the irradiated portion, when forming a recording mark is higher than the frequency f _1, a pulse train formed by superposing a frequency f ₂ which is independent of the information signal, laser power Is irradiated between the power level P ₁ and the power level P ₀ (where P ₂ > P ₀ ), and when the power level is converted from P ₁ to P ₂ , the power level always passes through the power level P ₀ is, paths corresponding to the frequency f ₂
P pulse width, the irradiation power from P ₁ corresponding to the frequency f ₁
The optical information recording and erasing method to _2, or the immediately after the switching from the P ₂ to P _1, characterized in longest <br/> it. 2. The optical information recording and erasing method according to claim 1, wherein the width of the first pulse of the pulse train corresponding to the frequency f ₂ is different from the width of the succeeding pulse. 3. A pulse width corresponding to the frequency f ₂ is the irradiation power corresponding to the frequency f ₁ to P ₂ from the P _1, or wherein the shortest just before switching from P ₂ to P ₁ The optical information recording / erasing method according to claim 1. 4. The optical information recording / erasing method according to claim 3, wherein the pulse width corresponding to the frequency f ₂ gradually changes in one direction. 5. The optical information recording and erasing method according to claim 4, wherein the pulse width corresponding to the frequency f ₂ converges to a constant width after the predetermined pulse width. 6. The method according to claim 1, wherein the laser power is modulated at a portion where no recording mark is formed between a power level P ₂ and a power level P ₀ (where P ₂ > P ₀ ). The optical information recording and erasing method described in the above .