JPH08235587A - Optical information recording and erasing method - Google Patents

Abstract

PURPOSE: To form a recording mark of a desired length at a desired position at the time of making an irradiating light a pulse train and switching the power level of a light by temporarily passing the light through a reproducing power level. CONSTITUTION: A laser power is pulse-modulated between a peak level p1 and a bias level p2 with a frequency f1 corresponding to the signals to be recorded. Further, the modulated laser is superimposed with a frequency f2 which is independent of the information signals and is sufficiently higher than the frequency f1 . Thus, the laser power is pulse-modulated between the level p1 or the level p2 and a reproducing light beam level p0 . The time width of the pulse train generated by the frequency f2 is maximized immediately after the change in the laser power corresponding to the frequency f1 , successively reduced and converged to a certain value. When the power is switched from the power p1 to the power p2 or vice versa, the power level passes through the power p0 once. By letting the power level pass through the level p0 once, the effect of a bias light beam is suppressed to a minimum.

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 / 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 crystalline of chalcogenide glass thin films based on tellurium and selenium,
Alternatively, a so-called phase-change type optical recording in which a phase change between crystals such as InSb and AgZn thin film is applied to a recording layer of an optical information recording medium and a minute signal mark is recorded, reproduced, erased and rewritten by using a laser beam. Techniques are well known.

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

Further, among the above, 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 recording medium. Also known is a method of irradiating a laser beam and erasing an already written old signal while directly recording a new signal on it, a so-called single laser beam overwrite method (JP-A-56-56). 145
530).

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

[0006]

However, the overwrite function with a single laser spot makes it possible to simplify the optical system, and shortens the access time for rewriting to 1/2 (if the number of rotations is the same). Although it has the advantage that it can be done, on the other hand, there is a problem that the length of the recording mark becomes longer than that when the recording is simply performed without overwriting.

This means that jitter easily occurs at the recording position of the recording mark. In other words, the conventional overwrite method has not yet fully coped with the recording method that requires strict determination of both the rising and falling positions of the recording mark, such as the PWM recording method.

Therefore, it is an object of the present invention to provide an optical information recording / erasing method for suppressing jitter in recording marks.

[0009]

SUMMARY OF THE INVENTION The present invention increases the intensity of light by
Frequency f corresponding to information signal₁And power level P₁And power
-Level P₂While pulse-modulating between
P₁Even if the light is radiated while being modulated,
Power level capable of instant melting, P₂Is the light
Even if irradiation is performed without modulation, it is impossible to melt the irradiated part.
At the power level, P ₁> P₂), At least power level P
₁In the part where the recording mark is formed by irradiation of
The frequency of the laser beam is f₁Higher than the above information signal
Frequency f independent of₂As a pulse train in which
User power to power level P₁And power level P₀(However
Then P₂> P₀) And irradiate by modulating
ー Level P₁To P₂, Or P₂To P₁When converting to
Always has power level P₀Optical information record
It has a structure of a recording / erasing method.

When a high frequency is superposed on the recording frequency f ₁ and the laser power is switched between P ₁ and P _2, it is once lowered to the reproduction light level to improve the heating / cooling profile by irradiation. It can be controlled precisely.

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

Further, when the power level is switched, the influence of heat conduction is reduced by temporarily passing through the P ₀ level, and the change of the mark shape due to the thermal interference effect between the marks is suppressed. That is, the recording mark can be formed at a desired position and with a desired length.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION First, problems in the conventional method will be analyzed, and then the present invention will be described.

The problem with the above conventional method is a phenomenon peculiar to so-called "heat mode recording". That is,
Amorphous / crystalline, phase-change type recording medium that applies phase change between crystals, and magneto-optical recording medium that uses the magnetic Kerr effect of a ferromagnetic thin film, the absorbed light is once converted 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 the irradiation light and / or the irradiation light intensity, the size of the recording mark will naturally change.

Using the model shown in FIG. 3 (a), the time change of temperature rising and cooling was calculated. Furthermore, recording was actually performed and the recording mark was observed. The structure of the recording medium 1 is a structure normally used for rewritable optical disks. Diameter 130m
A 90 nm thick GeTe thin film sandwiched between 100 nm and 200 nm thick ZnS thin films is formed on a polycarbonate substrate having a thickness of m and a thickness of 1.2 mm. On top of that, the same plate as the base material is attached using an adhesive.

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

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

From this, the following is shown. That is, 1) When there is bias power, the temperature rise at the irradiation start point is faster and the reached temperature is higher than when there is no bias power. Therefore, the part before the irradiation start point (the part where the bias light hits) is melted quite widely.

This is because as a result of heat conduction from the portion irradiated with the bias light, the temperature of the portion where the recording mark is about to be formed (the portion where irradiation is performed with the peak power) is already raised. It is thought to be because.

2) However, at the intermediate point, there is almost no difference in the profile of temperature rising / cooling between the two. This corresponds to the fact that the influence of the preheating by the bias light becomes small because the temperature rise approaches saturation in the middle part of the irradiation part.

3) Next, at the recording end point (irradiation end point), the temperature is less likely to drop in the presence of bias light than in the absence of bias light. In other words, the cooling rate is slow and the temperature is relatively high. It is kept in a molten state for a long time.

This is because in the presence of bias light, the irradiation at the bias level is continued even after the irradiation at the peak level.

From the above, the following can be said. In this way, in the presence of the bias light, the recording marks extended back and forth are formed as compared with the case without the bias light. If the peak power is simply lowered in order to solve this, the temperature of the central portion is lowered and the mark width is reduced.

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

In the figure, a point 6 represents a point at which the laser beam 7 is switched from off to on or from a bias level 10 to a peak level 9, and a point 8 is reversed from on to off or from a peak level to a bias. It shows the points that have changed to levels.

From the above, it was found that in the case of (b) with bias light, a recording mark longer than the period in which the peak power was on was formed before and after, that is, positioning was difficult. Also lowered the peak power
In the case of (c), it was confirmed that only thin marks were 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 carried out. The features are as follows 1 to 3.

1. The laser power is pulse-modulated between the peak level P ₁ and the bias level P ₂ at the frequency f ₁ corresponding to the information signal to be recorded.

2. Further, independently of the information signal, a frequency f ₂ sufficiently higher than the frequency f ₁ is superimposed. Therefore, the laser power is pulse-modulated between the peak level P ₁ or the bias level P ₂ and the reproduction light level P ₀ .

3. The time width (pulse duration) of the pulse train generated by the frequency f ₂ is maximum immediately after the laser power changes corresponding to the frequency f ₁ , and gradually decreases and converges to a constant value. 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, To 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.

By passing P ₀ once, the influence of the bias light is suppressed to the minimum. Although the bias level is also modulated in FIG. 1, the pulse shape of the peak level has a greater effect on the shape of the mark. Therefore, as shown in FIG. 7, DC irradiation may be performed only in the case of bias light. It is possible.

According to this method, it is possible to accurately determine the length of the recording mark to a predetermined length as shown below. That is, it is possible to determine exactly 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 / erasing method of the present invention shown in FIG. 1 using the same system as in FIG. It is an example of model calculation. The frequency f ₂ was set to 6 times f ₁ , and the power level P ₁ was set to 2 times P ₂ . The duty of the pulse width was set to 90%, 80%, 70%, 60%, 60%, 60% in order from the first pulse.

It is expected that the melting time is shortened as compared with the example of FIG. 3 and that it is difficult to affect the rear part. FIG. 6 is an observation result of the recording mark. 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 as large as that of f ₁ , preferably 4 times or more, because the temperature rise becomes smooth. Further, the width of each pulse at that time is preferably wide at the beginning and gradually narrowed in order to make the gradient of the temperature distribution uniform. However, the pulse width also converges to a constant value because it is necessary to maintain a certain temperature after irradiation with a certain pulse.

[0037]

According to the present invention, it is possible to realize an overwrite method with high signal quality, that is, with little jitter at the position of a recording mark.

[Brief description of drawings]

FIG. 1 is a diagram showing a state of a modulated pulse train of laser light 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.

FIG. 3A is a perspective view of a recording medium used for studying a temporal change in heating and cooling by a conventional overwrite method or a recording method, and an irradiation pulse waveform diagram, and FIG. 3B is a conventional overwrite method or a recording method. FIG. 6 is a diagram showing a temporal temperature change which an irradiation part receives when light is irradiated by the method.

FIG. 4 is a diagram showing an observation result of recording marks formed when light is irradiated by a conventional overwrite method or 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 received by an irradiation part and a shape of a recording mark formed when an optical information recording / erasing method of the present invention is applied.

FIG. 7 is a diagram showing a state of a modulated pulse train of laser light of another embodiment, which is applied to the optical information recording / erasing method of the present invention.

[Explanation of symbols]

1 recording medium 2 track 3 pulsed light (without bias light) 4 pulsed light (with bias light) 5 track 6 point where laser beam power switches from off to on 7 laser beam 8 from laser beam power on Point to switch to off 9 Peak level (on level) 10 Bias level 11 Playback level (off level) 12 Mark

Claims (7)

[Claims] 1. The intensity of light is changed to a power level P ₁ and a power level P ₂ at a frequency f ₁ corresponding to an information signal (where P ₁ >
P ₂ ) is pulse-modulated between P ₂ ) to overwrite-record an information signal on an optical information recording medium, and the power level P ₁ is set even when light is irradiated while being modulated.
The power level is set so that the irradiation part can be instantly melted, and the power level P ₂ is
When the irradiation part is set to a power level that cannot be melted and a recording mark is formed, the laser power is set as a pulse train that is higher than the frequency f ₁ and that has an independent frequency f ₂ superimposed on the information signal. the power level P ₁ and power level P ₀ (where, P _2> P ₀₎ when converting irradiated with modulated between the power level from P ₂ or P _2, from P ₁ to P ₁ is, An optical information recording / erasing method characterized by always passing through a power level P ₀ . 2. The optical information recording / erasing method according to claim 1, wherein the width of the head pulse of the pulse train corresponding to the frequency f ₂ is different from the width of the following pulse. 3. A pulse width corresponding to the frequency f ₂ is, the irradiation power from P ₁ corresponding to the frequency f ₁ to P _2, or wherein the longest immediately after switching from the P ₂ to P ₁ The optical information recording / erasing method according to claim 1. 4. 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. 5. 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. 6. The optical information recording / erasing method according to claim 5, wherein the pulse width corresponding to the frequency f ₂ converges to a constant width after a predetermined pulse width. 7. A laser power is modulated and irradiated between a power level P ₂ and a power level P ₀ (where P ₂ > P ₀ ) in a portion where a recording mark is not formed. Optical information recording medium.