JP2574379B2 - Optical information recording / erasing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention 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 (overwriting) a signal.

2. Description of the Related Art Amorphous-crystalline phase change, such as a chalcogenide glass thin film based on tellurium or selenium, or InS
b, Phase change between crystals, such as AgZn thin film, is applied to the recording layer of optical information recording media, and the recording, reproduction, erasure, and rewriting of small signal marks using a laser beam is a so-called phase change optical recording technology. Is known. Also, the magnetization direction of the ferromagnetic thin film is inverted using a laser beam with the help of an external magnetic field, and this is read out by the magnetic Kerr effect.
So-called magneto-optical recording technology is also already known.

Further, of the above, irradiating a phase-change type recording medium with a laser beam pulse-modulated between two levels of a recording level (peak value) and an erasing level (bias value) as shown in FIG. A method of directly recording a new signal on a previously written signal while erasing the already written signal, that is, a so-called single laser beam overwriting method is also already known (JP-A-56-145530). . That is, a portion irradiated with a high laser power is once melted and then quenched to form an amorphous material. A portion irradiated with a lower laser power is annealed and crystallized near a vitrification temperature without exceeding a melting point. It has been reported that overwriting can be performed with a single laser spot if this process occurs irrespective of the state before irradiation with the laser beam, that is, whether it is amorphous or crystalline.

However, the overwriting function with a single laser spot can simplify the optical system, shorten the access time for rewriting (if the rotation speed is the same) to half, etc. Although there is an advantage, on the other hand, there has been observed a phenomenon 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. That is, the conventional overwriting method has not yet fully coped with a recording method in which both the rising and falling positions of the recording mark need to be determined strictly, such as the PWM recording method.

Means for Solving the Problems In addition to the frequency corresponding to the information signal, the present invention simultaneously modulates the irradiation power at a second frequency that can be freely selected independently of the information signal, and irradiates the irradiation power. The duty of the light pulse is changed between the irradiation start part and the irradiation end part.

Action By superimposing a high frequency on the recording frequency, the heating-cooling profile by irradiation can be controlled more precisely. In other words, by changing the duty of the pulse corresponding to the high frequency between the recording start part and the recording end part, and further between the erasing start part and the erasing end part, the recording mark is formed at a desired place at a desired length. Can be easily performed.

EXAMPLES First, problems of 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-crystal,
In a phase-change recording medium that uses a phase change between crystals and crystals, and a magneto-optical recording medium that uses the magnetic Kerr effect of a ferroelectric thin film, the absorbed light is once converted to heat,
Transformation is caused by this heat. Therefore, the balance between heat generation and diffusion is determined by the irradiation time (pulse width) of the irradiation light,
If the strength differs, 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. A 90 nm thick GeTe thin film sandwiched between upper and lower 100 nm and 200 nm ZnS thin films is formed on a polycarbonate substrate having a diameter of 130 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 disk spins at 22.5m / s. The track 2 is irradiated with pulse light 3 (when there is no bias light) or 4 (when there is bias light). The peak power is 20 mW and the bias power is 10 mW. The irradiation pulse width is 88.8 nses. The recording medium moves a small distance of 2.0 μm during the irradiation of the pulse light. FIG. 3B shows a recording start point (irradiation start point) and a recording end point (irradiation end point).
And a calculation result of a temperature change at the center of the track at the intermediate point.

This indicates that the temperature rise at the irradiation start point is faster and the ultimate temperature is higher than when no bias power is present. Therefore, the portion before the irradiation start point (the portion to which the bias light is applied) is melted considerably widely.

The cooling rate at the end point of the irradiation is low, and the material remains molten for a long time. Therefore, the part after the irradiation end point is considerably widely melted.

However, there is almost no difference in the heating / cooling profile at the intermediate point.

In this way, when there is bias light, a recording mark that is elongated back and forth is formed. If the peak power is simply reduced to solve this problem, it is expected that the temperature at the center will decrease and the mark width will decrease.

FIG. 4 shows the result of observing the shape of the mark 12 actually recorded on the track 5 using an electron microscope. (A) shows a case where there is no bias light, (b) shows a case where bias power is present and (a) has the same peak power, and (c) shows a case where the peak power is lowered. In the figure, point 6 represents the point where the laser beam 7 switches from off to on or from the bias level 10 to the peak level 9, and point 8 conversely switches from on to off or from the peak level to the bias level. Represents a point. From this, it was found that when the bias light was present, a recording mark longer than before and after the peak power was on was formed, that is, it was difficult to position. It was also confirmed that when the peak power was reduced, 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. Features are 1 to
3

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

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

3. the duration of the pulse train produced by the frequency f ₂ (pulse du Ray Deployment) converges to a constant value by sequentially decreasing a maximum immediately after the laser power is changed in correspondence with the frequency f _1. Most large, then the bias power from the bias power P ₂ from the peak power P ₁ or peak power P ₁ that is immediately after the change from the bias power P ₂ to the bias power P ₂ or vice from the peak power P ₁ to the peak power P ₁ the smallest in just before the return to P _2.

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

FIG. 5 shows a model of the temperature change on the track at the irradiation end portion using the same system as in FIG. 3 when overwriting is performed by the optical information recording / erasing method of the present invention shown in FIG. It is a calculated example. 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 is 90%, 80%, 70%, 6
0%, 60%, and 60% were set. 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 result of observation of a recording mark. It can be seen that a recording mark of a predetermined length is formed.

the value of f ₂ at least twice that f _1, hopefully it is preferable that more than four times the smoother Atsushi Nobori. At this time, it is preferable that the width of each pulse is wide and gradually narrow at first because the gradient of the temperature distribution needs to be uniform. However, the pulse width also converges to a constant value because it is necessary to maintain a certain temperature range after a certain pulse irradiation.

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

[Brief description of the drawings]

FIG. 1 is a diagram showing a state of a modulated pulse train of a laser beam applied to the optical information recording and erasing method of the present invention, FIG. 2 is a diagram showing a modulation method of a conventional overwriting method, and FIG. A diagram showing a temporal temperature change received by an irradiation unit when light is irradiated by a writing method or a recording method,
FIG. 4 is a view showing a result of observation of a recording mark formed when light is irradiated by a conventional overwriting method or a recording method, and FIG. 5 is an erasure when the optical information recording / erasing method of the present invention is applied. FIG. 6 is a graph showing the relationship between the rate and the erasing light power. FIG. 6 shows the results of observing the temporal temperature change received by the irradiation unit and the shape of the formed recording mark when the optical information recording / erasing method of the present invention is applied. FIG. A: irradiation start part; B: irradiation end part.

Claims (4)

(57) [Claims] 1. The method according to claim 1, wherein the intensity of the light is adjusted to a frequency f ₁ corresponding to the information signal.
Performs pulse modulation between power level P ₁ and power level P ₂ (P ₁ > P ₂ ), and power level P ₁ and power level P ₀ , and power level at a frequency f ₂ independent of the information signal.
Pulse-modulated between P ₂ and power level _{P 0 (P 2> P 0} ), this time, power level P ₁ is capable of also be instantly melt the irradiated portion in the case of irradiation with modulated optical power Level, and the power level P ₂ is set to a power level at which the irradiated part cannot be melted even if the light is irradiated without modulation, and the light emission pulse width corresponding to the frequency f ₂ is
If the irradiation power is switched from the P ₁ corresponding to the frequency f ₁ to P _2, or the optical information recording according to claim longest that at least immediately after the one of when switching from the P ₂ to P ₁ Erase method. 2. A light emission pulse width corresponding to the frequency f ₂ is at least one of the case when the irradiation power is switched from the P ₁ corresponding to the frequency f ₁ to P _2, or to switch from P ₂ to P ₁ 2. The optical information recording and erasing method according to claim 1, wherein the optical information recording and erasing method is the shortest immediately before the step (c). 3. A light emission pulse width corresponding to the frequency f ₂ is, according to claim 1 or 2, characterized in that gradually changes in one direction
The optical information recording / erasing method according to any one of the above. 4. A light emission pulse width corresponding to the frequency f ₂ is the optical information recording and erasing method according to claim 3, wherein after the certain fixed number of pulses, characterized in that converges to a constant value.