JPH01253828A - Optical information recording and erasing method - Google Patents

Abstract

PURPOSE:To minutely generate a recording mark by simultaneously modulating irradiation power by means of a second frequency which can independently and freely be selected apart from a frequency corresponding to an information signal and changing the duty of a projected optical pulse in an irradiation start part and a termination part. CONSTITUTION:Laser power is pulse-modulated by the frequency f1 corresponding to the information signal to be recorded between a peak level P1 and a bias level P2. Furthermore, the frequency f2 which is independent of the information signal and which is sufficiently higher than f1 is superimposed. Consequently, laser power is pulse-modulated between P1 or P2 and a reproduced light level P0. The time width of a pulse string becomes maximum immediately after laser power changes in correspondence with f1, and it sequentially reduces and converged to a prescribed value. Thus, the rise and fall positions of the signal can minutely be decided to the prescribed positions at the time of recording. Consequently, the length of the recording mark can precisely be decided to the prescribed length.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for recording and erasing signals on a rewritable optical information recording medium, and more particularly to a method for overwriting signals.

Conventional technology Amorphous-crystal phase change such as chalcogenide glass thin film with tellurium and selenium, or rns
b. So-called phase-change optical recording technology that applies phase change between crystals such as AgZn thin films to the recording layer of optical information recording media, and records, reproduces, erases, and rewrites minute signal marks using laser beams. is publicly known. Furthermore, a so-called magneto-optical recording technique is already known in which the 6n direction of a strong 6n thin film is reversed using a laser beam with the help of an external magnetic field and read out using the magnetic Kerr effect.

Furthermore, among the above, a laser beam that is pulse-modulated between two levels, a recording level (peak value) and an erasing level (noquious value), as shown in FIG. 2, is irradiated onto a phase change type recording medium. A method of recording a new signal directly on top of the old signal while erasing the old signal that has already been written, the so-called override method using a single laser beam, is also already known (Japanese Patent Laid-Open No. 1455-1455).
30).

In other words, the part irradiated with high laser power melts and then rapidly cools to become amorphous, while the part irradiated with low laser power is annealed and crystallized at around the vitrification temperature without exceeding the melting point.

It has been reported that if this process occurs regardless of the state before laser beam irradiation, that is, regardless of whether it is amorphous or crystalline, it can be overridden with a single laser beam 7).

Problems to be Solved by the Invention However, the override function with a single laser spot simplifies the optical system, reduces the access time for rewriting to 1/2 (if the rotation speed is the same), etc. Although this method has advantages, on the other hand, a phenomenon has been observed in which the length of the recording mark becomes longer than when simply recording without overriding.

This means that jitter is likely to occur in the recording position of the recording mark. In other words, the conventional override method is not yet compatible with a recording method that requires strict determination of both the rising and falling positions of recording marks, such as the PWM recording method.

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

By superimposing a high frequency on the action recording frequency, the heating-cooling profile due to irradiation can be controlled more precisely. In other words, by changing the duty of the pulse corresponding to the above-mentioned high frequency between the recording start part and the recording end part, and also between the erasing start part and the erasing end part, the recording mark can be placed at the desired location and at the desired length. It can be easily formed.

Embodiments First, problems in the conventional method will be analyzed, and then the present invention will be explained.

The problem with the conventional method described above is a phenomenon peculiar to so-called heat mode recording. In other words, in phase-change recording media that utilize amorphous-crystal and crystal-crystal phase changes, and magneto-optical recording media that utilize the magnetic Kerr effect of ferroelectric thin films, absorbed light is once converted into heat. This heat causes metamorphosis. Therefore, if the balance between heat generation and diffusion changes depending on the irradiation time (pulse width), intensity, etc. of the irradiation light, the size of the recording mark will naturally change as well.

Temporal changes in heating and cooling were calculated using the model shown in Figure 3 fat. Furthermore, actual recording was performed and recording marks were observed. The structure of the recording medium 1 is a structure normally used for rewritable optical discs. Diameter 130m5. Thickness 1.2
100 and 2 each on the top and bottom polycarbonate substrates of 1-
90n thick sandwiched with 00nm ZnS thin film
A G e T e thin film of m is formed. On top of that, the same board as the base material is attached using adhesive. The disk is rotating at a speed of 22.5 m/s. Tiger,
Pulse light 3 (if there is no bias light) or 4 on R2
(if there is bias light). The peak power is 20 mW and the bias power is 10 mW. Further, the irradiation pulse width was 88.8 nsec.

During irradiation with pulsed light, the recording medium moves by a minute distance of 2.0 um. FIG. 3 (bl is the calculation result of the temperature change at the center of the trunk at the recording start point (irradiation start point), the recording end point (irradiation end point), and the intermediate point thereof.

From this, the following was shown: (1) The temperature rises faster at the irradiation starting point and the reached temperature is higher when bias power is present compared to when it is not present.

Therefore, the area before the irradiation start point (the area that was hit by the bias light) is considerably expanded (melted).

■ The cooling rate at the end of irradiation is slow and remains molten for a long time. Therefore, the area after the irradiation end point is melted considerably.

■ However, at the midpoint, there is almost no difference in the heating/cooling profile.

In this way, when bias light is present, recorded marks are formed that are stretched forward and backward, and to solve this problem, simply lowering the peak power lowers the temperature in the center and reduces the mark width. It was expected that this would happen.

FIG. 4 shows the result of observing the shape of the mark 12 actually recorded on the track 5 using an electron microscope. (a) is when there is no bias light, tb+ is with bias light and +a
When the peak power is the same as the + case, tel is the case when the peak power is lowered. In the figure, point 6 is when the laser beam 7 is switched from off to on, or from bias level 10 to peak level 9. Point 8 represents the point where the signal changes from on to off, or from the peak level to the bias level. From this, it was found that when bias light is present, recording marks are formed that are longer in the front and rear than in the period when the peak power is on, that is, positioning is difficult. It was also confirmed that when the peak power was lowered, only thin marks were formed overall.

FIG. 1 shows an example of the modulation waveform of irradiation light when the optical information recording/erasing method of the present invention is implemented. Features are 1 to 3 below.
It is as follows.

1. The laser power is pulse-modulated between a peak level P and a bias level P2 at a frequency f1 corresponding to the information signal to be recorded.

2. Further, a frequency f2, which is independent of the information signal and is sufficiently higher than the frequency f1, is superimposed. Therefore, the laser power is pulse modulated between the peak level P1 or bias level P2 and the reproduction light level P0.

3. The time width (pulse duration) of the pulse train generated at the frequency f2 is the frequency f2.

It is maximum immediately after the laser power changes corresponding to , and gradually decreases and converges to a constant value. That is, it is greatest immediately after changing from peak power P1 to bias power P2 or conversely from bias power P2 to peak power P1, and then immediately before changing from bias power P2 to peak power P1 or from peak power P to bias power P2. becomes the smallest.

According to this method, the length of the recording mark can be accurately determined to a predetermined length as shown below. In other words, it is possible to precisely determine the rising and falling positions of the signal at predetermined positions during recording.

Figure 5→ shows a model of the temperature change on the trunk at the end of irradiation using the same system as in Figure 3 when overriding is performed using the optical information recording erasing method of the present invention shown in Figure 1. This is an example of calculation.

The frequency f2 was set to six times fl, and the power level P1 was set to twice P2. Further, the duty of the pulse width is 90% and 80% from the first pulse.

These are the observation results of the weld marks set at 70%, 60%, 60%, 60%. It can be seen that a recording mark of a predetermined length is formed.

The value of f2 is at least twice that of fl, preferably 4.
It is preferable that the temperature increase is more than double that because the temperature rise will be smoother. Also,
In this case, the width of each pulse is preferably wide at first and gradually narrowed because it is necessary to make the gradient of the temperature distribution uniform. However, after a certain pulse irradiation, the pulse width also converges to a certain value because it is necessary to maintain the temperature within a certain range.

Effects of the Invention According to the present invention, an override method with high signal quality, that is, with fewer shifters at recording mark positions, has been realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a modulated pulse train of laser light applied to the optical information recording/erasing method of the present invention, FIG. 2 is a diagram showing a modulation method of a conventional override method, and FIG. 3 is a diagram of a conventional override method. Or a diagram showing the temporal temperature change experienced by the irradiated part when irradiated with light according to the recording method,
Figure 4 shows the observation results of recorded marks formed when light is irradiated by the conventional override method or recording method, and Figure 5 shows the erasure rate when applying the optical information recording and erasing method of the present invention. FIG. 6 shows the results of observing the temporal temperature change experienced by the irradiation section and the shape of the recorded mark formed when the optical information recording and erasing method of the present invention is applied. This is a diagram. A: Irradiation start part, B: Irradiation end part. Name of agent Patent attorney Toshio Nakao Haka1 person 20 − Bani −
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Claims (5)

[Claims] (1) The irradiation power is modulated by a first frequency corresponding to the information signal and a second frequency independent of the information signal, and the duty of the irradiation light pulse is changed between the irradiation start part and the irradiation end part. An optical information recording erasing method characterized by: (2) Change the intensity of light to power level P_1 and power level P_2 (P_1>P
_2), pulse modulation between power level P_1 or P_2 and power level P_0 (P_2>P_0) at a frequency f_2 independent of the information signal, and irradiation while modulating the light at power level P_1. The power level is set to a level that can instantaneously melt the irradiated part even in the case of
An optical information recording and erasing method characterized in that the power level is set to such a level that it is impossible to melt the irradiated part even if the light is irradiated without modulation. (3) The emission pulse width corresponding to the frequency f_2 changes the irradiation power from the above P_1 to the P_ corresponding to the above frequency f_1.
2 or immediately after switching from P_2 to P_1, the longest time is from P_1 to P_2 or P_2
3. The optical information recording/erasing method according to claim 2, wherein the shortest time is immediately before switching from P_1 to P_1. (4) The optical information recording/erasing method according to claim (3), wherein the change in pulse width progresses continuously in one direction. (5) The optical information recording/erasing method according to claim (4), wherein the pulse width converges to a constant value after a certain number of pulses.