JPH01229425A - Optical information recording/erasing method - Google Patents

Abstract

PURPOSE:To obtain a large erasion rate by erasing the hitherto histories of an irradiated part by dissolving once this part. CONSTITUTION:The two or more circles or the approximately circular spots 1 and 2 are set close to each other on a recording track 3. In other words, the preceding laser spot 1 is used to once dissolve a recording thin film and irradiated continuously with a fixed level of power. While the following laser spot 2 is modulated by a recording signal and the irradiated part of the spot 2 is cooled slowly for crystallization in an ON state. Then said irradiated part is cooled quickly and turned into an amorphous substance in an OFF state. Therefore both states of high and low reflectivity can be obtained in accordance with the modulation signal. Thus it is possible to obtain a large erasion rate and also to obtain an optical information recording/reproducing/erasing device that can be easily mass-produced.

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 particularly relates to a method for erasing old signals and recording new signals at the same time (override). .

BACKGROUND ART Two methods have been proposed for overwriting a rewritable phase-change optical information recording medium.

One is to irradiate a recording medium with a laser beam that is modulated between two levels: recording level and erasing level, which erases the old signal that has already been written and allows new signals to be written directly on top of it. It is a method of recording
6-145530). That is, 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 without exceeding the melting point. With this method, a new signal can be recorded regardless of whether the material was amorphous or crystalline before irradiation with the laser beam, that is, it can be overridden with a single laser spot.

The other method is to place two or more laser spots on a track, erase the old signal at the preceding spot, and record a new signal at the following spot (Proceedings of Laser Spots). IE (Proceedings of 5PIE)
Volume 420P, 173-P, 177
(1983)). That is, erasing and recording are performed at independent spots, and pseudo override is performed.

Problems to be Solved by the Invention The override function using a single laser spot has the advantage of a simple optical system and a simple control system, but on the other hand, there is the problem that a sufficient erasure rate cannot be obtained. There was a point.

In addition, a method in which two or more laser spots are installed on a track and recording and erasing signals in independent spots can achieve a higher erasure rate than overriding with a single laser spot due to the effect of the preceding erasure-only spot. Obtainable. However, in order to simplify the system, tracking control is generally performed for only one spot, and other spots are designed to follow it. Therefore, it becomes more difficult to accurately install two or more spots on a track with an interval between them as the interval between the spots increases, which becomes a big problem especially when mass production is considered.

Means for Solving the Problem Two or more circular or approximately circular spots are placed close to each other on the recording track, and old signals are erased by increasing the power of the leading spot to a level higher than that of melting the recording thin film. New signals are recorded by modulating subsequent spots with the signal to change the cooling rate of the portion melted by the leading spot.

In a working phase change type rewritable recording medium, by once melting the irradiated part, the history of that part can be almost erased. Therefore, the old signal is sufficiently erased using the first spot, and the cooling rate of the molten portion is controlled using the subsequent spots to achieve two states, crystalline and amorphous, and the signal is recorded. This method provides a high erasing rate, and at the same time, the laser spots are placed very close together (sometimes even partially overlapping), making it easy to place them on the same track.

EXAMPLE The reason why the erasure rate is low in the case of override recording using a single laser spot is considered to be that traces of old signals remain as differences in crystal grain size. That is, in the portion annealed below the melting point, the crystalline state differs depending on whether there was a recording bit previously, and this causes a difference in optical properties. In other words, in order to sufficiently erase old signals, it is sufficient to melt the recording track by continuously irradiating it with laser light and erase the history up to that point. This is the role of the leading spot in the present invention.

Whether the portion continuously irradiated with laser light ultimately becomes amorphous or crystalline depends on the recording thin film. In the present invention, a recording thin film that becomes an amorphous state is used (Whether it ultimately becomes an amorphous state or a crystalline state is not determined only by the composition of the recording thin film; for example, the thickness of the recording thin film, the thickness of the protective film, etc.) (It can also be controlled by the material, etc.) This is achieved when the cooling rate is too high to allow crystallization. Here, if the cooling rate can be temporarily reduced, that part should be able to be crystallized. This is 2
This is the role of the second (or second and subsequent) laser spot. That is, when the second laser spot is off, the molten part cools rapidly and becomes amorphous, but when it is on, the molten part cools slowly and becomes crystalline.

In other words, by modulating the second laser spot between on and off in response to the signal, a new signal can be recorded. This method records a new signal by controlling the cooling rate of the irradiated area of the erase spot, and uses two or more conventional laser spots to erase the old signal with the preceding spot and record it again with the subsequent spot. The way to record new signals is different. In the conventional example, the erasing spot and the recording spot needed to be spaced so that they did not affect each other thermally, but with the present invention, they can be placed very close together, making it extremely easy to position the laser spot. There are benefits.

FIG. 1 shows an example of a laser spot configuration and irradiation method for carrying out the optical information recording/erasing method of the present invention.

FIG. 1(a) shows an embodiment in which two circular laser spots are arranged on a track 3.

The preceding laser spot 1 is for temporarily melting the recording thin film, and is continuously irradiated with constant power. Further, the subsequent laser spot 2 is modulated by the recording signal, and the temperature profile when in the on state is the first.
The temperature profile in the OFF state is as shown in FIG. 1(C). In other words, when it is in the on state, the irradiated part cools slowly and becomes crystallized, but when it is in the off state, it cools rapidly and becomes amorphous.
A state of high reflectance and a state of low reflectance can be created depending on the modulation signal.

Note that all laser spot diameters in this specification are expressed in terms of half width of energy density.

Furthermore, since it is easier to install two spots on a track at the same time if the spot spacing is as close as possible, this embodiment shows a case where spots 1 and 2 partially overlap. However, if the condition is met that the signal is recorded by controlling the cooling rate of the melted part, spots 1 and 2
It doesn't matter if they are far apart.

Further, in this embodiment, the spot shapes are both circular, but may be approximately circular. In particular, if the subsequent spot 2 has a substantially circular shape that is long in the track direction, the difference in cooling rate between when the spot 2 is on and when it is off is large (because the circular spot is difficult to crystallize). (
Even such a thin recording film can be sufficiently crystallized.

However, since the shortest recording bit length is approximately proportional to the length of spot 2 in the track direction, making it too long in the track direction will increase the shortest recording bit length and reduce the recording density. You have to be careful about that.

Considering that the light emitting pattern of laser diodes currently in practical use is approximately circular with an ellipticity of approximately 1:2, if the shape of spot 2 is selected to be approximately circular, a simple lens can be created. It is possible to efficiently collect light using the system. In other words, it is possible to realize an optical system with high transmission efficiency and low cost.

The optical information recording/erasing method of the present invention can be effectively applied to any recording medium to which reversible phase change between amorphous and crystalline and crystalline and crystalline states is applied. Among phase change materials between amorphous and crystalline, Ge is a material that crystallizes very rapidly.
Te, Ge5b2Tea, Ge5b2Tea, In
Ge5nTeAu and Ge5bTeSe are materials that crystallize relatively quickly, such as Se and In5eTICo.
A Ge5nTeO system, a 3eTeSn system, etc. can be used. In addition, as a phase change material between crystals, In
Sb-based materials, AgZn-based materials, etc. can be used.

Next, the present invention will be explained in detail using specific examples.

Example 1 FIG. 2 shows a cross-sectional view of the optical disc used in the experiment.

A 1100nm ZnS protective layer and a 2.60nm G
e5b2Te4 recording layer 3. 200 nm ZnS protective layer 4
．． A 20 nm Au reflective layer 5 was sequentially laminated, and a back cover 7 made of the same polycarbonate as the substrate was laminated thereon with an adhesive 6 to prepare an optical disc. Each layer is lXl0−
It was formed by vapor deposition under a vacuum of about 'P. Three sources are used to form the recording layer, and the deposition rate of each is controlled, and the substrate is sequentially passed (rotated) over each source.Track grooves for light guides are formed on the substrate in advance. There is.

Recording and erasing tests using disks were conducted while comparing a dynamic tester (deck) equipped with a laser spot according to the present invention and a dynamic tester equipped with a conventional laser spot.

The configuration of the laser spot according to the present invention is shown in FIG. 3(a). That is, as the preliminary spot 8 for melting the recording film, a laser beam with a wavelength of 830 nm was focused into a circular light spot with a half width of 0.9 parts m. In addition, the subsequent spot 9 for recording information by controlling the cooling rate by modulating the signal uses a laser beam with a wavelength of 780 nm embedded in a round optical spot with a half width of 0.8 parts m. there was. Since the distance between the centers of the two spots was approximately 0.7 μm, they partially overlapped. Therefore, the distance from the beginning to the end of the two spots is about 1.5 μm.

The configuration of a conventional laser spot is shown in FIG. 3(b). The preceding elliptical spot (wavelength 830 nm, half width approximately 1×7 μm) is for erasing, and the old signal is erased by removing heat and slowly cooling the track groove to crystallize the amorphous mark. Subsequent spots (wavelength 780n)
m, half width of about 0.8 μm) is for recording, and signals are recorded by raising the temperature of the recording film above its melting point and then rapidly cooling it to form an amorphous mark. In this case, the erasing spot and the recording spot were placed approximately 5 μm apart so that the quenching conditions of the irradiated portion of the recording spot were not disturbed. In other words, the distance from the beginning to the end of the two spots is approximately 13μ.
It is m.

The disk rotates at 3600 rpm, with a linear velocity of 15
An override experiment was conducted at the m/sec point. The experimental procedure is shown below.

a) First, a signal with a frequency of 5 MHz is recorded on the track. The signal-to-noise ratio (C/N) at this time was about 53 dB.

b) Record a new 3 MHz signal while erasing the 5 MHz signal by overriding. In the case of the configuration of the present invention, the power of each spot is 16.
mW, the following spot is 7mW, in the case of the conventional configuration, the leading spot is 20mW, and the following spot is 18mW.
It was set as mW.

C) The erasure rate of the erased 5 MHz signal and the C/N of the newly recorded 3 MHz signal are measured and evaluated using a spectroanalyzer.

The experimental results are shown in Table 1.

Table 1 As can be seen from Table 1, the configuration according to the present invention has a higher erasure rate and comparable C/N than the conventional example. The reason why the erasing rate is higher in the configuration according to the present invention is considered to be because the recording film is once melted by the preceding spot, so that the old signal can be almost completely erased.

In other words, it can be seen that according to the present invention, recording and erasing characteristics equivalent to or better than those of the conventional example can be achieved with two spots placed very close together (about 0.7 μm in this example).

Effects of the Invention According to the present invention, a high erasing rate can be obtained, and at the same time, since the laser spots are installed very close together (sometimes they overlap), it is easy to install them on the same track. Furthermore, it is possible to provide an optical information recording/reproducing/erasing device that is easy to mass-produce.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the shape and arrangement of a laser beam spot applied to the optical information recording/erasing method of the present invention and its role; FIG. 2 is a sectional view showing the structure of an optical disc;
The figure shows a spot configuration according to the present invention used in a specific example and a spot configuration according to a conventional example. 1...Spot 1.2...Spot 2.3...
...Track groove. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1 (Hisun (C) Figure 2)

Claims (5)

[Claims] (1) On a reversible optical information recording medium, which has a thin film of phase-change recording material on a substrate whose optical properties change reversibly in response to light irradiation conditions, old signals can be erased while new signals can be created at the same time. A method of recording signals, in which two or more circular or nearly circular spots are placed close to each other on a recording track, and old signals are erased by increasing the power of the first spot to a level higher than that of melting the recording thin film. An optical information recording/erasing method characterized in that a new signal is recorded by modulating subsequent spots with the signal to change the cooling rate of the portion melted by the leading spot. (2) The optical information recording and erasing method according to claim 1, characterized in that two or more circular or substantially circular spots overlap each other. (3) The optical information recording/erasing method according to claim 1, wherein the number of spots is two. (4) The shape of the subsequent laser spot has an ellipticity of 1:1 to
2. The optical information recording and erasing method according to claim 1, wherein the optical information recording/erasing method has a substantially circular shape with a ratio of 2:1. (5) The optical information recording and erasing method according to claim 1, characterized in that the phase change type recording material thin film is made of a material that applies a reversible phase change between an amorphous and a crystal.