JP2708476B2 - Recording and playback of information - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing method, and more particularly to a so-called overwrite, in which new information is recorded while erasing existing information with one energy beam spot. And information recording / reproducing and erasing methods.

[Conventional technology]

A conventional recording / erasing method for a phase change type optical disk medium is, for example, to perform recording by irradiating a laser beam spot sufficiently and irradiating the recording film in an amorphous state by rapid heating and quenching. In addition, the erasure of the recording has been performed by returning the amorphous recording portion to the crystalline state by gradual heating using an oblong spot or the like which is long in the track direction. In this method, two beam spots having different shapes are used for recording and reproduction and for erasure. On the other hand, a method has also been used in which a single beam spot is used to erase recording by rotating the disk medium many times, and to record information in the next one rotation. In order to rewrite the recording by the latter method, the spot had to pass the same place on the recording film of the disk medium many times. However, recently, a recording film capable of high-speed erasing capable of performing crystallization in substantially the same time as the laser irradiation time required for recording has been developed. In this film, Japanese Patent Application No. 61-10113
As shown in FIG. 0, recording, reproducing and erasing of information can be performed by one energy beam spot, and new information is recorded while erasing existing information. Writing) is possible.

[Problems to be solved by the invention]

In the above prior art, overwriting can be performed by changing the power of a single laser beam between a high power level and an intermediate per level. In this case, the intermediate power level means that most of the track to be recorded is in a crystalline state, and the high power level means that most of the track to be recorded is almost amorphous after melting. Phase change.

Here, when recording is performed by changing the laser power between a high power level and an intermediate power level as in the prior art, a portion irradiated at a high power level (amorphous state)
In this case, the width in the direction perpendicular to the track is larger than that of the portion irradiated with an intermediate power level and crystallized. Therefore, when overwriting new information on a track on which information has already been written, the portion irradiated at a high power level becomes almost amorphous regardless of the previous state, but becomes amorphous. When light is applied to the portion that has been exposed at an intermediate power level, only the central portion is crystallized, and a portion of the peripheral portion remains in an amorphous state. In addition, a narrow region around the melted portion has a different crystalline state from the others. This results in an error at the time of reading because it remains unerased. Further, in order to make the film amorphous, the temperature of the recording film in the irradiated portion must be raised to the melting point, melted once, and then rapidly cooled. Therefore, film deformation (including a base film and a protective film) due to high heat occurs in the amorphous portion.
This led to an increase in noise, which led to problems such as lower C / N (carrier-to-noise ratio). Depending on the properties of the recording film, the melted part does not become amorphous after irradiation,
There may be a case where the crystallinity is relatively poor, or a state where the size and type of the crystal grains are different from those of the unmelted portion. However, also in this case, the portion where the unremoved portion easily occurs is almost the same as the case where the melted portion becomes amorphous.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a recording / reproducing method that minimizes unerased portions during overwriting, suppresses noise due to deformation as much as possible, and increases C / N. It is in.

[Means for solving the problem]

The objective is to use two irradiations on the same point on the recording film,
This is achieved by performing overwriting under the condition that the C / N is slightly reduced by the first irradiation (the first irradiation) and the remaining is as small as possible, and the C / N is improved by the second irradiation.

The intermediate power level in the first irradiation of the present invention is:
The power level is set between a conventional intermediate power level (the level at which crystallization is most likely at the center of the beam) and a high power level. That is, in the present invention, since a power higher than the power for crystallizing the central portion of the track is applied, the central portion of the track is made amorphous, and the crystallized region is enlarged in a direction perpendicular to the track. Therefore, by irradiation at a high power level, the outer peripheral portion of the previously formed amorphous region can be crystallized (erased).
Because the track center was melted once, the influence of the difference in crystallinity around the recording point was also reduced, and the unerased portion was reduced. As a method of changing the power of the first irradiation, any method may be used as long as the following condition is satisfied. The condition is that the state of the central portion of the portion formed by irradiation with the high power level and the state of the central portion of the portion irradiated with the intermediate power level are not the same but close (reflection Rate etc.). For example, these portions are all in a state close to amorphous, and the peripheral portion of the portion irradiated with the intermediate power level is in a crystalline state. On the other hand, in the conventional recording, when a portion formed by irradiation with a high power level is in a state close to amorphous, a central portion of a portion irradiated with an intermediate power level is in a crystalline state. In this case, the periphery of the portion irradiated with the intermediate power level did not change.

The power level in the middle of the first irradiation is preferably in a range of 0.4 or more and 0.9 or less, where 1 is a high power level. In particular, it is preferably 0.65 or more and 0.80 or less.

In the present invention, since the power level in the middle of the first irradiation is high, the unerased portion can be reduced. However, in this method, the central portion of the portion irradiated with the intermediate power level and the portion irradiated with the high power level approach the same state, so that the signal reproduction intensity decreases. Therefore, in the present invention, in order to solve this problem, after recording with the first irradiation so that the state of the central part and the state of the peripheral part of the part irradiated with the intermediate power level are close,
The same part of the second irradiation was performed with continuous light (DC light) having a lower power level than the intermediate power level of the first irradiation. As a result, the state of the central portion and the peripheral portion of the portion irradiated with the intermediate power level in the first irradiation became almost the same, and the signal reproduction intensity was increased.

The power level in the case of the DC light of the second beam is larger than the low power (reproduction) level, and is preferably a power level between 0.2 and 0.9 times the intermediate power level of the first beam. In particular, 0.5 to 0.8 times is preferable. At this time, in the first irradiation, the irradiation time of the high power level is shortened to reduce the power difference between the high power level and the intermediate power level so that the portion irradiated at the high power level is not changed by the second irradiation. It is preferable to increase the laser power, or to lower the power once from the high power level to the intermediate power level, and then increase the laser power to the intermediate power level. This is to prevent the cooling rate from lowering due to the residual heat and to make the state almost amorphous.

However, depending on the material, a portion irradiated at a high power level is irradiated with the second irradiation DC light, so that the portion is changed to a considerable extent (in this case, crystallization), and the reproduction signal intensity may be reduced. There is. In such a case, the power may be changed in a pulsed manner in the second irradiation, and the second irradiation at the above-mentioned power level may be performed only on the portion irradiated with the intermediate power level of the first irradiation. In other words, the state of the central portion is changed only in the portion irradiated with the intermediate power level of the first beam, and is made substantially the same as the peripheral portion. As a result, the intensity of the reproduced signal could be increased, and the C / N could be improved.

In this case, it is better to set a lower power level for most of the rest of the irradiation time. This level may be a read power level, a zero level, or another lower level.

When the second irradiation is performed only on a portion where the first irradiation is performed at an intermediate power level, the tracking method is a sample servo that can obtain an accurate clock signal from the disk so that the position is exactly matched. It is better to use the method.

Still, the second irradiation also has the effect of reducing noise. This is presumably because the recording film, the protective film, and the base film were deformed by the irradiation of the high power, but the stress was reduced by the irradiation of the weak light, and the original state was approached.

It is more preferable that the reflected light intensity is detected in the second irradiation to confirm (verify) whether the recording or rewriting of the record is correctly performed in the first irradiation.

In the information recording film used in the method of the present invention, a phase change reversibly occurs in the recording film only by changing the power of the energy beam within the same irradiation time, whereby the optical index such as the refractive index, the reflectance and the transmittance is changed. Any film may be used as long as it has a constant composition and other physical property constants, and has a component composition capable of recording and erasing information.

The reversible change in the physical property constant at the recorded value used in the present invention is performed by utilizing a state change (atomic arrangement change) of a recording material constituting the recording thin film, and the change between the amorphous state and the crystalline state of the thin film. Utilizing a transition or a transition between one amorphous state and another amorphous state, or a transition between one crystalline state and another crystalline state (difference in crystal form, difference in grain size, etc.). Can be performed. Such a change in the atomic arrangement hardly accompanies a change in the shape of the film. Therefore, the above-mentioned transition is performed stably and reversibly due to the power change of the energy beam, and the change of the physical property constant occurs reversibly and at high speed and stably. Examples of such a thin film include, for example, a thin film mainly containing In-Se, a thin film mainly containing Ge-Sb-Te, and the like.

In the state transition of the recording film, it is possible to arbitrarily select which state is to be the recording state or the erasing state. For example, when a high-power laser beam is irradiated by the first beam, the reflection state is changed. Low (or high) rate
The state may be a recording state, or it may be an erasing state. However, it is preferable to shorten the irradiation time of the high-power laser light as much as possible in order to avoid adverse effects such as deformation of the recording film. Preferred in many cases.

In the present invention, if the recording track is made to be in a uniform state by irradiating a semiconductor laser beam having a constant power once, the initial state is always constant, so that stable recording can be performed.

Further, as the recording medium used in the present invention, a recording medium that reversibly takes two or more states corresponding to two or more temperatures without causing a change in physical constants, It can be used in the method of the present invention. For example, a magneto-optical disk medium utilizing the reversal of magnetization may be used.

[Action]

In the present invention, since the intermediate power level of the first irradiation is set higher than the conventional intermediate power level, the phase change region becomes larger in the direction perpendicular to the track. As a result, the previously formed information (amorphous state) could be reliably erased. Also at this time C / N
Is smaller than the maximum value by the second irradiation. In addition, the second irradiation also serves as confirmation of information recorded in the first irradiation, so that reliable recording and erasing of information can be performed.

A recording head having a single light beam may be used, the first irradiation may be performed in one rotation of the disk, and the second irradiation may be performed in the second rotation. Or using two light heads of a single light beam,
The first irradiation may be performed with the light spot that is irradiated first on the disk, and the second irradiation may be performed with the light spot that is irradiated later. The head of a single light beam has the advantage that the optical system is simple, and when the head is a two-beam light head or two heads, it can be rewritten by one rotation of the disk, so that the information transfer speed can be increased. There are advantages.

〔Example〕

 Example 1 FIGS. 1A to 1D show an example of the present invention.

FIG. 1 (a) shows an example of a method for recording, reproducing and erasing information according to the present embodiment, in which a laser power (mW) is used.
5 is a graph showing a time transition of the data. As a disk serving as a medium, an optical disk having a diameter of 130 mm and having an In-Se-Tl-Co recording film capable of rewriting information by a crystal-amorphous phase change with one laser beam was used. The recording track of the recording medium is brought into an almost amorphous state by irradiating a semiconductor laser beam, and after rotating the medium, a semiconductor laser beam of a low power level (A) which is a reproduction power level (wavelength of 830 nm) is recorded on the recording track. Automatic focusing and tracking are performed while irradiating continuous light. Then, at the same time as reaching the required recording / rewriting location (i), the power is raised at once to the intermediate power level (B). Further, when it comes to the place (ii) where new information “1” is to be recorded, the power is raised to a high power level. Then (125n
s) reduce the power to an intermediate power level (ii
i). The above laser power modulation cycle is set to “1”
It was possible to overwrite information by repeating it at the place where it was written.

In this embodiment, the spot diameter of the semiconductor laser light is about 1 μm in half width. The disk speed is 1800rpm, the middle power level is 15mW, the high power level is 21
At about mW, good overwriting was performed. The power was set lower at the inner circumference of the disk, and at the innermost circumference, the power was about 1 / 1.4 of the above power.

FIG. 1B shows a recording state when the laser power shown in FIG. 1A is applied. Most of the part irradiated with the high power level (C) (A) and the central part (B) of the part irradiated with the intermediate power level (B) are in a state close to amorphous due to melting and quenching. I'm sorry. The periphery (c) of the portion irradiated with the intermediate power level (B) is in a crystalline state. The region 1 not irradiated with the laser beam is in the same state as immediately after the film formation.

In the intermediate power level (B) setting of the present embodiment, the crystal region (c) has a larger spread in the direction perpendicular to the track than the formed amorphous region (a). As a result, the amorphous portion of the previously recorded information can be surely erased (crystallized), and overwriting can be repeated.

Irradiation of the laser power shown in FIG. 1 (a) reduces the unerased portion and enables reliable rewriting of information.
Since the states of the parts (a) and (b) are almost amorphous, the reflected light of the part irradiated with the high power level (B) and the part irradiated with the intermediate power level (C) The intensity difference becomes small, and the signal reproduction intensity becomes small.
This can be solved by making the state of the part (b) substantially the same as the state of the part (c) by irradiating the laser beam again. The second laser beam irradiation was performed using the same light head in the next one rotation of the disk. As shown in FIG. 1 (C), this irradiation is set at a lower power level (B) than the intermediate power level of the first irradiation, at a higher power level (D) than at a lower power level (A), and continuously recorded. The part was irradiated. As a result, as shown in FIG. 1 (d), the portion (b) crystallized and became almost the same state as the portion (c), and the signal reproduction intensity increased. At this time, the central part of the part (a) is also somewhat crystallized, but the first irradiation makes the part (a) more amorphous than the part (b). Therefore, a large change does not occur in the reflected light intensity of the portion (a). In addition, by irradiating such weak continuous (DC) light, it was possible to reduce noise and confirm recording by reflected light intensity.

According to the present embodiment, the unerased residue can be reduced by 5 to 10 dB, and the decrease of the C / N from the maximum value can be suppressed to 3 dB or less.

Next, as another form of the present embodiment, the first irradiation and the second irradiation could be performed by two light beams from each laser by using a light head having two lasers. In this case, the light spot by the first beam and the light spot by the second beam were formed close to each other on the same track at a distance of about 20 μm. Both light spots were almost circular. Further, the wavelength of the first beam is 830 nm.
And the wavelength of the second beam was 780 nm. The optical system is such that the diameter in the direction perpendicular to the track of the light spot of the first beam is slightly larger than the diameter in the direction perpendicular to the track of the light spot of the second beam. The size ratio is 1: 1.05-1: 1:
The effect of improving C / N was obtained in the range of 1.3.

In this embodiment, the intermediate power level (B)
May be considered as a recording portion.

Different light beams, such as tracking, auto focus, etc.
Alternatively, when performing another method, the low power level of at least one of the first and second irradiations may be set to the 0 level.
A similar effect can be obtained in a magneto-optical disk medium.

Second Embodiment FIGS. 2A, 2B, and 2C show an example of a temporal transition of the power level of the first irradiation laser in the second embodiment.

As in the first embodiment, when the second irradiation is continuous (DC light) irradiation, there is a possibility that the amorphous portion formed by the irradiation of the first irradiation at a high power level may be crystallized. There is. In this case, as shown in FIG. 2 (a), the laser power is reduced from the high level (C) to the intermediate level (B) or lower (between (iii) and (iv)), and then the intermediate level is returned. By raising to the level (B), it was possible to surely make it amorphous. In addition, it was possible to prevent the recording point from spreading backward due to heat conduction.
At this time, the average laser power between (iii) and (iv) is 0
It is preferably from the level to just below the intermediate power level (B), and a more preferable range is from 0.2 times to 0.8 times the power of the intermediate power level (B). (Iii)
The time from (iv) to (iv) is preferably in the range of 1/5 or more and 1 or less of the unit time (time indicated by 0 or 1). (Iii)-(i
When shortening the time of v), it is preferable to lower the power during this period. In addition, as shown in FIG. 2 (b), an effect was obtained in which, even if the high power level of the first irradiation was set higher and the irradiation time was shortened, the remaining disappearance was reduced.

Further, in a short time in which the temperature does not significantly change, the power may be changed up and down from an intermediate power level or a high power level.

As shown in FIG. 2 (c), when there is only one 0 between 1 and 1 of the digital signal, the power of the first irradiation of that part is lower than the intermediate power level (B). This is effective in reducing the error rate. The power at this level is particularly preferably 0.3 to 0.8 times the intermediate level. Even when there are two or more 0s between 1 and 1, the power immediately after 1 is lower than the intermediate power level and higher than the power level when there is only one 0 between 1 and 1. Is more preferred. However, as indicated by the dotted line, the power in this part may be equal to the intermediate power level in some cases. In order to lower the power in this way, the power may be set to an intermediate power level for a part of the zero period, not for the entire period.

The fall of the power after the pulse and the reduction of the pulse width as in the first irradiation of the present embodiment are effective even when the intermediate power level is reduced as in the related art or when the second irradiation is not performed. It is.

 The second irradiation in this example was performed in the same manner as the first irradiation.

As in the first embodiment, the low power level may be set to the zero level.

[Embodiment 3] FIGS. 3A and 3B show temporal changes in laser power of the first irradiation and the second irradiation in this embodiment.

In the first embodiment, in the recording film having a low activation energy, a portion near an amorphous state formed by irradiation with a high power level C may be slightly crystallized by irradiation with a second beam. . In this case, as shown in FIG. 3 (b), the power of the second irradiation is changed in a pulsed manner, and a power level (B) intermediate to the first irradiation of FIG. 3 (a) is applied. Irradiation may be performed by increasing the power of the second irradiation only to the portion where the second irradiation is performed. Thereby, in the first irradiation,
The portion near the amorphous portion at the center among the portions irradiated at the intermediate power level (B) is crystallized. As a result, the reflectance difference between the portion irradiated at the high power level (C) and the portion irradiated at the intermediate power level (B) became large, and the C / N could be increased. here,
The power level (E) of the second irradiation is preferably 0.3 times or more and 0.9 times or less of the intermediate power level (B) of the first irradiation.

When the method of this embodiment is performed with two laser heads or two laser heads, the pulse irradiation timing of the first beam and the second beam is set on the disk by setting the interval between the two light spots to 2 μm. The second irradiation is performed in a predetermined case with a predetermined power by shifting by a time during which the point passes.

As in the first embodiment, the low power level may be set to the zero level.

〔The invention's effect〕

According to the present invention, a reversible phase-change optical disk medium capable of high-speed erasing or a recording medium capable of recording and erasing by changing the state only by a change in irradiation power level is used. In addition, new information can be rewritten at high speed and surely while erasing existing information. Further, by performing the second irradiation, the verification can be simultaneously performed while improving the C / N. Further, the irradiation beam to be used is not limited to a light beam, and other energy beams such as an electron beam and an ion beam can be used. The method of the present invention can be applied not only to a disk-shaped recording medium but also to a tape-shaped recording medium. It is also effective for other types of recording media such as a card and a card.

The present invention relates to a reversible phase-change optical disk medium, that is, a medium in which the atomic arrangement changes with almost no change in the outer shape of the film, particularly, a medium in which a change between crystal and crystal or between an amorphous and crystal occurs. Great effect.

[Brief description of the drawings]

FIG. 1A is a graph showing a temporal transition of the laser power of the first beam in Embodiment 1 of the present invention, and FIG.
Is a plan view showing a state of a place irradiated with the first beam,
FIG. 4C is a graph showing the temporal transition of the laser power of the second beam, and FIG. 4D is a diagram in which only the portion irradiated with the intermediate power level of the first beam is irradiated with the second beam. FIGS. 2 (a), 2 (b) and 2 (c) are graphs showing three examples of a temporal change of the laser power of the first beam in the second embodiment, and FIGS. 14 is a graph illustrating a temporal transition of the laser power of the second beam in the third embodiment. 1 ... state immediately after film formation 2 ... area close to amorphous 3
... Crystal region.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuya Nishida 1-280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Inside the Hitachi, Ltd. Central Research Laboratory (72) Inventor Keikichi Ando 1-280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Hitachi (72) Inventor Reiji Tamura 1-1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell, Inc. (56) References JP-A-63-117325 (JP, A) JP-A-56-148740 ( JP, A) JP-A-60-247828 (JP, A) JP-A-59-148144 (JP, A)

Claims (1)

(57) [Claims] An information recording / reproducing method in which information is rewritten by irradiating an energy beam to a recording member, wherein the information is stored between at least a high power level and an intermediate power level of the power of the first energy beam. The first beam spot formed by the energy beam on the recording medium changes according to the signal, and erases the existing information while passing through the recording medium once, and then records the new information. A constant power level of 0.2 to 0.9 times the intermediate power level of the first energy beam, and from 1 / 1.05 of the first beam spot diameter.
By irradiating the second beam spot having a spot diameter in the range of 1 / 1.3, it is necessary to confirm whether the first recording or the recording rewriting by the irradiation of the first beam spot is correctly performed (verify eye). Recording / reproducing method of characteristic information.