JP2719130B2 - Information recording / reproducing and rewriting method and device - Google Patents

Description

The present invention relates to a recording, reproducing and erasing method for an information recording apparatus such as an optical disk, and more particularly, to a method using a reversible phase-change type recording film capable of high-speed phase change, With a simple recording head, information recording, reproduction and erasing can be performed by one energy beam spot, and new information is recorded while erasing existing information. The present invention relates to a reproducing and rewriting method and an apparatus for executing the method. [Prior art] A method of focusing a light beam such as a laser beam into a minute light spot, recording and reproducing a signal at a high density on a reversible phase-change optical disc medium as an optical recording medium, and erasing a signal once recorded. As disclosed in JP-A-59-71140, information is recorded by irradiating the recording film with the light beam spot sufficiently converging and irradiating the recording film for a short time. By transitioning to a quality state,
On the other hand, when erasing the recording, the recording portion in the amorphous state is completely returned to the original crystalline state by gradually cooling it gradually using a long oval light spot or the like in the direction of the track (guide groove). It is done by that. As described above, two different light beam spots are used for recording and reproduction and for erasing, or a single light beam spot is used as disclosed in JP-A-56-148740. A method has been proposed in which recording is erased by rotating the medium many times, and information is recorded by the next one rotation. In order to rewrite the recording by the latter method, the light spot had to pass the same place on the recording film of the disk medium many times. [Problems to be Solved by the Invention] In the former of the prior arts described above, two different
The same track (guide groove) using two light beam spots
On top of that, if these two light beam spots are to be tracked, a control system required for the two light beam spots becomes complicated, and two light sources are required to form the two light beam spots. There were some problems. In addition, in the latter case of the above-mentioned prior art, even when a single light beam spot is used, it is necessary to rotate the disk medium many times when rewriting the recording, and it takes time to rewrite the recording. There was a problem. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art, and to use a reversible phase-change type recording film capable of high-speed phase change, to record, reproduce, and erase information with a simple optical system. It is an object of the present invention to provide a method of recording / reproducing and rewriting information which can be overwritten and which can record new information while erasing existing information, and a device therefor. [Means for Solving the Problem] An object of the present invention is to provide a high-speed erasing method such as an In-erasing method.
Using a reversible phase-change type information recording film such as a Se-based or Ge-Te-based system, during recording of information, the power of the energy beam such as light, electron, or ion beam changes the state of the recording film (phase (Variation) can be achieved by varying between multiple power levels. Note that, for example, an In—Se-based recording film is a recording film containing at least In and Se, and optionally containing one or more other elements. According to the method of the present invention, information can be rewritten (erased and re-recorded) with one energy beam spot while the spot passes through the recording film once. Note that the reproduction level of the rewriting light spot is used only for tracking and automatic focusing, or the reproduction level power is set to almost 0, and signal reproduction, or reproduction, tracking, and automatic focusing are performed by another energy beam spot. Is also good. 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 in the same irradiation time, whereby the refractive index, the reflectance, the transmittance, etc. Any film may be used as long as it has a change in optical constants and other physical constants, and has a component composition capable of recording and erasing information. The reversible change of the physical property constant in the recording film used in the method of the present invention is performed by utilizing the state transition of the recording material constituting the recording thin film, the transition between the amorphous state and the crystalline state of the thin film, or The transition between one amorphous state and another amorphous state, or the transition between one crystalline state and another crystalline state can be performed repeatedly,
The above-mentioned transition is stably and reversibly performed by a change in the power of the energy beam, and a change in the physical property constant is reversibly, and any thin film that can be stably generated at a high speed may be used. Te-based thin films and the like can be mentioned. In general, the recording material has a large number of states continuously or discretely between two states, for example, between a completely amorphous state and a completely crystalline (polycrystalline) state. Therefore,
By varying the power of the energy beam between the two levels, binary or digital recording can be performed.
Analog recording or multi-valued recording is possible by changing the level between two or more levels. [Operation] The method of recording, reproducing and erasing information according to the present invention comprises:
It is possible to record new information in its place while erasing existing information, so-called overwriting, and to rewrite (erase and re-record) information while the energy beam spot passes through the recording film once. Can be. For example, first, a disk having an amorphous state on a recording track (between tracking grooves) and a crystalline state between tracks is rotated, and information is reproduced using one laser or electron beam spot. Eventually, when a place where information is rewritten comes, a plurality of power levels different from the power of the reproduction level (continuous oscillation) (normally, two power levels, higher than the reproduction power level, the recording level and the erasing level). For example, the information is rewritten by changing the power. The recording level and the erasing level were defined as laser powers optimal for recording and erasing, respectively, when the power was continuously maintained.
(The reproducing power level is called the first power level because it has the lowest power among these power levels. Of the recording level and the erasing level, the lower power is the second power level, and the higher power is the third power level. Power level). In order to realize such a laser power change, recording and rewriting are performed on a waveform of a conventional write-once optical disc in which the power rises pulsewise from a reproduction level (first level) to a recording level (third level). It can also be realized by superimposing waveforms rising from the reproduction level to the erasing level (second level) in the region (the higher power of both is used as the output power). By adjusting the power of the waveform to be superimposed, a rewritable optical disk and a write-once optical disk can be recorded / reproduced by the same device. When information is rewritten by changing the power between two power levels of recording and erasing (the higher one is the third level and the lower one is the second level), immediately after the power level is changed to the higher one,
Once the power is lower than the lower power level, it is possible to prevent the cooling speed from decreasing due to the residual heat of the recording film, which is effective. On the other hand, for example, using a reversible phase change type recording material, the crystalline state is changed to the recording state, and the amorphous state is changed to the erased state, and the power (the third level) is lower than the erase level (third level). In the case of performing recording at a level of (2), for example, the recording may be performed by lowering the power in a pulsed manner from the erase level. In this case, it is preferable that the above-mentioned pulse-like power reduction is performed such that the power is particularly greatly reduced at the beginning. Thereby, the temperature can be quickly lowered to a temperature suitable for erasing. Also, during erasing, a method that uses a combination of a wavelength change accompanying a mode change due to a change in laser power, a decrease in the amount of high-frequency superposition, a change in the amount of return light, and chromatic aberration of the lens, or a beam deflector or the like is used. Increasing the beam spot on the disk medium by, for example, changing the optical path length and changing the focal position to achieve defocusing has the effect of increasing erasing time and preventing information from being left unerased. Note that, in two or more state transitions of the recording film, it is possible to arbitrarily select which one is to be a recording state or an erasing state. A state with a low rate may be set as a recording state, and conversely, it may be set as an erased state. However,
Since it is preferable to minimize the time during which high-power (third power level) laser light is irradiated in order to avoid adverse effects such as deformation of the recording film, the state in which high-power laser light is irradiated is referred to as a recording state. Is more preferable. In the present invention, when recording is performed using a reversible phase change between the crystal and the amorphous of the recording film, if the recording tracks are made to be in a crystalline state in advance, the recording tracks become uneven during rewriting. Crystallization and generation of noise can be prevented. When the rotation speed of the disk is high, for example, even if the energy beam at the crystallization level is
The irradiation time of the point may be so short that it may not be completely crystallized. In this case, the crystallization proceeds when light of the crystallization level is applied again at the time of recording / rewriting, so that the reflectance of the crystallized portion is not constant but varies depending on the location. In such a case, of the crystallized portion, the reflectance of the portion closest to the reflectance of the field in another state (amorphous state), or this reflectance and the reflectance of the amorphous portion (If there is a width, the reflectance closest to the crystalline state) Set the comparator level to a voltage corresponding to any reflectance between
It is preferable that the signal voltage in the crystallized state is adjusted to a constant value. In this case, the voltage between the voltage corresponding to the reflectance of the crystalline state closest to the amorphous state and the voltage corresponding to the reflectance of the amorphous state closest to the crystalline state, or the amorphous state closest to the crystalline state. If the comparator level is set to a voltage close to the voltage corresponding to the reflectance of the quality state, reliable reproduction can be performed.
If the voltage is set between the above-mentioned intermediate voltage and the voltage in the crystal state closest to the intermediate voltage, the original waveform can be reproduced faithfully. The shaping may be performed using another waveform shaping device. Example An example of the present invention will be described below in more detail with reference to the drawings. Embodiment 1 FIG. 1 is an example of a method for recording, reproducing and erasing information according to the present invention, and is a graph showing a temporal transition of laser power (mW). First, a recording track of an optical disk medium having a diameter of 130 mm having an In-Se-based recording film in which information can be rewritten by a crystal-amorphous phase change is set to an amorphous state, and a space between recording tracks is set to a crystalline state. . The recording track may be in a crystalline state. In this case, it is preferable that the recording track has a crystalline state in which the reflectivity is substantially equal to that of the part in the crystalline state of the track on which recording was actually performed. By maintaining a perfect crystalline state between the recording tracks, during recording and rewriting, heat diffuses between the tracks, causing the crystal to gradually crystallize non-uniformly, and the previously recorded information is mixed into the reproduced signal of new information. It is possible to prevent (a kind of remaining disappearance) and noise increase. After the optical disc medium is rotated, automatic focusing and tracking are performed while irradiating a laser beam (continuous light) of a reproduction level (first level) with one light beam spot along a groove-like track. Do. Then, the record rewriting location (A)
At the same time, the power is increased at a stretch to the power of the crystallization level (the erasing level <second level>). Then, when a new recording location (B) is reached, the laser power is pulsed up to the laser power at the amorphization level (recording level <third level>). Thereafter, the laser power is reduced to the crystallization level [second level] (C). However, if the cooling rate is likely to be reduced due to the residual heat, the laser power is changed from the amorphization level (third level) to the crystallization level (second level) or lower ([C) to (dashed lines). D), and the laser power is raised (D) to the crystallization level (second level), and then the existing information is erased. In this case, the average laser power between (C) and (D) is preferably from level 0 to just below the crystallization level (second level), and a more preferable range is the crystallization level (second level). It is 1/4 or more and 3/4 or less of the power. Information can be overwritten by repeating the above laser power cycle. For example, when a 1.8 MHz carrier was recorded at a disk rotation speed of 2400 rpm, the carrier to noise ratio (C / N) measured at a bandwidth of 30 KHz was about 50 dB. Next, when rewriting is performed in the same place with a carrier of 0.9 MHz, a reproduced signal of 0.9 MHz is obtained, and its C /
N was also about 50 dB. At this time, the laser power at the amorphization level (third level) is about 15 mW, and the crystallization level (second level).
Level) laser power is about 7mW, reproduction level is about 1mW
And In the above-described laser power cycle, recording can be performed even when the level is immediately returned from the amorphization level (third level) to the crystallization level (second level). Is considered, the C / N and S / N (signal / noise) of the reproduced signal may be slightly deteriorated. Immediately after raising the laser power from the crystallization level (second level) to the amorphization level (third level), recording is performed by adding a peak power for slightly increasing the power as shown by a broken line. Amorphization of the film can be promoted. The magnitude of this peak power is higher than the amorphization level (third level).
Amorphization level (third level) and crystallization level (second level)
The power difference may be as high as 1), but a range of 1/4 to 3/4 of the above power difference is more preferable. The light beam spot was defocused during erasing to prevent unerased information. This was performed by using a focusing lens having chromatic aberration and utilizing the fact that the wavelength changes due to a mode change accompanying a change in laser power. If the focus is set during recording, defocus occurs at an erasing power (second power level) lower than the recording power (third power level). Next, FIG. 3 shows an example of the structure of the optical recording / reproducing / erasing apparatus used in the embodiment of the present invention. This optical system
It has almost the same structure as the optical system for write-once optical disks currently on the market. However, at the time of recording and erasing, since the reflected light from the recording film 2 may increase and cause a malfunction, the reflected light may be incident on the autofocus detector 16 and the tracking and signal reproducing detector 17 only before the reflected light is incident. The incident light amount was reduced by entering the filter 11. Further, the output voltage of the detector may be attenuated only during this period without using a filter. When the rotation speed of the disk is high, the irradiation time at one point on the disk is short, and the disk is not completely crystallized. In this case, when light at the crystallization level is applied again during recording / rewriting, crystallization proceeds, so that the reflectivity of the crystallized portion is not constant but varies depending on the location as shown in FIG. Therefore, the comparator level was set between the reproduction output voltage when the light of the reproduction level was applied to the amorphous portion and the reproduction output voltage of the crystallized portion where crystallization had not progressed most, and the waveform was shaped. If the comparator level is set between the two or closer to the output voltage of the amorphous part, the certainty of detection will increase, but if the comparator level is set closer to the output voltage of the crystal part than the middle, the reproduced waveform more faithful to the original waveform Is obtained. When the amorphization point comes first in the recording area, first, the laser power is changed from the reproduction level (first level) to the crystallization level (second level) without passing through the crystallization level (second level). (Third level). When the reproduction is performed by another method or another beam spot, the level is first changed from 0 level to the crystallization level or the amorphization level. Note that any of the crystallization state and the amorphous state may be considered as recording and any of them may be considered as erasing. However, since the laser power is higher in the amorphization, it is preferable that the time during which the power is at the amorphization level (third level) is shorter. In an optical disk device currently on the market, a recording pulse is emitted for a shorter time, so that it is preferable to consider amorphization as recording. In this case, a laser drive pulse of a commercially available optical disk device is supplied with a current corresponding to the difference between the reproduction level (first level) and the crystallization level (second level) as shown in FIG. A rewritable optical disk can be used only by making an improvement so that are superimposed. In the case of FIG. 5, the top of the waveform is limited because the amorphous level (third level) of the composite waveform becomes too high. By reducing the level of the current to be superimposed and, in some cases, setting it to 0, it is possible to record / reproduce data on a write-once optical disc with a rewritable optical disc apparatus. In this embodiment, if the amorphous state is changed to another crystalline state, or if the crystalline state is changed to another amorphous state, the present invention can be applied to a crystal-crystal or amorphous-amorphous phase change. Embodiment 2 FIG. 2 is another example of a method for recording, reproducing and erasing information according to the present invention, and is a graph showing a temporal transition of laser power (mW). This is an example where the recording level is lower than the erasing level. The recording film and the automatic focusing and tracking method used in this embodiment are the same as those in the first embodiment. First, at the same time as the place (a) to be rewritten comes, the power is raised at once to the power of the erasing level (third level) and is maintained at the same power. During this time, the information has been erased. When a new recording location (b) comes, the recording level (second level)
Recording is performed by reducing the power in a pulsed manner to the laser power of. At this time, it is possible to sufficiently record even if the power is lowered to the recording level as described above. However, at the beginning of the reduction in the power, as shown by a broken line [between (b) and (c)] in FIG. Once the power drops significantly below the recording level,
When the recording temperature is raised to a recording level and then returned to the recording level, the recording can be performed more reliably by increasing the time at the recordable temperature. The power at the time of lowering the recording level is preferably just below the power of the recording level, and a more preferable range is 1/4 or more and 3/4 or less. Thereafter, the laser power is raised to the erasing level. As shown by the broken line in FIG. 2, the power is once raised above the erasing level (c), and then lowered again to the erasing level (d).
Thus, erasure can be performed reliably. At this time (c) ~
The average power during (d) is larger than the erasing level, and the power of the erasing level may be added up to the power difference between the erasing level and the recording level.
A power obtained by adding 1/4 or more and 3/4 or less of the power difference between the erasing level and the recording level is more preferable. Further, the method for preventing the unerased portion of the information was performed in the same manner as in the first embodiment, and information recording, reproduction and erasing in the present embodiment were performed using the optical system shown in FIG. 3 in the first embodiment. FIG. 6 (a) shows a change in laser power when performing multi-level recording in this embodiment, and FIG. 6 (b) shows a reproduced waveform.
This is an example in which the recording state is ternary, but multi-level recording can be performed by increasing the number of levels, and analog recording can be performed by continuously changing the level. However, since the relationship between the change in the power level and the change in the reproduction voltage is usually not linear, conversion of at least one of the recording waveform and the reproduction waveform is necessary to obtain a desired reproduction waveform. [Effects of the Invention] As described in detail above, the information recording, reproducing and rewriting method according to the method of the present invention is a method of reversing a phase change type optical disc medium capable of high-speed erasing or other irradiation power level change only. By using a recording medium in which a change occurs and which can be recorded and erased, it is possible to quickly and reliably rewrite new information while erasing existing information with one beam spot using a simple system.
Further, the irradiation beam used is not limited to a light beam, and an energy beam such as an electron beam or an ion beam can be used. In addition, the recording medium is not limited to a disk, but may be in another form such as a tape or a card. It is applicable to recording media, and its industrial value is extremely large.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a temporal transition of laser power in Embodiment 1 of the present invention, FIG. 2 is a graph showing a temporal transition of laser power in Embodiment 2 of the present invention, FIG. 3 is a schematic view showing the structure of an optical recording, reproducing and erasing apparatus used in the embodiment of the present invention, and FIG. 4 is Embodiment 1 of the present invention.
FIG. 5 is a diagram showing an example of a reproduced signal waveform and a waveform shaping method in FIG. 5, FIG. 5 is a diagram showing a rewritten waveform synthesizing method in Embodiment 1 of the present invention, and FIG. It is a figure showing a principle. DESCRIPTION OF SYMBOLS 1 ... Optical disk substrate 2, ... Phase change type recording film 3 ... Protective film, 4 ... Focusing lens 5 ... Galvano mirror, 6 ... 1/4 wavelength plate 7 ... Polarizing prism, 8 ... Prism 9 Coupling lens 10 Semiconductor laser 11 Filter 12 Convex lens 13 Half mirror 14 Cylindrical lens 15 Knife edge 16 Automatic focusing detector 17 Tracking and signal reproduction Detector

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Noriyoshi Horigo               1-280 Higashi Koigabo, Kokubunji-shi               Central Research Laboratory, Hitachi, Ltd. (72) Inventor Norio Ota               1-280 Higashi Koigabo, Kokubunji-shi               Central Research Laboratory, Hitachi, Ltd.

Claims (1)

(57) [Claims] A method for recording, reproducing and rewriting information on an information recording medium by irradiating an energy beam, wherein the power of the energy beam irradiating the recording medium is changed at least among first, second and third levels. Where the first power level is a read power level, the second level is a power level higher than the first level, the third level is a power level higher than the second level, When recording or rewriting,
When raising the power of the energy beam from the second power level to the third power level, the power of the energy beam may be raised beyond the third power level and then reduced to the third power level, or
Recording / reproducing and reproducing information, wherein at least one of lowering the power level beyond the second power level and then returning to the second power level is performed when lowering the power level from the second power level to the second power level. Rewriting method. 2. 2. The information recording / reproducing and rewriting method according to claim 1, wherein when the power is raised from the second power level to the third power level, the power passes through the third power level once, and An information recording / reproducing and rewriting method, characterized in that the power is increased within the range of the third power level difference and then reduced to the third power level. 3. In the information recording / reproducing and rewriting method according to claim 1 or 2, when the power is raised from the second power level to the third power level, the power once passes through the third power level, When increasing the power by 1/4 or more and 3/4 or less of the difference between the second and third power levels and then lowering to the third power level or lowering the third power level to the second power level Once passing through the second power level, lowering the power value of the second power level by at least 1/4 to 3/4 below the second power level, and then returning to the second power level. Recording information characterized by performing at least one
Reproduction and rewriting methods. 4. An apparatus for recording / reproducing and rewriting information on an information recording medium by irradiating an energy beam, wherein the power of the energy beam irradiating the recording medium is changed at least among first, second and third levels. The second level is a power level higher than the first level, the third level is a power level higher than the second level, and the power of the energy beam is equal to the power of the energy beam when recording or rewriting information. Level 2 and 3
The power is reduced to the first level when information is not recorded or rewritten, and the power is changed from the second power level to the third power level. After raising above the third power level and then lowering to the third power level, or when lowering from the third power level to the second power level and lowering above the second power level An information recording / reproducing and rewriting apparatus having means for performing at least one of returning to a second power level. 5. 4. The information recording / reproducing and rewriting apparatus according to claim 4, wherein when the power is raised from the second power level to the third power level, the power passes through the third power level once, and An information recording / reproducing and rewriting apparatus, comprising: means for increasing the power within a range of the difference between the third power levels and then lowering the power to the third power level. 6. The information recording / reproducing and rewriting device according to claim 4 or 5, wherein when the power is raised from the second power level to the third power level, the power once passes through the third power level, When increasing the power by 1/4 or more and 3/4 or less of the difference between the second and third power levels and then lowering to the third power level or lowering the third power level to the second power level Once passing through the second power level, lowering the power value of the second power level by at least 1/4 to 3/4 below the second power level, and then returning to the second power level. An information recording / reproducing and rewriting apparatus characterized by having means for performing at least one of them.