JPH04313816A - Record erasing method and device for optical information recording medium - Google Patents

Abstract

PURPOSE:To obtain the rewritable optical disk of high C/N by making a recording film into the mixing condition of amorphous and crystal with optical beam irradiation, making amorphous easily with the beam of a high level continuously and crystal- recording easily at a low level. CONSTITUTION:A irradiation power level Ph of a recording beam 11 corresponds to '1' of data and a level Pl corresponds to '0' of data. A level Pe of an erasing beam 12 is set to Pl<Pe<Ph. A reproducing beam Pr is set to a low power level where the recording film is not changed. Since the temperature of the recording film exceeds the melting point a little by the irradiation of a beam Pe and it is the temperature lower than the time of the beam Ph irradiation, the difference in the absorption factor, etc., at the amorphous part and the crystal part is decreased. The film is effectively crystallized by the irradiation of the recording level Pl. The crystallization is promoted in a double manner by the irradiation of levels Pe and Pl. A level Pl irradiating part is hard to be influenced by the previous record, and the high erasing ratio and the high C/N are simultaneously obtained. At the time of the recording level Ph irradiation, the film temperature exceeds the melting point sufficiently and becomes amorphous at the quick cooling process.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a rewritable optical information recording medium, and in particular to recording of an optical information recording medium that can improve C/N or S/N by obtaining a high erasure ratio. This article relates to an erasing device and a recording erasing method.

0002

2. Description of the Related Art Information is read from optical information recording media such as optical disks by irradiating the medium with a light beam such as a laser beam and detecting the reflected or transmitted light. Furthermore, when recording or erasing information, the structural state of the medium is physically changed by irradiating it with laser light, for example. As such an information recording medium, chalcogenides are known which can take two different structural states, an amorphous state and a crystalline state. For chalcogenides, light beams
An amorphous state can be obtained by heating the material to a temperature above the melting point by irradiation with a fluorine and then rapidly cooling it, and a crystalline state can be obtained by heating the material to the crystallization temperature or above the melting point and cooling it slowly. That is, an amorphous state or a crystalline state can be obtained depending on the cooling method such as rapid cooling or slow cooling.

[0003] IEICE technical report Vol. 87. No. 310CPM87-88~9
0 discloses a method called the overwrite method in which data is overwritten on previous history by changing the irradiation level of a single laser beam. In this method, when the temperature is raised above the melting point, the temperature gradient during cooling increases (quick cooling), resulting in an amorphous state; when the temperature is lowered below the melting point, the temperature gradient during cooling decreases, resulting in a slow cooling state. This is how a crystalline state is obtained. Therefore, 1 of the data
At level, the laser beam output is increased to bring the temperature above the melting point, and at data level 0, the same output is lowered to bring the temperature below the melting point and overwrite the previous data (overwrite). I try to do that.

[0004] Furthermore, in JP-A-1-311422 and JP-A-2-5238, in order to obtain the above-mentioned crystalline state, the power level of the laser is temporarily increased to temporarily melt the recording medium, and then the recording medium is melted. A method for improving the erasure ratio in the above-mentioned overwriting method by gradually cooling the film is disclosed. Also,
IEICE technical research report published in 1978, IEICE Technical Report Vol. 87. No. 310CPM87-88, 2
On page 7, a method for erasing records using multi-beams is disclosed. In this method, in order to obtain a high erasure ratio, as shown in FIG. was irradiated to a temperature above the crystallization temperature and below the melting point to promote crystallization. Further, during recording, the area was irradiated with a circular beam 21 to make the area amorphous.

Further, methods using two circular beams are disclosed in JP-A-1-138620 and JP-A-2-177131. In this method, as shown in Fig. 3, an erasing beam 12 and a recording beam 11 with the same maximum power level are prepared, and the temperature of the erasing beam 12 is raised above the melting point to erase information tracks. When crystallizing and recording 0 level data, the temperature is raised slightly above the crystallization temperature Tx, and the subsequent slow cooling effect crystallizes the relevant portion.

[0006]

[Problems to be Solved by the Invention] The above-mentioned overwriting method has a problem in that a sufficient erasure ratio cannot be obtained. The first cause of this problem is that the cooling rate after laser irradiation at the erase level is too fast, and the crystallization of the amorphous part does not progress sufficiently, leaving the erased area (
(influence of previous history) may occur. The second reason is that because the light absorption rate and thermal conductivity of the amorphous and crystalline parts are different, the heating process during erasing and the subsequent cooling process differ depending on the previous history. impact).

As a countermeasure for the second cause, the erased area can be completely erased by heating and melting it to a temperature above the melting point but sufficiently lower than the recording temperature, but the subsequent crystallization will not occur. However, in reality, most of the material becomes amorphous, so that a sufficient signal level ratio between the erased portion and the recorded portion cannot be obtained and cannot be used. Further, although the multi-beam method shown in FIG. 2 can obtain a well-crystallized erased portion due to the effect of the elliptical beam 23, there is a problem in that the optical head becomes complicated.

Furthermore, in the two-beam method shown in FIG. 3, since the area after erasing cannot be sufficiently crystallized by irradiation with the low-level recording beam 11, similar to the above-mentioned overwrite method, There was a problem that the level ratio between the 1st level and the 0th level was insufficient. That is, in the two-beam method shown in Fig. 3,
Since the power level of the erasing beam 12 is made the same as that of the recording beam 11 to melt the entire recorded area, the width of the amorphous area becomes wider as shown in FIG. 4(A). After that, when rewriting is performed, the power distribution of the recording beam is Gaussian, so if the power level of the 0-level data is high,
As shown in (B), the central part of the information track 10 remains amorphous, and when the power level of the 0-level data is lowered, the peripheral part becomes crystallized as shown in (C) of the same figure. Because it is not present, it remains amorphous.

An object of the present invention is to prevent the amorphous portion from remaining in the 0 level data portion of the recording as shown in FIGS. 4(B) and 4(C), thereby improving the structure. It is an object of the present invention to provide a recording/erasing method and apparatus that can obtain a high erasing ratio using a relatively simple two-beam optical head.

0010

[Means for Solving the Problem] In order to solve the above problem, the power level Pe of the light beam at the time of erasing is set to the power level Ph of the light beam at the time of high level recording of the signal and the low level of the signal. Power level Pl of the above light beam during level recording
is set to an intermediate level, that is, Pl<Pe<Ph. Further, the erasing light beam is a pulsating light whose repetition frequency is higher than the recording frequency of the signal, and its high level Pe is set to be lower than the power level Ph of the recording light beam, and its low level is set as above. Optical beam during recording
so that the power level of the system is equal to or higher than Pl. Further, the wavelength of the light beam during erasing is made larger than the wavelength of the light beam during recording. Furthermore, the same track portion is irradiated with the light beam during erasing multiple times. The phase change recording film is brought into a mixed state of amorphous and crystalline by irradiation with each of the above-mentioned erasing light beams.

[0011]

[Operation] By irradiating each of the above erasing light beams, the phase change recording film of the optical disc is brought into a mixed state of amorphous and crystalline, and
By making the wavelength of the erasing light beam larger than the wavelength of the light beam during recording, the spot size of the erasing light beam is made larger than the spot size of the recording light beam. Further, by irradiating the same track portion with the erasing light beam a plurality of times, the phase change recording film, which is relatively resistant to phase change, is brought into a mixed state of amorphous and crystalline materials.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle and effects of the recording and erasing method according to the present invention will be explained with reference to FIG. 1 and FIGS. 5 and 6. In the present invention, as shown in FIG. 5A, the width of the amorphous portion of the information track 10 after erasing is narrowed, and at the same time, that portion is made to have a mixed state of crystal and amorphous. In this way, during recording, the information track can be made sufficiently amorphous at the 1st level of data, as in the conventional case, and at the 0th level of data, the information track 10 can be rendered amorphous. Since the crystalline region is a mixture of crystals and amorphous and its width is narrow, it can be sufficiently crystallized.

Therefore, in the present invention, as shown in FIG. 1, the (irradiation) power levels of the erasing beam 12 and the recording beam 11 are controlled. After the erasing beam 12 is irradiated, the recording beam 11 is irradiated. That is, the recording beam 11
The power level Ph corresponds to one level of data and is a level at which the information track can be sufficiently amorphized. Further, Pl corresponds to the 0 level of data. The power level Pe of the erasing beam 12 is set between the above-mentioned Ph and Pl, that is, Pl<Pe<Ph. Also,
The reproduction beam Pr is set at a low power level so that the phase change recording film does not change.

FIG. 6 is a schematic diagram showing how the temperature of the recording film changes. The temperature of the recording film due to the irradiation with the erasing beam 12 slightly exceeds the melting point Tm, but is lower than the temperature at the time of irradiation with the recording beam Ph. Therefore, as shown in FIG.
The central part of 0 becomes amorphous due to the rapid cooling effect, and the peripheral part is slowly cooled or does not reach the melting point, so it becomes a state in which there are many crystals. As a result, most of the data before rewriting is lost, the part that was amorphous before rewriting is partially crystallized, and the part that was crystalline is now amorphous. The state will be as follows. That is, the erasing power Pe is not set to melt all of the recording film, but is set to such an extent that the difference in characteristics such as absorption rate between the amorphous portion and the crystalline portion is reduced.

Furthermore, during irradiation at a low recording power level Pl, the temperature of the recording film is higher than the crystallization temperature and lower than the melting point, so that the recording film is effectively crystallized by the gradual cooling effect. Areas that were amorphous before rewriting are the most difficult to crystallize, but by irradiating these areas with the Pe erasing beam and the Pl recording beam, crystallization is doubly promoted, resulting in a lower The irradiated portion of the recording power level Pl becomes less susceptible to the influence of the previous history, and a high erasing ratio and high C/N can be obtained at the same time. When irradiated with a high recording power level Ph, the temperature of the recording film becomes sufficiently higher than the melting point Tm, and becomes amorphous during the rapid cooling process.

[Example 1] FIGS. 8 and 9 show experimental data showing the effects of the optical disc erasing and recording method according to the present invention. FIG. 7 is a partial cross-sectional view of an InSbTe-based optical disk in which the recording film used in the experiment undergoes a reversible phase change between crystalline and amorphous states. Polycarbonate substrate 13
A first interference film 14 made of ZnS-SiO2 with a film thickness of 70 nm, a phase change recording film 15 made of In3SbTe2 with a film thickness of 30 nm, a second interference film 16 made of ZnS-SiO2 with a film thickness of 110 nm, and a second interference film 16 made of ZnS-SiO2 with a film thickness of 120 nm are placed on top of the film. A reflective film 17 made of Ni--Cr, an organic protective film 18 made of ultraviolet curing resin having a film thickness of 30 μm, and the like are laminated. Also, the light beam
The beam is irradiated from below and changes the state of the recording film 15.

Furthermore, the present invention is not limited to the above-mentioned optical disks, but also includes GeTe-based, GeSbTe-based, GeS
bTeCo series, InSe series, SbSeBi series, TeSb
Se series, SbTe series, InSbSe series, GeSbTeS
It can also be applied to optical discs using phase change recording films such as e-based and GeSnTeO-based, and optical discs using crystal-to-crystal phase change recording films.

In FIGS. 8 and 9, the high recording power level Ph is fixed at 13 mW, the low recording power Pl is fixed at 6 mW, and the erasing power level Pe is varied, and in FIG. 8, the recorded signal level and the unerased level are examined. , in Figure 9, Figure 8
The results are summarized in terms of C/N ratio and cancellation ratio. The wavelength of the recording beam and the erasing beam is 830 nm, the NA of the objective lens is 0.6, and the medium moving speed is 13 m/s.

In FIG. 8, first, the frequency 7M is used as the previous history.
Hz data is recorded and then erased by an erasing beam. A curve 100 in the figure is the level of the 7 MHz unerased component measured after the above erasing. Erase power P
As e increases, the amorphization progresses and the unerased level decreases. Next, when 8 MHz data is recorded, the reproduction output level becomes 101. Erase power P
When e becomes approximately 10 mW or more, the amorphous portion generated during erasing increases, making it difficult for data to crystallize at a low level (0 level), and the reproduction output level of the signal begins to decrease.

Further, the level of the 7 MHz unerased component mixed into the 8 MHz reproduced output decreases with the erasing power Pe, as shown by a curve 102, and becomes saturated when Pe is approximately 10 mW or more due to an increase in the amorphous portion. Since it is best for an optical disc to maximize the recording level after sufficiently erasing the previous history, the results shown in FIG.

FIG. 9 shows the results of similarly measuring the C/N ratio and the erasure ratio, and shows that the maximum erasure ratio of 35 dB can be obtained when the erasure power Pe is about 10 mW. It is also seen that a C/N of approximately 60 dB or more can be obtained. These levels are more than sufficient for data as well as analog video. From the above, as explained in FIG. 1, the erasure ratio and C/N ratio can be maximized by setting the erasure power Pe to a level intermediate between the recording high level Ph and the same low level Pl. . In addition, in the above erasing process, if the wavelength of the erasing light is made longer than the wavelength of the recording light, the optical spot diameter of the erasing beam becomes larger than that of the recording beam, so it is necessary to sufficiently cover the previous history part when erasing. It can be done.

[Example 2] In the above-mentioned Example 1, the erase power level Pe was kept constant at 9 mW, but the above-mentioned Pe is modulated at a frequency higher than the recording signal frequency, and the power level is adjusted to the average recording signal frequency. It is also possible to set it to an intermediate value between the high level Ph and the same low level. When recording a signal, the period of the high level Ph is long enough to make the phase change film sufficiently amorphous, and the low level Pl is long enough to make the phase change film sufficiently amorphous. Make it. By modulating the erasing level Pe at a frequency higher than the maximum recording frequency determined in this way, and making the high level lower than the above Ph, and the low level higher than the above Pl, Since the phase change film temperature during erasing does not change much in terms of time constant, substantially the same effect as when the erasing power level Pe is kept constant can be obtained.

For example, the recording conditions are the same as in Example 1, and the erasing beam is set to a low power level of 7 mW and a high power level of 11 mW.
When modulating between mW at a frequency of 50 MHz, an erasure ratio of 33 dB and a C/N of 60 dB after rewriting were obtained. It should be noted that if the erasure beam modulation frequency is brought closer to the recording signal frequency, the erasure ratio will decrease, so it is preferable to set it to at least twice the highest frequency of the recording signal. Furthermore, the erasing ratio can be further improved by increasing the number of times the erasing beam is irradiated.

[Embodiment 3] FIGS. 10 to 12 are block diagrams showing the configuration of an optical disc device for performing recording and erasing according to the present invention. In FIG. 10, the spindle motor 29
The recording and erasing of the present invention is performed using a two-beam optical head 28 that can simultaneously generate two light beams, that is, an erasing beam 12 and a recording beam 11, on an optical disk 27 rotated by a I do. A focus/tracking control circuit 30 controls focus/tracking of the optical head 28 based on command signals from a system controller 34. The system controller 34 also sends command signals to the erase power control circuit 31 and the recording power control circuit 32.
The recording and recording level of the light beam of the beam optical head 28 is controlled.

The recording power control circuit 32 sets the high recording laser power level Ph and the low recording laser power level Pl in accordance with the above-mentioned command numbers, and controls the output of the recording laser in the two-beam optical head 28 accordingly. Similarly, the erasing power control circuit 31 sets the power level Pe of the erasing laser in the two-beam optical head 28 to the relationship Pl<Pe<Ph. For example, the above levels are Pl=6mW, Ph=1
Overwriting is performed by simultaneously oscillating the erasing laser and the recording laser at 3 mW and Pe=10 mW. In addition, a high frequency oscillation circuit and a laser power level setting circuit are added to the erase power control circuit 31, and even when the erase laser power Pe is a signal of a frequency of 40 MHz with a low erase power level of 8 mW and a high erase power level of 12 mW, good recording erase characteristics can be achieved. Obtainable.

FIG. 13 is a diagram showing an example of the configuration of the two-beam optical head 28. As shown in FIG. For example, the semiconductor laser array 51
If the output light of one of the lasers is irradiated onto the optical disk 27 through the collimator lens 52, half mirror 53, and objective lens 54 as shown by the dotted line, this becomes the erasing beam 12. The output light of the other lasers is the recording beam 1 as shown by the solid line.
1.

FIG. 11 is a block diagram of an embodiment of the recording/erasing apparatus of the present invention in which two one-beam optical heads 40 and 41 perform the above-mentioned erasing and recording. The output of the erasing optical head 41 is controlled by the erasing power control circuit 31, and the output of the recording optical head 40 is controlled by the recording power control circuit 32, so that similar overwrite characteristics and recording/erasing characteristics can be obtained.

FIG. 12 is a block diagram of an embodiment of the recording/erasing apparatus of the present invention, which performs the above erasing and recording using a one-beam optical head. The outputs of the erasing power control circuit 31 and the recording power control circuit 32 are switched by a recording/erasing switching circuit 37. Although overwriting is not possible, recording/erasing characteristics similar to those described above can be obtained. In addition to the circular recording beam and erasing beam, the recording and erasing device of the present invention may also use an elliptical or other shaped beam. Originally, the output beam of a semiconductor laser was 2:
The beam is often an ellipse of about 1.1 mm, and such a beam can be used without being shaped into a circle.

Furthermore, for an optical disk having a phase change film that is difficult to change phase when irradiated with the erasing beam, the same erasing effect as in each of the above embodiments can be obtained by increasing the number of times the erasing beam is irradiated. Can be done. For example, in an optical disk for still images having such a phase change film, it is possible to easily specify a still image portion to be erased, so that the above erasing is repeatedly performed on that portion a predetermined number of times.

[0030]

Effects of the Invention: By irradiating the erasing light beam according to the present invention, the phase change recording film of the optical disc is brought into an erasing state in which amorphous and crystalline materials are mixed, and the recording light beam that is irradiated thereafter is at a high level. Since the erased state can be easily amorphized and the erased state can be easily crystallized and recorded at the same low level, it is possible to provide a high-quality rewritable optical disc device with a high C/N. . Furthermore, since it is possible to significantly reduce the amount of the previous history left unerased, it is possible to provide a recording/erasing method with a high erasing ratio.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining a recording/erasing method according to the present invention.

FIG. 2 is an explanatory diagram of a conventional three-spot recording/erasing method.

FIG. 3 is an explanatory diagram of a conventional two-spot recording/erasing method.

FIG. 4 is a schematic diagram of the state of a recording film in a conventional two-spot recording/erasing method.

FIG. 5 is a schematic diagram of the state of a recording film in the present invention.

FIG. 6 is a schematic diagram of the temperature change of the recording film in the present invention.

FIG. 7 is an example of a partial cross-sectional view of an optical disc to which the present invention is applied.

FIG. 8 is an example of a reproduction level characteristic diagram of a recorded signal and an unerased signal in the present invention.

FIG. 9: C. in the present invention. This is an example of an N ratio and erasure ratio characteristic diagram.

FIG. 10 is a block diagram of an embodiment of the recording/erasing device of the present invention using a two-beam optical head.

FIG. 11 is a block diagram of an embodiment of the recording/erasing device of the present invention using two 1-beam optical heads.

FIG. 12 is a block diagram of an embodiment of the recording/erasing device of the present invention using one one-beam optical head.

FIG. 13 is a block diagram of a two-beam optical head.

[Explanation of symbols]

4 Recording section 5 Crystal 10 Information track 11 Recording beam 12 Erasing beam 13 Substrate 14 First interference film 15 Recording film 16 Second interference film 17 Reflection film 18 Organic protective film 21 Circular beam 23 Elliptical beam 27 Optical disk, 28 2-beam optical head 29 Spindle motor 30 Focus/tracking control circuit 31 Erasing power control circuit 32 Recording power control circuit 33 Recording/erasing control circuit 34 System control 35 1 beam Optical head 37 Recording/erasing switching circuit 40 Recording optical head 41 Erasing optical head 51 Semiconductor laser array 52 Collimator lens 53 Half mirror 54 Objective lens

Claims (8)

[Claims] Claim 1. In a recording erasing method for an optical information recording medium in which a phase change recording film on the optical information recording medium is irradiated with a light beam such as a laser to record, erase, and reproduce signals, the phase change recording film on the optical information recording medium is The power level Pe of the light beam is an intermediate level between the power level Ph of the light beam when recording a high level signal and the power level Pl of the light beam when recording a low level signal; In other words, a method for erasing recording on an optical information recording medium characterized by setting Pl<Pe<Ph. 2. According to claim 1, the erasing light beam
The beam is pulsating light whose repetition frequency is equal to or higher than the recording frequency of the signal, the high level of its power level Pe is equal to or lower than the power level Ph of the recording light beam, and its low level is the power of the recording light beam. A method for erasing records on an optical information recording medium, characterized in that the level is equal to or higher than level Pl. 3. The recording and erasing method for an optical information recording medium according to claim 1 or 2, characterized in that the wavelength of the light beam during erasing is made larger than the wavelength of the light beam during recording. . 4. A recording and erasing method for an optical information recording medium according to any one of claims 1 to 3, characterized in that the same track portion is irradiated with the light beam during erasing a plurality of times. 5. In any one of claims 1 to 4, the phase change recording film is brought into a mixed state of amorphous and crystalline by irradiation with a light beam having a power level of Pe. Characteristic method for erasing records on optical information recording media. 6. In a recording and erasing device for an optical information recording medium that records, erases, and reproduces signals by irradiating a phase change recording film on the optical information recording medium with a light beam such as a laser, the phase change recording film on the optical information recording medium is The power level Pe of the light beam is an intermediate level between the power level Ph of the light beam when recording a high level signal and the power level Pl of the light beam when recording a low level signal; That is, a recording and erasing device for an optical information recording medium is characterized by comprising an erasing power control circuit that sets Pl<Pe<Ph. 7. In claim 6, the power control circuit makes the erasing light beam a pulsating light whose repetition frequency is higher than the recording frequency of the signal, and the power level Pe
The power level Ph of the light beam when recording the high level of
A recording/erasing device for an optical information recording medium, characterized in that it is equipped with a light beam modulating means for making the low level of the light beam equal to or higher than the power level Pl of the light beam during recording. 8. In claim 6 or 7, the light beam irradiation means includes the recording light beam source and the erasing light beam having a longer wavelength than the recording light beam source. What is claimed is: 1. A recording and erasing device for an optical information recording medium, comprising: a source;