JPH0440629A - Optical information recorder - Google Patents

Abstract

PURPOSE:To reduce unerased parts in an area by superposing 1st and 2nd concentric optical spots and setting up the size of the 2nd optical spot to a value larger than that of the 1st optical spot. CONSTITUTION:The 1st and 2nd optical beams B1, B2 emitted from respective light emitting elements 21, 22 are made into almost parallel beams by respective collimeter lenses 23, 24 and applied to a beam superposing means 25 utilizing a polarized beam splitter from a direction intersecting orthogonally with the means 25. The 1st and 2nd optical beams B1, B2 superposed by the means 25 pass through an information reading partial reflection mirror 26 and condensed into the 1st circular optical spot S1 and the 2nd circular optical spot S2 larger than the 1st spot S1 by a condenser lens 27 to irradiate a medium film 13. Thus, unerased parts in an area can sharply be reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a device for recording information using light, such as a so-called optical disk device, in which an information recording medium is irradiated with light and reversible. The present invention relates to an optical information recording device that records information by causing a state change or phase change, and is capable of rewriting information by so-called override.

(Prior Art) As is well known, information recording using light allows for 10 to 100 times higher density recording than magnetic recording, and has the advantage that the recording medium is not damaged by contact with the head. Suitable for compact disk storage devices that record large amounts of information. This information recording format includes a read-only format that can only be read, and a write-once format that allows recording and reproduction but cannot be rewritten, but a rewritable format that allows information to be freely rewritten is used as an external storage device for a computer. This is the most popular method, and the magneto-optical method and the phase change method are also known for this rewritable method.

As is well known, the magneto-optical method uses a material that has a magneto-optical effect as a recording medium, and is a magnetic recording method that records information in the form of magnetic field direction, etc., and normally when rewriting information, the recorded information is Since it is necessary to once erase the data and then record the update information, it is difficult to perform overwriting, which is called overwriting, and there is a problem in that the access time of the disk storage device cannot be shortened below a certain limit.

In contrast, the phase change method controls the degree to which the recording medium is heated within a very short period of time by irradiating pulsed light such as a laser beam, changing the phase state of the recording medium to a crystalline state with high reflectivity to light and a low reflectivity state. The present invention relates to an optical information recording device that rewrites information by overriding using such a change in phase state. The outline will be explained below with reference to the figures.

FIG. 2 is a partially enlarged cross section of the optical disk 10 used in this phase change method. The substrate 11 of this disk IO is usually made of polycarbonate, and on its surface, a very shallow groove as shown in the figure is usually provided in a spiral shape with a width of about 1 p to form a track T for recording information. The film thickness includes a protective film 12 such as ZnS and Ge for information recording.
5bTe-based medium film 13, the same protective film 14 as above,
A reflective film 15 made of aluminum or the like is sequentially deposited by a spunter method or the like, and is further covered with a surface protection film 16 formed by spin-coating resin to a rather thick thickness.

When recording or rewriting information, a laser beam or the like is focused onto the medium film 13 from the substrate 11 side of the optical disc 10 to a diameter comparable to the width of the track T, and a light spot is focused on the content of the information to be recorded thereon. 90n with irradiation amount according to
It is irradiated only for a very short period of time, about S. As is well known, information is recorded on the disk 10 not in the form of the original information or data as is, but in the form of 0's and 1's as shown in the upper part of Figure 3, which are converted using the RLL system's 2-near code. The amount of irradiation of the light spot on the medium film 13 is as shown in FIG. 3(C), with respect to 1 in the write signal. For example, it is large, but when it comes to 0, it is reduced to about half or less.

At this time, the parts of the medium film 13 that were strongly irradiated with the light spot were thereby heated to a high temperature and then rapidly cooled, so that they became amorphous with low reflectivity, while the parts that were weakly irradiated were heated to a low temperature. It is then slowly cooled to become a highly reflective crystalline material.
The contents of recorded information are read using this difference in reflectance.

[Problem to be solved by the invention]

As mentioned above, in the phase change type optical information recording device, information can be overridden by simply switching the irradiation amount to the optical disk according to O and 1 in the write signal of a predetermined code type. Since the change in phase state between crystalline and amorphous depends on the process of heating by a light spot and subsequent cooling, please refer to “Overwrite C” for details.
hractsristics 1nPhase Cha
nge 0ptical Disk”+Takabas
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Journal of Applied Physics
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Volume 28, separate issue 28-3. p128. As described in , some information may remain unerased before the update.

For example, the medium film 1 is strongly irradiated in response to the write signal 1.
Considering the specific part in 3, since the write signal of any code system is O before and after it, the adjacent parts before and after it on the track will be irradiated even if it is weak, whereas the adjacent part in the direction perpendicular to the track will be completely irradiated. (Since it is not irradiated, the heating and cooling conditions and processes in this specific area and in the vicinity will differ between the circumferential direction and the radial direction of the disk.

Whether each part of the medium film 13 becomes crystalline or amorphous is determined by the temperature when heated by the light spot and the subsequent cooling rate, so such heating and cooling conditions are determined in the circumferential and radial directions of the disk. If this is different, unerased information is likely to remain in the vicinity of the newly rewritten portion, particularly in areas adjacent in the radial direction. In addition, when rewriting, the light spot is of course positioned on the track as accurately as possible, but in reality it is unavoidable that some tracking error will occur, so this error will make it more likely that information will remain unerased. If the tracking error during reading is further superimposed on this, a reading error will occur.

To solve this problem, as can be seen from the above, it is necessary to eliminate the directionality within the disk surface in the heating and cooling conditions in the portion of the medium film that is strongly irradiated in response to the write signal 1, for example. Conventionally, efforts have been made to, for example, reduce the amount of irradiation to areas adjacent to this in the circumferential direction more than in response to the write signal O.

However, in this solution, it is necessary to control the irradiation amount in three stages at high speed, which makes the driving circuit for the irradiation light source considerably complicated, and the period in which 1 appears in the write signal is the information to be recorded. Since it constantly changes depending on the content, it is actually very difficult to construct a drive circuit that can accurately control the dose without causing operational perturbations.

It is an object of the present invention to solve this problem and to reduce the amount of unerased data after information is rewritten by overriding using simple and reliable means.

[Means to solve the problem]

According to the present invention, this purpose is to collect a first light beam when recording information by irradiating a light spot onto a recording medium and changing the phase state that occurs in the recording medium in accordance with the irradiation intensity. The recording medium is irradiated with a light spot in which the first light spot and the second light spot, which is a second light beam condensed to a larger size than the first light spot, are concentrically superimposed. This is achieved by controlling the amount of irradiation by one light beam according to the recorded information.

Note that the spot size of the first light spot mentioned above is preferably about the same as the track width, and the size of the second light spot is 10 to 30% larger than this, preferably 20%.
It is advantageous to increase the degree.

It is simplest and usually sufficient to make these light spots circular, but in some cases it may be advantageous to make them slightly elongated in the radial direction of the disk.

Further, the total amount of irradiation from the first and second light beams is set to a level suitable for making the recording medium amorphous, and the amount of irradiation from only the second light beam is set to a level suitable for crystallizing the recording medium. It is reasonable to set these values for the implementation of the present invention, and if the recording medium is a Ge5bTe system as described above, the amount of irradiation from both beams should be the same, or the amount of irradiation from the first beam should be slightly smaller. It is better to do so.

The first and second light beams are preferably generated by separate light sources, and of course it is most advantageous to use a laser light source such as a laser diode.

[Effect]

As described in the configuration in the previous section, in the present invention, the light spot that irradiates the recording medium on the track is created by overlapping the first and second light spots that are concentric with each other, and the size of the second light spot is set to the size of the first light spot. The second light spot is made larger than the light spot, and the recording medium on the track is heated and cooled by heating not only the area on the track of the recording medium but also the area adjacent to it in the radial direction by irradiation with the second light spot as in the conventional method. The above conditions are made uniform in the circumferential and radial directions within the disk surface, and the unerased information after the information is rewritten by override, especially the unerased information in the area radially adjacent to the track, is reduced, and at the same time, the override This is intended to reduce the adverse effects of slight tracking errors that may occur in the optical spot at the time of the image. Furthermore, the present invention simplifies the drive circuit of the light beam source and ensures its operation by simply controlling only the irradiation amount of the first light beam according to the recorded information when rewriting information by overriding. It is.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings. 1st
The figure is a configuration circuit diagram illustrating the essential parts of the optical information recording apparatus of the present invention, and the optical disc of FIG. 2 described above is the same in the present invention. FIG. 3 illustrates changes over time in the irradiation amount of the first and second light spots and their superimposed light spots on the optical disc.

The optical information recording device in FIG. 1 is a disk storage device,
For example, the optical disc 1 with a diameter of 130 cm shown in the upper left
0 is driven at a constant speed by a spindle motor 1 via a shaft 3 rotatably supported on a base 2 of the device, and has a recording medium 13 on its upper surface whose phase state can be changed reversibly as described above. . In this example, the thickness of each film sequentially deposited on the transparent substrate 11 made of polycarbonate or the like shown in FIG. The thickness of the reflective film 15 made of aluminum or the like is 1000, and the surface protection film 16 made of ultraviolet curing resin or the like is about 10 fm.

The phase change type recording medium for the medium film 13 includes, for example, GeT.
Ge*5b consisting of 2 molecules of e and 1 molecule of Sb and Tex
zT@s is used, and the applicant's previous Ii (patent application 1986)
-244788), GeTe has ^U and C.
It is desirable to speed up the rewriting of information and stabilize the amorphous state by adding u to increase the activation energy that influences the temperature dependence of the crystallization rate.
The reflective film 15 also serves as a cooling film for the medium film 13, and is disclosed in another patent application II (Japanese Unexamined Patent Publication No. 63-21493) of the present applicant.
As described in 8), it is desirable to optimize the thickness of the heat insulating protective film 14 interposed between these two films in order to improve the information rewriting characteristics.

The head 20 for reading and writing information is shown surrounded by a dot M line in the center of FIG.
In the illustrated example, a first light emitting element 21 and a second light emitting element 22, which are separate laser diodes or the like, are incorporated into the head 20 for generating these light beams B1 and 82, and a laser with a wavelength of, for example, 8300 is incorporated into the head 20. generate light.

The first and second light beams B1 and 82 from these optical elements 2I and 22 are transmitted through collimator lenses 23 and 24, respectively.
In this example, the beams are applied to the beam superimposing means 25 using a polarizing beam splitter from directions perpendicular to each other. The first and second light beams Bl and 82 superimposed by this means 25 pass through a partial reflection mirror 26 for information reading, and then are enlarged and shown in the upper right corner of FIG. 1 by a condensing lens 27. In this example, the circular first light spora) SL and the second light spora)
The light beams S2 and S2 are respectively focused and irradiated onto the medium film 13.

The first light spot S1 of these is located on the track T as shown in the figure.
The diameter of the second light spot s is about the same as the width of
2 has a diameter of 1.2μ, which is about 20% larger than that.

Note that these light spots S1 and 32 are imaged by a common condensing lens 27 on the medium film 13 located almost at their focal position, but in order to make the spot sizes of the two different from each other as shown above, a collimator is used. The positions of lenses 23 and 24 are very slightly as shown by arrow M in the figure! Ilt! ! It is enough to do i.

Further, the output of the second light beam B2 focused on the second light spot S2, that is, the irradiation amount, is set to a value 1, for example, 7-, which is enough to bring the recording medium of the medium film 13 into a crystalline state. When the information is rewritten, it is maintained at this constant value as shown in FIG. 3, regardless of the content of the information. On the other hand, the output of the first light beam B1 focused on the first optical spora) SL is such that the total irradiation amount with the second light beam B2 is suitable for making the recording medium M13 into an amorphous state. The value is set to 1, for example 8-, and is controlled according to the content of the recorded information. In reality, the above-mentioned write signal representing the information content is switched to 0 or 8-1 as shown in FIG. 3 (chrysanthemum) depending on whether 0 is 1 or not.

Therefore, as shown in FIG. 3(C), the amount of irradiation by the light beam B obtained by superimposing the first light beam B1 and the second light beam B2 depends on whether the write signal is 0 or 1 in this example. So 71 and 1
Can be switched to 5-1.

Note that in the case of the present invention, when reading recorded information, the first
Only the light beam B1 is used, and its output is set to a value much lower than the irradiation amount for crystallizing the recording medium of the medium film 13, for example, about 1-.

In FIG. 1, the low-output first light beam B1 at the time of such readout is generated by a condensing lens 27 into a 1n-diameter optical spoiler).
The light is focused on Sl and applied to the medium film 13 , and the reflected light is reflected by a partial reflection mirror 26 and applied to a photodetector 29 via another condensing lens 28 .

Note that an optical signal for tracking the head 2o and focusing the condensing lens 27 is transmitted to this optical detection 82 via a similar optical path.
9, but is completely omitted in FIG. 1 for the sake of simplicity.

On the right side of FIG. 1, a drive circuit 31 for the first light emitting element 21 related to the head 20, a drive circuit 32 for the second light emitting element 22, and a read signal processing circuit that receives a detection signal from the photodetector 29 are shown. 33 is shown, and an encoder/decoder circuit 34, a data control circuit 35, and a processor 36 are shown as related main parts of the disk storage device. Further, the data control circuit 35 and the processor 36 are connected to a computer (not shown) via a bus 37, and a communication bus 38 is provided between them. When receiving an access command from the computer, the processor 36 issues a read/write command i based on the access command.

When reading is commanded by this read/write command R-, the drive circuit 31 causes the first light emitting element 21 to generate the first light beam B1 for reading at the low output of 1- described above. stops the light emitting operation of the second light emitting element 22. At this time, the read signal l? S is provided from the photodetector 29 via the read signal processing circuit 33 to the encoder/decoder circuit 34 in a predetermined code format, and further converted into digital information in the data control circuit 35 and sent to the computer.

When writing, that is, information recording is commanded by the read/write command R-, the drive circuit 31 transfers the information received from the computer to the data control circuit 35 and the encoder/decoder circuit 3.
A write signal -5 of a predetermined code format converted by 4 is received, and the first light emitting element switches the output of the first light beam B1 between 0 and 81 depending on whether the write signal is 0 or 1. Further, based on this command, the drive circuit 32 causes the second light emitting element 22 to generate a second light beam B2 with a constant output of 7 mW, so that the information is transferred to the optical disc 10 according to the above-mentioned method n.
is recorded in the recording medium of the medium film 13 of.

A performance confirmation test was conducted on the optical information recording device according to the embodiment of the present invention described above. First, the reflectance of an optical disk whose recording medium was still in an amorphous state immediately after production was measured using a laser beam having a wavelength of 8,300, and the result was 0.16.

1. of the second light beam of the output cuff.
When the reflectance is measured after irradiation with a 2n diameter spot, it is 0.
．． It had improved to 38. Even after repeated tests, the reflectance did not change any further. It can be seen from this that the recording medium can be brought into a crystalline state by just one irradiation with the second light beam.

For the information recording test, the write signal has a unit pulse width of 90n.
Using a so-called 8T pattern in which 7 O's and 1 1 are repeated in S, a 1n diameter spot of the 8- first light beam controlled by the 20 write signal and a 1n diameter spot of the 71 constant second light beam are used. 1
．． When we irradiated the recording medium with superimposed spots of 2n diameter and measured the CN ratio (carrier-to-noise ratio) of the read signal using a spectrum analyzer, we found that it was 55d, which is sufficient for practical use.
A good result of B was obtained.

Next, for an override characteristic test, a write signal of a 3-block pattern in which two 0s and one 1 repeat were overridden under the same irradiation conditions as above for the recorded optical disc with an 8T pattern, and this rewriting was performed. Using a spectrum analyzer, we measured the CN ratio of the previous 8 pattern components in the read signal, which corresponds to the unerased previous information, and found that it had decreased from 55 dB to 18 dB, indicating that the information before rewriting was It was confirmed that the data had been almost completely erased.

Furthermore, as a comparative test for evaluating the override characteristics according to the present invention, write signals of 3 patterns were applied to the recorded optical disk of 8T pattern under the same conditions as before, that is, the irradiation doses were 71 and 15. - After overriding using a 1 μ diameter spot of a single light beam that switches between
In the case of the present invention, the decrease from 5 dB was 25 dB, but in the case of the present invention, this decrease was 37 dB, and it can be seen that the amount of unerased information before overriding is significantly reduced compared to the conventional method.

[Effects of the Invention] As explained above, the present invention provides an optical information recording device that records information by irradiating a recording medium with a light spot and reversibly changing the state that occurs on the recording medium according to the irradiation intensity. A light spot is formed by concentrically overlapping a first light spot where one light beam is focused and a second light spot where a second light beam is focused to a size larger than the first light spot. By irradiating the recording medium and recording information on the recording medium while controlling the amount of irradiation by the first light beam,
You can increase the following effects.

(First and second light spots with different spot sizes are concentrically superimposed and irradiated onto the recording medium, heating not only the area on the trunk but also the area adjacent to the trunk in the radial direction.) By making the heating and cooling conditions uniform in the circumferential and radial directions within the disk surface, it is possible to significantly reduce the amount of unerased previous information after override, especially in the area radially adjacent to the track. can.

(c) Since the recording medium is irradiated with a double light spot, even if a slight tracking error occurs in the light spot during override operation, it is not only easy to erase the information before override, but also the updated information itself. writing becomes more reliable, and their synergistic effect further reduces the probability of read errors.

(C) When overriding information, only the irradiation amount of the first light beam can be opened/closed or binary controlled depending on the content of the information to be updated, so the configuration of the drive circuit for the light source for generating the light beam can be simplified; The operation can be performed reliably and at high speed.

[Brief explanation of the drawing]

Claims (1)

[Claims] A device that records information by irradiating a light spot onto a recording medium and causing a reversible state change in the recording medium according to the irradiation intensity, the device comprising: a first light spot condensing a first light beam; The recording medium is irradiated with a light spot obtained by concentrically superimposing the second light beam and a second light spot condensed to a larger spot size than the first light spot, and the amount of irradiation by the first light beam is controlled. An optical information recording device characterized in that information is recorded by.