JPH0954959A - Optical disk and access method of optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To embody an optical disk with which production is easy and errors in information reading are decreased. SOLUTION: A substrate 2 having the optical depth of grooves 4 within a range of λ/7 to λ/5 with respect to the wavelength λ of a light source for information reproduction is produced. The crosstalks between the adjacent lands 3 and grooves 4 are thereby decreased. A ground surface layer 5, a recording layer 6 and a protective layer similar to this layer 5 are formed on this substrate 2. Header information is recorded as phase changes only on the one recording layer 6 on the lands 3 or the grooves 4, by which the need for providing the substrate 2 with prepits for header information is eliminated. The regions on the tracks having no header information are accessed in accordance with the header information of the adjacent tracks in the case of the access to these regions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk such as a phase change optical disk or a magneto-optical disk, and a method of accessing this optical disk.

[0002]

2. Description of the Related Art In recent years, an optical recording / reproducing method satisfying various requirements including high density, large capacity, high access speed, and high recording and reproducing speed, recording apparatus, reproducing apparatus and recording medium used therefor. Efforts are being made to develop. Among the wide range of optical recording / reproducing methods, the magneto-optical recording / reproducing method and the phase change recording / reproducing method are the most attractive because of the unique advantage that the recorded information can be rewritten repeatedly. There is.

Here, the manufacturing process of an optical disk will be briefly described with reference to FIG. 3 by taking a magneto-optical disk as an example. In FIG. 3, 20 is a substrate made of plastic or the like, 23 is a land portion which is a convex portion of the substrate 20, and 24 is a guide groove (or groove portion) which is a concave portion. First, as shown in FIG. 3A, a glass master 22 having a photoresist 21 applied to its surface is prepared, and a portion corresponding to the groove 24 of the resist 21 is cut by using a laser beam. Then, after development is performed as shown in FIG.
As shown in FIG.
A master 22 (master) as shown in (c) is obtained. Subsequently, nickel electroforming is performed on this master 22 to obtain a nickel stamper 26 as shown in FIG. 3D, and injection molding is performed using this stamper 26 to obtain the nickel stamper 26 shown in FIG.
A substrate 20 with a guide groove as shown in (e) is obtained. Finally, by forming a recording layer (not shown) such as TbFeCo on the substrate 20, the manufacture of the magneto-optical disk is completed.

In such an optical disc, each track is divided into units called sectors, and header information including position information on the disc is recorded in each sector.
The header information recording method includes a method (preformat) of forming geometrical irregularities (hereinafter referred to as prepits) indicating header information on a substrate having guide grooves in a manufacturing process,
There is a method (soft format) of writing the header information on the recording layer after the disc is manufactured. Most of the magneto-optical disks currently on the market employ the pre-formatting method of the two methods.

On the other hand, in optical discs, land / groove recording has attracted attention for the purpose of further improving the capacity. This is a recording method that uses both the land portion and the groove portion as recording tracks. However, in the land / groove recording, both are used as recording tracks, and therefore pre-pits must be formed in each of the land portion and the groove portion. With a conventional disc that is not for land / groove recording, the formation of the land portion and the groove portion and the formation of the prepit provided on one side of the land portion and the groove portion can be simultaneously performed.
With a land / groove recording disk, these cannot be performed simultaneously. Therefore, for example, it is necessary to provide another process such as forming the pre-pits after forming the groove portion once, which takes a lot of time and effort at the time of producing the master.

In addition, if both the land portion and the groove portion are used as recording tracks, signal crosstalk between the tracks becomes large. Therefore, in a land / groove recording disc, adjacent land portions and group portions are formed. Signal crosstalk between the provided pre-pits becomes large, and information reading error occurs. In order to reduce this crosstalk, it is necessary to control the height of the prepits, which makes it more difficult to manufacture the master.

Further, if the soft format method is adopted instead of the above preformat method, the prepits are not required, so that the master fabrication becomes relatively easy. However, in order to use it as a land / groove recording disk, header information must be recorded in all sectors of all tracks (that is, both lands and grooves), which takes a very long time to format. .

[0008]

As described above, when land / groove recording is performed on a conventional optical disk, it is difficult to manufacture a master because pre-pits must be formed in both the land portion and the groove portion. There was a problem that became. In addition, since both the land portion and the groove portion are used as recording tracks, crosstalk between the tracks in both the header area and the data area becomes large and a signal reading error occurs, and it is attempted to reduce the crosstalk of the header information. However, there is a problem that it becomes more difficult to manufacture the master. If the soft format method is adopted instead of the pre-format method,
There was a problem that the format work took a very long time. The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical disc that is easy to manufacture and has few information reading errors, and an optical disc access method.

[0009]

The optical disc of the present invention comprises:
The recording layer is formed on a substrate having an optical depth of the groove in the range of λ / 7 to λ / 5 with respect to the wavelength λ of the information reproducing light source. The header information indicating the position on the disc is written in only one recording layer on the land or groove by optical recording without forming the concavo-convex pattern. By using a substrate in which the optical depth of the groove is in the range of λ / 7 to λ / 5, adjacent tracks (for example, adjacent grooves when the reproduction target track is a land and adjacent grooves when the reproduction target track is a groove) are used. Crosstalk from land) can be reduced. Furthermore, optical recording (soft format)
Since the header information is written only on one of the recording layers on the land or the groove, the prepits are unnecessary and the header information can be written easily.

The access method of the present invention is defined in claim 2.
When accessing the area on the first track, the header information recorded on the first track is detected and accessed, and the area on the second track is accessed. Is to detect the header information recorded on the first track adjacent to the second track, and to access based on the detected header information.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. FIG. 1 (a) is an external view of a phase change optical disc showing an embodiment of the present invention, and FIG. 1 (b) is an oblique view of a portion B of the phase change optical disc of FIG. 1 (a) taken along the line AA. It is an enlarged view seen from above. 1 is a phase change optical disk,
Reference numeral 2 denotes a land portion 3 which is a convex portion and a groove portion 4 which is a concave portion when viewed from the side (upper side in FIG. 1) opposite to the incidence of laser light.
A substrate with a guide groove having 5 is a Z formed on the substrate 2.
A base layer made of nS-SiO2 and a recording layer 6 made of GeSbTe formed on the base layer 5.

Next, a method of manufacturing such a phase change optical disc 1 will be described. First, the thickness is 1.2mm and the diameter is 1
30mm disc shape with track pitch P of 2μm and width W
Of 1 μm and depth D of 85 nm 4 (guide groove)
Figure 3 shows a plastic substrate 2 with a guide groove.
It is manufactured by the same method as.

At this time, the depth D of the guide groove 4 satisfies the relationship of the following equation. DL = D × n = λ / 7 to λ / 5 (1) In the formula (1), n is the refractive index of the substrate 2 (1.5 in this embodiment), and λ is a light source for reproducing information. , DL is the optical depth of the guide groove 4 considering the refractive index n. That is, the physical depth D is determined so that the optical depth DL of the guide groove 4 satisfies the expression (1).

Here, the phase change optical disk reads out the phase change of the recording film recorded as information as the intensity change of the reflected light, and the phase of the reflected light is hardly modulated and the intensity of the reflected light is modulated. Therefore, it can be called amplitude modulation recording. As described above, the optical depth DL of the guide groove 4
It is known that the signal crosstalk between the adjacent land portion 3 and groove portion 4 on the disc 1 can be extremely reduced by selecting the depth DL in the vicinity of λ / 6 in the amplitude modulation recording type optical disc. It is because it is being done.

On the substrate 2 with guide grooves thus produced, a base layer 5 made of ZnS-SiO2, a recording layer 6 made of GeSbTe, a protective layer made of ZnS-SiO2 (not shown), and an Al not shown (not shown) were formed by using a sputtering apparatus.
The manufacturing of the phase-change optical disc 1 is completed by sequentially forming the reflective layer consisting of.

Next, a laser beam is irradiated while modulating the light intensity to irradiate the phase of the recording layer 6 (crystalline state or amorphous state).
Information is recorded on the phase-change optical disk 1 by changing the phase change recording, and the crosstalk amount is evaluated. Since this phase-change optical disc 1 is for land / groove recording, information is recorded on both recording layers 6 on the land portion 3 and the groove portion 4. Here, one track is used for crosstalk evaluation. A mark (information) having a length of 3 μm was recorded only on the tape.

Subsequently, the phase-change optical disk 1 is irradiated with laser light, and a difference in reflectance depending on the phase is detected as a change in the intensity of the reflected light, and reproduction is performed. Adjacent tracks (adjacent groove portions 4 when the recording track is the land portion 3, and adjacent land portions 3 when the recording track is the groove portion 4)
The crosstalk amount was evaluated by the ratio R / S of the signal amplitude R when the signal was reproduced and the signal amplitude S when the recording track was reproduced. Since information is not recorded on the adjacent track, the leakage from the recording track is read when reading the adjacent track.

The wavelength λ of the light source used for recording and reproduction is 780
nm. The amount of crosstalk from the land portion 3 which is a recording track to the adjacent groove portion 4 was −40 dB, and similarly, the amount of crosstalk from the groove portion 4 to the adjacent land portion 3 was −38 dB. Signal crosstalk is -30
It is said that there is no problem if it is less than or equal to dB, and the value of the above-mentioned signal crosstalk is a level at which there is no problem in practical use.

From the above, even if information is recorded on both tracks of the land portion 3 and the groove portion 4, the influence of crosstalk from the adjacent tracks can be almost ignored. Further, since the crosstalk reducing effect as described above is derived from the shape of the substrate 2, it is established in the entire area regardless of the header area for recording header information and the data area for recording data. This allows the header area,
It is possible to realize an optical disk for land / groove recording in which the reading error of the signal is small in both the data area.

Next, in the present embodiment, such a phase change optical disc 1 is soft-formatted, but at this time, the header information is phase change recorded only on one recording layer 6 on the land portion 3 or the groove portion 4. To do. According to such a format, the time required for the format operation is halved and the efficiency of the format operation is improved as compared with the conventional soft format in which both the land portion 3 and the groove portion 4 are formatted.

However, since the phase change optical disk 1 thus formatted is for land / groove recording, it is different from the conventional one in order to access the groove portion 4 when the header information is recorded only in the land portion 3, for example. A method is needed. Therefore, the access method of the present invention will be described next.

FIG. 2 is a diagram showing a state of recording / reproducing tracks in the first portion C of the phase change optical disc 1 of FIG.
Reference numeral 4n is a groove portion, and 3n is a land portion adjacent to the inner peripheral side of the groove portion 4n. Similarly, the groove portion 4n + 1 and the land portion 3n + 1 are arranged on the inner peripheral side of the land portion 3n. Also, 11i and 11i + 1 are header areas for recording header information including synchronization information for reproducing the original signal and position information (address) indicating a position on the disc, and 12i and 12i + 1 are data. This is a data area for recording.

Since it is possible to access the sector 10i or 10i + 1 of the track (land portion) 3n + 1 in which the header information is recorded by a well-known technique, the description thereof is omitted here and the track (groove portion) is omitted. ) A method of accessing the 4n + 1 sector 10j will be described.

The sector 10j is a sector forming a pair with the sector 10i. The address of the sector 10i is the track number n + 1 and the sector number i, while the address of the sector 10j is the track number n + 1 and the sector number j.
At this time, i = j may be satisfied or i ≠ j may be satisfied. Also, the track numbers are the same, but they do not have to be the same.

Address management is performed by a pair of a sector of a track in which the header area is recorded and a sector of a track adjacent to which the header area is not recorded. The addresses are managed in correspondence. It may be set arbitrarily according to the form of management.

A recording / reproducing apparatus (not shown) for recording / reproducing information on / from the phase-change optical disk 1 stores the address correspondence as described above. When accessing the sector 10j, the paired sector 10i is first accessed. To do. Then, after reading the address of the sector 10i from the header area 11i, the tracking servo that causes the laser beam of the optical head to follow the track 3n + 1 is turned off, and the detection polarity of the tracking error is reversed.

Here, the reason why the detection polarity is inverted is as follows. The tracking error is detected by the push-pull method which is a well-known tracking error detection method. In the push-pull method, the output difference between the two light-receiving units in the optical head that receives the reflected light from the phase-change optical disc 1 is extracted as a tracking error signal, so tracking is performed when the laser beam accurately tracks the track. -The error signal becomes 0.

The polarity (+/-) of the tracking error signal is calculated when moving from the groove portion 4 to the land portion 3 and when moving from the land portion 3 to the groove portion 4.
Is different. Therefore, in this embodiment, the track 3n +
Since 1 is tracked and then the track is moved to the track 4n + 1, it is necessary to invert the detection polarity in order to correctly detect the tracking error.

Subsequently, the recording / reproducing apparatus moves the laser beam to the outer peripheral side of one track, and when the track 4n + 1 is reached, the tracking servo is turned on again. At this time, a certain amount of time is required from the input of the tracking servo to the stable follow-up operation, so after a certain amount of time has elapsed from the input and settling, the processing of the signal obtained by the optical head is started and reproduced. Get the output (that is, do not play if the output was obtained by the optical head before this).

Then, when the SYNC pattern for indicating the start position of the data area recorded at the head of the sector 10j is detected, it is determined that the sector is the target sector 10j, and the data is read. This allows the data recorded in the sector 10j to be reproduced. Further, in the case of recording in the sector 10j, it suffices to start recording after a predetermined time has elapsed from the re-input of the tracking servo. Thus, sector 10j can be accessed.

As described above, the header area is used as the land portion 3
Alternatively, since it is provided in only one of the groove portions 4, on the side without the header area, data can be recorded also in the portion which was the conventional header area, and the recording capacity can be increased. Further, even if the data recorded in the conventional header area and the header information of the adjacent track are adjacent to each other, a signal reading error does not occur due to the above-described crosstalk reducing effect.

Further, since the header information is written by the phase change recording, it is not necessary to provide prepits, and it is sufficient to pay attention only to the control of the depth of the groove portion 4 when manufacturing the master, and the master and the stamper can be easily manufactured. In the present embodiment, the sector paired with the sector of the track 3n + 1 is the sector on the outer track 4n + 1, but it may be the inner track.

In this embodiment, the case of accessing using the one-beam optical head has been described.
A beam optical head may be used. In this case, the first
The first track on which the header information is recorded may be traced to the laser beam, and the second track on which the header information is not recorded may be traced to the second beam. At this time, regarding the circumferential direction (track direction),
If the first beam is arranged so as to precede the second beam so that the header information of the first track can be read out first, the header information of the first track can be read out before the second beam is read out. The time to access the truck can be shortened.

Embodiment 2 The first embodiment is an example of a phase-change optical disk, which is an example of amplitude modulation recording. However, even in a magneto-optical disk, when the Kerr ellipticity of the disk is close to 0, it can be treated in the same manner as amplitude modulation recording. Are known (references: Fukumoto, Masuhara, Araya, “Analysis of reproduction crosstalk in land / groove recording of magneto-optical disk”, IEEJ Study Group materials, MAG-94-235〜23).
8, December 1994).

Therefore, also in the present embodiment, equation (1)
The thickness is 1.2 mm and the diameter is 30
A glass-made substrate with a guide groove having a 0 mm disk shape, a track pitch of 1.6 μm, a width of 0.8 μm, and a depth of 75 nm is provided in the same manner as in the first embodiment. Then, a magneto-optical disk is manufactured by sequentially forming a base layer made of SiN, a recording layer made of TbFeCo, and a protective layer made of SiN on the produced substrate by using a sputtering apparatus.

At this time, in order to bring the Kerr ellipticity of this magneto-optical disk close to 0, for example, the thickness and refractive index of the underlayer may be adjusted. The Kerr ellipticity at this time is ± 0.
It is preferably 2 ° or less, more preferably ± 0.1 ° or less.
Next, information is recorded on the magneto-optical disk by magneto-optical recording in which the direction of the magnetization of the recording layer is reversed by applying an external magnetic field while irradiating a laser beam to heat the recording layer, and as in the first embodiment. Evaluate the amount of crosstalk.

The wavelength λ of the light source used for recording and reproduction is 680.
nm. The crosstalk amount from the land portion which is the recording track to the adjacent groove portion is −35 dB, and the crosstalk amount from the groove portion to the adjacent land portion is −35 dB.
The level was 36 dB, which was a level at which there was no practical problem. Then, when the magneto-optical disk is formatted, the header information is magneto-optically recorded only on one recording layer on the land portion or the groove portion, so that the same effect as that of the first embodiment can be obtained. . Further, the method of accessing this magneto-optical disk may be the same as that of the first embodiment.

[0038]

According to the present invention, by using a substrate whose groove has an optical depth in the range of λ / 7 to λ / 5, adjacent tracks (for example, when the reproduction target track is a land) are used. Can reduce crosstalk from adjacent grooves, and adjacent lands in the case of grooves), and can realize an optical disk for land / groove recording with few signal reading errors in both the header area and the data area. Further, since the header information is written only on one of the recording layers on the land or groove by optical recording, prepits are not required and the master can be easily manufactured, and the time required for the format operation is shortened as compared with the conventional soft format. be able to.

When the area of the first track is accessed, the header information of this track is detected and accessed, and when the area of the second track is accessed, the first track adjacent to this track is detected. By accessing based on the header information of the track, it is possible to access both the first and second tracks in the optical disc in which the header information is recorded only on the first track, and both the land and the groove are recorded and reproduced. It can be used as a truck.

[Brief description of drawings]

FIG. 1 is an external view of a phase-change optical disk showing one embodiment of the present invention and an enlarged view of a part of the phase-change optical disk seen obliquely from above.

FIG. 2 is a diagram showing a state of recording / reproducing tracks in a part of the phase change optical disc of FIG.

3A to 3D are process cross-sectional views for explaining a conventional optical disc manufacturing method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Phase change optical disk, 2 ... Board | substrate with a guide groove, 3 ... Land part, 4 ... Groove part, 5 ... Underlayer, 6 ... Recording layer, 3n
3n + 1 ... Land recording / reproducing tracks, 4n, 4n
+1 ... Tracks for recording / reproducing in the groove portion, 10i, 10i
+1, 10j ... Sector, 11i, 11i + 1 ... Header area, 12i, 12i + 1 ... Data area.

Claims (2)

[Claims] 1. An optical disc using a substrate with a guide groove having a land that is a convex portion and a groove that is a guide groove, and using both the land and the groove as recording / reproducing tracks. For the wavelength λ of the light source,
A recording layer is formed on the substrate in which the optical depth of the groove is in the range of λ / 7 to λ / 5, and the header indicates the position on the disc by optical recording without forming the concavo-convex pattern. An optical disc in which information is written in only one recording layer on a land or a groove. 2. A recording layer is formed on a substrate having a guide groove in which the optical depth of the groove is within the range of λ / 7 to λ / 5 with respect to the wavelength λ of the information reproducing light source, and the disc is formed. The header information indicating the position above is 2 for land or groove.
A method of accessing an area on the optical disk, wherein the area on the optical disk is optical-recorded only on the first track of the types of tracks, and when accessing the area on the first track,
When the header information recorded on the first track is detected and accessed, and the area on the second track is accessed,
An optical disk access method, characterized in that header information recorded on a first track adjacent to the second track is detected and access is performed based on the detected header information.