JP2002260225A - Recording device for optical disk and method for controlling crosstalk from adjacent tracks in the optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a crosstalk from adjacent tracks in an optical disk. SOLUTION: Of marks and regions between the marks on the optical disk, the forms of the mark and the region between the marks which are comparatively long over a prescribed threshold length are modified respectively, thereby controls reproducing signals of high frequency reproduced from these marks and regions between the marks not to have a large amplitude which is not required. Accordingly, the crosstalk noise level from the adjacent tracks is controlled.

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 compact disk (CD).
More specifically, the present invention relates to an optical disc that suppresses crosstalk from adjacent tracks, a recording apparatus for such an optical disc, a recording apparatus used for manufacturing a master of such an optical disc, and a method for suppressing crosstalk from adjacent tracks on an optical disc.

[0002]

2. Description of the Related Art Various methods for increasing the information recording density of an optical disk have been proposed. One of these methods is to reduce the track interval (track pitch), which is applicable regardless of the size of the optical disk. However,
Since the spot size of a laser beam used to read information from an optical disk is substantially determined by the wavelength of the laser beam and the numerical aperture (NA) of the objective lens of the optical pickup, the spot size must be reduced. Is not easy. If the track pitch is narrowed without reducing the spot size, not only the target track to be read out, but also the adjacent track enters the laser spot. Occurs. As described above, as a method for suppressing the crosstalk generated by reducing the track pitch, a method of mixing the read signal from the target track based on the signal read from the target track and the signal read from the adjacent track is used. There has been proposed a method of calculating a crosstalk signal estimated to be performed, and subtracting the calculated crosstalk signal to obtain only the original data signal of the target track.

A specific example of this kind of known crosstalk removing method will be described below. According to the method, first, a light beam for reading is individually applied to each of a total of three tracks including a target track (hereinafter, referred to as a “center track”) and two adjacent tracks on both sides of the center track. To read a data signal from each of the tracks. The data signal read from the central track contains crosstalk components from two adjacent tracks on both sides. The mixing ratio of the signal derived from the adjacent track to the signal read from the center track is
It is called the crosstalk ratio. The value of this crosstalk ratio can be estimated based on several factors. The factor that has the greatest influence on the value of the crosstalk ratio is the dimensional ratio between the spot size of the laser beam and the track pitch,
Still other factors may be involved. After estimating the value of the crosstalk ratio, based on the estimated value,
A value of an appropriate attenuation coefficient to be multiplied by each read signal from two adjacent tracks on both sides is determined, and a pseudo crosstalk component is calculated by multiplying the read signal by the attenuation coefficient. Subsequently, by subtracting the pseudo crosstalk component from the read signal read from the center track, genuine data recorded on the target track (center track) can be obtained. This type of crosstalk removing method has been proposed in, for example, U.S. Pat. No. 5,280,466, JP-A-3-232118, JP-A-3-340225, and JP-A-5-205280.

[0004]

However, the crosstalk elimination method of the above-described method requires a considerable amount of calculation time to derive the optimum estimated value of the crosstalk ratio, and the calculation processing thereof. Requires a large-scale arithmetic circuit to execute the operation, and two adjacent tracks must be individually irradiated with a reading light beam. There are disadvantages such as having to equip parts.

The present invention has been made in view of such circumstances, and an object of the present invention is to eliminate the need to add hardware such as an arithmetic circuit and optical components to an optical disk reproducing system. The crosstalk from adjacent tracks on the optical disc can be suppressed without any modification of the optical disc, so that when the track pitch of the optical disc is the same, the crosstalk noise level from the adjacent tracks becomes lower, and If the level of crosstalk noise from adjacent tracks should be maintained at about the same level as in the related art, the track pitch can be narrowed to increase the recording density.

[0006]

In order to achieve the above-mentioned object, a recording apparatus used for manufacturing an optical disk master according to the present invention comprises: (a) performing a modulation process on a bit stream of a digital source signal in accordance with a predetermined modulation scheme; By applying the signal, a first modulated signal whose level is switched between a first signal level corresponding to a mark forming unit on the optical disk and a second signal level corresponding to an inter-mark area on the optical disk is generated. In this case, the duration during which the first modulated signal maintains the first signal level or the second signal level is a minimum duration corresponding to a predetermined minimum mark length / minimum mark length, and a predetermined duration. It is between the longest mark length / the longest duration corresponding to the longest inter-mark length, and is an integral multiple of the unit duration corresponding to the predetermined unit mark length / the inter-mark length. A first modulating means for, (b)
Determining means for sampling the first modulated signal to determine a mark length / inter-mark length corresponding to a duration during which the first modulated signal maintains the first signal level or the second level; (C) a portion where a mark length / inter-mark length corresponding to a duration during which the first modulated signal maintains the first signal level or the second level exceeds a predetermined threshold length; A second modulated signal is generated by subjecting the first modulated signal to additional modulation processing according to a predetermined additional modulation rule.
Modulating means; and (d) light beam modulating means for modulating a light beam for recording information on a master of the optical disk in response to the second modulated signal, and (e) performing the additional modulation processing. A mark or an inter-mark area formed on the optical disk copied from the master is subjected to a shape modification for suppressing the amplitude of a high-frequency reproduction signal reproduced from the mark or the inter-mark area. I do.

In order to achieve the above object, a recording apparatus for recording information on a recordable optical disk according to the present invention comprises: (a) performing a modulation process on a bit stream of a digital source signal in accordance with a predetermined modulation method; By applying the signal, a first modulated signal whose level is switched between a first signal level corresponding to a mark forming unit on the optical disk and a second signal level corresponding to an inter-mark area on the optical disk is generated. In this case, the duration during which the first modulated signal maintains the first signal level or the second signal level is a minimum duration corresponding to a predetermined minimum mark length / minimum mark length, and a predetermined duration. It is between the longest mark length / the longest duration corresponding to the longest inter-mark length, and is an integral multiple of the unit duration corresponding to the predetermined unit mark length / the inter-mark length. A first modulating means for, (b)
Determining means for sampling the first modulated signal to determine a mark length / inter-mark length corresponding to a duration during which the first modulated signal maintains the first signal level or the second level; (C) a portion where a mark length / inter-mark length corresponding to a duration during which the first modulated signal maintains the first signal level or the second level exceeds a predetermined threshold length; A second modulated signal is generated by subjecting the first modulated signal to additional modulation processing according to a predetermined additional modulation rule.
Modulating means; and (d) light beam modulating means for modulating a light beam for recording information on a recordable optical disk in response to the second modulated signal, and (e) the additional modulation processing. Accordingly, a mark or an inter-mark area formed on a recordable optical disk is subjected to shape modification for suppressing the amplitude of a high-frequency reproduction signal reproduced from the mark or the inter-mark area. .

According to these recording apparatuses, an unnecessary large amplitude of a high-frequency reproduction signal reproduced from a relatively long mark or an area between marks on an optical disk is suppressed, thereby reducing a crosstalk noise level from an adjacent track. Is suppressed. An optical disk manufactured or recorded by using such a recording device has complete compatibility with a conventional optical disk, so that there is no need to modify the optical disk reproducing system.

In order to achieve the above object, an optical disk according to the present invention has a track formed by a mark and an inter-mark area, and has a length of the mark and the inter-mark area according to a given modulation method. In one aspect, the optical disc has a predetermined threshold length in a recording structure on the optical disc recognized as a single mark or an inter-mark area by an optical disc reproducing system. The recording structure having a length exceeding the minimum is a plurality of marks sandwiching a short inter-mark area less than the shortest length recognized by the optical disc playback system as the inter-mark area, or the shortest mark recognized by the optical disc playback system as a mark. It is characterized by being formed of a plurality of inter-mark areas sandwiching a short mark less than the length Further, in another aspect, the optical disc reproducing system has a shape modification into a recording structure having a length exceeding a predetermined threshold length among recording structures on the optical disc recognized as a single mark or an inter-mark area. The shape modification is characterized in that the amplitude of the high-frequency reproduction signal reproduced from the recording structure is suppressed without deteriorating the eye pattern at the binary threshold level. Further, in another aspect of the optical disc, among the recording structures on the optical disc recognized by the optical disc reproducing system as a single mark or an inter-mark area, a recording structure having a length exceeding a predetermined threshold length is: A plurality of marks interposing a short mark area smaller than the resolution limit of the optical pickup of the optical disc reproduction system, or a plurality of marks interposing a short mark smaller than the resolution limit of the optical pickup of the optical disc reproduction system. It is characterized by being formed in a region. In another aspect, the optical disc has a recording structure having a length exceeding a predetermined threshold length among recording structures on the optical disc recognized by the optical disc reproducing system as a single mark or an inter-mark area. The shape is modified by reducing the width of at least a part of the entire length of the mark when the recording structure is a mark, and by reducing the width when the recording structure is an inter-mark area. By forming a narrow mark in at least a part of the entire length of the inter-mark region, the amplitude of a high-frequency reproduction signal reproduced from the recording structure is suppressed.

According to such an optical disk, an unnecessary large amplitude of a high-frequency reproduction signal reproduced from a relatively long mark or an inter-mark area on the disk is suppressed, whereby a crosstalk noise level from an adjacent track is reduced. Is suppressed. Further, since such an optical disk has complete compatibility with a conventional optical disk, there is no need to modify the optical disk reproducing system.

According to another aspect of the present invention, there is provided a track having a mark and an inter-mark area, and the length of the mark and the inter-mark area is determined according to a given modulation method. The method of suppressing crosstalk from adjacent tracks on an optical disc in which information is recorded by using the method described above includes, among marks and inter-mark areas formed on the optical disc, a mark and an inter-mark area having a length exceeding a predetermined threshold length. By applying shape modification to
It is characterized in that the amplitude of the high-frequency reproduction signal reproduced from the mark and the area between the marks is suppressed, thereby suppressing the level of crosstalk noise from an adjacent track.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a recording device used to manufacture a master of an optical disk. The optical disk in the illustrated embodiment is called a compact disk (CD).
For example, it is an audio CD or a CD-ROM. This type of optical disk has a track formed by a mark and an inter-mark area, and by defining the length of the mark and the inter-mark area according to a given modulation scheme, music data or computer data is recorded on the track. Etc. are recorded. However, the present invention can be applied to other types of optical discs as described later.

The recording apparatus shown in the block diagram of FIG. 1 includes an encoder 1 and an optical modulator 6. Encoder 1
, A source signal (source data signal) SD in the form of a digital signal is supplied as an input signal. The encoder 1 processes the received source signal SD,
An optical modulator drive signal (modulated data signal) MD is generated and output. The source signal SD contains information to be recorded on the optical disk, and this information is, for example, the above-described music data, computer data, or the like. The optical modulator drive signal MD output from the encoder 1 includes:
The same information as the information included in the source signal SD is included in an encoded form. In order to record the encoded information (data) on the master of the optical disk, a laser beam L
1 is radiated via a light modulator 6 to a master 7 made of a glass substrate. The optical modulator 6 is controlled by an optical modulator drive signal MD. The laser beam L1 is narrowed according to the signal MD to generate a modulated laser beam L2. The photosensitive layer applied on the surface is exposed. After exposure,
Various processes known in the art for producing a master including a developing process are performed to complete the master. Then, by performing duplication from the completed master, a track formed by pit marks and an area between pit marks is provided,
By determining the lengths of the mark and the area between the marks according to a given modulation method, an optical disk on which information included in the source signal SD is recorded can be obtained. In the recording apparatus described above, the width of the mark formed on the master 7 (and therefore the width of the pit mark finally formed on the optical disk) depends on the signal level of the optical modulator drive signal MD. It is changing. The fact that the width of the mark can be changed in this way is necessary in the additional modulation processing described later with reference to FIG. However, when the additional modulation processing described later with reference to FIG. 3 is adopted and the processing in FIG. 4 is not performed, it is not necessary to be able to change the width of the mark.

The encoder 1 includes a first modulation circuit 2. The first modulation circuit 2 performs a modulation process on a bit stream of a source signal SD which is a digital signal according to a predetermined modulation method. Is a circuit for encoding the source signal SD and generating a modulated signal S1. This modulation processing is performed by, for example, “EFM”,
This is performed using a general modulation method such as “EFM +” or “17PP”. Note that, as described later, the modulated signal S1 is further subjected to additional modulation processing. Therefore, in order to be distinguished from the modulated signal after being subjected to the additional modulation processing, in the following description, The modulated signal S1 output from the first modulation circuit 2 is referred to as a “first modulated signal”.

The first modulated signal S1 is a binary signal, that is, the first modulated signal S1 corresponding to the mark forming portion on the optical disk.
This is a two-level signal whose level is switched between a signal level and a second signal level corresponding to an inter-mark area on the optical disk. The duration during which the first modulated signal S1 maintains the first signal level or the second signal level is a shortest duration corresponding to a predetermined shortest mark length / shortest mark length, and a predetermined longest mark length / It is between the longest duration corresponding to the longest inter-mark length, and is set to an integral multiple of a predetermined unit mark length / the unit duration corresponding to the unit inter-mark length. Generating such a modulated signal in order to record information on a compact disk is a well-known matter. For example, when the "EFM" modulation method is used, the unit mark length / unit mark length is calculated as follows. When “T” is set, the shortest mark length / shortest mark interval length is “3T”, and the longest mark length / longest mark interval length is “11T”.
become.

Conventionally, an optical disk master has been manufactured by directly outputting the modulated signal S1 from the encoder and controlling the optical modulator to be turned on and off with the modulated signal S1. FIG. 2 shows a high-frequency signal observed on an oscilloscope when a master is manufactured in accordance with such a conventional method using an encoder of a standard “EFM +” modulation method and an optical disk manufactured by duplicating the master is reproduced. FIG. 3 is a schematic diagram showing an eye pattern of a reproduction signal. As shown in FIG. 2, a high frequency reproduced from a relatively long pit mark (for example, a pit mark having a length of "8T") among pit marks of various lengths formed on a conventional optical disk. The amplitude of the reproduced signal is considerably larger than that of a high-frequency reproduced signal reproduced from a relatively short pit (for example, a pit mark having a length of "3T"). The same tendency is observed in a crosstalk signal derived from an adjacent track mixed with a read signal from a target track. In other words, the longer the pit mark or the area between the pit marks, the greater the amplitude of the high-frequency reproduction signal reproduced from the pit mark or the area between the pit marks. Compared to the crosstalk signal derived from the short pit mark or the area between the pit marks,
Its level will be higher.

According to the present invention, the amplitude of a high-frequency reproduced signal reproduced from a relatively long pit mark or an area between pit marks is suppressed by modifying the shape of the pit mark or the area between the pit marks, thereby reducing the amplitude of the adjacent track. This is to suppress the level of crosstalk noise. In FIG. 2, a binary threshold level for separating the high-frequency reproduction signal into binary data “0” and “1” is also written. When modifying the shape of the pit mark or the area between the pit marks, an error is found in the comparison result between the level of the high-frequency reproduction signal reproduced from the pit mark or the area between the pit marks having the modified shape and the threshold level. The shape modification is made sufficiently small so as not to occur, thereby preventing a situation in which data read out due to the shape modification is changed.

For this shape modification, the encoder 1
A mark length / inter-mark length determination circuit 3 and a second modulation circuit 4 are provided. The mark length / inter-mark length determination circuit 3 includes a memory buffer 3a, which samples the first modulated signal S1,
A small portion (segment) of the modulated signal S1 is stored, and the length of the stored segment is a length necessary to determine the length of a pit mark or an area between pit marks to be formed. There is. The mark length / inter-mark length determination circuit 3 determines whether the first modulated signal S1 is the first modulated signal S1 based on the contents of the memory buffer 3.
A mark length / inter-mark length corresponding to the duration of maintaining the signal level or the second level is determined. This, in other words, is about to form (ie
This is nothing less than determining the length of the pit mark (formed next) or the area between the pit marks. Further, as is well known, the pit mark forming portion and the pit mark inter-region portion on the optical disc are functionally equivalent to each other except that they have opposite polarities as a recording structure for recording information. Therefore, in the following description, the pit mark and the area between the pit marks are collectively referred to as a “pattern”, and the pit mark length and the pit mark inter-length are collectively referred to as a “pattern length”.

The second modulation circuit 4 receives the first modulated signal S1 and a signal representing the pattern length determined by the determination circuit 3. The second modulation circuit 4 performs an additional modulation process on the first modulated signal S1 in accordance with a predetermined additional modulation rule for a portion where the pattern length exceeds the predetermined threshold length, thereby obtaining a second modulation signal. 2 A modulated signal MD is generated. The second modulated signal MD is output from the converter 1 and is supplied with the optical modulator drive signal M
Used as D. Therefore, the optical modulator 6 modulates the laser beam for recording information on the master of the optical disk in response to the second modulated signal MD.

In the additional modulation process in the second modulation circuit 4, the mark or the inter-mark region formed on the optical disk duplicated from the master is reproduced from the mark or the inter-mark region by the additional modulation process. This is for performing a shape modification (that is, a total or partial change of the shape) for suppressing the amplitude of the high-frequency reproduction signal, and the shape modification is included in the first modulated signal S1. Must not affect the information that is present. There are various additional modulation processes that can satisfy this condition, two of which are shown in FIG.
And FIG. 4 shows a specific example.

A specific example of the additional modulation processing shown in FIG.
A relatively long pattern on an optical disc is subjected to shape modification for inserting a short pattern having a polarity opposite to that of the pattern. FIG. 3A is a waveform diagram of the first modulated signal S1 before being subjected to the additional modification processing. The first modulated signal S1 shown here is used as it is as an optical modulator drive signal, and the optical modulator 6 is used. In response to this, as shown in FIG. 3B, the area 10 between the pit marks having a length of "9T" and the subsequent pit having the same length of "9T" The mark 12 is formed.

FIG. 3C is a waveform diagram of the second modulated signal MD obtained by performing an additional modulation process on the first modulated signal S1 shown in FIG. 3A. By controlling the optical modulator 6 using the 2 modulated signal MD, the length is correspondingly set to “9T” as shown in FIG.
The pit mark inter-region 10 ′ is subjected to a shape modification in which a short pit pattern 14 having a length “αT” is inserted at the center thereof. At the center thereof, a shape modification for inserting an inter-pit mark area 16 having a length of “αT” is performed. E in FIG.
Is, for the pattern subjected to such shape modification, α
Is changed from “0” to “2” in increments of “0.5” (α = 0 corresponds to a pattern that is not subjected to shape modification). FIG. 9 is a waveform diagram showing a high-frequency reproduction signal reproduced from the pattern “9T”. As is clear from this figure, the amplitude of the high-frequency reproduction signal can be appropriately suppressed by selecting an appropriate value as the value of α.

In the specific example of FIG. 3, the above-mentioned threshold length is set to "6T" which is twice the shortest pattern length "3T". However, this threshold length is not limited to twice the shortest pattern length,
Depending on the specific method of the additional modulation process, and on the binary threshold level and the actual amplitude of the high-frequency reproduced signal reproduced from the pattern of each length, an appropriate value is determined. I just need. Since the present invention aims to suppress crosstalk from adjacent tracks, it is advantageous to apply shape modification only to relatively long patterns, and to reduce the threshold length to the shortest pattern length. In many cases, good results can be obtained by making the length twice or more.

In the specific example shown in FIG. 3, a short pattern having a reverse polarity inserted into a relatively long pattern is a sufficiently short pattern that the optical disk reproducing system does not recognize it as a pattern. The reason for this is that if the inserted short pattern is recognized as one pattern by the optical disk reproducing system, the recorded information changes due to the insertion of the short pattern. Therefore, even if a short pattern is inserted, the pattern to be inserted must be sufficiently short so that the original relatively long pattern divided by the short pattern is recognized as a single pattern by the optical disc reproducing system. . That is, in FIG. 3D, since the inserted short pattern (pit mark) 14 is sufficiently short, the optical disk reproducing system does not recognize this as a pattern. 10b is recognized as one inter-pit mark area 10 '. Another inserted short pattern (area between pit marks) 1
6 is also sufficiently short, and the optical disk reproducing system ignores this, and recognizes the entirety of the inter-pit mark area 16 and the pit marks 12a and 12b before and after it as one pit mark 12 '.

Accordingly, in the embodiment of FIG. 3, of the recording structures (ie, patterns) on the optical disk which the optical disk reproducing system recognizes as a single mark or an inter-mark area, a length exceeding a predetermined threshold length is set. The recording structure has a plurality of marks sandwiching a short inter-mark area less than the shortest length recognized by the optical disc playback system as an inter-mark area, or less than the shortest length recognized by the optical disc playback system as a mark It is formed in a plurality of inter-mark regions sandwiching a short mark.

In order for an optical disk reproducing system to recognize a pattern divided into a plurality of portions due to shape modification as a single pattern, the optical disk reproducing system must have a length less than the shortest pattern length. A pattern recognition algorithm that ignores short patterns may be incorporated. As a result, the inserted short pattern is ignored, and a relatively long pattern before being divided is recognized as a single pattern.

If the short pattern to be inserted is smaller than the modification limit of the optical pickup of the optical disk reproducing system, the short pattern is not detected from the beginning, so a special pattern for ignoring the short pattern is used. Needless to incorporate a pattern recognition algorithm,
A relatively long pattern before being divided will be recognized as a single pattern. In such a case, among the recording structures on the optical disc recognized by the optical disc reproducing system as a single mark or an inter-mark area, a recording structure having a length exceeding a predetermined threshold length is used. Formed with a plurality of marks sandwiching a short inter-mark area smaller than the resolution limit of the optical pickup, or a plurality of inter-mark areas interposing a short mark smaller than the resolution limit of the optical pickup of the optical disc reproducing system. Will be done.

Another specific example of the additional modulation process shown in FIG. 4 is as follows. For a relatively long pattern on an optical disk, if the pattern is a pit mark, the total length of the pit mark is The width of the central portion is reduced, and when the pattern is a region between pit marks, a shape modification for forming a narrow pit mark in the central portion of the entire length of the region between the pit marks is performed. Things. These shape modifications correspond to the first modulated signal S1
And an additional modulation process that makes the amplitude an intermediate value between the upper limit and the lower limit.

FIG. 4A is a waveform diagram of the first modulated signal S1 before being subjected to the additional modification process. As shown, the signal rises from a low level (first level) to a high level (second level). After that, the second level is maintained for the time “10T”, and subsequently, after the fall from the high level to the low level, the first level is also maintained for the time “10T”. When the optical modulator 6 is controlled using the first modulated signal S1 shown in FIG. 4A as it is as the optical modulator drive signal, correspondingly, as shown in FIG. An area 20 between pit marks having a length of "10T" on the optical disk, and a subsequent area having a length of "1T"
0T "pit mark 22 is formed. The high-frequency reproduction signal reproduced from such a pattern has a large amplitude as the left waveform in the waveform diagram shown in FIG. 4E.

FIG. 4C is a waveform diagram of the second modulated signal MD obtained by subjecting the first modulated signal S1 shown in FIG. 4A to an additional modulation process. Of the length "10T" that maintains the level, the amplitude of the central length "4T" is reduced by 30%, and the center of the length "10T" that maintains the low level is reduced. Has been subjected to an additional modulation process to make the amplitude of the portion of length "4T" 60%. The second modulated signal M shown in FIG.
By controlling the optical modulator 6 using D, on the optical disc, as shown in D of FIG.
The pit mark inter-region 20 'is subjected to shape modification in which a narrow pit mark 24 having a length of "4T" is formed at the center thereof, and a pit mark having a length of "10T" is subsequently provided. 22 ′ is subjected to shape modification such that the width of the portion 26 having a central length of “4T” is reduced. The high-frequency reproduction signal reproduced from the pattern subjected to such shape modification has a small amplitude as the waveform on the right side in the waveform diagram shown in FIG. 4E. Therefore, as is apparent from FIG. 4E, the amplitude of the high-frequency reproduction signal is suppressed as a result of the shape modification described above.

In the additional modulation processing shown in FIG. 4, the amplitude of the first modulated signal S1 is changed by changing the amplitude of the first modulated signal S1 as shown in FIG.
Instead of applying the modulation signal S1 to only a part of the duration in which the low level or the high level is maintained, the modulation signal S1 may be applied to the entire duration. Therefore, in the specific example shown in FIG. 4, among the recording structures (that is, patterns) on the optical disk that the optical disk reproducing system recognizes as a single mark or an inter-mark area,
A shape modification is applied to a recording structure having a length exceeding a predetermined threshold length, and when the recording structure is a mark, the width of at least a part of the entire length of the mark is reduced, and If the recording structure is an inter-mark area, by forming a narrow mark on at least a part of the entire length of the inter-mark area,
This is to suppress the amplitude of the high-frequency reproduction signal reproduced from the recording structure.

Also in the specific example shown in FIG. 4, it is necessary to prevent the recorded information read by the optical disk reproducing system from being changed due to the shape modification. In the specific example of FIG. 4, this is achieved by appropriately determining the amplitude change amount due to the additional modulation processing. More specifically, as shown in FIG. 4D, a narrow pit mark 24 formed in the inter-pit mark area 20 ′ is not recognized as a pattern by the optical disk reproducing system. It is necessary to make the pit mark narrow enough,
The second modulated signal MD corresponding to the pit mark 24
In this case, the amount of decrease (30% in the illustrated example) of the level decrease portion should not be too large. Also, the pit mark 22 '
It is necessary to secure a sufficient width for the narrow portion 26 formed on the optical disk reproduction system so as not to be recognized as a pattern. The rise amount (60% in the illustrated example) of the level rise portion of the modulated signal MD should not be too small.

In addition, in the additional modulation processing in any of the embodiments shown in FIGS. 3 and 4, a predetermined threshold length of the recording structure on the optical disk recognized by the optical disk reproducing system as a single mark or an inter-mark area is used. Shape modification is applied to recording structures longer than
In addition, the shape modification suppresses the amplitude of the high-frequency reproduction signal reproduced from the recording structure without deteriorating the eye pattern at the binary threshold level.

Although two specific examples of the algorithm of the additional modulation process performed by the conversion circuit 4 have been described above, the additional modulation process can be performed according to not only those but also various other algorithms. It is.
For example, in the specific example shown in FIG. 3, only one short-polarity pattern having a reverse polarity is inserted at the center of a relatively long pattern. A pattern may be inserted. Further, both the pattern insertion method shown in FIG. 3 and the method of changing the width of the pattern shown in FIG. 4 may be used together. Further, even if the patterns have the same length, the method of the additional modulation processing to be applied may be changed depending on whether the pattern is a pit mark or an area between pit marks (landmark). In addition, the number and length of the short patterns to be inserted and the amount of change in the width of the patterns may be made different from each other, thereby accommodating the development process when the master is manufactured or the optical disk is duplicated. It is possible to suitably cope with non-linearity.

The embodiment described above relates to a recording device used for producing a master of a compact disk such as an audio CD or a CD-ROM. However, the present invention is applicable to other types of optical disks. For example, the present invention can be applied to a recording device for recording information on a recordable optical disk such as a CD-R or a CD-RW. That is, in the above-described embodiment, the optical modulator 6 of the recording device modulates the light beam for recording information on the master of the optical disk in response to the second modulated signal MD; By the additional modulation processing, a mark or an inter-mark area formed on the optical disk copied from the master is subjected to a shape modification for suppressing the amplitude of a high-frequency reproduction signal reproduced from the mark or the inter-mark area. Like that. On the other hand, when the present invention is applied to a recordable optical disc, the optical modulator of the recording device responds to the second modulated signal MD to record information on the recordable optical disc. Modulates the light beam and suppresses the amplitude of the high-frequency reproduction signal reproduced from the mark or the inter-mark area in the mark or the inter-mark area formed on the recordable optical disk by the additional modulation processing. What is necessary is just to make it perform the shape modification. When the present invention is applied to an optical disc such as a CD-R or a CD-RW, recording is performed using a mark baked by a laser beam or a mark that is made amorphous by instantaneously melting a metal surface with a laser beam. Therefore, it is advantageous to use the method shown in FIG. 3 as a method of modifying the shape of the mark. However, by appropriately modifying the optical head for recording, the method shown in FIG. 4 can be used, and various other methods can also be used.

[0036]

As is apparent from the above description, according to the optical disc, the recording apparatus for the optical disc, the recording apparatus used for producing the master of the optical disc, or the method for suppressing crosstalk in the optical disc according to the present invention, the "EF"
The optical modulator is controlled by a second modulated signal MD generated by performing an additional modulation process on the first modulated signal modulated by a general modulation method such as “M” or “EFM +”,
Shape modification is applied to relatively long marks and inter-mark areas on the optical disc, thereby suppressing unnecessary large amplitude of a high-frequency reproduction signal reproduced from the marks and inter-mark areas, and The crosstalk noise level from the track is suppressed. Therefore, when the track pitch of the optical disk is the same, the crosstalk noise level from the adjacent track becomes lower, and if the crosstalk noise level from the adjacent track should be maintained at the same level as before, the track pitch is reduced. The recording density can be increased by making the recording area narrower. Further, everything necessary to obtain the above-described functions and effects is performed at the stage of recording information on the master of the optical disk or the recordable optical disk, and the optical disk according to the present invention is different from the conventional optical disk. Since it has complete compatibility, there is no need to make any modifications to the optical disk playback system, including adding hardware. Furthermore, the recording device according to the present invention
Another advantage is that the structure is simple and the encoder can be manufactured with a small modification to an existing encoder.

[Brief description of the drawings]

FIG. 1 is a block diagram of a recording apparatus used to manufacture a master of an optical disk according to the present invention.

FIG. 2 is a schematic diagram showing a typical eye pattern of a reproduction signal obtained by reproducing a conventional optical disk, which is observed on an oscilloscope.

FIGS. 3A, 3B, 3C, 3D, and 3E are diagrams for explaining a specific example of an additional modulation process in the optical disk crosstalk suppression method according to the present invention; FIGS.

FIGS. 4A, 4B, 4C, 4D, and 4E are diagrams for explaining another specific example of the additional modulation process in the optical disk crosstalk suppression method according to the present invention. FIGS.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Encoder 2 ... 1st modulation circuit 3 ... Mark length / mark length determination circuit 3a ... Memory buffer 4 ... 2nd modulation circuit 5 ... Laser beam generator 6 ... Optical modulator 7, master SD, source signal S1, first modulated signal, MD second modulated signal (optical modulator drive signal).

Claims (18)

[Claims] 1. A recording apparatus used for manufacturing a master of an optical disk, comprising: (a) performing a modulation process on a bit stream of a digital source signal in accordance with a predetermined modulation method, thereby forming a first signal corresponding to a mark forming unit on the optical disk; Generating a first modulated signal whose level is switched between a level and a second signal level corresponding to an inter-mark area on the optical disk, wherein the first modulated signal is the first signal level or The duration for maintaining the second signal level is a shortest duration corresponding to a predetermined shortest mark length / shortest mark length, and a longest duration corresponding to a predetermined longest mark length / longest mark length. And (b) the first modulated signal, wherein the first modulating means is an integral multiple of a unit duration corresponding to a predetermined unit mark length / unit mark interval length. Determining means for sampling to determine a mark length / mark length corresponding to a duration during which the first modulated signal maintains the first signal level or the second level; (c) the first For the portion where the mark length / inter-mark length corresponding to the duration during which the modulated signal maintains the first signal level or the second level exceeds the predetermined threshold length, the first modulated signal is A second modulating means for generating a second modulated signal by performing an additional modulation process in accordance with a predetermined additional modulation rule; and (d) responding to the second modulated signal to a master of the optical disc. Light beam modulating means for modulating a light beam for recording information; and (e) a mark or a mark interval formed on an optical disk to be duplicated from a master by the additional modulation processing. To suppress the shape modification of the amplitude of the high frequency signal reproduced from the mark to the mark between regions is to be performed, the recording apparatus used in the fabrication of a master of an optical disk, characterized in that. 2. The recording apparatus according to claim 1, wherein said threshold length is at least twice as long as said shortest mark length / shortest mark interval length. 3. An optical disk master according to claim 1, wherein a shape-modifying portion formed in a mark or an inter-mark region by said additional modulation processing is smaller than a resolution limit of an optical pickup of an optical disk reproducing system. A recording device used for the production of 4. The first modulation method according to claim 1, wherein
In a portion where the mark length corresponding to the duration for which the modulated signal maintains the first signal level exceeds the threshold length, the mark corresponding to the portion is shorter than the shortest mark length / inter-mark length. In a portion where an inter-mark area is inserted and a length between marks corresponding to a duration in which the first modulated signal maintains the second signal level exceeds the threshold length, a space between marks corresponding to the portion is provided. 3. A mark shorter than said shortest mark length / inter-mark length is inserted into an area.
A recording device used for manufacturing a master of the optical disc described above. 5. The additional modulation process according to claim 1, wherein the mark length / inter-mark length corresponding to a duration of maintaining the first modulated signal at the first signal level or the second level is equal to the threshold length. 3. The recording apparatus according to claim 2, wherein the recording is performed by changing the level of the first modulated signal in at least a part of the portion exceeding the threshold. 6. A recording apparatus for recording information on a recordable optical disk, comprising: (a) performing a modulation process on a bit stream of a digital source signal in accordance with a predetermined modulation method, thereby supporting a mark forming section on the optical disk. Generating a first modulated signal whose level is switched between a first signal level corresponding to the first signal level and a second signal level corresponding to an inter-mark area on the optical disk. The duration for maintaining the first signal level or the second signal level corresponds to the shortest duration corresponding to a predetermined shortest mark length / shortest mark length and the predetermined longest mark length / longest mark length. A first modulating means which is between the set maximum duration and an integral multiple of a unit duration corresponding to a predetermined unit mark length / unit mark length; and (b) the first modulation means. Determining means for sampling a modulation signal to determine a mark length / inter-mark length corresponding to a duration during which the first modulated signal maintains the first signal level or the second level; (c) A portion where the mark length / inter-mark length corresponding to the duration for which the first modulated signal maintains the first signal level or the second level exceeds a predetermined threshold length is used as the first modulated signal. A second modulating means for generating a second modulated signal by subjecting the modulated signal to an additional modulation process according to a predetermined additional modulation rule; and (d) recording in response to the second modulated signal. Light beam modulating means for modulating a light beam for recording information on a recordable optical disc, and (e) marks formed on the recordable optical disc by the additional modulation processing. Pass to suppress the shape modification of the amplitude of the high frequency signal reproduced from the mark to the mark between regions is to be performed, the recording apparatus characterized by. 7. The recording apparatus according to claim 6, wherein the threshold length is at least twice the shortest mark length / the shortest mark interval length. 8. The recording apparatus according to claim 6, wherein a shape-modifying portion formed in a mark or an inter-mark area by the additional modulation processing is smaller than a resolution limit of an optical pickup of an optical disk reproducing system. 9. The method according to claim 1, wherein the first modulation is performed by the additional modulation processing.
In a portion where the mark length corresponding to the duration for which the modulated signal maintains the first signal level exceeds the threshold length, the mark corresponding to the portion is shorter than the shortest mark length / inter-mark length. In a portion where an inter-mark area is inserted and a length between marks corresponding to a duration in which the first modulated signal maintains the second signal level exceeds the threshold length, a space between marks corresponding to the portion is provided. 8. A mark which is shorter than said shortest mark length / inter-mark length is inserted into an area.
The recording device according to any one of the preceding claims. 10. The additional modulation processing may be such that a mark length / inter-mark length corresponding to a duration for which the first modulated signal maintains the first signal level or the second level is the threshold length. 8. The recording apparatus according to claim 7, wherein the recording is performed by changing the level of the first modulated signal in at least a part of the portion exceeding the value. 11. An optical disc having a track formed by a mark and an inter-mark area, and recording information by determining the length of the mark and the inter-mark area according to a given modulation method. Among the recording structures on the optical disc recognized as a single mark or an inter-mark area, a recording structure having a length exceeding a predetermined threshold length is shorter than the shortest length recognized by the optical disc reproducing system as the inter-mark area. It is characterized by being formed by a plurality of marks sandwiching an inter-mark region or a plurality of inter-mark regions sandwiching a short mark less than the shortest length recognized as a mark by an optical disc reproducing system. optical disk. 12. An optical disc having a track formed by a mark and an inter-mark area, and recording information by determining the length of the mark and the inter-mark area according to a given modulation method. Of the recording structures on an optical disc recognized as a single mark or an inter-mark area, a recording structure having a length exceeding a predetermined threshold length is subjected to shape modification, and this shape modification is performed at an eye at a binary threshold level. An optical disc characterized by suppressing the amplitude of a high-frequency reproduction signal reproduced from the recording structure without deteriorating a pattern. 13. An optical disc having a track formed by a mark and an inter-mark area and recording information by determining the length of the mark and the inter-mark area according to a given modulation method, an optical disc reproducing system comprising: Of the recording structures on an optical disc recognized as a single mark or an inter-mark area, a recording structure having a length exceeding a predetermined threshold length is used to define a short inter-mark area smaller than the resolution limit of an optical pickup of an optical disc reproducing system. An optical disc comprising a plurality of marks interposed therebetween, or a plurality of inter-mark areas interposing a short mark smaller than a resolution limit of an optical pickup of an optical disc reproducing system. 14. An optical disc having a track formed by a mark and an inter-mark area, and recording information by determining the length of the mark and the inter-mark area according to a given modulation method. Of the recording structures on an optical disc recognized as a single mark or an inter-mark area, the recording structure having a length exceeding a predetermined threshold length is subjected to shape modification. When the recording structure is an inter-mark area, a narrow mark is formed at least at a part of the entire length of the inter-mark area by reducing the width of at least a part of the entire length of the mark. An optical disc characterized by suppressing the amplitude of a high-frequency reproduction signal reproduced from the recording structure. 15. An adjacent track on an optical disc having a track formed by a mark and an inter-mark area, and recording information by defining the length of the mark and the inter-mark area according to a given modulation scheme. A method for suppressing crosstalk from a mark, wherein a mark having a length exceeding a predetermined threshold length and a mark-to-mark area out of a mark and a mark-to-mark area formed on an optical disc are subjected to shape modification, thereby providing the mark and the mark-to-mark area. A method for suppressing crosstalk, characterized by suppressing the amplitude of high-frequency reproduction reproduced from an inter-mark area, thereby suppressing the level of crosstalk noise from an adjacent track. 16. When applying a shape modification to a mark, a short inter-mark area less than the shortest length recognized by the optical disc reproduction system as an inter-mark area is inserted into the mark.
16. The method for suppressing crosstalk according to claim 15, wherein a short mark shorter than the shortest length recognized by the optical disk reproduction system as a mark is inserted into the inter-mark area when shape modification is performed on the inter-mark area. . 17. When modifying the shape of a mark, a short inter-mark area smaller than the resolution limit of the optical pickup of the optical disc reproducing system is inserted into the mark, and when modifying the shape of the inter-mark area, the optical disc is reproduced. 16. The method for suppressing crosstalk according to claim 15, wherein a short mark smaller than the resolution limit of the optical pickup of the system is inserted into the area between the marks. 18. A method for modifying a shape of a mark, wherein a width of at least a part of a total length of the mark is reduced.
16. The crosstalk suppressing method according to claim 15, wherein a narrow mark is formed on at least a part of the entire length of the inter-mark region when the shape modification is performed on the inter-mark region.