JP2904140B2 - Optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing apparatus and a recording apparatus for an optical recording medium for optically recording information, and more particularly to an improvement in the recording density.

[0002]

2. Description of the Related Art In recent years, the application of optical recording / reproducing technology has been remarkably widespread. In particular, audio disks and video disks exclusively for reproduction have been widely used in homes. These are recorded at a very high density, and a protective layer having a thickness of about 1.2 mm and a strong error correction code are used in order to ensure reliability of various recording media against defects and dust.

Hereinafter, an example of the above-described conventional optical reproducing apparatus and recording apparatus will be described with reference to the drawings. FIGS. 3 and 4 show a schematic configuration diagram of a compact disk player and a conceptual diagram of a recording format as an example of a conventional optical reproducing apparatus. In FIG. 3, reference numeral 21 denotes a recording medium, reference numeral 22 denotes a substrate thereof, reference numeral 23 denotes a recording film formed of a reflective film having irregularities called pits, and reference numeral 24 denotes a protective layer for protecting the recording film 23. Reference numeral 25 denotes a light beam for reading information, which is converged on the recording film 23 through the substrate 22. Reference numeral 30 denotes an optical head, 31 denotes an objective lens included in the optical head 30, and the objective lens 31 records the light beam 25 on a recording film.
The light converges on 23 and receives the reflected light, and the optical head 30 converts the received detection light into an electric signal and outputs it.
A reproduction channel 32 performs analog signal processing such as amplification of an electric signal output from the optical head 30. Reference numeral 33 denotes a synchronization circuit which extracts a clock from an output signal from the reproduction channel 32 to generate a read clock, detects a synchronization signal, and also generates a timing signal necessary for the operation of each unit. A demodulation circuit 34 restores the channel code output from the reproduction channel 32 to the original data while referring to the read clock and the timing signal output from the synchronization circuit 33. 35 is a data control circuit, 36 is a buffer memory, and 37 is an error correction circuit.The error correction circuit 37 reads data stored in the buffer memory 36, performs error correction, and then corrects the error in the buffer memory 36 again. The data control circuit 35 controls the flow of these data, and also accumulates the read data in the buffer memory 36 and outputs the data read from the buffer memory 36 to the outside.

[0004] The operation of the optical recording medium and the reproducing apparatus configured as described above will be described below. First,
The objective lens 31 converges the light beam 25 on the recording film 23 through the substrate 22. At this time, the thickness of the substrate 22 is about 1.2 mm, and the numerical aperture NA of the objective lens 31 is set so that the aberration is within an allowable range even if the substrate 22 is tilted to a degree that can be normally considered.
Is limited to about 0.5 or less. As the light beam 25, light having a wavelength of about 780 nm emitted from a semiconductor laser is usually used. The light spot formed on the recording film 23 cannot be narrowed down below the diffraction limit determined by the numerical aperture and the wavelength, and this becomes a factor limiting the recording density. actually,
Under the above optical conditions, the track period is 1.3 μm
Since the crosstalk increases if the distance is made small,
The thickness is set to about 5 μm or more.

On the recording film 23, a channel code obtained by converting data to be recorded into a modulation code suitable for high-density recording is recorded. . The optical head 30 converges the light beam 25 on the recording film 23 to form a light spot, and scans an information track on which the channel code is recorded.
The optical head 30 receives the light reflected from the recording film 23, converts the light into an electric signal, and outputs the electric signal. The reproduction channel 32 performs impedance conversion and amplification of the signal output from the optical head 30, and then shapes the waveform to output a binary signal. The synchronization circuit 33 locks the PLL to the edge of the binary signal output from the optical head 30, generates a channel clock synchronized with the bit cycle of the channel code,
By detecting a synchronization signal included in the binary signal, various timing signals are also generated. The demodulation circuit 34 synchronizes the binary signal output from the reproduction channel 32 with the channel clock to reproduce the channel code, and groups the channel codes by referring to the timing signal output from the synchronization circuit 33 to group the channel codes. Is converted back to data. The read data reproduced by the demodulation circuit 34 is stored in the buffer memory 36 via the data control circuit 35.

FIG. 4 is a conceptual diagram showing a recording format. Dn, 1, Dn + 1,2, Dn, 3, Dn + 1,
4 ... Dn + 1, 12, Qn, 1 ... Qn +
1,4, Dn, 13, Dn + 1,14, Dn, 15,
Dn + 1,16 ... Dn + 1,24, Pn, 1 ...
· N from left to right along the row direction of the figure as in Pn + 1,4
A data word is alternately recorded between a line and an (n + 1) th line after being converted into a channel code. Each data word is composed of one byte. Each byte represented by P and Q is a parity byte for error correction, and Q parity is generated so as to form a code word when each byte is collected every four rows in the diagonal direction of the drawing. The P parity is generated such that one row in FIG. That is, Dn, 1, Dn + 4,2,... Dn + 44,12
, Qn + 48, 1... Qn + 60, 4, Dn + 64,
13, Dn + 68, 14... Dn + 108, 24 are Qn + 48, 1.
0, 4 are generated, Dn, 1, Dn, 2,... Dn, 12, Qn, 1
..Qn, 4, Dn, 13, Dn, 14..Dn, 2
.. Pn, 4 are generated such that 4, Pn, 1... Pn, 4 become codewords. Thus, by forming a code word in two directions, it is configured as a kind of product code.

The data control circuit 35 of FIG. 3 reads out the code word in the row direction of FIG. 4 from the buffer memory 36, corrects the error, returns the corrected code word to the buffer memory 36 again, and The error correction circuit 37 is controlled so that the oblique direction code word of the portion where the code word correction operation is completed is read out from the buffer memory 36 to perform error correction, and the corrected code word is returned to the buffer memory 36 again. . Data control circuit
35 further reads out and outputs the data in the buffer memory 36 in which all correction operations have been completed at a predetermined speed in a predetermined order. (For example, Ohmsha "Compact Disc Reader" pages 103-110)

[0008]

However, in the above configuration, the symbols constituting the code word in the row direction are recorded close to each other on the recording medium, and the parity is only 4 symbols in any direction. Since the substrate 22 is not added, when the substrate 22 is thinned, burst errors due to surface flaws and dust frequently occur, and the correction capability is improved even when repeated corrections are performed alternately in two directions using erasure correction. It was insufficient, and the erroneous correction probability was not sufficiently reduced, so that it was difficult to use it for external storage of a computer. For this purpose, the thickness of the substrate must be 1 mm or more.
An object having a diameter of about 2 mm is used.
A is limited to about 0.5 or less, and there is a problem that improvement in recording density is hindered.

In view of the above problems, the present invention is practicable even if the thickness of a transparent layer through which a light beam for recording / reproduction passes is reduced to about 1 mm or less. An object of the present invention is to provide an optical recording medium capable of performing recording and a recording / reproducing apparatus.

[0010]

In order to solve the above problems, an optical recording medium according to the present invention records disk information to be recorded as an error correction code based on a product code, and at least one of the codewords is recorded. In order to prevent uncorrectable burst errors from occurring due to scratches and dust on the medium surface, the symbols included in the medium are configured to be sufficiently separated from each other, and the number of parity symbols included in at least one of the codewords is incorrectly corrected. The thickness of the protective layer through which a light beam for recording and reproduction passes is reduced to 1 mm or less, and the period of the information track is also reduced to 1.3 μm or less by adding a number necessary to sufficiently reduce the probability of the above. . The recording or reproducing apparatus of the present invention is for recording information on the optical recording medium or reproducing information from the storage medium, and converges a light beam with an objective lens having a numerical aperture NA of 0.58 or more. It has a simple configuration.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is the same as the conventional one because a transparent protective layer through which a light beam passes is as thin as 1 mm or less even when an objective lens having a large numerical aperture capable of recording or reproducing information at a high recording density is used. Since the product code allows the tilt of the recording medium and allows repetitive correction using erasure correction, sufficient reliability can be ensured even for scratches and dust on the surface of the recording medium. .

This will be described in more detail below. Generally, the recording density when performing optical recording is limited by the size of a light spot converging on a recording film. If the light spot becomes smaller, both the track period and the bit period can be reduced in proportion. However, the bit period can transmit a larger amount of information in a certain band by devising a modulation code, waveform equalization, and the like, so that it cannot be said that the bit period is limited solely by the light spot. However, it can be said that the track period is almost limited by the size of the light spot, because it is difficult to improve the crosstalk caused by reducing the track period by these methods. The size of the light spot is inversely proportional to the numerical aperture of the objective lens. Therefore, by increasing the numerical aperture of the objective lens, the track period can be reduced, and the recording density can be improved. In the conventional example, the numerical aperture is 0.1 mm.
For 5, the track period is set to about 1.5 μm.

On the other hand, the numerical aperture of the objective lens cannot be increased without limit, and there is another factor that limits this.
That is the aberration that occurs when the recording medium is tilted. This aberration increases as the numerical aperture or the thickness of the transparent protective layer through which the light beam passes increases. The numerical aperture allowed for the same inclination angle is inversely proportional to the cubic root of the thickness of the transparent protective layer. Conventionally, the thickness of the transparent protective layer is set to about 1.2 mm in order to defocus surface flaws and dust to reduce the influence on the read signal. for that reason,
A numerical aperture of about 0.55 is a practical limit. In order to increase the numerical aperture, it is necessary to reduce the thickness of the transparent protective layer. When the thickness becomes 1 mm or less, the influence of flaws and dust on the signal becomes conspicuous. Therefore, instead of defocusing and optically mitigating the effects of flaws and dust, if the effects are dispersed and mitigated by signal processing, even a thin transparent protective layer of 1 mm or less can withstand practical use.

In a normal use environment, the upper limit of the size of surface flaws and dust that must be allowed is experimentally and empirically about 200 μm. Therefore, even thin negligible thickness of the transparent protective layer, shall be a recording format that can withstand the loss of signal over 200 [mu] m. Further, when the thickness of the transparent protective layer is further increased and the diameter of the light beam on the surface thereof exceeds 200 μm, a signal format must be used which can withstand even if a signal corresponding to the beam diameter is lost. No. The refractive index of the transparent protective layer is n, and its thickness is t (m
m), if the numerical aperture of the objective lens is expressed as NA, the diameter D of the light beam on the surface of the transparent protective layer is D ≒ 2 · NA · t / n (mm). Practical limit of the numerical aperture with respect to the thickness 1.2mm of the transparent protective layer than 0.55, the limit NA numerical aperture with respect to the upper Symbol transparent protective layer, Therefore, D ≒ 1.2 · t ^2/3 / n. Since loss of a signal having such a length frequently occurs, the recording format must be able to withstand the loss. Then, this invention aims at solving the subject as follows. (1) Use product code to provide powerful
Error correction . (2) At least one of the codewords, even if the burst error due to the loss of the signal length as described above ,
At least half of the ability to correct random errors remains
To ensure the interleave length so. (3) A codeword in at least one of the directions is a bit of an error caused by erroneously correcting an error that exceeds the capability limit even if the corrective operation is performed up to the capability limit.
The error rate is a bit error in the auxiliary storage for the computer.
It adds parity必<br/> main number or more number of symbols to not exceed 10 ¹² which is the limit of the over rate, therewith to allow erasure correction in a direction perpendicular.

The product code means that data is arranged two-dimensionally,
Parity is added to each of the row and column directions,
Each direction is an independent code word. The repetitive correction refers to performing the correction operation in the row direction and the correction operation in the column direction alternately and repeatedly as long as the number of errors decreases. The repetitive correction of the product code can have extremely high correction capability, and is more effective if erasure correction is used together. Erasure correction is a correction method in which, when performing a correction operation on a certain codeword, if an erroneous symbol is known in advance, the symbol is regarded as being lost and the lost symbol is calculated from the remaining symbols. Yes, if all the symbols that have not been lost are correct,
Even if the same number of symbols as the number of parity symbols are lost, the symbols can be calculated. For example, when the parity is 16 symbols, the normal correction operation can correct only 8 symbols, but when only erasure correction is performed, even if 16 symbols are lost, the original codeword can be decoded. To use this erasure correction for correcting the product code, for example, the following is performed. First, when a product code arranged two-dimensionally is defined as one unit block, 1
The data of the block is read and stored in the memory, and a correction operation in the row direction is performed for each row.

At this time, a flag is set for an uncorrectable code word in the row direction. When the number of flags set in the row-direction codewords is less than the number of column-direction parities, it is considered that all of these codewords have been lost,
By performing erasure correction on the code word in the column direction, complete error correction can be performed. When there are too many flags, normal error correction is performed instead of erasure correction. At this time, if at least one codeword in the column direction has been corrected and not all have been corrected, the above-described correction operation in the row direction may be repeated once. When performing such erasure correction, the reliability of the flag is important. For example, in the correction operation in the row direction, the flag is not set when an error that cannot be corrected is erroneously corrected, and when the erasure correction is performed to the full capacity in the column direction, the error correction is overlooked and the error is overlooked. Despite the inclusion, it is regarded as correct and the correction operation is completed. In order to solve such an erasure correction problem, a bit error rate of an error caused by an erroneous correction in a row-direction correction operation is required.
Is generally required for computer auxiliary storage
It is necessary to make the 10- ¹² or less.

The number of parity symbols required to sufficiently reduce the probability of erroneous correction will be described below. Now, it is assumed that each symbol is composed of k bits, that is, the codeword is generated on a Galois field GF (2 ^k ). Assuming that the number of parity symbols is d, the number of symbols that can be corrected is [d / 2] symbols (where [] is a Gaussian symbol and [X] exceeds X
Not the largest integer ). If the number of erroneous symbols is equal to or more than [d / 2] +1, erroneous correction may be performed.

The codeword is composed of m data symbols and d packets.
Reed-Solomon mark
Be the most efficient codeword, such as
You. Arbitrarily m symbols from such a codeword
When you remove a file, even if it contains an error,
Is the correct value that contains such an error.
Is always present. m data is optional
Because it can take the value of However, such other codewords
For the remaining d symbols in
Compared to the original codeword with no symbol errors
All have different values. However, the remaining d
D- [d / 2] symbols out of these symbols are in error
And their symbols are those of the other codewords above.
If the same value is wrong, the remaining [d /
2] only the symbols appear to be in error,
The correction operation is performed on another codeword. As a result, the codeword
Will be corrected to the wrong codeword. Each symbol is
If it consists of k bits, the symbol is incorrect
Since there are (2 ^k -1) possible values,
The probability of being erroneous to the same value as the symbol at the corresponding position in the word is 1 / (2 ^k -1) . Therefore, d- [d / 2] symbols are all
And the value of the symbol at the position corresponding to those of the other codewords
The probability of being erroneous to the same value is d− [d / 2] = [(d−1) / 2] +1.
And 1 / (2 ^k -1) ^{[(d-1) / 2] +1} . In general, it is said that the allowable frequency of occurrence of errors in a data storage device is once per 10 ¹² bits. Therefore, assuming that the number of symbols of information included in this codeword is m, d is set so as to satisfy (2 ^k −1) ^{[(d−1) / 2] + 1} ≧ 10 ¹² / ( km ). Once determined, erasure correction with sufficiently high reliability can be performed. Symbol bit number k is 8
If the number m of information symbols is 30 or more, d may be 7 or more.

Next, the interleaving will be described.
The interleaving means that the symbols in one codeword are not continuously recorded on a recording medium, but are rearranged and recorded so as to be recorded at fixed intervals. At least one of the product codes
Code words are interleaved. By doing so, even if there is a burst error due to a relatively long loss in the read signal, it is possible to prevent a number of errors from occurring in one codeword due to the burst error due to the loss. Ideally, for burst errors that occur relatively frequently, at most one error occurs in one codeword, but the number of error symbols caused by one burst error is limited. If the number of symbols that can be corrected is equal to or less than half the number of symbols that can be corrected, even if there is another burst error in the block, there is enough capacity to correct it, and it can be said that interleaving is sufficiently effective. Assuming that the number of parity symbols included in the codeword is d, the number of symbol errors that can be corrected is [d /
2], the distance between the symbols included in the codeword is determined by the length of the burst error of the read signal [d / 2].
It is sufficient if the value is equal to or more than the value obtained by dividing by / 2. The length of the frequently occurring burst error of the read signal is 200 μm, 2 · NA · t / n or 1.2 ·
Since t ^2/3 / n, the mutual distance between the symbols is 400 / [d / 2] 4 · NA · t / (n · [d / 2]) 2.4 · t ^2/3 / ( n · [d / 2]).

By using all of the means described above, even if the thickness of the transparent protective layer is reduced to about 1 mm or less,
Practically enough reliability can be secured, and the recording density can be improved. Hereinafter, an optical recording medium and a recording / reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic block diagram of an optical recording medium and a recording / reproducing apparatus according to an embodiment of the present invention. In FIG. 1, 1 is a recording medium, 2 is a substrate thereof, 3 is a recording film for recording information, and 4 is a protective layer for protecting the recording film 3. Reference numeral 5 denotes a light beam for reading information, which is converged on the recording film 3 through the protective layer 4. 10 is an optical head, 11 is an objective lens included in the optical head 10, 12 is a recording / playback channel, 13 is a synchronization circuit, 14 is a demodulation circuit, 15
Is a data control circuit, 16 is a buffer memory, and 17 is an error correction circuit, all of which have basically the same functions as the conventional example of FIG.

The operation of the optical recording medium and the recording / reproducing apparatus configured as described above will be described below with reference to FIGS. First, the recording medium 1 differs from the conventional example in that information is not recorded and reproduced through the substrate 2 but recorded and reproduced through a thinner protective layer 4. Here, the protective layer 4 has a refractive index of 1.5 and a thickness of 0.5 mm. The numerical aperture NA of the objective lens 11 is 0.7
4. At this time, the period of the information track on the recording film 3 can be set to 1 μm. When reading information from the recording medium 1, the optical head 10, the recording / reproduction channel
The operations of the synchronizing circuit 13, the demodulation circuit 14 and the synchronizing circuit 13 are the same as those of the conventional example, and therefore, detailed description is omitted.

FIG. 2 is a conceptual diagram showing a recording format in this embodiment. In the figure, Di, j represents a data symbol, and the symbol consists of 8 bits. 129 symbols of data are arranged in the row direction, and these data Di, 0 to Di, 128 To the parity of the 16 symbols Pi, 0 to P
i, 15 is added to form a Reed-Solomon code. Further, in the column direction, data of 129 symbols are arranged, and these D0, j to D128, j And P0, k to P128, k In addition, the parity Q0, j to Q15, j of 16 symbols are added to the data to form a Reed-Solomon code. The whole of these product codes is recorded as one block at a predetermined position on a recording medium assigned an address for each block. At this time, the arrangement is recorded on the recording medium in the order in which the arrangement is scanned in an oblique direction. That is, each symbol on a recording _{medium, D 0,0 · D 1,1 ...... D} 128, 128 · Q 0,129 ...... Q 15,144 ·
D _1,0 · D _2,1 ……… D _128,127 · Q _0,128 …… Q
_15,143 · P _0,15 · D _2,0 · D _3,1 …… D _128,126 · Q
_0,127 are arranged as shown in _{...... Q 15,142 · P 0,14 · P} 1,15 · D 3,0 ....... This block is further divided into a plurality of sectors every four rows. Lines 0 to 3 are divided into the first sector, lines 4 to 7 are divided into the second sector, and lines 124 to 127 are the 32nd sector.
In line 128, the attributes of this block and each sector in this block can be recorded. Each sector has a capacity of 516 bytes, and 51
A 4-byte CRC code can be included in addition to the 2-byte user data.

The operation for reading data recorded in such a format will be further described. When an external device such as a host computer specifies the address of a sector from which information is to be read, the data control circuit 15
Calculates the address of the block including the sector and the number of the sector in the block. When the address of the block is known, this is instructed to the access means, not shown in the figure, and the optical head 10 is positioned at a predetermined position. When a predetermined block address is found from the read signal, the data control circuit 15 stores the data read from the block in the buffer memory 16. When reading is completed, the data control circuit 15 controls the error correction circuit 17 to perform an error correction operation in the column direction. Since each codeword contains parity of 16 symbols, it is possible to correct up to eight-fold error. Flags are set for codewords that cannot be corrected. When the correction operation in the column direction is completed, the error correction circuit 17 is controlled so as to perform the correction operation in the row direction next. The number of flags set in the correction operation in the column direction is 16
In the following cases, it is assumed that all the codewords in the column direction in which the flag is set have been lost, and all errors can be corrected by performing erasure correction in the row direction.
When the number of the flags exceeds 16, a correction operation up to an octuple error is performed in the row direction. At this time, if the correction is impossible, a flag is set to the code word. After one round of the row-direction correction operation is completed, a correction operation similar to the row-direction correction operation is performed again in the column direction. In this way, the correction operation in the column direction and the row direction is alternately repeated. When all the erroneous symbols are corrected, or when the number of erroneous symbols does not decrease at all, the correction operation ends. When all errors in a given sector have been corrected, the data control circuit 15 reads the data of that sector from the buffer memory 16 and outputs it to the outside. When an error remains in a predetermined sector, a read error signal is output to the outside.

On the other hand, when rewriting data in a predetermined sector, data of a block including the predetermined sector is first read out and buffered, as in the case of reading.
The data is stored in the memory 16 and a correction operation is performed. If the correction has failed, a write error signal is output. When the correction operation is completed normally, the data in the predetermined sector is rewritten, and only the parity in the row direction of the rewritten row is calculated and rewritten. Since the buffer memory 16 has a capacity capable of storing a plurality of blocks of data, it is not necessary to rewrite the block of the recording medium immediately after rewriting the data in the buffer memory 16; What is necessary is just to move the contents of the memory 16 to a recording medium. Therefore, the parity in the column direction may be calculated and rewritten between the last rewriting of the sector information of the buffer memory 16 and the transfer of the rewritten block data to the recording medium.

As described above, according to this embodiment, the error correction code is a product code, the number of parity symbols is sufficiently increased so that repetitive correction can be performed using highly reliable erasure correction, and the interleave length is further increased. By making it sufficiently large, it is possible to reduce the thickness of the transparent protective layer through which the light beam for recording and reproduction passes, thereby enabling the use of an objective lens with a large numerical aperture NA and achieving a high recording density. can do. Also, such a product code has a large block size, and it is necessary to perform recording / reproduction on a recording medium in units of this block. However, this block is divided into a plurality of sectors, and the sector is rewritten in units of sectors on the buffer memory. By configuring to perform
The recording medium can be used efficiently without consuming the entire large block for a small amount of data.

In the above embodiment, the recording format as shown in FIG. 2 has been described. However, the present invention is not limited to such a specific format. It is also possible to adopt a configuration in which the length is reduced to about half and two code words are arranged in the row direction. In this case, the same operation as in the above embodiment may be performed.

Further, in this embodiment, a thin protective layer 4 is provided on the side opposite to the substrate 2 with the recording film 3 interposed therebetween, through which information is recorded and reproduced. With the configuration, the substrate 22 may be merely thinned.

[0029]

As described above, according to the present invention, there is provided a product code in which information to be recorded is substantially two-dimensionally arranged and a parity is added to each of a column direction and a row direction to form a code word. One codeword is interleaved so that even if there is a defect of about 200 μm, at most a double error occurs,
Furthermore, by limiting the number of parity symbols so that the probability of erroneous correction of a code word in either direction is sufficiently small, the thickness of the protective layer of the optical recording medium through which the light beam for recording and reproducing information passes is 1 mm or less. , The numerical aperture of the objective lens is increased to 0.58 or more, and the track cycle is set to 1.
By reducing the size to 3 μm or less, high-density recording can be performed with the same crosstalk characteristics as in the related art.

Further, the codewords in any direction constituting the product code are interleaved so that even if there is a defect of about 200 μm, an error of not more than half of the correction capability is generated at most. By limiting the number of parity symbols so that the erroneous correction probability becomes sufficiently small, the effect of further increasing the resistance to scratches and dust on the recording medium surface can be obtained.

Further, if the interleave is long in both the row and column directions, the size of the block becomes large. However, this block is divided into a plurality of sectors so that rewriting can be performed on a sector-by-sector basis. Can be used well. In addition, by dividing the sector along the row direction or column direction,
When data in a sector is rewritten, immediately after that, only the parity related to that sector is calculated and rewritten.Parity over multiple sectors is rewritten from the last data rewriting until the data is transferred to the recording medium. By performing the process only once during the process, the effect that the processing speed can be increased is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram of a recording format in the embodiment.

FIG. 3 is a schematic configuration diagram of a conventional optical reproducing apparatus.

FIG. 4 is a conceptual diagram of a recording format in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording medium 4 Protective layer 10 Optical head 11 Objective lens 15 Data control circuit 16 Buffer memory 17 Error correction circuit

Claims (2)

(57) [Claims] 1. Digital information spanning a plurality of sectors
And two-dimensional array of attribute information of each sector in a predetermined order
Parity is added to each row and each column when
The encoded block is recorded as information, and the recorded
Information can be read optically, and the above information can be read.
The thickness t of the transparent protective layer through which the luminous flux is transmitted is 1 mm or less.
Below, the codeword in at least one direction of the product code is included in this
When the number of symbols included is d,
Each symbol along the information track at least
Is larger, whichever is larger , 2.4 · t ^2/3 / (n · [d / 2]) mm and 400 / [d / 2] μm (where [x] represents the largest integer not exceeding x). Place them at least a distance apart
A recording medium characterized by comprising: 2. Digital information spanning a plurality of sectors.
And errors for each sector to detect errors in one sector
Each row when the detection code is two-dimensionally arranged in a predetermined order
And a parity code added to each column to form a product code.
Information is recorded as information, and the recorded information is
Readable and the luminous flux for reading the above information is
When the thickness t of the transparent protective layer to be transmitted is 1 mm or less,
The codeword in at least one direction is the symbol
When the number is d, each symbol constituting this codeword is
At least along information tracks with each other, 2.4t ^2/3 / (N · [d / 2]) mm and 400 / [d / 2] μm (However, [x] represents the largest integer not exceeding x) Which is larger than the larger one
A recording medium characterized by comprising: