FR2557344A1 - HIGH DENSITY CODE FOR DATA CODE RECORDING, AND ASSOCIATED RECORDING AND READING APPARATUS - Google Patents

Abstract

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

Description

The present invention relates to high density codes used in

  coded data recording, as well as an associated recording and reading apparatus, and, without limitation, the high density codes used for coded optical data recording. In high density optical recording, it is often preferred that a clock signal, or pilot signal, be prerecorded on the optical medium in order to be read by an optical system when the data is read. For a prerecorded clock signal, or pilot signal, to be read, the data must be recorded so that a zero appears in the frequency spectrum when the data is read. The frequency of the clock signal, or pilot signal, is chosen so that it coincides with the zero of the frequency spectrum of the data. A similar code producing a zero in the frequency spectrum is the so-called four-phase code. In this code, two bits of binary code are coded into a symbol. In optical recording, the two bits are coded by writing holes corresponding to the configuration of the bits in the first half of a symbol and by writing holes corresponding to the inversion of the configuration of bits in the second half of the symbol . Thus, each symbol has four symbol positions. Binary signal 00 must be written using two holes in symbol positions 1 and 2 and two spaces in symbol positions 3 and 4. Binary signal 01 must have a hole in symbol position 1 and one

  hole in symbol position 4, with no hole in posi-

  2 and 3. Binary signal 10 must have a hole in the positions

  2 and 3 and have no holes in positions 1 and 4, while binary signal 11 must have no holes in positions 1

  and 2 and have holes in posithns 3 and 4. The quadri- coding

  phased produces a zero in the frequency spectrum of the data for

  a frequency F corresponding to half the frequency of the posi-

  Symbol options. This frequency is the frequency of binary data, i.e. four symbol positions correspond to two bits

binary data.

  For high density optical recording, it is desirable to place the symbol positions at close mutual distances such that the size of a hole, i.e. its diameter, can be greater than a symbol position . This leads to an obvious problem when reading and decoding a symbol, because

  the signal corresponding to a symbol "spreads" to positions

  adjacent symbol states. This problem is made more important by the optical system of laser reading beams commonly used in optical recording systems. The spots corresponding to these beams are not narrowly defined beams, but

  rather have the shape of a gaussian curve o the width at mid

  power is approximately equal to the diameter of the holes produced when writing using this same beam spot. For holes or groups of holes, the width at half power of a signal

  produced by reading roughly corresponds to the diameter of the holes.

  Thus, a non-negligible part of the power of the read signal

  ture extends beyond the diameter of the hole.

  These two problems, namely that of the relative values of the diameter of the hole and the spacing distance of the symbol positions and that of the overlap of the read signals, combine to limit the writing density of the bits in the optical recording. . There are a very large number of fixed block codes which produce a zero in the frequency spectrum. However, the prior art does not provide a method for finding

  one or more codes to reach the recording density

  highest on an optical recording medium.

  According to a first aspect of the invention, a high density code is proposed for the coded recording of binary data having several symbols which each have several symbol positions, four hole holes or even a higher number, and at least one empty symbol position at the limit of the symbol, no empty symbol position existing between adjacent holes or two

  or more empty symbol positions between adjacent holes.

  According to a first embodiment, the holes are made in a support to represent a certain state and the absence of a hole represents the complementary state, a zero being present in the frequency spectrum during recording or reading if although the optical medium can comprise a prerecorded clock signal making it possible to assist in the writing and reading of the data, the high density code comprising: a symbol comprising fifteen positions also separated inside the symbol and serving to code eight binary bits of data, a constraint being that only four holes appear inside each symbol, another constraint being that, for each hole appearing in an even position, there appears a hole in a

  odd position, another constraint being that the fifteenth posi-

  There is never a hole, and another constraint is that either there is no empty symbol position between adjacent holes, or there are at least two empty symbol positions between adjacent holes. may have an additional constraint, according to which the four holes are not recorded consecutively. The high density code may also include a constraint such that groups of three holes are not recorded in positions 1, 2 and 3,

  in positions 2, 3 and 4, or in positions 12, 13 and 14.

  According to another embodiment of the invention, holes are made in the. support to represent a certain state, while the absence of holes represents the complementary state,

  a zero being present in the frequency spectrum when recording

  recording or reading so that the optical medium may include a prerecorded clock signal making it possible to assist in writing and reading data, the high density code comprising: a symbol having eighteen positions also separated inside the symbol and making it possible to code eight binary bits of a data, a constraint being that only six holes appear inside each symbol, another constraint being that, for each hole appearing in an even position , a hole appears in an odd position, another constraint being that the seventeenth and eighteenth positions never have a hole, and another constraint being that, or else there is no empty symbol position between adjacent holes,

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  or there are at least three empty symbol positions between adjacent holes. High density code may include constraint

  additional that five or six holes are not allowed

  cutively recorded. The high density code may further include the constraint that groups of four holes

  are not saved in positions 1, 2, 3 and 4.

  According to another aspect of the invention, there is provided a reading device comprising: a disc type means carrying data coded according to the high density code of the invention; means for moving said disc type means; laser type means for directing a laser beam onto said disk type means; control means for controlling said laser beam; detection means which optically detects said laser beam after it has struck said disk-like means; and means which responds to said detection means by decoding said

coded data.

  According to another aspect of the invention, there is provided a recording apparatus comprising: disc type means; means for moving said disc type means; laser type means for directing a laser beam onto said disk type means; control means for controlling said

  laser beam; detection means for detecting optical-

  said laser beam after it strikes said disc type means; and an encoding means which, when used, is used to encode data according to the high density code of the invention on said disc type means, said control means responding to said encoding means by bringing the type means laser to record

  data encoded on said disk type means.

  According to another aspect of the invention, a data recording method is proposed which consists in coding data according to the high density code of the invention on a means of the type

  disk. Said data can be optically coded.

  According to another aspect of the invention, a disk-type means carrying data which has been

  encoded by the method according to the invention.

  The following description, intended for illustration

  of the invention, aims to give a better understanding of its characteristics and advantages; it is based on the appended drawings, among which: FIG. 1 is a graph showing the intensity of a signal detected by an optical reading system of an optical disc recording device relative to a symbol position , o the diameter of the hole is 0.9 micron, the dimension of the symbol position is 0.6 micron, and the half-power width of a light spot is 0.8 micron; - Figure 2 is a graph similar to Figure 1, but the diameter of the hole is 1.25 microns; FIG. 3 is a graph similar to FIGS. 1 and 2,

  but the configuration of the holes consists of two holes

  cutifs, a space, then a hole; - Figure 4 is a graph similar to Figure 3, but the configuration of the holes consists of two consecutive holes, two spaces, then a hole; - Figure 5 is a graph showing the vision openings of several codes in the worst cases, the ordinate representing fractions of the amplitude of a single hole, and the abscissa representing a parameter equal to the ratio of the dimension of the hole at the distance traveled during a clock period; and - Figure 6 is a block diagram of an apparatus

  optical recording and reading according to the invention.

  In many optical recording systems, coded symbols represent binary data. For block codes with a fixed number of holes, it is conventional to determine

  the position of the hole or holes inside these symbols in com-

  paring the signals received from each symbol position with the signals received from each of the other symbol positions and choosing the N most intense signals for the position of the hole or holes (N e.st is the number of holes in a symbol and is therefore a predetermined fixed number). For example, if a given symbol has four positions among which two positions must contain holes, the conventional optical reading device compares the signal strength associated with a hole with each of the four positions and chooses the two positions having the strongest powers. high as

  positions where the holes are placed.

  The abscissa in FIG. 1 represents the configuration of the symbol 01010010 written on an optical medium, the "ones" corresponding to the holes and the "zeros" corresponding to the spaces. In this context, spaces are represented as elevations on

  the abscissa and the holes are represented as hollows on the abscissa.

  The group of eight positions globally represents a single symbol.

  The ordinate of FIG. 1 represents the intensity of the signals produced

  through the holes for an optical reading system and an electrical system

  conventional optical recording tronic. If the signal is observed in reflection, the signal "produced" by a hole is then the inverse of the power of the reflected beam. Conversely, if the signal is measured in transmission, the beam coming from one side of the disc being observed from the other side, the signal is a direct function of the laser power received. The dashed lines in FIG. 1 represent the intensity of the signal read which is associated with each of the three holes. These curves are approximately Gaussian,

  the half-power level of the signal roughly corresponding to the diameter

  meter of the hole. In Figure 1, the hole diameter is 0.9 micron, while the width of the symbol position, or the distance between centers of the symbol, is 0.6 micron. The solid line in Figure 1 represents the addition of the signals produced by holes

adjacent.

  The study of FIG. 1 shows that, at no point, the signal produced by holes, or adjacent holes, does not reach a level such that the peaks, produced by the holes themselves, are indistinguishable. An optical system can correctly read the Symbol Configuration shown in Figure 1 because it can correctly identify the peaks associated with the holes and determine

  also the hollows associated with the spaces.

  However, variations in media sensitivity and variations in optical recording devices (intensity

  light, aberrations of the beams) cause a certain dispersion

  hole diameters. It can happen that holes with a very large diameter are written. For example, in Figure 2, the diameter of the hole is 1.25 microns. The same symbol configuration, i.e. 01010010, is represented by the abscissa of the same

  so as in figure 1. Again, the lines in inter-

  broken represent the signals produced by the holes and the solid lines represent the addition of the signals produced by close holes. Examination of Figure 2 shows that there is only a very small decrease in signal strength between the

  configuration 101 holes. Analog comparison systems

  classical gics attempting to determine whether this part is a hole or a space may incorrectly decide that it is a hole and not a space. The last hole in Figure 2 can then be read as a space, as the comparison system will not identify

  only three holes in the symbol, not four.

  Figures 1 and 2 show symbol patterns produced by single isolated holes, in other words "single holes". Figure 3 shows a signal pattern produced by two holes written in a row. The configuration

  of symbol of figure 3 indicated according to the abscissa is the confi-

  guration 01101001. The diameter of a hole is 1.25 micron and the distance from the symbol position is 0.6 micron. When two holes are written next to each other, they overlap and

  appear to be a large and long hole, as shown in Figure 3.

  This large long hole produces a somewhat intense signal

  greater than that of the signal produced in a single hole, as re-

  present. We can usefully compare the signal produced by the

  group of two holes with the signals produced by the two mono-

following holes.

  Again, in Figure 3, the lines in inter-

  broken represent the signal produced by the holes themselves. As

  previously, the configurations of the single holes are gaus-

  but the double hole signal has Gaussian sides and a flatter top. The solid lines represent the addition of near hole signals. A device which searches for symbol positions having the four strongest signals will find, incorrectly, the holes corresponding to positions 2, 3, 4 and 5 and spaces in all other positions, since, in positions 2, 3, 4 and 5, the signal intensity produced by the configuration 1101 in these positions is higher at any point, including the space, than the signal produced by the single hole from position 8.

  We now go to Figure 4, where the abscissa represents

  has a symbol configuration such as 01100100, with a hole diameter of 1.25 micron and a distance from the symbol position of 0.6 micron. A device can correctly detect the positions of the three holes, since the signal due to the double hole and the signal from the next single hole do not add, at the space level, to a signal which is approximately equal to or greater than the signal produced by the single hole itself, even if the signal produced by the double hole has a greater amplitude than the signal produced by the next single hole and overlaps with a notable power

  signal three positions further.

  The process described above can be extended to groups of three holes in a row. However, the signal power produced by the three holes in a row is not significantly greater than the signal power produced by two holes in a row. Again, in connection with FIG. 4, the configuration produced by the fact that there are holes in the first three positions of the symbol illustrated, instead of this

  either in positions 2 and 3 only, will be identical to the confi-

  guration shown, and the device would correctly decode the holes in positions 1, 2, 3 and 6 and the spaces in positions 4 and 5. As shown in Figures 3 and 4, it is necessary that there is at least an empty position between adjacent symbols. Otherwise, adjacent symbols with a 1101 or 1011 configuration at the boundary could be incorrectly interpreted as having a hole in place of space. These configurations can still appear with an "additional" position between the symbols, but, however, the question of whether the signal strength of a hole is present in this "additional" position is not relevant,

  since it is not provided in the comparison apparatus as a cor-

  corresponding to one of the positions which may include a hole.

  Analysis of FIGS. 1 to 4 has shown that the presence of two spaces between the holes and the groups of holes allows correct decoding of the symbol. Analogous reasoning shows the additional advantage of providing three spaces between holes or chains of holes and at least two empty positions at the limits

  symbols when the dimension of the hole diameter increases relatively

  the dimension of the symbol position.

  To determine which code will produce the maximum bit density, it is desirable to examine only those codes capable of encoding a number of bits equal to the powers of two, namely two bits, four bits, eight bits, sixteen bits, etc. For example, the four-phase code deals with the case of two bits and has four symbol positions and two holes inside a symbol. A code called "two positions out of eight", or DPSH (or TOEP in Anglo-Saxon literature), has eight positions in the symbol and makes it possible to code four bits of information. In general, to code two bits of information in a symbol, the code must have at least four different hole patterns. To code four bits in a symbol, the code must have at least sixteen different hole patterns. Similarly, to code eight bits of information, the code must have at least two hundred

  fifty-six different configurations.

  To some extent, the more holes in a symbol, the greater the number of possible configurations that can be contained within the symbol. For example, in a symbol with four positions, if the code obeys the constraint according to which there is only one hole per symbol, there will only be four different possible configurations, namely a hole in

  position 1, in position 2, in position 3, or in position 4. Any-

  times, if the symbol can have two holes, the number of codes

sibles is then six, namely

1100 1010 1001 0110 0101 0011

  (In the four-phase code, the configurations 1010 and 0101 are eli-

  undermined, because they do not obey the constraint that the configuration of the first two positions is reversed into that of the two second positions in order to allow the existence of a zero in

the frequency spectrum).

  We can therefore see that the discovery of the code which opti-

  Putting the number of bits processed on the extent of a unit of space is a difficult and complex operation. We now refer to FIG. 5, where the abscissa represents the sigma parameter of the dimension of the hole, divided by the minimum spacing of the position of the symbols,

  or the distance traveled over half a clock period.

  For a certain dimension of the laser spot used, below a hole diameter of 0.95 micron, the calculation of the dimension of the

  hole depends on the optical system considered and that of the spot.

  The formula for its calculation is complex and is not present-

  well to consider, being well known. However, for dimensions

  holes greater than 0.95 micron, the signa parameter is approxima-

  tively equal to 5 / 7th of the diameter of the hole. Thus, the following dimension

  The abscissa is proportional to the diameter of the hole, in general by the factor 5/7. In addition, the dimension along the abscissa is in

  inverse proportion of the spacing of symbol positions.

  When bit densities of 1.2 micron per bit are kept constant, the spacing of symbol positions varies in inverse proportion to the number of positions within a symbol. Thus, the dimension along the abscissa again varies in

  proportion of the number of symbol positions of a code.

  The ordinate of FIG. 5 represents the opening of "eye", or of vision, corresponding to the worst case, in fractions of the signal produced in the reading device by a single hole. The "eye" opening can be defined as the difference between the amplitude of the signal due to a single hole and the amplitude of the signal of addition due to adjacent holes which is measured at the level of a space (figures 1 to 4). Formulas for calculating an "eye" configuration from a coding configuration, a hole size, a light spot size, etc. are well known in the art. We can deduce the "eye" opening of the worst case by examining the coding configurations with the smallest distance between holes or groups of holes. The smaller the "eye" opening, the higher the risk of incorrect decoding due to

inevitable noise from the system.

  The process by which the configuration can be determined

  ration of "eye" of the worst case of a given code having been defined, the following comparison criteria were established. The compared codes must have the same bit density, that is to say the same number of binary bits to be coded per unit length of the medium. The standard comparison example was chosen at 1.2 micron per bit (one bit for 1.2 micron). In this way, one can compare symbols with actual lengths and different position spacings significantly. If two bits are coded, the length of the whole symbol is 2.4 microns. If four bits are coded, the symbol length is 4.8 microns. If eight bits are coded,

  the length of the symbol is 9.6 microns.

  All the codes shown in Figure 5 have the same bit density, namely 1.2 microns per bit. All have a zero in the frequency spectrum. The first dashed line in Figure 5 represents the worst case "eye" opening for codes D = 1, where the expression D = 1 indicates that there is at least one symbol position between single holes, or between single holes and groups of holes, or between groups of holes. The second solid line is the "worst case" eye opening for D = 2 codes. The third solid line corresponds to codes D = 3. The "eye" openings are determined for three dimensions of the hole diameter: (1) 0.95 micron, (2) 1.25 micron and (3) 1.45 micron. The codes with the best "eye" configurations of the worst case are listed in Figure 5. The

  code "two out of nine", either DSN (or TOON in English literature

  Saxon), - is represented by a circle. This code corresponds to a "two out of eight" code (DPSH), previously mentioned, to which a ninth position "empty" has been added. Both DSN and DPSH codes provide four-bit coding. The DPSH code is represented by a square. The code "six out of twelve", which ensures the coding of eight bits, is represented by a triangle placed the point downwards. The code "four out of fifteen", which ensures the coding of eight bits is represented by an X cross. The code "six out of eighteen", which ensures the coding of eight bits,

is represented by a triangle.

  Examination of FIG. 5 shows that, for a density of 1.2 microns per bit and for holes with a diameter less than or equal to 1.45 microns, the code "four out of fifteen" produces the best opening "beil ", that is to say that its" eye "opening in the worst case is 0.6 times the amplitude of a single hole with a diameter of 0.95 microns and 0.3 times that of a 1.25 micron diameter single hole, while the other codes produce, for identical diameters, less good "eye" openings. "Six out of eighteen" code produces

  better "eye" opening for holes with a larger diameter

  less than 1.45 micron. It also produces the best aperture

  "eye" with higher bit density and smaller holes.

  FIG. 5 shows that, in most situations, the best "eye" opening of the worst case corresponding to

  a & nsity of bits dnnnée is obtained with the code "four out of fifteen".

  In some cases, you may prefer the code "six out of eighteen", although it imposes a heavier load on the laser. The codes of the invention make it possible to achieve the highest binary bit density for optical recording or signal compatible block codes

  8-bit predetermined clock times.

  The code "four out of fifteen" of the invention has a constraint in the position of symbol 15, namely that it must never have holes. There is also a constraint relating to the production of a zero in the frequency spectrum to allow a system with preset clock signals by using an equal number of holes in the odd positions and the even positions. These constraints combine, leaving 441 configurations

  different possible. Among these 441 different configurations pos-

  if necessary, a certain number must be eliminated, because only 256 confi-

  gurations are required. The first eliminated are those which do not satisfy the constraint D = 2, that is to say that which does not

  at least two spaces between the single holes, or between the single

  holes and groups of holes, or between groups of holes, in other words those which have no space between adjacent holes

  or which have at least two spaces between adjacent holes. The configu-

  The rations to be removed next are the ones that place the greatest load on the laser diodes of the conventional optical recording device. The laser diodes of most devices

2557344.

  Optical recording should not be pulsed at write power for a long time. The last constraint aims to eliminate the configurations having three holes in a row near the limits of a symbol, as well as the configurations having four holes in a row. The specific set of 256 configurations that produce

  this optimal code is presented in table 1.

  Table 1. Code "four out of fifteen" (D = 2), compatible, with preset clock signals

1 2 3 4 5 6 710 a b -

1 X X XX X

1- X X 'X X

2 X X X X

3 X X X X

4 X X X X

S X X X X

6 X X- X

7 X X X X

8 X X X X

9 X X X X

X X X X

11 XX 'X X

12 X X X X

13 X X X X

14 X X X

X X X X

16 X X X X

17 XX X

18 X X X X

19 X X X X

X X X X

21 X X X X

22 X X X X

23 X X X X

X X X ES

X XX X tg

X X X OS

  X X X X 6t X XX X 8t X X XX Lt SZ XX t - XX X, XSt

X X X X "

  X X X ú t X X X X tr Z - X X X X 'lt X X XXX t

X X.X X 6ú

X X X XX8E

X 'X X X'Lú S

X X X X g

X- XX X 5

X X X X K

X X X X E

X X X X zt XXXX X l

X XX X 8

X X X X 8Z

X K X X LZ S

X X X 'X 9Z

XX X X X 5Z

X X X X tK P p3.q * OlK K L 9StE Z

K K K K

X X K K 6C

K K K K LE ç

K K K K OC

IK K K S

K K K K b

K XX K C

x x KK LaC

K K K OC9

  K K Kx S * P l eOîia L 9 s 9 a I 1 2 3 4 5 6 7 8 9 10 a b c d e

54 X X X X

X X X X

56X X X X

57 X X X X

58 X X X X

59 X X X X

X X X X

61 X X X X

62 X X X X

63 X X X X

64 X X X X

X X X X

66 X X X X

67 X X X X

68 XX X X

69 X X X X

X X X. X

71X X X X

72X X X X

73 X X X X

74 X X X X

X X X X

76 X X X X

77 x x x x

78 XX X X

79 X X X X

X X X X

81 X X X X

82 X X X

83 X X X X

1 2 3 4 i 6 7 8 9 10 a b c d t

84 X X X

X X X X

86 X X X X

87 X X X X

88 X X. X X

89 X X X X

X X X X

91 X X X X

* 92 X X X X

93 X X X X

94 X X X X

X X X

96 X X X

97 X X X

98 X X XX

99 x x x x

X X X X

101 X - X X

1OQx xx X

103 X X X X

103X X X X

104X X X

K X X

106 X X X

107 X X X X

108 X X X X

109 X X X

X X X X

111 X X X X

112 X X X

113 X X X X

  -X X X X t1 X XSX ZltlOr X X X Xt t XX i X 01t

X X X X 6ú1

X K XX X8

X X X XL1 S

  X Xg X ú X XX Sil XXX X gtt X X XX úú1t

X XX X Zú O

X-X X X 1ú1

X X X Kút O XX XX 6tú

X X XX OZI

X X X X tZl

X X K K 9ZI

X X X K SZI

X X X X tZL

XX X K úZI

  - x x x x 0: X X X X: lZ X X X X O oI X X X XX6l

X X X X 811

XX X X 61t5

K K KK SUL

XKX X X 911

XX X X 11

  Po q OL68 L9 S Z I f, 4, x x LU çs /, 1 2 3 4 S 6 7 8 9 10 b c d e

144 X X X X

X X X X

146 X X X

147 X X X X

148 X X X

149 X X X

X X X

151 X X X X

152 X X X X

153 X X X X

154 X X X X

X X X X

156 X X X X

157. X X X X

158 X X X X

159 X X X X

X X X X

161 x x x x

162 X X X X

163 X X X X

164 X X X X

X X X X

166 X X X X

167 X X X X

168 X X X X

169 X X X X-

X X X X

171 X X X X

30. 172 X x X X

173 X X X X

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1 2 3 4 S 6 7 8 9 10 b c d e

174 X X X X

X X X X

116 X X X X

176 x x xx

177 X X X X

178 X X X X

179 X X X X

X X X X

181 X X X X

182 X X X X

183 X X X X

184 X X X

X X X x

186X X X X

187 X X X X

18C X X X x

189 X X X X

1tg X X X X

191 X X X X

192 X X x

193 X X X X

194 X X X X

X X X

196 X- X X X

197 X X X X

198 X X X X

199 X X X X

X X X X

201 X X X X

202 X X X X

203 X X X X

x x x- x

X X X_ X - úZ O

X X X X Z

x K x icz X X X X tCZ

X X X X 6Z

X X X X 8Z

X X X X 95

X X. X K

X X X - X tZZ

X X X X EZZ

x x x x zao x x x x caz X X X zz o

X X X X 61

X X X X 81Z

X X X i LU

X X X X - -91

X X X XC SIZ

X X X X 9LZ

X X X X SIZ

XX X X ZlZ 0 X X X X LlZ

KK K K LLZ

K X X X ZX oIZ X X X X ttZ

X X X X OLZ

X X X X LO 60

X- X X X gOZ X X X x oo (

X X X X KIZ

  p q Ol 6 L 9 S Z I 8 oz9 P 1 2 3 4 5 6 7 8 9 10 * b c d t

234 X X X X

235 X X X

236 X X X X

237 X X X X

238 X X X X

239 X X X X

240 X X X

241 X X X

242 X X X X

243 X X X X

244 X X X X

245 X X X X

246 X X X X

247 X X X X

248 X X X

249 X X X

250 X X X

251 X X X

252 X X X X

253 X X X

254 X X X X

255 X X X X

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  The code "six out of eighteen" according to the invention includes a constraint on its seventeenth and eighteenth positions, according to

  which never have holes.

  There is also a production constraint

  tion of a zero in the frequency spectrum. The constraints are

  combine removing 3,136 different possible configurations.

  Among these configurations, those that do not meet the constraints D = 3 are eliminated, which leaves 316 configurations. Second, we eliminate the configurations with five and six holes in a row, and four holes in the first four positions, which leaves the two hundred and fifty-six configurations required, as shown in Table 2. (Due to purely limitations typographic, we only represented sixteen of the eighteen positions of

  symbol. The last two positions never have holes).

  Table 2. Code "six out of eighteen" (D = 3), compatible, with preset clock signals 1 2 3 4 5 6 7 8 9 10 a b c d e f

0 X X X X X X

i X X X X X X

2 X X X.X X-

3 X X X X X

4 X X X X X X

S X X X XX X X

6 X X X X X X

7 X X X X X X

8 X X X X X X

9 X X X X X X

X X X X X X

11 X X X X X X

12 X X X X X X

13 X X X X X X

1 2 3 4 S 6 7 8 9 10 a b c d e f

14 X X X X X X

X X X X X X

16 X X X X X X

17 X X X X X X

18 X X X X X X

19 X X X X X X

X X X X X X

21 X X X X X X

22 X X X X X X

23 X X X X X X

24 X X X X X X

X X X X X X

26 X X X X X X

27 X X X X X X

28 X X X X X X

29 X X X X X X

XX X X X X

31 X X X X X X

32 X X X X X X

33 X X X X X X-

34 X X X X X X

X X X X X X

36 X X X X X X

37 X X X X X X

38 X X X X X X

39 X X X X X

X X X X X X

41 X X X X X X

42 X X X X X X

1 2 3 4 5 6 7 8 9 10 b e d

43 X X X X X X

44 XX X X X X

X X X X X X

46 XX X X X X

47 X X X X X X

48 X X X X X X

49 X X X X X X

X X X X X X

51 X X X X XX

52 XX X X X X

53 X X X X X X

54 XX XX X X

X X X X X X

56 X X X X X X

57 XX X X X X

58 X X X X X

59 X X X X X X

X X X X X X

61 X X X X X X

62 X X X X X X

63 X X X X X X

64 X x x x x x

X X X X X X

66 X X X X X X

67 X X X X X X

68 X x X X X

69 X X X X X X

X X X X X X

71 X X X X X X

72 X X X X X X

1 2 3 4 5 '6 7 8 9 10 a b c d e f

73 X X X X X X

74 X X X X X X

X X X X X X

76 X X X X X

77 X X X X

78 X X X X X X

* 79 X X X X X X

X X X X X X

81 X X X X X X

82 X X X X X X

83 X X X X X

84 X X X X X X

X X X X X X

86 X X X X X X

87 X X X X X X

88 X X X X X X

89 X X X X X X

X X X X X X

9o x x x x x x

91 X X X X X X

92 X X X X X

93 x: {x x

93 X X X X

94 X X X X X X

X X X X X X

96 X X X X X X

97 X X X X X X

98 X X XX X X

99 X X X X X X

X X XX X X

101 X X X X X X

X X X X X X OCL OC

X X X X X X 6Z1

  X X X X X X 8Zl X X X X X X LtZ xxx x x x K i ai X X X X X X 9Zl

X X X X X SZL Z

  XX X'X X X X tl XX X X x x L X X X X X x Zl

X X X X X X IZL

X X X XX X OZL OR

X X X X X X 611

K X X X X 8LL

X X X X X X ZLL

X X X X X 9LL

X X X X X X SLL ST

  X X X X X i LL Xx Kx K K K M1 XX -X X X X ll

X X X X X X ZLL

X X X X X X LLL

X X X X X X OLL 01

X X X X X X 60L

X X X X X X 9Ql

X X X X X X LOL

X X X X X X 90L

X X X X X X SOL 5

X X X X X X trL01 X X X X X X ú0l

X X X X X X ZOL

3; PW i-i Z 'O i T z l

XX X X X X

K 651 O

XX X X X X Sl X X X XX X / Sl

X X X X X X SL

X X X X X X 81 S

XX X X X X ZStI

X X XXX X LSL

XX X X X X OSI

  X- X X X X X 6t1 O XX X ', X X X 8tt

_XX X X X X OL

X X X X X X 6tL 9 O1 X X X X Stl

XX X X X /.151

XX XX X XX9tl XK X X X X SlL

X X X X XX L Z

XX X X XX E: IT

X X X X X XL

XX XX Ylt

XX X X X X LSL

KX X X X K LX O

X g X X X X KEL

X X X X X X SCL

XX X X X X úCLI

XX X X X X

x X X I EL

KX X X K L

fiP X X X Ol68 C9SúL LZ

K K K KK LúI

X X X X X X 881 O (

X X X X X X L8,

xK K K I

XX XX XX 98

X XX X X S L

XX X X X X ú81

X X X X X ú L 5Z

X K X X X X XZt X: X XX X X l81

XX X-X X X 081

X X XX X x 6LL

X X X X X 8LI OZ

X XX X XX ULt XKX x x x 9tk

X XXX X SLI

  X X X XX X tll K X X X XX: Lt Sl X K X X XX X Li X X X X X ILl XX XX X OLl

X X XX X 691

XX X xX 89l O 1 XX X X x L91

X XX X XX 99L

XX X X XX S91

X X X X X X t9t1 XX X XX ú ú9k 5

X X -XX XX K91

XX X XX X L91

X X XX X X O9L

8Z 1 2 3 4 5 6 7 8 9 10 a b c d e f

189 X X X X X X

X X X X X X

191 X X X X X X

192 X X X X X X

193 X X X X X X

194 X X X X X X

X X X X X X

196 X X X X X X

197 X X X X X X

198 X X X X X X

199 X X X X X X

X X X X X X

201 X X X X X X

202 X X X X X X

203 X X X X X X

204 X X X X X X

205 X X X X X X

206 X X X X x x

207 X X X X X X

08 X X X X X X

209 X X X X X

210 X X XX X X

211 X X X X XX

212 X X X X X X

213 X X X X X X

214 X X X X X X

l15 X X X X X X

216 X X X X X X

217 X X X X X X

2 557 344

1 2 3 4 5 6 7 8 9 10 b c d e f

218 X X X X X X

219 X X X X X X

220 X X X X X X

221 X -X X X X X

222 X X X X X X

223 X X X X X X

224 X X X X X

225 X X X X X X

226 X X X X X X

227 X X X X X X

228 X X X X X X

229 X X X X X - X

230 X X X X X X

231 X X X X X X

232 X X X X X X

233 X X X X X

234 X X X X X

235 X X X X X X

236 X X X X X X

237 X X X X X X

238 X X X X X X

239 X X X X X X

240 XX X X X X

241 X X X X XX

242 X X X X X X

243 X X X X XX

244 X X X X X X

245 X X X X X X

246 X X X X X X

2557344.

1 2 3 4 5 6 7 8 9 10 to b c d e

247 X X X X X X

248 X X X X X X

249 X X X X X X

250 X X X X X X

251 X X X X X

252 X X X X

253 X X X X X

254 X X X X

255 X X X XX

  An embodiment of an optical recording apparatus according to the invention is presented in FIG. 6. A laser type disc consists of a disc made of an optically reflecting material in which holes can be formed by combustion to reduce the reflectivity of the surface at the hole. The disc 10 is typically made up of grooves (not shown) which are etched in a substrate by a reproduction process. The grooves are modulated in depth using a clock frequency. Next, the surface of the substrate is coated with an optically reflective material which is suitable for recording data in the form of holes. A motor 12 rotates the disk 10 during the recording of the data and during their reading. A laser 14 is used to record and read the data. In the recording mode, the laser

  operates at a higher power than in read mode.

  The power is fixed at a level such that it burns the reflective material of the disc 10 by forming a hole. Therefore, to register a hole, one can pulsate the laser itself, which can consist of a laser diode, or one can divert the laser beam from disc 10, for example a gas laser. In the read mode, the laser operates continuously at a lower power, which is not

  not sufficient to alter the reflecting nature of the disc 10.

  The laser is placed under control of a laser control device 16. The laser controller 16 adjusts the power level of the laser and its pulsation or deflection of the beam. The data to be written comes from a data coding device 18 which receives the binary data to be written on the disk 10, the codes according to the invention according to a "four in fifteen" or "six in eighteen" code, transmits the coded data to the laser control device 16, which controls the laser 14 so that it registers the

  data on disk 10 in rotation.

  In the writing mode as in the reading mode, a reading means 20 detects the reflection of the laser beam by the

  disc 10. The reading means is conventionally a photodiode trans-

  forming light into electrical signals. The output signal of the read means 20 is supplied to a servo device 24 which maintains the position of the laser 14 and of the read means 20 directly above a track of the disc 10. The output signal of the read means reading 20 is also delivered to a device 22 for decoding data and to a circuit 26 for verification by reading after writing. The circuit 26 for verification by reading after writing compares the data written on the disc with the data read on the disc during writing in order to verify that the data has been correctly written. If the data was incorrectly written to disk 10, a rewrite can be carried out or an error correction means can be used. In the read mode, the

  data supplied to the data decoding device 18 is trans-

  formed of the code "four out of fifteen" or "six out of eighteen" in 8-bit binary code corresponding to the initial data. In the preferred embodiment, error correction is performed

  (not shown) on the 8-bit binary data.

  In summary, the first code represented according to the invention comprises a symbol with fifteen positions, also separated inside a symbol, making it possible to code a binary data item of 8 bits. Of

  holes are inscribed in the center of a symbol and may have diameters

  meters larger than the spacing of symbol positions. Four holes and only four holes appear inside a symbol. For each hole appearing in an even position, there appears a hole in an odd position, and vice versa. This produces a zero in the frequency spectrum, so that a clock signal

2557344 '

  pre-recorded can be read and encoded by other electronic means

  (not shown). The fifteenth position never has holes.

  At least two symbol positions appear between the single holes or between the single holes and the groups of holes, or between the groups of holes.

  To increase the number of configurations from 441 to 256

  coded, we eliminate those that do not satisfy the constraint D = 2. In addition, although this is not essential to the invention, all the symbols having four consecutive holes are eliminated. All symbols with three holes in symbol positions 1, 2 and 3, in positions 2, 3 and 4 and in positions 12, 13

and 14 are eliminated.

  We build a code "six out of eighteen" in the same way, with D = 3 and two empty spaces at the end of each symbol. Symbols that have five and six holes in a row, as well as those that have four holes in a row at positions

1 to 4 are eliminated.

  In general, for a symbol having Y positions and X holes (Z positions of the limit of the symbol never having holes) and, when there is a hole in an odd position for each hole appearing in an even position, the number maximum possible of coded configurations is given by:

IY-Z 2

X! _Z)

  We then reduce this maximum possible number by applying

  a constraint of the type D = N (where N is worth at least 2).

  Of course, those skilled in the art will be able to imagine,

  from the methods and devices of which the description comes

  to be given by way of illustration only and in no way limiting, various variants and modifications not departing from the scope of the invention.

Claims (15)

R E V E N D I C A T I 0 N S   1. High density code allowing the coded recording of binary data, characterized in that it has several symbols each having several symbol positions, four holes, or even a greater number, and at least one empty symbol position at the symbol limit, no empty symbol position lying between adjacent holes or two empty symbol positions,   or more, lying between adjacent holes.   2. High density code according to claim 1, characterized in that holes are made in a support to represent a   certain state, while the absence of a hole represents the complementary state   shut up, a zero being present in the frequency spectrum during recording or reading if the optical medium can   include a prerecorded clock signal to assist writing   data reading and reading, the high density code including:   a symbol with fifteen positions also separated inside   laughing at the symbol and allowing the coding of eight binary bits of   given, a constraint being such that only four holes ap-   appear inside each symbol, another constraint being such that, for each hole appearing in an even position, there appears a hole in an odd position, another. constraint being such that the fifteenth position never has a hole, and another constraint being such that either there is no empty symbol position between adjacent holes, or else there are at least two.   3. High density code according to claim 2, characterized in that it includes a constraint such that the four holes do not   are not recorded consecutively.   4. High density code according to claim 2 or 3, characterized in that it includes a constraint such that groups of three holes are not recorded in positions 1, 2 and 3,   in positions 2, 3 and 4, or in positions 12, 13 and 14.   5. High density code according to claim 1, character-   laughed at in that holes are made in the support to represent a certain state while the absence of a hole represents in the complementary state, a zero being present in the frequency spectrum during recording or playback so well that the optical medium may include a prerecorded clock signal to assist the writing and reading of data, the high density code comprising: a symbol having eighteen positions also separated inside the symbol and making it possible to encode eight binary bits of data, a constraint being such that only six holes appear inside each symbol, another constraint being such that, for each hole appearing in an even position, there appears a hole in an odd position, a other constraint being such that the seventeenth and eighteenth positions never have a hole, and another constraint being such that, or else there is no empty symbol position between adjacent holes , or there are at least three.   6. High density code according to claim 5, character-   laughed at in that it involves a constraint such as five or six   holes are not consecutively recorded.   7. High density code according to claim 5 or 6, characterized in that it includes a constraint such that groups of four holes are not recorded in the positions 1, 2, 3 and 4.   8. Reading device characterized in that it comprises: a means (10) of the disc type carrying data coded according to a high density code as claimed in any one of   previous claims, means (12) for moving said   medium disc type; laser type means (14) for directing a laser beam onto said disc type means (10); control means (16) for controlling said laser beam; detection means for optically detecting said laser beam   after it has struck said disc type means; and a means (22) -   responding to said detection means by decoding said coded data. 9. Recording apparatus characterized in that it comprises: a means (10) of the disc type; means (12) for moving said disc-like means; laser type means (14) for directing 2557344-   a laser beam on said disk-like means; a means of   a command (16) for controlling said laser beam; detection means (20) for optically detecting said laser beam after it strikes said disc-like means; and coding means (18) which, when used, is used to code the data according to a high density code as defined in any one   of claims 1 to 7 on said disc type means, said means   control (16) responding to said coding means (18) by causing the laser type means (14) to record the coded data on said disk type means.   10. Data recording method, characterized in that it consists in coding a data according to a high density code such   as claimed in any one of claims 1 to 7, on a disc type medium.   11. Method according to claim 10, characterized in that   that said data is optically coded.   12. High density data processing apparatus,   intended to process data recorded on a medium, character-   laughed at in that it comprises several symbols each comprising: a predetermined number of positions each having the same length   predetermined; four holes, or even more,   killing a first state of the support, each hole being centered on a symbol position and having a variable length, the maximum of which is predetermined; the equilibrium state of a symbol having a second support state; reading means for reading said symbols and determining the location of the center of said holes, the reading means comprising means for creating and measuring signals indicative of said states of the medium, the intensity of said signals depending on the length said states of the support and weakening, from the limit of a state of the support, along a Gaussian curve centered at a predetermined distance from the edge of a state of the support; the centers of the holes being separated by a predetermined number of symbol positions so that the signals of one or more holes centered on adjacent symbol positions measured at a position on which no hole is centered are less than the signal produced by a single hole of nominal size; and at least one symbol position   located at the first limit of said symbol with no holes.   13. Apparatus according to claim 12, characterized in that said predetermined maximum length of a hole is less than the length of two symbol positions, the number of holes in a symbol is four and the holes are so arranged that they are centered on adjacent symbol positions or on positions   symbols separated by at least two symbol positions.   14. Apparatus according to claim 12 or 13, characterized in that said predetermined maximum length of a hole is less than the length of two symbol positions, the number of holes in a symbol is six and the holes are centered on positions symbol adjacent or centered on symbol positions separated by at least three symbol positions, at least two symbol positions having no holes at said level first limit.   15. A disc type medium, characterized in that it carries data coded by a process as claimed in the claims 12 or 13.