| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that the reading rate of main information decreases, when the additional amount of sub information is increased for improving the reliability in reading the sub information, which results in the addition of jitters to recording marks of the main information, in recording sub digital information in which an edge position of a mark is varied with a very small amount synchronized with a random number series, for the mark to be recorded on an optical disk, in order to prevent the copying of a digital book recorded on the optical disk on another optical disk. SOLUTION: In two bits of a plurality of sub information pieces, one bit is used for selecting the random number series used for the information addition/ detection among a plurality of random pulse series. A plurality of sub information pieces are added by repeating a method, in which it is determined whether the displacement direction of a recording mark edge of the disk is in the advancing phase direction or in the lagging phase direction, depending on whether the signal, for which the value of the exclusive OR between the other bit of the sub information pieces and the random number series is PE modulated, is 'H' or 'L'. |
