Patent ID: 7035181

Claim:
An optical disc apparatus, comprising: a main modulation signal generating unit configured to generate a main modulation signal according to main data; laser beam irradiating unit configured to irradiate a laser beam on said optical disk according to said main modulation signal, thereby forming a pit string or a mark string on said optical disk; timing detecting means for detecting a timing of an edge of said each pit or each mark and outputting a detected timing; a random number series generating unit configured to generate a M-senes random number series; modulating means for generating a sub-modulation signal from said subdata according to said M-series random number series and said detected timing; and a deviating unit configured to deviate an irradiation point of said laser beam towards an inner/outer region of said disc to express said sub-modulation signal wherein said subdata comprises bits or marks for key data, and bits or marks for a fixed data that is different than the key data.