| 摘要 |
PROBLEM TO BE SOLVED: To optimize a pattern of projections and recesses corresponding to a pre-formatted recorded signal pattern, by forming a section of the projection in a longitudinal direction of a bit of a digital information signal to be a trapezoid having an upper base at the side of a front face and a lower base at the side of a base body which is longer than the upper base, and making a difference of lengths of the upper and lower bases to be not smaller than a specific multiplication of a height. SOLUTION: A section of a projection in a longitudinal direction of a bit of a digital information signal is trapezoidal, having an upper base at the side of a front face and a lower base at the side in touch with a base body 1. A length (a) of the upper base is smaller than a length (b) of the lower base, and a difference (b-a) of the bases is not larger than twice a height (h) of the trapezoid. Because of the projection formed trapezoidal in section, even when the digital information signal of severalμm bit length is to be pre-formatted and recorded, a change of an S/N ratio because of a minute difference of the sectional shape can be limited to a permissible range. Since the section of the projection is permitted to be trapezoidal, advanced photolithography is eliminated.
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