| 摘要 |
PURPOSE:To additionally stabilize a servo signal and to decrease the error rate at the time of information recording and reproducing by forming the sectional shape of the projecting parts of preformats to a triangular or trapezoidal shape when the preformat surface of a substrate is faced upward. CONSTITUTION:The sectional shape of the projecting parts 4 for tracking is formed to the triangular shape or the trapezoidal shape with which the length of top base b is <=1/10 the spat diameter of irradiation light so that the quantity of reflected light from the projecting parts 4 is sufficiently small compared with that of the recess parts 3. In this case, recording layers are hardly formed in the vertex (top bottom b) parts of the projecting parts or even if the recording layers are formed, the quantity of the reflected light from the projecting parts 4 is hardly detected as the length of (b) is smaller than the spot diameter of the irradiation light. The recording layers are formed along hypotenuses 7 of the projecting parts but the reflected light therein receives the diffraction effect of the hypotenuses, by which the quantity of the reflected light detected by the optical head is sufficiently decreased. As a result, the contrast ratio of the track crossing signal is improved. The identification and detection of the projecting parts which are the track regions are facilitated in this way and the off-tracking of a laser beam for recording and reproducing is decreased. |
