| 摘要 |
PURPOSE: To prevent an unauthorized copying by adding a copying preventing pattern P which does not affect the reading of a pit column and can not be detected by copying to an optical disk and prohibiting the reproducing of an optical disk for which the pattern P is not detected. CONSTITUTION: A copying preventing pattern P of a transparent ink layer 6 is printed on a laser beam incident surface 8 of a transparent substrate foundation section 7a and a laser beam 10 is focused on a recording information surface of a reflecting film 9 at a point 'a'. At that time, a beam image B becomes a circle on a 4D-PD3, a focus error signal 4 becomes zero volt. If the beam 10 is located at points 'b' and 'd', the focusing is deviated by the thickness of the layer 6 and the image B becomes an ellipse, short longitudinally and long laterally. Therefore, the signal 4 fluctuates between plus and minus voltages. If the beam 10 is located at a point 'c', the image B becomes a circle by a focus servo circuit and the signal 4 returns to zero volt. The fluctuation of the signal 4 is demodulated, the pattern P is detected, an optical disk for which the pattern P is not detected is discriminated as an unauthorized copy and the reproducing operation is prohibited. Thus, an unauthorized copying is prevented. |
