| 摘要 |
PURPOSE:To attain the recording or reproduction of high density information, by recording sreviously tracking signals of different frequencies on the top and the bottom of a V-shaped or inverted trapezoidal grooves as pits in advance, and tracking the optical spot at the center of a tilt surface of the groove. CONSTITUTION:Grooves having V-shaped or trapezoidal radial cross section are provided on the optical disc, signals in frequency f1 are formed on the top and signals in frequency f2 are formed on the top as tracking pits, for example. Laser light is collected and irradiated on the optical disc, and when the distribution (b) of light intensity is obtained with a little shift from the center of the tilt surface to the top, the change in the amount of light in the frequency f2 is larger than that in the frequency f1, and when the optical beam is shifted to the bottom inversely (distribution c), the change in the amount of light in frequency f1 is larger. Thus, the tracking to the center of the tilt surface is executed by making the amplitude of the change in the amount of light changing in the two frequencies f1, f2 equal with each other. |
