| 摘要 |
PURPOSE:To eliminate the need for the position sensor of a head by providing the pre-group of a prescribed phase depth and a pre-group having a different phase depth at every prescribed track number and counting the track only. CONSTITUTION:The pre-group guide an optical head is provided to an optical disk. The pre-groups consist of a pre-group (N-PG) having a phase depth of lambda/8n and a pre-group (S-PG) having a different phase depth from that of the pre-group N-PG, where lambda is the wavelength of a recording/reproduction beam and (n) in the refractive index of the light transmission layer transmitting the beam, and tracks comprising the S-PG are provided repetitively at every track number comprising the N-PG. Through the constitution above, the difference of the reflected luminous quantity between the N-PG and the S-PG is utilized and only the track of the S-PG is counted to eliminate the need for the position sensor of the head and the drive cost is reduced. |
