| 摘要 |
PROBLEM TO BE SOLVED: To verify accurate follow-up performance against surface wobbling even at the time of high-speed revolution by forming a recessed and projected part in a prescribed depth and size on a signal surface, generating a focussing change in the vertical direction and obtaining a desired wobbling acceleration. SOLUTION: A projected part 9 in a sine wave shape with a height d and a width w is formed on the signal surface 7 side of a plastic layer 3 in a recording medium 1. Assuming the linear velocity of the recording medium 1 is s and the refractive index of the plastic layer 3 is n, the displacement y of an objective lens in the vertical direction is y=(d/2/n)×Cos(2πs/w.t), the acceleration a in the vertical direction is a=yx(2πs/w)2, and the acceleration α is α=2(d/2/n)×(2πs/w)2. Thus, by constituting so as to generate the focussing change in the vertical direction, a wobbling acceleration can be obtained in proportion to the revolution even at the time of high-speed revolution. The manufacturing is such that a stamper with a recessed part formed on the rear side is set inside the die of an injection molding machine, and a high pressure thermoplastic resin is injected. |
