| 摘要 |
PROBLEM TO BE SOLVED: To reduce modulation due to the leakage of a track cross into a focus error signal by providing a double Foucault prism and setting the parting line of the lens parallel to the radial direction of a disk of incident lights. SOLUTION: The parting line of a double Foucault prism 113 is set parallel to the radial direction of an optical disk. Reflected lights from the optical disk are converged on hexapartite sensors with a convex lens 111 and a concave lens 114. In this case, when the amplitude between peaks of the focus error signal at the time a focus servo is turned off and the amplitude between peaks of the level of the leakage of the track cross are respectively defined as A, B, a modulation due to the leaking of the track cross becomes such a small modulation that the ratio of B to A is almost <=10%. Since the parting line of the double Foucault prism 113 is set parallel with the radial direction of the optical disk, a constant random access is made possible because modulations of ±1st-order diffracted lights are included in bisected beams of semicircles when converged beams are crossed. |
