| 摘要 |
PROBLEM TO BE SOLVED: To exactly record or reproduce information in the case of using a two-group lens by recording the information of layer thickness and the information of refractive index of a light transmission layer of a recording medium. SOLUTION: An optical disk 1 is irradiated with a laser beam from a pickup 14, by which the information is recorded or reproduced thereon. When the optical disk 1 is inserted, a control microcomputer 23 fetches the production information recorded on the optical disk 1 and stores the same in RAM 25. The production information stored therein contains a specification value of the light transmission layer thickness of the optical disk 1, a refractive index of the light transmission layer and an average and variation of the layer thickness in a radial direction of the optical disk 1 which is obtained as a result of inspection of the layer thickness after the production of the optical disk 1. The control microcomputer 23 records a data table or an approximate calculation expression of optimum interval of the two-group lens on ROM 26 in a case where the thickness and the refractive index of the light transmission layer is changed, by which the driving value to an actuator for correcting aberration which achieves the optimum interval of the two-group lens lessening spherical aberration is outputted. |
