| 摘要 |
PURPOSE:To constitute so that a double refractive index of an optical system reduced to zero equivalently by placing the direction of anisotropy of a transparent compensating plate having an optical anisotropy, at a right angle with the direction of anisotropy of an optical disk board. CONSTITUTION:When forming a plastic board 7, it is formed in a state that refractive indexes in the X and Y directions are different each other. In a constitution consisting of a transparent plate 8, objective lens 9, the optical disk board 7 and a recording layer 10, when the refractive indexes in the X and Y directions of the disk substrate 7 are denoted as nsx, nsy, and the refractive indexes in the X and Y directions of the transparent compensating plate 8 are denoted as ncx, ncy, they are made to obtain the refractive index nsx=ncy and the refractive index nsy=ncx. For that purpose, the transparent plate 8 having an anisotropy of the same formation as the board 7 is set at a right angle with the direction of anisotropy of the board 7. Accordingly, the double refractive index becomes zero even if a board of polycarbonate resin, etc. which is not influenced by a temperature nor humidity is used, and recording and reproducing can be executed exactly by just focusing. |
