| 摘要 |
PURPOSE:To improve the C/N value of a high birefringence part and to make an optical disk applicable in a wide area by setting reproduced luminous energy with respect to the high birefringent part on a transparent substrate larger than a low birefringent part. CONSTITUTION:A reproduced light beam 9 from a semiconductor laser 3 is condensed on the information medium layer of the substrate 1 by an objective lens 7. The reflected light beam becomes a circularly deflected light beam if there is no birefringence on the substrate 1 and reflected by a beam spliter 5, and all split light enter a detector 8 as an effective signal light beam 13. If the substrate has the birefringence, the beam 11 becomes an elliptical light beam. Its vertical component becomes the effective light beam 13, and the horizontal one becomes an invalid signal light beam 14 to make a detection signal smaller. Since the birefringence becomes larger at the outer diameter side of the disk, the reproduced quantity of light 9 is increased or decreased in the disk diameter direction in accordance with the magnitude of the birefringence value to obtain the effective signal light beam 13 with the fixed quantity of light. Accordingly the high C/N value can be obtained even in the part at the high birefringence on the substrate, and the disk can be used in the wide area. |
