| 摘要 |
PURPOSE:To obtain a regenerative signal having the large degree of modulation, and to reduce the level change of a tracking signal regardless of the presence or absence of a recording by constituting each of the state of a recording layer before the recording and the difference of the actual number parts of the refractive index of the recording layer before and after a photoirradiation for the recording so as to fulfill a specific condition. CONSTITUTION:An optical disk is composed of a transparent substrate 1 having a tracking groove 5 whose depth is G, whose refractive index is n1, recording layer 2 having a sensitivity at the wave length lambda of a light for recording, whose refractive index is changed from n2 to n2r by the photoirradiation, metallic reflecting layer 3, and a protecting layer 4 or the like. The state of the layer 2 before the recording fulfills the expression I, and the difference DELTAn of the actual numbers of the refractive index before and after the photoirradiation fulfills the expression II. Thus, the optical disk in which the regenerative signal having the large degree of modulation can be obtained, and the change of the tracking signal level can be reduced regardless of the presence or absence of the recording, can be obtained. In the expression, d1 indicates the thickness of the layer 2 at a part except the guide groove of the transparent substrate, and d2 indicates the thickness of the layer 2 at the guide groove part. |
