Optical recording medium and method for manufacturing the same

#1. Field of the Invention

#The present invention relates to an optical recording medium having three or more information recording layers and a method for manufacturing the optical recording medium.

#2. Description of the Related Art

#FIG. 1 is a block diagram illustrating an optical recording medium according to a first exemplary embodiment of the present invention and the structure of an optical pickup for reading and writing on the optical recording medium;

#FIG. 2 is a partially enlarged view illustrating the structure of the optical recording medium;

#FIG. 3 is a table showing first verified results for determining whether the optical recording medium has been appropriately designed;

#First, a description will be made to the principle of occurrence of crosstalk in an optical recording medium having four information recording layers. Note that crosstalk is mainly caused by multi-reflected beams or reflections of adjacent information recording layers.

#FIG. 8 shows a quad-layer optical recording medium 40. The optical recording medium 40 includes an L3 information recording layer 40a, an L2 information recording layer 40b, an L1 information recording layer 40c, and an L0 information recording layer 40d, in the order starting from the side of a light incident surface 40z. The optical recording medium 40 also has a cover layer 42, a third intermediate layer 43, a second intermediate layer 44, and a first intermediate layer 45. It is assumed that the thickness of the cover layer 42 (the material between the light incident surface 40z and the L3 information recording layer 40a) is TC, the thickness of the third intermediate layer 43 (the material between the L3 information recording layer 40a and the L2 information recording layer 40b) is T3, the thickness of the second intermediate layer 44 (the material between the L2 information recording layer 40b and the L1 information recording layer 40c) is T2, and the thickness of the first intermediate layer 45 (the material between the L1 information recording layer 40c and the L0 information recording layer 40d) is T1. It is also assumed that the distance from the light incident surface 40z to the L3 information recording layer 40a is d1 (approximately equal to TC), the distance from the light incident surface 40z to the L2 information recording layer 40b is d2 (approximately equal to TC+T3), the distance from the light incident surface 40z to the L1 information recording layer 40c is d3 (approximately equal to TC+T3+T2), and the distance from the light incident surface 40z to the L0 information recording layer 40d is d4 (approximately equal to TC+T3+T2+T1).

#Now, a description will first be made to the principle of occurrence of crosstalk caused by multi-reflected beams with reference to FIGS. 8 to 11. FIG. 8 shows that a beam 70 condensed on the L0 information recording layer 40d for reading or writing thereon is split into a plurality of optical beams due to the translucency of the information recording layer. FIG. 9 shows a phenomenon that a beam 71 split from the read and write beam for the L0 information recording layer 40d is reflected on the L1 information recording layer 40c and focused on the L2 information recording layer 40b. This reflected beam is reflected again on the L1 information recording layer 40c and then detected. This phenomenon is referred to as the rear focus beam of the information recording layer.