| 摘要 |
PROBLEM TO BE SOLVED: To improve recording density and to increase a processing speed by recording disk information to be recorded as an error correction code by a product code and constituting so that respective symbols incorporated in a one side code word are separated sufficiently. SOLUTION: A recording medium 1 is constituted so as to record/reproduce information through a thinner protective layer 4 not to record/reproduce through a substrate 2. Here, the protection layer 4 is defined 1.5 in a refractive index and 0.5mm in a thickness. A numerical aperture NA of an objective lens 11 is 0. 74. At this time, a period of an information track on a recording layer 3 is capable of making 1μm. Thus, the thickness of the transparent protection layer through which a light beam for recording/reproducing transmits is thinned, and thus, the objective lens with the large NA becomes usable, and the high recording density is realized. |
