Optical disk having reduced track pitch and optical disk playback apparatus containing the same

摘要

An optical disk comprises a substrate, and a recording layer which is formed on the substrate and on which information is recorded at specific pitches in the form of pit trains, wherein the information is reproduced by projecting a light beam via an object lens, and when the wavelength of the light beam is lambda mu m and the numerical aperture of the object lens is NA, the track pitch is set in the range of (0.72 to 0.8)x lambda /NA/1.14 mu m, and each of the pits has a trapezoid cross section whose upper width is in the range of (0.3 to 0.5)x lambda /NA/1.14 mu m and whose lower width is in the range of (0.2 to 0.32)x lambda /NA/1.14 mu m or whose inner wall has an angle of 30 DEG to 70 DEG .