| 摘要 |
The present invention relates to a data medium to be read out by a focused reading beam having a predetermined wavelength. The data medium implements a new concept of generating a reference beam, by comprising a reference beam interface, which, in the propagation direction of the impinging reading beam, is arranged either in front of a data layer with a pit-and-land structure, and is partially reflective while the pit and land interface sections are fully reflective for the reading beam. Or the reference layer is arranged behind the first and second reflective interface sections, and is fully reflective while the pit and land interlace sections are partially reflective for the reading beam. The data medium of the invention has a number of between 5 and 20 channel-bit cells contained in a reference area A-ef defined by the square of the ratio between the reading beam wavelength WL and the numerical aperture NA of an optical system focusing the reading beam. The ratio between the sum of the areas of all pit interface sections and the sum of the areas of all land interface sections of the pit-and-land structure is between 0.4 and 0.6. |
