Optical disk and recording/reproducing method thereof

DETAILED DESCRIPTION OF THE INVENTION FIG.
1 shows an example of the structure of an optical disk according to the present invention.
On the optical disk 1, a super-resolution film for reproduction 2, a first interference film 3, a recording layer 4, a second interference film 5, a super-resolution film for recording 6, and a reflective film 7 are formed.
In case of this optical disk, the super-resolution film for reproduction 2 is formed in the light entering side in which a light beam enters of the recording layer 4 while the super-resolution film for recording 6 is the side opposite to the light entering side.
FIG.
2 shows a curve (R) showing relationship between transmittance (Tr) of the super-resolution film for reproduction 2 and irradiation photon number density (Np), and a curve (W) showing relationship between transmittance (Tr) of the super-resolution film for recording 6 and the irradiation photon number density (Np).
Note that the abscissa in FIG.
2 can be replaced with the film temperature if the super-resolution film is a heat mode material.
The super-resolution film for reproduction 2 shows low transmittance within a range in which the irradiation photon number density is lower than the photon number density (Nr) during reproduction, but shows high transmittance within a range in which the irradiation photon number density is higher than Nr.
This means that an optical aperture smaller than the spot size can be formed in the region of the super-resolution film for reproduction 2 corresponding to the central portion of the reproduction beam spot by appropriately setting the reproduction power.
Further, the reproduction beam reaches the recording layer 4 through the optical aperture and is reflected therefrom, and therefore, super-resolution reproduction can be realized by detection the reflected light therefrom.
The super-resolution film for reproduction 2 may be referred to as a masking film for super-resolution reproduction because of the above functions.
Meanwhile, the super-resolution film for recording 6 shows low transmittance within a range in which the irradiation photon number density is lower than photon number density (Nw) during recording, but shows a high transmittance within a range in which the irradiation photon number density is higher than Nw