Optical disk and optical disk drive

#The present invention relates to an optical disk and an optical disk drive which are capable of super-resolution reproduction.

#Optical disk memories, which accomplish information reproduction alone or information recording and reproduction by irradiation of a light beam, have been put to practical use as high capacity, fast-access and portable storage media for various files, such as audio data, image data and computer data, and it is expected that their development will continue. Techniques for increasing the density of optical disks include shortening the wavelength of a gas laser for cutting a master, shortening the wavelength of a semiconductor laser as an operating light source, increasing the numerical aperture of an objective lens and making optical disks thinner. Further, with regard to recordable optical disks, various approaches such as mark length recording and land/groove recording are possible.

#As a technique having a great effect on improvement on the density of an optical disk, a super-resolution reproduction technique utilizing a medium film has been proposed. The super-resolution reproduction technique was originally proposed as a technique specific to a magneto-optical disk. According to the super-resolution reproduction technique for the magneto-optical disk, a magnetic film (a super-resolution film) is disposed on the reproduction-beam incident side with respect to a recording layer, and both are exchange-coupled or magnetostatically coupled. Then, the temperature of the super-resolution film is raised by irradiation of a reproduction beam to change exchange force or magnetostatic force, thereby forming an optical mask or an optical aperture in the super-resolution film to realize super-resolution reproduction.

#FIG. 1 is a cross-sectional view showing a basic construction of the optical disk according to the present invention;

#FIG. 2 is a graph showing a relationship between number of incident photons (Np) and transmittance (Tr) with a super-resolution film according to the present invention;

#FIG. 3 is a diagram showing a relationship among recording marks, a reproduction beam spot and an optical aperture;

#The present invention will be explained in more detail hereinafter.

#FIG. 1 shows a cross-sectional view illustrating an example of an optical disk according to the present invention. The optical disk shown in FIG. 1 has a structure in which a super-resolution film 12, an intermediate layer 13, a recording layer 14 and a protective layer 15 are formed on a disk substrate 11. The intermediate layer 13 and the protective layer 15 are provided if desired. A reproduction beam enters the substrate 11, passes through the super-resolution film 12 and the intermediate layer 13 and is incident on the recording layer 14. Thus, the super-resolution film 12 is disposed on the reproduction-beam incident side with respect to the recording layer 14. The reflected beam from the recording layer 14 is detected by a photodetector, and then the output signals from the photodetector are processed to generate reproduction signals.

#The super-resolution film employed in the present invention should be formed of a semiconductor fine-particle dispersed film having a structure in which semiconductor fine particles are dispersed in a matrix, or formed of a semiconductor continuous film. The semiconductor fine particles may be agglomerated in the fine-particle dispersed film. The super-resolution film consisting of the semiconductor continuous film may have a quantum well structure constituted by a superlattice in which two or more semiconductor layers are stacked. A quantum size effect is expected with the quantum well structure. Among these super-resolution films, the fine-particle dispersed film is most preferable.