As optical information recording mediums for use in recording/reproducing information by irradiation with laser light, a magnetic optical disk (MO) or CD-R, or CD-RW, DVD-R, DVD-RAM, DVD-RW and the like have been generally known. As means for raising recording densities in the optical information recording mediums, land/groove recording has been known in which the recording is performed in recording layer portions corresponding to both a flat portion (land) between adjacent guide grooves for tracking, the guide grooves being formed into substantially circular shapes in parallel with one another in a substrate surface, and the inside of each guide groove (JP(A)-57-50330, JP(A)-9-73665, JP(A)-9-198716, JP(A)-10-64120 and the like).
Moreover, in recent years, as a method of raising a recording density, a technique has been proposed in which NA of an objective lens of an optical head constituting a device for recording/reproducing information is raised to about 0.85. When the NA is raised, a beam diameter in condensing laser light can be reduced, and therefore it is possible to record/reproduce a finer mark. When the NA is raised in this manner, instead of applying the laser light from the side of a support substrate having a thickness of 0.6 to 1.2 mm as in a conventional technique, a light-transmitting layer having a thickness of about 0.1 mm is formed on the surface of the optical information recording medium in which the guide groove for tracking is formed, and the laser light can be applied from the side of the light-transmitting layer to record/reproduce information.
Moreover, the raising of the recording density by shortening of a wavelength of a laser light source has also been intensively studied. It has been expected that three times or higher recording density be realized by use of a bluish-purple semiconductor laser having a wavelength of around 405 nm as compared with a red semiconductor laser for use in recording/reproducing a conventional DVD.
On the other hand, to improve a signal quality of the optical information recording medium, a low-to-high (L-H) recording system is effective in which reflectance of the recording layer before the recording is lowered in such a manner as to raise the reflectance of the recording layer after the recording. In this system, since the reflectance of the recording layer before the recording is lowered beforehand, a modulation degree can be raised, and therefore C/N can be raised as compared with a conventional high-to-low (H-L) recording system for use in DVD-RAM or DVD-RW, whose reflectance of the recording layer after the recording lowers.
It is considered that these techniques are combined, that is, the land/groove recording is performed with respect to the optical information recording medium of the L-H system having a high signal quality, using a short-wavelength light source such as a bluish-purple semiconductor laser, and an optical head having a high NA, so that the recording density is significantly increased.
Additionally, one of large technique problems in performing the land/groove recording is leakage of a signal from an adjacent track, so-called crosstalk. When a pitch of the guide groove for tracking is reduced in order to increase the recording density, crosstalk components from information recorded in the adjacent track are increased, and it is therefore difficult to correctly reproduce the information in a target track (self track).
USPTO Backgrounds
USPTO Backgrounds