Conventionally, as an optical recording medium, a disk-shaped optical recording medium has widely spread, and CDs (Compact Discs), DVDs (Digital Versatile Discs), Blu-ray Discs (registered trademark, which Blu-ray Discs will hereinafter be referred to as BDs), and the like are generally used.
In this optical recording medium, a recording layer is irradiated with condensed light, and the presence or absence of a recording mark formed in the recording layer is detected from an amount of light reflected from the recording layer. At this time, the size of the spot of the light condensed by an objective lens is given by approximately λ/NA (λ=Wavelength of Light and NA=Numerical Aperture of Objective Lens), and resolution is proportional to this value.
In the optical recording medium, an amount of information recordable per recording layer can be increased by reducing the size of the spot of the light. For example, Non-Patent Document 1 describes details of a BD, which optical recording medium of 12 [cm] in diameter has information of 25 [GB] recorded thereon.
The optical recording medium causes a spherical aberration according to a distance from the surface thereof to the recording layer. Thus, an optical information recording and reproducing device ready for such an optical recording medium adds a spherical aberration to condensed light in advance, and thereby suppresses the spherical aberration in the vicinity of the focus of the light and keeps the size of the spot small.
Incidentally, the optical information recording and reproducing device records various information such as various kinds of contents including music contents and video contents, various kinds of data for computers, or the like onto the optical recording medium. In particular, there have recently been an increase in amount of information due to higher definition of video, higher sound quality of music, and the like, and a demand for an increase in number of contents to be recorded on one optical recording medium. There is thus a desire for even higher capacity of the optical recording medium.
Accordingly, as one method for increasing the capacity of the optical recording medium, an optical recording medium has been proposed in which a material forming a recording mark according to light is used and information is recorded three-dimensionally in a direction of thickness of the optical recording medium (see Patent Document 1, for example).
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