Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Utility Patent
1998-08-26
2001-01-02
Neyzari, Ali (Department: 2752)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S275100, C428S064100
Utility Patent
active
06169721
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium, and more particularly to a recording medium on which information is recorded at high density by a laser beam having a comparatively short wavelength.
Heretofore, as an optical recording medium having a recording layer of an organic coloring matter, a CD-R is used with a laser beam having a recording and reproducing wavelength of 780 nm.
In order to enable the organic recording medium to be increased in recording density, the recording track pitch must be reduced and the width of a recording pit must also be reduced. In the case that a small pitch is accurately recorded on the recording truck having a narrow pitch, it is necessary to focus a small recording beam on the truck by restricting the distribution of the diffraction of the laser beam in the recording optical system. To this end, it is necessary to increase the numerical aperture (NA) of the objective lens, and to reduce the wavelength of the laser beam.
On the other hand, it is desirable to provide an optical recording medium having a recording layer on which information can be recorded by a laser beam having a wavelength smaller than 780 nm, 830 nm.
In the case of CD-R, if a laser beam having a wavelength shorter than 780 nm is focused on the disc at a pit smaller than the conventional pit, a sufficient reflectance can not be obtained. Consequently, the modulation factor of a high frequence (HF) signal which is obtained by the reflectance is extremely low, so that information is not adequately recorded and reproduced.
Furthermore, on the optical disc, the wobble groove is spirally formed so as to guide the laser beam to the truck.
The width and depth of the wobble groove are selected in accordance with the wavelength of the laser beam so that the jitter and reflectance are adjusted.
Therefore, the shape of the wobble groove must be determined so as to meet the short wavelength.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical recording medium which is suitable for optical recording with a laser beam having a short wavelength, specifically a wavelength of 600-700 nm.
According to the present invention, there is provided an optical recording medium having a substrate having a spiral groove or annular grooves, prepits between the grooves, a recording layer including an organic coloring matter and formed on the substrate, and a metallic reflection layer, comprising the recording layer having a thickness so as have an absorbance between 0.65 and 0.75, whereby information can be recorded in the recording layer by a laser beam having a wavelength between 600 and 700 nm, using an objective lens having a numerical aperture between 0.55 and 0.70.
The organic coloring matter included in the recording medium is a complex of an azo compound.
The metallic reflection layer is made of a gold film, depth of the groove is between 140 and 160 nm, width thereof is between 0.25 and 0.35 &mgr;m.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.
REFERENCES:
patent: 5955168 (1999-09-01), Min et al.
Hanzawa Shinichi
Kondo Atsushi
Kusama Miki
Matsukawa Makoto
Mitsumori Ayumi
Arent Fox Kintner Plotkin & Kahn PLC
Neyzari Ali
Pioneer Electronic Corporation
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