Optical storage medium
View Patent ↗An optical disc has a first transparent substrate, a second substrate, and at least a first and a second recording layer formed between the substrates. The first substrate has a first surface and an opposing second surface, the first surface is a beam incidence surface for a laser beam, the second surface having a first concave section and a first convex section formed adjacent to each other thereon, the first concave section being farther than the first convex section from the incidence surface, first pre-pits being formed on the first concave section. The second substrate has a second concave section and a second convex section formed adjacent to each other thereon, the second concave section being farther than the second convex section from the incidence surface, second pre-pits being formed on the second concave section, a top surface of each second pre-pit being closer than a top surface of the second convex section to the beam surface. The second recording layer is farther than the first recording layer from the incidence surface. The second recording layer is formed with a dye mixture of cyanine dye and imonium dye having relations Wa>Wb and na>nb, in which Wa and Wb are a mass of the cyanine dye and the imonium dye, respectively, and “na” and “nb” are refractive indices of the cyanine dye and the imonium dye, respectively, to the laser beam having a specific wavelength, and having a relation na−nc>0.1 in which “nc” is a refractive index of the dye mixture.
1. An optical disc comprising:
a first transparent substrate having a first surface and an opposing second surface, the first surface being a beam incidence surface for a laser beam in recording or reproduction of data, the second surface having a first concave section and a first convex section formed adjacent to each other on the second surface, the first concave section being farther than the first convex section from the beam incidence surface, first pre-pits carrying auxiliary information related to the data being formed on the first concave section;
a second substrate having a third surface having a second concave section and a second convex section formed adjacent to each other, the second surface of the first substrate and the third surface facing each other, the second concave section being farther than the second convex section from the beam incidence surface, second pre-pits carrying auxiliary information related to the data being formed on the second concave section, a top surface of each second pre-pit being closer than a top surface of the second convex section to the beam incidence surface; and
at least a first recording layer and a second recording layer formed between the first and second substrates, the second recording layer being farther than the first recording layer from the beam incidence surface, the second recording layer being formed with dye mixture including cyanine dye and imonium dye having relations Wa>Wb and na>nb, in which Wa and Wb are a mass of the cyanine dye and the imonium dye, respectively, and “na” and “nb” are refractive indicies of the cyanine dye and the imonium dye, respectively, to the laser beam having a specific wavelength, and having a relation na−nc>0.1 in which “nc” is a refractive index of the dye mixture.
2. The optical disc according to claim 1 wherein a percentage of the imonium dye in the dye mixture is in the range from 10% to 50%.
3. The optical disc according to claim 1 wherein the specific wavelength is 650 nm.