Phase-change optical storage medium
An optical storage medium has a substrate having a first surface and a second surface on both sides, the first surface allowing light to pass therethrough in recording or reproduction. The medium also has at least one composite layer having at least a first protective film, a second protective film and a recording film formed in order on the second surface, the first and second protective films exhibiting refractive indices n 1 and n 2 , respectively, having the following relations therebetween, to the light having a specific wavelength λ: n 1 >n 2 , n 1 −n 2≧ 0.02 and 2.1≦n 1≦ 2.5, 1.5≦n 2≦ 2.1. The composite layer may have at least a first protective film, a second protective film, a third protective film and a recording film formed in order on the second surface, the first, second and third protective films exhibiting refractive indices n 21, n 22 and n 23, respectively, having a relation n 21 >n 22 >n 23 or n 22 >n 21 >n 23 thereamong, to the light having a specific wavelength λ.
1 . An optical storage medium comprising:
a substrate having a first surface and a second surface on both sides, the first surface allowing light to pass therethrough in recording or reproduction; and
at least one composite layer having at least a first protective film, a second protective film and a recording film formed in order on the second surface, the first and second protective films exhibiting refractive indices n 1 and n 2 , respectively, having the following relations therebetween, to the light having a specific wavelength λ:
n1>n2 (1)
n1−n2≧0.02 (2)
2.1≦n1≦2.5, 1.5≦n2<2.1 (3).
2 . The optical storage medium according to claim 1 , wherein the specific wavelength λ is in the range from 405 nm to 680 nm.
3 . The optical storage medium according to claim 1 , wherein the first and second protective films have thicknesses d 1 and d 2 , respectively, having a relation 0.17≦(d 1 +d 2 )/λ≦0.25 with the specific wavelength λ.
4 . The optical storage medium according to claim 1 , wherein the first protective film is formed with a material including at least ZnS and the second protective film is formed with a material including at least ZnS and SiO 2 .
5 . The optical storage medium according to claim 1 , wherein the first protective film is formed with a material including at least ZnS and SiO 2 with a molar ratio α 1 of 0<α 1 ≦0.2 for SiO 2 and the second protective film is formed with a material including at least ZnS and SiO 2 with a molar ratio α 2 of 0.3≦α 2 ≦0.8 for SiO 2 .
6 . The optical storage medium according to claim 1 further comprising another composite layer that is located closer than the one composite layer to the second surface, the one composite layer exhibiting a reflectivity of 28% or higher to the specific wavelength α.
7 . An optical storage medium comprising:
a substrate having a first surface and a second surface on both sides, the first surface allowing light to pass therethrough in recording or reproduction; and
at least one composite layer having at least a first protective film, a second protective film, a third protective film and a recording film formed in order on the second surface, the first, second and third protective films exhibiting refractive indices n 21 , n 22 and n 23 , respectively, having either of the following relations thereamong, to the light having a specific wavelength λ:
n21>n22>n23 (1)
n22>n21>n23 (2).
8 . The optical storage medium according to claim 7 , wherein the specific wavelength λ is in the range from 405 nm to 680 nm.
9 . The optical storage medium according to claim 7 , wherein the smallest difference Δn among absolute values of differences between two refractive indices |n 21 −n 22 |, |n 22 −n 23 | and |n 21 −n 23 | is 0.01 or larger.
10 . The optical storage medium according to claim 7 , wherein the first, second and third protective films have thicknesses d 21 , d 22 and d 23 , respectively, having a relation 0.17≦(d 21 +d 22 +d 23 )/λ≦0.26 with the specific wavelength λ.
11 . The optical storage medium according to claim 7 , wherein the first and second protective films are formed with a material including at least ZnS and the third protective film is formed with a material including at least ZnS and SiO 2 .
12 . The optical storage medium according to claim 7 , wherein each of the first, second and third protective film is formed with a material including at least ZnS and SiO 2 with a molar ratio a of 0<α<0.8 for SiO 2 .
13 . The optical storage medium according to claim 7 further comprising another composite layer that is located closer than the one composite layer to the second surface, the one composite layer exhibiting a reflectivity of 28% or higher to the specific wavelength λ.