Patent ID: 8189452

Claim:
An optical recording medium having a plurality of information recording surfaces, the optical recording medium comprising: a cover layer having a refractive index nr 1 , and formed between a surface of the optical recording medium where light is incident and a first information recording surface closest to a medium surface; a first intermediate layer having a refractive index nr 2 , and formed between the first information recording surface and a second information recording surface second closest to the medium surface; and a second intermediate layer having a refractive index nr 3 , and formed between the second information recording surface and a third information recording surface third closest to the medium surface, wherein an actual thickness tr 1 of the cover layer is in such a range that a spherical aberration lies in a predetermined range, the range is determined based on a product of a thickness of the cover layer having a predetermined refractive index “no”, and a function g(n) expressed by the following formula (1), the thicknesses tr 1 , tr 2 , and tr 3 of the cover layer, the first intermediate layer, and the second intermediate layer are respectively converted into thicknesses t 1 , t 2 , and t 3 having a predetermined refractive index “no”, referring to a defocus value, the thicknesses t 1 , t 2 , and t 3 are calculated by products of a function f(n) expressed by the following formula (2), and the thicknesses tr 1 , tr 2 , and tr 3 , and the thicknesses t 1 , t 2 , and t 3 satisfy the following formula (3): g ( n )=−1.1111 n 3 +5.8143 n 2 −9.8808 n+ 6.476 (1) f ( n )=−1.088 n 3 +6.1027 n 2 −12.042 n+ 9.1007 (2) | t 1−( t 2+ t 3)|≧1 μm (3) in the formulas (1) and (2), n is the refractive index of each layer.