Optical recording medium, and optical information device

An optical recording medium having a plurality of information recording surfaces, the optical recording medium comprising:

• the first information recording surface closest to a medium surface of the optical recording medium where light is incident;
• the second information recording surface second closest to the medium surface;
• the third information recording surface third closest to the medium surface;
• the fourth information recording surface fourth closest to the medium surface;
• a cover layer having a refractive index nr1 and formed between the medium surface and the first information recording surface;
• a first intermediate layer having a refractive index nr2 and formed between the first information recording surface and the second information recording surface;
• a second intermediate layer having a refractive index nr3 and formed between the second information recording surface and the third information recording surface;
• and
• a third intermediate layer having a refractive index nr4 and formed between the third information recording surface and the fourth information recording surface, wherein
• in the case where shape-wise thicknesses tr1, tr2, tr3, and tr4 of the cover layer, the first intermediate layer, the second intermediate layer, and the third intermediate layer are respectively converted into thicknesses t1, t2, t3, and t4 of the respective corresponding layers each having a predetermined refractive index “no”, and
• in the case where a thickness of the layer having the refractive index nrα is set to trα (satisfying:
• 1≦α≦n (where α is a positive integer and n is an integer of 4 or more)), a convergence angle of light in the layer having the refractive index nrα is set to θrα (satisfying:
• 1≦α≦n (where α is a positive integer and n is an integer of 4 or more)), a thickness of the layer having the refractive index “no” is set to tα (satisfying:
• 1≦α≦n (where α is a positive integer and n is an integer of 4 or more)), and a convergence angle of light in the layer having the refractive index “no” is set to θo, if the thickness trα is converted into the thickness tα based on the following equation,
• tα=trα·tan(θrα)/tan(θo)),
• the thicknesses t1, t2, t3, and t4 satisfy
• |t1−(t2+t3+t4)|≧1 μm,
• a difference between any two values of the thicknesses t1, t2, t3, and t4 is set to 1 μm or more in any case, and
• |(t1+t2)−(t3+t4)|≧1 μm.

An optical recording medium having a plurality of information recording surfaces, the optical recording medium comprising:

• the first information recording surface closest to a medium surface of the optical recording medium where light is incident;
• the second information recording surface second closest to the medium surface;
• the third information recording surface third closest to the medium surface;
• a cover layer having a refractive index nr1 and formed between the medium surface and the first information recording surface;
• a first intermediate layer having a refractive index nr2 and formed between the first information recording surface and the second information recording surface;
• and
• a second intermediate layer having a refractive index nrα and formed between the second information recording surface and the third information recording surface, wherein
• in the case where shape-wise thicknesses tr1, tr2, tr3, and tr4 of the cover layer, the first intermediate layer, and the second intermediate layer are respectively converted into thicknesses t1, t2, t3, and t4 of the respective corresponding layers each having a predetermined refractive index “no”,
• a defocus amount with respect to a layer having a refractive index nrα and a thickness trα (satisfying:
• 1≦α≦n (where α is a positive integer and n is an integer of 3 or more)), and a defocus amount with respect to a layer having the refractive index “no” and a thickness tα (satisfying:
• 1≦α≦n (where α is a positive integer and n is an integer of 3 or more)) are equal to each other, and
• the thicknesses t1, t2, and t3 satisfy
• |t1−(t2+t3)|≧1 μm, and
• a difference between any two values of the thicknesses t1, t2, and t3 is set to 1 μm or more in any case.

An optical recording medium having a plurality of information recording surfaces, the optical recording medium comprising:

• the first information recording surface closest to a medium surface of the optical recording medium where light is incident;
• the second information recording surface second closest to the medium surface;
• the third information recording surface third closest to the medium surface;
• a cover layer having a refractive index nr1 and formed between the medium surface and the first information recording surface;
• a first intermediate layer having a refractive index nr2 and formed between the first information recording surface and the second information recording surface;
• and
• a second intermediate layer having a refractive index nr3 and formed between the second information recording surface and the third information recording surface, wherein
• in the case where shape-wise thicknesses tr1, tr2, and tr3 of the cover layer, the first intermediate layer, and the second intermediate layer are respectively converted into thicknesses t1, t2, and t3 of the respective corresponding layers each having a predetermined refractive index “no”, and
• in the case where a thickness of the layer having the refractive index nrα is set to trα (satisfying:
• 1≦α≦n (where α is a positive integer and n is an integer of 3 or more)), a convergence angle of light in the layer having the refractive index nrα is set to θrα (satisfying:
• 1≦α≦n (where α is a positive integer and n is an integer of 3 or more)), a thickness of the layer having the refractive index “no” is set to tα (satisfying:
• 1≦α≦n (where α is a positive integer and n is an integer of 3 or more)), and a convergence angle of light in the layer having the refractive index “no” is set to θo, if the thickness trα is converted into the thickness tα based on the following equation,
• tα=trα·(tan(θrα)/tan(θo)),
• the thicknesses t1, t2, and t3 satisfy
• |t1−(t2+t3)|≧1 μm, and
• a difference between any two values of the thicknesses t1, t2, and t3 is set to 1 μm or more in any case.