Optical recording medium, and optical information device

Abstract

An object of the invention is to provide an optical recording medium and an optical information device that enable to improve the quality of a servo signal and a reproduction signal. In the case where shape-wise thicknesses tr 1, tr 2, tr 3, and tr 4 of a cover layer ( 42 ), a first intermediate layer ( 43 ), a second intermediate layer ( 44 ), and a third intermediate layer ( 45 ) are respectively converted into thicknesses t 1, t 2, t 3, and t 4 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 4 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 4 or more)) are equal to each other; and the thicknesses t 1, t 2, t 3, and t 4 satisfy |t 1− (t 2+ t 3+ t 4 )|≧1 μm, a difference between any two values of the thicknesses t 1, t 2, t 3, and t 4 is set to 1 μm or more in any case, and |(t 1+ t 2 )−(t 3+ t 4 )|≧1 μm.

1 . 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 nr 1  and formed between the medium surface and the first information recording surface; 
 a first intermediate layer having a refractive index nr 2  and formed between the first information recording surface and the second information recording surface; 
 a second intermediate layer having a refractive index nr 3  and formed between the second information recording surface and the third information recording surface; and 
   a third intermediate layer having a refractive index nr 4  and formed between the third information recording surface and the fourth information recording surface, wherein   in the case where shape-wise thicknesses tr 1 , tr 2 , tr 3 , and tr 4  of the cover layer, the first intermediate layer, the second intermediate layer, and the third intermediate layer are respectively converted into thicknesses t 1 , t 2 , t 3 , and t 4  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 4 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 4 or more)) are equal to each other, and   the thicknesses t 1 , t 2 , t 3 , and t 4  satisfy
   | t 1−( t 2 +t 3 +t 4)|≧1 μm,
 
 a difference between any two values of the thicknesses t 1 , t 2 , t 3 , and t 4  is set to 1 μm or more in any case, and
   |( t 1+ t 2)−( t 3+ t 4)|≧1 μm.
 
 
   
     
     
         2 . 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 nr 1  and formed between the medium surface and the first information recording surface; 
 a first intermediate layer having a refractive index nr 2  and formed between the first information recording surface and the second information recording surface; 
 a second intermediate layer having a refractive index nr 3  and formed between the second information recording surface and the third information recording surface; and 
   a third intermediate layer having a refractive index nr 4  and formed between the third information recording surface and the fourth information recording surface, wherein   in the case where shape-wise thicknesses tr 1 , tr 2 , tr 3 , and tr 4  of the cover layer, the first intermediate layer, the second intermediate layer, and the third intermediate layer are respectively converted into thicknesses t 1 , t 2 , t 3 , and t 4  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(θ r α)/tan(θ o )),
 
   the thicknesses t 1 , t 2 , t 3 , and t 4  satisfy
   | t 1−( t 2+ t 3+ t 4)|≧1 μm,
 
 a difference between any two values of the thicknesses t 1 , t 2 , t 3 , and t 4  is set to 1 μm or more in any case, and
   |( t 1+ t 2)−( t 3+ t 4)|≧1 μm.
 
 
   
     
     
         3 . The optical recording medium according to  claim 1 , wherein
 in the case where a range of the thickness tα of the layer having the refractive index “no” and whose spherical aberration amount falls in a predetermined allowable range is converted into a range of the thickness trα of the layer having the refractive index nrα,   the thickness trα is included in the range of the thickness trα after conversion.   
     
     
         4 . The optical recording medium according to  claim 1 , wherein
 the refractive index “no” is set to 1.60.   
     
     
         5 . The optical recording medium according to  claim 1 , wherein
 the thicknesses t 1 , t 2 , t 3 , and t 4  are each set to 10 μm or more.   
     
     
         6 . 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 nr 1  and formed between the medium surface and the first information recording surface; 
 a first intermediate layer having a refractive index nr 2  and formed between the first information recording surface and the second information recording surface; and 
 a second intermediate layer having a refractive index nr 3  and formed between the second information recording surface and the third information recording surface, wherein 
 in the case where shape-wise thicknesses tr 1 , tr 2 , tr 3 , and tr 4  of the cover layer, the first intermediate layer, and the second intermediate layer are respectively converted into thicknesses t 1 , t 2 , t 3 , and t 4  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 t 1 , t 2 , and t 3  satisfy
   | t 1−( t 2+ t 3)|≧1 μm, and
 
 
 a difference between any two values of the thicknesses t 1 , t 2 , and t 3  is set to 1 μm or more in any case. 
   
     
     
         7 . 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 nr 1  and formed between the medium surface and the first information recording surface; 
 a first intermediate layer having a refractive index nr 2  and formed between the first information recording surface and the second information recording surface; and 
   a second intermediate layer having a refractive index nr 3  and formed between the second information recording surface and the third information recording surface, wherein   in the case where shape-wise 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  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(θ r α)/tan(θ o )),
 
   the thicknesses t 1 , t 2 , and t 3  satisfy
   | t 1−( t 2+ t 3)|≧1 μm, and
 
 a difference between any two values of the thicknesses t 1 , t 2 , and t 3  is set to 1 μm or more in any case. 
   
     
     
         8 . The optical recording medium according to  claim 6 , wherein
 in the case where a range of the thickness tα of the layer having the refractive index “no” and whose spherical aberration amount falls in a predetermined allowable range is converted into a range of the thickness trα of the layer having the refractive index nrα,
 the thickness trα is included in the range of the thickness trα after conversion. 
   
     
     
         9 . The optical recording medium according to  claim 6 , wherein
 the refractive index “no” is set to 1.60.   
     
     
         10 . The optical recording medium according to  claim 6 , wherein
 the thicknesses t 1 , t 2 , and t 3  are each set to 10 μm or more.   
     
     
         11 . An optical information device for reproducing or recording with respect to the optical recording medium of  claim 1 , the optical information device comprising:
 an optical head device; and   a motor which rotates the optical recording medium, wherein   the optical head device shifts a focus position of the laser light to be irradiated onto the optical recording medium from a certain information recording surface to another information recording surface out of the plurality of the information recording surfaces to reproduce or record information with respect to the plurality of the information recording surfaces.   
     
     
         12 . The optical information device according to  claim 11 , further comprising:
 an electric circuit which controls and drives the motor and the optical head device, based on a signal to be obtained from the optical head device, wherein   the electric circuit controls the optical head device in such a manner as to correct a spherical aberration with respect to a targeted information recording surface out of the plurality of the information recording surfaces, before shifting the focus position.   
     
     
         13 . An optical information device for reproducing or recording with respect to the optical recording medium of  claim 6 , the optical information device comprising:
 an optical head device; and   a motor which rotates the optical recording medium, wherein   the optical head device shifts a focus position of the laser light to be irradiated onto the optical recording medium from a certain information recording surface to another information recording surface out of the plurality of the information recording surfaces to reproduce or record information with respect to the plurality of the information recording surfaces.   
     
     
         14 . The optical information device according to  claim 13 , further comprising:
 an electric circuit which controls and drives the motor and the optical head device, based on a signal to be obtained from the optical head device, wherein   the electric circuit controls the optical head device in such a manner as to correct a spherical aberration with respect to a targeted information recording surface out of the plurality of the information recording surfaces, before shifting the focus position.