Optical recording medium, manufacturing method for optical recording medium, information recording/reproducing method and information recording/reproducing device

Abstract

An optical recording medium is capable of preventing a back focus at the face thereof and reducing the interference between beams reflected by each recording surface, thereby improving the quality of a servo signal and a reproductive signal. In a disk having (N-1) layers if N is a natural number (more than three), if a cover-layer thickness and intermediate-layer thicknesses are d 1 , d 2 , . . . dN, then a difference of 1 μm or above is set between the sum of di to dj and the sum of dk to dm for arbitrary natural numbers i, j, k, m (i≦j≦k≦m≦N). If the refractive indexes are different from a standard value or different for each layer, the thickness of each layer is converted on the basis of the spread width of light according to the thickness.

1 . A manufacturing method for an optical recording medium which has information recording surfaces in (N-1) layers if N is a natural number (more than three), wherein:
 if a cover-layer thickness and intermediate-layer thicknesses are d 1 , d 2 , . . . dN, then a difference DFF between the sum of di to dj and the sum of dk to dm for arbitrary natural numbers i, j, k, m (i≦j≦k≦m≦N) is 1 μm or above; and   the difference DFF is calculated by converting a shape thickness dr of a part having a refractive index nr different from a standard value no into a thickness do corresponding to the refractive index no which generates the same light-beam spread width as a light-beam spread width at the thickness dr.   
     
     
         2 . The manufacturing method for an optical recording medium according to  claim 1 , wherein
 if NA is a numerical aperture when light converged on the optical recording medium by an objective lens, θr and θo are a convergent angle of light inside of a substance having the refractive index nr and no, respectively, and sin and tan are a sine function and a tangent function, respectively, then   the thickness dr of the part having the refractive index nr is converted into the thickness do of the refractive index no in relational expressions:
   θ r =arc sin( NA/nr ), θ o =arc sin( NA/no ) and 
     do=dr ·tan(θ r )/tan(θ o ). 
   
     
     
         3 . A manufacturing method for an optical recording medium which has information recording surfaces in (N-1) layers if N is a natural number (more than three), wherein:
 if a cover-layer thickness and intermediate-layer thicknesses are d 1 , d 2 , . . . dN, then a difference DFF between the sum of di to dj and the sum of dk to dm for arbitrary natural numbers i, j, k, m (i≦j≦k≦m≦N) is 1 μm or above; and   a target value for a shape thickness dr of a part having a refractive index nr different from a standard value no is obtained by calculating a thickness do corresponding to the refractive index nr which generates the same light-beam spread width as a light-beam spread width at the thickness do corresponding to the refractive index no.   
     
     
         4 . The manufacturing method for an optical recording medium according to  claim 3 , wherein
 if NA is a numerical aperture when light converged on the optical recording medium by an objective lens, θr and θo are a convergent angle of light inside of a substance having the refractive index nr and no, respectively, and arc sin and tan are an inverse sine function and a tangent function, respectively, then   the thickness do of the part having the refractive index no is converted into the thickness dr of the refractive index nr in relational expressions:
   θ r =arc sin( NA/nr ), θ o =arc sin( NA/no ) and 
     dr=do ˜tan(θ o )/tan(θ r ). 
   
     
     
         5 . The manufacturing method for an optical recording medium according to  claim 1 , wherein the intermediate-layer thickness and the refractive index are set in such a way that a spherical aberration is within a specified range. 
     
     
         6 . An optical recording medium which has three or more recording layers manufactured by the manufacturing method for an optical recording medium according to  claim 1 . 
     
     
         7 . An optical information device which executes reproduction or recording for the optical recording medium according to  claim 6 , comprising:
 an optical head unit;   a motor rotating an optical disk; and   an electric circuit which receives a signal obtained from the optical head unit and controls and drives the motor, an objective lens or a laser light source,   wherein prior to a focus jump, the electric circuit corrects a spherical aberration generated on an intermediate layer at which the focus jump is to be made and moves a focal position.   
     
     
         8 . The manufacturing method for an optical recording medium according to  claim 3 , wherein the intermediate-layer thickness and the refractive index are set in such a way that a spherical aberration is within a specified range. 
     
     
         9 . An optical recording medium which has three or more recording layers manufactured by the manufacturing method for an optical recording medium according to  claim 3 . 
     
     
         10 . An optical information device which executes reproduction or recording for the optical recording medium according to  claim 9 , comprising:
 an optical head unit;   a motor rotating an optical disk; and   an electric circuit which receives a signal obtained from the optical head unit and controls and drives the motor, an objective lens or a laser light source,   wherein prior to a focus jump, the electric circuit corrects a spherical aberration generated on an intermediate layer at which the focus jump is to be made and moves a focal position.