On-groove recordation type optical disc

Abstract

Hardness of a resin substrate of an optical disc is selected to be greater than hardness of a cover layer of the optical disc, at least when information is recorded on the optical disc. A laser beam is transmitted to an organic dye layer of the optical disc through the cover layer and a protection layer when information is recorded on the optical disc. The organic dye layer is sandwiched by the protection layer and a reflection layer. The substrate has grooves on its surface, and information is recorded between the grooves. The organic dye is heated and expands upon information recording, but a stress generated by the deforming organic dye layer is mainly transferred toward the cover layer. Deformation of the reflection layer and crosswrite upon information recording can be prevented. Therefore, the optical disc can record information between the grooves at a high density. Alternatively, the optical disc may be configured such that heat transfer toward the protection layer from the organic dye layer is set to be greater than heat transfer toward the reflection layer from the organic dye layer when the light beam is radiated for information recording.

What is claimed is:  
     
         1 . An optical disc for recording information between grooves of the disc, comprising: 
 a resin substrate having the grooves on a surface of the substrate;    a reflection layer formed over the surface of the resin substrate such that the reflection layer has a concavo-convex shape corresponding to the grooves;    an optical-characteristic-changeable layer formed over the reflection layer such that the optical-characteristic-changeable layer has a concavo-convex shape corresponding to the concavo-convex shape of the reflection layer, the optical characteristic-changeable layer having an optical characteristic which varies when a light beam is radiated on the optical-characteristic-changeable layer;    a light-transmissive protection layer formed over the optical characteristic-changeable layer; and    a light-transmissive cover layer formed over the protection layer for sealing the reflection layer, optical characteristic-changeable layer and protection layer to the resin substrate, wherein hardness of the resin substrate is greater than hardness of the cover layer, at least after the optical characteristic of the optical characteristic-changeable layer changes when a light beam is radiated to a convex portion of the optical characteristic-changeable layer.    
     
     
         2 . The optical disc according to  claim 1 , wherein the light beam is radiated to the convex portion of the optical-characteristic-changeable layer through the cover layer and protection layer in order to record information on the optical disc.  
     
     
         3 . The optical disc according to  claim 1 , wherein the optical-characteristic-changeable layer is an organic dye layer which has a refractive index changeable when radiated by a light beam.  
     
     
         4 . The optical disc according to  claim 1 , wherein the optical disc is a DVR-R disc.  
     
     
         5 . The optical disc according to  claim 1 , wherein the substrate is about 1.1 mm in thickness and the cover layer is about 0.1 mm in thickness.  
     
     
         6 . The optical disc according to  claim 3 , wherein the hardness of the substrate is greater than the hardness of the cover layer after the refractive index of the optical characteristic-changeable layer has changed.  
     
     
         7 . An optical disc for recording information between grooves of the disc, comprising: 
 a resin substrate having the grooves on a surface of the substrate;    a reflection layer formed over the surface of the resin substrate such that the reflection layer has a concavo-convex shape corresponding to the grooves;    an optical-characteristic-changeable layer formed over the reflection layer such that the optical-characteristic-changeable layer has a concavo-convex shape corresponding to the concavo-convex shape of the reflection layer, the optical characteristic-changeable layer having an optical characteristic which varies when a light beam is radiated on the optical-characteristic-changeable layer;    a light-transmissive protection layer formed over the optical characteristic-changeable layer; and    a light-transmissive cover layer formed over the protection layer for sealing the reflection layer, optical characteristic-changeable layer and protection layer to the resin substrate, wherein heat, which is generated at a convex portion of the optical characteristic-changeable layer as the light beam is radiated to the convex portion, is transferred toward the protection layer from the optical-characteristic-changeable layer in a greater amount than toward the reflection layer from the optical-characteristic-changeable layer.    
     
     
         8 . The optical disc according to  claim 7 , wherein the light beam creates a beam spot having a diameter on the convex portion of the optical-characteristic-changeable layer, a product of the beam spot diameter, the beam spot diameter, a thickness of the protection layer and a thermal conductivity of the protection layer is greater than a product of the beam spot diameter, the beam spot diameter, a thickness of the reflection layer and a thermal conductivity of the reflection layer.  
     
     
         9 . The optical disc according to  claim 7 , wherein the light beam is radiated to the convex portion of the optical-characteristic-changeable layer through the cover layer and protection layer in order to record information on the optical disc.  
     
     
         10 . The optical disc according to  claim 7 , wherein the optical-characteristic-changeable layer is an organic dye layer which has a refractive index changeable when radiated by a light beam.  
     
     
         11 . The optical disc according to  claim 7 , wherein the optical disc is a DVR-R disc.  
     
     
         12 . The optical disc according to  claim 7 , wherein the substrate is about 1.1 mm in thickness and the cover layer is about 0.1 mm in thickness.  
     
     
         13 . The optical disc according to  claim 7 , wherein the reflection layer is made from a material having a high thermal conductivity.  
     
     
         14 . The optical disc according to  claim 7 , wherein the reflection layer is made from an aluminum alloy, and the protection layer is made from an aluminum nitride.  
     
     
         15 . An optical disc for recording information comprising: 
 a substrate having grooves on a surface of the substrate;    a reflection layer formed over the surface of the substrate such that the reflection layer has a concavo-convex shape corresponding to the grooves;    an optical-characteristic-changeable layer formed over the reflection layer such that the optical-characteristic-changeable layer has a concavo-convex shape corresponding to the concavo-convex shape of the reflection layer, the optical characteristic-changeable layer having an optical characteristic which varies when a light beam is radiated on the optical-characteristic-changeable layer;    a protection layer formed over the optical characteristic-changeable layer; and    a cover layer formed over the protection layer, wherein heat, which is generated at a convex portion of the optical-characteristic-changeable layer as the light beam is radiated to the convex portion, is transferred toward the protection layer and the reflection layer in a sufficient amount to prevent crosswrite with respect to adjacent convex portions of the optical-characteristic-changeable layer.