Optical recording medium inspecting method and optical recording medium manufacturing method

Abstract

It is an object of the present invention to provide an inspection method for judging whether or not a phase change type medium can be used as a write-once type medium. In the present invention, shortest signals are recorded in an optical recording medium having a phase change type recording layer so that the CNR of the shortest signal is equal to or higher than 45 dB, an area in which the shortest signal was recorded is irradiated with a constant-current laser beam whose power level cannot melt the recording layer at the same linear speed as that at which the shortest signal was recorded, and decrease in the carrier of the shortest signal is measured. When the decrease in the carrier of the shortest signal is equal to or lower than 20 dB, the optical recording medium is judged to be a write-once type medium.

1 . A method for inspecting an optical recording medium comprising steps of recording a shortest signal in an optical recording medium having a phase change type recording layer so that CNR of the shortest signal is equal to or higher than 45 dB, irradiating an area in which the shortest signal was recorded with a constant-current laser beam whose power level cannot melt the recording layer at the same linear speed as that at which the shortest signal was recorded, measuring decrease in the carrier of the shortest signal and judging the optical recording medium to be a write-once type medium when the decrease in the carrier is equal to or lower than 20 dB.  
     
     
         2 . A method for inspecting an optical recording medium in accordance with  claim 1 , wherein the shortest signal is recorded so that the CNR is equal to or higher than 48 dB.  
     
     
         3 . A method for inspecting an optical recording medium in accordance with  claim 1  or  2 , wherein the optical recording medium is judged to be a write-once medium when the decrease in the carrier is equal to or lower than 18 dB.  
     
     
         4 . A method for inspecting an optical recording medium in accordance with  claim 3 , wherein the optical recording medium is judged to be a write-once medium when the decrease in the carrier is equal to or higher than 5 dB.  
     
     
         5 . A method for inspecting an optical recording medium in accordance with  claim 4 , wherein the optical recording medium is judged to be a write-once medium when the decrease in the carrier is equal to or higher than 10 dB.  
     
     
         6 . A method for inspecting an optical recording medium comprising the steps of recording random signals in the optical recording medium having a phase change type recording layer, conducting reproducing operation of the signals on an area in which the random signals were recorded, thereby measuring a highest reflective level Rini, irradiating the area in which the random signals were recorded with a constant-current laser beam at the same linear speed as that at which the random signals were recorded, conducting reproducing operation of the signals on the area irradiated with the constant-current laser beam, thereby measuring a highest reflective level Rtop and a lowest reflective level Rbottom, and judging the optical recording medium to be a write-once type medium when (Rtop+Rbottom)/2Rini<1 is satisfied, irrespective of whether the constant-current laser beam has a power level which can melt the recording layer.  
     
     
         7 . A method for inspecting an optical recording medium in accordance with  claim 6 . wherein the optical recording medium is judged to be a write-once medium when (Rtop+Rbottom)/2Rini<0.95 is satisfied.  
     
     
         8 . A method for inspecting an optical recording medium comprising the steps of recording random signals in the optical recording medium having a phase change type recording layer, again recording the random signals so as to be superposed on the first mentioned random signals at the same linear speed as that at which the first mentioned random signals were recorded, conducting reproducing operation of the signals, and judging the optical recording medium to be a write-once type medium when the signals cannot be reproduced.  
     
     
         9 . A method for inspecting an optical recording medium in accordance with  claim 8 , wherein it is judged that the signals cannot be reproduced when the reproduced signal contains error which cannot be corrected.  
     
     
         10 . A method for inspecting an optical recording medium in accordance with  claim 9 , wherein it is judged that the signals cannot be reproduced when clock jitter exceeds 13%.  
     
     
         11 . A method for inspecting an optical recording medium in accordance with  claim 10 , wherein it is judged that the signals cannot be reproduced when clock jitter exceeds 15%.  
     
     
         12 . A method for inspecting an optical recording medium comprising the steps of recording random signals in the optical recording medium having a phase change type recording layer, irradiating an area in which the random signals were recorded with a constant-current laser beam at the same linear speed as that at which the random signals were recorded, thereby again recording random signals in the area irradiated with the constant-current laser beam, conducting reproducing operation of the signals, and judging the optical recording medium to be a write-once type medium when the signals cannot be reproduced.  
     
     
         13 . A method for inspecting an optical recording medium in accordance with  claim 12 , wherein it is judged that the signals cannot be reproduced when the reproduced signal contains error which cannot be corrected.  
     
     
         14 . A method for inspecting an optical recording medium in accordance with  claim 13 , wherein it is judged that the signals cannot be reproduced when clock jitter exceeds 13%.  
     
     
         15 . A method for inspecting an optical recording medium in accordance with  claim 14 , wherein it is judged that the signals cannot be reproduced when clock jitter exceeds 15%.  
     
     
         16 . A method for manufacturing an optical recording medium comprising a layer forming step of forming at least a phase change recording layer, an initialization step of crystallizing at least an area of the recording layer in which data are to be recorded and an inspection step of judging whether the optical recording medium subjected to the initialization step is a write-once type medium or a rewritable type medium, the inspecting step comprising the steps of recording a shortest signal in an optical recording medium having a phase change type recording layer so that CNR of the shortest signal is equal to or higher than 45 dB, irradiating an area in which the shortest signal was recorded with a constant-current laser beam whose power level cannot melt the recording layer at the same linear speed as that at which the shortest signal was recorded, measuring decrease in the carrier of the shortest signal and judging the optical recording medium to be a write-once type medium when the decrease in the carrier is equal to or lower than 20 dB.  
     
     
         17 . A method for manufacturing an optical recording medium comprising a layer forming step of forming at least a phase change recording layer, an initialization step of crystallizing at least an area of the recording layer in which data are to be recorded and an inspection step of judging whether the optical recording medium subjected to the initialization step is a write-once type medium or a rewritable type medium, the inspecting step comprising the steps of recording random signals in the optical recording medium having a phase change type recording layer, conducting reproducing operation of the signals on an area in which the random signals were recorded, thereby measuring a highest reflective level Rini, irradiating the area in which the random signals were recorded with a constant-current laser beam at the same linear speed as that at which the random signals were recorded, conducting reproducing operation of the signals on the area irradiated with the constant-current laser beam, thereby measuring a highest reflective level Rtop and a lowest reflective level Rbottom, and judging the optical recording medium to be a write-once type medium when (Rtop+Rbottom)/2Rini<1 is satisfied, irrespective of whether the constant-current laser beam has a power level which can melt the recording layer.  
     
     
         18 . A method for manufacturing an optical recording medium comprising a layer forming step of forming at least a phase change recording layer, an initialization step of crystallizing at least an area of the recording layer in which data are to be recorded and an inspection step of judging whether the optical recording medium subjected to the initialization step is a write-once type medium or a rewritable type medium, the inspecting step comprising the steps of recording random signals in the optical recording medium having a phase change type recording layer, again recording the random signals so as to be superposed on the first mentioned random signals at the same linear speed as that at which the first mentioned random signals were recorded, conducting reproducing operation of the signals, and judging the optical recording medium to be a write-once type medium when the signals cannot be reproduced.  
     
     
         19 . A method for manufacturing an optical recording medium comprising a layer forming step of forming at least a phase change recording layer, an initialization step of crystallizing at least an area of the recording layer in which data are to be recorded and an inspection step of judging whether the optical recording medium subjected to the initialization step is a write-once type medium or a rewritable type medium, the inspecting step comprising the steps of recording random signals in the optical recording medium having a phase change type recording layer, irradiating an area in which the random signals were recorded with a constant-current laser beam at the same linear speed as that at which the random signals were recorded, thereby again recording random signals in the area irradiated with the constant-current laser beam, conducting reproducing operation of the signals, and judging the optical recording medium to be a write-once type medium when the signals cannot be reproduced.