Information recording medium evaluation method, information recording medium, method for manufacturing information recording medium, signal processing method and access control apparatus

Abstract

A method for rating an information recording medium according to the present invention includes the steps of: receiving a digital read signal, which has been generated based on an analog read signal representing information that has been read from the information recording medium, and shaping the waveform of the digital read signal; subjecting the shaped digital read signal to maximum likelihood decoding, thereby generating a binarized signal showing a result of the maximum likelihood decoding; and calculating the quality of the digital read signal based on the shaped digital read signal and the binarized signal. If the quality of the read signal is calculated by a PRML method in which a number of zero-cross portions are included in a merging path of a minimum difference metric, the quality is calculated by using only a state transition pattern in which only one zero-cross portion is included in a merging path of a non-minimum difference metric.

1 . A method for rating an information recording medium, the method comprising the steps of:
 receiving a digital read signal, which has been generated based on an analog read signal representing information that has been read from the information recording medium, and shaping the waveform of the digital read signal;   subjecting the shaped digital read signal to maximum likelihood decoding, thereby generating a binarized signal showing a result of the maximum likelihood decoding; and   calculating the quality of the digital read signal based on the shaped digital read signal and the binarized signal,   wherein if the quality is calculated by a PRML method in which a number of zero-cross portions are included in a merging path of a minimum difference metric, the quality is calculated by using only a state transition pattern in which only one zero-cross portion is included in a merging path of a non-minimum difference metric.   
     
     
         2 . The method of  claim 1 , wherein the spatial frequency of the shortest mark that has been left on the information recording medium is higher than an OTF (optical transfer function) cutoff frequency. 
     
     
         3 . The method of  claim 1 , wherein the quality is calculated by further using an index that is defined to be the ratio of the center of a signal amplitude, associated with a combination of the longest mark and the longest space that have been left on the information recording medium, to the center of energy of the read signal waveform. 
     
     
         4 . The method of  claim 1 , wherein the PRML method is a PR 12221 mL method. 
     
     
         5 . The method of  claim 1 , wherein at least one of the degree of SNR of the read signal and the degree of edge shifting thereof is determined by the quality calculated. 
     
     
         6 . The method of  claim 5 , wherein the degree of edge shifting of the read signal is determined by the average of a distribution of values representing the qualities calculated. 
     
     
         7 . The method of  claim 5 , wherein the degree of SNR of the read signal is determined by the standard deviation of a distribution of values representing the qualities calculated. 
     
     
         8 . An apparatus for reading and/or writing information from/on an information recording medium to be rated by the method of  claim 1 . 
     
     
         9 . An information recording medium to be rated by the method of  claim 1 . 
     
     
         10 . An information recording medium comprising:
 a substrate;   a protective coating; and   at least one recording layer, which is arranged between the substrate and the protective coating,   wherein if the information recording medium is rated by a PRML method in which a number of zero-cross portions are included in a merging path of a minimum difference metric, the medium is rated by using only a state transition pattern in which only one zero-cross portion is included in a merging path of a non-minimum difference metric.   
     
     
         11 . The information recording medium of  claim 10 , wherein the at least one recording layer includes two or more recording layers, and
 wherein the recording medium has a storage linear density of 31 GB or more per recording layer.   
     
     
         12 . The information recording medium of  claim 11 , wherein the storage linear density per recording layer is 31.8 GB or more. 
     
     
         13 . The information recording medium of  claim 12 , wherein the storage linear density per recording layer is approximately 33.3 GB. 
     
     
         14 . The information recording medium of  claim 10 , wherein the at least one recording layer includes three or more recording layers. 
     
     
         15 . The information recording medium of  claim 14 , wherein the storage linear density of the three recording layers combined is approximately 100 GB. 
     
     
         16 . The information recording medium of  claim 10 , wherein an objective lens for use to rate the information recording medium has a numerical aperture of 0.7 to 0.9. 
     
     
         17 . The information recording medium of  claim 16 , wherein the objective lens has a numerical aperture of 0.85. 
     
     
         18 . The information recording medium of  claim 10 , wherein a laser beam for use to rate the information recording medium has a wavelength of 410 nm or less. 
     
     
         19 . The information recording medium of  claim 16 , wherein the laser beam has a wavelength of 405 nm. 
     
     
         20 . The information recording medium of  claim 10 , wherein the substrate has a thickness of 1.1 mm. 
     
     
         21 . The information recording medium of  claim 10 , wherein the protective coating has a thickness of 10 μm to 200 μm. 
     
     
         22 . The information recording medium of  claim 21 , wherein the protective coating has a thickness of 100 μm or less. 
     
     
         23 . An apparatus for reading and/or writing information from/on the information recording medium of  claim 10 . 
     
     
         24 . A method of making an information recording medium, the method comprising the steps of:
 making a stamper to form pits and/or grooves on an information recording medium; and   forming pits and/or grooves on the substrate of the information recording medium using the stamper,   wherein if the information recording medium made by this method is rated by a PRML method in which a number of zero-cross portions are included in a merging path of a minimum difference metric, the medium is rated by using only a state transition pattern in which only one zero-cross portion is included in a merging path of a non-minimum difference metric.   
     
     
         25 . The method of  claim 24 , wherein the pits are depressed when the information recording medium is viewed from a light source that irradiates the medium with a laser beam. 
     
     
         26 . The method of  claim 24 , wherein the pits are raised when the information recording medium is viewed from a light source that irradiates the medium with a laser beam. 
     
     
         27 . The method of  claim 24 , wherein land portions and groove portions are defined on the substrate by the grooves, and
 wherein the groove portions are located farther away from the light source that irradiates the information recording medium with the laser beam than the land portions are, and   wherein when information is written on the information recording medium, marks are left on the groove portions of the information recording medium.   
     
     
         28 . The method of  claim 24 , wherein land portions and groove portions are defined on the substrate by the grooves, and
 wherein the land portions are located closer to the light source that irradiates the information recording medium with the laser beam than the groove portions are, and   wherein when information is written on the information recording medium, marks are left on the land portions of the information recording medium.   
     
     
         29 . An apparatus for reading and/or writing information from/on an information recording medium made by the method of  claim 24 . 
     
     
         30 . A signal processing method comprising the steps of:
 receiving a digital read signal, which has been generated based on an analog read signal representing information that has been read from the information recording medium, and shaping the waveform of the digital read signal;   subjecting the shaped digital read signal to maximum likelihood decoding, thereby generating a binarized signal showing a result of the maximum likelihood decoding; and   calculating the quality of the digital read signal based on the shaped digital read signal and the binarized signal,   wherein if the quality is calculated by a PRML method in which a number of zero-cross portions are included in a merging path of a minimum difference metric, the quality is calculated by using only a state transition pattern in which only one zero-cross portion is included in a merging path of a non-minimum difference metric.   
     
     
         31 . The method of  claim 30 , wherein the quality is calculated by further using an index that is defined to be the ratio of the center of a signal amplitude, associated with a combination of the longest mark and the longest space that have been left on the information recording medium, to the center of energy of the read signal waveform. 
     
     
         32 . The method of  claim 30 , wherein the quality is calculated by classifying the read signals according to a combination of lengths of marks and spaces that have been left on the information recording medium. 
     
     
         33 . The method of  claim 32 , wherein the shortest lengths of the marks and the spaces are both equal to 2T. 
     
     
         34 . An apparatus for reading and/or writing information from/on an information recording medium rated by the signal processing method of  claim 30 . 
     
     
         35 . An information recording medium rated by the signal processing method of  claim 30 . 
     
     
         36 . An access controller comprising:
 a shaping section, which receives a digital read signal, which has been generated based on an analog read signal representing information that has been read from an information recording medium, and shapes the waveform of the digital read signal;   a maximum likelihood decoding section for subjecting the shaped digital read signal to maximum likelihood decoding, thereby generating a binarized signal showing a result of the maximum likelihood decoding;   a calculating section for calculating the quality of the digital read signal based on the shaped digital read signal and the binarized signal; and   a modifying section for modifying conditions to access the information recording medium based on the quality calculated,   wherein the shaping section and the maximum likelihood decoding section change the methods of signal processing to perform according to the type of the access from a first PRML method with a first characteristic into a second PRML method with a second characteristic, which is different from the first characteristic, and vice versa.   
     
     
         37 . The access controller of  claim 36 , wherein compared to the first characteristic, the second characteristic is a non-treble-boosted one. 
     
     
         38 . The access controller of  claim 36 , wherein when information is written on the information recording medium, the shaping section and the maximum likelihood decoding section perform signal processing by the first PRML method. 
     
     
         39 . The access controller of  claim 36 , further comprising a control section for controlling the operations of the calculating section and the modifying section,
 wherein when the shaping section and the maximum likelihood decoding section perform signal processing by the first PRML method, the control section instructs the calculating section and the modifying section to follow the first PRML method, and   wherein when the shaping section and the maximum likelihood decoding section perform signal processing by the second PRML method, the control section instructs the calculating section and the modifying section to follow the second PRML method.