Device and method for reading multilayer optical disk

Abstract

Device and method for reading multilayer optical disk The invention refers to a device and a method for scanning an optical data carrier ( 1 ) by means of a main scanning beam ( 3 ) being reflected by the data carrier ( 1 ) and being detected by means of a photodetector ( 10 ), the data carrier ( 1 ) having first and second layers ( 11,12 ) to be scanned, the second layer ( 12 ) being scanned through the first layer ( 11 ), light passing the first layer ( 11 ) being shaded dependent on local properties of the first layer ( 11 ). An object of the invention is to propose a device having increased performance even for use with multi layer disks ( 1 ) having a layer ( 11 ) causing light fluctuations on a layer ( 12 ) to be scanned, as well as a respective method. According to the invention such device is provided with means ( 2,7,17 ) for keeping an output signal (D) of the photodetector ( 10 ) independent of variations of shading.

1 - 5 . (canceled)  
     
     
         6 . Method for preparing for scanning an optical data carrier having first and second layers to be scanned, the second layer being scanned through the first layer, light passing the first layer being shaded dependent on local properties of the first layer, having the step of providing the first layer with a shading pattern for compensating for local differences in shading effect.  
     
     
         7 . Method according to  claim 6 , wherein the shading pattern is provided only in areas having predetermined characteristics.  
     
     
         8 . Method according to  claim 6 , wherein the shading pattern is either a grey level pattern or a pit pattern, the pits of the pit pattern being either larger than the largest data recording pits or smaller than the smallest data recording pits.  
     
     
         9 . Method according to  claim 6 , wherein the shading pattern is used to store additional information.  
     
     
         10 . Device for performing a method according to  claim 6 .  
     
     
         11 . Optical data carrier having first and second layers to be scanned, the second layer being scanned through the first layer, light passing the first layer being shaded dependent on local properties of the first layer, wherein the first layer has a shading pattern for compensating for local differences in shading effect.  
     
     
         12 . Optical data carrier according to  claim 11 , having said shading pattern only in areas having predetermined characteristics.  
     
     
         13 . Optical data carrier according to  claim 11 , wherein the shading pattern is either a grey level pattern or a pit pattern, the pits of the pit pattern being either larger than the largest data recording pits or smaller than the smallest data recording pits.  
     
     
         14 . Optical data carrier according to  claim 11 , wherein the shading pattern is used to store additional information.