Interference of converging spherical waves with application to the design of light-readable information recording media and systems for reading such media

Abstract

An improved light-readable information recording medium is provided that comprises an optical data storage structure having lands and pits, in which the depth of the pits is about: λ 2  n  m 1 + M T 2 , wherein λ is the wavelength of light used to read the information recording medium, m is the order of interference selected from a group consisting of odd integers, M T is the transverse magnification, and n is the refractive index encountered by the reading light inside the pits. The invention also provides an improved optical reading system with the parameters satisfying the relationship: n     d ≃ λ 2  m 1 + M T 2 , wherein λ is the wavelength of light used to read the information recording medium, m is the order of interference selected from a group consisting of odd integers, M T is the transverse magnification, n is the refractive index encountered by the reading light inside the pits, and d is the depth of the pits.

The invention claimed is:  
     
         1 . An information recording medium readable by a reader using reflected light comprising an optical data storage structure including pits and lands, in which the optical depth of said pits is equal to about:  
       
         
           
             
               
                 
                   λ 
                   2 
                 
                  
                 
                   m 
                   
                     1 
                     + 
                     
                       M 
                       T 
                       2 
                     
                   
                 
               
               , 
             
           
           
           
               
           
         
       
       wherein λ is a wavelength of the light used to read the information recording medium, m is selected from a group consisting of odd integers, and M T  is a transverse magnification of the reader, wherein said optical pit depth, Δ opt  is selected to satisfy the following condition:  
       Δ opt <λ/5.3  
     
     
         2 . The information recording medium defined in  claim 1 , wherein said medium is disc-shaped.  
     
     
         3 . An information recording medium readable by an optical reader comprising: 
 a transparent substrate having one substantially planar surface and a second surface opposite to said first surface, said second surface formed as a data storage structure including pits and lands, in which the depth of said pits is equal to about:                λ     2      n            m     1   +     M   T   2           ,                      wherein λ is a wavelength of the light used to read the information recording medium, n is a refractive index of the substrate, m is selected from a group consisting of odd integers, and M T  is a transverse magnification of the reader, wherein said pit depth, d, is selected to satisfy the following condition:      d<λ/ 5.3  n      a light reflecting coating on said second surface for reflecting said light passed through said transparent substrate, said coating conforming to the contours of said second surface so that said light is reflected back through the transparent substrate in accordance with the information recorded by means of said pits and lands.    
     
     
         4 . The information recording medium defined in  claim 3 , wherein said medium is disc-shaped.  
     
     
         5 . The information recording medium defined in  claim 3 , wherein said transparent substrate is selected from the group consisting of polymethyl methacrylate, photo polymer and polycarbonate.  
     
     
         6 . The information recording medium defined in  claim 3 , wherein said light-reflecting coating is selected from the group consisting of gold, silver and aluminum.  
     
     
         7 . An information recording medium readable by an optical reader comprising: 
 a transparent substrate having one substantially planar surface and a second surface opposite to said first surface, said second surface formed as a data storage structure including pits and lands, in which the depth of said pits is equal to about:                λ     2      n            m     1   +     M   T   2           ,                      wherein λ is a wavelength of the light used to read the information recording medium, n is a refractive index of the substrate, m is selected from a group consisting of odd integers, and M T  is a transverse magnification, wherein said pit depth, d, is selected to satisfy the following condition:      d<λ/ 5.3  n      a light-reflecting coating on said second surface for reflecting said light passed through said transparent substrate, said coating conforming to the contours of said second surface so that said light is reflected back through the transparent substrate in accordance with the information recorded by means of said pits and lands; and    a protective coating having a first surface conforming to the contours of said light-reflecting coating and a second surface opposite to said first surface being substantially planar.    
     
     
         8 . The information recording medium defined in  claim 7 , wherein said medium is disc-shaped.  
     
     
         9 . The information recording medium defined in  claim 7 , wherein said transparent substrate is selected from the group consisting of polymethyl methacrylate, photo polymer and polycarbonate.  
     
     
         10 . The information recording medium defined in  claim 7 , wherein said light-reflecting coating is selected from the group consisting of gold, silver and aluminum.  
     
     
         11 . The information recording medium defined in  claim 7 , wherein said protective coating is lacquer.  
     
     
         12 . An information-recording medium readable by an optical reader comprising a light-reflecting surface formed as a data storage structure including pits and lands, in which the optical depth of said pits is equal to about:  
       
         
           
             
               
                 
                   λ 
                   2 
                 
                  
                 
                   m 
                   
                     1 
                     + 
                     
                       M 
                       T 
                       2 
                     
                   
                 
               
               , 
             
           
           
           
               
           
         
       
       wherein λ is a wavelength of the light used to read the information recording medium, m is selected from a group consisting of odd integers, and M T  is a transverse magnification of the reader, wherein said optical pit depth, Δ opt , is selected to satisfy the following condition:  
       Δ opt <λ/5.3  
     
     
         13 . The information recording medium defined in  claim 12 , wherein said medium is disc-shaped.  
     
     
         14 . The information recording medium defined in  claim 12 , wherein said light-reflecting surface is selected from the group consisting of gold, silver and aluminum.