Multi-layer Optical Disc And System

Abstract

A multi-layer optical disc comprises multiple storage and reference layers. The storage layers each have a distinct distance from its reference layer. Beam portions of a read-out beam are reflected by the storage and reference layers respectively. Interference among the reflected beam portions is tuned to retrieve stored information.

1 . A multi-layer optical data storage medium comprising: 
 1) a plurality of storage layers as storage reflectors for storing data; and    2) at least one reference layer as a reference reflector;    3) said storage and reference layers being arranged such that there is a distinct optical path length between said reference reflector and each of said storage reflectors in a direction a read-out beam is transmitted.    
     
     
         2 . The storage medium according to  claim 1  wherein at least one of said storage layer is disposed in a discrete storage unit.  
     
     
         3 . The storage medium according to  claim 1  wherein said reference layer is disposed in a discrete storage unit.  
     
     
         4 . The storage medium according to  claim 1  wherein at least one of said storage reflectors has an adjustable reflectivity.  
     
     
         5 . The storage medium according to  claim 1  wherein said storage and reference layers are arranged sharing one substrate.  
     
     
         6 . The storage medium according to  claim 1  wherein at least one of said storage layers is disposed to function as said reference layer for another said storage layer.  
     
     
         7 . An optical data storage system comprising: 
 1) a light source for generating a read-out beam;    2) a multi-layer optical data storage medium comprising a plurality of storage layers for storing data and at least one reference layer, said read-out beam being transmitted to impinge onto said storage medium and reflected by said storage and reference layers respectively, and said storage and reference layers being arranged such that there is a distinct optical path length between said reference reflector and each of said storage reflectors in a direction said read-out beam is transmitted; and    3) a detector for sensing interference among the reflected beams reflected by said storage and reference layers.    
     
     
         8 . The storage system according to  claim 7 , further including a spatial phase modulator for dividing said read-out beam into a plurality of beam portions by wavefront division and producing phase shift on each said beam portion respectively.  
     
     
         9 . The storage system according to  claim 8 , further including tuning means for adjusting phase shift of at least one of said beam portions.  
     
     
         10 . The storage system according to  claim 7  wherein said light source has relatively low coherence.  
     
     
         11 . The storage system according to  claim 7 , further including optics means for focusing said read-out beam onto said medium and said reflected beams onto said detector respectively.  
     
     
         12 . A method for retrieving information from an optical data storage medium, comprising: 
 1) causing a light source to generate a read-out beam;    2) providing a multi-layer optical data storage medium comprising at least one storage layer and at least one reference layer;    3) transmitting a first beam portion of said read-out beam through a first optical path, said first optical path being arranged to connect said source and a detector via said storage layer;    4) transmitting a second beam portion of said read-out beam through a second optical path, said second optical path being arranged to connect said source and said detector via said reference layer;    5) adjusting path length difference between said first and second paths; and    6) sensing interference between said first and second beam portions by said detector.    
     
     
         13 . The method according to  claim 12  wherein said light source has relatively low coherence.  
     
     
         14 . The method according to  claim 12  wherein said first and second beam portions are generated using methods including wavefront division.  
     
     
         15 . The method according to  claim 12 , further including focusing said beam portions onto said medium and said detector respectively.