Method and apparatus for retrieving information from a 3d storage medium

Abstract

A method and apparatus for retrieving information from a three dimensional storage medium uses a three dimensional storage medium having an active medium capable of exhibiting first and second states, a data unit being represented by the ratio between the concentration of the first and second states in a given volume portion of the medium and a data sequence is represented by a sequence of data units. The active medium is irradiated with light as to concentrate light flux through a volume portion of the storage medium so as to generate in the volume portion a detectable non-linear optical response characteristic of the concentration ratio, which is detected and used for tracking.

1 . An optical storage medium comprising active medium embedded in a supporting matrix, said active medium being capable of being in first and second states of different non-linear optical responses related to χ (n)  processes, where n is greater than 2, said supporting matrix being transparent for irradiation inducing the non-linear optical process and for light generated by the non-linear optical process, thereby enabling data recording in said optical storage medium by creating a sequence of data units of said second state of the active medium spaced-apart by the first state medium, the data units sequence being arranged along multiple tracks in different layers of the optical storage medium, and enabling data retrieval by identifying of the first and second states by detecting the different non-linear optical responses.  
     
     
         2 . The optical storage medium of  claim 1 , wherein the active medium is doped into the supporting matrix.  
     
     
         3 . The optical storage medium of  claim 1 , wherein said supporting matrix is a polymer.  
     
     
         4 . The optical storage medium of  claim 3 , wherein the active medium is a monomer co-polymerized with the supporting matrix.  
     
     
         5 . The optical storage medium of  claim 1 , wherein the supporting matrix comprises one of the following: polyethylene, polypropylene, polycarbonate, and polymethylmethacrylate (PMMA).  
     
     
         6 . A method for retrieving data from the optical storage of  claim 1 , the method comprising: irradiating said optical storage medium with light to cause a detectable non-linear optical response; detecting said non-linear optical response; and tracking the data sequence for retrieving said data sequence in a reproducible manner.  
     
     
         7 . The method of  claim 6 , wherein said tracking the data sequence comprises detecting a tracking feedback signal for controlling the irradiation of the optical storage medium.  
     
     
         8 . The method of  claim 7 , comprising correcting tracking errors in the optical storage medium, said correcting of the tracking errors comprising: 
 (a) focusing the light beam on to the track in the optical storage medium, and continually moving said light beam in axial and radial directions,    (b) receiving the optical response signals of amplitude which varies according to respective offsets from the track in radial and axial directions,    (c) using the received signals to determine a direction of a respective offset from the track in radial and axial directions, and    (d) adjusting a location of the focused light beam accordingly.    
     
     
         9 . The method of  claim 8 , comprising modulating a position of the focused light beam with a cyclic function in at least one of axial and radial directions.  
     
     
         10 . The method of  claim 9 , comprising multiplying the received signal by the cyclic modulation signal to form a modulated data/information signal, and applying low pass filtering to the modulated data signal.  
     
     
         11 . The method of  claim 10 , comprising window integrating the modulated data signal.  
     
     
         12 . An error correction device for carrying out the method of  claim 8 , the device comprising: a position modulator for modulating a position of the light beam, an error unit for receiving a data signal having an amplitude which varies according to respective offsets from the track in radial and axial directions, and is responsive to the data/information signal to determine a direction of a respective offset from the track in radial and axial directions, which offsets may be fed to an optical head to correct radial and axial position errors of the focused light beam.