High Areal Density Holographic Data Storage System

Abstract

An apparatus for recording or reading high areal density holographically stored information with high signal-to-noise ratio. The apparatus comprises a holographic imaging system for recording or reconstructing a holographic image, having a first numerical aperture and a first focal length and an additional optical system for filtering the signal beam, having a second numerical aperture and a second focal length, wherein the numerical aperture of the additional optical system is less than the numerical aperture of the holographic imaging system and/or the focal length of the additional optical system is greater than the optical length of the holographic imaging system.

1 . An apparatus for reading or writing holographically stored information, comprising:
 a holographic imaging system, having a first focal length, for recording or reconstructing a hologram; and   an additional optical system, having a second focal length, said additional optical system configured to receive a reconstructed hologram from the holographic imaging system,   wherein the first focal length is less than the second focal length.   
   
   
       2 . The apparatus of  claim 1  wherein
 the holographic imaging system includes a first imaging lens element, having focal length f 1  and a second imaging lens element, having focal length f 2 , spaced apart; and   the additional optical system includes a first additional lens element, having focal length f 3  and a second additional lens element, having focal length f 4 , spaced apart.   
   
   
       3 . The apparatus of  claim 2  wherein f 3 >f 2 . 
   
   
       4 . The apparatus of  claim 3  wherein f 3 =f 4 . 
   
   
       5 . The apparatus of  claim 3  wherein f 3 ≠f 4 . 
   
   
       6 . The apparatus of  claim 2  further including an apertured filter disposed between the first and the second additional lens elements. 
   
   
       7 . The apparatus of  claim 6  wherein the aperture of the apertured filter of the additional optical system is adjustable in position or size or shape. 
   
   
       8 . The apparatus of  claim 2 , further including:
 a spatial light modulator for encoding a signal beam; and   a detector for detecting a holographic image,   wherein the first and the second imaging lens elements are disposed between the spatial light modulator and the detector.   
   
   
       9 . The apparatus of  claim 2  wherein the first and second imaging lens elements of are substantially telecentric. 
   
   
       10 . The apparatus of  claim 2  wherein the first and the second additional lens elements are substantially telecentric. 
   
   
       11 . The apparatus of  claim 8  wherein the additional optical system is disposed between the second imaging lens element and the detector. 
   
   
       12 . The apparatus of  claim 8  wherein the holographic imaging system further includes a holographic recording media disposed between the first and the second imaging lens elements. 
   
   
       13 . The apparatus of  claim 12  wherein the holographic recording media stores fully or partially overlapped multiplexed holograms in at least one storage location on the holographic recording media. 
   
   
       14 . The apparatus of  claim 13  wherein holograms are recorded by angle-multiplexing or by combining at least two methods of multiplexing. 
   
   
       15 . A method of reading a holographically recorded image, comprising:
 directing a reference beam into a holographic imaging system that includes a holographic recording media, said reference beam directed onto the holographic media at a storage location, and said holographic imaging system having a first focal length, thereby reconstructing a signal beam;   directing the reconstructed signal beam through an additional optical system, having a second focal length, said additional optical system configured so that the second focal length is greater than the first focal length; and   detecting the reconstructed signal beam.   
   
   
       16 . The method of  claim 15  wherein the holographic recording media stores fully or partially overlapped multiplexed holograms in at least one storage location on the holographic recording media. 
   
   
       17 . The method of  claim 16  wherein the first multiplexed hologram in a sequence recorded in a storage location is recorded with a smaller interbeam angle than holograms recorded later in the sequence. 
   
   
       18 . An apparatus for reading a holographically recorded image, comprising:
 means for directing a reference beam into a holographic imaging system and reconstructing a signal beam, the holographic imaging system including a holographic recording media, said reference beam directed onto the holographic media, said holographic imaging system having a first focal length;   means for directing the reconstructed signal beam through an additional optical system and filtering the reconstructed signal beam, said additional optical system having a second focal length and configured so that the second focal length is greater than the first focal length; and   means for detecting the filtered reconstructed signal beam.   
   
   
       19 . The apparatus of  claim 18  wherein the holographic recording media stores fully or partially overlapping multiplexed holograms in at least one storage location on the holographic recording media. 
   
   
       20 . An apparatus for recording or reading holographically stored information, comprising:
 a holographic imaging system for recording or reconstructing a hologram, said holographic imaging system having a first focal length;   a holographic recording media optically coupled to the holographic imaging system;   a detector, optically coupled to the holographic recording media; and   an additional optical system, having a second focal length, wherein the first focal length is less than the second focal length, and further wherein the additional optical system is disposed between the holographic recording media and the detector.   
   
   
       21 . The apparatus of  claim 1 , wherein
 the holographic imaging system includes a first imaging lens element, having focal length f 1 ; and   the additional optical system includes a first additional lens element, having focal length f 3 , and a second additional lens element, having focal length f 4 , spaced apart.   
   
   
       22 . The apparatus of  claim 21 , wherein f 3 =f 4 . 
   
   
       23 . The apparatus of  claim 21 , wherein f 3 ≠f 4 . 
   
   
       24 . The apparatus of  claim 21  further including an apertured filter disposed between the first and the second additional lens elements, and, optionally, a second apertured filter disposed along the optical path of the reconstructed hologram or the optical path of a signal beam. 
   
   
       25 . The apparatus of  claim 21  wherein the aperture of the apertured filter of the additional optical system is adjustable in position or size or shape. 
   
   
       26 . The apparatus of  claim 21 , further including
 a holographic recording media; and   a spatial light modulator for encoding a signal beam,   wherein the first imaging lens element is disposed between the spatial light modulator and the holographic recording media.   
   
   
       27 . The apparatus of  claim 21  wherein the first and the second additional lens elements are substantially telecentric. 
   
   
       28 . The apparatus of  claim 26  further including a detector for detecting a reconstructed hologram, wherein the additional optical system is disposed between the first imaging lens element and the detector. 
   
   
       29 . The apparatus of  claim 26 , wherein the holographic recording media stores fully or partially overlapped multiplexed holograms in at least one storage location on the holographic recording media. 
   
   
       30 . The apparatus of  claim 13 , wherein holograms are recorded by in-plane or out-of-plane shift multiplexing. 
   
   
       31 . The apparatus of  claim 1 , wherein the additional optical system includes a first additional lens element and a second additional lens element, spaced apart, and wherein the apparatus further includes:
 a spatial light modulator for encoding a signal beam; and   a detector for detecting a holographic image,   wherein the first and the second additional lens elements are disposed between the spatial light modulator and the detector.