Patent ID: 8199628

Claim:
An apparatus for reading from a multilayer holographic storage medium, with a coaxial arrangement of a reference beam and a reconstructed object beam, the apparatus comprising: an objective lens for focusing the reference beam into the multilayer holographic storage medium such that the reference beam has a focal point behind or in front of a reflective layer of the multilayer holographic storage medium; wherein a distance between the objective lens and the multilayer holographic storage medium is set in accordance with an addressed layer of the multilayer holographic storage medium; and an imaging system with a fixed lens of focal length f and a movable lens of focal length f for re-collimating a reconstructed object beam wherein for a specific position of the movable lens the imaging system assumes a 4 f configuration; wherein for re-collimating the reconstructed object beam the apparatus is adapted to shift the movable lens of the 4 f imaging system by substantially twice the shift of the objective lens necessary for addressing a specific layer of the multilayer holographic storage medium.