Holographic data storage with an orthogonally coded reference beam

Claim 1

In a system for holographically recording a plurality of object transparencies on one area of a photographic plate comprising: a light source; means for forming light from said source into an object beam and a reference beam; means for sequentially positioning each object transparency at a fixed location; and a photographic plate holder and means for modulating the reference beam so as to provide a uniquely coded reference beam for each object transparency, the improvement wherein said means for modulating the reference beam consists of a plurality of equally sized electro-optic phase plates arranged in a planar array, each electro-optic phase plate providing one of two phase shifts, wherein one of said two phase shifts is a uniform pi phase shift with respect to the other phase shift, the phase shift produced by said plate being selectable in response to an electric signal, and the total number of phase plates being an integral power of two, said array of phase plates being operated to be in one of a set of mutually orthogonal states for each object transparency recorded, each array state being such that exactly half the total number of phase plates produce the same phase shift and such that each plate produces a phase shift which is equal to the sum of the phase shifts produced by that plate in any two other states, whereby upon reconstruction all images other than the desired one destructively interfere.

Claim 4

A method for holographically recording a plurality of object transparencies on one area of a photographic plate comprising the steps of: forming from a light source an object beam and a reference beam; sequentially positioning each object transparency at a fixed location; and modulating the reference beam so as to provide a uniquely coded reference beam for each object transparency, wherein said modulating the reference beam step includes arranging a plurality of equally sizEd electro-optic phase plates in a planar array, providing each electro-optic phase plate with one of two phase shifts, wherein one of said two phase shifts is a uniform pi phase shift with respect to the other phase shift, the phase shift produced by said plate being selectable in response to an electric signal with the total number of phase plates being an integral power of two, and operating said array of phase plates to be in one of a set of mutually orthogonal states for each object transparency recorded, each array state being such that exactly half the total number of phase plates produce the same phase shift and such that each plate produces a phase shift which is equal to the sum of the phase shifts produced by that plate in any two other states, whereby upon reconstruction all images other than the desired one destructively interfere.

Claim 5

A method for holographically recording a plurality of object transparencies on one area of a photographic plate comprising the steps of: forming from a light source an object beam and a reference beam; sequentially positioning each object transparency at a fixed location; and modulating the reference beam so as to provide a uniquely coded reference beam for each object transparency, wherein said modulating the reference beam step includes arranging a plurality of equally sizEd electro-optic phase plates in a planar array, providing each electro-optic phase plate with one of two phase shifts, wherein one of said two phase shifts is a uniform pi phase shift with respect to the other phase shift, the phase shift produced by said plate being selectable in response to an electric signal with the total number of phase plates being an integral power of two, and operating said array of phase plates to be in one of a set of mutually orthogonal states for each object transparency recorded, each array state being such that exactly half the total number of phase plates produce the same phase shift and such that each plate produces a phase shift which is equal to the sum of the phase shifts produced by that plate in any two other states, whereby upon reconstruction all images other than the desired one destructively interfere.