Holography

Abstract

An iterative algorithm for hologram design with multiple output image planes arranged in close proximity to create continuous patterns within an imaging volume is disclosed. These may then be used for photolithography on 3D surfaces, or for generation of holograms for use in consumer devices.

1 . A method of generating a wave-optical exposure mask comprising:
 modifying the exposure mask via an iterative process until a modulation pattern produced by the exposure mask produces a desired non-planar pattern in object space;   wherein said iterative process comprises specifying an intensity pattern that is defined over a bounded three dimensional geometrical surface by a series of multiple planes provided at differing positions within an image volume, extending from a diffraction plane formed by the modulation; and   said iterative process is confined to a defined discrete array of amplitude and/or phase altering elements.   
     
     
         2 . The method of  claim 1 , wherein said iterative process includes:
 a long propagation from a diffraction plane to a first endpoint of the object space where the pattern is to be produced;   one or more short propagations traversing the object space while applying different amplitude constraints across successive planes;   a second long propagation from a second endpoint of the object space where the pattern is to be produced back to the diffraction plane; and   the application of a phase-only constraint in the diffraction plane.   
     
     
         3 . The method of  claim 2 , wherein the iterative process further includes filtering and spatial constraints applied at the diffraction plane. 
     
     
         4 . The method of  claim 1 , wherein amplitude correction is applied to only a sub-portion of each image plane where the sampled pixels intersect a pseudo-continuous surface function. 
     
     
         5 . The method of  claim 1 , wherein amplitude and phase information is unconstrained in unimportant selected areas of an image volume such as to allow the convergence of the algorithm. 
     
     
         6 . The method of  claim 1 , wherein a propagation routine adopted to move between image planes and hologram is that of a convolution form of the Fresnel diffraction integral. 
     
     
         7 . The method of  claim 1 , wherein said propagation routine is an application of a Rayleigh-Somerfield propagator. 
     
     
         8 . The method of  claim 1 , wherein said propagation routine is an angular spectrum method. 
     
     
         9 . The method of  claim 1 , wherein each image plane is corrected with an ideal amplitude profile, whilst retaining the propagated phase. 
     
     
         10 . The method of  claim 1 , wherein the hologram plane itself is corrected with unit amplitude to give a phase only pattern. 
     
     
         11 . A wave-optical method of generating a hologram comprising:
 providing coherent or partially coherent radiation;   modulating said incident radiation according to a modulation pattern; and   varying said modulation pattern via an iterative process until said modulation pattern produces a desired non-planar pattern in object space; wherein said iterative process comprises specifying an intensity pattern that is defined over a bounded three dimensional geometrical surface by a series of multiple planes provided at differing positions within an image volume, extending from a diffraction plane formed by the modulation; and said iterative process is confined to a defined discrete array of amplitude and/or phase altering elements.   
     
     
         12 . The method of  claim 11 , further including the steps of  claim 1 . 
     
     
         13 . An apparatus for generating a hologram having a desired non-planar pattern in object space, comprising:
 a radiation source for emitting coherent or partially coherent radiation;   a modulator for modulating said incident radiation according to a modulation pattern;   said modulator being controllable to vary a pattern of modulation that is applied;   said apparatus comprising a controller adapted to vary said modulation pattern via an iterative process until said modulation pattern produces a desired non-planar pattern in object space;   wherein said iterative process comprises specifying an intensity pattern that is defined over a bounded three dimensional geometrical surface by a series of multiple planes provided at differing positions within an image volume, extending from a diffraction plane formed by the modulation; and   said iterative process is confined to a defined discrete array of amplitude and/or phase altering elements.   
     
     
         14 . The apparatus of  claim 13 , wherein said modulator comprises a spatial light modulator (SLM). 
     
     
         15 . The apparatus of  claim 13 , wherein said radiation source comprises a laser. 
     
     
         16 . A lithographic apparatus comprising the apparatus of  claim 13  and arranged for carrying out the method of  claim 1 . 
     
     
         17 . A consumer device for generating holograms comprising the apparatus of  claim 13  and arranged for carrying out a method of generating a wave-optical exposure mask, the method comprising:
 modifying the exposure mask via an iterative process until a modulation pattern produced by the exposure mask produces a desired non-planar pattern in object space; 
 wherein said iterative process comprises specifying an intensity pattern that is defined over a bounded three dimensional geometrical surface by a series of multiple planes provided at differing positions within an image volume, extending from a diffraction plane formed by the modulation; and 
 said iterative process is confined to a defined discrete array of amplitude and/or phase altering elements. 
 
     
     
         18 . The consumer device of  claim 17 , comprising a holographic television with suitable projection means for projecting a hologram according to said predefined pattern into a viewing space or a display to be viewed by a user. 
     
     
         19 . A computer program product including instructions that, when run on an computer, enables said computer to implement a method of generating a wave-optical exposure mask, the method comprising:
 modifying the exposure mask via an iterative process until a modulation pattern produced by the exposure mask produces a desired non-planar pattern in object space;   wherein said iterative process comprises specifying an intensity pattern that is defined over a bounded three dimensional geometrical surface by a series of multiple planes provided at differing positions within an image volume, extending from a diffraction plane formed by the modulation; and   said iterative process is confined to a defined discrete array of amplitude and/or phase altering elements.