APPARATUS FOR COPYING A HOLOGRAM
A holographic recording apparatus having a source of illumination, a master hologram containing at least one hologram lamina overlaying, a copy substrate containing a holographic recording medium, and a voltage generator for applied a voltage across at least one of the master hologram and the copy substrate. The master hologram diffracts the illumination light into zero order light and diffracted light which interfere in the copy substrate to form a copy of the master hologram. The source of illumination is applied for a predefined exposure time during which the voltage varies the refractive index modulation of at least one of the master hologram and the copy hologram.
1 . A holographic recording apparatus comprising:
a source of illumination;
a master hologram containing at least one hologram lamina overlaying;
a copy substrate containing a holographic recording medium; and
a voltage generator for applied a voltage across at least one of said master hologram and said copy substrate;
said master hologram diffracting said illumination into zero order light and diffracted light, said zero order light and diffracted light interfering in said copy substrate to form a copy of said master hologram,
said source of illumination being applied for a predefined exposure time,
wherein said voltage varies the refractive index modulation of at least one of said master hologram and said copy hologram during said exposure time.
2 . The apparatus of claim 1 wherein said voltage spatially varies said refractive index modulation.
3 . The apparatus of claim 1 wherein said master hologram is one of a photo thermal refractive or photopolymer, a forward mode SBG or a reverse mode SBG.
4 . The apparatus of claim 1 wherein said master hologram is a SBG comprising transparent plates to which electrodes coupled to said voltage generator have been applied, said plates sandwiching a layer containing HPDLC material components.
5 . The apparatus of claim 1 wherein said master hologram comprises a multiplicity of electrically addressable SBG lamina.
6 . The apparatus of claim 1 wherein said at least one hologram lamina has a grating vector selected from a predefined set of grating vectors.
7 . The apparatus of claim 1 wherein said at least one hologram lamina has a grating vector selected from a predefined set of randomly orientated grating vectors
8 . The apparatus of claim 1 wherein said at least one hologram lamina has spatially varying grating vector.
9 . The apparatus of claim 1 wherein said holographic recording medium comprises HPDLC material components for forming one of a forward mode SBG or a reverse mode SBG.
10 . The apparatus of claim 1 wherein said zero order light and diffracted light have power substantially in the ratio of 1:1.
11 . The apparatus of claim 1 wherein said copy substrate is fabricated from optical plastic.
12 . The apparatus of claim 1 wherein said master hologram and said copy substrate are separated by an air gap.
13 . The apparatus of claim 1 wherein said master hologram and said copy substrate are in contact.
14 . The apparatus of claim 1 wherein said copy substrate forms part of a mechanically translatable continuous lamina.