Encrypted holographic data storage based on orthogonal phase code multiplexing

DETAILED DESCRIPTION In a method of the present invention, a data page S.
sub.
m is stored using a reference beam R.
sub.
m whose wavefront is modulated using a phase function W.
sub.
m and an encryption key K.
A second page S.
sub.
m+v is then stored using a reference beams R.
sub.
m+v whose wavefront is modulated using a second phase function W.
sub.
m+v and the encryption key K.
The encryption key K specifies phase delays added to components of the reference beams.
It is preferred, for crosstalk considerations, that W.
sub.
m and W.
sub.
m+v be orthogonal functions, and that the encryption key K not destroy the orthogonality of the reference beams.
It is also preferred that W.
sub.
m correspond to an array of pixel rows, where adjacent rows are separated by an angular separation larger than the vertical angular bandwidth of the signal beam.
Preferably, W.
sub.
m and W.
sub.
m+v are orthogonal Walsh functions.
In a preferred embodiment, K is represented by a device such as a difusser, i.
e.
a device capable on imparting uncorrelated phase delays on parts of a reference beam.
In another preferred embodiment, K represents a set of phase delays imparted on parts of a reference beam by the same spatial light modulator used to generate the orthogonal phase functions.