PHASE MODULATION HOLOGRAPHIC DATA RECORDING APPARATUS

A holographic apparatus for recording digital data comprising a recording medium and means for producing coherently related reference and signal beams in combination with a plurality of phase modulators disposed across the path of the signal beam and each responsive to a discrete bit of the digital data to be recorded. In the absence of electrical excitation applied to the modulators, the entire signal beam would normally interfere with the reference beam to produce high intensity interference fringes. Application of electrical energy representative of discrete digital bits, however, to one or more of the modulators causes the associated portions of the signal beam to be varied in phase such that interference thereof with the reference beam is substantially weakened whereby upon illumination of the developed hologram for readout only the unmodulated parts of the signal beam are reproduced.