Electrical fixing of 1000 angle-multiplexed holograms in SBN:75

Nondestructive readout of a photorefractive hologram by phase-conjugate copying in a one-crystal configuration

We propose a novel phase-conjugate copying method for nondestructive readout of a volatile photorefractive hologram. In the one-crystal configuration, two holographic memories and a mutually pumped phase conjugator (MPPC) are formed within a single photorefractive crystal, instead of using multiple crystals. Two memories share the same hologram and complement each other in refreshing the hologram. A MPPC suppresses fanning noise and automatically aligns the wavefront of the reference and readout beams. We found the optimum configuration to achieve nondestructive readout from calculations and geometric consideration. In the experiments with a BaTiO(3) crystal, a continuous readout of 20 times longer than the recording time was achieved.

Electrical fixing in near-stoichiometric lithium niobate crystals

Photorefractive gratings are recorded in lithium niobate crystals in the presence of externally applied electric fields close to the coercive field. After optical erasure a voltage pulse above the poling threshold is applied, and by these means a photorefractive grating reappears that can be erased optically. The results point to electrical fixing, i.e., ferroelectric domain reversal induced by a space-charge field.

Storage of multiple holograms of equal diffraction efficiency in a phase-code multiplexing system

Computer simulations of 8-, 32-, and 128-bit phase-code multiplexing systems are presented, and exposure schedules are obtained numerically for equal diffraction efficiency. An analytic prediction of the exposure schedule is derived as a double exponential function that can be applied to the three different systems for variation of diffraction efficiency of less than +/- 13.5%. Eight holograms were experimentally recorded in a BaTiO3 crystal according to our exposure schedule and also to conventional schedules, which had originally been derived for an angle-multiplexing system. It is shown that the experimental data agree well with the computer simulations.

Three-dimensional color holographic display

Three-dimensional (3D) color holograms are recorded in a cerium-doped, strontium barium niobate (SBN:60) photorefractive crystal. These holograms are shown to reconstruct true color reproductions of the original object with an observable field of view of 37 degrees. Angle multiplexing of two or more 3D color holograms is also demonstrated with angle tuning of the reference beam corresponding to a separation angle between stored images of 0.082 degrees. Each of these results is compared with corresponding theoretical predictions.