Lifetime of thermally fixed holograms and gratings in Zn:Fe:LiNbO3 crystals

Doped with various mole fractions of ZnO (2%, 4%, 7%, 8%) and 0.03 wt.% Fe2O3 in LiNbO3, a series of Zn:Fe:LiNbO3 crystals were grown by Czochralski method and then the crystals were polarized and oxidized. Holograms were thermally fixed in Zn (2 mol%):Fe (0.03 wt.%):LiNbO3 crystal by heating the crystal to roughly 120 °C for 40 min. After the developing process, 200-h lossless readout data were obtained in the thermal fixing and developing experiments. The 200-h data are predicted to be read out around 72 million times, which is superior to the lifetime of hard disks. Furthermore, decays of thermally fixed holograms in Zn:Fe:LiNbO3 crystals with various mole fractions of ZnO (2%, 4%, 7%, 8%) were measured at 20 °C. The results show that the ionic activation energies are 1.115 eV, 1.128 eV, 1.275 eV, 1.278 eV, respectively. Extrapolated hologram lifetimes as long as 20 times up to 30 times longer than that of Fe:LiNbO3 crystal (5.2 years) at 20 °C were determined. Finally, the threshold value of Zn2+ concentration was identified by the location of OH− absorption peak of infrared spectra and the ionic activation energy relative to thermal fixing of grating suggests significant threshold effect along with the variation of Zn2+ concentrations.