The non-uniformity of the nonvolatile volume grating in doubly doped LiNbO<sub>3</sub> crystals mainly caused by strong UV absorption is studied in detail. The average saturation space-charge field is small and the diffraction efficiency is low as a result of the non-uniformity of the grating. Optimization for the uniformity of the grating using two sensitizing beams from the two opposite sides of the crystals is performed. Theoretical simulations and experimental verifications are presented. Well uniform gratings can be obtained and diffraction efficiency can be greatly enhanced by using this optimization scheme.

© 2005 Optical Society of America

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