The electrooptic effect of lithium niobate crystals (LiNbO<sub>3</sub>) is investigated in the regime of high fields (up to 65 kV/mm). The results are of interest for electrooptic modulators and tunable wavelength filters as well as for holographic data-storage systems that use electric-field multiplexing. Holographic gratings are recorded and thermally fixed, and the impact of external electric fields on hologram read-out is studied. The Bragg angle is detuned by applying electric fields of up to 65 kV/mm along the crystallographic c-axis during the reading process. Homogeneous refractive-index changes of up to -4.8×10<sup>-3</sup> are measured for ordinarily polarized light. Even for the highest fields used, no significant contribution of the quadratic electrooptic effect is found. From this we conclude that the quadratic electrooptic coefficient <i>s</i>
<sub>13</sub> is smaller than 2.3×10<sup>-21</sup> m<sup>2</sup>/V<sup>2</sup>.
© 2003 Optical Society of America