Unusual short response times and high coupling efficiency can appear with fiber-like Bi_(12)TiO_(20) crystals when applying an electric ac square wave field. Using fiber-like (long and narrow) crystals leads to an extended interaction region inside the crystal and enables to apply strong electric fields to the crystal using moderate voltages. With this method writing of a TWM grating and readout with high efficiency is temporally separated. This can be used, e.g., for high amplification within short times of a signal while suppressing fanned light and extends the possibilities for the application of photorefractive crystals. Wave mixing processes and the fast response are studied experimentally.
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