Bi-directional two-wave coupling in ac- and dc-biased photorefractive cubic crystals

We study the symmetrical vectorial two-wave mixing in cubic photorefractive crystals when the weak beam is always amplified in spite of its mutual direction in respect of the strong pump beam. We show that this effect takes place both in ac- and dc-biased crystals although the mechanisms underlying this effect are different for local and non-local photorefractive gratings. We present the results of analytical and numerical analyses along with the experimental results obtained with a Bi 12 TiO 20 crystal.