We demonstrate, for the first time to our knowledge, that a fast coherent collision between two Kerr spatial solitons can give rise to a significant phase shift for both interacting beams. The maximal collision-induced phase shift ∼ π rad takes place when the amplitudes of the solitons are equal (η1 = η2) and the length of the interaction zone is comparable with a soliton phase period. Depending on the ratio η2/ η1 and the collision angle between the solitons, the magnitude of the phase shift can be varied within a reasonable range, for example from 180° to 40° . The analysis of the effect performed by the finite-difference beam-propagation method has shown that it is insensitive to the initial phase difference between the incident beams (δi),even in the case when η1 != η2. It has been demonstrated that the phenomenon can be used for all-optical three-soliton logic elements, which are capable of providing more than 3-dB signal amplification and possess δi-independent output characteristics.
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